Bidirectional vehicle-mounted charging circuit and circuit control method

Abstract

The invention discloses a bidirectional vehicle-mounted charging circuit and a circuit control method. The topology comprises a front-stage totem-pole bridgeless PFC and a rear-stage bidirectional CLLC converter; the bidirectional totem-pole bridgeless PFC converter is connected with a 220V single-phase power grid; the rear-stage bidirectional CLLC converter is connected with the bidirectional totem-pole bridgeless PFC converter; the forward resonance link and the reverse resonance link of the rear-stage bidirectional CLLC converter are the same so that soft switching can be achieved conveniently, and the rear-stage bidirectional CLLC converter is finally connected with the power battery of the electric vehicle and is combined with the front-stage totem-pole bridgeless PFC to charge the power battery. According to the invention, the vehicle-mounted charging circuit has G2V and V2G functions, the output voltage range is adjustable in a range of 300V-500V, and the applicability and the safety are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of on - vehicle charging circuits for electric vehicles, and particularly relates to a bidirectional on - vehicle charging circuit and a circuit control method. Background Art

[0002] Traditional fuel - powered vehicles have many disadvantages due to problems such as high noise, high energy consumption, and serious environmental pollution caused by exhaust emissions. With the rapid progress of society, the energy crisis has intensified and the public's environmental awareness has increased. As an alternative to traditional fuel - powered vehicles, new energy vehicles have become a development direction actively encouraged by governments in many countries around the world because of their advantages such as cleanliness and high efficiency.

[0003] The widespread application of electric vehicles has an increasingly significant impact on the power grid. A large number of electric vehicles randomly connecting to the grid for charging will increase the load pressure on the grid and lead to a decline in grid stability. To solve this problem, vehicle - to - grid (V2G) technology has emerged. By using the electric vehicle battery as a flexible energy storage unit of the grid, the regulation function of the grid can be realized. However, when the existing on - vehicle charging circuit operates bidirectionally, there are problems such as a narrow input - output voltage range and low efficiency, which limit its application under different types of vehicle batteries and grid conditions. Therefore, it is of great significance to develop a bidirectional on - vehicle charging circuit with a wide voltage range and a circuit control method. Summary of the Invention

[0004] The first object of the present invention is to provide a bidirectional on - vehicle charging circuit.

[0005] The second object of the present invention is to provide a control method for the bidirectional on - vehicle charging circuit, which solves the technical problem that the existing on - vehicle charging circuit has a narrow input - output voltage range and low efficiency when operating bidirectionally.

[0006] The first technical solution adopted by the present invention is that the bidirectional on - vehicle charging circuit includes a front - stage totem - pole bridgeless PFC converter and a rear - stage CLLC resonant converter; the input of the front - stage totem - pole bridgeless PFC converter is connected to a 220V single - phase power grid, and the output of the front - stage totem - pole bridgeless PFC converter is connected to the input of the rear - stage CLLC resonant converter; the output of the rear - stage CLLC resonant converter is connected to the power battery of the electric vehicle; A capacitor is connected in parallel between the front - stage totem - pole bridgeless PFC converter and the rear - stage CLLC resonant converter C dc , and a capacitor is connected in parallel between the rear - stage CLLC resonant converter and the power battery of the electric vehicle C o .

[0007] The characteristics of the first technical solution of the present invention are further as follows: The front - stage totem - pole bridgeless PFC converter includes a switching transistor Q1 , switching transistor Q 2 , switching transistor Q 3 , switching transistor Q 4 , switching transistor Q 1 and switching transistor Q 3 is connected to one end of capacitor C dc , switching transistor Q 2 and switching transistor Q 4 is connected to the other end of capacitor C dc ; switching transistor Q 1 and switching transistor Q 2 are connected in series, and switching transistor Q 3 and switching transistor Q 4 are connected in series; The pre - stage totem - pole bridgeless PFC converter further includes an inductor L1. One end of the inductor L1 is connected to the connection point of switching transistor Q 1 , switching transistor Q 2 . The power grid is connected to the other end of the inductor L1 and is connected to the connection point of switching transistor Q 3 , switching transistor Q 4 .

[0008] The post - stage CLLC resonant converter includes a primary full - bridge circuit, a high - frequency transformer T, and a secondary full - bridge circuit. The primary full - bridge circuit is connected to the secondary full - bridge circuit through the high - frequency transformer T; The primary full - bridge circuit is connected in parallel with capacitor C dc , and the secondary full - bridge circuit is connected in parallel with capacitor C o .

[0009] The turns ratio of the high - frequency transformer T is 1.

[0010] The primary full - bridge circuit includes switching transistors S 1 , switching transistors S 2 , switching transistors S 3 , switching transistors S 4 , switching transistor S 1 and switching transistor S 3 are connected to one end of capacitor C dc , switching transistor S 2 and switching transistor S 4 are connected to the other end of capacitor C dc , switching transistor S 1 and switching transistor S 2 are connected in series, and switching transistor S 3 and switching transistor S 4 are connected in series; The primary full - bridge circuit further includes a resonant inductor L r1 connected to the primary side of the high - frequency transformer T, an exciting inductor L m and a resonant capacitor C r1 , resonant inductor Lr1 One end is connected to the switching transistor S 1 and the connection point of the switching transistor S 2 and the other end is connected to one end of the excitation inductor L m One end of the resonant capacitor C r1 One end is connected to the switching transistor S 3 and the connection point of the switching transistor S 4 and the other end is connected to the other end of L m ; The secondary full-bridge circuit includes switching transistors S 5 , switching transistors S 6 , switching transistors S 7 , switching transistors S 8 . The switching transistor S 5 and the switching transistor S 7 are connected to one end of the capacitor C o . The switching transistor S 6 and the switching transistor S 8 are connected to the other end of the capacitor C o . The switching transistor S 5 and the switching transistor S 6 are in series. The switching transistor S 7 and the switching transistor S 8 are in series; The secondary full-bridge circuit further includes a resonant inductor L connected to the secondary side of the high-frequency transformer T r2 and a resonant capacitor C r2 . The resonant inductor L r2 is connected to the connection point of the switching transistor S 7 and the switching transistor S 8 . The resonant capacitor C r2 is connected to the connection point of the switching transistor S 5 and the switching transistor S 6 .

[0011] All the switching transistors adopt SiC MOSFETs.

[0012] The second technical solution adopted by the present invention is a bidirectional vehicle-mounted charging circuit control method, which adopts the above-mentioned bidirectional vehicle-mounted charging circuit and specifically includes the following steps: S1: Determine the charging stage according to the working mode of the vehicle-mounted charging circuit and the magnitude of the output voltage Uo; wherein, when the two-stage circuit operates forward, it is the G2V mode, and when it operates backward, it is the V2G mode; S2: When the vehicle-mounted charging circuit operates in the G2V mode and Uo is less than the set threshold, the SOC value of the power battery is relatively low, and single-current-loop control is adopted; when the SOC value of the power battery reaches the set threshold, voltage-current double-loop control is adopted; When the vehicle-mounted charging circuit operates in the V2G mode, single-current-loop control is adopted; S3: Through the DC bus voltage controller, adjust the magnitude of the DC bus voltage Ud output by the front-stage PFC circuit according to the change of the output voltage Uo in different charging stages.

[0013] The features of the second technical solution of the present invention are further as follows: Specifically, S3 is as follows: When U dmin ≤U o ≤U dmax , the voltage gain of the rear-stage CLLC resonant converter is 1, and PWM control is performed on the front-stage totem-pole bridgeless PFC converter to adjust the DC bus voltage U d , at this time U d =U o ; When Uo > Udmax and the output voltage is required to continue increasing, PWM control is used for the totem-pole bridgeless PFC converter to keep the DC bus voltage at U dmax unchanged; the gain M of the rear-stage bidirectional CLLC converter is > 1, and the PFM modulation method is used to control the output voltage of the on-vehicle charging circuit. The output voltage is controlled by controlling the switching frequency of the rear-stage CLLC converter, so that the converter operates in the under-resonant region, and the slope of the gain curve is negative to ensure ZCS implementation; When U o <U dmin , and the output voltage is required to continue decreasing, PWM control is used for the bidirectional totem-pole bridgeless PFC converter to keep the DC bus voltage at U dmin unchanged; the gain M of the rear-stage bidirectional CLLC converter is < 1, and the PWM modulation method is used to control the output voltage of the on-vehicle charging circuit.

[0014] During forward operation, when the voltage gain M of the CLLC resonant converter is ≥ 1, a variable-frequency modulation strategy is adopted. In one switching period, the drive signals of switch S1 and switch S4 are the same, the drive signals of switch S2 and switch S3 are the same, and the drive signals of switch S1 and switch S2 differ by half a period, with a dead time left during this period to prevent shoot-through. Switches S5 to S6 are uncontrolled rectification; When the voltage gain M of the CLLC resonant converter is < 1, voltage regulation is performed in a PWM manner; During reverse operation, when the voltage gain M of the CLLC resonant converter is ≥ 1, a traditional variable-frequency modulation strategy is adopted. In one switching period, the drive signals of switch S5 and switch S8 are the same, the drive signals of switch S6 and switch S7 are the same, and the drive signals of switch S5 and switch S6 differ by half a period, with a dead time left during this period to prevent shoot-through. Switches S1 to S4 are uncontrolled rectification; When the voltage gain M of the CLLC resonant converter is less than 1, the PWM modulation method is adopted for voltage regulation.

[0015] The PWM modulation method for the CLLC resonant converter includes: During forward operation, when M < 1, the switching frequency of the bidirectional CLLC resonant converter is fixed at the series resonance frequency. The duty cycles of the primary-side switching tubes S1 and S3 are equal, the duty cycles of the switching tubes S2 and S4 are equal and equal to 0.5, and the switching frequencies of the four switching tubes are constant and equal to the resonance frequency. The duty cycles of the switching tubes S1 and S3 are adjusted to regulate the output voltage. During reverse operation, when M < 1, the switching frequency of the bidirectional CLLC resonant converter is fixed at the series resonance frequency. The duty cycles of the secondary-side switching tubes S5 and S7 are equal, the duty cycles of the switching tubes S6 and S8 are equal and equal to 0.5, and the switching frequencies of the four switching tubes are constant and equal to the resonance frequency. The duty cycles of the switching tubes S5 and S7 are adjusted to regulate the output voltage.

[0016] The beneficial effects of the present invention are: The present invention realizes the efficient operation of the on-vehicle charging circuit under different working conditions through a segmented modulation strategy, and at the same time broadens its input and output voltage ranges to adapt to various battery and grid conditions.

[0017] Aiming at the problems of the existing on-vehicle charging circuit, such as single function, narrow output voltage range, and poor adaptability, the present invention enables the on-vehicle charging circuit to have functions of grid-to-vehicle (G2V) and vehicle-to-grid (V2G). Moreover, the output voltage range is adjustable within the range of 300V - 500V, meeting the requirements of various small and medium-sized electric vehicles for the on-vehicle charging circuit, and having good applicability and safety.

[0018] The variable DC bus voltage control method based on single and double loop switching of the present invention can effectively solve the problem of current discontinuity during the charging process of the power battery of an electric vehicle, and at the same time avoid the impact of instantaneous large current on the power battery, prevent overcharging of the power battery, and ensure the rapidity and safety of charging. On the other hand, the CLLC control method based on "PFM + PWM" hybrid modulation performs segmented modulation according to the voltage gain, giving play to the advantages of both PFM and PWM modulation methods, broadening the output voltage range of the on-vehicle charging circuit, enabling a charger to be applied to multiple electric vehicles for charging, and enhancing the adaptability of the on-vehicle charging circuit. Description of the Drawings

[0019] Figure 1 is a schematic diagram of the topological structure of the bidirectional on-vehicle charging circuit of the present invention; Figure 2It is a schematic diagram of segmented hybrid modulation when the two-way on-vehicle charging circuit of the present invention operates in the forward direction; Figure 3 It is a schematic diagram of segmented hybrid modulation when the two-way on-vehicle charging circuit of the present invention operates in the reverse direction; Figure 4 It is an overall control block diagram of the control method of the two-way on-vehicle charging circuit of the present invention. Specific embodiments

[0020] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0021] Embodiment 1 As Figure 1 shown, the two-way on-vehicle charging circuit disclosed by the present invention includes a front-stage totem-pole bridgeless PFC converter and a rear-stage CLLC resonant converter; the input of the front-stage totem-pole bridgeless PFC converter is connected to a 220V single-phase power grid, and the output of the front-stage totem-pole bridgeless PFC converter is connected to the input of the rear-stage CLLC resonant converter; the output of the rear-stage CLLC resonant converter is connected to the power battery of the electric vehicle.

[0022] In this embodiment, the front-stage totem-pole bridgeless PFC converter plays the role of unity power factor correction, stabilizing the grid voltage, and improving the power quality; the rear-stage two-way CLLC converter plays the role of electrical isolation and power conversion.

[0023] Furthermore, a capacitor is connected in parallel between the front-stage totem-pole bridgeless PFC converter and the rear-stage CLLC resonant converter C dc , and a capacitor is connected in parallel between the rear-stage CLLC resonant converter and the power battery of the electric vehicle C o .

[0024] Embodiment 2 Based on Embodiment 1, the front-stage totem-pole bridgeless PFC converter includes switching tubes Q 1 , switching tubes Q 2 , switching tubes Q 3 , switching tubes Q 4 , switching tubes Q 1 and switching tubes Q 3 are connected to one end of the capacitor C dc , switching tubes Q 2 and switching tubes Q 4 are connected to the capacitorC dc is connected to the other end; switching transistor Q 1 and switching transistor Q 2 are in series, and switching transistor Q 3 and switching transistor Q 4 are in series; The front-stage totem-pole bridgeless PFC converter further includes an inductor L1. One end of the inductor L1 is connected to the connection point of switching transistor Q 1 , switching transistor Q 2 . The power grid is connected to the other end of the inductor L1 and is connected to the connection point of switching transistor Q 3 , switching transistor Q 4 .

[0025] In this embodiment, when the bidirectional totem-pole bridgeless PFC converter operates in the forward direction and the grid voltage is positive, switching transistor Q 3 is always turned off, switching transistor Q 4 is always turned on, and switching transistor Q 1 and switching transistor Q 2 perform high-frequency switching and form a Boost circuit with the inductor L1. The operating states of switching transistor Q 1 and switching transistor Q 2 can be further divided into two cases: when switching transistor Q 2 is the main switching transistor and switching transistor Q 1 is the freewheeling diode, that is, when switching transistor Q 2 is turned on and switching transistor Q 1 is turned off, the inductor L1 charges and stores energy, and the DC bus capacitor C dc supplies energy to the subsequent stage; when switching transistor Q 1 is turned on and switching transistor Q 2 is turned off, the inductor L1 releases energy to the DC side, and the power grid and the inductor L1 jointly charge. When the grid voltage is negative, Q 4 is always turned off, Q 3 is always turned on, Q 1 and Q 2 perform high-frequency switching and form a Boost circuit with the inductor L. The operating states of Q1 and Q 2 can be further divided into two cases: when Q 1 is the main switching transistor and Q2 is the freewheeling diode, that is, when Q 1 is turned on and Q 2 is turned off, the inductor L charges and stores energy, and the DC bus capacitor C dc supplies energy to the subsequent stage; when switching transistor Q 2 is turned on and switching transistor Q 1When turned off, the inductor L releases energy to the DC side, and is charged by the power grid and the inductor together. When operating in reverse, the PFC circuit can be implemented with a full-bridge PWM rectifier for reverse operation. Specifically: within one switching period, the drive signals of Q1 and Q4 are the same, and Q 2 and Q 3 have the same drive signals, and the drive signals of Q 1 and Q2 differ by half a period, and the voltage is regulated by changing the duty cycle.

[0026] Embodiment 3 Based on Embodiment 2, the subsequent CLLC resonant converter includes a primary full-bridge circuit, a high-frequency transformer T, and a secondary full-bridge circuit. The primary full-bridge circuit is connected to the secondary full-bridge circuit through the high-frequency transformer T; The primary full-bridge circuit is connected in parallel with the capacitor C dc , and the secondary full-bridge circuit is connected in parallel with the capacitor C o .

[0027] Furthermore, the turns ratio of the high-frequency transformer T is 1.

[0028] Furthermore, the primary full-bridge circuit includes switching transistors S 1 , switching transistors S 2 , switching transistors S 3 , switching transistors S 4 . The switching transistors S 1 and the switching transistors S 3 are connected to one end of the capacitor C dc . The switching transistors S 2 and the switching transistors S 4 are connected to the other end of the capacitor C dc . The switching transistors S 1 and the switching transistors S 2 are connected in series, and the switching transistors S 3 and the switching transistors S 4 are connected in series; The primary full-bridge circuit further includes a resonant inductor L r1 , an exciting inductor L m , and a resonant capacitor C r1 . One end of the resonant inductor L r1 is connected to the connection point of the switching transistors S 1 and the switching transistors S 2 , and the other end is connected to one end of the exciting inductor L m . One end of the resonant capacitor C r1 is connected to the connection point of the switching transistors S 3 and the switching transistors S 4 , and the other end is connected to the other end of L m ; Furthermore, the secondary full-bridge circuit includes switching transistors S 5 , switching transistors S6 , switch tube S 7 , switch tube S 8 , switch tube S 5 and switch tube S 7 is connected to one end of capacitor C o , switch tube S 6 and switch tube S 8 is connected to the other end of capacitor C o , switch tube S 5 and switch tube S 6 are in series, and switch tube S 7 and switch tube S 8 are in series; The secondary full-bridge circuit further includes a resonant inductor L connected to the secondary side of the high-frequency transformer T r2 and a resonant capacitor C r2 , resonant inductor L r2 is connected to the connection point of switch tube S 7 and switch tube S 8 , and resonant capacitor C r2 is connected to the connection point of switch tube S 5 and switch tube S 6 .

[0029] In this embodiment, the post-stage symmetric CLLC resonant converter realizes power control and wide voltage range through a hybrid segmented modulation strategy, specifically: During forward operation, drive signals are applied to switch tube S 1 ~switch tube S 4 , and switch tube S 5 ~switch tube S 8 perform uncontrolled rectification; during reverse operation, drive signals are applied to switch tube S 5 ~switch tube S 8 , and switch tube S 1 ~switch tube S 4 perform uncontrolled rectification.

[0030] Furthermore, SiC MOSFETs are used for all switch tubes.

[0031] In this embodiment, SiC MOSFETs are used for all switching devices in the on-vehicle charging circuit, which is beneficial to improving the efficiency and power density of the on-vehicle charging circuit, and realizing the miniaturization and light weight of the on-vehicle charging circuit. The bidirectional CLLC converter uses a high-frequency transformer with a turns ratio set to 1, which is beneficial for frequency gain analysis of the bidirectional CLLC converter, simplifies its transfer function, and is beneficial for the design and implementation of the control method.

[0032] Embodiment 4 As Figure 4As shown, the present invention also discloses a control method for a bidirectional on-vehicle charging circuit, including a variable DC bus voltage control method and a CLLC resonant converter control method based on segmented hybrid modulation of pulse frequency modulation (PFM) and pulse width modulation (PWM). Specifically, it includes the following steps: To further broaden the output voltage range of the on-vehicle charging circuit and reduce the variation range of the switching frequency of the CLLC resonant converter, the output voltage of the front-stage totem-pole bridgeless PFC, that is, the DC bus voltage, varies with the different output voltages of the on-vehicle charging circuit.

[0033] S1: Determine the charging stage according to the working mode and output voltage U o of the on-vehicle charging circuit; among them, when the two-stage circuit operates forward, it is the G2V mode, and when it operates backward, it is the V2G mode. When both the front-stage totem-pole bridgeless PFC and the rear-stage symmetric CLLC resonant converter operate forward, the on-vehicle charging circuit operates in the G2V mode, and when it operates backward, the on-vehicle charging circuit is in the V2G mode. The on-vehicle charging circuit provided by the present invention enables the electric vehicle to be charged by the power grid and also discharge to the power grid, meeting the grid connection requirements. During the low electricity consumption period, the power grid charges the electric vehicle, and during the high electricity consumption period, the electric vehicle discharges and feeds back to the power grid. This function is beneficial to the implementation of the orderly charging of electric vehicles and plays a role in peak shaving and valley filling.

[0034] S2: When the on-vehicle charging circuit operates in the G2V mode and U o is less than the set threshold, it is in the initial stage of charging, and the state of charge (SOC) value of the power battery is relatively low. At this time, constant current charging is adopted for rapid charging, which is single current loop control to ensure a constant output current and avoid the impact that a large instantaneous current may cause to the battery; when the SOC reaches the set threshold, the charging is switched from constant current charging to constant voltage charging. At this time, it is voltage-current double closed-loop control, and the output of the voltage outer loop control is used as the given value of the current inner loop, providing a variable charging current for the power battery and controlling the output voltage to be constant to ensure continuous charging current and avoid overcharging of the battery. When the on-vehicle charging circuit operates in the V2G mode, it only needs to keep the output current constant. In this mode, it is always constant current charging, adopting single current loop control; switching between single and double loop control for charging mode transformation. S3: Through the DC bus voltage controller, adjust the output DC bus voltage U o of the front-stage PFC circuit according to the change of the output voltage U d in different charging stages. S3 is specifically as follows: When U dmin ≤U o≤U dmax When ≤U dmax , the voltage gain of the secondary CLLC resonant converter is 1. The output voltage is controlled by the PFM modulation method. The secondary CLLC converter always operates at the resonant frequency point to achieve zero-voltage turn-on of the primary side and zero-current turn-off of the secondary side, reaching the peak efficiency. The DC bus voltage U is regulated by PWM controlling the front-stage totem-pole bridgeless PFC converter. d At this time, U d =U o ; When U o >U dmax and the output voltage is required to continue increasing, the totem-pole bridgeless PFC converter is PWM controlled to keep the DC bus voltage at U dmax constant. At this time, the gain M of the secondary bidirectional CLLC converter is > 1. The output voltage is controlled by the PFM modulation method. The output voltage is controlled by controlling the switching frequency of the secondary CLLC converter, making the converter operate in the under-resonant region. The slope of the gain curve is negative to ensure ZCS is achieved. When U o <U dmin and the output voltage is required to continue decreasing, the bidirectional totem-pole bridgeless PFC converter is PWM controlled to keep the DC bus voltage at U dmin constant. At this time, the gain M of the secondary bidirectional CLLC converter is < 1. The CLLC resonant converter uses the PWM modulation method to control the output voltage of the on-vehicle charging circuit.

[0035] Embodiment 5 Based on Embodiment 4, as Figure 2 shown, during forward operation: When the voltage gain M of the CLLC resonant converter is ≥1, a variable-frequency modulation strategy is adopted. In one switching period, the drive signals of switch tube S 1 and switch tube S 4 are the same, the drive signals of switch tube S 2 and switch tube S 3 are the same, the drive signals of switch tube S 1 and switch tube S 2 differ by half a period, and a certain dead time is left to prevent shoot-through. Switch tubes S 5 ~ switch tubes S 6 are uncontrolled rectification; When the voltage gain M of the CLLC resonant converter is < 1, voltage regulation is performed by the PWM method.

[0036] As Figure 3 shown, during reverse operation, when the voltage gain M of the CLLC resonant converter is ≥1, a traditional variable-frequency modulation strategy is adopted. In one switching period, switch tube S 5and the switching transistor S 8 has the same driving signal. The switching transistor S 6 and the switching transistor S 7 has the same driving signal. The switching transistor S 5 and the switching transistor S 6 have driving signals that differ by half a cycle, with a certain dead time left to prevent shoot-through. The switching transistor S 1 ~the switching transistor S 4 Uncontrolled rectification; When the voltage gain M of the CLLC resonant converter is less than 1, PWM modulation is used for voltage regulation.

[0037] Embodiment 6 Based on Embodiment 5, the PWM modulation method for the CLLC resonant converter includes: During forward operation, when M < 1, the switching frequency of the bidirectional CLLC resonant converter is fixed at the series resonance frequency. The primary-side switching transistor S 1 and the switching transistor S 3 have equal duty cycles (i.e., D 1 = D 2 ). The switching transistor S 2 and the switching transistor S 4 have equal duty cycles and are equal to 0.5. The switching frequencies of the four switching transistors are constant and equal to the resonance frequency. The duty cycles of the switching transistor S 1 and the switching transistor S 3 are adjusted to regulate the output voltage.

[0038] During reverse operation, when M < 1, the switching frequency of the bidirectional CLLC resonant converter is fixed at the series resonance frequency. The secondary-side switching transistor S 5 and the switching transistor S 7 have equal duty cycles (i.e., D 1 = D 2 ). The switching transistor S 6 and the switching transistor S 8 have equal duty cycles and are equal to 0.5. The switching frequencies of the four switching transistors are constant and equal to the resonance frequency. The duty cycles of the switching transistor S 5 and the switching transistor S 7 are adjusted to regulate the output voltage.

[0039] Embodiment 6 Specific embodiments of the present invention are given in combination with Embodiments 1-5: S1: Determine the charging stage based on the operating mode of the on-vehicle charging circuit and the magnitude of the output voltage U o When the on-vehicle charging circuit operates in the G2V mode, U oWhen it is less than the set threshold value, it is in the initial stage of charging, and the SOC value of the power battery is relatively low. At this time, the constant current (CC) method is used for fast charging, which is a single current loop control to ensure a constant output current and avoid the impact that a large instantaneous current may cause to the battery. When the SOC reaches the set threshold value, the charging switches from CC to constant voltage (CV) charging. At this time, it is a double closed-loop control of voltage and current. The output of the voltage outer loop control is used as the given value of the current inner loop to provide a variable charging current for the power battery and control the output voltage to be constant, ensuring continuous charging current and avoiding overcharging of the battery. When the on-vehicle charging circuit operates in the V2G mode, only the output current needs to be kept constant. In this mode, it is always CC charging and uses a single current loop control.

[0040] S2: As Figure 2 shown, when running forward, U dmin = 380V, U dmax = 420V. When U dmin ≤ U o ≤ U dmax , the on-vehicle charging circuit is in the variable bus voltage mode. The voltage gain of the subsequent CLLC resonant converter is 1, and the PFM modulation method is used to control the output voltage. The subsequent CLLC converter always operates at the resonant frequency point to achieve zero voltage turn-on of the primary side and zero current turn-off of the secondary side, reaching the peak efficiency. At this time, the PWM control is used for the front-stage totem-pole bridgeless PFC converter to adjust the DC bus voltage U d , and there is U d = U o ; When U o > U dmax , and the output voltage is required to continue to increase, at this time the on-vehicle charging circuit is in the boost mode, and the PWM control is used for the totem-pole bridgeless PFC converter to keep the DC bus voltage as U dmax unchanged; At this time, the gain M of the subsequent bidirectional CLLC converter is > 1, and the PFM modulation method is used to control the output voltage. The output voltage is controlled by controlling the switching frequency of the subsequent CLLC converter, so that the converter operates in the under-resonant region, and the slope of the gain curve is negative to ensure the realization of ZCS; When U o < U dmin , and the output voltage is required to continue to decrease, the on-vehicle charging circuit is in the buck mode, and the PWM control is used for the bidirectional totem-pole bridgeless PFC converter to keep the DC bus voltage as U dmin unchanged. At this time, the gain M of the subsequent bidirectional CLLC converter is < 1, and the PWM modulation method is used to control the output voltage of the on-vehicle charging circuit.

[0041] As Figure 3 shown, the working principle during reverse operation is similar to that during forward operation and will not be described in detail.

[0042] S3: As Figure 4 shown, first, the G2V / V2G module determines whether the on-vehicle charging circuit is in a charging or discharging state. Then, according to the method in S2, the subsequent modulation method is determined, and the output voltage is PID-regulated. The PID output result is sent to the PFM / PWM controller. The PFM controller controls the output voltage to be stably a given value U by changing the switching frequency of the CLLC converter, so that the converter works as close as possible to the resonant frequency point. oref ; The PWM controller controls the output voltage to reach the expected value U by adjusting the duty cycle of the switching transistor. oref .

[0043] Finally, it should also be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0044] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0045] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. Bidirectional vehicle charging circuit, characterized in that: It includes a front-stage totem pole bridgeless PFC converter and a rear-stage CLLC resonant converter; the input of the front-stage totem pole bridgeless PFC converter is connected to a 220V single-phase power grid, the output of the front-stage totem pole bridgeless PFC converter is connected to the input of the rear-stage CLLC resonant converter; the output of the rear-stage CLLC resonant converter is connected to a power battery of an electric vehicle; A capacitor is connected in parallel between the front-stage totem pole bridgeless PFC converter and the rear-stage CLLC resonant converter. C dc A capacitor is connected in parallel between the rear CLLC resonant converter and the power battery of the electric vehicle. C o .

2. The bidirectional vehicle-mounted charging circuit according to claim 1, characterized in that: The front-stage totem pole bridgeless PFC converter includes switch tube Q1, switch tube Q2, switch tube Q3, and switch tube Q4. The switch tube Q1 and the switch tube Q3 are connected to the capacitor C dc One end is connected to the switch tube Q2 and the switch tube Q4 and the capacitor C dc The other end is connected; the switch tube Q1 is connected in series with the switch tube Q2, and the switch tube Q3 is connected in series with the switch tube Q4; The front-stage totem pole bridgeless PFC converter also includes an inductor L1, one end of which is connected to the connection point of the switch tube Q1 and the switch tube Q2, and the other end of the inductor L1 is connected to the grid and is connected to the connection point of the switch tube Q3 and the switch tube Q4.

3. The bidirectional vehicle-mounted charging circuit according to claim 2, characterized in that: The post-stage CLLC resonant converter includes a primary full-bridge circuit, a high-frequency transformer T and a secondary full-bridge circuit, and the primary full-bridge circuit is connected to the secondary full-bridge circuit through the high-frequency transformer T; Primary full bridge circuit and capacitor C dc In parallel, the secondary full bridge circuit and capacitor C o in parallel.

4. The bidirectional vehicle-mounted charging circuit according to claim 3, characterized in that: The turns ratio of the high frequency transformer T is 1.

5. The bidirectional vehicle-mounted charging circuit according to claim 4, characterized in that: The primary full-bridge circuit includes switch tube S1, switch tube S2, switch tube S3, and switch tube S4. Switch tube S1 and switch tube S3 are connected to capacitor C dc One end is connected to the switch tube S2 and the switch tube S4 and the capacitor C dc The other end is connected, the switch tube S1 is connected in series with the switch tube S2, and the switch tube S3 is connected in series with the switch tube S4; The primary full-bridge circuit also includes a resonant inductor L connected to the primary side of the high-frequency transformer T. r1 , Excitation inductance L m and resonant capacitor C r1 , resonant inductor L r1 One end is connected to the connection point of switch tube S1 and switch tube S2, and the other end is connected to the excitation inductor L m One end of the resonant capacitor C r1 One end is connected to the connection point of switch tube S3 and switch tube S4, and the other end is connected to L m The other end of The secondary full-bridge circuit includes switch tube S5, switch tube S6, switch tube S7, and switch tube S8. Switch tube S5 and switch tube S7 are connected to capacitor C o One end is connected to the switch tube S6 and the switch tube S8 and the capacitor C o The other end is connected, the switch tube S5 is connected in series with the switch tube S6, and the switch tube S7 is connected in series with the switch tube S8; The secondary full-bridge circuit also includes a resonant inductor L connected to the secondary side of the high-frequency transformer T. r2 and resonant capacitor C r2 , resonant inductor L r2 The connection point between the switch tube S7 and the switch tube S8, the resonant capacitor C r2 A connection point connecting the switch tube S5 and the switch tube S6.

6. The bidirectional vehicle-mounted charging circuit according to claim 5, characterized in that: The switch tubes are all SiC MOSFET.

7. A bidirectional vehicle-mounted charging circuit control method, using the bidirectional vehicle-mounted charging circuit as claimed in claim 6, characterized in that: The specific steps include: S1: The charging stage is determined by the working mode of the on-board charging circuit and the output voltage Uo; when the two-stage circuit is running forward, it is in G2V mode, and when it is running reversely, it is in V2G mode; S2: When the on-board charging circuit works in G2V mode and Uo is less than the set threshold, the power battery SOC value is low and single current loop control is adopted; when the power battery SOC value reaches the set threshold, voltage and current dual closed-loop control is adopted; When the on-board charging circuit works in V2G mode, single current loop control is adopted; S3: Through the DC bus voltage controller, the output DC bus voltage Ud of the front-stage PFC circuit is adjusted according to the change of the output voltage Uo in different charging stages.

8. The bidirectional vehicle charging circuit control method according to claim 7, characterized in that: S3 is specifically: When U dmin ≤U o ≤U dmax When the voltage gain of the rear CLLC resonant converter is 1, the front totem pole bridgeless PFC converter is controlled by PWM to adjust the DC bus voltage U d , at this time U d =U o ; When Uo>Udmax and the output voltage requirement continues to increase, PWM is used to control the totem pole bridgeless PFC converter to keep the DC bus voltage at U dmax The gain M of the subsequent bidirectional CLLC converter is greater than 1, and the output voltage of the on-board charging circuit is controlled by PFM modulation. The output voltage is controlled by controlling the switching frequency of the subsequent CLLC converter, so that the converter works in the sub-resonance region, and the slope of the gain curve is negative, ensuring the realization of ZCS. When U o <U dmin , and the output voltage is required to continue to decrease, PWM is used to control the bidirectional totem pole bridgeless PFC converter to keep the DC bus voltage at U dmin The gain M of the subsequent bidirectional CLLC converter is less than 1, and the output voltage of the on-board charging circuit is controlled by PWM modulation.

9. The bidirectional vehicle charging circuit control method according to claim 8, characterized in that: In forward operation, when the voltage gain M of the CLLC resonant converter is ≥ 1, a variable frequency modulation strategy is adopted. In one switching cycle, the driving signals of switch tubes S1 and S4 are the same, the driving signals of switch tubes S2 and S3 are the same, and the driving signals of switch tubes S1 and S2 differ by half a cycle. A dead time is left during this period to prevent direct conduction, and switch tubes S5 and S6 are not controlled for rectification. When the voltage gain M of the CLLC resonant converter is less than 1, PWM is used for voltage regulation; In reverse operation, when the voltage gain M of the CLLC resonant converter is ≥ 1, the traditional variable frequency modulation strategy is adopted. In one switching cycle, the driving signals of switch tubes S5 and S8 are the same, the driving signals of switch tubes S6 and S7 are the same, and the driving signals of switch tubes S5 and S6 differ by half a cycle. A dead time is left during this period to prevent direct conduction, and switch tubes S1 to S4 are not controlled for rectification; When the voltage gain M of the CLLC resonant converter is less than 1, PWM modulation is used for voltage regulation.

10. The bidirectional vehicle charging circuit control method according to claim 9, characterized in that: The PWM modulation methods for the CLLC resonant converter include: During forward operation, when M<1, the switching frequency of the bidirectional CLLC resonant converter is fixed to the series resonant frequency, the duty ratios of the primary side switch tubes S1 and S3 are equal, the duty ratios of the switch tubes S2 and S4 are equal and equal to 0.5, the switching frequency of the four switch tubes is constant and equal to the resonant frequency, and the output voltage is adjusted by adjusting the duty ratios of the switch tubes S1 and S3; During reverse operation, when M<1, the switching frequency of the bidirectional CLLC resonant converter is fixed to the series resonant frequency and remains unchanged, the duty ratios of the secondary side switch tubes S5 and S7 are equal, the duty ratios of the switch tubes S6 and S8 are equal and equal to 0.5, the switching frequencies of the four switch tubes are constant and equal to the resonant frequency, and the output voltage is adjusted by adjusting the duty ratios of the switch tubes S5 and S7.

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