JP2003513603A - Static regulator - Google Patents

Abstract

(57) [Summary] A static voltage regulator is composed of a booster transformer, a regulator transformer, an electronic switching system, and a control system. The booster transformer includes a booster primary winding and a booster secondary winding, the booster secondary winding being connected in series with the input and the output to generate an output voltage. The regulator transformer includes a regulator primary winding and a regulator secondary winding, wherein the regulator primary winding is electrically coupled to the output. An electronic switching system is coupled between the regulator secondary winding and the booster primary winding to supply voltage to the booster primary winding. The control system includes a voltage sensor for sensing an input voltage, and a gating system coupled to the switching system for switching an output voltage in response to the sensed change in the input voltage. The voltage regulator also includes a notch filter coupled to the booster transformer to reduce transients induced in the booster transformer when the output voltage is switched.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a voltage regulator that adjusts an AC voltage at a load terminal according to a change in power supply voltage. In particular, the present invention relates to a medium voltage regulator using a feedforward method to regulate the load voltage.

[0002]

[Prior art]

Commercial and industrial users of sensitive electronic and electrical devices are continually powered at reasonably constant frequencies and voltages depending on the use of their power. Excessive or undervoltage conditions in power lines that supply such high power to consumers (hereinafter referred to as power events) increase the cost of the device and / or cause process line interruptions and May damage electronic devices. As a result, many moderate power users use voltage regulators to eliminate or substantially reduce the impact of power events on their electronic and electrical devices.

Conventional medium power voltage regulators include booster transformers, regulator transformers with multi-tap secondary windings, primary windings of booster transformers and secondary transformer regulators. It comprises an electromechanical tap switch coupled between each winding tap and a mechanical bur switch connected in parallel with the booster transformer. The secondary winding of the booster transformer is connected in series with the distribution line and the load (such as electronic equipment), and the primary winding of the regulator transformer is in parallel with the power supply side of the distribution line preceding the booster transformer. Connected.

Under normal power line conditions, the crowbar switch is closed and the booster transformer is operated simply as an inductance in series with the load. The control logic monitors the load voltage and closes one of the tap switches in response to a load power event. The crowbar switch is then opened and the voltage from the regulator transformer secondary winding appears across the booster transformer primary winding and is added to the supply voltage. The particular tap switch that is closed is chosen so that the voltage induced in the booster transformer secondary winding is of sufficient magnitude and of opposite polarity to the power event.

However, mechanical switches add to the maintenance cost of conventional voltage regulators. Moreover, conventional voltage regulators have slow response times due to the presence of mechanical switches (typically several seconds are required to correct an undervoltage condition). Industrial users of microprocessor-controlled devices and other power-sensitive devices cannot tolerate large changes in supply voltage, so the delays in operation associated with conventional voltage regulators are often unacceptable. Is.

[0006]

[Problems to be Solved by the Invention]

Due to the faster response of semiconductor switches than mechanical switches, semiconductor static voltage regulators have recently been developed as a replacement for conventional mechanical voltage regulators. Such a voltage regulator is described in Schoendube, US Pat. No. 3,732,486, which includes a booster transformer, a multi-tap shunt transformer, and one end of the booster transformer primary winding and a shunt transformer. It consists of a series of thyristor tap switches coupled between each tap. The other end of the primary winding of the booster transformer is connected to a half H-bridge circuit, which allows the voltage regulator to operate in either booster or buck mode. The secondary winding of the booster transformer is connected in series between the input terminal and the load terminal, while the shunt transformer is connected between the input terminal and the voltage reference. The regulator comprises a bypass thyristor switch connected in parallel with the primary winding of the booster transformer.

In operation, the line voltage is supplied to the input terminal of the Schoendube voltage regulator. If the output voltage is within the acceptable range, the bypass thyristor switch is closed, thereby shorting the primary winding of the booster transformer and providing a voltage gain of one. During undervoltage conditions, the H-bridge is configured for boost mode, one of the tap switches is closed and the bypass thyristor is turned off to induce a voltage on the secondary winding of the booster transformer, which is fed to the input terminal. to add. Conversely, during an overvoltage condition, the H-bridge is configured for buck mode and one of the tap switches is closed, causing it to induce in the secondary winding of the booster transformer and subtract it from the voltage at the input terminal. Although Schoendube voltage regulators can obtain shorter response times than regular mechanical regulators, forced thyristor switching can induce unwanted transients in the load.

Another voltage regulator with improved response time is described in Flynn, US Pat. No. 4,896,092, which discloses a booster transformer, an output transformer, an output transformer and a booster transformer. And a switch matrix coupled between them.
The output transformer comprises a primary winding, an output winding and a multi-tap winding. The secondary winding of the booster transformer is connected in series with the input terminal and the primary winding of the output transformer, and the output winding of the output transformer is connected to the output terminal. The switch matrix includes a series of triac switches, which are connected between the primary winding of the booster transformer and each tap of the multi-tap winding.

In operation, the line voltage is applied to the input terminals of Flynn's voltage regulator. The control circuit monitors the peak voltage of each half-cycle at the output terminals and either boosts the output voltage (when operating in boost mode) or reduces the output voltage (when operating in buck mode). The gate signal is applied to the switch matrix. However, Flynn's voltage regulator does not consider the problem of transients that can be induced in the load when the triac is switched. Therefore, there remains a need for a medium voltage regulator that provides a shorter response time than a conventional mechanical regulator and reduces the risk of transients being induced in the load when the load voltage is compensated. ing.

According to the present invention, a static voltage regulator is provided which overcomes the drawbacks of conventional voltage regulators.

[0011]

[Means for Solving the Problems]

The static voltage regulator according to the present invention comprises an input, an output, a booster transformer, a regulator transformer, an electronic switching system and a control system. The booster transformer comprises a booster primary winding and a booster secondary winding. The booster secondary winding is connected in series with the input and the output to produce the output voltage. The regulator transformer comprises a regulator primary winding and a regulator secondary winding. The regulator primary winding is electrically coupled to the output. The electronic switching system is coupled between the regulator secondary winding and the booster primary winding to provide voltage to the booster primary winding. The control system includes a voltage sensor that senses the voltage at the input terminal and a gate system that is coupled to the switching system to switch the output voltage in response to a sensed change in the input voltage. The voltage regulator also includes a notch filter coupled to the booster transformer to reduce transients induced in the booster transformer when the output voltage is switched.

In a preferred embodiment of the present invention, the regulator secondary winding comprises a plurality of voltage taps, which taps are a voltage boost tap for increasing the output voltage and a voltage back tap for decreasing the output voltage. Is included. The electronic switching system comprises a plurality of electronic switches. Each switch has a respective gate input for controlling the conduction period and is coupled between the booster primary winding and each of a plurality of taps for supplying one of a plurality of voltages to the booster primary winding. Has been done. The gating system is coupled to the voltage sensor and includes a gating input that switches the output voltage in response to a sensed change in the input voltage, and switches on the conducting switch of the electronic switch before one of the non-conducting switches of the electronic switch closes. It is configured to open.

[0013]

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings, but it should be understood that this is merely an example and does not limit the technical scope of the present invention.

Referring to FIG. 1, only one phase portion of a three phase static voltage regulator is shown. However, it should be understood that the static voltage regulator may be configured as a single phase, or may be configured as another number of phases, as desired.

A static voltage regulator, shown generally at 100, includes an input port 102 that is coupled to a power source, such as a power distribution line, and an output port 104 that is coupled to a load (not shown). A booster transformer 110, a regulator transformer 112, an electronic switching system 114 connected between the booster transformer 110 and the regulator transformer 112, and a control system 116 coupled to the electronic switching system. , A notch filter 118 coupled to the booster transformer 110. Booster transformer
110 has a booster primary winding 120 and a booster secondary winding 122. The booster secondary winding 122 is provided in series with the input port 102 and the output port 104.

The regulator transformer 112 has a regulator primary winding 124 and a regulator secondary winding 126. The regulator primary winding 124 is connected to the output port 104, and the regulator secondary winding 126 includes a plurality of taps 126a, 126b, 126c, ... 126n, each of which outputs a discrete analog output voltage.

Electronic switching system 114 includes a plurality of electronic tap switches 128. Each electronic switch 128 includes a first end 120a of the booster primary winding 120 and a tap 12
The booster primary winding 120 is connected between each of the six and one of the plurality of voltages.
Give to. The second end 120b of the booster primary winding 120 is directly connected to one of the taps, in the illustrated example tap 126m. Taps 126a, 126b in this arrangement
, 126c-1, ... 126m-1 applies voltage to the booster primary winding 120 to adjust the voltage to the regulator 100.
Is configured to boost or increase the output voltage of the. Remaining taps,
That is, the taps 126m + 1, ... 126n are configured to provide a voltage to the booster primary winding 120 that causes the output voltage of the regulator 100 to buck or decrease. However, it is not mandatory that the voltage regulator 100 include both boost and back taps. Rather, the voltage regulator 100 may include only boost taps or only back taps without departing from the scope of the invention. Furthermore, it is not essential that the regulator transformer secondary winding have multiple taps 126 and that the electronic tap switch 128 be connected to each tap 126. Instead, in low voltage applications, the regulator transformer secondary winding produces a single voltage and the electronic switching system 114 supplies the booster primary winding 120 with one of a plurality of voltages to provide an amplifier. May be provided.

The electronic switching system 114 may also include an electronic bar switch 130 connected in parallel with the booster primary winding 120. In the illustrated embodiment, each electronic switch 128, 130 comprises a pair of anti-parallel connected SCR switches. However, other electronic switches including FETs, IGBTs, GTOs, IGCTs, triacs and bipolar transistors can be used instead of SCRs.

Each electronic switch 128, 130 has a pair of gate inputs 132 for controlling the conduction period of the switch extending between each electronic switch and the control system 118.
As shown in FIG. 2, the control system 116 includes an analog voltage sensor 134 for sensing the voltage at the input port 102, a sample & hold circuit 136 connected to the analog output of the voltage sensor 134, and a sample & hold circuit 136. Analog-to-digital (AD) converter 138 connected to the output of the device, a zero-crossing voltage detector 140 for detecting the zero-crossing of the input voltage, and a zero-crossing current detection for detecting the zero-crossing of the current through the electronic switches 128, 130. And the container 142. The current detector 142 is a booster primary winding 120.
Is preferably coupled to the first end 120a of, but may be relocated to another node of the voltage regulator if desired.

The control system 116 also includes a microprocessor-based gating system 144, which has a break input that receives a break signal from the zero-crossing voltage detector 140, a data input that receives a control signal from the current detector 142, and an analog-to-digital conversion. A data input port that receives the digitized input voltage from the instrument 138 and a sample and hold circuit 136
A control output for triggering and a gate input 13 of an electronic switching system 114 that switches the output voltage of the voltage regulator 100 in response to a change in the sensed input voltage.
And a gate driver 146 connected to 2. As will be appreciated, the voltage regulator 100 may include a separate control system 116 for each phase of the input voltage, or a single control system for all phases.

Notch filter 118 includes RLC filters connected in series and is connected in parallel to booster primary winding 120. The dual purpose of this filter 118 is to reduce the notches and transients induced in the booster transformer 120 during the dead time of switching, and to set the initial load voltage when all electronic switches are off. Therefore, other suitable filter structures will be apparent to those skilled in the art and are intended to be within the scope of the present invention.

In operation, the voltage sensor 134 senses the voltage at the input port 102, preferably 32 times per cycle of the input voltage. Zero crossing voltage detector at the same time
140 monitors the input voltage for zero crossings. When a zero crossing of the input voltage is detected, the zero crossing voltage detector 140 issues a break signal to the gating system 144. Based on the fundamental frequency of the input voltage and the sampling rate of the voltage sensor 134, the gating system 144 sends a command to the sample & hold circuit 136 for time control, which causes the sample & hold circuit 136 to enter at each half cycle of the input voltage. Sample at the instantaneous peak value of the voltage.

The analog output of the sample and hold circuit 136 is converted to digital form by the analog-to-digital converter 138 and the digitized output is input to the gate system 144. Gating system 144 compares the sensed input voltage to the expected normal value. Deviation between sensed input voltage and normal, deviation period, and output port 104
Based on the voltage regulation required by the load connected to the gate system 144
Performs the steps, if any, necessary to counter the effects that changes in the input voltage have on the output voltage of regulator 100.

If the sensed input voltage is above the minimum threshold, which is preferably 90% of normal, the voltage regulator 100 operates in the no boost mode. In this mode, the control system 116 closes the bar switch 130 and all tap switches 128.
open. As a result, during normal line voltage conditions, booster transformer 110 appears as a short circuit between input port 102 and output port 104. Does not include leakage inductance in series with the load.

If the gate system 144 detects a drop in the input voltage for a period sufficient for warranty intervention, the control system 116 first determines which tap switch 128 is closed. Appropriate switch 128 is selected to boost the output voltage of voltage regulator 100 back above the minimum threshold, as will become apparent below.

Subsequently, the control system 116 removes the gating signal from the burl switch 130 and opens the burl switch 130 when the current through each SCR drops to zero. The current detector 142 indicates that the conduction state of the bar switch 130 has been stopped by the gate system 144.
After reporting to, the gating system 144 provides a gating signal to the selected tap switch 128 before the next zero crossing of the input voltage. By opening the booster primary winding 120, the magnitude of the voltage spike that would otherwise be induced across the booster transformer 120 is reduced by the presence of the notch filter 118. Notch filter 11
8 also limits the magnitude of the voltage "notch" that would otherwise be present during the period between the moment when the burl switch 130 is switched off and the moment when the selected tap switch 128 is switched on. Furthermore, the risk of damage to the var switch 130 at turn-on, which exists as a result of the rate of change of the current flowing through the SCR exceeding the maximum limit, is reduced by the presence of the notch filter 118, in particular the notch filter.
Reduced by 118 inductive components.

If the undervoltage condition improves or worsens, the control system 116 again determines the appropriate tap switch 128 and closes based on the deviation of the input voltage from its normal value. After notifying the gate system 144 that the current detector 142 is conducting and the tap switch 128 is no longer conducting, the gate system 144 gates the selected tap switch 128 before the next zero crossing of the input voltage. To supply. This process is continued and the gate system 144 continuously monitors the input voltage and determines the appropriate tap switch 128 to close each half cycle. When the undervoltage condition disappears, the gating system 144 removes the gating signal from the conducting tap switch 128. After the current detector 142 notifies the gate system 144 that the conducting tap switch 128 is no longer conducting, the gate system 144 provides a gate signal to the bar switch 130 before the next zero crossing of the input voltage. .

Similarly, if the gate system 144 detects that the input voltage has risen above the maximum threshold for a period sufficient for warranty intervention, the control system first determines which tap switch 128 to close. . Appropriate switch 12 to reduce the output voltage of voltage regulator 100 back below the maximum threshold, as will be seen later.
8 is selected. The control system 116 then sends the gate signal to the bar switch 130.
, And opens the bar switch 130 when the current through each SCR drops to zero. After the current detector 142 informs the gate system 144 that the Burl switch 130 is no longer conducting, the gate system 144 provides a gate signal to the selected tap switch 128 before the next zero crossing of the input voltage. To do. As a result, the regulator responds to an overvoltage condition about one quarter of the input voltage cycle.

If the overvoltage condition improves or worsens, the control system 116 again determines the appropriate tap switch 128 and closes it based on the deviation of the input voltage from its normal value. After notifying the gate system 144 that the current detector 142 is conducting, the tap switch 128 is no longer conducting, the gate system 144 then gates the selected tap switch 128 before the next zero crossing of the input voltage. To supply. This process is continued and the gate system 144 continuously monitors the input voltage to determine the appropriate tap switch 128 to close each half cycle. When the overvoltage condition disappears, the gating system 144 removes the gating signal from the conducting tap switch 128. After the current detector 142 notifies the gate system 144 that the conducting tap switch 128 is no longer conducting, the gate system 144 provides a gate signal to the bar switch 130 before the next zero crossing of the input voltage. .

In each case, it is assumed that each selected tap switch 128 is continuously closed for at least consecutive half cycles. Therefore, the regulator 100 responds to changes by one of a plurality of voltage steps. However, the invention is not so limited and in a variant, the electronic switch 128 is composed of a triac switch having a gate system 144, the gate system 144 providing a continuous output voltage of the regulator 100 between each discrete voltage step. Trigger the tap switch 128 selected by the pulse train to change to.

Also, as mentioned above, in each case the control system 116 selects the appropriate tap switch 128 to close each half cycle of the input voltage based on the instantaneous peak value of the input voltage. The selected tap switch 128 is the previously conducting tap switch 12
Since 8 (or crowbar switch 130) closes after it ceases to conduct, it responds to an overvoltage or undervoltage condition about one quarter of the input voltage cycle. Also, because regulator 100 monitors the input voltage rather than the output voltage, regulator 100 can use a "feedforward" method for voltage regulation rather than the typical "feedback" method of the prior art. As a result, the regulator 100 can respond to changes in the input voltage before it has a significant impact on the output voltage, the response time of which is generally within about 16.7 ms at an input voltage frequency of 60 Hz.

The above description is intended to exemplify the preferred embodiments of the invention, and those skilled in the art may make additions, removals, and / or modifications to the described embodiments that are outside the scope of the invention. It is possible to think without thinking.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a system including a one-phase booster transformer, a regulator transformer, an electronic switching system, a control system, and a notch filter of a three-phase static voltage regulator according to the present invention.

[Fig. 2]   2 is a block diagram of the control system shown in FIG. 1. FIG.

[Procedure amendment]

[Submission date] May 29, 2002 (2002.5.29)

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Contents of correction]

[Figure 1]

─────────────────────────────────────────────────── ─── Continued front page    (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE), OA (BF, BJ , CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, K E, LS, MW, MZ, SD, SL, SZ, TZ, UG , ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, C N, CR, CU, CZ, DE, DK, DM, EE, ES , FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE, KG, KP, K R, KZ, LC, LK, LR, LS, LT, LU, LV , MA, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, S I, SK, SL, TJ, TM, TR, TT, TZ, UA , UG, US, UZ, VN, YU, ZA, ZW (72) Inventor Rajda, Janos             Canada, L4 Z / 3 W4,             Winde, Mississauga, Ontario             Lee Hill Court 5471 (72) Inventor Dewan, chassis             Canada, M8X, 1K7, O             King George, Toronto, Ntario             Su Road 18 (72) Inventor Wu, Luson             Canada, M4 W / 4 Sea 3, O             Tree View, Etobicoke, State of Antario             Drive 126 (72) Inventor Lee, Jiang Ping             Canada, M8V-3J9, ON             Sixty, Etobicoke, State of Tario             Nance Street 103-8 F-term (reference) 5H750 AA02 BA01 BA05 CC03 CC04                       CC06 CC12 CC14 CC16 DD25                       DD26 FF03 FF05

Claims (17)

[Claims] 1. A static voltage regulator having an input and an output, comprising a booster primary winding and a booster secondary winding, the booster secondary winding being connected in series with the input and the output. A booster transformer producing an output voltage, a regulator transformer having a regulator primary winding and a regulator secondary winding, the regulator primary winding electrically coupled to the output, An electronic switching system coupled between the regulator secondary winding and the booster primary winding to supply voltage to the booster primary winding, a voltage sensor for sensing the input voltage, and a sensing coupled to the switching system. A control system that includes a gate system that switches the output voltage in response to a change in the input voltage applied to the booster transformer and is induced in the booster transformer when the output voltage is switched. Static type voltage regulator that includes a notch filter to reduce that transients. 2. The electronic switching system comprises a plurality of electronic switches each having a gate input for controlling a conduction period, and a booster transformer coupled to a voltage sensor and responsive to the sensed input voltage. A gate system having a gate input for selectively supplying one of a plurality of voltage levels from a regulation transformer, said gate system comprising: closing one of the non-conducting switches of the electronic switch. A static voltage regulator according to claim 1, wherein the static voltage regulator is arranged to open one of the conducting switches of the electronic switch. 3. The voltage sensor is configured to sense the instantaneous peak value of the input voltage, and the gating system opens one switch conducting for 1/4 cycle of the input voltage after the sensed peak value. The static voltage regulator according to claim 2, which is configured as follows. 4. The voltage sensor is configured to sense the instantaneous peak value of the input voltage, and the gate system senses the current flowing through the one switch that is conducting and then switches the one switch that is not conducting. The static voltage regulator according to claim 2, wherein the static voltage regulator is configured to be closed. 5. The notch filter causes distortion of the output voltage that occurs between a first moment after one conducting switch is opened and a second moment before the non-conducting switch is closed. 3. The static voltage regulator of claim 2 configured to reduce 6. The static voltage regulator of claim 5 wherein the notch filter comprises a series RLC filter connected in parallel with the booster primary winding. 7. The static type according to claim 2, wherein the plurality of electronic switches comprises an electronic bur switch connected in parallel with the booster primary winding for selectively short-circuiting the booster primary winding. Voltage regulator. 8. The regulator transformer secondary winding includes a plurality of voltage taps, each electronic switch being connected to one of the taps, the tap being a voltage boost tap for increasing the output voltage, and an output voltage. 3. A static voltage regulator as claimed in claim 2 including a voltage back tap for reducing. 9. A static voltage regulator having an input and an output, comprising a booster primary winding and a booster secondary winding, the booster secondary winding providing an input and an output voltage for producing an output voltage. It includes a booster transformer connected in series with the output, a regulator primary winding and a regulator secondary winding, the regulator primary winding being electrically coupled to the output, and the regulator secondary winding. Includes a plurality of voltage taps, the taps including a voltage boost tap for increasing the output voltage, a voltage transformer tap including a voltage back tap for decreasing the output voltage, and a conduction period control. And a plurality of electronic switches each coupled to a booster primary winding and coupled to each of the plurality of taps to provide one of the plurality of voltages to the booster primary winding. is doing An electronic switching system, a voltage sensor for sensing an input voltage, and a gate system coupled to the voltage sensor for switching the output voltage in response to a change in the sensed input voltage are provided. A control system configured to open one conducting switch of the electronic switch before the switch is closed, and an induction in the booster transformer when the output voltage is switched when coupled to the booster transformer. And a notch filter for reducing transients caused by the static voltage regulator. 10. The voltage sensor is configured to sense an instantaneous peak value of the input voltage, and the gating system includes a switch conducting for 1/4 cycle of the input voltage after the sensed peak value. The static voltage regulator according to claim 9, wherein the static voltage regulator is configured to open. 11. The voltage sensor is configured to sense the instantaneous peak value of the input voltage, and the gate system turns on one switch that is non-conducting after the current flowing through the one switch that is conducting is stopped. 10. The device according to claim 9, which is configured to be closed.
The static voltage regulator described. 12. The static voltage regulator of claim 9, wherein the notch filter comprises a series RLC filter connected in parallel with the booster primary winding. 13. The static type of claim 9, wherein the plurality of electronic switches comprises an electronic bur switch connected in parallel with the booster primary winding to selectively short the booster primary winding. Voltage regulator. 14. A booster transformer comprising a booster primary winding and a booster secondary winding, the booster secondary winding connected in series with the input and the output to produce an output voltage, and a regulator. A primary transformer and a multi-tap regulator secondary winding, with the regulator primary winding electrically coupled to the output, and a transformer transformer for supplying voltage to the booster primary winding. Method of controlling output voltage in a voltage regulator comprising an electronic switching system comprising a plurality of electronic switches coupled between a booster primary winding and each tap of a regulator secondary winding To sense the voltage at the input, determine the deviation between the sensed value and the expected normal value, and counteract the change in output voltage resulting from said deviation by opening one of the conducting switches, Then the non-conduction A method of controlling an output voltage in a voltage regulator including the step of closing one of the switches, one switch of which is non-conducting is selected according to the deviation. 15. The method of claim 14, wherein the sensing step senses an instantaneous peak value of the input voltage every half cycle of the input voltage. 16. The method of claim 15, wherein the counteracting step opens a switch that is conducting for 1/4 cycle of the input voltage after the peak has been sensed. 17. The method of claim 15, wherein the counteracting step includes the step of closing the non-conducting switch after the current flowing through the conducting switch has stopped.