WO2007056089A2

WO2007056089A2 - Automated ac line filter and surge suppression apparatus and method

Info

Publication number: WO2007056089A2
Application number: PCT/US2006/042864
Authority: WO
Inventors: Joseph S. Lewis; Mark L. Rudiger
Original assignee: Dollar Energy Group, Inc.
Priority date: 2005-11-02
Filing date: 2006-11-02
Publication date: 2007-05-18
Also published as: WO2007056089B1; AU2006311944A1; EP1952501A2; US20060056127A1; WO2007056089A3; US7940506B2

Abstract

An automated AC line filter and surge suppression apparatus (100) having an inductive current sense loop (ICSL) circuit (10) for sensing inductive current at a load and controlling the application of AC line filter (112) to an AC power line to the load. Current sensor (12) in series with the input line senses inductive load current. A first bridge rectifier (14) rectifies the sensed load current to a proportionate DC voltage, which triggers a switch (24). The output of switch (24) is fed into an opto-isolator (26), which in turn controls second switch (28). Switch (28) connects or disconnects AC line filter (112) from the system according to a predetermined sensed inductive current at the load. MOVs (102) and capacitive elements (104) provide continuous surge suppression protection to the load. Selectable biasing (255) provides line filtering corresponding with a phase difference in inductive load current and a load voltage.

Description

AUTOMATED AC LINE FILTER AND SURGE SUPPRESSION APPARATUS AND METHOD

BACKGROUND OF THE INVENTION

Field of the Invention (Technical Field):

The present invention relates generally to the field of alternating current (AC) line filters and surge suppression circuitry, and more particularly to the application of line filtering based upon a predetermined sensed inductive current at the load.

Background Art: The basic alternating current (AC) line filter is an inductive-capacitive

(LC) filter circuit that is inserted into a power supply to filter out unwanted high-frequency interference present in the input line supply. Line filters also aid in the reduction of voltage spikes, or "surges", as well as aid in the elimination of radio frequency (RF) interference by the power supply. Line filters are typically placed before the transformer of a power supply to prevent these unwanted signals and spikes from reaching the load.

The difficulties encountered when AC voltage surges occur in power supplies are well known. Sudden spikes or dips in the input voltage are particularly problematic to sensitive circuitry, such as digital integrated circuits, but are also problematic to larger scale circuitry. A change in the power supply output voltage, particularly sudden increases in output voltage, may damage or destroy circuit components. Most power supplies are regulated to prevent or minimize the effect of power surges as well as to maintain a constant output voltage regardless of load. Metal oxide varistors (MOVs) and other transient voltage surge suppression (TVSS) technology, such as those manufactured by Redivolt® and Innovative Technologies, are commonly used for surge suppression. Examples of surge protection circuitry can be found in U.S. Patent No. 6,229,682 to Mechanic, entitled, "Transient Voltage Surge Suppressor;" U.S. Patent No. 6,055,147 to Jeffries, et al., entitled, "Apparatus for Providing Independent Over-Current Protection to a Plurality of Electrical Devices and Transient-Voltage Suppression System Employing the Apparatus;" U.S. Patent No. 5,761 ,021 to Yu, entitled, "Voltage Surge Suppression Device;" U.S. Patent No. 5,617,284 to Paradise, entitled, "Power Surge Protection

Apparatus and Method;" U.S. Patent No. 5,388,021 to Stahl, entitled, "Voltage Surge Suppression Power Circuits;" U.S. Patent No. 4,023,071 to Fussell, entitled, "Transient and Surge Protection Apparatus;" U.S. Patent No. 5,153,806 to Corey, entitled, "Transient Surge Suppressor and Alarm Signal Circuit;" U.S. Patent No. 4,587,588 to Goldstein, entitled, "Power Line

Transient Surge Suppressor;" U.S. Patent Application Pub. No. 0055186 to Wodrich, et al., entitled, "Zero Threshold Surge Suppressor;" U.S. Patent No. 6,118,639 to Goldstein, entitled, "Fast Acting Disconnect System For Protecting Surge Suppressors and Connected Utilization Equipment From Power Line Overvoltages;" U.S. Patent No. 5,786,974 to Zaretsky, entitled, "Apparatus For and Method of Suppressing Power Surges Utilizing Electrical Striplines;" U.S. Patent No. 4,587,588 to Goldstein, entitled, "Power Line Transient Surge Suppressor;" U.S. Patent No. 4,630,163 to Cooper et al., entitled, "Method and Apparatus for a Transient-Suppression Network;" U.S. Patent No. 4,870,534 to Harford, entitled, "Power Line Surge Suppressor;" U.S. Patent No. 5,398,150 to Standler, entitled, "Coordinated Electric Surge Suppressor with Means for Suppressing Oscillatory Transient Overvoltages;" U.S. Patent No. 4,587,588 to Goldstein, entitled, "Power Line Transient Surge Suppressor;" U.S. Patent No. 6,188,557 to Chaudhry, entitled, "Surge Suppressor;" and U.S. Patent No. 4,870,528 to Harford, entitled, "Power Line Surge Suppressor." Additional AC filtering is achieved by including capacitive filtering in the line. Capacitive filters further aid in the electrical performance of various inductive loads such as pumps, fans, air conditioning units, refrigeration units, etc., because the capacitive reactance of the filter offsets the inductive load reactance to balance the phase variation caused by the inductive load. Examples of combination surge protection and line filtering circuitry can be found in U.S. Patent No. 5,392,188 to Epstein, entitled, "Power Surge Transient Voltage Protection and Filtering Circuit Having Current Controlling Characteristics," and U.S. Patent No. 4,675,772 to Epstein, entitled, "Protector Network for A-C Equipment."

Surge protection is useful on a continuous basis for equipment connected to a power line. However, during load non-operation periods, capacitive line filtering may not be necessary and in some cases may add interference back into the electrical supply. The capacitive reactance of the filter can cause harmonic distortion on the line because the normal inductive load is not present to absorb, or cancel, the capacitive reactance. Prior art surge suppression and filtering circuits do not address inductive load disparities that occur due to varying operating parameters of the load. It would be useful if such circuitry were able to sense an inductive current at the load and provide line filtering only when inductive current was present.

Attempts have been made to sense current within surge protection circuitry devices, but not for the purpose of controlling capacitive filtering on the line. Examples include U.S. Patent No. 4,870,528 to Harford, which discloses a surge suppression circuit that includes a sensing circuit for sensing the charging current to a capacitor used for storing relatively high- energy surges. However, this patent addresses the need for additional energy storage capacity in a particularly high energy surge condition and allows current flow to an additional capacitor upon sensing current through a simple diode and rectifier configuration. Harford does not address the need for control of line filtering. U.S. Patent No. 5,818,672 to Hilbe, entitled, "Ground Loop Current Suppressor" discloses a sensing transformer used for sensing ground loops in electrical equipment interconnections. The sensed ground loop current is used to induce a second current for counteracting the ground loop current. U.S. Patent No. 6,388,852 to Bobash, entitled, "Flicker Protection Circuit" discloses a circuit for removing AC power to a load upon sensing an interruption in the power supply by an auto-reset watchdog circuit.

Problems of varying load-operating parameters have also been addressed with motor control circuitry that is used to change the running characteristics of the inductive load. Examples include variable frequency drives (VFDs) and soft starts which do not allow full transfer of power upon start-up but instead slowly ramp up power to the load. Although such control circuitry may provide significant energy savings, it often requires changing the frequency of and/or the voltage supply to the load and does not address the need for control of the application of line filtering.

The present invention overcomes the limitations of the prior art by applying AC line filtering only when the load is operational. The inventive method and apparatus monitors the inductive load via an inductive current sense loop (ICSL) circuit to control the application of line filtering according to the presence or absence of inductive current at the load. The ICSL circuit monitors current flux from an inductive load to determine if capacitive AC line filtering should be added to the circuit. If the inductive current benefits by the addition of filtering elements, then the ICSL circuit remains energized to provide such filtering elements. When the inductive load is not operational, the ICSL circuit automatically switches the line filtering elements to an "off' position, thereby removing line filtering from the system. The present invention also combines automated line filtering with surge suppression circuitry. The surge suppression circuitry is in continuous electrical communication with the power line and load for continuous provision of surge protection.

SUMMARY OF THE INVENTION (DISCLOSURE QF THE INVENTION) The present invention is an automated AC line filter and surge suppression apparatus comprising surge suppression circuitry in continuous electrical communication with an AC power line to a load, and an inductive current sense loop (ICSL) circuit for controlling the application of line filtering. The inductive current sense loop circuit comprises a current sensor for sensing current at the load and a switching mechanism in electrical communication with the current sensor. The switching mechanism is in electrical communication with an AC line filter. The switching mechanism applies AC line filtering only when a predetermined amount of current is sensed at the load by the current sensor.

The surge suppression circuitry of the present invention preferably comprises one or more MOVs and capacitors. The AC line filter preferably comprises a capacitance in the range of 5μF to 285μF.

The current sensor is preferably a current transformer in line with an AC power line to the load. The switching mechanism preferably comprises a first switch, a level converter, and a second switch. A bridge rectifier connected to the output of the current sensor provides the voltage input to the first switch, preferably a timer IC configured as a bi-stable binary flip-flop. Alternatively, the first switch comprises a flip-flop, bilateral switch, counter, or combination thereof. The level converter is preferably an opto-isolator, or alternatively, a transistor, digital isolator, silicon control rectifier, solid-state relay, photo- transistor, or combination thereof. The second switch preferably comprises a logic triac. In the alternative, the second switch comprises an electromechanical relay, solid-state relay, power triac, or combination thereof. The present invention is further a method of automatically providing AC line filtering to an AC power line to a load according to sensed current at the load. The method comprises the steps of providing an AC line filter; monitoring current at a load with a current sensor in electrical communication with an AC power line to the load; and applying AC line filtering to the load based upon the output from the current sensor. The step of applying AC line filtering comprises switching AC line filtering into or out of electrical communication with the AC power line to the load based upon the output from the current sensor with a switching mechanism.

Also disclosed is a method and apparatus for activating the line filtering for only an inductive load or a sensed lagging inductive current. This is preferably accomplished with an operational amplifier (OP Amp.) to discriminate between resistive and inductive loads.

A primary object of the present invention is to provide AC line current filtering only when inductive current is present at the load. Another primary object of the present invention is to combine the benefits of surge suppression with line filtering.

A primary advantage of the present invention is a reduction of power usage by the load. Another primary advantage of the present invention is the reduction of load start-up demand for power. Still another primary advantage of the present invention is an improvement of the load phase power factor. Yet another primary advantage of the present invention is the reduction of line transient anomalies and the provision of a more constant AC waveform. Another advantage of the present invention is the reduction of noise and total harmonic distortion (THD) at the load. Still another primary advantage of the present invention is that it extends the useful life of the load. Still yet another primary advantage of the present invention is that it is cost-effective to manufacture, utilizing available components. And, another primary advantage of the present invention is that it can be used in conjunction with a wide variety of inductive load equipment.

Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated into and form a part of the specification, illustrate a preferred embodiment of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are not to be construed as limiting the invention.

Fig. 1 is the automated AC line filtering and surge suppression apparatus of the present invention; Fig. 2a is the preferred embodiment of the inductive current sense loop

(ICSL) circuit of the present invention;

Fig. 2b is an expanded view of the timer of Fig. 2a defining the IC input and output pins;

Fig. 3 is a plot of voltage (V) as a function of time (min) for three phases of a power supply to a 50 horsepower motor over a one-hour time period;

Fig. 4 is a plot of voltage (V) as a function of time (min) for three phases of a power supply to the 50 horsepower motor of Fig. 3 over a one-hour time period with the present invention of Figs. 1 and 2 implemented;

Fig. 5 is a plot of current (A) as a function of time (min) for three phases of a power supply to the 50 horsepower motor of Fig. 3 over a one-hour time period; Fig. 6 is a plot of current (A) as a function of time (min) for three phases of a power supply to the 50 horsepower motor of Fig. 3 over a one-hour time period with the present invention of Figs. 1 and 2 implemented;

Fig. 7 is a plot of total real power (W) as a function of time (min) for the power supply to the 50 horsepower motor of Fig. 3 over a one-hour time period;

Fig. 8 is a plot of total reactive power (VAR) as a function of time (min) for the power supply to the 50 horsepower motor of Fig. 3 over a one-hour time period; Fig. 9 is a plot of total real power (W) as a function of time (min) for the power supply to the 50 horsepower motor of Fig. 3 over a one-hour time period with the present invention of Figs. 1 and 2 implemented;

Fig. 10 is a plot of total reactive power (VAR) as a function of time (min) for the power supply to the 50 horsepower motor of Fig. 3 over a one-hour time period with the present invention of Figs. 1 and 2 implemented;

Fig. 11 is a plot of voltage (V) and current (A) in combination as a function of time (msec) upon start-up of a 0.5 horsepower motor without implementation of the present invention on the line;

Fig. 12 is a plot of voltage (V) and current (A) in combination as a function of time (msec) upon start-up of a 0.5 horsepower motor with the present invention of Figs. 1 and 2 implemented;

Fig. 13 is a plot of current (A) as a function of time (msec) upon startup of a 0.05 horsepower exhaust fan motor without implementation of the present invention; Fig. 14 is a plot of current (A) as a function of time (msec) upon startup of a 0.05 horsepower exhaust fan motor with the present invention of Figs. 1 and 2 implemented;

Fig. 15 is an alternative embodiment of the circuit for filtering and surge suppression that is activated only during an inductive load condition Fig. 16 is a functional schematic block diagram of adaptive circuitry for setting a selectable biasing element and filtration parameters according to one embodiment of the invention based upon changing load conditions; and

Fig. 17 and Fig. 18 are functional block diagrams of a selectable biasing element and a selectable filtering element, respectively, that are operably coupled to receive control signals from logic according to one embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (BEST MODES FOR CARRYING OUT THE INVENTION)

Referring in combination to Fig. 1 , Fig. 2a and Fig. 2b, a schematic of the automated line filter and surge suppression apparatus 100 of the present invention is shown. Surge suppression is provided continuously to the load by surge suppression circuitry, preferably MOVs 102 and capacitance elements 104. An ICSL circuit 10 provides AC line filtering via line filter 112 only when current is sensed at the load.

Surge suppression is accomplished by a plurality of MOVs 102 connected between line and ground, neutral and ground, and line and neutral. MOVs are also provided line to line where applicable, for example when the power source is 240V single phase. While three MOVs are depicted in Fig. 1 for the purpose of surge suppression, it will be understood by those of skill in the art that the number of MOVs can be varied according to the particular load, in accordance with the principles of the invention. Preferably, a minimum of one MOV is connected neutral to ground, one MOV connected line to neutral, one MOV connected line to ground, and one MOV connected line to line if appropriate, depending upon the voltage and phase configuration of the power supply. In addition to MOVs 102, surge suppression capacitive elements 104 are connected neutral to ground and line to ground to provide a total capacitance value appropriate to the load application. Capacitance is also provided line to line where appropriate to the power source configuration. Surge sensing elements 106, 106' such as fuses, thermal sensing devices, or a combination of both, at the power source open the circuit to the load in the event of a current overload. Series resistances 108, 108' limit current to indicators 110, 110', preferably light sources, which remain lighted to indicate an available power source to the load. Should sensing elements 106, 106' open in response to an overload condition, indicators 110, 110' cease to be illuminated indicating to the user that power is not available to the load.

In addition to surge suppression components, line filter 112 provides AC line filtering to the load. Line filter 112 filters undesired frequencies from the AC supply and provides a reactive component to the load impedance to balance the reactive component found in inductive loads such as pumps, fans, air conditioning units, and refrigeration units. According to convention, the capacitance value of AC line filter 112 is dependent upon the particular load for which the apparatus 100 is to be used, such value likely ranging from 5μF to 285μF. An optional decoupling capacitance, ranging in value from 0.001 μF to 0.1 μF, (not shown) aids in the reduction of noise associated with digital switching.

Referring to Fig. 2a and Fig. 2b, a schematic of the inductive current sense loop (ICSL) circuit 10 of the line filter and surge suppression apparatus of Fig. 1 is shown. ICSL circuit 10 controls the application of line filter 112 to the power source. Line filtering is applied, or switched "on", by a switch mechanism only upon sensing an inductive current at the load. When switched "on", the line filtering is in electrical communication with the AC power line to the load.

A male connector 11 is provided in ICSL circuit 10 for connection to the power outlet and female connector 13 is provided for connection to the load, for example a refrigerator plug. Current sensor 12, a current transformer, is connected in series with the line between male connector 11 and female connector 13. When an inductive load is present, current sensor 12 senses the current at the load. Current sensor 12 is of a size appropriate to sense a predetermined current that is typical of a particular load. For example, a single phase 120V home appliance may operate on approximately 800 mA of current, while a large load, such as a 50 horsepower motor, may require as much as 50 A of current. The sensed current is rectified with bridge rectifier 14, thereby providing a DC signal. Input line resistance 16 interfaces with bridge rectifier 14 and dampens particular over-current conditions that might occur, such as when the load is being shorted or overloaded. Capacitance 18 and resistance 20 comprise a timing network to filter AC ripple from the DC voltage of bridge rectifier 14.

The DC voltage from rectifier 14, through resistances 22 and 38, operates as the trigger for switch 24, a timer IC such as the conventional CMOS 555 timer connected in a switch configuration. (See also Fig. 2b) Switch 24 is configured so that it does not operate in an astable or monostable mode, but is instead configured to perform in the manner of a bi- stable binary flip-flop, so that whenever an input exists from the current sense loop bridge rectifier 14 the switch is triggered into the "on" position, and whenever there is no input from rectifier 14 the switch is forced into the "off' position. Once triggered, switch 24 remains in the "on" position until inductive current is no longer sensed at the load at which point it is switched "off". When in the "off' position, switch 24 remains "off' until current is again sensed by current sensor 12. Switch 24 alternatively comprises a CMOS flip-flop IC, such as a dual resettable flip-flop or a dual D-type flip-flop, a quad bilateral switch, or a counter IC. However, the low power requirement and low heat generation of a CMOS 555 timer are preferable. During load operating conditions, switch 24 is forced into the "on" state with the output held low. The low output from switch 24 energizes opto- isolator 26, which operates as the level converter between the output of switch 24 and the input of second switch 28 and also provides electrical isolation between switch 24 and switch 28. Opto-isolator 26 provides a smooth transition from the small current (mA) output of switch 24 to that required to trigger the gate of second switch 28.

The iso-amplifier output of opto-isolator 26 energizes second switch 28, such as a logic triac, which in turn controls the application of line filter 112 to the power supply. When the load is operational and current sensor 12 senses inductive current, second switch 28 provides electrical continuity with line filter 112 so that line filtering is applied, or "on". When current sensor 12 does not sense inductive current, electrical continuity with line filter 112 is interrupted by second switch 28, thereby turning line filter 112 "off'.

The function of opto-isolator 26 is alternatively provided by one or more transistors, such as NPN transistors, digital isolators, silicon control rectifiers (SCRs), solid-state relays, and photo-transistors, alone υr in combination. Switch 28 is alternatively an electromechanical or solid-state relay, or power triac.

When switch 28 provides electrical continuity with line filter 112 due to a load current-sense condition, an indicator 30 - such as a bicolor LED illustrated as 30 and 30' - glows to indicate that AC line filtering is present. When inductive load current is not sensed through current sensor 12, indicator 30 glows a different color than in the sensed current condition, to indicate no AC line filtering is present. A single indicator 30, 30' is illustrated for a 120V single-phase application in Fig. 2a. However, a pair of indicators could be used in a 240V application, where one indicator is provided on each line. To provide an indication of the presence or absence of line filtering, the red lead of indicator 30 is connected to the line side of fuse, or thermal cutoff device, 42, while the green lead of indicator 30' is connected to the switched side of line filter 112. The black lead of indicator 30, 30' is connected to the neutral line. The red and green leads of indicator 30, 30' are connected through a voltage divider half-wave rectifying network consisting of resistances 52, 52' in series with diodes 54, 54'. Although a bicolor LED is depicted in Fig. 2a for presenting information regarding the presence or absence of AC line filtering, it will of course be understood that other types of illumination or indicator devices can be used in accordance with the invention to indicate the presence or absence of line filtering.

In addition to indicator 30, an optional fault indicator (not shown), such as an LED, neon, or other light source, indicates a fault condition in the ICSL circuit 10 such as the absence of power on the AC power line.

A second bridge rectifier 40 rectifies line voltage and provides a small DC power supply. Line current is fed to bridge rectifier 40 through a surge- sensing device 42 such as a thermal sensing device or a fuse. Resistance 44 reduces the line voltage to bridge rectifier 40. Neutral is fed to rectifier 40 through resistance 45. Bridge rectifier 40 supplies the reference voltage to switch 24 and the reference voltage to opto-isolator 26 through resistance 32. Capacitances 46 and 50 together with resistance 48, remove filtering ripple from the output of bridge rectifier 40. The negative or the grounded side of bridge rectifier 40 is tied common to the grounded side of bridge rectifier 14 so that both rectifiers operate at the same potential. Surge suppression for ICSL circuit 10 is provided by MOV 56 and capacitance 58, although a multitude of component configurations can be substituted for MOV 56 and capacitance 58 to provide surge suppression. When the load discontinues or disengages from normal operation, for example, when a refrigerator achieves a pre-programmed temperature and ceases drawing power for refrigeration, current sensor 12 no longer senses an inductive current. Once inductive current is no longer sensed at the load, bridge rectifier 14 will discontinue the rectifying process. Discontinuation of rectification is sensed by the trigger input to switch 24 causing switch 24 to "reset". This occurs because the active low reset input to switch 24 is tied high through resistance 36 to the output of second bridge rectifier 40. The threshold input to switch 24 is also tied high through resistance 34. When the trigger input is low, the output of switch 24 becomes high, ceasing operation of opto-isolator 26, which then changes the state of switch 28 to disconnect line filter 112 from the system.

In addition to switching line filter 112 on and off according to sensed inductive load current, the present invention allows for the added feature of selecting line filter capacitance values appropriate to the sensed load via an optional inductive current comparator stage (not shown). This additional stage is used for selecting additional capacitive filtering under higher inductive load demands and is particularly useful in three-phase applications.

The present invention as depicted in Figs. 1 , 2a, and 2b is preferably comprised of a circuit board upon which the ICSL circuitry as well as filter elements, surge suppression components, fuses or thermal cutoffs, and other components are located. The board is preferably enclosed in a standard PVC plastic or heavy UL plastic enclosure, or is alternatively enclosed in a metal enclosure. Preferably the enclosure serves as a heat sink for the circuitry within. Depending upon the application, the device includes plug-in ports for the electrical hook-ups rated to the load specifications. Alternatively, the hook-ups are standard stranded electrical wire for both input and output. Fig. 15 shows an alternative circuit embodiment of the invention for activating line filtering for inductive loads only. In this embodiment of ICSL circuit 10, a Differential Comparator OP Amp 250 is added that is situated between CT transformer 12 and switch 24. In this case, the circuit preferably employs an OP A680 Wideband voltage feedback OP Amp with a disable function, or the like. There are a wide variety of substitute circuits which can accomplish the same results; however, this method is preferred because both the comparator function and a "LINE FILTER" disable can be accommodated with one eight (8) pin integrated circuit (IC). By adding the differential comparator embodiment, this allows the ICSL circuit 10 to accurately discriminate between "purely resistive" and "inductive" loads. This allows the line filter to be energized only during times when the current waveform lags the voltage waveform sample.

The modifications to the circuit of Fig. 2a. are shown in Fig. 15 as follows:

Line/Component Deletions:

1. Delete line between the +Vd out of bridge rectifier 14 and switch

24. 2. Delete bridge rectifiers 14 and second bridge rectifier 40 and reconfigure for proper AC/DC configuration, as shown. Line/Component additions:

1. Add OP Amp. 250 between bridge rectifier 14 and switch 24, with corresponding resistors 254, 259, 257 and 255, capacitor 253 and diode components 252, 260 and 251 as shown in Fig.

15.

2. OP Amp. 250 is wired as follows:

Pin 2, the inverting input, is connected to the reduced line voltage point located between resistor 44 and second bride rectifier 40. A resistor 254, diode 260, and resistor 257 are connected in series between pin 2 of OP Amp. 250 and aforementioned voltage sampling point. Also, resistor 259 is added between the diode (cathode) and input resistor 254 (resistor side of pin 2), and ground.

Pin 3, the non-inverting input, is connected to sample the current waveform generated by current sensor 12. Resistor 22 and diode 256 are connected between pin 3 of OP Amp. 250 and a point between resistor 16 and bridge rectifier 14. A trim potentiometer 255 is connected from this point to ground.

Pin 7 is Vs, which is connected to the plus side of bridge rectifier 40.

Pin 8, is the OP Amp. 250 disable bus Vd. The disable signal is connected between the plus side of bridge rectifier 14 and Vd.

Pin 4 is ground.

Pin 6 is the output which is connected between switch 24 and pin 6.

Also added to this circuit is a diode 252 acting as a half wavebridge, and a capacitor 253 on the output (cathode) side of diode 252 and ground.

Finally a Zener diode 251 is added between Vs and ground, for better voltage regulation.

Whereas the first embodiment of the ICSL would add line filtering reactance to a load whether resistive or inductive once sufficient current was sensed, with the addition of OP Amp. 250, which is preferably a differential comparator OP Amp, the ICSL activated only during a truly inductive load condition.

OP Amp. 250 is connected so that voltage samples are sensed on the inverting and non-inverting inputs of the OP Amp. 250 pins 2 and 3 respectively. Each sample is half wave rectified so that only the positive going portion of the wave is passed onto OP Amp. 250. Then with regard to how the phase angle relationship of both waveforms compare, OP Amp. 250 will generate a differential output waveform which correlates to this phase difference, producing an "error" output. This "error" output will be positive in nature when the current from current sensor 12 lags the voltage of the line input sample, by as little as two and one-half percent (2.5%). The "error" output will be positive cycle rectified by diode 252 on the output of pin 6, so that only the positive going differential output "error" produced by the current lagging the voltage conditions on Op Amp. 250's inputs, is then charged across capacitor 253 until the switch select threshold of two and one-half (2.5) volts DC is reached, thus energizing switch 24. Switch 24 will run continuously and remain "on" while the ICSL load remains active and inductive. Once the inductive load is removed, the circuit will remain active for a short duration before deactivating. This allows the line filters to discharge slowly and reset the ICSL back to a standby mode.

The present invention has application to a variety of inductive load equipment such as air conditioners, motors, fans, pumps, compressors, and the like. The invention can be adapted for various voltage configurations, such as 120V and 240V single-phase, 240V three-phase and 480V three- phase configurations. For three-phase applications an ICSL circuit is provided for each line. Examples

Application and benefits of the present invention were demonstrated in a series of tests. Implementation of the present invention on an AC power line to a load resulted in significant energy savings.

Test i

In a first test, voltage, current, and power factor measurements were taken on a 480V, 70.5A, 50 horsepower motor operating at 830 rpm, used for driving an oil well pump. Measurements were taken both with and without the present invention implemented in the system. Measurements were taken over a time period of sixty minutes with a DataLogger™ measurement device. Test results without the present invention implemented in the system are summarized in Tables 1-4 below.

Table 1

Table 2

Table 3

Table 4 Test results on the same motor with the present invention implemented e system are summarized in Tables 5-8 below.

Table 5

Table 6

*Ambient temperature 12° F higher than testing performed in Tables 1-4.

Table 7

Table 8

A comparison of the results without the apparatus of the present invention (Tables 1-4) with the results when the apparatus of the present invention was implemented in the system (Tables 5-8) revealed a significant energy savings. Implementation of the present invention resulted in reduced current at the load. Total real power, total reactive power, and total demand for power by the load were also reduced. This is supported by the formula for determining kilowatt-hours: _v _ E - I - PF Λ.73 -t ...

Kwh = , (1)

1000 ^V ' where E is voltage in volts, I is current in amperes, PF is the power factor and t is time in hours.

Test 2

A second test was performed on the identical motor as in the test described immediately above, on a different day and time. Referring to Figs. 3 -10, measurements of voltage, current, total real power and total reactive power were plotted as a function of time, first without the automated AC line filter and surge suppression apparatus, then with the automated AC line filter and surge suppression apparatus implemented in the system. Measurements were taken over a one-hour period of time.

Referring to Figs. 3 and 4, voltage measurements across each of three phases are plotted in volts as a function of time. Fig. 3 shows the voltage across the A, B, and C phases before implementation of the present invention. Numerical averages are provided directly beneath the plots for each three-minute interval. These same measurements were then taken with the automated AC line filter and surge suppression apparatus implemented in the system. The results are depicted in Fig. 4. An overall comparison of voltage on each phase without implementation of the inventive apparatus (Fig. 3) to voltage with implementation of the inventive apparatus (Fig. 4) reveal a larger voltage at the load with implementation of the present invention, and reduced voltage variance between the three phases.

Referring to Figs. 5 and 6, current measurements across each of three phases are plotted in amperes as a function of time. Fig. 5 shows the current at the A, B and C phases before implementation of the present invention. Numerical averages are provided directly beneath the plots for each three- minute interval. These same measurements were then taken with the automated AC line filter and surge suppression apparatus implemented in the system. The results are depicted in Fig. 6. An overall comparison of current flow without implementation of the inventive apparatus (Fig. 5) to current flow with implementation of the inventive apparatus (Fig. 6) reveal a significant reduction in current flow with implementation of the present invention.

Figs. 7 and 8 show total real power in watts plotted as a function of time, and total reactive power in VAR plotted as a function of time, without implementation of the present invention. Numerical averages are provided directly beneath the plots at two to four minute intervals.

Figs. 9 and 10 show total real power in watts plotted as a function of time, and total reactive power in VAR plotted as a function of time, with implementation of the present invention. Numerical averages are provided directly beneath the plots at two to four minute intervals.

A comparison of total real power without the inventive apparatus (Fig. 7) to total real power with the inventive apparatus (Fig. 9) reveals a significant reduction with implementation of the present invention. For example, the maximum total real power depicted in Fig. 7 is approximately 25 kW in approximately the fifth minute of testing, while the maximum total real power depicted in Fig. 9 is approximately 23kW in approximately the seventeenth minute of testing.

A comparison of total reactive power without the inventive apparatus (Fig. 8) to total reactive power with the inventive apparatus (Fig. 10) also reveals a significant reduction with implementation of the inventive apparatus. For example, Fig. 8 reveals total reactive power often reaching 16kVAR, while Fig. 10 shows total reactive power not exceeding 1OkVAR with implementation of the inventive apparatus. Test 3

A third test was performed to examine the effects of the present invention upon current, voltage, power and power factor on a 0.5 horsepower motor upon motor start-up. Measurements were taken across a single phase of the load with PowerSight™ on a Summit™ instrument.

Referring to Fig. 11 , a plot of current 200 and voltage 202 are provided in combination as a function of time (ms) without implementation of the present invention. Voltage values are provided on the left of the graph and current values are provided on the right. Without the present invention implemented, the root-mean-square (RMS) values of voltage and current were 121.9 Vm₈ and 5.5 A respectively. True power was 202.2 watts and the true power factor was 0.30.

Referring to Fig. 12, a plot of current 204 and voltage 206 are provided in combination as a function of time (ms) with implementation of the present invention. Voltage values are provided on the left of the graph and current values are provided on the right. The results in Fig. 12 reveal root-mean- square (RMS) values of voltage and current were 118.3 Vrm_S and 4.4 A respectively. True power was 186.1 watts and the true power factor was 0.35. With the present invention implemented, start-up current was reduced, the power factor improved and power usage decreased by 16.1 watts.

Test 4

Smaller loads also benefit from implementation of the present invention. Referring to Figs. 13 and 14, plots of current draw upon start-up of a 0.05 horsepower exhaust fan motor are shown. Current measurements were taken with Summit™ instrument PowerSight™. Fig. 13 is a plot of current (A) as a function of time (ms) prior to implementation of the present invention on the line. The RMS current value during start-up was 0.6 A. Fig. 14 is a plot of current (A) as a function of time (ms) with implementation of the present invention. The RMS current value upon start-up with the present invention implemented on the line was 0.1 A revealing a significant current savings upon start-up through implementation of the present invention.

The disclosed circuitry is generally operable to provide automated line filtering to reduce phase differences between current and voltage and thus to improve a power factor for a specified application in addition to improving expected signal characteristics. Figure 2a illustrates circuitry that is operable to provide automated line filtering, i.e., to trigger operation of line filter 112 whenever a current is detected for an inductive device. As such, automated line filter 112 is in an "ON" mode whenever an inductive device, such a motor or other device having inductive coils, is powered and operating. Automated line filter 112, therefore, provides filtering to improve the power factor and energy efficiency.

More specifically, an alternating current is detected whenever an inductive load is coupled and operating by current sensor 12. Current sensor 12 produces an alternating voltage signal having a peak value that corresponds to a detected voltage signal. The alternating voltage signal produced by current detector 12 is thus produced to a full wave rectifier with output filtering to produce a filtered DC signal having a reduced ripple at peak values. The output DC value is then utilized to trigger switch 24 to generate output signals that result in the activation of line filter 112 as described before.

Figure 15, on the other hand, provides an embodiment of the invention that is operable to provide adjustable and selective operation of the ICSL Circuit 10 to facilitate operation of a single device for a wide range of applications. The embodiment of Figure 15 supports real time adjustment of the inventive apparatus according to loading characteristics of the inductive device whose power factor and power efficiency is to be improved. As may be seen from referring to Figure 15, a potentiometer 255 is coupled between an input for a full wave rectifier and ground. As one of average skill in the art may readily determine from examining the circuit, adjustment of the potentiometer selectively lowers the signal magnitude that is input to the full wave rectifier. As such, the input and output voltage may be scaled to match a peak value of the full wave rectifier that operably receives the load voltage signal. Thus, the embodiment of Figure 15 is operable to activate line filter 112 only for a portion of a signal cycle or period that correlates to a phase difference between the load current and the load voltage.

More specifically, by adjusting potentiometer 255, the voltage signal produced by current sensor 12 is reduced by conducting a portion of the signal to circuit common or ground. In general, potentiometer 255 desirably adjusts or scales the peak levels of the signal magnitude of the signal produced by current sensor 12 to match a signal magnitude of an input voltage to full wave rectifier 40. Full wave rectifier 40 is generally operable to rectify a detected voltage signal for the load. Such operation is inherent and may readily be seen by one of average skill in the art examining Figure 15.

While a potentiometer 255 is shown in Figure 15, it should be understood that any known circuitry for scaling the input signal may be used. Thus, a resistor bank in any selectable configuration may be used including a resistor ladder. Thus, for example, if the line filter 112 is to be used for a select number of applications each having unique current loading requirements, the resistors that are switched in may be scaled to appropriately scale the input magnitude level. For example, one resistive value may be used for an expected load of 1 Amp while a second resistive value may be used for an expected load of 50 Amps. As such, the peak voltage produced by current sensor 12 is scaled to a specified peak or magnitude value. As such, embodiments of the invention may include logic that selects resistive levels to correspond to changes in loading. Such an adaptive approach would desirably improve overall efficiency because human interaction to improve efficiency would not be required.

Continuing to refer to Figure 15, a comparator 250 is operably disposed to receive the voltage input to full wave rectifier 40 at a negative input as well as the scaled voltage input of full wave rectifier 14 at a positive input which is output by current sensor 12. Based upon these differences, comparator 250 generates an output signal based upon a difference in magnitude of the input signals. Thus, by scaling the voltage signal magnitude produced to the input of the full wave rectifier 14 to match the signal magnitude of the input of full wave rectifier 40 merely by adjusting potentiometer 255, a true phase difference between the inductive load current and inductive load voltage may be detected and may be used to activate the line filter to reduce the phase difference and improve the power factor of the circuit. As one of average skill in the art may readily ascertain, if the input signals to comparator 250 have different peak magnitudes, comparator 250 would generate an output that would, in part, be based upon the different signal magnitudes even if the current and voltage signals were aligned. This output signal would then trigger switch 24 to prompt line filter 112 to activate even though no real phase difference exists. Thus, by calibrating the signal magnitude of the output signal of current sensor 12, i.e., by adjusting potentiometer 255 to reduce the input to full wave rectifier 14, to match the input signal magnitude of full wave rectifier 40, the output of comparator 250 reflects a true phase difference between the inductive current and inductive voltage of the load device. As such, line filter 112 and its active filtration, is biased into an operational state to adjust a power factor by accurately determining an amount of capacitive impedance that would counteract the adverse effects upon phase differences between the current and voltage signals due to the inductive nature of the load. Finally, while Figure 15 illustrates a single line filter and a single line, it should be understood that the embodiment of Figure 15 may be used for each of a plurality of loads to improve overall efficiency of a system of load devices.

Figure 16 is a functional schematic block diagram of adaptive circuitry for setting a selectable biasing element and filtration parameters according to one embodiment of the invention based upon changing load conditions. As may be seen, a plurality of load devices 300, 304 and 308 are operably disposed in parallel a common node coupled to receive a line voltage. A corresponding plurality of current sensors 312, 316 and 320 are operably disposed to sense load current (inductive load current) whenever a corresponding load device 300, 304, and 308, respectively is on and drawing inductive current. A voltage signal is produced by each of the current sensors 312, 316 and 320 to logic 324. Logic 324 is operable to generate a bias control signal on a bias control line and a filter control signal on a filter control ϋne to a selectable biasing element 328 and to a line filter 332, respectively. In an alternate embodiment, a logic signal generated by the load device being in an operational mode based upon a different type of determination (e.g., a power switch is on) may be used to indicate to logic 324 that the load device is in an operational state.

In operation, a single load device or a plurality of load devices operating as a single system will draw differing amounts of load current based upon work load of the load device(s). For example, for air-conditioning and refrigerating cooling systems, it is known to have a primary cooling unit and one or more additional staged cooling units that are operable to only operate when the primary cooling unit is unable to meet cooling demand. As such, each time an additional cooling unit is activated, overall inductive load current of the cooling system increases thereby potentially increasing a phase difference between the load current and the load voltage. As such, logic 324 is operable to receive a load current indication from each current sensor 312, 316 and 320 that is detecting load current and to determine a corresponding biasing element value. Since the current increases with the addition of load devices, the scaling of the current sensor outputs must be adjusted so that a true phase difference may be detected between the load current and the load voltage as described before. For example, a primary load device may require 25 Amps of current, a second load device may require 15 Amps, and a third load device may require 10 Amps. In another embodiment, each load device may require an equivalent amount of current. For either application, however, logic 324 is operable to select a specified biasing element value that corresponds to the known loading condition.

Additionally, in one embodiment of the invention, the filter 332 includes selectable filtering elements to maximize filtration characteristics including frequency of operation, bandwidth and settle time according to specified loading conditions. Thus, logic 324 is operable to generate filter control signals and bias element control signals based upon loading conditions, and in the illustrated example of Figure 16, upon which load devices are on and drawing inductive load current.

In contrast to the embodiment of Figure 15, the embodiment of Figure 16 provides a system in which a single line filter may be used for a plurality of load devices by adaptively setting biasing levels biasing elements to adjust a magnitude of the signal generated by at least one current sensor to match signal magnitude levels corresponding to a load voltage to enable a comparator, such as comparator 250 of Figure 15 to accurately generate an error signal based upon phase differences of the varying load current and the load voltage. The embodiment of Figure 15 would require a complete system for each load device. Figure 17 illustrates one embodiment of selectable biasing element 328 and its operation in relation to logic 324. As may be seen, logic 324 is operable disposed to receive current sensor output signal from a plurality of current sensors on a corresponding plurality of input lines. Generally, one embodiment contemplates a single current sensor for each load device though alternate approaches may be employed. For example, one current sensor may be used to detect a total current value to generate a corresponding voltage that reflects the current magnitude. In such an embodiment, additional logic is used to detect how many load devices are drawing inductive load current. The inputs to logic 324, therefore, may be in any form than enable logic 324 to determine loading conditions. In a system in which a single load device is operable to draw differing load currents, corresponding logic is included to identify the load conditions to the logic 324.

Logic 324, therefore, based upon load conditions, is operable to select a corresponding biasing level to result in a signal amplitude being scaled to match a voltage signal magnitude prior to being produced to a comparator 250 for comparison to determine the phase difference between the load voltage and the load current.

In the specific embodiment of Figure 17, logic 324 generates a signal to a multiplexer that operably couples a specified resistor to the line carrying the current sensor signal (input to the full wave rectifier as shown in Figure 15) to provide the desired biasing to properly scale the input signal to the comparator 250.

Similarly, Figure 18 illustrates operation of logic 324 in relation to line filter 328. Line filter 328 includes filter circuitry that includes a selectable filtering element. As such, logic 324 generates a filter control signal to select one of a plurality of capacitive values to adjust overall filter operation. One of average skill in the art may readily determine appropriate capacitive values in relation to design requirements. Generally, though, it may be seen that the selectable filtering element includes one permanently coupled capacitor and a plurality of selectable capacitors operably disposed in parallel. As such, the filter settle times, bandwidth and center frequency may be adjusted as necessary. It should be understood that there are many filter configurations that are known and that may be used. Generally, though, each filter configuration includes at least on capacitive element that substantially affects filter operation. Thus, such circuitry is represented generally herein and the selectable filtering element corresponds to the capacitive element within the filter that substantially affects filter performance.

Although the invention has been described in detail with reference to this preferred embodiment, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents. The entire disclosures of all references, applications, patents, and publications cited above are hereby incorporated by reference.

Claims

CLAIMSWhat is claimed is:

1. An automated AC line filter which is activated when a lagging inductive current is detected at a load, the automated line filter comprising: an AC line filter; a current sensor adapted for electrical communication with an AC power line to the load for sensing the lagging inductive current at the load; and a switch mechanism in electrical communication with said current sensor and said AC line filter, said switch for providing electrical continuity between said AC line filter and the AC power line to the load upon a predetermined sensed lagging inductive current at said current sensor.

2. The automated line filter of claim 1 wherein said current sensor comprises an operational amplifier to discriminate between inductive loads and resistive loads.

3. The automated line filter of claim 2 wherein said operational amplifier comprises a differential comparator.

4. The automated line filter of claim 2 wherein said operational amplifier comprises an error output when a difference in a phase angle is detected between a voltage at the current sensor and a line input sample.

5. The automated line filter of claim 1 further comprising a reset for said switch mechanism for disengaging said AC line filter when the predetermined sensed lagging inductive current falls below a level.

6. A method of automatically providing AC line filtering to an AC power line to a load based on a predetermined lagging inductive current at the load, the method comprising the steps of: providing an AC line filter; sensing an amount of lagging inductive current at the load with a current sensor; and applying AC line filtering to the AC power line to the load based upon an output from the current sensor.

7. The method of claim 6 wherein the step of sensing comprises discriminating between inductive loads and resistive loads.

8. The method of claim 7 wherein the step of discriminating comprises discriminating with a differential comparator.

9. The method of claim 7 wherein the step of discriminating comprises creating an error output when a difference in a phase angle is detected between a voltage at the current sensor and a line input sample.

10. The method of claim 6 further comprising disengaging the AC line filter when the predetermined sensed lagging inductive current falls below a level.

11. An automated AC line filter which is activated when a lagging inductive current is detected at a load that is coupled to receive a power signal characterized by a load current and a load voltage, the automated line filter comprising: an AC line filter; a current sensor adapted for electrical communication with an AC power line to the load for sensing load current at the load, wherein the current sensor produces a voltage output that reflects a current magnitude of the load current; a biasing element for selectively reducing a magnitude of the current sensor voltage output; a comparator operably disposed to receive the load voltage and the current sensor voltage output, wherein the comparator produces an error signal based upon a phase difference in the load current and the load voltage; a switch mechanism operably disposed to receive the error signal and to activate the AC line filter as long as the error signal is greater than a specified value.

12. The automated line filter of claim 11 wherein the error signal is below the specified threshold for resistive loads and above the specified threshold for inductive loads before activation of the AC line filter.

13. The automated line filter of claim 12 wherein said comparator comprises an operational amplifier and wherein the output error signal reflects a difference in a phase angle that is detected between the load voltage and the current sensor voltage output.

14. The automated line filter of claim 11 further comprising a reset for said switch mechanism for disengaging said AC line filter when the error signal falls below the specified value.

15. The automated line filter of claim 11 wherein the biasing element includes circuitry for automated selection of biasing levels of the biasing element.

16. The automated line filter of claim 15 including logic operably disposed to receive at least one current loading indication wherein the logic generates a biasing element control signal based upon the at least one current loading indication.

17. The automated line filter of claim 15 including logic operably disposed to receive at least one current loading indication wherein the logic generates a filter control signal based upon the at least one current loading indication to select at least one capacitive value within filter circuitry to set filter operation.