Power booster switching at zero current

Abstract: A power booster module is described for use in a zero-current switching converter array which includes a signal pulse train generator external to the power booster module, the pulse train having a frequency corresponding to the frequency of energy transfer cycles occurring in the array. The power booster module includes a zero-current switching converter and a control input port to which the pulse train is applied to trigger energy transfer cycles in the booster module at the frequency of the pulse train, whereby the booster module operates coherently with the array to provide a share of the power drawn by a load.

Description: This invention relates to DC-to-DC power converters of the zero-current switching type, and to power booster modules useful therein. In some such zero-current switching converters (for example the single-ended forward zero-current switching converters of the kind disclosed in Vinciarelli, U.S. Patent 4,415,959, the disclosure of which is incorporated herein by reference, or series- resonant converters, or other resonant converters), power from a DC source is converted by way of a series of quantized energy transfer cycles into power for delivery to a load. Each energy transfer cycle has a period governed by the time constant of a coupled effective inductance (L) and capacitance (C) in the circuit. A switching device is connected in series with the source. The switching device is switched on and off (at times of essentially zero current) by a controller involving a feedback loop which senses the voltage across the load. The feedback loop spaces the energy transfer cycles at such time intervals that the voltage across the load is kept at a desired level. The power rating of the converter depends on the values of L and C. Such converters typically provide up to 200 watts of power. One approach to delivering more power is simply to scale up the electrical components. Another approach is to operate an array of converter modules in parallel, but independently. Some of the modules in the array will then typically saturate, while others make up any shortfall in power needed by the load. In a third approach, converters within the array are forced to share power but without having to switch coherently at the same frequency. Such incoherent masterslaves configurations lead to beat frequencies. Other power converters operating on different principles have been proposed. Thus Hergenhan in US4 290 101 proposes an N-phase digital inverter for inverting an input DC voltage level to an output DC voltage level in which a plurality of N parallel switching circuits is interposed between the input and output terminals, each switching circuit comprising in series a power switch and a transformer. The output of each transformer is coupled through a diode to a common point for filtering to generate the output DC voltage. The output DC voltage is sensed and fed to a logic generator for generating a ring sequence of pulses which activate sequentially each power switch in the plurality thereof. The logic generator controls the ratio of pulse time ON divided by pulse time ON plus pulse time OFF to maintain a desired level of output DC voltage. The present invention is expressly concerned with zero-current switching converters and is derived from the concept that the pulse by pulse energy quantization inherent in zero-current switching converters provides a mechanism for power sharing by an array of such converters. In accordance with a first aspect of the present invention, we provide a D.C.-D.C. power conversion array for converting power from a D.C. source for use by a load, characterised in comprising a plurality of zero-current switching converters mounted in parallel, each being connected to receive D.C. power via a respective input power port from said source and to deliver power via a respective output power port to said load in a series of quantized energy transfer cycles with a time constant determined by the equivalent inductance (L b , L d ) and equivalent capacitance (C b , C d ) of said converter, and each said converter having a controller for triggering in response to a pulse train the start of each said energy transfer cycle in said converter and for terminating each said energy transfer cycle at a time determined by zero-current switching of said converter; one said converter in said array together with its controller serving as a driver module in said array; the or every other converter in said together with its respective controller serving as a power booster module in said array, the controller of the or each power booster module having a control input line thereto which is coupled to another converter of said array to receive a controlling pulse train for the said controller; and said driver module including a signal pulse train generator coupled to its controller for producing said pulse train having a frequency corresponding to the frequency of the energy transfer cycles throughout said array; power being shared between the converters in said array in a constant ratio determined by the said inductances and capacitances. In a second and alternative aspect of the present invention, there is provided a D.C.-D.C power conversion array for converting power from a D.C. source for use by a load, characterised in comprising a plurality of zero-current switching converters mounted in parallel, each being connected to receive D.C. power via a respective input power port from said source and to deliver power via a respective output power port to said load in a series of quantized energy transfer cycles with a time constant determined by the equivalent inductance (L b ) and equivalent capacitance (C b ) of said converter, and each said converter having a controller for triggering in response to a pulse train the start of each said energy transfer cycle in said converter and for terminating each said energy transfer cycle at a time determined by zero-current switching of said converter; each converter in said array together with its respective controller serving as a power booster module in said array; each said controller having a control input line thereto, and said array including a signal pulse train generator coupled to each said control input line for producing said pulse train having a frequency corresponding to the frequency of the energy transfer cycles throughout said array; power being shared between the converters of said array in a constant ratio determined by the said inductances and capacitances. Thus, seen another way, the invention proposes use of a power booster module in a D.C-D.C. power conversion array for converting D.C. power from a source for use by a load, and comprising a plurality of zero-current switching converters mounted in parallel, each being connected to receive D.C. power via a respective input power port from said source and to deliver D.C. power via a respective output power port to said load in a series of quantized energy transfer cycles with a time constant determined by the equivalent inductance and equivalent capacitance of said converter, and each said converter having a controller for triggering in response to a pulse train, the start of each said energy transfer cycle in said converter and for terminating each said energy transfer cycle at a time determined by zero-current switching of said converter, the array further including a signal pulse train generator for producing said pulse train having a frequency corresponding to the frequency of energy transfer cycles throughout said array, power being shared between the converters in said array in a constant ratio determined by the said inductances and capacitances; said power booster module comprising a zero-current switching converter of said array together with its controller, the controller of the power booster module having a control input line thereto coupled either to said signal pulse generator or to another converter of said array to receive a controlling pulse train. It will be seen that in some embodiments there is a daisy chain array including a driver module and booster modules. The driver module contains a feedback loop sensing the voltage across the load and controlling the frequence of energy transfer cycles, which are time delayed along the chain to reduce ripple and noise. In other embodiments there is a phased array of booster modules driven through a phase shifter to minimize ripple and noise. Such time or phase controlled arrays of zero-current switching converters with matching energy transfer cycle time constants are effective in providing arbitrarily large amounts of power to a load through coherent power sharing by a sufficiently large number of modules. The invention is hereinafter more particularly described by way of example only with reference to the accompanying drawings, in which:- Figs. 1, 2 are block diagrams of a power conversion system; Fig. 3 is a block diagram of the power booster; Fig. 4 is a timing chart for Fig. 3; Fig. 5 is a power conversion system using converters of the forward, single ended type; Figs. 6, 7 are a block diagram of a daisy chain converter array and a related timing chart; and Figs. 8, 9 are a block diagram of a phase controlled converter array and a related timing chart. Referring to Fig. 1, a power converter system 10 converts DC power from a source 12 at an input voltage level (V in ) for delivery to a load 14 at an output voltage level (V out ). System 10 includes a zero-current switching converter 16 connected between source 12 and load 14, and a controller 18. Controller 18 has an input connected between a pair of series-connected resistors 20, 22 for sensing the voltage level across load 14 and an output connected to converter 16 for carrying switching signals to a switching device (not shown in Fig. 1) in converter 16. Converter 16, controller 18, and resistors 20, 22, together make up a driver module 24. A power booster module 26 for increasing the amount of current deliverable to load 14 is connected in parallel with driver module 24. Power booster module 26 includes a zero-current switching converter 28 connected via input and output ports 29, 31, between source 12 and load 14, and a controller 30 whose output delivers switching signals to a switching device (not shown in Fig. 1) in converter 28. The input of controller 30 is connected via a control input port 31 to the output of generator 18 to receive a train of control pulses. Referring to Fig. 2, converter 16 and 28 can be of the type which include one or more switching devices, for example, a switching device 23 in converter 16, and a switching device 32 in converter 28. Converter 16, 28 are characterized respectively by inductance and capacitance L d , C d and L b , C b which define characteristic time constants respectively of π L d C d and π L b C b . In driver module 24, controller 18 includes an error amplifier 50 which compares the voltage at the load to a reference voltage and delivers a DC voltage output to a timer 52. Timer 52 generates pulses indicative of the intervals at which switches 23, 32 should be switched on and off in order to maintain the voltage across the load at the desired level. Timer 52 is connected to a switch controller 54, which causes switch 23 to turn on and off at essentially zero current, and via a control output port 56 to controller 30 which, after a controlled time delay, causes switch 32 to turn on and off at essentially zero current. In operation, as shown in Figs. 3, 4, in power booster module 26 at time t₁ a pulse is received by controller 30 from port 31. After a delay determined by the switch controller circuitry, at time t₂ controller 30 throws switch 32 on. The current I in converter 28 then rises and falls until at time t₃ it again reaches zero. Controller 30 senses this zero-current condition and at time t₃ throws switch 32 off. At time t₄ another pulse appears at port 31 and the steps are repeated. Thus the energy transfer cycles of converter 16, 28 occur at the same frequency but with a time delay between them. Referring to Fig. 5, converters 16, 28 can be of the forward, single-ended type disclosed in vinciarelli, U.S. Patent 4,415,959. The converters then respectively include transformers 40, 40¹; rectifier diodes 42, 42¹; rectifier diodes 44, 44¹; capacitors 46, 46¹; and inductors 48, 48¹. Transformers 40, 40¹ are characterized respectively by primary winding self-inductances L1 d , L1 b , secondary winding self-inductances L2 d , L2 b , and mutual inductances M d , M b . The tranformers are also characterized by secondary leakage inductances L d 2e = ( L d 1 L d 2 -M d 2 )/ L d 1 , L b 2e = ( L b 1 L b 2 -M b 2 )/ L b 1 . In each converter, the secondary leakage inductance and the capacitance define characteristic time constants respectively of π L d 2e C d , and π L b 2e C b . The transformers and capacitors in the two converters are specified so that the values of the time constants for the two are sufficiently close to provide for a natural sharing between the converters of the current to be supplied to load 14. The sharing is not necessarily 50/50 but rather corresponds to the ratio of the two capacitances. Referring to Figs. 6, 7, the converter array can be extended to include one or more additional power boosters (for example, a power booster 60). The power boosters are arranged in a daisy chain such that each power booster 60 delivers to the next power booster in the chain a signal pulse train corresponding to the occurrences of the energy transfer cycles in the earlier power booster. And each power booster has each of its own energy transfer cycles triggered in response to (but delayed after) each signal pulse in the train from the prior booster in the chain. Fig. 7 shows the resulting states of the switches 1, 2, and 3 in modules 24, 25, 60, respectively. Thus, larger amounts of power (limited only by the number of modules) can be delivered to the load. The load current is shared naturally. Ripple and noise are reduced. Other arrangements are possible within the scope of this invention. For example, referring to Figs. 8, 9, a power converter array can be formed of any number N of identical power boosters (for example, boosters 70, 72, 74). The control input port of each booster is connected to a phase shifter 76 which receives from a timer 78 (like timer 52) pulses indicative of the intervals at which switches 1, 2, 3 (respectively in boosters 74, 72, 70) should be switched on. Phase shifter 76 then delivers a switch-triggering signal pulse train to each of the boosters to trigger the switching. As shown in Fig. 9, the switching in the different boosters is phase-arrayed at intervals of 360/N degrees.

Claims: A D.C.-D.C. power conversion array for converting power from a D.C. source (12) for use by a load (14), comprising a plurality of zero-current switching converters (24,26) mounted in parallel, each being connected to receive D.C. power via a respective input power port (29) from said source and to deliver power via a respective output power port (33) to said load in a series of quantized energy transfer cycles with a time constant determined by the equivalent inductance (L b , L d ) and equivalent capacitance (C b , C d ) of said converter, and each said converter having a controller (18,30) for triggering in response to a pulse train the start of each said energy transfer cycle in said converter and for terminating each said energy transfer cycle at a time determined by zero-current switching of said converter; one said converter (24) in said array together with its controller serving as a driver module in said array; the or every other converter (26) in said array together with its respective controller serving as a power booster module in said array, the controller of the or each power booster module having a control input line (31) thereto which is coupled to another converter of said array to receive a controlling pulse train for the said controller; and said driver module including a signal pulse train generator (50,52) coupled to its controller for producing said pulse train having a frequency corresponding to the frequency of the energy transfer cycles throughout said array; power being shared between the converters in said array in a constant ratio determined by the said inductances and capacitances. An array according to Claim 1, including a plurality of power booster modules, further characterised in that said driver module and said power booster modules are arranged in a daisy chain, each of said modules delivering power to said load in a series of energy transfer cycles, the energy transfer cycles in one said power booster module (26) being triggered in response to a pulse train provided from said driver module (24) and the energy transfer cycles in each one of said other power booster modules (60) being triggered in response to a pulse train provided from and corresponding to the occurrences of the energy transfer cycles in the next previous power booster module in said daisy chain. A D.C-D.C. power conversion array for converting power from a D.C. source (12) for use by a load (14), comprising a plurality of zero-current switching converters (24) mounted in parallel, each being connected to receive D.C. power via a respective input power port (29) from said source and to deliver power via a respective output power port (33) to said load in a series of quantized energy transfer cycles with a time constant determined by the equivalent inductance (L b ) and equivalent capacitance (C b ) of said converter, and each said converter having a controller (30) for triggering in response to a pulse train the start of each said energy transfer cycle in said converter and for terminating each said energy transfer cycle at a time determined by zero-current switching of said converter; each converter in said array together with its respective controller serving as a power booster module (70, 72,74) in said array; each said controller having a control input line thereto, and said array including a signal pulse train generator (76,78,80) coupled to each said control input line for producing said pulse train having a frequency corresponding to the frequency of the energy transfer cycles throughout said array; power being shared between the converters of said array in a constant ratio determined by the said inductances and capacitances. An array according to any preceding claim, further characterised in that the controller of the or each power booster module is so arranged that the triggering of said energy transfer cycles in said booster module is phased relative to the triggering of said energy transfer cycles of the others modules in said array, thereby to reduce ripple in the voltage delivered to said load. An array according to any preceding claim, further characterised in that the time constant defined by the equivalent inductance L b and equivalent capacitance C b of the or each power booster module is sufficiently close to the time constants of said energy transfer cycles of said array to provide a natural sharing of said current drawn by said load. An array according to both Claim 1 and Claim 5, wherein said driver module has a driver capacitance C d , said array being further characterised in that C b is chosen so that the ratio C b /C d defines the sharing of the current drawn by said load. Use of a power booster module in a D.C.-D.C. power conversion array for converting D.C. power from a source for use by a load, and comprising a plurality of zero-current switching converters mounted in parallel, each being connected to receive D.C. power via a respective input power port from said source and to deliver D.C. power via a respective output power port to said load in a series of quantized energy transfer cycles with a time constant determined by the equivalent inductance and equivalent capacitance of said converter, and each said converter having a controller for triggering in response to a pulse train the start of each said energy transfer cycle in said converter and for terminating each said energy transfer cycle at a time determined by zero-current switching of said converter, the array further including a signal pulse train generator for producing said pulse train having a frequency corresponding to the frequency of energy transfer cycles throughout said array, power being shared between the converters in said array in a constant ratio determined by the said inductances and capacitances; said power booster module comprising a zero-current switching converter (26) of said array together with its controller (30), the controller of the power booster module having a control input line (31) thereto coupled either to said signal pulse generator or to another converter of said array to receive a controlling pulse train.

Inventors: VINCIARELLI PATRIZIO, VINCIARELLI, PATRIZIO
Applicants: VLT CORP, VLT CORPORATION
Application year: 1986
Main classification: H02M3
IPC codes: H02M3