A bi-wpt system control method suitable for input and output voltage mismatch

Abstract

The application discloses a Bi-WPT system control method suitable for input and output voltage mismatching, which comprises a Bi-WPT system, wherein the Bi-WPT system comprises a bidirectional DC-DC circuit, a control module, the bidirectional DC-DC circuit comprises a first conversion unit, a second conversion unit and a third conversion unit, the first conversion unit is connected with an energy storage station, the first conversion unit is a primary full-bridge converter, the third conversion unit is a secondary full-bridge converter, the second conversion unit comprises a compensation network and a transformer, the compensation network comprises a compensation inductor L1, a switch control capacitor C1, a compensation capacitor C p s and a compensation capacitor Cs; the control module obtains a sampling voltage, performs calculation according to a working mode, obtains a conduction angle sigma of a required control Q x , Q y , controls a driving circuit to input a corresponding PWM signal wave to MOSFET switch tubes Q x , Q y , adjusts the capacitance value of the switch control capacitor C1, and finally realizes effective bidirectional wireless energy transmission of the system. The application can solve the power transmission problem of system voltage mismatching.

Description

Technical Field

[0001] This invention belongs to the field of bidirectional wireless power transfer technology for electric vehicles, specifically a control method for Bi-WPT systems with input-output voltage mismatch. Background Technology

[0002] Electric vehicles (EVs) serve as a concrete example of the application and development of Bidirectional Wireless Power Transfer (Bi-WPT) technology. Through V2X technology, EVs can function as mobile energy storage units, storing and utilizing renewable energy sources such as solar and wind power, optimizing energy distribution, and reducing dependence on fossil fuels. V2X technology enhances user charging convenience through wireless charging and bidirectional energy flow, enabling efficient energy transfer without physical connections. It also makes it possible for EVs to participate in grid peak shaving, home power supply (V2H, Vehicle-to-Home), and vehicle-to-vehicle energy sharing (V2V, Vehicle-to-Vehicle), further expanding the application scenarios of EVs. Taking energy storage stations and EVs as an example, the EV's battery can be used as a distributed power source in the energy storage station. During off-peak hours, the EV is charged using rectification technology, while during peak hours, energy is fed back to the energy storage station using inverter technology. This enables bidirectional energy flow between the energy storage station and the EV, reducing fluctuations in the energy storage station's performance and achieving peak shaving and valley filling.

[0003] However, due to the wide variety of electric vehicle types, their battery voltage levels may differ, while the voltage of energy storage stations is fixed, leading to a system voltage mismatch problem. In this situation, when an electric vehicle connects to an energy storage station, if the voltage is mismatched, power transmission will be impossible, or the power output will be either too low or too high. Summary of the Invention

[0004] The purpose of this invention is to provide a control method for Bi-WPT systems with input-output voltage mismatch, which can solve the power transmission problem caused by system voltage mismatch.

[0005] To achieve the above objectives, the present invention provides a control method for a Bi-WPT system with input-output voltage mismatch, comprising a Bi-WPT system, the Bi-WPT system including a bidirectional DC-DC circuit and a control module. The bidirectional DC-DC circuit includes a first conversion unit, a second conversion unit, and a third conversion unit. The first conversion unit is connected to the energy storage station and is a primary-side full-bridge converter composed of four MOSFET switches S1-S4. The emitter of switch S1 and the collector of switch S2 are connected in series to form the first bridge arm on the primary side, and the connection point between the emitter of switch S1 and the collector of switch S2 is denoted as the midpoint A of the first bridge arm on the primary side. The emitter of switch S3 and the collector of switch S4 are connected in series to form the second bridge arm on the primary side, and the connection point between the emitter of switch S3 and the collector of switch S4 is denoted as the midpoint B of the second bridge arm on the primary side. The first bridge arm and the second bridge arm on the primary side are connected in parallel across the equivalent DC voltage source Uin of the energy storage station.

[0006] The second conversion unit includes a compensation network and a transformer. The compensation network includes a compensation inductor L1, a switch control capacitor C1, and a compensation capacitor C. p The compensation capacitor Cs forms an LCC-C compensation topology; the transformer includes the primary winding L... P The secondary coil Ls; the input terminal of the compensation inductor L1 is connected to the midpoint B of the second bridge arm on the primary side, and the output terminal of the compensation inductor L1 is connected in series with the compensation capacitor Cp and then connected to the primary coil Ls. P The input terminal is connected, and the primary coil L P The output terminals are connected in series with parasitic resistors R. p Parasitic resistance R L1 It is then connected to the midpoint A of the first bridge arm on the original side; one end of the switch control capacitor C1 is connected to the compensation inductor L1 and the compensation capacitor C. p Between, the other end is connected to the parasitic resistance R p With parasitic resistance R L1 Between; the input terminal of the compensation capacitor Cs is connected to the output terminal of the secondary coil Ls, the output terminal of the compensation capacitor Cs is connected to the third conversion unit, and the input terminal of the secondary coil Ls is connected to one end of the parasitic resistance Rs.

[0007] The third conversion unit is a secondary-side full-bridge converter, consisting of four MOSFET switches S5-S8. The emitter of switch S5 and the collector of switch S6 are connected in series to form the first bridge arm on the secondary side, and the junction of the emitter of switch S5 and the collector of switch S6 is denoted as midpoint a of the first bridge arm on the secondary side. The emitter of switch S7 and the collector of switch S8 are connected in series to form the second bridge arm on the secondary side, and the junction of the emitter of switch S7 and the collector of switch S8 is denoted as midpoint b of the second bridge arm on the secondary side. The first and second bridge arms on the secondary side are connected in parallel to capacitor C. filter At both ends, capacitor Cfilter With battery voltage U out Parallel connection; the midpoint a of the first bridge arm on the secondary side is connected to the output terminal of the compensation capacitor Cs, and the midpoint b of the second bridge arm on the secondary side is connected to the other end of the parasitic resistance Rs.

[0008] The control module includes a control module, a sampling voltage, control signals, and a drive circuit. The sampling voltage is used to acquire the electric vehicle battery voltage U. out ;

[0009] The switching control capacitor C1 includes two MOSFET switching transistors Q. x Q y Switch Q x The emitter and the switch Q y The collector of the capacitor is connected in series with the capacitor Ca and then in parallel with the capacitor C. b .

[0010] As a further aspect of the present invention: the control method includes a bidirectional DC-DC circuit comprising a forward charging mode and a reverse feeding mode. When the bidirectional DC-DC circuit is in either the forward charging mode or the reverse feeding mode, the control module acquires the electric vehicle battery voltage U. out The information is transmitted to the control module. Since the target output power is constant, the control module receives the sampled voltage and calculates the required control Q based on the operating mode. x Q y The conduction angle σ controls the corresponding PWM signal input to the MOSFET switch Q via the drive circuit. x Q y By adjusting the switch to control the capacitance value of capacitor C1, the system can ultimately achieve effective bidirectional wireless power transmission.

[0011] As a further aspect of the present invention: the capacitance value C of the switch control capacitor C1 is... eq It can be represented as:

[0012]

[0013] Among them, Ca and C b Capacitors Ca and C are respectively. b The capacitance value, C′ eq The equivalent capacitance is expressed as shown in (1), and the value range of σ is [π / 2, π].

[0014]

[0015] As a further aspect of the present invention: in the forward charging mode, the battery load is equivalent to a pure resistor, that is, the third conversion unit and the battery load are equivalent to a resistor R. L Establish a mathematical model:

[0016]

[0017] P L =I2 2 R L (11)

[0018] U ab '=jωMI P (12)

[0019] Where j is the imaginary part, ω is the operating frequency of the system, and M is the primary coil L P The mutual inductance between the secondary coils Ls is given by: a = jωL1 + 1 / jωC1, b = 1 / jωC1 + 1 / jωC p +jωL P c=jωL S +1 / jωC S +R L U AB It is a DC voltage source U in An AC voltage source equivalent to the first conversion unit, where I1 represents the output current of the first conversion unit, I p It flows through the primary coil L P The current, I2 is the current flowing through the secondary coil Ls, U' ab It is the resistance R L The voltage on;

[0020] Switch control capacitor C1 and battery voltage U out The functional relationship between the two is as follows:

[0021] C1=f(U out (13).

[0022] As a further aspect of the present invention: in the reverse-feed mode, the load of the energy storage station is equivalent to a pure resistor, that is, the first conversion unit (1) and the load of the energy storage station are equivalent to a resistor R′. L Establish a mathematical model:

[0023]

[0024] P L =(-I1) 2 R′ L (twenty one)

[0025] in Uab is the equivalent AC voltage source of the battery Uout and the third conversion unit (3), I2 represents the output current of the third conversion unit (3), I p It flows through the primary coil L P The current, I1 is the current flowing through the load side;

[0026] Since the target output power of the electric vehicle charging the energy storage station is constant, the switching control capacitor C1 and the battery voltage U can be obtained. out The functional relationship between the two is as follows:

[0027] C1=f(U out ) (twenty two).

[0028] Compared with existing technologies, this invention addresses the bidirectional energy transfer problem caused by voltage mismatch between the energy storage station and the electric vehicle battery. It adjusts the switch control capacitor C1 based on the change in the electric vehicle battery voltage, prioritizing the target output power, to achieve the system's target output power. Furthermore, it eliminates the need for additional circuitry at the energy receiving end and changes to the system's operating frequency. The process is simple and enables effective bidirectional energy transfer. Attached Figure Description

[0029] Figure 1 This is a main circuit diagram of a Bi-WPT system applicable to input-output voltage mismatch according to the present invention;

[0030] Figure 2 This is a circuit diagram of the switch-controlled capacitor in this invention;

[0031] Figure 3 This is a graph showing the change in the equivalent capacitance of the switch-controlled capacitor in this invention;

[0032] Figure 4 This is the equivalent circuit diagram of the forward charging mode in this invention.

[0033] Figure 5 This is the equivalent circuit diagram of the reverse-feed mode in this invention;

[0034] Figure 6 This is a graph showing the bidirectional output power of the system of the present invention as a function of the control switch capacitor C1 and the load, where 6a is in the forward charging mode and 6b is in the reverse feeding mode.

[0035] Figure 7 This is a graph showing the relationship between the switch control capacitor parameters and the electric vehicle battery voltage in the system of this invention.

[0036] Figure 8 The diagram shows the power and efficiency of the system during forward charging and reverse feeding according to the present invention.

[0037] Figure 9 This is a flowchart of the system operation of the present invention;

[0038] Figure 10 This is a simulation diagram of the system control switch controlling the charging and discharging of the capacitor according to the present invention.

[0039] In the diagram: 1. First transformation unit, 2. Second transformation unit, 3. Third transformation unit. Detailed Implementation

[0040] The invention will now be further described with reference to the accompanying drawings.

[0041] like Figure 1 As shown, the main circuit diagram of a Bi-WPT system suitable for input-output voltage mismatch according to the present invention includes a bidirectional DC-DC circuit and a control module. The bidirectional DC-DC circuit includes a first conversion unit 1, a second conversion unit 2, and a third conversion unit 3. The first conversion unit 1 is connected to the energy storage station. The first conversion unit 1 is a primary-side full-bridge converter, which is composed of four MOSFET switches S1-S4. The emitter of switch S1 and the collector of switch S2 are connected in series to form the first bridge arm on the primary side, and the connection point of the emitter of switch S1 and the collector of switch S2 is denoted as the midpoint A of the first bridge arm on the primary side. The emitter of switch S3 and the collector of switch S4 are connected in series to form the second bridge arm on the primary side, and the connection point of the emitter of switch S3 and the collector of switch S4 is denoted as the midpoint B of the second bridge arm on the primary side. The first bridge arm and the second bridge arm on the primary side are connected in parallel across the equivalent DC voltage source Uin of the energy storage station.

[0042] The second conversion unit 2 includes a compensation network and a transformer. The compensation network includes a compensation inductor L1, a switch control capacitor C1, and a compensation capacitor C. p The compensation capacitor Cs forms an LCC-C compensation topology; the transformer includes the primary winding L... P The secondary coil Ls; the input terminal of the compensation inductor L1 is connected to the midpoint B of the second bridge arm on the primary side, and the output terminal of the compensation inductor L1 is connected in series with the compensation capacitor Cp and then connected to the primary coil Ls. P Connect the input terminal to the primary coil L. P The output terminals are connected in series with parasitic resistors R. p Parasitic resistance R L1 It is then connected to the midpoint A of the first bridge arm on the original side; one end of the switch control capacitor C1 is connected to the compensation inductor L1 and the compensation capacitor C. p Between, the other end is connected to the parasitic resistance R p With parasitic resistance R L1 Between; the input terminal of the compensation capacitor Cs is connected to the output terminal of the secondary coil Ls, the output terminal of the compensation capacitor Cs is connected to the third conversion unit 3, and the input terminal of the secondary coil Ls is connected to one end of the parasitic resistance Rs.

[0043] The third conversion unit 3 is a secondary-side full-bridge converter, consisting of four MOSFET switches S5-S8. The emitter of switch S5 and the collector of switch S6 are connected in series to form the first bridge arm on the secondary side, and the junction of the emitter of switch S5 and the collector of switch S6 is denoted as midpoint a of the first bridge arm on the secondary side. The emitter of switch S7 and the collector of switch S8 are connected in series to form the second bridge arm on the secondary side, and the junction of the emitter of switch S7 and the collector of switch S8 is denoted as midpoint b of the second bridge arm on the secondary side. The first and second bridge arms on the secondary side are connected in parallel to capacitor C. filter At both ends, capacitor C filter It is connected in parallel with the battery voltage Uout; the midpoint a of the first bridge arm on the secondary side is connected to the output terminal of the compensation capacitor Cs, and the midpoint b of the second bridge arm on the secondary side is connected to the other end of the parasitic resistance Rs.

[0044] When the bidirectional DC-DC circuit is in forward charging mode, the first conversion unit receives a control signal, while the third conversion unit receives no control signal. The control module collects the electric vehicle battery voltage Uout information and sends it to the control module. The control module calculates the capacitance of the corresponding switch control capacitor C1 according to a formula, thereby controlling the conduction angle σ of the switch control capacitor C1 and adjusting its capacitance value to achieve the target output power. When the bidirectional DC-DC circuit is in reverse charging mode, the third conversion unit receives a control signal, while the first conversion unit receives no control signal. The control module collects the electric vehicle battery voltage Uout information and sends it to the control module. The control module calculates the capacitance value of the corresponding switch control capacitor C1 according to a formula, thereby controlling the conduction angle of the switch control capacitor and adjusting its capacitance value to achieve the target output power.

[0045] like Figure 1 , Figure 2 As shown, the switch control capacitor C1 includes two MOSFET switching transistors Q. x Q y Switch Q x The emitter and the switch Q y The collector of the capacitor is connected in series with the capacitor Ca and then in parallel with the capacitor C. b If the switch control capacitor C1 is not connected in series with capacitor C... b Then the equivalent capacitance C′ eq It can be expressed as Equation (1). Considering the relationship between the charging and discharging time of the capacitor and the conduction angle σ of the controllable switch, the range of σ is [π / 2, π].

[0046]

[0047] C′ eq It increases with the increase of the conduction angle σ, because a small change in the conduction angle σ will cause C′ eqDrastic changes lead to increased sensitivity in the system's closed-loop regulation, making accurate control extremely difficult. To address this issue, such as... Figure 2 As shown, the equivalent capacitance C′ is used. eq Series capacitor C b Its capacitance value C eq It can be represented as:

[0048]

[0049] like Figure 2 As shown, when the bidirectional DC-DC circuit is in forward charging mode or reverse feeding mode, the control module collects the electric vehicle battery voltage Uout information and sends it to the control module. Since the target output power is constant, the control module calculates the required control Q based on the sampled voltage according to the working mode. x Q y The conduction angle σ controls the corresponding PWM signal wave input to the MOSFET switch Q of the drive circuit. x Q y By adjusting the capacitance value of the control capacitor C1 via the switch, the system can ultimately achieve effective bidirectional wireless power transmission. For example... Figure 3 The figure shown is a graph illustrating the change in the equivalent capacitance of the switch control capacitor C1 according to the present invention.

[0050] The transformer in the second transformation unit 2 is a loosely coupled transformer, with two primary coils L... P The coupling between the secondary coil Ls and the primary coil Ls is low, and energy is transferred through the air. P The secondary coil Ls is connected to the compensation network. Due to the asymmetry of the compensation network, the forward power and reverse power of the system need to be studied and analyzed separately.

[0051] When the bidirectional DC-DC circuit is in forward charging mode, the control module uses single phase shift control for the first conversion unit 1; when the bidirectional DC-DC circuit is in reverse power feeding mode, the control module uses single phase shift control for the third conversion unit 3.

[0052] In the forward charging mode, the output voltage of the first conversion unit 1 is controlled by adjusting the inward shift angle of the first conversion unit 1; in the reverse power feeding mode, the output voltage of the third conversion unit 3 is controlled by adjusting the inward shift angle of the third conversion unit 3.

[0053] The first conversion unit 1 outputs voltage U AB and the input voltage U of the third conversion unit ab The expression is:

[0054]

[0055] Wherein, α and β are the inner phase shift angles of the first transformation unit 1 and the third transformation unit 3, respectively.

[0056] When the system voltage is mismatched, under different operating modes, i.e., forward charging or reverse feeding, adjusting the inward shift angle of the first conversion unit 1 or the third conversion unit 3 cannot effectively achieve the target output power. Therefore, the capacitance value of the switch control capacitor C1 in the second conversion unit 2 is controlled and adjusted. By sampling the charging and discharging voltage information of the electric vehicle and feeding it back to the control module, the control module controls the drive circuit to change the conduction angle σ of the switch control capacitor C1 according to the sampling information, thereby adjusting the capacitance value of the switch control capacitor C1, and finally realizing the effective bidirectional wireless power transmission of the system.

[0057] like Figure 4 The diagram shown is the equivalent circuit diagram of the forward charging mode in this invention, that is, the equivalent circuit diagram of the energy storage station charging the electric vehicle.

[0058] In the first conversion unit 1, the signals of the upper and lower bridge arms of the same group of bridge arms are opposite, that is, when the signal of one bridge arm is positive, the signal of the other bridge arm is negative; in the third conversion unit, no signal is applied to the two groups of bridge arms, which is equivalent to an uncontrolled rectifier.

[0059] The signals from switches S1 and S2 in the first conversion unit 1 are out of phase by an angle. This angle is the phase shift angle within the first conversion unit, denoted as α, and α = π. The output voltage U of the first conversion unit 1 is... AB The expression is:

[0060]

[0061] The electric vehicle battery is equivalent to a pure resistance R. La R La The expression is formula (5), which can be used to combine the third transformation unit and the resistor R. La Equivalent to a resistor R L The relationship between the two is expressed by formula (6).

[0062]

[0063] R L ≈0.85R La (6)

[0064] Without considering resonance and ignoring parasitic resistance, the battery load can be equivalent to a pure resistor, thus the third conversion unit and the battery load can be equivalent to a resistor R. L Establish a mathematical model:

[0065]

[0066] P L =I22 R L (11)

[0067] U ab '=jωMI P (12)

[0068] Where j is the imaginary part, ω is the operating frequency of the system, and M is the primary coil L P The mutual inductance between the secondary coils Ls is given by: a = jωL1 + 1 / jωC1, b = 1 / jωC1 + 1 / jωC p +jωL P c=jωL S +1 / jωC S +R L ;U AB It is a DC voltage source U in An AC voltage source equivalent to the first conversion unit, where I1 represents the output current of the first conversion unit, I p It flows through the primary coil L P The current, I2 is the current flowing through the secondary coil Ls, U' ab It is the resistance R L The voltage on it.

[0069] Since the power of the energy storage station charging the electric vehicle is constant, by combining formulas (6), (10) and (11), the switch control capacitor C1 and the battery voltage U can be obtained. out The functional relationship between the two is as follows:

[0070] C1=f(U out (13)

[0071] If the battery voltage level changes, the constant target output power can be achieved by adjusting the switch to control capacitor C1, thus solving the problem of system voltage mismatch during the charging process of electric vehicles by the energy storage station.

[0072] There are several reasons for the battery charging process: First, battery charging is a process of converting electrical energy into chemical energy through an electrochemical reaction. In order to charge the battery, the charging voltage must be higher than the current voltage of the battery so that the electrochemical reaction can be reversed and the chemical substances in the battery can be replenished. Second, if the output voltage of the charger is lower than the voltage of the battery, the battery will not accept charging because the voltage at both ends of the battery is already higher than the output voltage of the charger, and there is not enough voltage difference to drive the current into the battery. Ideally, the current always flows from the high potential to the low potential. If the voltage of the charger is lower than the voltage of the battery, the current will flow from the battery to the charger, which will actually cause the battery to discharge instead of charge. Therefore, the input voltage of the third conversion unit 3 must be higher than the battery charging voltage. When the voltage of the energy storage station and the electric vehicle battery are mismatched, since the voltage of the energy storage station is fixed and the voltage of the electric vehicle battery is variable, the equivalent resistive load changes with the battery charging process, but a constant power needs to be maintained. As can be seen from formulas (11) and (12), the load power P of the system is L and voltage U' ab Closely related to the switch control capacitor C1, the voltage mismatch between the energy storage station and the electric vehicle battery can be effectively solved by controlling the capacitance value of the switch control capacitor C1.

[0073] like Figure 5 The diagram shown is the equivalent circuit diagram of the reverse power supply mode of the present invention, that is, the equivalent circuit diagram of an electric vehicle charging an energy storage station.

[0074] In the third conversion unit 3, the signals of the upper and lower bridge arms of the same group of bridge arms are opposite, that is, when the signal of one bridge arm is positive, the signal of the other bridge arm is negative; in the first conversion unit, no signal is applied to the two groups of bridge arms, which is equivalent to an uncontrolled rectifier.

[0075] The signals from switches S5 and S6 in the third conversion unit 3 are out of phase by an angle. This angle is the inner phase shift angle of the third conversion unit 3, denoted as β, where β = π. The expression for the output voltage Uab of the third conversion unit 3 is:

[0076]

[0077] The energy storage station terminal is equivalent to a pure resistance R′ La , R′ La The expression is given by formula (15), which can be used to combine the third transformation unit and the resistor R′. La Equivalent to a resistor R′ L The relationship between the two is expressed by formula (16).

[0078]

[0079] R′ L ≈0.85R′La (16)

[0080] Without considering resonance and ignoring parasitic resistance, the load of the energy storage station can be equivalent to a pure resistor, that is, the first conversion unit 1 and the load of the energy storage station can be equivalent to a resistor R′. L Establish a mathematical model:

[0081]

[0082]

[0083] P L =(-I1) 2 R′ L (twenty one)

[0084] in Uab is the equivalent AC voltage source of battery Uout and third conversion unit 3, I2 represents the output current of third conversion unit 3, I p It flows through the primary coil L P The current I1 is the current flowing through the load side.

[0085] Since the target output power of the electric vehicle charging the energy storage station is constant, by combining formulas (16), (20) and (21), the switch control capacitor C1 and the battery voltage U can be obtained. out The functional relationship between the two is as follows:

[0086] C1=f(U out ) (twenty two)

[0087] If the battery voltage level changes, a constant power output can be achieved by adjusting the switch to control capacitor C1, thus solving the problem of system voltage mismatch during the charging process of electric vehicles to energy storage stations.

[0088] The mismatch between the electric vehicle's battery voltage and the energy storage station's voltage level means that when the electric vehicle charges the energy storage station, there may be differences in battery voltage. Simultaneously, the equivalent resistive load changes during battery charging, but a constant power supply is required. This leads to a series of problems, including the electric vehicle's inability to effectively charge the energy storage station. As shown in the above formula, the system's load power P... L and voltage U ab Closely related to the switch control capacitor C1, the voltage mismatch between the energy storage station and the electric vehicle battery can be effectively solved by controlling the capacitance value of the switch control capacitor C1.

[0089] When the bidirectional DC-DC circuit is in forward charging mode, the control module controls the first conversion unit 1 to be in inverter mode and the third conversion unit 3 to be in rectification mode; when the bidirectional DC-DC circuit is in reverse power supply mode, the control module controls the third conversion unit 3 to be in inverter mode and the first conversion unit to be in rectification mode.

[0090] like Figure 9 As shown in the flowchart of the system of the present invention, when the bidirectional DC-DC circuit is in forward charging mode or reverse feeding mode, the control module collects the electric vehicle battery voltage Uout information and sends it to the control module. Since the target output power is constant, the control module obtains the sampled voltage and calculates the capacitance value of the switch control capacitor C1 according to the working mode and formula (13) or formula (22), thereby obtaining the required control Q. x Q y The conduction angle σ controls the corresponding PWM signal input to the MOSFET switch Q via the drive circuit. x Q y By adjusting the switch to control the capacitance value of capacitor C1, the system can ultimately achieve effective bidirectional wireless power transmission.

[0091] DC voltage U at the energy storage station in The voltage is 200V, the battery voltage of the electric vehicle is 200V~500V, the system operating frequency is 85kHz, and the coil L... P and L S The parameters are 215.3uH and 153.4uH respectively, the mutual inductance M is 54uH, the compensation inductance L1 is 54.45uH, and the compensation capacitor C... P C S The parameters are 21.9nF, 22.9nF, and resistance R. L1 R P R S The parameters are 0.03Ω, 0.08Ω, and 0.06Ω, respectively. The power of the energy storage station charging the electric vehicle battery is 1–1.2kW, and the power of the electric vehicle battery charging the energy storage station is also 1–1.2kW. In MATLAB / Simulink, both the energy storage station and the electric vehicle battery are simulated using the battery as a model for charging and discharging. The simulation time is 0.1s, which yields the relationship curves between the switch control capacitor parameters and the electric vehicle battery voltage during the forward charging and reverse feeding processes, respectively. Figures 6 to 8 As shown.

[0092] In MATLAB / Simulink, both the energy storage station and the electric vehicle battery were simulated using the battery as a model for charging and discharging. The total simulation time was 0.1s.

[0093] like Figure 10As shown, taking the charging of an electric vehicle battery at 400V by an energy storage station as an example, the analysis of the battery charging state waveform shows that the battery's SOC state is constantly increasing. At the same time, the battery's voltage and current remain stable, indicating that the system's output power is constant.

[0094] When the voltage of the energy storage station and the electric vehicle battery is mismatched, this invention adjusts the switch control capacitor C1 according to the change of the electric vehicle battery voltage, with the target output power as the primary task, to achieve the system's target output power. This solves the bidirectional energy transfer problem caused by the voltage mismatch between the energy storage station and the electric vehicle battery. Furthermore, it does not require adding extra circuitry at the energy receiving end or changing the system's operating frequency. The steps are simple, and it achieves effective bidirectional energy transfer in the system.

[0095] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A control method for a Bi-WPT system with input-output voltage mismatch, comprising a Bi-WPT system, the Bi-WPT system comprising a bidirectional DC-DC circuit, a control module, the bidirectional DC-DC circuit comprising a first conversion unit (1), a second conversion unit (2), and a third conversion unit (3), the first conversion unit (1) being connected to an energy storage station, the first conversion unit (1) being a primary-side full-bridge converter, consisting of four MOSFET switches S1-S4, the emitter of switch S1 and the collector of switch S2 being connected in series to form the first bridge arm on the primary side, and the junction of the emitter of switch S1 and the collector of switch S2 being denoted as the midpoint A of the first bridge arm on the primary side, the emitter of switch S3 and the collector of switch S4 being connected in series to form the second bridge arm on the primary side, and the junction of the emitter of switch S3 and the collector of switch S4 being denoted as the midpoint B of the second bridge arm on the primary side, the first bridge arm on the primary side and the second bridge arm on the primary side being connected in parallel across the equivalent DC voltage source Uin of the energy storage station; characterized in that, The second conversion unit (2) includes a compensation network and a transformer. The compensation network includes a compensation inductor L1, a switch control capacitor C1, and a compensation capacitor C. p The compensation capacitor Cs forms an LCC-C compensation topology; the transformer includes the primary winding L... P The secondary coil Ls; the input terminal of the compensation inductor L1 is connected to the midpoint B of the second bridge arm on the primary side, and the output terminal of the compensation inductor L1 is connected in series with the compensation capacitor Cp and then connected to the primary coil Ls. P Connect the input terminal to the primary coil L. P The output terminals are connected in series with parasitic resistors R. p Parasitic resistance R L1 It is then connected to the midpoint A of the first bridge arm on the original side; one end of the switch control capacitor C1 is connected to the compensation inductor L1 and the compensation capacitor C. p Between, the other end is connected to the parasitic resistance R p With parasitic resistance R L1 Between; the input terminal of the compensation capacitor Cs is connected to the output terminal of the secondary coil Ls, the output terminal of the compensation capacitor Cs is connected to the third conversion unit (3), and the input terminal of the secondary coil Ls is connected to one end of the parasitic resistance Rs; The third conversion unit (3) is a secondary-side full-bridge converter, consisting of four MOSFET switches S5-S8. The emitter of switch S5 and the collector of switch S6 are connected in series to form the first bridge arm on the secondary side, and the junction of the emitter of switch S5 and the collector of switch S6 is denoted as the midpoint a of the first bridge arm on the secondary side. The emitter of switch S7 and the collector of switch S8 are connected in series to form the second bridge arm on the secondary side, and the junction of the emitter of switch S7 and the collector of switch S8 is denoted as the midpoint b of the second bridge arm on the secondary side. The first bridge arm and the second bridge arm on the secondary side are connected in parallel to capacitor C. filter At both ends, capacitor C filter With battery voltage U out Parallel connection; the midpoint a of the first bridge arm on the secondary side is connected to the output terminal of the compensation capacitor Cs, and the midpoint b of the second bridge arm on the secondary side is connected to the other end of the parasitic resistance Rs. The control module includes a sampling voltage, control signals, and a drive circuit. The sampling voltage is used to acquire the electric vehicle battery voltage U. out ; The switching control capacitor C1 includes two MOSFET switching transistors Q. x Q y Switch Q x The emitter and the switch Q y The collector is connected in series with capacitor C a Connect in parallel, then connect in series with capacitor C b ; The bidirectional DC-DC circuit includes a forward charging mode and a reverse power supply mode. When the bidirectional DC-DC circuit is in either forward charging or reverse power supply mode, the control module collects the electric vehicle battery voltage U. out The information is transmitted to the control module. Since the target output power is constant, the control module receives the sampled voltage and calculates the required control based on the operating mode. , conduction angle The corresponding PWM signal wave is input to the MOSFET switching transistor in the control drive circuit. , Adjusting the switch controls the capacitance value of capacitor C1, ultimately achieving effective bidirectional wireless power transmission in the system; The capacitance value C of the switch control capacitor C1 eq It can be represented as: ； Among them, C a C b Capacitor C a Capacitor C b The capacitance value, The equivalent capacitance is expressed as shown in (1), and the conduction angle is... The range of values ​​for is [ , ], ； In forward charging mode, the battery load is equivalent to a pure resistor, so the third conversion unit (3) and the battery load can be equivalent to a resistor. Establish a mathematical model: ； Where j is the imaginary part. M is the operating frequency of the system, and L is the primary coil frequency. P Mutual inductance between secondary coils Ls, U AB It is a DC voltage source U in The AC voltage source equivalent to the first conversion unit (1), I1 represents the output current of the first conversion unit (1), I p It flows through the primary coil L P I2 is the current flowing through the secondary coil Ls. It is a resistor The voltage on; Switch control capacitor and battery voltage The functional relationship between the two is as follows: ； In reverse-feed mode, the load of the energy storage station is equivalent to a pure resistor, which means that the first conversion unit (1) and the load of the energy storage station are equivalent to a resistor. Establish a mathematical model: ； Where Uab is the equivalent AC voltage source of battery Uout and the third conversion unit (3), I2 represents the output current of the third conversion unit (3), and I p It flows through the primary coil L P The current, I1 is the current flowing through the load side; Since the target output power of electric vehicles charging energy storage stations is constant, the switching control capacitor can be obtained. and battery voltage The functional relationship between the two is as follows: 。 2. The control method for Bi-WPT systems with input-output voltage mismatch according to claim 1, characterized in that, When the bidirectional DC-DC circuit is in forward charging mode, the control module adopts single phase shift control for the first conversion unit (1) and controls the output voltage by adjusting the inner phase shift angle α of the first conversion unit (1); when the bidirectional DC-DC circuit is in reverse feeding mode, the control module adopts single phase shift control for the third conversion unit (3) and controls the output voltage by adjusting the inner phase shift angle β of the third conversion unit (3).

3. The control method for Bi-WPT systems with input-output voltage mismatch according to claim 1, characterized in that, When the bidirectional DC-DC circuit is in forward charging mode, the control module controls the first conversion unit (1) to be in inverter mode and the third conversion unit (3) to be in rectification mode; when the bidirectional DC-DC circuit is in reverse power supply mode, the control module controls the third conversion unit (3) to be in inverter mode and the first conversion unit (1) to be in rectification mode.

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