Secondary side no-load constant-voltage control method of MC-WPT system

Abstract

The invention provides a secondary side no-load constant voltage control method of an MC-WPT system. The MC-WPT system is a bidirectional wireless charging system. The technical problem that an existing secondary side constant-voltage control system of a bidirectional wireless charging system is complex and slow in control response is solved. The method comprises the following specific steps: constructing a current and voltage stress expression and an active and reactive power and load current expression of the bidirectional wireless charging system; analyzing the load current expression of the system to obtain influence parameters, and selecting control parameters from the influence parameters according to the mathematical relationship among the load current, the load voltage and the output power; and carrying out constant voltage control on the load voltage when the system is in a no-load state through the selected influence parameters. According to the method, the bidirectional wireless charging system is analyzed, the system outward shift phase angle is selected as the secondary side no-load constant-voltage control parameter to carry out constant-voltage control when the secondary side is in the no-load state, the control method does not need communication between the primary side and the secondary side or excessive voltage and current collection, and the complexity of constant-voltage control is reduced.

Description

Technical Field

[0001] The present invention relates to the field of wireless power transmission, and in particular to a secondary side no-load constant voltage control method of a MC-WPT system. Background Art

[0002] Traditional wired power supply has problems such as insufficient flexibility, exposed lines, wear and aging, which will undoubtedly reduce the safety and reliability of the power supply process. Wireless charging has the characteristics of convenience, high operational reliability and strong environmental adaptability, so it has shown great advantages in the field of electric vehicle charging. The electric vehicle wireless charging technology based on magnetically coupled wireless power transmission (MC-WPT) has become the best solution for future electric vehicle charging with its significant advantages such as flexibility, safety and high reliability, and has attracted widespread attention from industry and academia.

[0003] The resonant compensation topology used in the MC-WPT system of electric vehicles is generally divided into constant voltage topology or constant current topology. From the perspective of practical application, the constant current topology is more common and mature in wireless charging of electric vehicles. It can ensure the stability of current during charging, avoid battery overheating and damage, and improve charging efficiency. In terms of bidirectional power transmission, the primary and secondary sides need to adopt symmetrical resonant compensation topologies, so two constant current symmetrical resonant compensation topologies such as SS or bilateral LCC can be selected. However, when the coupling coefficient changes, the bilateral LCC topology can better maintain the resonant state and is more in line with the scenario of wireless charging of electric vehicles. Therefore, it is recommended as a reference topology by the national standard.

[0004] However, in the scenario of wireless charging of electric vehicles, the system's constant voltage output is sometimes required. The constant voltage output technologies commonly used in MC-WPT systems include: DC-DC converter, inverter phase shift control, tuning control, resonant compensation network optimization design, and short-circuit decoupling. DC-DC converter technology is one of the most common voltage regulation technologies in MC-WPT systems. It has a wide regulation range and can complete the constant voltage regulation control of the system output when the load, mutual inductance, and input voltage range change.

[0005] In the wireless charging scenario of electric vehicles, the secondary side will be in a no-load state before the devices connected to the secondary side are started. If the output voltage of the secondary side is not controlled, the output voltage of the secondary side will increase sharply, which may seriously damage the system. Summary of the invention

[0006] The purpose of the present invention is to provide a secondary side no-load constant voltage control method for a MC-WPT system, which is used to solve the technical problem of complex control and slow response of the secondary side constant voltage control system of the existing bidirectional wireless charging system.

[0007] A secondary side no-load constant voltage control method for a MC-WPT system, wherein the MC-WPT system is a bidirectional wireless charging system, wherein the primary side and the secondary side of the bidirectional wireless charging system respectively include a primary side full-controlled bridge inverter circuit and a secondary-controlled bridge inverter circuit, and the specific steps of the secondary side no-load constant voltage control are as follows:

[0008] S1: Construct the current and voltage stress expressions of the bidirectional wireless charging system, and construct the system transmission active and reactive power and load current expressions based on the current and voltage stress expressions;

[0009] S2: Analyze the system's load current expression to obtain influencing parameters, and select control parameters from the influencing parameters based on the mathematical relationship between load current, load voltage and output power;

[0010] S3: The load voltage when the system is unloaded is controlled at a constant voltage by means of the selected influencing parameters.

[0011] Optionally, the primary side and the secondary side of the bidirectional wireless charging system include a primary side compensation circuit and a secondary side compensation circuit respectively, and the primary side compensation circuit and the secondary side compensation circuit are symmetrically arranged LCC network topology structures.

[0012] Optionally, the specific method for constructing the current and voltage stress expressions of the bidirectional wireless charging system in step S1 is:

[0013] S1.1: Construct a fundamental wave approximation model of the bidirectional wireless charging system, and construct the basic components of the primary full-bridge output voltage and the secondary full-bridge output voltage through the fundamental wave approximation model;

[0014] S1.2: Write out the KVL equations for the primary and secondary sides respectively. Based on the KVL equations, list the expressions for the primary compensation inductor current, primary coil current, secondary compensation inductor current and primary coil current when the system resonates.

[0015] Optionally, the basic component of the primary full-bridge output voltage is a functional relationship between the primary DC voltage and the primary internal phase shift angle;

[0016] The basic component of the secondary full-bridge output voltage is a function of the secondary DC voltage, the secondary internal phase shift angle and the system external phase shift angle. The system external phase shift angle is the phase angle of the secondary output fundamental voltage lagging the primary output fundamental voltage.

[0017] Optionally, the specific steps of constructing the expressions of system transmission active and reactive power and load current according to the current and voltage stress expressions in step S1 are:

[0018] S1.3: Obtain the absolute values ​​of active power and reactive power transmitted by the system through the expressions of primary compensation inductor current, primary coil current, secondary compensation inductor current and primary coil current when the system resonates;

[0019] S1.4: Based on the conservation of energy between the primary and secondary sides, construct an expression for the output current of the auxiliary control bridge inverter circuit.

[0020] Optionally, the expression of the output current of the auxiliary control bridge inverter circuit is a functional relationship between the output current and the primary side internal phase shift angle, the secondary side internal phase shift angle and the system external phase shift angle.

[0021] Optionally, in step S2, the control parameter selected from the influencing parameters is the system outward shift phase angle.

[0022] Optionally, the specific steps of performing constant voltage control on the load voltage when the system is unloaded by using the selected influencing parameters in step S3 are:

[0023] S3.1: Give the secondary side reference voltage to be controlled;

[0024] S3.2: Collect the no-load voltage of the secondary side at the nth sampling time through the voltage sensor, where n is a positive integer;

[0025] S3.3: Determine whether the secondary side no-load voltage is equal to the secondary side reference voltage. If so, the secondary side no-load control is completed. If not, go to step S3.3;

[0026] S3.4: Calculate the difference between the secondary side no-load voltage and the secondary side voltage reference at the nth sampling time;

[0027] S3.4: input the calculated voltage difference into the PI controller;

[0028] S3.5: The PI controller updates the driving signal by processing the outward shift phase angle of the output system and transmitting it to the auxiliary control bridge inverter circuit;

[0029] S3.6: Set n=n+1 and return to step S3.2.

[0030] Due to the adoption of the above technical solution, the present invention has the following advantages:

[0031] This application analyzes the bidirectional wireless charging system and selects the system outward shift phase angle as the secondary side no-load constant voltage control parameter to perform constant voltage control when the secondary side is no-load. This control method does not require communication between the primary and secondary sides or excessive voltage and current collection, which greatly simplifies the constant voltage control scheme and reduces the complexity of constant voltage control.

[0032] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings of the present invention are as follows.

[0034] Figure 1 Schematic diagram of the bidirectional wireless charging system of the present invention.

[0035] Figure 2 It is a circuit diagram of the double-sided LCC fundamental wave approximation model compensation BIPT system of the present invention.

[0036] Figure 3 The circuit diagram of the secondary side no-load constant voltage control of the present invention is shown in FIG.

[0037] Figure 4 This is a flow chart of the method for performing constant pressure control by selecting influencing parameters of the present invention.

[0038] Figure 5 For the present invention V ref =The secondary side no-load voltage diagram of constant voltage simulation control when 100V.

[0039] Figure 6 For the present invention V ref =200V secondary side no-load voltage diagram of constant voltage simulation control.

[0040] Figure 7 For the present invention V ref =The secondary side no-load voltage diagram of constant voltage simulation control when 300V.

[0041] Figure 8 For the present invention V ref =100V, secondary side no-load voltage diagram of constant voltage simulation control when k=0.1.

[0042] Fig. 9 For the present invention V ref =100V, secondary side no-load voltage diagram of constant voltage simulation control when k=0.15.

[0043] Fig.10 For the present invention V ref =100V, secondary side no-load voltage diagram of constant voltage simulation control when k=0.2. DETAILED DESCRIPTION

[0044] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0045] Embodiment 1:

[0046] like Figure 1 The MC-WPT system shown in the figure is a bidirectional wireless charging system, which includes a primary circuit and a secondary circuit, wherein the primary circuit includes a primary DC power supply V dp, primary full-controlled bridge inverter circuit, primary compensation circuit and primary coil L p The secondary circuit includes a secondary coil L connected in sequence s , secondary side compensation circuit, secondary side full-controlled bridge inverter circuit and secondary side DC power supply V ds , the secondary coil L s and the primary coil L p Constitute a coupling mechanism.

[0047] In this embodiment, the primary compensation circuit and the secondary compensation circuit are symmetrically arranged LCC network topology structures, such as Figure 1 As shown, the primary compensation circuit includes a primary compensation inductor L rp , primary compensation capacitor C fp And the primary compensation capacitor C p The secondary side compensation circuit includes a secondary side compensation inductor L rs , secondary compensation capacitor C fp And the primary compensation capacitor C p The primary side full-controlled bridge inverter circuit consists of S 1 -S 4 A total of 4 switch tubes are formed, and the secondary side full-controlled bridge inverter circuit is composed of T 1 -T 4 It consists of 4 switching tubes in total.

[0048] In this embodiment, the primary DC power supply V dp is the grid power supply, the secondary DC power supply V ds It is the battery power source for electric vehicles.

[0049] Embodiment 2:

[0050] A secondary side no-load constant voltage control method for a MC-WPT system, the specific steps are:

[0051] S1: Construct the current and voltage stress expressions of the bidirectional wireless charging system, and construct the system transmission active and reactive power and load current expressions based on the current and voltage stress expressions; the specific method is:

[0052] S1.1: If Figure 2 As shown in the figure, the fundamental wave approximation model of the bidirectional wireless charging system is constructed, and the basic component U of the primary full-bridge output voltage is constructed through the fundamental wave approximation model. p_1 And the basic component U of the secondary full-bridge output voltage s_1 ;

[0053] The basic component U of the primary full-bridge output voltage p_1 is the primary DC voltage V dp Phase angle β with the primary side p The basic component U of the secondary full-bridge output voltages_1 is the secondary DC voltage and the secondary internal phase shift angle β s and a system external phase shift angle δ, wherein the system external phase shift angle δ is the phase angle of the secondary side output fundamental wave voltage lagging the primary side output fundamental wave voltage.

[0054] In this implementation, the basic component U p_1 and U s_1 The mathematical expression is:

[0055]

[0056] S1.2: Write out the KVL equations for the primary and secondary sides respectively. According to the KVL equations, the primary compensation inductor current I Lrp , primary coil current I Lp , secondary side compensation inductor current I Lrs and the primary coil current I Ls expression.

[0057] In this embodiment, the KVL equations for the primary and secondary sides are:

[0058]

[0059] When the system resonates, it can be written as:

[0060]

[0061] S1.3: Obtain the absolute values ​​of active power and reactive power transmitted by the system through the expressions of primary compensation inductor current, primary coil current, secondary compensation inductor current and primary coil current when the system resonates;

[0062] In this embodiment, the absolute values ​​of active power and reactive power transmitted by the system are:

[0063]

[0064] The inductance ratio of the coil self-inductance to the compensation inductance is:

[0065]

[0066] X p and X s are the characteristic impedances of the primary and secondary sides respectively, and the expressions are:

[0067]

[0068] S1.4: According to the conservation of energy of the primary and secondary sides, an expression for the output current of the auxiliary control bridge inverter circuit is constructed. The expression for the output current of the auxiliary control bridge inverter circuit is a functional relationship between the output current and the primary side internal phase shift angle, the secondary side internal phase shift angle and the system external phase shift angle.

[0069] In this embodiment, in order to simplify the analysis, the equivalent internal resistance of the coil in the system and the loss of the active bridge are ignored, and according to the law of energy conservation, it can be obtained that:

[0070]

[0071] After solving the simultaneous equations, the output current I of the auxiliary control bridge inverter circuit can be obtained: eq for:

[0072]

[0073] Where U dp is the primary DC power supply V dp The output voltage, U ds V is the secondary DC power supply sp The output voltage of the auxiliary control bridge inverter circuit can be obtained from this. eq The equivalent load X of the next stage eq It has nothing to do with the output current I of the auxiliary control bridge inverter circuit. eq constant current characteristics. When the system is not running and the equivalent load is not connected to the loop, the output end of the auxiliary control bridge inverter circuit is in a no-load state, which means that the output equivalent load of the auxiliary control bridge inverter circuit is infinite. Since the output current of the auxiliary control bridge inverter circuit remains unchanged, this will cause its output voltage to increase sharply. This extreme situation will also cause the primary current to surge to a very large value, causing serious damage to the MC-WPT system.

[0074] S2: Analyze the system's load current expression to obtain influencing parameters, and select control parameters from the influencing parameters based on the mathematical relationship between load current, load voltage and output power;

[0075] In this embodiment, the influencing parameters include the primary DC voltage U dp , the primary side internal phase shift angle β p , secondary side internal phase shift angle β s The output current I from the auxiliary control bridge inverter circuit is eq It can be seen from the expression that if the secondary voltage needs to be controlled, the secondary current I needs to be controlled eq .I eq Can be controlled by controlling the primary DC voltage U dp Or the primary side internal phase shift angle β pHowever, this requires communication between the primary and secondary sides, which not only increases the complexity of the system, but also the delay of communication will make the control of the system difficult. It is also possible to control the phase shift angle β in the secondary side. s The control of the no-load voltage of the secondary side of the system, but this method needs to be based on the original secondary side synchronization, and needs to increase the control of the external phase angle, which increases the complexity of the voltage control scheme. Therefore, this application chooses to select the control parameter as the system external phase angle δ in the influencing parameters.

[0076] S3: Figure 3 and Figure 4 As shown in the figure, the load voltage is controlled at a constant voltage when the system is unloaded by selecting the influencing parameters. The specific steps are:

[0077] S3.1: Given the secondary reference voltage V to be controlled ref ;

[0078] S3.2: Collect the no-load voltage V of the secondary side at the nth sampling time through the voltage sensor ds , n is a positive integer;

[0079] S3.3: Determine the secondary side no-load voltage V ds Is it equal to the secondary reference voltage V ref , if yes, then the secondary side no-load control is completed, if no, go to step S3.3;

[0080] S3.4: Calculate the secondary side no-load voltage V at the nth sampling time ds With the secondary voltage reference V ref The difference between

[0081] S3.4: input the calculated voltage difference into the PI controller;

[0082] S3.5: The PI controller updates the drive signal by processing the outward shift phase angle δ of the output system and transmitting it to the auxiliary control bridge inverter circuit;

[0083] S3.6: Set n=n+1 and return to step S3.2.

[0084] In this embodiment, n=1 is assumed at the initial moment.

[0085] S4 simulation verification:

[0086] S4.1: System parameter setting,According to the resonance conditions of the MC-WPT system with bilateral LCC topology compensation, the designed system parameters are shown in Table 1. The system simulink simulation model consists of a PWM generator, a PI external phase angle controller, a voltage measurement unit and a main circuit.

[0087] Table 1 System parameters

[0088]

[0089]

[0090] S4.2: System constant voltage control effect verification. In order to verify the effectiveness of the proposed constant voltage control method, the primary DC side voltage is 700V and different secondary side reference voltages V are set. ref The simulation results are as follows Figure 5 , Figure 6 and Figure 7 As shown, Figure 5 Set the secondary side reference voltage V ref is 100V, Figure 6 Set the secondary side reference voltage V ref is 200V, Figure 7 Set the secondary side reference voltage V ref is 300 V. Through simulation, we can see that the system achieves constant voltage control.

[0091] S4.3: System robustness verification, in order to verify the robustness of the proposed constant voltage control method, simulation is carried out under the conditions of primary DC voltage of 700V and different coupling coefficients. The simulation results are shown in Figure 8 , Fig. 9 and Fig.10 As shown, Figure 8 Set the secondary side reference voltage V ref is 100V, the coupling coefficient k is 0.1, Fig. 9 Set the secondary side reference voltage V ref is 100V, the coupling coefficient k is 0.15, Fig.10 Set the secondary side reference voltage V ref is 100V, and the coupling coefficient k is 0.2. Figure 8 , Fig. 9 and Fig.10 It can be seen that the system achieves constant pressure control, which proves that the system using the proposed method has certain robustness.

[0092] In summary, the present application is aimed at the bilateral LCC topology MC-WPT system based on the dual fully-controlled bridge inverter circuit, and the constant voltage control of the secondary side full-controlled bridge inverter circuit under no-load state. The control method does not require primary and secondary side communication or excessive voltage and current collection, which greatly simplifies the control constant voltage scheme, and verifies the constant voltage control effect and robustness of the system through simulation, which has certain theoretical value and practical significance.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A secondary side no-load constant voltage control method for a MC-WPT system, wherein the MC-WPT system is a bidirectional wireless charging system, wherein the primary side and the secondary side of the bidirectional wireless charging system respectively include a primary side full-controlled bridge inverter circuit and a secondary-controlled bridge inverter circuit, wherein: The specific steps of secondary side no-load constant voltage control are: S1: Construct the current and voltage stress expressions of the bidirectional wireless charging system, and construct the system transmission active and reactive power and load current expressions based on the current and voltage stress expressions; S2: Analyze the system's load current expression to obtain influencing parameters, and select control parameters from the influencing parameters based on the mathematical relationship between load current, load voltage and output power; S3: The load voltage when the system is unloaded is controlled at a constant voltage by means of the selected influencing parameters.

2. The secondary side no-load constant voltage control method of a MC-WPT system according to claim 1 is characterized in that: The primary side and the secondary side of the bidirectional wireless charging system respectively include a primary side compensation circuit and a secondary side compensation circuit, and the primary side compensation circuit and the secondary side compensation circuit are symmetrically arranged LCC network topology structures.

3. The secondary side no-load constant voltage control method of a MC-WPT system according to claim 2 is characterized in that: The specific method of constructing the current and voltage stress expressions of the bidirectional wireless charging system in step S1 is: S1.1: Construct a fundamental wave approximation model of the bidirectional wireless charging system, and construct the basic components of the primary full-bridge output voltage and the secondary full-bridge output voltage through the fundamental wave approximation model; S1.2: Write out the KVL equations for the primary and secondary sides respectively. Based on the KVL equations, list the expressions for the primary compensation inductor current, primary coil current, secondary compensation inductor current and primary coil current when the system resonates.

4. The secondary side no-load constant voltage control method of a MC-WPT system according to claim 3 is characterized in that: The basic component of the primary full-bridge output voltage is a function of the primary DC voltage and the primary internal phase shift angle; The basic component of the secondary full-bridge output voltage is a function of the secondary DC voltage, the secondary internal phase shift angle and the system external phase shift angle. The system external phase shift angle is the phase angle of the secondary output fundamental voltage lagging the primary output fundamental voltage.

5. The secondary side no-load constant voltage control method of a MC-WPT system according to claim 3 is characterized in that: The specific steps of constructing the system transmission active and reactive power and load current expressions according to the current and voltage stress expressions in step S1 are: S1.3: Obtain the absolute values ​​of active power and reactive power transmitted by the system through the expressions of primary compensation inductor current, primary coil current, secondary compensation inductor current and primary coil current when the system resonates; S1.4: Based on the conservation of energy between the primary and secondary sides, construct an expression for the output current of the auxiliary control bridge inverter circuit.

6. The secondary side no-load constant voltage control method of the MC-WPT system according to claim 5 is characterized in that: The expression of the output current of the auxiliary control bridge inverter circuit is a functional relationship between the output current and the primary side internal phase shift angle, the secondary side internal phase shift angle and the system external phase shift angle.

7. The secondary side no-load constant voltage control method of a MC-WPT system according to claim 1 is characterized in that: In step S2, the control parameter selected from the influencing parameters is the system outward shift phase angle.

8. The secondary side no-load constant voltage control method of the MC-WPT system according to claim 7 is characterized in that: The specific steps of performing constant voltage control on the load voltage when the system is unloaded by using the selected influencing parameters in step S3 are: S3.1: Give the secondary side reference voltage to be controlled; S3.2: Collect the no-load voltage of the secondary side at the nth sampling time through the voltage sensor, where n is a positive integer; S3.3: Determine whether the secondary side no-load voltage is equal to the secondary side reference voltage. If so, the secondary side no-load control is completed. If not, go to step S3.3; S3.4: Calculate the difference between the secondary side no-load voltage and the secondary side voltage reference at the nth sampling time; S3.4: input the calculated voltage difference into the PI controller; S3.5: The PI controller updates the driving signal by processing the outward shift phase angle of the output system and transmitting it to the auxiliary control bridge inverter circuit; S3.6: Set n=n+1 and return to step S3.2.

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