An asymmetric dual phase-shift control method for dual active bridge DC / DC converters

Abstract

The present invention discloses an asymmetric dual phase shift control method for a dual active bridge DC / DC converter, wherein the dual active bridge DC / DC converter comprises a primary full bridge circuit and a secondary full bridge circuit; the primary and secondary full bridge circuits are respectively composed of four switch tubes, namely Q1 to Q4 and Q a ~Q d , both circuit structures are full-bridge; the method includes: the duty cycle of the drive signals for the switches in the primary and secondary full-bridge circuits is not all 0.5, and some switches receive asymmetric drive signals. The direction and magnitude of power transmission in the dual-active-bridge DC / DC converter are controlled by two variables: an internal shift ratio D1 between the full-bridge and an external shift ratio D2 between the primary and secondary full-bridges. The present invention utilizes an asymmetric dual-phase-shift control method for a dual-active-bridge converter. When the circuit components and external conditions of the DAB converter are identical, the control method proposed by the present invention can significantly increase the power transmitted by the converter, while maintaining essentially unchanged current stress, compared to conventional dual-phase-shift control methods.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to an asymmetric dual phase-shift control method for a dual-active-bridge DC / DC converter. Background Art

[0002] The AC sides of the two full-bridge converters in a Dual Active Bridge Converter (DAB) are connected through an inductor and a transformer. The full-bridge converter uses square wave modulation to generate a high-frequency square wave on the AC side. The DAB converter is equivalent to two AC sources connected across the inductor. By adjusting the phase shift between the two AC sources, the magnitude and direction of power flow can be adjusted. The use of a DAB converter can achieve electrical isolation of the DC transformer and bidirectional power flow, while the high-frequency isolation transformer significantly improves power density and modularity.

[0003] Control strategies are a key research area in DAB control. Scholars have proposed various control methods, including single phase shift (SPS), extended phase shift (EPS), dual phase shift (DPS), and triple phase shift (TPS). In these methods, the duty cycle of both the primary and secondary switches is 50%, and the phase shift between the primary and secondary switches is used to control power flow. Compared to single phase shift, dual phase shift increases the phase shift angle within the primary and secondary H-bridges, resulting in a three-level output voltage after H-bridge inversion. Dual phase shift reduces current stress and backflow power, but does not increase maximum transmission power. With traditional dual phase shift, increasing maximum transmission power also increases current stress, which leads to increased losses and heat generation in the circuit, while also placing higher voltage and current requirements on the components. Summary of the Invention

[0004] In order to solve at least one technical problem existing in the above-mentioned background technology, the present invention provides an asymmetric dual phase-shift control method for a dual active bridge DC / DC converter. When the circuit elements and external conditions of the DAB converter are the same, compared with the traditional dual phase-shift control method, the control method proposed by the present invention can significantly improve the power transmitted by the converter while keeping the current stress basically unchanged.

[0005] To achieve the above object, the technical solution of the present invention is:

[0006] An asymmetric dual phase shift control method for a dual active bridge DC / DC converter, wherein the dual active bridge DC / DC converter comprises a primary full bridge circuit and a secondary full bridge circuit, wherein the primary and secondary full bridge circuits are respectively composed of four switching tubes, namely Q1 to Q4 and Q a ~Q d , the circuit structure is full bridge;

[0007] The method comprises:

[0008] The duty cycle of the driving signals of the switching tubes in the primary full-bridge circuit and the secondary full-bridge circuit is not all 0.5. Some switching tubes receive asymmetric driving signals. The direction and size of the power transmission of the dual active bridge DC / DC converter are controlled by the two variables of the full-bridge inward shift ratio D1 and the outward shift ratio D2 between the primary and secondary full-bridges.

[0009] Furthermore, the duty cycles of the driving signals of the switching tubes of the primary full-bridge circuit and the secondary full-bridge circuit are not all 0.5, and some switching tubes receive asymmetric driving signals. By using two variables, the inward shift ratio D1 of the full bridge and the outward shift ratio D2 between the primary and secondary full bridges, the control of the direction and magnitude of power transmission of the dual active bridge DC / DC converter is achieved, including:

[0010] The driving signals of the first switch Q1 of the primary full-bridge circuit and the third switch Q3 of the primary full-bridge circuit are complementary, and the duty cycle of their driving signals is not 0.5; the driving signals of the second switch Q2 of the primary full-bridge circuit and the fourth switch Q4 of the primary full-bridge circuit are complementary, and the duty cycle of their driving signals is 0.5; Q1 and Q4 are turned off simultaneously, and Q4 is turned off later than Q1, and the lag is the primary side internal shift phase D1;

[0011] The first switch tube Q of the secondary full-bridge circuit a The third switch tube Q of the secondary full bridge circuit c The signal of the secondary side full bridge circuit is complementary, and its driving signal duty cycle is 0.5; the second switch tube Q b and the fourth switch tube Q of the secondary full-bridge circuit d The driving signal is complementary, and the duty cycle of the driving signal is not 0.5; Q a With Q d At the same time, Q d Lagging behind Q a When shutting down, the hysteresis is the secondary side inward shift ratio kD1; where k is the voltage regulation ratio, k = U1 / nU2; n is the turns ratio of the transformer;

[0012] The first switch tube Q of the secondary full-bridge circuit a The first switch tube Q1 is turned on after the primary full-bridge circuit, and the lag is the outward shift phase D2.

[0013] Furthermore, the method further comprises:

[0014] Let the moment when Q1 is turned on in steady state be the moment when a cycle starts and be recorded as t0, the moment when Q4 is turned on be t1, and Q a and Q d The opening time is t2, the closing time of Q1 and Q4 is t3, and Q a The shutdown time is t4, Q d The time of shutdown is t5, the time of end of a cycle is t6, and the phase difference between each time is: t1-t0=D1T s / 2, t2-t0=D2 T s / 2, t3-t0=(1+D1)T s / 2, t4-t0=(1+D2)T s / 2, t5-t0=(1+kD1+D2)T s / 2, t6-t0=T s , where D1 is the inward shift ratio, D2 is the outward shift ratio, and T s is a duty cycle of the switching tube.

[0015] Furthermore, the transmission power of the dual active bridge DC / DC converter under the asymmetric dual phase shift control method is:

[0016]

[0017] Furthermore, the switch tube of the full-bridge circuit is composed of a MOSFET and an anti-parallel diode; two switch tubes are connected in series to form a bridge arm of the full bridge, and two bridge arms are connected in parallel to form a full-bridge circuit; the driving signals of the two switch tubes on the same bridge arm are complementary.

[0018] Furthermore, the two ends of the primary voltage-stabilizing capacitor C1 are connected to the external DC voltage source U1 and are connected in parallel with the input end of the primary full-bridge circuit; one end of the output end of the primary full-bridge circuit is connected in series with the auxiliary inductor L to the same-name end of the primary side of the transformer T, and the other end is connected to the opposite-name end of the primary side of the transformer T; the two ends of the secondary voltage-stabilizing capacitor C2 are connected to the external DC voltage source U2 and are connected in parallel with the input end of the secondary full-bridge circuit; the output end of the secondary full-bridge circuit is connected to the secondary side of the transformer T.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention uses an asymmetric dual phase-shift control method for a dual active bridge converter. When the circuit elements and external conditions of the DAB converter are the same, compared with the traditional dual phase-shift control method, the control method proposed by the present invention can significantly improve the power transmitted by the converter while keeping the current stress basically unchanged. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the circuit structure diagram of the dual active bridge DC / DC converter;

[0022] Figure 2 This is a simplified circuit diagram of the dual active bridge DC / DC converter equivalent to the primary side;

[0023] Figure 3 The waveform diagram of the asymmetric dual phase-shift control working principle of the dual active bridge DC / DC converter;

[0024] Figure 4 A comparison diagram of the main waveforms of the asymmetric dual phase-shift control method and the traditional dual phase-shift control method in an embodiment of the present invention;

[0025] Figure 5 A comparison diagram of the primary voltage source current between the asymmetric dual phase-shift control method and the traditional dual phase-shift control method in an embodiment of the present invention;

[0026] Figure 6 A comparison diagram of the transmission power ratio of the asymmetric dual phase-shift control method and the traditional dual phase-shift control method according to the embodiment of the present invention as a function of the voltage regulation ratio;

[0027] Figure 7 4 is a control block diagram of the asymmetric dual phase shift control method in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] Example:

[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0030] The circuit topology of the dual active bridge DC / DC converter is as follows: Figure 1 As shown. It consists of transformer T, primary full-bridge circuit, primary voltage stabilizing capacitor C1, auxiliary inductor L, secondary full-bridge circuit, and secondary voltage stabilizing capacitor C2; u h1 is the voltage difference between the midpoints of the two bridge arms of the primary full-bridge circuit; u h2 is the voltage difference between the midpoints of the two bridge arms of the secondary full-bridge circuit; i L is the inductor current; U1 is the DC voltage on the primary side; U2 is the DC voltage on the secondary side.

[0031] The two ends of the primary voltage stabilizing capacitor C1 are connected to the external DC voltage source U1 and connected in parallel with the input end of the primary full-bridge circuit; one end of the output end of the primary full-bridge circuit is connected in series with the auxiliary inductor L to the same-name end of the primary side of the transformer T, and the other end is connected to the opposite-name end of the primary side of the transformer T; the two ends of the secondary voltage stabilizing capacitor C2 are connected to the external DC voltage source U2 and connected in parallel with the input end of the secondary full-bridge circuit; the output end of the secondary full-bridge circuit is connected to the secondary side of the transformer T; the dual active bridge DC / DC converter also includes: primary and secondary full-bridge circuits, each consisting of four switch tubes, namely Q1~Q4 and Q a ~Q d , the circuit structure is full-bridge; the switch tube of the full-bridge circuit is composed of a MOSFET and an anti-parallel diode; two switch tubes are connected in series to form a bridge arm of the full bridge, and two bridge arms are connected in parallel to form a full-bridge circuit; the driving signals of the two switch tubes on the same bridge arm are complementary.

[0032] The method provided in this embodiment is for an asymmetric dual phase-shift control method for a dual-active-bridge DC / DC converter. The main features are: the duty cycles of the drive signals of the switching tubes of the primary full-bridge circuit and the secondary full-bridge circuit are not all 0.5, some switching tubes receive asymmetric drive signals, and the direction and magnitude of power transmission of the dual-active-bridge DC / DC converter are controlled by using two variables: the inward shift ratio D1 of the full bridge and the outward shift ratio D2 between the primary and secondary full bridges.

[0033] Specifically, the above method includes:

[0034] The drive signals of the first switch Q1 of the primary full-bridge circuit and the third switch Q3 of the primary full-bridge circuit are complementary, and the duty cycle of their drive signals is not 0.5; the drive signals of the second switch Q2 of the primary full-bridge circuit and the fourth switch Q4 of the primary full-bridge circuit are complementary, and the duty cycle of their drive signals is 0.5; Q1 and Q4 are turned off simultaneously, with Q4 turning off later than Q1, and the lag is the primary side internal shift phase D1;

[0035] The first switch tube Q of the secondary full-bridge circuit a The third switch tube Q of the secondary full bridge circuit c The signal of the secondary side full bridge circuit is complementary, and its driving signal duty cycle is 0.5; the second switch tube Q b and the fourth switch tube Q of the secondary full-bridge circuit d The driving signal is complementary, and the duty cycle of the driving signal is not 0.5; Q a With Q d At the same time, Q d Lagging behind Q a When shutting down, the hysteresis is the secondary side inward shift ratio kD1; where k is the voltage regulation ratio, k = U1 / nU2; n is the turns ratio of the transformer;

[0036] The first switch tube Q of the secondary full-bridge circuit a The first switch Q1 of the primary full bridge is turned on later than the first switch Q1 of the primary full bridge, and the lag is the outward shift D2.

[0037] Let the moment when Q1 is turned on in steady state be the moment when a cycle starts and be recorded as t0, the moment when Q4 is turned on be t1, and Q a and Q d The opening time is t2, the closing time of Q1 and Q4 is t3, and Q a The shutdown time is t4, Q d The time of shutdown is t5, the time of end of a cycle is t6, and the phase difference between each time is: t1-t0=D1T s / 2, t2-t0=D2 T s / 2, t3-t0=(1+D1)T s / 2, t4-t0=(1+D2)T s / 2, t5-t0=(1+kD1+D2)T s / 2, t6-t0=T s , where D1 is the inward shift ratio, D2 is the outward shift ratio, and T s is a duty cycle of the switching tube.

[0038] A typical voltage and current waveform timing diagram of a dual active bridge DC / DC converter modulated by asymmetric dual phase shift control method is shown in the figure below: Figure 3 From top to bottom are the driving signals of the first switch tube Q1 of the primary full bridge and the fourth switch tube Q4 of the primary full bridge, the first switch tube Q a With the secondary side full bridge fourth switch tube Q d The driving signal of the primary full-bridge output voltage u h1 , equivalent secondary full-bridge input voltage u h2 ′, inductor voltage u L , inductor current i L , primary voltage source current i1.

[0039] like Figure 3 As shown, this solution uses the rising edge of the first switch Q1 of the primary full bridge as the reference time, D1 is the internal shift ratio between the two bridge arms of the primary full bridge; D2 is the positive duty cycle of the secondary voltage, and k is the voltage regulation ratio. According to the definition, the following relationship is obtained:

[0040]

[0041] Among them, T s is a duty cycle of the switching tube.

[0042] The constraints of the asymmetric dual phase-shift control method in this control method are:

[0043]

[0044] Based on the volt-second balance of the positive and negative half-cycles within each inductor cycle, combined with a typical voltage and current waveform timing diagram of a dual-active bridge DC / DC converter modulated by the asymmetric dual phase-shift control method, the current value of the inductor at each moment within a cycle can be analyzed as follows:

[0045]

[0046] Among them, k is the voltage regulation ratio, k=U1 / nU2, k≥1; U1 is the input voltage; U2 is the output voltage; n is the turns ratio of the transformer T, n=N1 / N2; L is the inductance of the auxiliary inductor, and f is the frequency of the switching tube (the same for all switching tubes).

[0047] The power transmitted by the dual active bridge DC / DC converter under the asymmetric dual phase shift control method is:

[0048]

[0049] Take the maximum transmission power under traditional dual phase shift control as the reference transmission power P base , then:

[0050]

[0051] The power transfer ratio P′ is obtained according to the actual working conditions, where:

[0052]

[0053] Given an inward shift relative to D1 and an outward shift relative to D2, if Figure 6 As shown, there is a comparison diagram of the transmission power ratio of the asymmetric dual phase-shift control method and the traditional dual phase-shift control as the voltage regulation ratio changes in the embodiment of the present invention. It can be seen from the figure that within the working condition constraints, when the inner shift ratio D1 and the outer shift ratio D2 are the same, under different voltage regulation ratios, the transmission power ratio of the asymmetric dual phase-shift control is always greater than the transmission power ratio of the traditional dual phase-shift control.

[0054] When implementing it specifically, Figure 7 As shown, given the value of D1, the given output voltage U 2ref The difference between it and the actual output voltage U2 is input into the PI controller, and D2 is closed-loop adjusted to keep the output voltage constant. Finally, a PWM signal is jointly given to drive the 8 switching tubes of the DAB converter.

[0055] After verification by Matlab / Simulink simulation platform, we get Figure 5The experimental results shown are a comparison of the current of the asymmetric dual phase-shift control method and the traditional dual phase-shift control primary voltage source in the embodiment of the present invention. From top to bottom, the output current of the traditional dual phase-shift control primary voltage source and the output current of the asymmetric dual phase-shift control primary voltage source are respectively shown. The simulation results show that the current stress in the dual active bridge DC / DC converter is basically unchanged, but the output current of the traditional dual phase-shift control primary voltage source is zero for a longer period of time than the output current of the asymmetric dual phase-shift control primary voltage source within one cycle, that is, no power is transmitted during this period of time when the current is zero, while the output current of the asymmetric dual phase-shift control primary voltage source maintains a larger positive current value during this period. Therefore, under the asymmetric dual phase-shift control method, the transmitted power is higher, which improves the transmission efficiency of the converter.

[0056] It can be seen that the asymmetric dual phase-shift control method of the dual active bridge converter proposed in the present invention can significantly improve the power transmitted by the converter when the circuit elements and external conditions of the DAB converter are the same, compared with the traditional dual phase-shift control method, while the current stress remains basically unchanged.

[0057] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made based on the essence of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. An asymmetric dual phase shift control method for a dual active bridge DC / DC converter, wherein the dual active bridge DC / DC converter comprises a primary full bridge circuit and a secondary full bridge circuit, wherein the primary and secondary full bridge circuits are each composed of four switching transistors, namely Q1 to Q4 and Q a ~Q d , the circuit structure is full bridge; it is characterized by, The method comprises: The duty cycle of the driving signals for the switches in the primary and secondary full-bridge circuits is not all 0.

5. Some switches receive asymmetric driving signals. By using two variables—the inward shift ratio D1 of the full bridge and the outward shift ratio D2 between the primary and secondary full bridges—the direction and magnitude of power transmission in the dual-active-bridge DC / DC converter can be controlled. The duty cycles of the driving signals of the switches of the primary full-bridge circuit and the secondary full-bridge circuit are not all 0.5, and some switches receive asymmetric driving signals. By using two variables, the inward shift ratio D1 of the full bridge and the outward shift ratio D2 between the primary and secondary full bridges, the control of the direction and magnitude of power transmission of the dual active bridge DC / DC converter is achieved, including: The driving signals of the first switch Q1 of the primary full-bridge circuit and the third switch Q3 of the primary full-bridge circuit are complementary, and the duty cycle of their driving signals is not 0.5; the driving signals of the second switch Q2 of the primary full-bridge circuit and the fourth switch Q4 of the primary full-bridge circuit are complementary, and the duty cycle of their driving signals is 0.5; Q1 and Q4 are turned off simultaneously, and Q4 is turned on later than Q1, and the lag is the primary side internal shift phase D1; The first switch tube Q of the secondary full-bridge circuit a The third switch tube Q of the secondary full bridge circuit c The signal of the secondary side full bridge circuit is complementary, and its driving signal duty cycle is 0.5; the second switch tube Q b and the fourth switch tube Q of the secondary full bridge circuit d The driving signal is complementary, and the duty cycle of the driving signal is not 0.5; Q a With Q d At the same time, Q d Lagging behind Q a When shutting down, the hysteresis is the secondary side inward shift ratio kD1; where k is the voltage regulation ratio, k = U1 / nU2; n is the turns ratio of the transformer; The first switch tube Q of the secondary full-bridge circuit a The first switch Q1 of the primary full-bridge circuit is turned on after a lag of D2. The method further comprises: Let the moment when Q1 is turned on in steady state be the moment when a cycle starts and be recorded as t0, the moment when Q4 is turned on be t1, and Q a and Q d The opening time is t2, the closing time of Q1 and Q4 is t3, and Q a The shutdown time is t4, Q d The time of shutdown is t5, the time of end of a cycle is t6, and the phase difference between each time is: t1-t0=D1T s / 2, t2-t0=D2 T s / 2, t3-t0=(1+D1)T s / 2, t4-t0=(1+D2)T s / 2, t5-t0=(1+kD1+D2)T s / 2, t6-t0=T s , where D1 is the inward shift ratio, D2 is the outward shift ratio, and T s is a duty cycle of the switching tube.

2. The asymmetric dual phase shift control method for a dual active bridge DC / DC converter according to claim 1, wherein: The transmission power of the dual active bridge DC / DC converter under the asymmetric dual phase shift control method is:

3. The asymmetric dual phase shift control method for a dual active bridge DC / DC converter according to claim 1, wherein: The switch tube of the full-bridge circuit is composed of a MOSFET and an anti-parallel diode; two switch tubes are connected in series to form a bridge arm of the full bridge, and two bridge arms are connected in parallel to form a full-bridge circuit; the driving signals of the two switch tubes on the same bridge arm are complementary.

4. The asymmetric dual phase shift control method for a dual active bridge DC / DC converter according to claim 1, wherein: The dual active bridge DC / DC converter further includes a transformer T, a primary side voltage stabilizing capacitor C1, an auxiliary inductor L, and a secondary side voltage stabilizing capacitor C2; The two ends of the primary side voltage stabilizing capacitor C1 are connected to the external DC voltage source U1 and are connected in parallel to the input end of the primary side full-bridge circuit; one end of the output end of the primary side full-bridge circuit is connected in series with the auxiliary inductor L to the same-name end of the primary side of the transformer T, and the other end is connected to the opposite-name end of the primary side of the transformer T; the two ends of the secondary side voltage stabilizing capacitor C2 are connected to the external DC voltage source U2 and are connected in parallel to the input end of the secondary side full-bridge circuit; the output end of the secondary side full-bridge circuit is connected to the secondary side of the transformer T.

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