TWI823250B - Bidirectional dc-dc energy converter with isolation - Google Patents

Abstract

The invention provides a high voltage gain, which contains zero voltage switching (ZVS), zero current switching (ZCS), and resonant bidirectional converter with isolated. It is suitable to be used in occasion such as battery charging and discharging systems, distributed power supply systems, and battery energy storage systems. The converter includes a high-voltage side and a low-voltage side. A high-voltage side power switching/rectifier module. A low-voltage side power switching/rectifier module. An isolation transformer, A resonance tank circuit is arranged between the isolation transformer and the high-voltage power switching/rectifier module. The power switching/rectifier module of high-voltage side adopts a structure of full bridge or half bridge, both of which is suitable for high-voltage coupling. The power switching/rectifier module of low-voltage side adopts a structure of push-pull, which is suitable for low-voltage battery system of the high-current charging and discharging applications. The resonant tank circuit contains an inductor-inductor-capacitor (LLC) structure. The inductor-inductor-capacitor (LLC) operates on during the forward step-down energy transmission. The inductor-capacitor (LC) operates on the reverse step-up energy transmission. A novel control method of pulse frequency modulation (PFM) and pulse width modulation (PWM) is proposed to improve the resonant tank circuit, which achieves soft switching without adding auxiliary inductor when the power flows in both directions. It increases the conversion efficiency and improves the electromagnetic compatibility of the high-gain bidirectional DC to DC energy converter.

Description

Bidirectional DC/DC energy conversion device with isolation

The invention relates to the field of power electronics applications and a bidirectional DC/DC power conversion device with soft switching and no loss. The direction of energy transmission can be controlled by controlling the switch operation.

With the increasing scarcity of traditional energy, new energy technology is becoming the main force in the development of energy technology, among which power electronics technology has also developed rapidly and become increasingly important. The green energy industry is booming, and the bidirectional DC/DC power conversion device of the present invention will be suitable for bidirectional energy conversion systems. For example, Battery Energy Storage System (BESS) and Vehicle to Grid (V2G). How to eliminate switching losses, reduce electromagnetic interference, and improve energy conversion efficiency has always been a concern of power electronics technology. As a key device for energy conversion, bidirectional DC/DC conversion devices have naturally become an important breakthrough point in these issues. Therefore, research on efficient Bidirectional DC/DC conversion devices will become important. In the traditional Pulse Width Modulation (PWM) mode control method, the switching elements of the bidirectional DC/DC conversion device work in a hard switching state. When the switching elements switch, there will be an overlap area between the current and voltage to cause switching. Loss, therefore, the switching loss limits the improvement of the power density of the conversion device, and also limits the miniaturization and weight reduction.

It is known that research on bidirectional DC/DC conversion devices focuses on traditional LLC and Phase Shifted Full Bridge (PSFB) control topologies. By changing the pulse frequency The switching technology of Pulse Frequency Modulation (PFM) changes the impedance of the resonant tank circuit, thereby changing the voltage and current state of the switching element, thus making the switching element operate at zero voltage switching (Zero Voltage Switching, ZVS) and Zero Current switching (ZCS), which are in the soft switching state to reduce the switching loss of the switch, thereby allowing higher switching frequency, reducing the size of magnetic components, improving electromagnetic compatibility, increasing power density and reducing cost. Inheriting the traditional LLC primary side switching element zero voltage switching (ZVS) and the secondary side diode zero current switching (ZCS), it has no reverse recovery problem and small switching loss, and is suitable for high frequency and high power density designs. Require. In order to achieve simple control, a symmetrical resonant tank circuit with similar characteristics is designed on both sides of the transformer. Generally, the symmetrical circuit structure on both sides is more suitable for situations where the voltage and current levels on both sides are similar. For example, Chinese Invention Patent Announcement No. CN 102201739 B "A Symmetrical Half-Bridge LLC Resonant Bidirectional DC-DC Converter" and U.S. Patent Announcement No. US 10,581,334 B2 "DC/DC Converter and Control Method" CLLC topology.

In addition to the above-mentioned bidirectional DC-DC converter with symmetrical resonant tank circuit topology, the Bidirectional DC-DC Converter proposed by Texas Instruments in the United States. Phase-shifted full-bridge (PSFB) control with synchronous rectification control in buck forward power transfer mode and current-fed push-pull control in boost reverse power transfer mode. This control mode can only achieve switching with zero-voltage switching (ZVS) under partial load, thus reducing efficiency and power density.

In order to further improve the bidirectional DC/DC converter proposed by Texas Instruments in the United States and improve the conversion efficiency. In the traditional LLC topology, the control method is controlled by changing the switching technology of pulse frequency modulation (PFM) mode operation, so that the impedance of the resonant tank circuit also changes. By adding an auxiliary inductor L _new , the two-way energy transmission has its own LLC resonance characteristics. For example, U.S. Patent Publication No. US 8,363,427 B2 "Bidirectional power converter with adjustable output and soft switching" and Chinese Invention Patent Application Publication No. CN 108988645 A "A novel soft-switching bidirectional DC/DC converter based on LLC resonance"topology".

The aforementioned US patents and Chinese patent applications are only references for the technical background of the present invention and illustrating the current state of technological development, and are not intended to limit the present invention. In view of this, in order to meet the requirements of a bidirectional DC/DC power conversion device with soft switching and lossless, the present invention proposes a method that does not need to add an auxiliary inductor L _new on the traditional LLC topology and has its own resonance characteristics when realizing bidirectional energy transmission. , in order to improve power conversion efficiency, improve electromagnetic compatibility and reduce production and manufacturing parts costs.

According to the main purpose of the preferred embodiment of the present invention, a control method for a bidirectional DC/DC energy conversion device with isolation is provided. The bidirectional DC/DC energy conversion device with isolation includes: a power supply/load with a primary side high-voltage DC end. terminal; one of the first plurality of high-voltage power switching elements with back-connected diodes is a primary-side high-voltage switching/rectification module, and its two terminals located in the primary side direction are connected to the primary-side high-voltage DC terminal power supply/load for Accepts the input DC power from the first DC terminal or the output load of the first DC terminal; an LLC composed of three components including a resonant inductor (L _r ), a magnetizing inductor (L _m ) and a resonant capacitor (C _r ) A resonant tank circuit, one end of which is connected to the primary side high-voltage switching/rectifier module; an isolation transformer, including a primary winding (N _p ) and a secondary first winding (N _s1 ) with a center tap, a secondary Second winding (N _s2 ), both ends of the secondary winding are connected to the secondary side low-voltage switching/rectification module of the second low-voltage power switching element, and the center tap node end is connected to the high potential end of the second DC end. , used to accept input DC power or output load from the second DC terminal; a second plurality of secondary side low-voltage switching/rectification modules with back-connected diodes of low-voltage power switching elements, which are located on the secondary side The direction end is connected to the low potential of the secondary side low-voltage DC end power supply/load end and is used to receive the DC power supply or output load from the second DC end.

The above-mentioned bidirectional DC/DC energy conversion device with isolation, in the step-down forward power transmission mode, uses a variable frequency control method on the high-voltage side, by changing the pulse frequency modulation (PFM) and setting the duty cycle to 0.5. control method. Control the primary-side high-voltage switching/rectification module, one of the first plurality of high-voltage power switching elements with back-connected diodes, to make the resonant inductance (L _r ), magnetizing inductance (L _m ), and resonant capacitance (C) of the resonant tank circuit _r ) The change in the impedance of the LLC resonant tank circuit composed of three components, thereby changing the voltage and current states on the switching components, making the first primary-side high-voltage switching module of multiple high-voltage power switching components with back-connected diodes Operates under zero voltage switching (ZVS). The low-voltage power switching elements of the second plurality of secondary-side low-voltage switching/rectification modules with back-connected diodes operate in zero-current switching (ZCS) under output rectification.

The bidirectional DC/DC energy conversion device with isolation controls the secondary side low-voltage switching/rectification module by changing the pulse width modulation (PWM) mode at a fixed switching frequency in the boost reverse power transmission mode. Low-voltage switching elements operate in a push-pull manner. And through the LC resonant circuit composed of the two components of the resonant inductor (L _r ) and the resonant capacitor (C _r ) in the resonant tank circuit, the second plurality of low-voltage power switching elements with back-connected diodes The low-voltage power switching components of the secondary-side low-voltage switching/rectifier module operate with zero-voltage switching (ZVS). The high-voltage rectifier circuit of the primary-side high-voltage switching/rectification module of the first plurality of high-voltage power switching elements with back-connected diodes operates in zero-current switching (ZCS) under output rectification.

The bidirectional DC/DC energy conversion device with isolation, in the step-down forward power transmission mode, has a second secondary side low-voltage switching/rectification module with a plurality of low-voltage power switching elements with back-connected diodes. The low-voltage power switching components adopt synchronous full-wave rectification control.

In the above-mentioned bidirectional DC/DC energy conversion device with isolation, in the boost reverse power transmission mode, the primary side high-voltage switching/rectification module is one of the first plurality of high-voltage power switching elements with back-connected diodes. The high-voltage power switching components adopt synchronous full-wave rectification control.

Preferably, in order to reduce the number of magnetic components, the primary winding (N _p ) of the isolation transformer and the first secondary winding (N _s1 ) and the second secondary winding (N _s2 ) of the center tap can be connected by The slotted spool is made in such a way that the resonant inductor (L _r ) is embedded in the magnetic structure of the isolation transformer.

Preferably, the power switching element can be made of metal oxide semiconductor field effect transistor (MOSFET), gallium nitride (GaN) and silicon carbide (SiC).

Due to the above conventional technical description, the present invention has the following advantages compared with the existing technology. By controlling the controllable power switching elements on both sides of the isolation transformer, the present invention does not require the LLC topology of the traditional one-way DC converter. Add any components and use different control methods to complete a bidirectional DC/DC power conversion device with soft switching and lossless, thereby improving power conversion efficiency and reducing manufacturing production and parts costs.

1: Primary side high voltage DC power supply/load

2: Primary side high voltage terminal capacitor

3A: Primary side high voltage switching/rectifier module

31A:S ₁ switch/rectifier element

32A:S ₂ switch/rectifier element

33A:S ₃ switch/rectifier element

34A:S ₄ switch/rectifier element

4A: Resonant tank circuit

41A:L _r resonant inductor

42A:C _r resonance capacitor

43A:L _m magnetizing inductor

5A: Isolation transformer

51A:N _p primary winding

52A:N _s1 secondary first winding

53A:N _s2 secondary second winding

6A: Secondary side low voltage switching/rectifier module

61A:S ₅ switch/rectifier element

62A:S ₆ switch/rectifier element

7: Secondary side low voltage terminal capacitor

8: Secondary side low-voltage DC terminal power supply/load

3B: Primary side high voltage switching/rectifier module

31B:S ₁ switch/rectifier element

32B:S ₂ switch/rectifier element

4B: Resonant tank circuit

41B:C _r1 resonant capacitor

42B:C _r2 resonant capacitor

43B:L _r resonant inductor

44B:L _m magnetizing inductor

5B: Isolation transformer

51B:N _p primary winding

52B:N _s1 secondary first winding

53B:N _s2 secondary second winding

6B: Secondary side low voltage switching/rectifier module

61B:S ₃ switch/rectifier element

62B:S ₄ switch/rectifier element

100A: Bidirectional DC/DC converter of the first embodiment

100B: Bidirectional DC/DC converter of the second embodiment

D: Responsibility cycle

V _x : Equivalent resonant circuit high voltage terminal voltage

V _y : equivalent resonant circuit low-voltage terminal voltage

R _ac : AC equivalent load

R _L : load

i _Lr : resonant inductor current

V _H : primary side high voltage

V _L : Secondary side low voltage

Figure 1 is a designated representative diagram of this case.

Figure 2 is a circuit schematic diagram of the preferred embodiment 1.

Figure 3 is a circuit schematic diagram of the second preferred embodiment.

Figure 4 is a simplified circuit architecture diagram of the LLC topology for forward energy transmission of the present invention.

Figure 5 is the equivalent circuit of the LLC topology resonant converter using the First Harmonic Approximation (FHA) method.

Figure 6 is a simplified circuit architecture diagram of the push-pull topology of reverse energy transmission of the present invention.

Figure 7 shows the equivalent circuit of the push-pull topology resonant converter using the first harmonic approximation method (FHA).

Figure 8. The voltage (V _ds ) and current (I ds ) waveforms of the forearm switching elements (31A) and ( _33A ) simulating the forward energy transfer of the LLC topology all exhibit zero-voltage switching (ZVS).

Figure 9 The voltage (Vds) and current (Ids) waveforms of the back arm switching elements (32A) and (34A) simulating the forward energy transfer of the LLC topology all show zero voltage switching (ZVS).

Figure 10 The voltage (Vds) and current (Ids) waveforms of the rectifier switching elements (61A) and (62A) simulating the forward energy transfer of the LLC topology all exhibit zero-current switching (ZCS).

Figure 11 shows zero voltage switching (ZVS) in the (61A) and (62A) voltage (Vds) and current (Ids) waveforms of the switching element simulating push-pull topology reverse energy transfer when the duty cycle is 0.48.

Figure 12: When the duty cycle of the switching element simulating push-pull topology reverse energy transfer is 0.48, the voltage (Vds) and current (Ids) waveforms of the rectifier switching elements (31A) and (33A) all exhibit zero-current switching (ZCS).

Figure 13. When the duty cycle of the switching element simulating push-pull topology reverse energy transfer is 0.48, the voltage (Vds) and current (Ids) waveforms of the rectifier switching elements (32A) and (34A) are shown. Exhibits zero flow pressure switching (ZCS).

Figure 14. The push-pull topology reverse energy transfer of the physical circuit. When the duty cycle of the switching element is 0.48, the voltage (Vds) and current (Ids) waveforms of the switching element (61A) both show zero voltage switching (ZVS). The rectifier switching element ( 31A) The voltage (Vds) and current (Ids) waveforms both exhibit zero current switching (ZCS).

Figure 15 shows zero voltage switching (ZVS) in the (61A) and (62A) voltage (Vds) and current (Ids) waveforms of the switching element simulating push-pull topology reverse energy transfer when the duty cycle is 0.42.

Figure 16: When the duty cycle of the switching element simulating push-pull topology reverse energy transfer is 0.42, the voltage (Vds) and current (Ids) waveforms of the rectifier switching elements (31A) and (33A) all exhibit zero-current switching (ZCS). .

Figure 17: When the duty cycle of the switching element simulating push-pull topology reverse energy transfer is 0.42, the voltage (Vds) and current (Ids) waveforms of the rectifier switching elements (32A) and (34A) all exhibit zero-current switching (ZCS).

Figure 18: When the duty cycle of the switching element of the push-pull topology reverse energy transfer in the physical circuit is 0.42, the voltage (Vds) and current (Ids) waveforms of the switching element (61A) both show zero voltage switching (ZVS), and the rectifier switching element ( 31A) The voltage (Vds) and current (Ids) waveforms both exhibit zero current switching (ZCS).

The embodiments described below are intended as descriptions of exemplary designs of the invention and are not intended to represent the only designs in which the invention may be practiced. The term "exemplary" is used herein to mean "an example, instance, or illustration." Any design described herein as "exemplary" is not necessarily to be construed as Preferred or advantageous over other designs. The detailed description includes specific details in order to provide an understanding of the exemplary designs of the invention. It will be apparent to one of ordinary skill in the art that the exemplary designs described herein may be practiced without these embodiments. The exemplary embodiments described herein are for illustration only and are not intended to limit the application.

The structural topology diagram of the bidirectional DC/DC energy conversion device with isolation proposed in this application is shown in Figure 1. From left to right, in order: the primary side high-voltage DC terminal power supply/load (1), the primary side high-voltage terminal capacitor (2 ), primary-side high-voltage switching/rectifier module (3A), resonant tank circuit (4A), isolation transformer (5A), secondary-side low-voltage switching/rectifier module (6A), secondary-side low-voltage end capacitor (7), Secondary side low voltage DC power supply/load(8).

The primary side high-voltage DC terminal power supply/load (1) is used to receive an external DC power supply or output load from the high-voltage terminal.

The primary-side high-voltage terminal capacitor (2) is located between the primary-side high-voltage DC terminal power supply/load (1) and the primary-side high-voltage switching/rectifier module (3A). Its function is to filter the input of the primary-side high-voltage DC terminal. or output voltage, filtering out high-frequency voltage ripples.

The primary-side high-voltage switching/rectification module (3A) is the first high-voltage power switching element with back-connected diodes. Its structural topology is full bridge or half bridge and other methods are not excluded. It is located on the primary side. The two ends in the lateral direction are connected to the primary side high-voltage DC terminal power supply/load (1) and the primary side high-voltage terminal capacitor (2), which are used to accept the input DC power supply or output load from the first DC terminal.

The resonant tank circuit (4A), a bidirectional DC/DC conversion device, is composed of three components: a resonant inductor (L _r ), a magnetizing inductor (L _m ), and a resonant capacitor (C _r ) in the step-down forward power transmission mode. The LLC resonant tank circuit controls the primary-side high-voltage switching/rectifier module (3A) by changing the pulse frequency modulation (PFM), so that the impedance of the resonant tank circuit (4A) changes, thereby changing the voltage and current state on the switching element. ; In the boost reverse power transfer mode, the magnetizing inductor (L _m ) does not participate in the operation of the resonant tank. Only the resonant inductor (L _r ) and the resonant capacitor (C _r ) in the resonant tank circuit participate in the operation of the resonant circuit. The fixed switching frequency changes the pulse width modulation (PWM) mode to control the operation of the secondary side low-voltage switching/rectifier module (6A), thereby changing the voltage and current state on the switching element.

The isolation transformer (5A) includes a first secondary winding (N _s1 ) and a second secondary winding (N _s2 ) with a primary winding (N _p ) and a center tap. According to the primary high-voltage power switching element, it is a full bridge Or half-bridge topology, but the turns ratio of the primary winding (N _p ), the first secondary winding (N _s1 ), and the second secondary winding (N _s2 ) are different. The ratio of turns between the primary and secondary windings is n:1:1 (n=N _p /N _s1 , N _s1 =N _s2 ). In the full-bridge topology, n = V _H / V _L and in the half-bridge topology, n = V _H /2 V _L .

The secondary side low-voltage switching/rectification module (6A) is a second plurality of low-voltage power switching components with back-connected diodes. Its structural topology is a push-pull structure and is connected to the isolation transformer (5A). both ends of.

The secondary side low-voltage terminal capacitor (7) is located between the secondary side low-voltage DC terminal power supply/load (8) and the isolation transformer (5A). Its function is to filter the input or output voltage of the secondary side low-voltage DC terminal. , filter out high-frequency voltage ripples.

The secondary side low-voltage DC terminal power supply/load (8) is used to accept an external input DC power supply or output load from the low-voltage terminal.

The bidirectional DC/DC energy conversion device with isolation can be operated in one of the following two states according to the needs of the same device or component: the first state is from the primary side high voltage Energy is transmitted to the secondary side low pressure, and the second state is to transmit energy from the secondary side low pressure to the primary side high pressure.

[Example 1]

Figure 2 shows the first embodiment of the present invention, the primary-side high-voltage switching/rectifier module (3A), which adopts a topology of a bidirectional DC/DC energy conversion device 100A with isolation in a full-bridge structure.

In the case of step-down power transmission in Figure 2, the bidirectional DC/DC energy conversion device 100A with isolation inputs a high voltage source from the left primary side high voltage DC terminal power supply/load (1) and is connected to the primary side high voltage terminal. The capacitor (2) filters out the high-voltage switching ripple voltage and passes through the primary-side high-voltage switching/rectifier module (3A) in the primary-side full-bridge architecture. Switching elements (31A) and (33A) form the front arm switching elements of the full-bridge architecture, (32A) and (34A) form the rear-arm switching elements of the full-bridge architecture, and maintain a dead time between the upper and lower arm switching to avoid upper and lower arm switching. Components conduct at the same time causing a short circuit. The pulse frequency modulation (PFM) is controlled to turn on and off at the same time with a duty cycle width of about 0.5, so that the primary-side high-voltage switching/rectification module (3A) of the full bridge generates a duty cycle width of 0.5 and can be generated between node a and node b. Square wave voltage waveform with variable frequency. A resonant tank circuit including a resonant inductor (41A), a resonant capacitor (42A) and a magnetizing inductor (43A) is connected to nodes a and b. The exciting inductor (43A) is connected in parallel with the primary winding (51A) of the isolation transformer (5A). Transformers such as the isolation transformer (5A) are schematically represented by dashed lines in the relevant figures. To reduce the number of magnetic components, the magnetizing inductor (43A) is usually embedded in the magnetic structure of the isolation transformer (5A). In this case, the magnetizing inductance value can be controlled by introducing an air gap in the core and adjusting its width. The secondary first winding (52A) and the secondary second winding (53A) located on the secondary side of the isolation transformer (5A) include an equal number of winding turns and And connected in a center tap configuration, the center tap node c is connected to the positive terminal of the load of the secondary side low-voltage terminal capacitor (7) and the secondary side low-voltage DC terminal power supply/load (8), and the node d of the secondary winding, e is connected to the push-pull rectifier circuit of the secondary side low-voltage switching/rectification module (6A), which circuit includes controlled switching elements (61A) and (62A). The switching elements (61A) and (62A) are controlled with a variable frequency with a duty cycle width of approximately 0.5, and the square wave voltage generated by the first secondary winding (52A) and the second secondary winding (53A) is rectified in a synchronous rectification manner. waveform. The common point of the switching elements (61A) and (62A) is connected to the negative terminal of the load of the secondary low voltage side capacitor (7) and the secondary side low voltage DC side power supply/load (8). In this load circuit, the secondary side low-voltage terminal capacitor (7) is connected in parallel with the load of the secondary side low-voltage DC terminal power supply/load (8), and filters out the DC low-voltage switching ripple voltage. In this exemplary embodiment, a push-pull rectifier circuit is used as the synchronous full-wave rectification circuit. The operation of the converter will provide zero voltage switching (ZVS) for the switching element connected to the supply side and zero current switching (ZCS) for the rectifying switching element connected to the load.

In the case of boosted power transmission in Figure 2, the power supply and load exchange positions. The bidirectional DC/DC energy conversion device with isolation 100A inputs a low voltage source from the right secondary side low-voltage DC end power supply/load (8). The DC low voltage switching ripple voltage is filtered out by the capacitor (7) connected to the secondary side low voltage terminal. The switching elements (61A) and (62A) become pulse width modulation (PWM) controlled push-pull switches with a controlled switching duty period width at both ends of the primary winding (51A) of the isolation transformer (5A) Generates a square wave voltage. In addition, the full-bridge primary-side high-voltage switching/rectification module (3A) becomes a synchronous full-wave rectifier circuit with a duty cycle control pulse width of approximately 0.5, which is suitable for the switching elements (31A), (32A), (33A) and (34A). The square wave voltage generated between node a and node b is rectified. This converter will provide zero voltage switching (ZVS) for the switching element connected to the supply side and zero current switching for the rectifying switching element connected to the load. (ZCS).

In the case of step-down power transfer from Figure 2, the resonant converter (4A) is a series-type, frequency-controlled resonant converter that typically has three resonant components: a resonant capacitor (42A), a resonant inductor (41A), and Magnetizing inductor (43A). For analytical modeling of converters, the first harmonic approximation method (FHA) is widely used, especially when the LLC converter operates near its resonant frequency, since the resonant current consists only of the pure first harmonic current. Based on this equivalent circuit assumption, it is shown in Figure 5. The first harmonic approximation method (FHA) equivalent model of the converter consists of the voltage source V _x and the resonant elements L _r , L _m , _Cr and R _ac . R _ac is the AC equivalent resistance of the load on the primary side of the isolation transformer (5A). The parameters that control the resonant characteristics of the converter from the equivalent circuit can be expressed by the following relationship:

where converter gain is defined as the ratio of output voltage to input voltage: M = V _L / V _H .

The AC equivalent resistance of the primary side load: R _ac =8 _n ² R _L /π ² .

。 where f _r is the resonant frequency:

.

Among them, the inductance ratio L _n = L _m / L _r during primary side-secondary side power transmission

where the normalized frequency: F _N = f _s / f _r .

。 Among them Q factor:

.

In the case of boosted power transmission from Figure 2, the resonant converter is a series-type resonant converter with two resonant components: a resonant capacitor (42A) and a resonant inductor (41A), of which the exciting inductor (43A ) does not participate in the operation, the first harmonic approximation method (FHA) is used to analyze the LC converter. When operating near its resonant frequency, the resonant current only consists of the pure first harmonic current. Based on the equivalent circuit assumption, as shown in Figure 7, the present invention uses pulse width modulation (PWM) mode operation at a fixed frequency instead of pulse frequency modulation (PFM) mode operation control, and takes the fixed switching frequency f _s When f _s = f _r at the resonance point, its resonance characteristics are similar to those of the LLC resonance circuit. In its pulse width modulation (PWM) mode, the converter gain is defined as the ratio of the output voltage to the input voltage V _H / V _L = 2 Dn , so the output voltage is adjusted by controlling the pulse width of the duty cycle (Duty Cycle, D).

[Example 2]

Figure 3 shows a second embodiment of the present invention, a primary-side high-voltage switching/rectification module (3B), a bidirectional DC/DC energy conversion device 100B with isolation using a half-bridge structure topology.

In the case of step-down power transmission from Figure 3, the bidirectional DC/DC energy conversion device 100B with isolation inputs a high voltage source from the left primary side high voltage DC terminal power supply/load (1) and is connected to the primary side high voltage terminal. The capacitor (2) filters out the high-voltage switching ripple voltage, and then passes through the primary-side high-voltage switching/rectifier module (3B) of the half-bridge structure. The switching elements (31B) and (32B) form a half-bridge structure, and maintain a dead time between the upper and lower arm switches to avoid short circuit caused by the upper and lower arm switches being turned on at the same time. The pulse frequency modulation (PFM) is controlled to turn on and off with a duty cycle width of about 0.5 at the same time, so that the primary-side high-voltage switching/rectification module (3B) of the half-bridge structure generates a duty cycle width of 0.5 and between node a and node b. Variable frequency square wave voltage waveform. A resonant tank circuit including a resonant inductor (43B), resonant capacitors (41B), (42B) and a magnetizing inductor (44B) is connected to nodes a and b. The exciting inductor (44B) is connected in parallel with the primary winding (51B) of the isolation transformer (5B). Transformers such as the isolation transformer (5B) are schematically represented by dashed lines in the relevant figures. To reduce the number of magnetic components, the magnetizing inductor (44B) is usually embedded in the magnetic structure of the isolation transformer (5B). In this case, the magnetizing inductance value can be controlled by introducing an air gap in the core and adjusting its width. Located on the secondary side of the isolation transformer (5B) The side first winding (52B) and the secondary side second winding (53B) include an equal number of winding turns and are connected in a center tap configuration, with the center tap node c connected to the secondary side low voltage side capacitor (7) and the secondary side The positive terminal of the load of the low-voltage DC side power supply/load (8), while the nodes d and e of the secondary winding are connected to the push-pull rectifier circuit of the secondary-side low-voltage switching/rectifier module (6B), which circuit includes a controlled switch Components (61B) and (62B) control switching components (61B) and (62B) with a duty cycle width variable frequency of approximately 0.5, and are rectified in a synchronous rectification mode by the first secondary winding (52B) and the second secondary winding. (53B) produces a square wave voltage. The common point of the switching elements (61B) and (62B) is connected to the negative terminal of the load of the secondary low voltage side capacitor (7) and the secondary side low voltage DC side power supply/load (8). In this load circuit, the secondary side low-voltage terminal capacitor (7) is connected in parallel with the load impedance of the secondary side low-voltage DC terminal power supply/load (8), and filters out the DC low-voltage switching ripple voltage. In this exemplary embodiment, a push-pull rectifier circuit is used as the synchronous full-wave rectification circuit. This converter will provide zero voltage switching (ZVS) for the switching element connected to the power supply side and zero current switching (ZCS) for the rectifying switching element connected to the load.

In the case of boosted power transmission in Figure 3, the power supply and load exchange positions. The bidirectional DC/DC energy conversion device 100B with isolation inputs a low voltage source from the right secondary side low-voltage DC end power supply/load (8). The DC low voltage switching ripple voltage is filtered out by the capacitor (7) connected to the secondary side low voltage terminal. In addition, the switching elements (61B) and (62B) become pulse width modulation (PWM) controlled push-pull switches with a controlled switching duty cycle width, so that they are connected to the primary winding (51B) of the isolation transformer (5B). A square wave voltage is generated at both ends. In addition, the half-bridge structure primary-side high-voltage switching/rectification module (3B) becomes a synchronously controlled half-bridge voltage doubler full-wave rectifier circuit with a duty cycle control pulse width of approximately 0.5, generating a square wave between node a and node b. The wave voltage is rectified. This way the converter will provide zero voltage to the switching element connected to the supply side switching (ZVS) and zero-current switching (ZCS) of the rectifier switching element connected to the load.

1: Primary side high voltage DC power supply/load

2: Primary side high voltage terminal capacitor

3A: Primary side high voltage switching/rectifier module

4A: Resonant tank circuit

5A: Isolation transformer

6A: Secondary side low voltage switching/rectifier module

7: Secondary side low voltage terminal capacitor

8: Secondary side low-voltage DC terminal power supply/load

Claims (9)

A control method for an isolated bidirectional DC/DC energy conversion device. Based on the LLC resonant tank circuit topology of a traditional one-way DC converter, a novel control method is used to achieve bidirectional energy transmission with respective resonance characteristics, completing soft switching. , Lossless bidirectional DC/DC power conversion, the novel control method includes: in the buck forward power transfer mode, the primary side high-voltage switching/rectification module (3A) is driven by pulse frequency modulation (PFM) mode Controlled by the switching element method, the secondary side low-voltage switching/rectifier module (6A) is controlled by the synchronous full-wave rectification drive switching element method; in the boost reverse power transmission mode, the secondary side low-voltage switching/rectifier module (6A), The primary-side high-voltage switching/rectifier module (3A) is controlled by driving the switching element in a fixed switching frequency pulse width modulation (PWM) mode. The primary-side high-voltage switching/rectifier module (3A) is controlled by driving the switching element with synchronous full-wave rectification. According to the bidirectional DC/DC energy conversion method with isolation described in claim 1 of the patent application, the fixed switching _frequency is determined by taking the resonant frequency f _s = fr of the resonant tank circuit. An isolated bidirectional DC/DC energy conversion device, which realizes bidirectional energy transmission and has its own resonance characteristics, and completes bidirectional DC/DC power conversion with soft switching and no loss. It is characterized by including: a primary side high-voltage switching/rectifier Module (3A), in the buck forward power transfer mode, by changing the switching control of pulse frequency modulation (PFM), its two ends located in the primary side direction are connected to the first DC terminal 1 for Accept the DC power supply from the first DC terminal input or the first DC terminal output load; a resonant tank circuit (4A), which has a three-element resonant tank circuit connected to a primary side through nodes a and node b. High-voltage switching/ _{rectifier module (3A); an isolation transformer (5A), including a first secondary winding (N s1 ) and a second winding (N s2 )} with a primary winding (N _p ) and a center tap. Both ends of the side winding are connected to the resonant tank (4A), the secondary winding is connected to the secondary side low-voltage DC power supply/load (8) with node c, and is connected to the secondary side low-voltage switching/rectifier module (8) with nodes d and e. 6A); a secondary side low-voltage switching/rectification module (6A), in the boost reverse power transfer mode, controlled by a fixed switching frequency changing pulse width modulation (PWM) mode, connected to nodes d and e The secondary winding of an isolation transformer (5A), with its low-potential end located in the secondary side direction connected to the secondary side low-voltage DC end power supply/load (8), is used to receive DC power from the second DC end or to Second DC terminal load output. According to claim 3 of the patent application, the bidirectional DC/DC energy conversion device with isolation includes the primary side high-voltage switching/rectification module (3A), which is the first of a plurality of high-voltage devices with back-connected diodes. The power switching element, as a high-voltage switching function, has a topology with a full-bridge structure of four high-voltage power elements or a half-bridge structure with two high-voltage power elements. According to claim 3 of the patent application, the bidirectional DC/DC energy conversion device with isolation is provided, wherein the resonant tank circuit (4A) includes a resonant inductor (L _r ), a magnetizing inductor (L _m ) and a resonant capacitor. An LLC resonant tank circuit composed of three components (C _r ), in which the resonant inductor (L _r ) can be an independent component or embedded in the magnetic structure of the isolation transformer. According to claim 5 of the patent application, the bidirectional DC/DC energy conversion device with isolation includes the resonant tank circuit (4A), which has a resonant inductor (L _r ), Characteristics of the LLC resonant tank circuit consisting of three components: the magnetizing inductor (L _m ) and the resonant capacitor (C _r ). In the boost reverse power transfer mode, it has the resonant inductor (L _r ) and the resonant capacitor (C _r ) of the two components that form the operating characteristics of the LC resonant tank circuit. According to the bidirectional DC/DC energy conversion device with isolation described in claim 3 of the patent application, the isolation transformer (5A) has a primary winding (N _p ) and a center-tapped secondary winding (N _s1 , N _s2 ), where the primary winding (N _p ) and secondary windings (N _s1 , N _s2 ) can be made by using slotted bobbins to embed the resonant inductor (L _r ) in the magnetic structure of the isolation transformer. . According to the bidirectional DC/DC energy conversion device with isolation described in claim 3 of the patent application, the secondary side low-voltage switching/rectification module (3A) is the first of a plurality of high-voltage modules with back-connected diodes. The structural topology of power switching components is full-bridge or half-bridge structure. According to the bidirectional DC/DC energy conversion device with isolation described in claim 3 of the patent application, the secondary side low-voltage switching/rectification module (6A) is a second plurality of low-voltage low-voltage modules with back-connected diodes. The power switching element has a push-pull structure topology.