WO2007016789A1

WO2007016789A1 - High voltage to low voltage bi-directional converter

Info

Publication number: WO2007016789A1
Application number: PCT/CA2006/001316
Authority: WO
Inventors: David A. Kelly
Original assignee: Kelly David A
Priority date: 2005-08-09
Filing date: 2006-08-08
Publication date: 2007-02-15
Also published as: CA2513599A1

Abstract

A high voltage to low voltage bi-directional converter using a plurality of switches connected in series to a high voltage DC source such that the switches are operated as an even number of pairs to form a plurality of half bridges, which are further connected to make a plurality of full bridges. The switches are operated using a predefined, controlled switching sequence, which may change depending on the type of input DC or AC and the desired output waveform.

Description

HIGH VOLTAGE TO LOW VOLTAGE BI-DIRECTIONAL CONVERTER

FIELD OF THE INVENTION

The present invention relates generally to a power supply for DC or AC devices and in particular, to a power supply for converting any type of high voltage DC or AC to another voltage DC or AC, alternately the power supply may be restricted to just High Voltage DC to

DC conversion, High Voltage AC to AC, high voltage DC to AC, High voltage AC to DC, or any other combination therein.

BACKGROUND OF THE INVENTION

Efficient conversion of high voltage to low voltage has become a problem with the advancement of a number of technologies. One such emerging market pertains to advances in energy storage in high voltage capacitors, which involve the need to efficiently convert bi- directionally a high voltage to a lower voltage. The requirement for higher efficiency in basic electric power transmission has lead to a search for alternative methods of distributing electric power throughout a transmission system. Further the increasing costs and shortage of industrial metals has created the need by Electric Utilities for an economical replacement for the distribution transformer. An electronic distribution transformer would be able to provide a regulated output, operate from a high voltage DC electric transmission system and have very low idle power loss. Another requirement -to operate high power electrical devices, has necessitated the transition to high voltage DC power distribution by Electric Utilities, systems on ships, aircraft and ground vehicles. The operation of these systems requires a number of different High Voltage to Low Voltage power converters. FIG. 1 shows part of the typical technology employed by the power industry for transmitting high voltage, high power DC across large distances. The technical reference Dennis A. Woodford "HVDC Transmission" Manitoba HVDC Research Centre, 18 March 1998, 27 pages, provides more detail. The typical voltages are 50OkV, using 200 or more high voltage solid-state switches in series. These solid-state switches are slow, are designed for very high levels of power, and are therefore not suitable for use at low power levels. In FIG. 1, switches 101, 102, 103 are in series and pull the end of capacitor 107 to Vdc+ 150 when the SWITCH DRIVE 155 is in the first state shown by the table called SWITCH DRIVE 154. Alternately, as you progress along the clock table switches 101, 102, 103 open and then 104, 105, 106 are closed and connect the end of capacitor 107 to Vdc- 151. The resulting action of alternating the connections of capacitor 107 between Vdc+ 150 and Vdc- 151 creates a square wave on the primary of transformer 108, which is then reduced in voltage, rectified into a lower voltage DC Vout+ 152 and Vout- 153. Alternately, the output of transformer 108 is filtered to make a clean AC waveform by removing rectifiers 109, 110 and replacing them with a suitable filter. The disadvantage of this technology is that for lower power operation the switch losses are large when the frequency of operation is increased. The very high losses encountered when operating at high frequency are undesirable for a cost of operation standpoint. Further, the cost benefits of operating at high frequency, smaller size for transformer 108 and capacitors 107, 111 are not possible with currently used methods. As well the large number of switches stacked in series requires special protection circuits, not shown in FIG. 2, to ensure that all switches share the voltage equally, increasing the cost of manufacture.

The following patents are converters but not all are designed specifically for high voltage to low voltage: U.S. Pat. No. 5,199,285, Jun 2, 1992, "Solid State Power Transformer Circuit"; U.S. Pat. No. 5,666,278, Sept 9, 1997, "High Voltage Inverter Utilizing Low Voltage Power Switches"; and U.S. Pat. No. 5,943,229, Aug 24, 1999, "Solid State Transformer". Other related patents are art that are either bi-directional, specifically designed for DC to DC operation or related in some way DC to AC conversion include; U.S. Pat. No. 4,105,939 Aug. 8, 1978, "Direct Digital Technique For Generating An AC Waveform"; U.S. Pat. No. 4,290,108, Sept. 15, 1981, "Control Unit For A Converter"; U.S. Pat. No. 4,399,499, Aug. 16, 1983; "Bi-Lateral Four Quadrant Power Converter"; U.S. Pat. No. 4,742,441, May 3, 1988, "High Frequency Switching Power Converter"; U.S. Pat. No. 5,255,174, Oct. 19, 1993, "Regulated Bi-Directional DC-to-DC Voltage Converter Which Maintains A Continuous Input Current During Step-UP Conversion"; U.S. Pat. No. 5,815,384, Sept. 29, 1998, "Transformer Which Uses Bi-directional Synchronous Rectification To Transform The Voltage Of An Output Signal Having A Different Voltage And Method For Effecting Same". Of all of these fore mentioned documents U.S. Pat. No. 4,399,499, Aug. 16, 1983; "Bi-Lateral Four Quadrant Power Converter" and U.S. Pat. No. 4,742,441, May 3, 1988, "High Frequency Switching Power Converter" are representative of the technological base in this field. SUMMARY OF THE INVENTION

The invention provides an improved method of converting a high voltage DC or AC into a regulated lower voltage DC or AC. In one aspect of the invention, there is provided a plurality of switches connected in series to a high voltage DC source. The switches are operated as an even number of pairs to form a plurality of half bridges, which are further connected to make one or a plurality of full bridges. The switches are operated using a predefined, controlled switching sequence, which may change depending on the type of input DC or AC and the desired output waveform. In an embodiment, the SWITCH DRIVE operates using a phase shifted PWM (pulse width modulated) method of control such that the phase difference between two full duty square-wave half bridge inverters, forming a full bridge is controlled, with the combined output of the bridge being a PWM (pulse width modulated) waveform. The SWITCH DRIVE may be generated using many different methods such as using an existing integrated circuited designed for this purpose, a lookup memory device with a microprocessor combined with additional analogue and or logic circuits or a set of analogue or logic circuits with or without the use of a lookup memory device. The SWITCH DRIVE circuit may be powered by a separate power source or by a special start-up run control circuit that operates from the high voltage input. In specific embodiments of the invention, the outputs of the switches are connected to the primary of one or more isolation transformers that have a single or multiple primaries. In one specific embodiment, each primary of the isolation transformer(s) will have one or more capacitor in series to block the flow of DC voltage. In this preferred embodiment, at least one or more isolated secondaries are provided that have the output rectified and filtered to provide the intended regulated low voltage DC output.

In accordance with a second aspect of the invention, there is provided a universal converter that provides a well-regulated low voltage DC or AC output, from either a DC or AC input. In AC operation, the input switches are bi-directional, or AC switches, connected in series to a high voltage DC or AC source. The switches are operated as an even number of pairs to form a plurality of half bridges, which are further connected to make one or more full bridge(s). The switches are operated using a predefined, controlled switching sequence, which may change depending on the type of input used or on the desired output.

In an embodiment, the SWITCH DRIVE operates using a phase shifted PWM (pulse width modulated) duty such that the phase difference between two full duty square-wave half bridge inverters, forming a full bridge is controlled, with the combined output of the bridge being a PWM (pulse width modulated) waveform. The SWITCH DRIVE may be generated using many different methods such as using an existing integrated circuit designed for this purpose, a lookup memory device with a microprocessor combined with additional analogue and or logic circuits or a set of analogue or logic circuits with or without the use of a lookup memory device. The switch drive circuit may be powered by a separate power source or alternately a special start-up run control circuit that operates from the high voltage input. The outputs of the switches are then connected to the primary of either one or more isolation transformers with single or multiple primaries. In a preferred embodiment of this aspect of the invention, each primary of the isolation transformers) will have one or more capacitor in series to block the flow of DC voltage. This embodiment has at least one or more isolated secondary that have output rectified by switches with the outputs of these switches feeding the input of one or more inductor(s). The output of this inductor(s) is then connected to a capacitor to filter out any undesired ripple voltage. The resulting output waveform may be then changed or regulated using feedback and a control circuit that alters the duty of the drive signals applied to the switches.

In an embodiment of the above aspects of the invention, a plurality of diodes or DC switches or combination are provided in the transformer secondary circuit, for a regulated DC output. In another embodiment of the above aspects of the invention, a plurality of bi- direction AC switches are provided in the secondary circuit for regulated bi-directional DC or AC output.

In another embodiment of the above aspects of the invention, one or more converters are powered by a battery, fuel cell, capacitor or flywheel or combination thereof and converts it as appropriate to accelerate or maintain the speed of a Drive Motor. When it is desired to slow the Drive Motor then the converter transfers the power from the Drive Motor, operating as a generator to transfer power back to the power source.

In further embodiments, a plurality of half-bridges may not be paired into full bridges but are instead connected in series to a high voltage DC input to drive the primary of a transformer combined with switches on the secondary side to rectify the transformer secondary into a DC or AC output of desired polarity.

In additional embodiments, a plurality of bi-directional half-bridges are provided in series across a high voltage input to drive the primary of a transformer instead of bi-directional full bridges connected in series, which are combined with bi-directional switches on the transformer secondary side to generate a DC or AC output as determined by the duty of the PWM and polarity of the secondary switches' operation with respect to the primary.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic of a prior art method using series switches for high voltage to low voltage DC;

FIG. 2 is a schematic representation of a DC to DC converter showing a method for providing a regulated output;

FIG. 3 a schematic representation of a converter configured in accordance with an embodiment of the invention for providing a regulated DC output;

FIG. 4 is a schematic representation of a converter configured in accordance with an embodiment of the invention for providing a regulated bi-directional DC or AC output;

FIG. 5A, 5B, 5C is a schematic representation of switches suitable for use in accordance with certain embodiments of the invention; FIG. 6 A, 6B is a schematic representation showing various types of filter arrangements suitable for use in accordance with certain embodiments of the invention;

FIG. 7 is a schematic representation showing a secondary side switch arrangement in accordance with an embodiment of the invention;FIG. 8 is a schematic representing a method of connecting a power source to an output device in accordance with an embodiment of the invention;

FIG. 9 is a schematic representing a method of connecting a power source to an output device in accordance with an embodiment of the invention; and

FIG. 10 is a schematic representing alternate switch and power supply waveforms in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 is reproduced from applicant's copending US application US 11/133,189 entitled DC HIGH VOLTAGE TO DC LOW VOLTAGE CONVERTER, filed 20 May, 2005. A detailed explanation is as follows. The converter is capable of producing a well regulated output as it has components such as PWM MODULE 232, SWITCH DRIVER 233 that may be PWM (Pulse Width Modulation) in a similar manner as used by commercial AC to DC switching power supplies. Switches 200, 201; 202, 203; 204, 205 form three half bridges that are connected in series. Capacitors 206, 207, 211,212 filter the switch current pulses reducing the AC that is generated by the half bridges across the high voltage DC input Vdc+ 250 and Vdc- 251. The addition of resistors 214, 215 and 216 are used to force the voltages to be equal across capacitors 206, 207 and 211 during the start-up time that the half bridges are off. Capacitor 212 is used to provide a start-up for the START MODULE 231 which has various components that store sufficient charge to run the half bridges for a specific time after which an auxiliary winding 260 from transformer 218 supplies the necessary power to run the control electronics. Alternately, an external DC or AC power source, not shown, provides the power to operate the DC to DC converter and is either common to or close to either Vdc+ 250 or Vdc- 251.

In FIG. 2 the FEEDBACK 230 supplies a signal used by the PWM MODULE 232 to generate the appropriate width clock signals that are supplied to the SWITCH DRIVER 233, which then drives the switches 200, 201, 202, 203, 204, 205, with SWITCH DRIVE 254 a typical set of waveforms. The additional circuits function as follows. When high voltage power is first applied to Vdc+ 250 and Vdc- 251, the resistors 214, 215 and 216 charge capacitor 212. The START MODULE 231 determines when it has enough charge to operate the PWM MODULE 232 and SWITCH DRIVER 233 for a predetermined time. Alternately, the START MODULE 231 may be power by an external low voltage DC or AC source. After initially powering the converter electronics, the START MODULE 231 receives a low voltage AC from transformer 218 through secondary 260. The powered from this secondary 260 then provides the low voltage power to sustain operation of the PWM MODULE 232 and SWITCH DRIVER 233. Further in FIG. 2, once the START MODULE 231 has started the DC-to-DC converter, the FEEDBACK 230 provides a signal to the PWM MODULE 232 that is proportional in some way to the output voltage. The FEEDBACK 230 may use optical isolation, an isolation transformer etc. (not shown) to provide this isolated feedback signal to the PWM MODULE 232. When the SWITCH DRIVE 254 is decreased from full duty, 50% of full duty is shown as an example, then the waveform that appears on the secondary of transformer 218 is not a full duty square wave but has positive and negative pulses which are proportional in width to the SWITCH DRIVE 254 wave form. Diodes 219, 220 rectify the secondary AC into a pulsating DC, which is then filtered by inductor 221 and capacitor 210. The output inductor 221 and capacitor 210 filters the pulsating DC into an average value equal to the duty of the waveform multiplied by its amplitude. The circuit thereby provides a regulated low DC voltage output from a very High voltage input.

The switches, 200, 201, 202, 203, 204, 205 are typically semi-conductor devices that have a reverse diode across them to clamp any reverse voltage that may be generated by transformer 218 during the time the SWITCH DRIVE 254 changes state. The combination of the switches 200, 201, 202, 203, 204, 200 capacitor 208, 209, 213 and primary of transformer 218 may be combined in many different ways though function in the same method as shown in FIG 2.

In accordance with an embodiment of the invention, and with reference to Figure 3, there is provided a means for producing a regulated DC output or unregulated DC output. The HIGH VOLTAGE input is connected to INPUT 350 and 351. SWITCHES 300 through 307 are DC type if DC HIGH VOLTAGE is applied to INPUT 350, 351 and bi-directional or AC type if connected to an AC HIGH VOLTAGE.

SWITCHES 300, 301 form one half-bridge and 302, 303 form the other side of a half- bridge which is combined and operated as a full bridge with capacitor C319 blocking the DC component from being applied to the primary of transformer 321. Both half bridges operate at full duty cycle with each switch ON for 50% of the time. To create a PWM output the phase of the half bridge 302, 303 is shifted from that of switches 300, 301 by an amount equal to the desired pulse width. SWITCH DRIVE 354 provides and example of this, with signal A the position of the SWITCH 300, HIGH or UP representing the ON or CLOSED state. B, C, D corresponds to SWITCH 301, 302, 303 accordingly and J represents the rectified difference signal that appears across the primary of TRANSFORMER 321. The duty of the primary waveform J on TRANSFORMER 321 can be changed by varying the phase of SWITCH signals A, B with respect to C, D. This type of switching method facilitates the use of isolation transformers for coupling the gate signals to the switches and can accommodate any PWM duty from 0 to 100% without worry of saturation of the switch driver transformers (not shown). SWITCHES 304, 305 form one half-bridge and 306, 307 form a second half bridge together making a full bridge and function in combination with CAPACITOR 320 and TRANSFORMER 323 in the same manner as SWITCH 300, 301, 302, 303, CAPACITOR 319, TRANSFORMER 321. An example of the switch drive waveforms is shown by SWITCH DRIVE 354 which demonstrates operation at a duty cycle of 33%. In this example separate TRANSFORMERS 321, 323 are used but the primary of a single TRANSFORMER may be shared with additional capacitor isolation or through the use of separate primaries on a common transformer. DIODES 325 and 326 rectify the output of TRANSFORMER 321 and apply the pulsating rectified DC pulses shown by waveform J on the SWITCH DRIVE table 354. These pulses are filtered by INDUCTOR 329 and CAPACITOR 331 to the desired degree. In a similar manner DIODES 327, 328 rectify the output of TRANSFORMER 323 and the pulsating DC is filtered by INDUCTOR 330 and CAPACITOR 331. If the phase of TRANSFORMER 323 is operated shifted by 67 degrees from TRANSFORMER 321 as in SWITCH DRIVE 354, then the ripple frequency across CAPACITOR 331 will be increased and the pulsating DC currents greatly reduced allowing a much smaller capacitor value to be used and this technique maybe extended to a plurality of transformers. Alternately, by combining the switches in such a way to use a single TRANSFORMER, then only one set of diodes and inductor will be required, reducing the number of components and manufacturing cost of the design.

Capacitors 308, 309, 310, 311, 312 filter the SWITCH 300 through 307 current pulses reducing the high frequency AC that is generated by the half bridges across the INPUT 350 and 351. The addition of resistors 314, 315, 316, 317 and 318 are used to force the voltages to be equal across capacitors 308, 309, 310, 311, 312 during the start-up, the time that the half bridges are off. Capacitor 313 is used to provide start-up power for the START MODULE 341, which has various internal components that store sufficient charge to run the half bridges for a specific time after which an auxiliary winding 324 from transformer 323 supplies the necessary power to run the control electronics. Alternately, an external DC or AC, not shown, provides the power to operate the DC to DC converter and may be common to or close to either INPUT 350 or 351.

In FIG. 3 REFERENCE 390 provides a voltage proportional to the desired output voltage and FEEDBACK 340 supplies a feedback signal proportional to the secondary output voltage, both of which are used by the PWM MODULE 342 to generate the appropriate PWM phased clock signals that are supplied to the SWITCH DRIVER 343, which then drives the switches 300, 301, 302, 303, 304, 305, 306, 307. The additional circuits function as follows. When HIGH VOLTAGE is first applied to INPUT 350 and 351, the resistors 314, 315, 316, 317 and 318 charge capacitor 313. The START MODULE 341 takes the charge from CAPACITOR 313 and determines when it is sufficient to operate the PWM MODULE 342 and SWITCH DRIVER 343 for a predetermined time. For operation from a HIGH VOLTAGE AC INPUT the START MODULE 342 takes the current normally charging CAPACITOR 313 and rectifies it and stores the charge internally until a sufficient level has built up to initiate startup of the power supply. Alternately, the START MODULE 341 may be powered by an external low voltage DC or AC source, not shown in FIG. 3. After initially powering the converter electronics, the START MODULE 341 receives low voltage AC power from transformer 323 through secondary 324. The power from this secondary 324 then provides the low voltage power to sustain operation of the PWM MODULE 342 and SWITCH DRIVER 343. Further in FIG. 3, once the START MODULE 341 has started the DC-to-DC converter the FEEDBACK 340 provides a signal to the PWM MODULE 342 that is proportional to the out put voltage. The FEEDBACK 340 may use optical isolation, an isolation transformer etc. none of which are shown to provide this isolated feedback signal to the PWM MODULE 342. However, the typical design requires higher isolation voltage between the primary and secondary of TRANSFORMER 321, 323 and across the FEEDBACK 340 than that required by conventional commercial power supply designs. PWM MODULE 342 generates two or more square-wave outputs that have the phase of their outputs shifted proportional to the duty of the waveform that is to be applied to the primary of transformers 321 and 323. SWITCH DRIVE 343 provides all necessary isolation of the drive signals with the correct phase to switches 300, 301, 302, 303, 304, 305, 306 and 307. Typical waveforms are shown in SWITCH DRIVE 354, representing an operating duty of 33%. Diodes 325, 326, 327 and 328 rectify the AC of the secondary of transformer 321, 323 into a pulsating DC, shown as J, K, which is then filtered by inductor 329, 330 and capacitor 331. The output inductor 329, 330 and capacitor 331 filters the pulsating DC into an average value equal to the duty of the waveform multiplied by its amplitude, see equation 2 further derived in a later section. The circuit functions in similar manner to a switching power supply commonly called a FORWARD CONVERTER, except the present configuration provides a regulated low DC voltage output from a HIGH VOLTAGE DC applied to INPUT 350 and 351. HIGH VOLTAGE AC maybe applied to INPUT 350 and 351 if SWITCH 300 through 307 are BI- DIRECTIONAL.

The switches, 300, 301, 302, 303, 304, 305, 306 and 307 are typically semi-conductor devices that have a reverse diode across them to clamp any reverse voltage that may be generated by transformer 321, 323 during the time the SWITCH DRIVE 354 changes state. Should an AC output be desired from the power supply then DIODE 325, 326, 327, 328 may be omitted. The Embodiment in FIG. 4, in accordance with the present invention represents the full capability of the HIGH VOLTAGE TO LOW VOLTAGE BI-DIRECTIONAL CONVERTER. Typically HIGH VOLTAGE in this embodiment refers to voltages greater than 800 Volt and LOW VOLTAGE to less than 200 Volt, though the CONVERTER may be designed to operate at any INPUT and OUTPUT voltage. With proper PWM MODULE 432 signals, the CONVERTER in this embodiment, when designed with AC or BIDIRECTIONAL SWITCHES in all SWITCH locations, 400 through 407, 423, 424, 425 is capable of the following

1. Converting a HIGH VOLTAGE DC or AC INPUT into a regulated LOWER VOLTAGE DC or AC output.

2. Converting a LOWER VOLTAGE DC or AC INPUT into a regulated HIGH VOLTAGE DC or AC output. 3. Converting a HIGH VOLTAGE DC INPUT into a regulated LOW VOLTAGE AC

OUTPUT of a frequency equal to or typically much lower than the switch frequency.

4. Converting a LOW VOLTAGE DC INPUT into a regulated HIGH VOLTAGE AC OUTPUT of a frequency equal to or typically much lower than the switch frequency.

5. Converting a HIGH VOLTAGE AC INPUT of a frequency equal to or typically much lower than the SWITCH frequency into a regulated LOW VOLTAGE DC OUTPUT.

6. Converting a LOW VOLTAGE AC INPUT of a frequency equal to or typically much lower than the SWITCH frequency into a regulated HIGH VOLTAGE DC OUTPUT.

FIG. 4 is similar in design to FIG. 3 except that the output section has been changed by replacing each DIODE in the secondary circuit with a SWITCH. The converter is intended to produce a regulated DC or AC output but may be modified to produce an unregulated DC or AC output by omitting FEEDBACK 430.

An explanation of the function of the various parts of the embodiment is as follows. The HIGH VOLTAGE is connected to INPUT 450 and 451. SWITCHES 401 through 407 are bi-directional or AC type and allow the operation from a DC or AC HIGH VOLTAGE power source. SWITCHES 401 through 407 may be DC type if the HIGH VOLTAGE is always going to be DC and will allow full bi-directional operation if the DC switches have a reverse diode across them to bypass reverse current around the switch. SWITCHES 423, 424, 426 are typically bi-directional and may be replaced with diodes if the circuit operation similar to FIG. 3 is required.

SWITCH 400, 401 form one half-bridge and 402, 403 form the other side of a half- bridge which is combined and operated as a full bridge with CAPACITOR 419 blocking the DC component from being applied to the primary of transformer 421. Both half bridges operate at full duty, with each switch ON for 50% of the time. To create a PWM output the phase of the half bridge 402, 403 is shifted from that of switches 400, 401 by an amount equal to the desired pulse width. SWITCH DRIVE 454 provides an example of this, with signal A the position of the SWITCH 400, HIGH or UP representing the ON or CLOSED state, B, C, D corresponds to SWITCH 401, 402, 403 accordingly and N represents the difference signal that appears across the primary of TRANSFORMER 421. The duty of the primary waveform N on TRANSFORMER 421 can be changed by varying the phase of SWITCH signals A, B with respect to C, D. This type of switching method facilitates the use of isolation transformers for coupling the gate signals to the SWITCHES and can accommodate any PWM duty from 0 to 100% without worry of saturation of the SWITCH driver transformers, not shown in the drawing. SWITCHES 404, 405 form one half-bridge and 406, 407 form the other half-bridge of a full-bridge and function in combination with CAPACITOR 420 and another primary of TRANSFORMER 421 in the same manner as SWITCH 400, 401, 402, 403, CAPACITOR 419. The same primary of TRANSFORMER 421 may be used for each full bridge if at least one additional CAPACITOR is used in series with the junction of SWITCH 402 and 403 or 405,407.

An example of the switch drive waveforms is shown by SWITCH DRIVE 454, which demonstrates operation at a duty cycle of 33%. In this example a single TRANSFORMER 421 is used but the use of separate TRANSFORMERS as in FIG. 3 will not change the basic function of the converter, with the secondary combined or operated with their own output SWITCH. In FIG. 4 SWITCH 423, 424 replace the DIODES 325, 326 in FIG. 3. In FIG. 4 SWITCH 425 is added to enable different operating modes, and improves the efficiency. SWITCH 425 is closed or ON when ever SWITCH 423 or 424 are both OFF or open, thus providing a return path for INDUCTOR 426 current to CAPACITOR 427, preventing build up of a very high voltage across SWITCH 423 and 424 when they are first OPENED. SWITCH 425 may be omitted in designs that use PWM control on the primary of TRANSFORMER 421 so long as the drive for SWITCH 423 and 424 is modified such that they are both ON as indicated in SWITCH DRIVE 454 as well as both are turned ON or remain ON when ever the SWITCH 425 was indicated as being ON. When SWITCH 425 is left out or replaced by a DIODE then SWITCH 423, 424 may be operated as synchronous rectifiers and derive their switch signals directly from extra windings on TRANSFORMER 421, (not shown). The inclusion of SWITCH 425 allows for a special operating mode where the primary of TRANSFORMER 421 is a full duty square wave, not PWM modulated, but instead SWITCH 423, 424 are operated in a PWM mode. The output circuit of FIG. 4 comprising of SWITCH 423, 424, 425, Inductor 426 and CAPACITOR 427 may generally otherwise be applied and used in a similar manner to that shown in FIG.l and FIG. 2.

SWITCH 423, 424 rectify the output of TRANSFORMER 421 and apply the pulsating rectified DC pulses shown by waveform M on the SWITCH DRIVE table 454 to an INDUCTOR 426 and CAPACITOR 427, which are then filtered to the desired degree. IF a second output circuit and TRANSFORMER is used similar to FIG. 3 and the second TRANSFORMER is operated phase shifted by 90 degrees then the ripple frequency across CAPACITOR 427 will be doubled and the pulsating DC currents greatly reduced allowing a much smaller capacitor value to be used. This technique may be extended further using a plurality of TRANSFORMERS and plurality of secondary combined in this manner.

CAPACITORS 408, 409, 410, 411, 412 filter the switch current pulses reducing the high frequency AC that is generated by the half bridges in series across the INPUT 450 and 451. The addition of RESISTORS 414, 415, 416, 417 and 418 forces the voltages to be equal across CAPACITORS 408, 409, 410, 411, 412 during the start-up time that the half bridges are off. CAPACITOR 413 is used to provide start-up power for the START MODULE 431, which has various internal components that store sufficient charge to run the SWITCHES for a specific time after which an auxiliary winding 422 from TRANSFORMER 421 supplies the necessary power to run the control electronics. Alternately, an external DC or AC power source, not shown, provides the power to operate the DC-to-DC converter and may be common to or close to either INPUT 450 or 451.

In FIG. 4 INPUT VOLTAGE REFERENCE 434 provides input polarity, REFERENCE 490 provides a voltage proportional to the desired output voltage and FEEDBACK 430 supplies a feedback signal proportional to the secondary output voltage all of which are used by the PWM MODULE 432 to generate the appropriate PWM phase clock signals that are supplied to the SWITCH DRIVER 433, which then drives the switches 400, 401,402, 403, 404, 405, 406, 407, 423, 424, 425. These circuits function as follows. When HIGH VOLTAGE is first applied to INPUT 450 and 451, the RESISTORS 414, 415, 416, 417 and 418 charge CAPACITOR 413. The START MODULE 431 takes the charge from CAPACITOR 413 and determines when it has enough charge to operate the PWM MODULE 432 and SWITCH DRIVER 433 for a predetermined time. For operation from a HIGH VOLTAGE AC INPUT the START MODULE

431 takes the current normally charging CAPACITOR 413, rectifies it and stores the charge internally until a sufficient level has built up to initiate startup of the power supply. Alternately, the START MODULE 431 may be powered by an external low voltage DC or AC source, not shown in FIG. 4. After initially powering the converter electronics, the START MODULE 431 receives a low voltage AC from TRANSFORMER 421 through SECONDARY 422. The power from this SECONDARY 422 then provides the low voltage power to sustain operation of the PWM MODULE 432 and SWITCH DRIVER 433. Further in FIG. 4, after the START MODULE 431 has started the converter the

FEEDBACK 430 provides a signal to the PWM MODULE 432 that is proportional to the output voltage. The FEEDBACK 430 may use optical isolation, an isolation transformer etc., none of which are shown, to provide this isolated feedback signal to the PWM MODULE 432. However, the typical design requires higher isolation voltage between the primary and secondary of TRANSFORMER 421 and across the FEEDBACK 430 than that required by conventional commercial power supply designs. PWM MODULE 432 generates two or more square-wave outputs that have the phase of their outputs shifted proportional to the duty of the waveform that is to be applied to the primary of TRANSFORMER 421. SWITCH DRIVE

433 isolates the drive signals with the correct phase to switches 400, 401, 402, 403, 404, 405, 406, 407, 423, 424 and 425. Typical waveforms are shown in SWITCH DRIVE 454, representing an operating duty of 33%. SWITCH 423, 424 rectify the pulsating AC waveform (shown as signal N) of the SWITCH DRIVE 454 of the of the secondary of TRANSFORMER 421 into a pulsating DC, shown as M, which is then filtered by INDUCTOR 426 and CAPACITOR 427. The output INDUCTOR 426 and CAPACITOR 427 filters the pulsating signal M into a average value equal to the duty of the waveform multiplied by its peak amplitude. The circuit functions in a similar manner as a switching power supply commonly called a FORWARD CONVERTER. In FIG.4 when HIGH VOLTAGE AC is applied to INPUT 450 and 451, acceptable as all switches are bi-directional, then the low voltage output VOUT 452 and 453 will be regulated AC and reduced in amplitude. A expression for the output voltage when the input AC or DC is being converter to a regulated lower voltage of the same type of waveform is

1 Vp = Vin / Bn

2 Vout = Vp * D / N Where: Vp => TRANSFORMER PRIMARY VOLTAGE Vin => HIGH VOLTAGE INPUT

Bn => NUMBER HALF-BRIDGES Vout => OUTPUT VOLTAGE

N => TRANSFORMER TURNS RATIO; Number Primary turns divided by Number

Secondary turns

D => DUTY

DLITY is the ratio of the time the Primary is ON divided by the sum of Primary OFF plus ON time.

Equation 2 is important as it establishes the ratio between the input and output voltage.

The power supply is fully bi-directional such that should the power supply output rise to a value greater than equation 2 allows, power will flow from the output back to the input. This has numerous advantages, for example accelerating a car with an electric motor from a high voltage battery, then by changing the power supply duty the power supply acts as a regenerative brake, the electric motor now a generator, returning the energy from stopping the car to recharge the high voltage battery.

In FIG. 4 the INPUT VOLTAGE REFERENCE 434 is used by the PWM MODULE

432 when it is necessary to convert from AC to DC or vice versa. The signal is used to determine whether the phase of the SWITCH 423 and 424 has to be inverted from its normal condition, thus changing equation 2 to

3. Vout = P * Vp * D / N

Where:

P => POLARITY is either +1 or - 1 depending on whether the phase of SWITCH 423 and 424 is inverted to the normal stated, providing a reversed OUTPUT voltage with respect to the INPUT. The effect of the phase is to change VOUT 452, 453 polarity with respect to the INPUT 450, 451. For example using a PHASE of -1 changes a positive HIGH VOLTAGE DC INPUT to a negative LOWER VOLTAGE DC OUTPUT. Alternately, a PHASE of -1 would convert a positive HIGH VOLTAGE AC INPUT to a negative or reversed phase LOWER VOLTAGE AC OUTPUT.

INPUT VOLTAGE REFERENCE 434 has other uses as well, especially when converting a HIGH VOLTAGE AC INPUT to a LOWER VOLTAGE DC OUTPUT or vice versa. For example when converting a HIGH VOLTAGE AC INPUT in to a positive LOWER VOLTAGE DC OUTPUT then the POLARITY signal +1 when the HIGH VOLTAGE AC INPUT is positive and -1 when the HIGH VOLTAGE AC INPUT is negative. The resultant DC OUTPUT will be the same as any full wave rectified AC signal, the amplitude and ripple characteristics will be determined by the value of the filter made up of INDUCTOR 426 and CAPACITOR 427 however, the voltage at point M will be determined by equation 3.

To convert a HIGH VOLTAGE DC INPUT to a LOW VOLTAGE AC OUTPUT, the POLARITY control is used to toggle (or change to opposite state) the LOW VOLTAGE OUTPUT every time the AC REFERENCE 490 waveform goes through a zero crossing. To synthesize an AC waveform it is necessary for the PWM MODULE 432 to use a modified REFERENCE 490 as it requires a value, which is proportional to the desired output waveform. Typically a look up table in a micro-processor memory or logic storage device is used to synthesize a suitable REFERENCE 490 signal. The FEEDBACK 430 value is compared to the REFERENCE 490 waveform and the PWM is adjusted as required to produce the correct output, which technique is well known in art. Conversely, a LOW VOLTAGE DC OUTPUT may be converted to a HIGH VOLTAGE AC OUTPUT if the magnitude of the DC OUTPUT present on VOUT 452, 453 is greater than that allowed by equation 3. The power under this circumstance will then flow from the LOW VOLTAGE VOUT side to the HIGH VOLTAGE INPUT. FIG. 7 shows that the SWITCH 423, 424 in FIG. 4 can be substituted with a full wave bridge, using 4 SWITCHES instead of the two in FIG. 4. This is the case when the use of a center-tapped secondary such as that used by TRANSFORMER 421 in FIG. 4 is not desired. The arrangement in FIG. 7 shows a typical full bridge secondary circuit where SWITCH 722, 723 are the same phase as SWITCH 423 in FIG. 4 and SWITCH 721, 724 are the same phase as SWITCH 424 in FIG. 4. Other similarities between FIG. 7 and Fig. 4 are TRANSFORMER 720 & 421; SWITCH 725 & 425; INDUCTOR 726 & 426; CAPACITOR 727 & 427; FEEDBACK 730 & 430 etc. are all the same as well as remaining components except instead of a leading 4 there is leading 7 substituted in FIG. 7. The function of the circuit with the changed secondary circuit similar to that shown in FIG. 4. FIG. 5 B shows the definition of what is meant by a DC switch. The DC switch behaves as a switch blocking voltage in one direction but when a reverse voltage is applied it either conducts as in the case of DIODE 505 or is destroyed. That is why typically a DIODE 505 is placed across the SWITCH 504 as shown in FIG. 5B. The FIG. 5C shows a BIDIRECTIONAL SWITCH 508 made up using two mosfets 506 and 507. Each mosfet is in this example has their SOURCE terminals connected together and the control signal is applied across the G and S terminals. The terminals labeled A on device 506 and B on device 507 are the equivalent SWITCH input and output terminals. The Mosfets 506 and 507 may be connected Drain to Drain instead of the way shown, however in that method each should use a separate isolated G and S drive signal. Any type of switch semiconductor or otherwise may be substituted for Mosfet 506 and 507 so long as they are combined in a way that the switch will block voltage of any polarity when turned off and pass current of any polarity when turned on. It should be pointed out that most switch designs that use semi-conductor devices use additional components not shown in any FIG. 1 through 7. These additional devices are used following manufacturer's recommendation or through good design practice for the purpose of protecting the switch from overload current, reverse voltage, voltage, power, temperature and for reducing electronic radiated noise. Mounting and cooling of the switches is selected to suit a designs mechanical and performance requirements and the preferred embodiments do not have any special design requirements other than that required to meet a specific product reliability.

FIG. 6A shows a typical filter block that may be added to the LOW VOLTAGE OUTPUT side to improve the quality of the output. FIG. 6B shows a typical filter block that may be added to the HIGH VOLTAGE INPUT side to reduce the radiated noise caused by the INPUT SWITCH action. These filters typically are composed of a combination of INDUCTORS, CAPACITORS and RESISTORS in differing combinations to generate the desired noise attenuation ratio. No particular filter design other than that used by good practice is required.

The embodiments of FIG. 3 and FIG. 4 may be operated using PWM control or alternately using a variable frequency-switching rate with a fixed or variable ON pulse width. FIG. 8 Is a preferred embodiment that uses the converter for powering an electric motor, such as in hybrid electric car etc. The POWER SOURCE 800 such as a battery or capacitor bank, fuel cell, or any combination of these or an AC source such as the output from a motor-generator connected to a flywheel provides a source of power to operate the DRIVE MOTOR 813. The DRIVE MOTOR 813 may be DC or a poly-phase AC motor using one or plurality of AC phases provided by a plurality N of converters as shown by SUPPLY A 810, SUPPLY B 811, through SUPPLY N 812. These power supplies may be wholly independent or share various common elements from each other, such as feedback or PWM CONTROL signals and they may even have a common primary section but multiple secondary, each providing a different output phase. In FIG. 8, DC POWER SOURCE 800 is connected to the HIGH VOLTAGE side of the converter, the low voltage side is connected to the DRIVE MOTOR 813 or another electric device. In keeping with the preferred embodiment of the converter it can use an AC source of a differing frequency, such as that put out by the motor- generator of a flywheel to create a different frequency AC output to the DRIVE MOTOR 813. During acceleration or steady operation of the DRIVE MOTOR 813 the converters SUPPLY A 810, SUPPLY B 811, SUPPLY N 812 takes its power from the POWER SOURCE 800, energy may be transferred from the DRIVE MOTOR 813 back to the POWER SOURCE 800 using regenerative-breaking, where DRIVE MOTOR 813 is changed to a generator and used to decelerate the rate that it is turning. The operation in this mode exploits the use of equation 2 or 3 from earlier in this section along with specific clocking signals that are unique to each application. The best example of this would be where the DRIVE MOTOR 813 is used in an automobile as either the whole or partial motive source, though the preferred embodiment is not limited to this application.

FIG. 9 is similar to FIG. 8 but the POWER SOURCE 904 is now located on the LOW VOLTAGE side and the DRIVE MOTOR 903 is on the HIGH VOLTAGE side. The operation in this mode is identical just the direction of power flow is different under the same circumstance.

In another embodiment, a HIGH VOLTAGE to HIGH VOLTAGE converter is provided in which a HIGH VOLTAGE arrangement of half-bridges in series forms the secondary crcuit in similar configuration to the primary side.

In another embodiment the HIGH VOLTAGE switch arrangement of FIG. 1 or FIG. 2 is used on the primary, with the secondary arrangement shown in FIG. 4 or FIG. 7. A variation of this would be where the secondary switch arrangement of FIG. 4 or FIG. 7 would be PWM operated and the primary side would be a 100% duty square-wave and the variable DUTY of the secondary switches would provide the PWM regulation. This arrangement is shown in FIG. 10 the SWITCH DRIVE 1054A, where SWITCH signals A through G are the same as those from SWITCH DRIVE 154 of FIG. 1. SWITCH DRIVE signals J, K, L, M, N are the same signals as that from SWITCH DRIVE 454 of FIG. 4 and would be the switching signals of the secondary SWITCH 423 as J, SWITCH 424 as K and SWITCH 425 as L where M is the rectified output the same as FIG. 4 and N is the secondary or primary waveform. The operation is similar to FIG. 4 or FIG. 7 except that the secondary side is the only switches that have their signals PWM. Another arrangement is possible as shown by FIG. 10 SWITCH DRIVE 1054B again the same circumstance but where the primary is PWM as well as the secondary. The signals from SWITCH DRIVE 1054B relates to A through G as the switch signals of FIG. 2 SWITCH 200 through 205 respectively and FIG. 4 or 7 is the secondary SWITCH 423 as J, SWITCH 424 as K and SWITCH 425 as L where M is the rectified output the same as FIG. 4 and N is the secondary or primary waveform. FIG. 10 is bi-directional of any polarity input or output if the secondary switches are bi-directional and the primary side switches of FIG. 1 or FIG. 2 are made bi-direction.

Although the invention has been described in connection with a preferred embodiment, it should be understood that various modifications, additions and alterations may be made to the invention by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A high voltage to low voltage bi-directional converter comprising:

- a plurality of bi-directional switches adapted to connect in series to a high voltage AC source, the switches operated in pairs as half bridges, each half bridge operated in opposite phase to another half bridge to form a full bridge;

- a transformer having a primary to which a first half bridge of a full bridge is coupled through a capacitor on one side of the primary, with the other side of the primary coupled to a second half bridge of the full bridge; and

- one or more transformer secondary circuits, each secondary using at least one switch, or diode, in combination with one or more inductor, to make at least one lower voltage power output.

2. The converter as in claim 1 wherein each half bridge is coupled, through a capacitor to one side of a primary of one or more transformers, and the other side of the primary is connected to the high or low side of the half bridge.

3. The converter as in claim 1, wherein both half bridges operate at full duty, and wherein the second half bridge of each full bridge is operated with a variable phase shift, the converter further comprising: - a PWM module for controlling the variable phase shift of the second half bridge ;

- a control circuit for providing a feedback signal to the PWM module to change the phase of the second half bridge, resulting in a pulse width modulated voltage across the transformer primary in relation to the feedback; and

- a switch driver for turning the switches on and off under control of the PWM module; wherein the lower output voltage is substantially equal to the average of the pulsating inductor input voltage.

4. The converter as in claim 3 further comprising control electronics adapted to be powered by a start module, the start module powered at starting by a start-up capacitor, and powered after starting by a secondary of a transformer.

5. The converter as in claim 3, further comprising control electronics adapted to be powered by a start module, the start module powered by an external power source.

6. The high voltage to low voltage bi-directional converter as in claim 3, wherein the secondary includes at least one switch, or diode, in combination with one or more inductor, to make one or a plurality of lower voltage outputs, which are then filtered.

7. The high voltage to low voltage bi-directional converter as in claim 3, wherein there are two or more separate transformers, each transformer operated in a phase shifted manner with respect to each other, and each transformer having one or more secondary circuits having at least one switch, or diode, in combination with one or more inductor, to make one or more lower voltage outputs.

8. The high voltage to low voltage bi-directional converter as in claim 3, wherein a secondary is connected to another device or circuit.

9. The high voltage to low voltage bi-directional converter as in claim 3, wherein the full bridges are coupled through a plurality of capacitors to a common primary.

10. The high voltage to low voltage bi-directional converter as in claim 3 that is connected to one or more additional high voltage to low voltage converter, each operating independently or sharing various common parts, to power an AC or DC electric motor or other electric device.

11. The high voltage to low voltage bi-directional converter assembly as in claim 10, wherein the electric motor is used to drive a mechanical device, and wherein the motor may be operated as a generator when slowing the operation of the mechanical device, with the generator output converted through the high voltage to low voltage converters to return energy back to the high voltage source.

12. The high voltage to low voltage bi-directional converter assembly as in claim 3, wherein the converter is operated in reverse to generate a higher voltage AC or DC output from a low voltage input.

13. The high voltage to low voltage bi-directional converter assembly as in claim 12, wherein the high voltage output is used to operate an electric motor or other electrical device.

14. The high voltage to low voltage bi-directional converter as in claim 3, wherein a reference signal and output polarity value modifies or controls the PWM MODULE to provide one or plurality power outputs of a specific desired amplitude, polarity, phase and frequency.

15 The high voltage to low voltage bi-directional converter as in claim 14, wherein a feedback signal is used in conjunction with a reference signal and output polarity value to modify or control the PWM MODULE to provide one or plurality of outputs of a specific desired amplitude, polarity, phase and frequency.

16. The high voltage to low voltage bi-directional converter as in claim 1, wherein each half bridge is operated using a variable frequency switching rate with fixed or variable ON pulse width.

17. The converter as in claim 1, wherein a PWM module controls the ON time of each half bridge switch, the converter further comprising:

- a control circuit for providing a feedback signal to the PWM module to change the ON time of each half bridge switch, resulting in a pulse width modulated voltage across the transformer primary in relation to the feedback; and

18. The high voltage to low voltage bi-directional converter as in claim 17, wherein a feedback signal, reference signal and output polarity value modifies or controls the PWM MODULE to provide one or plurality power outputs of a specific desired amplitude, polarity, phase and frequency.

19. The converter as in claim 17 further comprising control electronics adapted to be powered by a start module, the start module powered at starting by a start-up capacitor, and powered after starting by a secondary of a transformer.

20. The converter as in claim 17, further comprising control electronics adapted to be powered by a start module, the start module powered by an external power source.

21. The high voltage to low voltage bi-directional converter as in claim 17, wherein the secondary includes at least one switch, or diode, in combination with one or more inductor, to make one or a plurality of lower voltage outputs, which are then filtered.

22. The high voltage to low voltage bi-directional converter as in claim 17, wherein there are two or more separate transformers, each transformer operated in a phase shifted manner with respect to each other, and each transformer having one or more secondary circuits having at least one switch, or diode, in combination with one or more inductor, to make one or more lower voltage outputs.

23. The high voltage to low voltage bi-directional converter as in claim 17, wherein a secondary is connected to another device or circuit.

24. The high voltage to low voltage bi-directional converter as in claim 17, wherein the full bridges are coupled through a plurality of capacitors to a common primary.

25. The high voltage to low voltage bi-directional converter as in claim 17, that is connected to one or more additional high voltage to low voltage converter, each operating independently or sharing various common parts, to power an AC or DC electric motor or other electric device.

26. The high voltage to low voltage bi-directional converter assembly as in claim 25, wherein the electric motor is used to drive a mechanical device, and wherein the motor may be operated as a generator when slowing the operation of the mechanical device, with the generator output converted through the high voltage to low voltage converters, returning energy back to the high voltage source.

27. The high voltage to low voltage bi-directional converter assembly as in claim 17, wherein the converter is operated in reverse to generate a higher voltage AC or DC output from a low voltage input.

28. The high voltage to low voltage bi-directional converter assembly as in claim 27, wherein the output is used to operate an electric motor or other electrical device.

29. The high voltage to low voltage converter as in any of claims 1 through 28, wherein the bi-directional switches are replaced by DC switches in the primary side if it is only operated with a DC input or output, or by DC switches in the secondary side if it is operated with only DC voltage present as an output or input and DC switches in the primary or secondary circuits may be replaced with diodes if the primary or secondary circuit is used as an output.

30. The high voltage to low voltage converter as in any of claims 1 through 29, wherein an energy storage device such as a battery, capacitor assembly, flywheel, electric motor-generator combination, or any other similar device that is capable of storing energy, is connected to the secondary circuit, and wherein the power converter flows power from the primary circuit to the secondary circuit to store energy and flows power in the opposite direction from the secondary circuit to the primary to draw power from the energy storage device, or if the energy storage device is connected to the primary circuit the power converter flows power in the opposite direction from the secondary circuit to the primary circuit to store energy and flows power from the primary circuit to the secondary circuit to draw power from the energy storage device.