Used in LCC / LCC type wireless charging system and mutual inductance measurement method thereof

Abstract

The present invention relates to an LCC / LCC type wireless charging system and a mutual inductance measurement method thereof. The topology of the wireless charging system includes a primary DC voltage source, an inverter, a compensation resonant circuit, a rectifier bridge, a filter circuit and a secondary DC voltage source; the total bus voltage of the primary DC voltage source is U i The total bus voltage of the secondary DC voltage source is U o The inverter is composed of four switch tubes forming a full-bridge structure, and the four switch tubes are respectively denoted as S P1 , S P2 , S P3 and S P4 , where S P1 and S P2 The leading bridge arm of the inverter, S P3 and S P4 The rectifier bridge is composed of four switch tubes forming a full-bridge structure, and the four switch tubes are respectively denoted as S S1 , S S2 , S S3 and S S4 , where S S1 and S S2 The leading arm of the rectifier bridge, S S3 and S S4 The lagging bridge arm of the rectifier bridge is formed; the compensation resonant circuit includes a primary compensation resonant circuit and a secondary compensation resonant circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless charging of electric vehicles, and in particular to an LCC / LCC type wireless charging system and a mutual inductance measurement method thereof. Background Art

[0002] In recent years, with the development of electric vehicles, wireless charging technology has received widespread attention due to its safety and convenience. During the wireless charging process, the mutual inductance affects the voltage and current of each branch of the system, thereby changing the implementation conditions of soft switching and the on-state loss of the system. In addition, the maximum output power also changes with the change of mutual inductance. Therefore, the measurement of mutual inductance coefficient has great research significance and engineering value.

[0003] Reference "Development of a constant current and constant voltage wireless charging system with primary side mutual inductance identification function" [J]. Journal of Electric Machines and Control, 2021, 25(04): 52-60. DOI: 10.15938 / j.emc.2021.04.007. The mutual inductance between the primary and secondary coils can be measured based on the load resistance and the output current, but in practical applications, the load resistance cannot be accurately measured online.

[0004] Literature YIN Jian, LIN Deyan, PARISINI T, et al. Front-end monitoring of the mutual inductance and load resistance in a series–series compensated wireless power transfer system [J]. IEEE Transactions on Power Electronics, 2016, 31(10): 7339-7352. A method of obtaining the mutual inductance between coils by changing the system operating frequency and measuring the input impedance amplitude and phase angle of the wireless charging system under non-resonant state was proposed. However, the output characteristics of the LCC / LCC system show a nonlinear relationship with the frequency, and the frequency modulation control is complicated.

[0005] The invention patent "A wireless charging device and charging method for electric vehicles loaded with auxiliary coils" (application number: 202011607155.3) proposes a method of adding a mutual inductance measurement module to the auxiliary coil to obtain the mutual inductance value. This method adds hardware circuits and significantly increases the cost.

[0006] In summary, the existing wireless charging system control technology still has the following problems:

[0007] 1. In actual work, the load resistance cannot be accurately measured online;

[0008] 2. The frequency modulation control of LCC / LCC wireless charging system is complex;

[0009] 3. Measuring mutual inductance through additional hardware is costly and bulky. Summary of the invention

[0010] The purpose of the present invention is to provide a method for measuring mutual inductance of an LCC / LCC type wireless charging system and a method for measuring mutual inductance thereof, and the technical problem solved is to accurately measure the mutual inductance value. The present invention provides a method for measuring the primary and secondary inductances, thereby laying a foundation for the optimized operation of the wireless charging system.

[0011] The technical solution of the present invention is: a wireless charging system for LCC / LCC type, wherein the topology of the wireless charging system includes a primary DC voltage source, an inverter, a compensation resonant circuit, a rectifier bridge, a filter circuit and a secondary DC voltage source; the total bus voltage of the primary DC voltage source is U i The total bus voltage of the secondary DC voltage source is U o The inverter is composed of four switch tubes forming a full-bridge structure, and the four switch tubes are respectively denoted as S P1 , S P2 , S P3 and S P4 , where S P1 and S P2 The leading bridge arm of the inverter, S P3 and S P4 The rectifier bridge is composed of four switch tubes forming a full-bridge structure, and the four switch tubes are respectively denoted as S S1 , S S2 , S S3 and S S4 , where S S1 and S S2 The leading arm of the rectifier bridge, S S3 and S S4 The compensating resonant circuit comprises a primary compensation resonant circuit and a secondary compensation resonant circuit, wherein the primary compensation resonant circuit comprises a series branch composed of a primary series compensation capacitor C1 and a transmitting coil L1 and a resonant capacitor C f1 After parallel connection with the compensation inductor L f1 The secondary compensation resonant circuit consists of a series branch consisting of the secondary series compensation capacitor C2 and the receiving coil L2 and the resonant capacitor C f2 After parallel connection with the compensation inductor L f2 The positive electrode of the primary DC voltage source is connected to the positive electrode of the inverter input terminal, the negative electrode of the primary DC voltage source is connected to the negative electrode of the inverter input terminal, and the output terminal of the inverter is connected to the input side of the compensation resonant circuit.

[0012] Furthermore, the filtering circuit includes a filtering capacitor C0.

[0013] A method for measuring mutual inductance of an LCC / LCC type wireless charging system, comprising sampling a load output current, comprising the following steps:

[0014] Step 1: Four drive signal inverter switches S on the primary side P1 The driving signal Q P1 , inverter switch tube S P2 The driving signal Q P2 , inverter switch tube S P3 The driving signal Q P3 and inverter switch tube S P4 The driving signal Q P4 , the switching frequency is recorded as f, where the drive signal Q P1 and Q P4 The time difference between them is 0, and the driving signal Q P2 Lagging behind the driving signal Q P1 , driving signal Q P3 Lagging behind the driving signal Q P4 , the hysteresis time is 1 / 2f, and the driving signal Q P1 , Q P2 , Q P3 and Q P4 They are used to drive the switch tube S P1 , S P2 , S P3 and S P4 ;

[0015] Step 2: Four drive signal rectifier bridge switches S on the secondary side s1 The driving signal Q s1 , rectifier bridge switch tube S s2 The driving signal Q s2 , rectifier bridge switch tube S s3 The driving signal Q s3 and the rectifier bridge switch tube S s4 The driving signal Q s4 , the switching frequency is recorded as f, where the drive signal Q s1 and Q s3 is high level, driving signal Q s2 and Q s4 is low level, the switch tube S s1 , S s3 Equivalent long closed, switch tube S s2 , S s4 The equivalent long open, the secondary side is equivalent to short circuit, the output current I Lf2 The average value after rectification and filtering is sampled, and the average value is set as I avg2 ;

[0016] Step 3: Obtain I by using the following average effective value conversion equation sRMS

[0017]

[0018] Step 4: The effective value of the current is recorded as I sRMS , the primary compensation inductor is recorded as L f1 , the secondary compensation inductor is denoted as L f2 , DC source voltage is U i , the switching frequency of the inverter is recorded as f, and the primary and secondary mutual inductance coefficient M is obtained by the following mutual inductance calculation equation to achieve the measurement of mutual inductance

[0019]

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The measurement of mutual inductance has nothing to do with the load;

[0022] 2. No additional frequency conversion operation is required;

[0023] 3. Accurate detection of mutual inductance can be achieved in the original system without adding or changing any hardware. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a topological diagram of the wireless charging system of the present invention;

[0025] Figure 2 It is the input and output AC voltage and current waveform diagram of the primary and secondary sides of the present invention; that is, when the secondary side is equivalently short-circuited in the embodiment, the input and output AC voltage and current waveform diagram of the primary and secondary sides of the circuit working waveform diagram.

[0026] Figure 3 It is a comparison diagram of the actual mutual inductance value and the measured mutual inductance value of the present invention; that is, the mutual inductance value measured in the embodiment and the actual mutual inductance value. DETAILED DESCRIPTION

[0027] The structure and effects of the nested dual-arm planar helical antenna of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0028] The present invention discloses a method for online measurement of mutual inductance of LCC / LCC type wireless charging. The method is based on the characteristics of a constant current source of an LCC / LCC type wireless charging system, utilizes the action of a secondary side switch tube to short-circuit a secondary side load, and implements online measurement of the mutual inductance of the wireless charging system by sampling and measuring the output current, thereby laying a foundation for optimized operation of the wireless charging system.

[0029] A method for measuring mutual inductance of LCC / LCC type wireless charging online. The topology of the wireless charging system involved in the method includes a primary DC voltage source, an inverter, a compensation resonant circuit, a rectifier bridge, a filter circuit and a secondary DC voltage source; the total bus voltage of the primary DC voltage source is U i The total bus voltage of the secondary DC voltage source is U o The inverter is composed of four switch tubes forming a full-bridge structure, and the four switch tubes are respectively denoted as S P1 , S P2 , S P3 and S P4 , where S P1 and S P2 The leading bridge arm of the inverter, S P3 and S P4 The rectifier bridge is composed of four switch tubes forming a full-bridge structure, and the four switch tubes are respectively denoted as S S1 , S S2 , S S3 and S S4 , where S S1 and S S2 The leading arm of the rectifier bridge, S S3 and S S4 The compensating resonant circuit comprises a primary compensation resonant circuit and a secondary compensation resonant circuit, wherein the primary compensation resonant circuit is composed of a series branch consisting of a primary series compensation capacitor C1 and a transmitting coil L1 and a resonant capacitor C f1 After parallel connection with the compensation inductor L f1 The secondary side compensation resonant circuit is composed of a series branch consisting of the secondary side series compensation capacitor C2 and the receiving coil L2 and the resonant capacitor C f2 After parallel connection with the compensation inductor L f2 The filter circuit is composed of a filter capacitor C0; the positive electrode of the (primary) DC voltage source is connected to the positive electrode of the inverter input terminal, the negative electrode of the (primary) DC voltage source is connected to the negative electrode of the inverter input terminal, and the inverter output terminal is connected to the input side of the compensation resonant circuit.

[0030] The control method of the present invention includes sampling the load output current, including the following steps:

[0031] Step 1: Four driving signals on the primary side, i.e. the inverter switch tube S P1 The driving signal Q P1 , inverter switch tube S P2 The driving signal Q P2 , inverter switch tube S P3 The driving signal Q P3 and inverter switch tube S P4 The driving signal Q P4, the switching frequency is recorded as f, where the drive signal Q P1 and Q P4 The time difference between them is 0, and the driving signal Q P2 Lagging behind the driving signal Q P1 , driving signal Q P3 Lagging behind the driving signal Q P4 , the hysteresis time is 1 / 2f, and the driving signal Q P1 , Q P2 , Q P3 and Q P4 They are used to drive the switch tube S P1 , S P2 , S P3 and S P4 , achieving full duty cycle output for the wireless charging system.

[0032] Step 2: Four drive signals on the secondary side, i.e. the rectifier bridge switch tube S s1 The driving signal Q s1 , rectifier bridge switch tube S s2 The driving signal Q s2 , rectifier bridge switch tube S s3 The driving signal Q s3 and the rectifier bridge switch tube S s4 The driving signal Q s4 , the switching frequency is recorded as f, where the drive signal Q s1 and Q s3 is high level, driving signal Q s2 and Q s4 is low level, the switch tube S s1 , S s3 Equivalent long closed, switch tube S s2 , S s4 The secondary side is equivalent to a short circuit. In order to ensure high reliability under high frequency conditions, the secondary side output current I Lf2 The average value after rectification and filtering is sampled, and the average value is set as I avg2 ,like Figure 1 shown.

[0033] Step 3: Obtain I by using the following average effective value conversion equation sRMS .

[0034]

[0035] Step 4: The effective value of the current is recorded as I sRMS , the primary compensation inductor is recorded as L f1 , the secondary compensation inductor is denoted as L f2 , DC source voltage is U i, the switching frequency of the inverter is recorded as f, and the primary and secondary mutual inductance coefficient M is obtained by the following mutual inductance calculation equation to achieve the measurement of mutual inductance

[0036]

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] 1. The measurement of mutual inductance has nothing to do with the load;

[0039] 2. No additional frequency conversion operation is required;

[0040] 3. Accurate detection of mutual inductance can be achieved in the original system without adding or changing any hardware.

[0041] Specifically, referring to the accompanying drawings, the wireless charging system topology involved in the present invention is as follows Figure 1 The present invention provides a method for online measurement of mutual inductance of an LCC / LCC type wireless charging system. The topology of the wireless charging system involved in the method includes a primary DC voltage source, an inverter, a compensation resonant circuit, a rectifier bridge, a filter circuit and a secondary DC voltage source; the total bus voltage of the primary DC voltage source is U i The total bus voltage of the secondary DC voltage source is U o The inverter is composed of four switch tubes forming a full-bridge structure, and the four switch tubes are respectively denoted as S P1 , S P2 , S P3 and S P4 , where S P1 and S P2 The leading bridge arm of the inverter, S P3 and S P4 The rectifier bridge is composed of four switch tubes forming a full-bridge structure, and the four switch tubes are respectively denoted as S S1 , S S2 , S S3 and S S4 , where S S1 and S S2 The leading arm of the rectifier bridge, S S3 and S S4 The compensating resonant circuit comprises a primary compensation resonant circuit and a secondary compensation resonant circuit, wherein the primary compensation resonant circuit is composed of a series branch consisting of a primary series compensation capacitor C1 and a transmitting coil L1 and a resonant capacitor C f1 After parallel connection with the compensation inductor L f1 The secondary side compensation resonant circuit is composed of a series branch consisting of the secondary side series compensation capacitor C2 and the receiving coil L2 and the resonant capacitor C f2 After parallel connection with the compensation inductor L f2The filter circuit is composed of a filter capacitor C0; the positive electrode of the (primary) DC voltage source is connected to the positive electrode of the inverter input terminal, the negative electrode of the (primary) DC voltage source is connected to the negative electrode of the inverter input terminal, and the inverter output terminal is connected to the input side of the compensation resonant circuit.

[0042] The control method of the present invention includes sampling the load output current, including the following steps:

[0043] Step 1: Four driving signals on the primary side, i.e. the inverter switch tube S P1 The driving signal Q P1 , inverter switch tube S P2 The driving signal Q P2 , inverter switch tube S P3 The driving signal Q P3 and inverter switch tube S P4 The driving signal Q P4 , the switching frequency is recorded as f, where the drive signal Q P1 and Q P4 The time difference between them is 0, and the driving signal Q P2 Lagging behind the driving signal Q P1 , driving signal Q P3 Lagging behind the driving signal Q P4 , the hysteresis time is 1 / 2f, and the driving signal Q P1 , Q P2 , Q P3 and Q P4 They are used to drive the switch tube S P1 , S P2 , S P3 and S P4 , achieving full duty cycle output for the wireless charging system.

[0044] Step 2: Four drive signals on the secondary side, i.e. the rectifier bridge switch tube S s1 The driving signal Q s1 , rectifier bridge switch tube S s2 The driving signal Q s2 , rectifier bridge switch tube S s3 The driving signal Q s3 and the rectifier bridge switch tube S s4 The driving signal Q s4 , the switching frequency is recorded as f, where the drive signal Q s1 and Q s3 is high level, driving signal Q s2 and Q s4 is low level, the switch tube S s1 , S s3 Equivalent long closed, switch tube S s2 , S s4The secondary side is equivalent to a short circuit. In order to ensure high reliability under high frequency conditions, the secondary side output current I Lf2 The average value after rectification and filtering is sampled, and the average value is set as I avg2 ,like Figure 1 shown.

[0045] Step 3: Obtain I by using the following average effective value conversion equation sRMS .

[0046]

[0047] Step 4: The effective value of the current is recorded as I sRMS , the primary compensation inductor is recorded as L f1 , the secondary compensation inductor is denoted as L f2 , DC source voltage is U i , the switching frequency of the inverter is recorded as f, and the primary-secondary mutual inductance coefficient M is obtained through the following mutual inductance calculation equation to achieve the measurement of mutual inductance.

[0048]

[0049] For the dual LCC system, its LC circuit is equivalent to a low-pass filter, so its harmonic components cannot enter the transformer circuit, so the fundamental and harmonic components of the input and output currents should be discussed separately. The fundamental component of the primary input current is determined by the secondary voltage, and the harmonic component is determined by the primary voltage; the fundamental component of the secondary output current is determined by the primary voltage, and the harmonic component is determined by the secondary voltage. Therefore, when the load is short-circuited, the secondary voltage is 0, and the output AC current only has the fundamental component. The output effective value at this time is used to infer the numerical value of the mutual inductance M with high accuracy. Figure 2 As shown, it is the input and output AC voltage and current waveform of the primary and secondary sides. When the load is equivalently short-circuited, the primary current has only harmonic components and the secondary current has only fundamental components.

[0050] In order to verify the method of online measurement of mutual inductance of LCC / LCC type wireless charging system proposed in this invention, a MATLAB / Sinmulink simulation model of wireless charging system was built. The circuit parameters of the simulation model are as follows: the total bus voltage of the primary DC voltage source is Ui, which is 300V, and the total bus voltage of the secondary DC voltage source is Uo, which is 300V; the transmitting coil L1 is 240uH, the receiving coil L2 is 30uH, the primary series compensation capacitor C1 is 46.58nF, the secondary series compensation capacitor C2 is 365.2nF, and the primary parallel compensation capacitor C f1 The secondary side is connected in parallel with the compensation capacitor C f2 is 171.86nf; the primary side series compensation inductor L f1 is 34.74uH, the secondary side series compensation inductor Lf2 is 20.4uH. In the simulation, M is set to 9.76uH, and M is calculated and verified according to the sampled current value, such as Figure 3 As shown, the results show that the method of determining the mutual inductance M by measuring the average current value through the load equivalent short circuit method is more accurate.

Claims

1. A mutual inductance measurement method for an LCC / LCC type wireless charging system, wherein the topology of the wireless charging system includes a primary DC voltage source, an inverter, a compensation resonant circuit, a rectifier bridge, a filter circuit and a secondary DC voltage source; the total bus voltage of the primary DC voltage source is U i The total bus voltage of the secondary DC voltage source is U o The inverter is composed of four switch tubes forming a full-bridge structure, and the four switch tubes are respectively denoted as S P1 , S P2 , S P3 and S P4 ,in, S P1 and S P2 The leading bridge arm of the inverter, S P3 and S P4 The rectifier bridge is composed of four switch tubes forming a full-bridge structure, and the four switch tubes are respectively denoted as S S1 , S S2 , S S3 and S S4 , where S S1 and S S2 The leading arm of the rectifier bridge, S S3 and S S4 The compensating resonant circuit comprises a primary compensation resonant circuit and a secondary compensation resonant circuit, wherein the primary compensation resonant circuit comprises a series branch composed of a primary series compensation capacitor C1 and a transmitting coil L1 and a resonant capacitor C f1 After parallel connection with the compensation inductor L f1 The secondary compensation resonant circuit consists of a series branch consisting of the secondary series compensation capacitor C2 and the receiving coil L2 and the resonant capacitor C f2 After parallel connection with the compensation inductor L f2 The positive electrode of the primary DC voltage source is connected to the positive electrode of the inverter input terminal, the negative electrode of the primary DC voltage source is connected to the negative electrode of the inverter input terminal, and the inverter output terminal is connected to the input side of the compensation resonant circuit; the filter circuit includes a filter capacitor C0; it is characterized in that the mutual inductance measurement method is used for sampling the load output current of the LCC / LCC type wireless charging system, and includes the following steps: Step 1: Four drive signal inverter switches S on the primary side P1 The driving signal Q P1 , inverter switch tube S P2 The driving signal Q P2 , inverter switch tube S P3 The driving signal Q P3 and inverter switch tube S P4 The driving signal Q P4 , the switching frequency is recorded as f, where the drive signal Q P1 and Q P4 The time difference between them is 0, and the driving signal Q P2 Lagging behind the driving signal Q P1 , driving signal Q P3 Lagging behind the driving signal Q P4 , the lag time is 1 / (2f), the driving signal Q P1 , Q P2 , Q P3 and Q P4 They are used to drive the switch tube S P1 , S P2 , S P3 and S P4 ; Step 2: Four drive signal rectifier bridge switches S on the secondary side s1 The driving signal Q s1 , rectifier bridge switch tube S s2 The driving signal Q s2 , rectifier bridge switch tube S s3 The driving signal Q s3 and the rectifier bridge switch tube S s4 The driving signal Q s4 , the switching frequency is recorded as f, where the drive signal Q s1 and Q s3 is high level, driving signal Q s2 and Q s4 is low level, the switch tube S s1 , S s3 Equivalent long closed, switch tube S s2 , S s4 The equivalent long open, the secondary side is equivalent to short circuit, the output current I Lf2 The average value after rectification and filtering is sampled, and the average value is set as I avg2 ; Step 3: Obtain I by using the following average effective value conversion equation sRMS ； Step 4: The effective value of the current is recorded as I sRMS , the primary compensation inductor is recorded as L f1 , the secondary compensation inductor is denoted as L f2 , DC source voltage is U i , the switching frequency of the inverter is recorded as f, and the primary and secondary mutual inductance coefficient M is obtained by the following mutual inductance calculation equation to achieve the measurement of mutual inductance 。

Images