Three-port bidirectional dc-dc converter with partial power conversion function for electric vehicle

Abstract

The application discloses a three-port bidirectional DC converter with partial power conversion function for an electric vehicle, which mainly comprises a power factor correction full-bridge circuit, a main power full-bridge circuit, a partial power full-bridge circuit, a partial power post-stage voltage regulation circuit, a low-voltage full-bridge circuit and a high-frequency transformer; the high-frequency transformer is used for connecting the power factor correction full-bridge circuit, the main power full-bridge circuit, the partial power full-bridge circuit and the low-voltage full-bridge circuit; the partial power full-bridge circuit is connected in cascade with the partial power post-stage voltage regulation circuit; the output port of the partial power post-stage voltage regulation circuit and the output port of the main power full-bridge circuit are connected in series to form a port as a high-voltage port, which is connected with a power battery; the output port of the low-voltage full-bridge circuit is used as a low-voltage port, which is connected with a storage battery; the partial power full-bridge circuit and the partial power post-stage voltage regulation circuit constitute a partial power conversion circuit, which is used for transmitting partial power in a total power range, so that the port voltage of the converter is matched with the turns ratio of the high-frequency transformer, and the soft switching operation of the converter in a full working voltage range is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electric vehicle charging, and particularly relates to a three-port bidirectional DC converter with partial power conversion function for electric vehicles. TECHNICAL BACKGROUND

[0002] The power supply system of an electric vehicle mainly comprises an on-board charger (OBC), a low-voltage DC-DC converter (LDC), a power battery (i.e., a high-voltage battery), a storage battery (i.e., a low-voltage battery), a load, and a motor drive system, all of which are interconnected through high-voltage and low-voltage DC buses. The OBC mainly converts AC power from a power grid into DC power, which is then converted by a DC converter to charge the power battery; the LDC converts the energy of the power battery into low-voltage power to charge the storage battery or to supply power to loads such as vehicle lighting and electronic devices; and the motor drive system uses the power battery as the main energy source to provide driving force for the vehicle.

[0003] The on-board charger only charges the power battery when the electric vehicle stops, and does not play any role when the vehicle is running, and the utilization rate is low, which becomes a "dead weight" of the power supply system. In order to improve the utilization rate of the on-board charger and improve the power density of the electric vehicle power supply system, researchers have proposed various integrated schemes of OBC and LDC topology, among which the more mainstream scheme is to switch the on-board charging and low-voltage conversion functions of the electric vehicle through a function selection switch. For example, the paper "An Integrated Battery Charger With High Power Density and Efficiency for Electric Vehicles" published in IEEE Power Electronics Journal proposes a non-isolated OBC and LDC integrated topology, which realizes the functions of on-board charging, low-voltage conversion and other functions of electric vehicles by setting a function selection switch. In the power supply system proposed in the literature "Onboard Reconfigurable Battery Charger for Electric Vehicles With Traction-to-Auxiliary Mode" and the literature "Multifunctional Onboard Battery Charger for Plug-in Electric Vehicles", the bidirectional transmission of power in the on-board charging mode is realized by adjusting the control strategy, and the functions of on-board charging, low-voltage conversion and other functions of electric vehicles are realized by setting a function selection switch. However, such design schemes still have shortcomings: (1) Most of them cannot realize the composite mode of on-board charging and low-voltage conversion; (2) The introduction of auxiliary switches will produce additional loss; (3) Multiple power switch devices need to be added, and the system cost increases.

[0004] To this end, some researchers integrate the DC-DC stage and the LDC stage of the OBC based on the multi-active bridge topology, realize the switching of different working modes through phase-shift control, thereby omitting the function selection switch, so as to reduce the system volume, improve the power density and reduce the cost. The documents "Modelling and control of a triple-active-bridge converter" and "Multi-Port Multi-Cell DC / DC Converter Topology for Electric Vehicle's Power Distribution Networks" both propose an integrated charging system based on an isolated voltage source type triple active bridge converter, which can realize the vehicle charging mode and the low voltage conversion mode at the same time, and can also support the bidirectional flow of power in the vehicle charging mode. However, under a wide voltage range, the existing solutions based on the multi-active bridge topology have high reactive circulating current and current stress, and it is difficult to ensure the soft switching operation of the power devices.

[0005] The present application is directed to the above problems, and proposes a three-port bidirectional DC converter for electric vehicles with partial power conversion function. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application proposes a three-port bidirectional DC converter for electric vehicles with partial power conversion function to solve the problem of soft switching implementation of the three-port bidirectional DC converter for electric vehicles based on the multi-active bridge topology under a wide voltage range.

[0007] The technical solution adopted by the present application to solve the technical problem is that the present application provides a three-port bidirectional DC converter for electric vehicles with partial power conversion function, which includes a power factor correction full-bridge circuit, a main power full-bridge circuit, a partial power full-bridge circuit, a partial power post-stage voltage regulation circuit, a low-voltage full-bridge circuit, a high-frequency transformer, first to fourth capacitors, first to third inductors, a filter capacitor and a filter inductor.

[0008] The first inductor and the first winding of the high-frequency transformer are connected in series between two groups of power switches of the power factor correction full-bridge circuit, the second winding of the high-frequency transformer is connected in series between two groups of power switches of the main power full-bridge circuit, the second inductor and the third winding of the high-frequency transformer are connected in series between two groups of power switches of the partial power full-bridge circuit, and the third inductor and the fourth winding of the high-frequency transformer are connected in series between two groups of power switch tubes of the low-voltage full-bridge circuit; the first capacitor is connected in parallel at the port side of the power factor correction full-bridge circuit, the second capacitor is connected in parallel at the port side of the main power full-bridge circuit, the third capacitor is connected in parallel between the output port of the partial power full-bridge circuit and the input port of the partial power post-stage voltage regulation circuit, and the fourth capacitor is connected in parallel at the port side of the low-voltage full-bridge circuit; the output port of the partial power full-bridge circuit and the input port of the partial power post-stage voltage regulation circuit are connected in cascade, the output port of the partial power post-stage voltage regulation circuit is connected in series with a filter inductor and a filter capacitor, and the output port of the partial power post-stage voltage regulation circuit and the output port of the main power full-bridge circuit are connected in series to form a port as a high-voltage port of the converter, which is connected with a power battery of the electric vehicle; the output port of the low-voltage full-bridge circuit is as a low-voltage port of the converter, which is connected with a storage battery of the electric vehicle; the partial power full-bridge circuit and the partial power post-stage voltage regulation circuit constitute a partial power conversion circuit, which is used for transmitting partial power in a total power range and compensating for a variation range of the voltage of the power battery and the voltage of the storage battery, so that the port voltage of the converter matches the turns ratio of the high-frequency transformer, and the converter realizes soft switching operation in a full working voltage range.

[0009] Further, when the above-mentioned converter is applied to the power supply system of the electric vehicle, the power transmission of the converter is controlled by adjusting the phase shift angles φ 12 、φ 13 、φ 14 and the duty ratio, so that the electric vehicle realizes operation in different charging and discharging modes; wherein the phase shift angle φ 12 is the phase angle difference between the bridge arm midpoint voltage of the power factor correction full-bridge circuit and the bridge arm midpoint voltage of the main power full-bridge circuit, the phase shift angle φ 13 is the phase angle difference between the bridge arm midpoint voltage of the power factor correction full-bridge circuit and the bridge arm midpoint voltage of the partial power full-bridge circuit, and the phase shift angle φ 14 is the phase angle difference between the bridge arm midpoint voltage of the power factor correction full-bridge circuit and the bridge arm midpoint voltage of the low-voltage full-bridge circuit; the output voltage of the partial power post-stage voltage regulation circuit is adjusted by the duty ratio, so that the sum of the output voltage of the partial power post-stage voltage regulation circuit and the output voltage of the main power full-bridge circuit is equal to the high-voltage port voltage; when the port voltage V M PP ​> 0, the duty cycle of the power switch on the left side of the upper bridge arm of the partial power post-stage voltage regulation circuit should be adjusted, i.e. the power switch on the right side of the upper bridge arm of the partial power post-stage voltage regulation circuit is turned off, the power switch on the right side of the lower bridge arm is kept on, and the power switch on the left side of the lower bridge arm and the power switch on the left side of the upper bridge arm are turned on complementarily; when the port voltage V M > 0, the duty cycle of the power switch on the left side of the upper bridge arm of the partial power post-stage voltage regulation circuit should be adjusted, i.e. the power switch on the right side of the upper bridge arm of the partial power post-stage voltage regulation circuit is turned off, the power switch on the right side of the lower bridge arm is kept on, and the power switch on the left side of the lower bridge arm and the power switch on the left side of the upper bridge arm are turned on complementarily; when the port voltage V PP < 0, the duty cycle of the power switch on the left side of the lower bridge arm of the partial power post-stage voltage regulation circuit should be adjusted, i.e. the power switch on the right side of the upper bridge arm of the partial power post-stage voltage regulation circuit is kept on, the power switch on the right side of the lower bridge arm is kept off, and the power switch on the left side of the upper bridge arm and the power switch on the left side of the lower bridge arm are turned on complementarily.

[0010] Further, the charging and discharging modes of the electric vehicle include a vehicle-mounted charging mode, a low-voltage conversion mode, and a composite mode, and the composite mode refers to the simultaneous operation of the vehicle-mounted charging mode and the low-voltage conversion mode; in the vehicle-mounted charging mode, the port voltage V1 of the power factor correction full-bridge circuit is adjusted so that the reference value V 1ref of the port voltage of the power factor correction full-bridge circuit is V1 = n1 / n4*V3; the high-frequency transformer port current is adjusted by adjusting the phase shift angle φ 12 to meet the specified reference value and remain constant, i.e. constant current charging; the phase shift angle φ 13 is adjusted to control the port voltage V P of the partial power full-bridge circuit so that the reference value V Pref of the port voltage of the partial power full-bridge circuit is V3 = n3 / n4*V3; the low-voltage full-bridge circuit port voltage V3 is adjusted by adjusting the phase shift angle φ 14 to meet the specified reference value V 3ref ; the port voltage V M of the main power full-bridge circuit is calculated according to the ratio of the second winding number to the fourth winding number of the high-frequency transformer, i.e. V M = n2 / n4*V3, and the output voltage V PP of the main power post-stage voltage regulation circuit is determined according to the difference between the high-voltage port voltage V2 and the port voltage V PPref of the main power full-bridge circuit, i.e. V2 = n1 / n4*V3, and the reference value V M of the output voltage of the main power post-stage voltage regulation circuit is V2-n2 / n4*V3, so that the ratio of the port voltages of the power factor correction full-bridge circuit, the main power full-bridge circuit, the partial power full-bridge circuit, and the low-voltage full-bridge circuit is equal to the winding number ratio of the high-frequency transformer, i.e. V1:V P :V3 = n1:n2:n3:n4, thereby realizing the matching of the port voltages of the converter and the winding number ratio of the high-frequency transformer; wherein n1-n4 are the first-four winding numbers of the high-frequency transformer.

[0011] In low-voltage conversion mode, by adjusting the phase shift angle φ 12 Control the voltage V1 at the ports of the power factor correction full-bridge circuit to make the reference value V of the power factor correction full-bridge circuit port voltage equal to the reference value V. 1ref =n1 / n4*V3; by adjusting the phase shift angle φ 13 Control section power full-bridge circuit port voltage V P This makes the reference value V of the partial power full-bridge circuit port voltage... Pref =n3 / n4*V3; by adjusting the phase shift angle φ 14 Control the low-voltage full-bridge circuit port voltage V3 to meet the specified reference value V 3ref The output voltage V of the main power full-bridge circuit is calculated based on the ratio of the number of turns n2 in the second winding to the number of turns n4 in the fourth winding of the high-frequency transformer. M =n2 / n4*V3, based on the high-voltage port voltage V2 and the main power full-bridge circuit output voltage V M The difference in power is calculated to determine the output voltage V of the subsequent voltage regulation circuit. PP By adjusting the duty cycle D, the reference value V of the output voltage of the partial power stage voltage regulation circuit is made possible. PPref =V2-n2 / n4*V3, which ultimately makes the ratio of the port voltages of the power factor correction full-bridge circuit, the main power full-bridge circuit, the partial power full-bridge circuit, and the low-voltage full-bridge circuit equal to the ratio of the number of turns in the winding of the high-frequency transformer. This achieves the matching of the voltage at each port of the converter with the turns ratio of the high-frequency transformer, thereby enabling soft switching of the converter across the entire operating voltage range.

[0012] Compared with the prior art, the beneficial effects of the present invention are:

[0013] This invention addresses the integration of on-board chargers and low-voltage converters in the power systems of electric vehicles, proposing a three-port bidirectional DC-DC converter with partial power conversion capabilities. This converter simultaneously achieves high efficiency and high power density. Specifically, the converter transforms the DC-DC stage of the on-board charger into a two-port series output structure. One end is the main power full-bridge circuit, and the other end is a partial power conversion circuit. This partial power conversion circuit transmits a portion of the total power range. Therefore, by utilizing the adjustable characteristics of the power factor correction circuit's port voltage, the variation range of the power battery voltage and the storage battery voltage is compensated, ensuring the matching of all port voltages of the three-port bidirectional DC-DC converter with the turns ratio of the high-frequency transformer. This enables soft-switching operation of the converter across the entire operating voltage range, reducing power switching losses and simultaneously lowering reactive circulating current and voltage stress in the power system. This provides favorable conditions for the power system to achieve high-frequency and high-efficiency operation across the entire operating voltage range (from light to heavy load). BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 Circuit topology of the three-port bidirectional DC converter of the present application;

[0015] Figure 2 Control logic timing diagram for phase-shift modulation;

[0016] Fig. 3(a) is a control logic block diagram in the on-board charging mode;

[0017] Fig. 3(b) is a control logic block diagram in the low voltage conversion mode;

[0018] Fig. 4(a) is a topology diagram of the PP post-stage voltage regulation circuit;

[0019] Fig. 4(b) is an equivalent circuit diagram of the first working mode of the PP post-stage voltage regulation circuit;

[0020] Fig. 4(c) is an equivalent circuit diagram of the second working mode of the PP post-stage voltage regulation circuit;

[0021] Fig. 4(d) is an equivalent circuit diagram of the third working mode of the PP post-stage voltage regulation circuit;

[0022] Fig. 4(e) is an equivalent circuit diagram of the fourth working mode of the PP post-stage voltage regulation circuit;

[0023] Fig. 5(a) is a simulation waveform diagram of the converter in the state of the AC power grid charging the electric vehicle when the power battery voltage is 369.15V;

[0024] Fig. 5(b) is a simulation waveform diagram of the converter in the state of the power battery charging the storage battery;

[0025] Fig. 5(c) is a simulation waveform diagram of the converter in the composite mode;

[0026] Fig. 5(d) is a simulation waveform diagram of the converter in the state of the AC power grid charging the electric vehicle when the power battery voltage is 320.85V. DETAILED DESCRIPTION

[0027] The technical solutions of the present application will be described in detail below in combination with the drawings and specific embodiments, but the protection scope of the present application is not limited thereto.

[0028] The present application is a three-port bidirectional DC converter for electric vehicles with partial power conversion function, Figure 1The circuit topology of this three-port bidirectional DC-DC converter includes a power factor correction (PFC) full-bridge circuit, a main power (MP) full-bridge circuit, a partial power (PP) full-bridge circuit, a partial power (PP) post-stage voltage regulation circuit, a low voltage (LV) full-bridge circuit, a high-frequency transformer, capacitor C1, and capacitor C. 2M Capacitor C 2P Filter capacitor C 2PP Capacitor C3, inductors L1, L2, L3, and filter inductor L f The PFC full-bridge circuit includes the first and second groups of power switches; the MP full-bridge circuit includes the third and fourth groups of power switches; the PP full-bridge circuit includes the fifth and sixth groups of power switches; the PP post-stage voltage regulation circuit includes the seventh and eighth groups of power switches; and the LV full-bridge circuit includes the ninth and tenth groups of power switches.

[0029] A high-frequency transformer is used to connect PFC full-bridge circuits, MP full-bridge circuits, PP full-bridge circuits, and LV full-bridge circuits. The first winding and the first inductor L1 of the high-frequency transformer are connected in series between the first and second power switches. The second winding of the high-frequency transformer is connected in series between the third and fourth power switches. The third winding and the second inductor L2 of the high-frequency transformer are connected in series between the fifth and sixth power switches. The fourth winding and the third inductor L3 of the high-frequency transformer are connected in series between the ninth and tenth power switches. Capacitor C1 is connected in parallel on the port side of the PFC full-bridge circuit. 2M A capacitor C3 is connected in parallel to the port side of the MP full-bridge circuit, and a capacitor C3 is connected in parallel to the port side of the LV full-bridge circuit. The output port of the LV full-bridge circuit serves as the low-voltage port of the three-port bidirectional DC-DC converter; capacitor C 2P A filter inductor L is connected in series between the output port of the PP full-bridge circuit and the input port of the PP subsequent voltage regulator circuit. f and filter capacitor C 2PPThe output port of the PP full-bridge circuit is connected with the input port of the PP post-stage voltage regulating circuit, and the output port of the PP post-stage voltage regulating circuit and the output port of the MP full-bridge circuit are connected in series to form a port as a high voltage (HV) port of the three-port bidirectional DC converter; when the three-port bidirectional DC converter is used in the power supply system of an electric vehicle, the alternating current power grid is connected with the port side of the PFC full-bridge circuit of the three-port bidirectional DC converter through the power factor correction circuit, and the high voltage port and the low voltage port of the three-port bidirectional DC converter are connected with the power battery and the storage battery of the electric vehicle respectively; the PP full-bridge circuit and the PP post-stage voltage regulating circuit jointly constitute a partial power conversion circuit, which is used for transmitting partial power in the total power range and compensating the change range of the power battery voltage and the storage battery voltage, so that the port voltage of the three-port bidirectional DC converter is matched with the turns ratio of the high-frequency transformer, and the soft switching operation of the converter in the whole working voltage range is realized.

[0030] The PFC full-bridge circuit comprises power switches S 11 -S 14 , the power switches S 11 and S 14 constitute a first group of power switches, the power switches S 12 and S 13 constitute a second group of power switches; similarly, the power switches S 21 and S 24 in the MP full-bridge circuit constitute a third group of power switches, the power switches S 22 and S 23 constitute a fourth group of power switches; the power switches S p1 and S p4 in the PP full-bridge circuit constitute a fifth group of power switches, the power switches S p2 and S p3 constitute a sixth group of power switches; the power switches S p5 and S p8 in the PP post-stage voltage regulating circuit constitute a seventh group of power switches, the power switches S p6 and S p7 constitute an eighth group of power switches; the power switches S 31 and S 34 in the LV full-bridge circuit constitute a ninth group of power switches, and the power switches S 32 and S 33 constitute a tenth group of power switches.

[0031] The present application adopts phase-shift modulation to realize the control of the converter, Figure 2 the control logic timing diagram of the phase-shift modulation, the power switches S 11 and S 14 are consistent in timing, the power switches S 12 and S13 Timing consistent; power switch S 21 and S 24 Timing consistent, power switch S 22 and S 23 Timing consistent; power switch S p1 and S p4 Timing consistent, power switch S p2 and S p3 Timing consistent; power switch S 31 and S 34 Timing consistent, power switch S 32 and S 33 Timing consistent. The three-port bidirectional DC converter of the present invention includes four control variables, phase shift angle φ 12 , φ 13 , φ 14 and duty cycle D, phase shift angle φ 12 is the phase angle difference between PFC full-bridge circuit bridge arm midpoint voltage v h1 and MP full-bridge circuit bridge arm midpoint voltage v h2 , phase shift angle φ 13 is the phase angle difference between PFC full-bridge circuit bridge arm midpoint voltage v h1 and PP full-bridge circuit bridge arm midpoint voltage v hp , phase shift angle φ 14 is the phase angle difference between PFC full-bridge circuit bridge arm midpoint voltage v h1 and LV full-bridge circuit bridge arm midpoint voltage v h3 ; the controller controls the magnitude and direction of power transfer between PFC full-bridge circuit, MP full-bridge circuit, PP full-bridge circuit and LV full-bridge circuit by adjusting the magnitude and polarity of phase shift angle φ 12 , φ 13 and φ 14 , see Figure 2 When phase shift angle φ 12 increases, PFC full-bridge circuit bridge arm midpoint voltage v h1 shifts right relative to MP full-bridge circuit bridge arm midpoint voltage v h2 ; when phase shift angle φ 13 increases, PP full-bridge circuit bridge arm midpoint voltage v hp shifts right relative to MP full-bridge circuit bridge arm midpoint voltage v h2 ; when phase shift angle φ 14 decreases, LV full-bridge circuit bridge arm midpoint voltage v h3 shifts left relative to PP full-bridge circuit bridge arm midpoint voltage v hp .

[0032] Electric vehicles primarily employ three charging and discharging modes: on-board charging, low-voltage conversion, and a hybrid mode. On-board charging refers to the grid's electrical energy charging the battery via an on-board charger. Low-voltage conversion refers to the battery discharging to a low-voltage load. The hybrid mode combines both on-board charging and low-voltage conversion, simultaneously charging both the battery and the storage battery. This is achieved by adjusting the phase shift angle φ. 12 φ 13 φ 14 The duty cycle D controls the power transmission of the three-port bidirectional DC-DC converter, enabling different charging and discharging modes of the electric vehicle. The duty cycle D is adjusted when the port voltage V of the MP full-bridge circuit... M <High voltage port voltage V2, i.e., the output voltage V of the PP subsequent voltage regulation circuit> PP If the duty cycle D is greater than 0, then the power switch S located on the left side of the upper bridge arm of the voltage regulation circuit after PP is the one with the duty cycle D. p5 The duty cycle; when the port voltage V of the MP full-bridge circuit M The high-voltage port voltage V2, i.e., the output voltage V of the PP subsequent voltage regulation circuit. PP If the duty cycle D is less than 0, then the power switch S is located on the left side of the lower bridge arm of the voltage regulation circuit after PP. p6 The duty cycle. In practical applications, to prevent the upper and lower arms of the full-bridge circuit from conducting simultaneously due to switching speed issues, the power switch needs to take the dead time into account. Therefore, the actual duty cycle is less than the theoretical value. The smaller the dead time, the better the output waveform, but the reliability will decrease. For ease of description, the switching of the power switch includes the dead time, and the actual duty cycle should be less than the duty cycle mentioned above.

[0033] Figure 3(a) shows the control logic block diagram in on-board charging mode. In on-board charging mode, the PFC full-bridge circuit port voltage V1 is adjusted by the PFC controller, and the reference value V of the PFC full-bridge circuit port voltage is adjusted according to the ratio of the number of turns n1 of the first winding to the number of turns n4 of the fourth winding of the high-frequency transformer. 1ref =n1 / n4*V3; by adjusting the phase shift angle φ 12 Make the high-voltage port current I2 meet the specified reference value I 2ref And maintain a constant current, i.e., constant current charging; by adjusting the phase shift angle φ 13 Control the port voltage V of the PP full-bridge circuit P Simultaneously, based on the ratio of the number of turns n3 in the third winding to the number of turns n4 in the fourth winding of the high-frequency transformer, the reference value V of the PP full-bridge circuit port voltage is set. Pref =n3 / n4*V3; by adjusting the phase shift angle φ 14 Control the LV full-bridge circuit port voltage V3 to meet the specified reference value V. 3ref; according to the ratio of the second winding number n2 of the high frequency transformer to the fourth winding number n4, the MP full bridge circuit port voltage V M is determined, i.e. V M = n2 / n4*V3, and according to the difference between the high voltage port voltage V2 and the MP full bridge circuit port voltage V PP , the PP post-stage voltage regulation circuit output voltage V PPref is determined, i.e. V M = V2-n2 / n4*V3, and finally the ratio of the port voltages of the PFC full bridge circuit, the MP full bridge circuit, the PP full bridge circuit and the LV full bridge circuit is equal to the winding number ratio of the high frequency transformer, i.e. V1:V P :V3 = n1:n2:n3:n4, so that the matching of the port voltages of the converter and the winding number ratio of the high frequency transformer is realized, and the soft switching of the converter in the full working voltage range is realized; wherein n1-n4 are the first-four winding numbers of the high frequency transformer.

[0034] Fig. 3(b) is a control logic block diagram in the low voltage conversion mode. In the low voltage conversion mode, the PFC full bridge circuit port voltage V1 is controlled by adjusting the phase shift angle φ 12 , and at the same time, according to the ratio of the first winding number n1 of the high frequency transformer to the fourth winding number n4, the reference value V 1ref of the PFC full bridge circuit port voltage is determined, i.e. V 13 = n1 / n4*V3; the PP full bridge circuit port voltage V P is controlled by adjusting the phase shift angle φ Pref , and at the same time, according to the ratio of the third winding number n3 of the high frequency transformer to the fourth winding number n4, the reference value V 14 of the PP full bridge circuit port voltage is determined, i.e. V 3ref = n3 / n4*V3; the LV full bridge circuit port voltage V3 is controlled by adjusting the phase shift angle φ M , so that it satisfies the specified reference value V M ; the MP full bridge circuit output voltage V M is determined according to the ratio of the second winding number n2 of the high frequency transformer to the fourth winding number n4, i.e. V PP = n2 / n4*V3, and the PP post-stage voltage regulation circuit output voltage V PPref is calculated according to the difference between the high voltage port voltage V2 and the MP full bridge circuit output voltage V M , i.e. V PV3=n1:n2:n3:n4, so as to realize the matching of the voltage of each port of the present transformer and the turns ratio of the high-frequency transformer, and realize the soft switching of the transformer in the full working voltage range.

[0035] Fig. 4(a) is a topology diagram of the PP post-stage voltage regulation circuit. The soft switching of the three-port bidirectional DC converter in the full working voltage range is mainly realized by the PP full-bridge circuit and the PP post-stage voltage regulation circuit, that is, the change of the voltage of the power battery in the charging and discharging process is realized by adjusting the duty cycle D to change the output voltage V PP of the PP post-stage voltage regulation circuit, and finally affects the voltage V2 of the high-voltage port, that is, V2=V M +V PP . Since the port voltage V M of the MP full-bridge circuit and the port voltage V P of the PP full-bridge circuit conform to the turns ratio of the high-frequency transformer, they remain relatively constant, when the high-voltage port voltage V2 changes, the port voltage V P of the PP full-bridge circuit changes by adjusting the phase shift angle φ 13 to ensure the voltage matching, and the voltage value ratio is equal to the turns ratio of the high-frequency transformer; in order to ensure that the port voltage V M of the MP full-bridge circuit meets the voltage matching, the duty cycle D needs to be adjusted, so that the output voltage V PP of the PP post-stage voltage regulation circuit is V P or V PP =-D*V P , and then the port voltage V M of the MP full-bridge circuit is V2-V PP =n2 / n4*V3. Fig. 4(b)-(e) are equivalent circuit diagrams of the PP post-stage voltage regulation circuit in various working modes; when V M <V2, that is, V PP >0, the duty cycle D is the duty cycle of the power switch S p5 located on the left side of the upper bridge arm of the PP post-stage voltage regulation circuit, at this time, the power switch S p7 located on the right side of the upper bridge arm of the PP post-stage voltage regulation circuit is turned off, the power switch S p8 located on the right side of the lower bridge arm remains turned on, and the power switch S p6 located on the left side of the lower bridge arm and the power switch S p5 located on the left side of the upper bridge arm are turned on complementarily; Fig. 4(b) is an equivalent circuit diagram of the PP post-stage voltage regulation circuit in the first working mode, in which the power switch S p5 is turned on and S p6 is turned off; Fig. 4(c) is an equivalent circuit diagram of the PP post-stage voltage regulation circuit in the second working mode, in which the power switch S p5 is turned off and S p6 is turned on; when V MV2, i.e. V PP <0, the duty cycle D is the duty cycle of the power switch S p6 on the right side of the upper bridge arm of the post-stage voltage regulation circuit of the PP p7 is kept on, the power switch S p8 on the left side of the lower bridge arm of the post-stage voltage regulation circuit of the PP p5 is kept off, the power switch S p6 on the left side of the lower bridge arm of the post-stage voltage regulation circuit of the PP is complementary on; Fig. 4(d) is an equivalent circuit diagram of the post-stage voltage regulation circuit of the PP in the third working mode, the power switch S p6 is on, and the power switch S p5 is off; Fig. 4(e) is an equivalent circuit diagram of the post-stage voltage regulation circuit of the PP in the fourth working mode, the power switch S p6 is off, and the power switch S p5 is on.

[0036] Embodiment

[0037] The present application is explained below in conjunction with an embodiment. The turns ratio of the first winding to the second winding of the high-frequency transformer is n1 / n2=1.16, the turns ratio of the first winding to the third winding is n1 / n3=4.14, and the turns ratio of the first winding to the fourth winding is n1 / n4=29. The circuit parameters of the three-port bidirectional DC converter are: L1=6.64 μH, L2=2.11 μH, and L3=0.0483 μH. It is assumed that the power battery voltage, i.e. the high-voltage port voltage V2, is 369.15 V; the storage battery voltage, i.e. the LV full-bridge circuit port voltage V3, is 13.8 V, the PFC full-bridge circuit port voltage V1 is 400.2 V, the MP full-bridge circuit port voltage is V M 345 V, the PP full-bridge circuit port voltage V P is 96.6 V, the post-stage voltage regulation circuit output voltage V PP of the PP is 24.15 V; since V M <V2, i.e. V PP >0, the post-stage voltage regulation circuit of the PP operates in the first and second working modes, and the duty cycle D of the power switch S M is calculated to be 0.25 according to V2=V P +D*V p5 .

[0038] According to the above parameters, the converter is simulated in the electric vehicle on-board charging mode and the low-voltage conversion mode, respectively. The simulation waveform diagrams are shown in Figs. 5(a)-(b). In the diagrams, i1 is the current at the transformer side of the PFC full-bridge circuit, i2 is the current at the transformer side of the MP full-bridge circuit, i3 is the current at the transformer side of the PP full-bridge circuit, i4 is the current at the transformer side of the LV full-bridge circuit, and vh1 Vpfc is the voltage at the transformer side of the PFC full-bridge circuit, v h2 Vmp is the voltage at the transformer side of the MP full-bridge circuit, v hp Vpp is the voltage at the transformer side of the PP full-bridge circuit, v h3 Vlv is the voltage at the transformer side of the LV full-bridge circuit.

[0039] Fig. 5(a) is a simulation waveform diagram of the converter in the vehicle charging mode, i.e. the state that the AC power grid charges the power battery of the electric vehicle; in this mode, the input power P1 at the port side of the PFC full-bridge circuit is 3300W, the output power P2 at the port side of the MP full-bridge circuit is 3084W, the output power P3 of the output voltage regulation circuit at the back stage of the PP full-bridge circuit is 216W, the sum of the output powers P2 and P3 is the output power P HV = 3300W at the high voltage port, and the output power P4 at the port side of the LV full-bridge circuit is 0, i.e. the electric energy of the AC power grid charges the power battery through the PFC full-bridge circuit, wherein the phase shift angle φ 12 is 10.448°, the phase shift angle φ 13 is 14.06°, and the phase shift angle φ 14 is 10.448°.

[0040] Fig. 5(b) is a simulation waveform diagram of the converter in the low voltage conversion mode, i.e. the state that the power battery of the electric vehicle charges the storage battery; in this mode, the input power P1 at the port side of the PFC full-bridge circuit is 0, the input power P2 at the port side of the MP full-bridge circuit is 934.6W, the input power P3 of the output voltage regulation circuit at the back stage of the PP full-bridge circuit is 65.4W, the sum of the input powers P2 and P3 is the input power P HV = 1000W at the port side of the power battery, and the output power P4 at the port side of the LV full-bridge circuit is 1000W, i.e. the electric energy of the power battery charges the storage battery through the high voltage port of the three-port bidirectional DC converter, wherein the phase shift angle φ 12 is 0°, the phase shift angle φ 13 is -1.088°, and the phase shift angle φ 14 is 20.649°.

[0041] Fig. 5(c) is a simulation waveform diagram of the converter in the composite mode, i.e. the state that the AC power grid charges the power battery and the storage battery of the electric vehicle at the same time; in this mode, the input power P1 at the port side of the PFC full-bridge circuit is 4300W, the output power P2 at the port side of the MP full-bridge circuit is 3084W, the output power P3 of the output voltage regulation circuit at the back stage of the PP full-bridge circuit is 216W, the sum of the output powers P2 and P3 is the output power P HV = 3300W at the high voltage port, and the output power P4 at the port side of the LV full-bridge circuit is 1000W, i.e. the electric energy of the AC power grid charges the power battery and the storage battery at the same time through the PFC full-bridge circuit, wherein the phase shift angle φ12 φ 13 φ 14 φ

[0042] Assuming the power battery voltage V2 is 320.85V, and the rest of the port voltage is unchanged, in order to ensure voltage matching, the working mode of the PP post-stage voltage regulation circuit needs to be changed, since V M >V2, that is, V PP <0, so the PP post-stage voltage regulation circuit works in mode three and mode four, the PP post-stage voltage regulation circuit output voltage V PP =V2-V M =-24.15V, at the same time according to V2=V M -D*V P The duty cycle D of the power switch S p6 is calculated to be 0.25. Fig. 5(d) is a simulation waveform diagram of the converter in the state of charging the power battery of the electric vehicle by the alternating power grid, at this time the input power P1 of the PFC full-bridge circuit port side is 3208.5W, the output power P2 of the MP full-bridge circuit port side is 3450W, the output power P3 of the PP post-stage voltage regulation circuit is-241.5W, and the sum of the output powers P2 and P3 is the output power P HV of the high-voltage port, which is 3208.5W, and the output power P4 of the LV full-bridge circuit port side is 0, that is, the electric energy is charged to the power battery through the PFC full-bridge circuit, wherein the phase shift angle φ 12 is 10.139°, φ 13 is 6.095°, and φ 14 is 10.139°.

[0043] In each of the above simulation cases, the matching of each port voltage of the converter and the turns ratio of the high-frequency transformer is achieved, and all the power switches of the converter achieve soft switching.

[0044] The unmentioned parts of the present application are applicable to the prior art.

Claims

1. A three-port bidirectional DC-DC converter for electric vehicles with partial power conversion function, characterized in that, The converter includes a power factor correction full-bridge circuit, a main power full-bridge circuit, a partial power full-bridge circuit, a partial power subsequent voltage regulation circuit, a low-voltage full-bridge circuit, a high-frequency transformer, first to fourth capacitors, first to third inductors, a filter capacitor, and a filter inductor. The first inductor and the first winding of the high-frequency transformer are connected in series between the two sets of power switches in the power factor correction full-bridge circuit. The second winding of the high-frequency transformer is connected in series between the two sets of power switches in the main power full-bridge circuit. The second inductor and the third winding of the high-frequency transformer are connected in series between the two sets of power switches in the partial power full-bridge circuit. The third inductor and the fourth winding of the high-frequency transformer are connected in series between the two sets of power switches in the low-voltage full-bridge circuit. The first capacitor is connected in parallel on the port side of the power factor correction full-bridge circuit. The second capacitor is connected in parallel on the port side of the main power full-bridge circuit. The third capacitor is connected in parallel between the output port of the partial power full-bridge circuit and the input port of the partial power subsequent voltage regulation circuit. The fourth capacitor is connected in parallel on the port side of the low-voltage full-bridge circuit. The output port of the partial power full-bridge circuit and the input port of the partial power subsequent voltage regulation circuit are connected in parallel. The input ports of the power-advanced voltage regulation circuit are cascaded. The output port of the partial power-advanced voltage regulation circuit is connected in series with a filter inductor and a filter capacitor. The output port of the partial power-advanced voltage regulation circuit and the output port of the main power full-bridge circuit are connected in series to form the high-voltage port of the converter, which is connected to the power battery of the electric vehicle. The output port of the low-voltage full-bridge circuit is the low-voltage port of the converter, which is connected to the battery of the electric vehicle. The partial power full-bridge circuit and the partial power-advanced voltage regulation circuit constitute a partial power conversion circuit, which is used to transmit part of the power in the total power range, compensate for the variation range of the power battery voltage and the battery voltage, so that the port voltage of the converter matches the turns ratio of the high-frequency transformer, and realizes the soft-switching operation of the converter in the full operating voltage range.

2. The three-port bidirectional DC-DC converter for electric vehicles with partial power conversion function according to claim 1, characterized in that, When the converter is applied to the power system of an electric vehicle, by adjusting the phase shift angle φ 12 φ 13 φ 14 The power transmission of the converter, along with the duty cycle control, enables the electric vehicle to operate under different charging and discharging modes; among which, the phase shift angle φ 12 To correct the phase angle difference between the midpoint voltage of the full-bridge arm and the midpoint voltage of the main power full-bridge arm, the phase angle φ is shifted. 13 To correct the phase angle difference between the midpoint voltage of the full-bridge arm and the midpoint voltage of the partial-power full-bridge arm, the phase angle φ is shifted. 14 To correct the phase angle difference between the midpoint voltage of the full-bridge circuit arm and the midpoint voltage of the low-voltage full-bridge circuit arm, the output voltage of the partial power stage voltage regulator circuit is adjusted by changing the duty cycle so that the sum of the output voltage of the partial power stage voltage regulator circuit and the output voltage of the main power full-bridge circuit equals the high-voltage port voltage; when the main power full-bridge circuit port voltage V M <High-voltage port voltage V2, i.e., the output voltage V of the partial power stage voltage regulation circuit> PP If the voltage is >0, the duty cycle of the power switch located on the left side of the upper bridge arm of the partial power stage voltage regulation circuit should be adjusted. That is, the power switch on the right side of the upper bridge arm of the partial power stage voltage regulation circuit should be turned off, the power switch on the right side of the lower bridge arm should remain on, and the power switch on the left side of the lower bridge arm should be complementary to the power switch on the left side of the upper bridge arm. When the main power full-bridge circuit port voltage V... M The high-voltage port voltage V2, i.e., the output voltage V of the partial power stage voltage regulation circuit. PP If the duty cycle is less than 0, the duty cycle of the power switch located on the left side of the lower bridge arm of the partial power stage voltage regulation circuit should be adjusted. That is, the power switch located on the right side of the upper bridge arm of the partial power stage voltage regulation circuit should be kept on, the power switch located on the right side of the lower bridge arm should be kept off, and the power switch located on the left side of the upper bridge arm and the power switch located on the left side of the lower bridge arm should be complementaryly turned on.

3. The electric vehicle three-port bidirectional DC-DC converter with partial power conversion function according to claim 2, characterized in that, Electric vehicle charging and discharging modes include on-board charging mode, low-voltage conversion mode, and hybrid mode. Hybrid mode refers to the simultaneous operation of on-board charging mode and low-voltage conversion mode. In on-board charging mode, the power factor correction full-bridge circuit port voltage V1 is adjusted so that the reference value V of the power factor correction full-bridge circuit port voltage is... 1ref =n1 / n4*V3; by adjusting the phase shift angle φ 12 To ensure the high-voltage port current meets and remains constant according to a specified reference value, i.e., constant current charging; this is achieved by adjusting the phase shift angle φ. 13 Control section power full-bridge circuit port voltage V P This makes the reference value V of the partial power full-bridge circuit port voltage... Pref =n3 / n4*V3; by adjusting the phase shift angle φ 14 Control the low-voltage full-bridge circuit port voltage V3 to meet the specified reference value V 3ref ; Calculate the main power full-bridge circuit port voltage V based on the ratio of the number of turns in the second winding to the number of turns in the fourth winding of the high-frequency transformer. M =n2 / n4*V3, based on the high-voltage port voltage V2 and the main power full-bridge circuit port voltage V M The difference determines the output voltage V of the main power stage voltage regulation circuit. PP By adjusting the duty cycle D, the reference value V of the output voltage of the main power stage voltage regulation circuit is made possible. PPref =V2-n2 / n4*V3, ultimately making the ratio of the port voltages of the power factor correction full-bridge circuit, the main power full-bridge circuit, the partial power full-bridge circuit, and the low-voltage full-bridge circuit equal to the ratio of the number of turns in the windings of the high-frequency transformer, i.e., V1:V M :V P V3 = n1:n2:n3:n4, thereby achieving the matching of the voltage at each port of the converter with the turns ratio of the high-frequency transformer; where n1 to n4 are the turns of the first to fourth windings of the high-frequency transformer; In low-voltage conversion mode, by adjusting the phase shift angle φ 12 Control the voltage V1 at the ports of the power factor correction full-bridge circuit to make the reference value V of the power factor correction full-bridge circuit port voltage equal to the reference value V. 1ref =n1 / n4*V3; by adjusting the phase shift angle φ 13 Control section power full-bridge circuit port voltage V P This makes the reference value V of the partial power full-bridge circuit port voltage... Pref =n3 / n4*V3; by adjusting the phase shift angle φ 14 Control the low-voltage full-bridge circuit port voltage V3 to meet the specified reference value V 3ref The output voltage V of the main power full-bridge circuit is calculated based on the ratio of the number of turns n2 in the second winding to the number of turns n4 in the fourth winding of the high-frequency transformer. M =n2 / n4*V3, based on the high-voltage port voltage V2 and the main power full-bridge circuit output voltage V M The difference in power is calculated to determine the output voltage V of the subsequent voltage regulation circuit. PP By adjusting the duty cycle D, the reference value V of the output voltage of the partial power stage voltage regulation circuit is made possible. PPref =V2-n2 / n4*V3, which ultimately makes the ratio of the port voltages of the power factor correction full-bridge circuit, the main power full-bridge circuit, the partial power full-bridge circuit, and the low-voltage full-bridge circuit equal to the ratio of the number of turns in the winding of the high-frequency transformer. This achieves the matching of the voltage at each port of the converter with the turns ratio of the high-frequency transformer, thereby enabling soft switching of the converter across the entire operating voltage range.

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