Inductive power transmission system with rectifier fault protection and fault detection method

Abstract

The present invention discloses an inductive power transmission system with rectifier fault protection and a fault detection method, wherein the inductive power transmission system comprises an inverter, a primary side compensation network, a primary side coil, a secondary side coil, a secondary side compensation network, a bridge rectifier and a rectifier fault protection circuit, wherein the rectifier fault protection circuit comprises a protection inductor, and the rectifier fault protection circuit is connected in parallel to two input ends of the bridge rectifier. The present invention can prevent the entire system from being damaged after a single tube open circuit fault occurs in the rectifier, thereby improving the reliability and safety of the system.

Description

Technical Field

[0001] The present invention belongs to the field of wireless power transmission, and more specifically, relates to an inductive power transmission system with rectifier fault protection and a fault detection method. Background Art

[0002] Due to the rapid development of new energy, the traditional fuel vehicle market is gradually being replaced by new energy electric vehicles. Wireless power charging technology is becoming more and more popular in the field of electric vehicle charging due to its convenience and efficiency. However, the safety issues of new technologies and equipment have been questioned due to the demand for high reliability. As an electronic device, the wireless power transmission system contains a large number of semiconductor components and has a higher failure rate than traditional mechanical equipment in recent years. In order to reduce the complexity and cost of the inductive power transfer (IPT) system, uncontrolled rectifiers are usually used as the AC / DC part of the system in the market, resulting in the most common failure of the system being the failure of a single diode, including a single diode open circuit failure or a short circuit failure.

[0003] When a diode in a commonly used SS-type IPT system rectifier fails, it should be repaired as soon as possible. Therefore, it is necessary to perform fault protection and detection on the uncontrolled rectifier in the IPT system.

[0004] There are many traditional power electronics fault diagnosis methods, including: (1) signal-based classes, such as wavelet transform and DS (Dempster Shafer, DS) evidence theory fault diagnosis methods, harmonic analysis methods, residual change rate methods, current distortion characteristics methods; (2) algorithm-based classes, such as convolutional neural network methods, random forest algorithms, shape sub-feature transformation algorithm fault diagnosis methods, etc.; (3) hybrid logic dynamic fault diagnosis methods based on mathematical modeling, etc.

[0005] Unlike conventional power electronics diagnostic methods that operate at industrial frequencies, IPT systems operate in the switching frequency range of tens to hundreds of kilohertz. After an electronic product fails, the transient process time of the voltage and current of each component is short, and the system needs to initiate protection actions within tens of microseconds. A fault-tolerant SRC topology is proposed in the prior art to enhance the reliability of the inverter. When a single IGBT in the inverter is short-circuited, the system quickly builds a voltage multiplier rectifier through hardware to restore the system output, and the whole process is completed within 10 microseconds. The prior art also proposes to derive the rotor current of the brushless synchronous motor through parameter identification, and extract the second harmonic component of the rotor current to accurately locate the fault position of the rotating rectifier diode. The prior art also proposes to divide the IPT system into three modes: no load, safe operation, and fault state. The system automatically powers off when an external magnet that changes the coupling coil parameters is detected. The change of the transmitted power over time is monitored in real time to determine whether a fault occurs on the receiving side. The prior art also proposes to improve the reliability and fault tolerance of the system by balancing the power distribution between the multi-stage transmitting and receiving coils. This is achieved by introducing a mid-stage resonator (MSR), which allows the system to operate under various fault conditions including single transmitting coil, single receiving coil and dual receiving coil open circuit faults. It is also proposed in the prior art to improve the reliability of the system by introducing a directional switch in the AC-DC converter. A fault-tolerant method is also proposed in the prior art for a dual active bridge (DAB) DC-DC converter, which has a low-power bypass arm on the primary side and the secondary side. A fault diagnosis method and reconstruction scheme for an isolated phase-shifted full-bridge DC-DC converter is also proposed in the prior art, by adding an auxiliary winding in the transformer to obtain the secondary voltage as a fault feature to detect the operating status of the converter. The above methods mitigate the impact of device-level faults on the system to a certain extent, but they do not take into account the problem of system damage at the moment of fault, nor do they take into account system protection and fault detection at the same time, which is unacceptable for actual IPT system scenarios. In addition, complex fault detection methods will increase the difficulty and cost of hardware design. Summary of the invention

[0006] In view of the above defects or improvement needs of the prior art, the present invention provides an inductive power transmission system with rectifier fault protection and a fault detection method, which can prevent the entire system from being damaged after a single-tube open-circuit fault occurs in the rectifier, thereby improving the reliability and safety of the system.

[0007] To achieve the above-mentioned purpose, according to one aspect of the present invention, there is provided an inductive power transmission system with rectifier fault protection, comprising an inverter, a primary side compensation network, a primary side coil, a secondary side coil, a secondary side compensation network, a bridge rectifier and a rectifier fault protection circuit, wherein the output end of the inverter is connected to the primary side coil through the primary side compensation network, and the secondary side coil is connected to the bridge rectifier through the secondary side compensation network; the primary side compensation network comprises a primary side series compensation capacitor, and the secondary side compensation network comprises a secondary side series compensation capacitor; the primary side coil and the secondary side coil are coupled; the bridge rectifier comprises a first diode, a second diode, a third diode and a fourth diode, and in the positive half cycle of the bridge rectifier, the first diode and the fourth diode are turned on, and in the negative half cycle of the bridge rectifier, the second diode and the third diode are turned on; the rectifier fault protection circuit comprises a protection inductor, and the rectifier fault protection circuit is connected in parallel to the two input ends of the bridge rectifier.

[0008] Preferably, the capacitance value of the primary-side series compensation capacitor is adjusted so that the total input impedance of the inductive power transmission system is weakly inductive.

[0009] Preferably, the step of adjusting the capacitance value of the primary-side series compensation capacitor so that the total input impedance of the inductive power transmission system is weakly inductive comprises the following steps:

[0010] Calculating the resonance value of the primary-side series compensation capacitor;

[0011] The adjustment value of the primary-side series compensation capacitor is calculated to obtain the actual value of the primary-side series compensation capacitor, so that the total input impedance of the inductive power transmission system is weakly inductive.

[0012] Preferably,

[0013] ;

[0014] ;

[0015] ;

[0016] ;

[0017] in, is the total input impedance of the inductive power transfer system, for The real part of for The imaginary part of Indicates plural, is the system resonant angular frequency, is the self-inductance of the primary side coil, is the actual value of the primary side series compensation capacitor, is the resonant value of the primary side series compensation capacitor, is the adjustment value of the primary side series compensation capacitor, is the mutual inductance of the primary side coil and the secondary side coil, is the inductance value of the protection inductor, is the equivalent resistance of the bridge rectifier, is the internal resistance of the secondary coil, is the internal resistance of the protection inductor, Auxiliary calculation value.

[0018] Preferably, the inductive power transmission system is a constant current output type inductive power transmission system.

[0019] Preferably, the capacitance value of the primary-side series compensation capacitor is adjusted so that the impedance angle of the total input impedance of the inductive power transmission system is in the range of (0,10°].

[0020] According to another aspect of the present invention, a fault detection method for any of the above-mentioned inductive power transmission systems is provided, monitoring the current of the protection inductor, and determining the diode fault type and location of the bridge rectifier according to the current of the protection inductor.

[0021] Preferably, the step of determining the diode fault type and position of the bridge rectifier according to the current of the protection inductor comprises the following steps:

[0022] S1, obtaining the current of the protection inductor;

[0023] S2, performing Fourier decomposition on the current of the protection inductor to obtain a DC component, an AC component and an effective value of the current of the protection inductor, and calculating a DC threshold coefficient and an AC threshold coefficient;

[0024] S3, determining the diode fault type and position of the bridge rectifier according to the DC component, AC component, effective value, DC threshold coefficient and AC threshold coefficient of the current of the protection inductor.

[0025] Preferably, the method of determining the diode fault type and position of the bridge rectifier according to the DC component, AC component, effective value, DC threshold coefficient and AC threshold coefficient of the current of the protection inductor comprises the steps of:

[0026] S31, if the current of the protection inductor has a DC component, it is determined that the bridge rectifier has a fault and S32 is executed; otherwise, it is determined that the bridge rectifier has not a fault and the process ends;

[0027] S32, determining whether the DC threshold coefficient is greater than zero. If the DC threshold coefficient is greater than zero, determining that one of the first diode and the fourth diode of the bridge rectifier is faulty. Otherwise, determining that one of the second diode and the third diode of the bridge rectifier is faulty.

[0028] S33, if the current of the protection inductor has an AC component, it is determined that the bridge rectifier has an open circuit fault; otherwise, it is determined that the bridge rectifier has a short circuit fault.

[0029] Preferably, the calculation formula for Fourier decomposition of the current of the protection inductor is:

[0030] ;

[0031] ;

[0032] in, is the current of the protection inductor, is the DC component of the current of the protection inductor, The current of the protection inductor is The effective value of the subharmonic components, The current of the protection inductor is The phase angle of the subharmonic component, =1,2,…∞, is the effective value of the current of the protection inductor;

[0033] The calculation formulas of the DC threshold coefficient and the AC threshold coefficient are:

[0034] ;

[0035] in, is the DC threshold coefficient, is the AC threshold coefficient, is the AC component of the current of the protection inductor.

[0036] In general, compared with the prior art, the above technical solution conceived by the present invention is that after a diode open-circuit failure occurs, the input voltage of the rectifier no longer reaches the boundary voltage, and compared with the traditional system, the steady-state voltage is significantly reduced, thereby providing an effective protection mechanism to prevent the entire system from being damaged after a single-tube open-circuit failure occurs in the rectifier, thereby improving the reliability and safety of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the circuit diagram of the traditional SS type IPT system;

[0038] Figure 2It is the primary side circuit of the decoupling circuit of the traditional SS type IPT system;

[0039] Figure 3 It is the secondary side circuit of the decoupling circuit of the traditional SS type IPT system;

[0040] Figure 4 When Equivalent current path of the secondary side fault channel in the traditional SS type IPT system after an open circuit fault;

[0041] Figure 5 When After an open circuit fault, the equivalent current path of the secondary side normal channel in the traditional SS type IPT system;

[0042] Figure 6 yes Changes in rectifier input electrical quantities after an open circuit fault;

[0043] Figure 7 yes Changes in rectifier input electrical quantities after an open circuit fault;

[0044] Figure 8 When The forward current path of the secondary side circuit after a short circuit fault occurs;

[0045] Fig. 9 When The reverse current path of the secondary side loop after a short circuit fault occurs;

[0046] Fig.10 yes Changes in the electrical quantity output by the system inverter before and after the short-circuit fault;

[0047] Fig.11 yes Changes in the electrical quantity input to the system rectifier before and after the short-circuit fault;

[0048] Fig.12 yes Schematic diagram of the protection effect on the input side of the rectifier after an open circuit fault;

[0049] Fig.13 It is a main circuit of an improved topology structure of an IPT system according to an embodiment of the present invention;

[0050] Fig.14 is a fundamental wave equivalent circuit of an improved topology structure of an IPT system according to an embodiment of the present invention;

[0051] Fig.15 is a curve of AC transmission efficiency and protection inductance variation under load variation of the IPT system of an embodiment of the present invention;

[0052] Fig.16 is the spatial structure of the coupling coil of the IPT system of the embodiment of the present invention;

[0053] Fig.17 is the internal structure of the coupling coil of the IPT system of the embodiment of the present invention;

[0054] Fig.18 Schematic diagram of a fault detection method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0056] In the description of the embodiments of the present application, the terms "first", "second", "third", and "fourth" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", "third", and "fourth" may explicitly or implicitly include at least one of the features. "Multiple" means at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0057] The terms "including" and "having" and any variations thereof in the embodiments of the present invention are intended to cover non-exclusive inclusions. For example, a process, method, apparatus, product or equipment comprising a series of steps or modules is not necessarily limited to those steps or modules clearly listed, but may include other steps or modules not clearly listed or inherent to these processes, methods, products or equipment.

[0058] The naming or numbering of the steps in the embodiments of the present invention does not mean that the steps in the method flow must be executed in the time / logical sequence indicated by the naming or numbering. The execution order of the named or numbered process steps can be changed according to the technical purpose to be achieved, as long as the same or similar technical effects can be achieved.

[0059] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0060] The present invention provides an inductive power transmission system with rectifier fault protection and a fault detection method, which are respectively described below.

[0061] (1) Rectifier failure analysis in traditional series-series compensation constant current output IPT system

[0062] A. System Structure

[0063] The IPT system consists of four key parts: DC / AC high-frequency inverter, electromagnetic loosely coupled coil (primary side coil and secondary side coil), AC / DC rectifier output, reactive power compensation and output filter circuit. Figure 1 As shown, the DC voltage source is converted into AC power by a high-frequency inverter and enters the primary side compensation network. Then, the secondary side coil is exposed to the alternating magnetic field generated by the primary side coil, generating an induced potential to supply power to the back-end network. Since the AC power generated on the secondary side is high frequency, it needs to be converted into DC power by a rectifier for use by the load. Among them, ~ Stands for Silicon Carbide Field Effect Transistor (SiC MOSFET), L p , L s Represent the self-inductance of the primary coil and the secondary coil respectively, r p , r s Represent the internal resistance of the primary coil and the secondary coil respectively. C p , C ss They represent the primary side series compensation capacitor and the secondary side series compensation capacitor respectively. M represents the mutual inductance of the coupled coils, R eq represents the equivalent resistance of the bridge rectifier (which does not actually exist), R L represents the load resistance, D 1~ D 4 constitutes a full-bridge uncontrolled rectifier, C f Represents the filter capacitor. In the positive half cycle of the bridge rectifier, the first diode D 1. The fourth diode is turned on D 4. In the negative half cycle of the bridge rectifier, the second diode D 2. The third diode D 3Conduction.

[0064] In order to achieve the zero power absorption (ZPA) and constant current output characteristics of the traditional SS compensation topology, the system parameters must meet the following resonant conditions:

[0065] ;

[0066] in, is the system resonant angular frequency.

[0067] To further decouple Figure 1 The mutual inductance in the circuit shown can be converted into an equivalent circuit on the primary or secondary side, as Figure 2 and Figure 3 shown.

[0068] After decoupling, the equivalent circuit of the secondary side on the primary side consists of reflected impedance Z ref The equivalent circuit of the primary side on the secondary side is represented by a controlled voltage source U s The specific expression is as follows:

[0069] ;

[0070] The corresponding impedance of the system can be obtained:

[0071] ;

[0072] The corresponding electrical quantities of each part of the system are:

[0073] ;

[0074] in Z s represents the total impedance of the secondary side circuit, Z in represents the total input impedance of the system, I p is the current in the primary coil, I s is the current in the secondary coil, Indicates the output voltage of the inverter. Usually, the resistance in the coil is between 0.15 and 0.25Ω. By simplifying I s , we can get:

[0075] ;

[0076] According to the derivation results of formulas (3) and (5), it can be observed that the equivalent resistance of the secondary side load is inversely proportional to the total input impedance of the system. The current of the secondary side coil is independent of the load and is completely determined by the mutual inductance of the coil, the resonant frequency and the DC input voltage.

[0077] At the same time, the efficiency of AC transmission is expressed as :

[0078] ;

[0079] B. Diode Failure Analysis

[0080] a. Single diode open circuit fault

[0081] When a diode fails as an open circuit, two fault conditions can occur: D 1 and D 4 open circuit, or D 2 and D 3 is open circuit. If any diode in the same channel is open circuited, the electrical characteristics of the rectifier will be exactly the same. D 1 open circuit as an example, such as Figure 4 and Figure 5 As shown, the focus is on the transient and steady-state processes of the fault. D 2 and D 3 will produce an open circuit with D 1 and D 4 Opposite results.

[0082] Fault channel stage: Figure 4 and Figure 5 As shown, in D 1 After the circuit is opened, the secondary side current path can be divided into a fault channel and a normal channel. Assume D 1 open circuit, D 1 The resistance across the terminals tends to a very high value, which is used in the analysis R eq+ express.

[0083] Using the fundamental wave analysis method, after replacing the inverter output voltage with its fundamental wave component, U s The expression is as follows:

[0084] ;

[0085] in, is the DC input power supply voltage, For time.

[0086] like Figure 6 As shown, when I s >0, if D 1 Suddenly open the road, I s will drop to zero quickly. According to the voltage formula on the secondary coil , d represents the differential, and obviously a high peak voltage will appear on the coil. According to formula (4), U s andI p The current in the primary coil will not undergo drastic changes. U s Keep constant, C s The voltage on the secondary coil will not change suddenly. Applying the Thevenin theorem, a spike voltage with the opposite polarity to the voltage on the secondary coil will appear on the secondary coil. U ab , is the voltage between the two input terminals of the bridge rectifier, that is, node a With Node b The voltage between.

[0087] In order to quantify the failure U ab Assuming that the internal resistance of the coil is negligible, the Kirchhoff voltage law (KVL) equation for the secondary circuit of the fault path is as follows:

[0088] ;

[0089] in, For the moment The instantaneous value of the secondary circuit current, For the moment The instantaneous value of the rectifier input voltage, For the moment The instantaneous value of the induced electromotive force in the secondary circuit, E It is an auxiliary calculation value and has no actual physical meaning.

[0090] because , in the fault channel U ab Over time, U ab ( t ) will decay to zero. The corresponding time domain solution is:

[0091] ;

[0092] in Respectively represent right t The first and second derivatives of , are the coefficients of the homogeneous equation, is the specific solution of the rectifier input voltage. Without initial values, it is impossible to obtain an exact analytical expression. However, The steady-state value tends to .becauseR eq+ tends to a very high value, the fault channel U ab will exceed the safety range.

[0093] Normal channel stage: The current in the fault channel is blocked and tends to zero. According to the law of conservation of energy, the current in the normal channel will also be very small. U ab When switching channels, a significant voltage difference Δ is formed. U ab When charging the filter capacitor, according to its current characteristics , is the filter capacitor branch current, For filter capacitors, small I s This results in an increase in the time required to fully charge, which may even exceed half a cycle. After the filter capacitor is fully charged, the charge on the plates remains constant, producing a stable voltage effect.

[0094] like Figure 7 As shown, when D 2 When open circuit, D 1 and D 4 conduction. The current usually drops to zero and then transitions to the fault path without any sudden current change. Therefore, in this process U ab No spike voltage will be experienced. D 1Open circuit is the opposite; U ab ( t ) increases in the opposite direction until it exceeds the safety range.

[0095] b. Single diode short circuit fault

[0096] When a diode fails in a short circuit, the normal current path of the faulty diode remains unchanged; however, the current path of the opposite bridge arm shorts out the secondary side. D 1 short circuit fault as an example, Figure 8 and Fig. 9 As shown, according to formulas (4) and (5), the secondary loop current is only , M and U dc The effect is independent of the load. Figure 8 In the positive half cycle after the fault I s The forward current path is usually provided by the inverter; the secondary current flows from node b Inflow, through D 3. D1, then by Fig. 9 Nodes in a At this time, the secondary circuit is short-circuited. R eq According to formula (4), I p The inverter output is as follows: Fig.10 As shown, the rectifier input is Fig.11 After the fault, the entire system is converted to half-bridge output, and the DC side output current is shown in formula (10):

[0097] ;

[0098] in Represents the load current after a diode short-circuit fault, Represents the load current during normal operation.

[0099] Similarly, when the reverse channel D2 or D3 of the rectifier is short-circuited, the reverse current path is not affected, the forward current path is short-circuited, the rectifier changes to half-bridge operation mode, and the DC output becomes half of that in normal operation.

[0100] (2) Analysis of open circuit protection SS compensation topology

[0101] In the previous section, the consequences and risks of a single diode failure in the rectifier of an SS-type inductive power transfer (IPT) system were explored in depth. An open-circuit failure of a diode may cause damage to the rectifier, inverter, and various compensation devices, while a short-circuit failure mainly affects the output capacity of the system.

[0102] In order to prevent the irreversible damage to the system caused by an open-circuit failure of a single diode in the SS-type IPT system, an embodiment of the present invention introduces an enhanced topology structure, which is intended to protect against an open-circuit failure of the rectifier.

[0103] like Fig.13 As shown, an inductive power transmission system with rectifier fault protection according to an embodiment of the present invention includes an inverter, a primary side compensation network, a primary side coil, a secondary side coil, a secondary side compensation network, a bridge rectifier and a rectifier fault protection circuit, wherein the output end of the inverter is connected to the primary side coil through the primary side compensation network, and the secondary side coil is connected to the bridge rectifier through the secondary side compensation network; the primary side compensation network includes a primary side series compensation capacitor , the secondary side compensation network includes the secondary side series compensation capacitor ; The primary side coil and the secondary side coil are coupled; The bridge rectifier includes a first diode D 1. The second diode D 2. The third diode D 3 and the fourth diodeD 4. In the positive half cycle of the bridge rectifier, the first diode and the fourth diode are turned on, and in the negative half cycle of the bridge rectifier, the second diode and the third diode are turned on; the rectifier fault protection circuit includes a protection inductor, and the rectifier fault protection circuit is connected in parallel to the two input ends of the bridge rectifier.

[0104] Fig.13 middle, To protect the inductance of the inductor, To protect the internal resistance of the inductor.

[0105] This novel topology connects a protection inductor in parallel before the rectifier. In the event of an open-circuit diode failure, the protection inductor establishes a new circuit with the secondary side, thus ensuring continued safe and stable operation of the system. Fig.12 As shown in Figure 1, in a system equipped with a protection inductor, after a diode open-circuit fault occurs, the input voltage of the rectifier no longer reaches the boundary voltage, and the steady-state voltage is significantly reduced compared to a traditional system, thereby providing an effective protection mechanism.

[0106] A. Topological analysis

[0107] The system topology is simplified through fundamental wave analysis, and its equivalent circuit is as follows: Fig.14 As shown, the resonant angular frequency of the system is defined , the frequency satisfies the following equation:

[0108] ;

[0109] in, is the load resistance.

[0110] For the calculation and simplification of the equation, the primary reactance, secondary reactance, secondary parallel inductive reactance, mutual inductive reactance, equivalent impedance and reflected impedance are expressed as and Z ref , as shown in formula (12):

[0111] ;

[0112] In formula (13), and Represent the actual value, resonant value and adjustment change of the primary side compensation capacitor respectively:

[0113] ;

[0114] in, Indicates plural, for The real part of for The imaginary part of , Auxiliary calculation value.

[0115] Since the protection inductor is introduced, according to equation (12), this will increase the capacitive component of the reflected impedance, which does not conform to the inverter ZVS (zero voltage switching technology) operation under the resonance conditions of the primary and secondary sides. Therefore, it is necessary to adjust C p The total input reactance is weakly inductive. Specifically, the system input impedance angle is in the range of (0,10°):

[0116] ;

[0117] According to Kirchhoff's voltage law, the calculation results of the transmitting coil current and the receiving coil current are shown in formula (14).

[0118] When estimating the gain of the system, it can be observed that the internal resistance of the system coil and the protection inductor has a relatively small effect on the impedance modulus of each part. Therefore, in order to simplify the calculation process, the influence of these internal resistances can be ignored. Based on this, the DC output current gain of the system is It can be expressed according to formula (15). This not only makes the calculation simpler, but also highlights the impact of other key system parameters on the gain:

[0119] ;

[0120] AC side transmission efficiency of the system The coil loss and the internal resistance of the protection inductor are taken into account. When only these factors are considered, the transmission efficiency of the system AC side changes with the load as shown below: Fig.15 As shown in the figure, there is an optimal load area in the system, which makes the AC transmission efficiency reach the maximum value, and when the load exceeds the optimal value, the transmission efficiency gradually decreases. In addition, a smaller protection inductor value will share more output current, which will affect the transmission capacity and efficiency of the system:

[0121] ;

[0122] in, I p , I s , I 1 and I 2 represent the effective values ​​of the primary side, secondary side coil current, current passing through the protection inductor branch and rectifier input current respectively; R eq , r p , r s and r proThey represent the equivalent load including the rectifier, the internal resistance of the primary coil, the internal resistance of the secondary coil, and the internal resistance of the protective inductor. Auxiliary calculation value.

[0123] In order to ensure that the DC input current remains basically unchanged after the diode has an open circuit fault, the protection inductor value needs to satisfy formula (17):

[0124] ;

[0125] in is the switching frequency of the system, R L is the load resistance.

[0126] Table 1. Coupler parameters

[0127] parameter value Vertical distance between plates h (mm) 130 Coil turns (N) 14 Coil internal width C1 (mm) 280 Coil outer width C2 (mm) 530 Coupling coefficient K 0.24 Wire diameter 0.00785*800 ;

[0128] like Fig.16 and Fig.17 As shown, in one embodiment, two square coil plates are used as a coupling mechanism, the z-axis transmission distance is 130 mm, and under normal working conditions, there is no offset in the x-axis and y-axis directions, and the corresponding coil mutual inductance and harmonic plate coupling coefficient are 29.45 μH and 0.24 respectively. The size parameters of the plate are shown in Table 1. The coil in the plate is wound with 0.00785*800 square millimeter Litz wire, with 19 turns.

[0129] (3) Improved single diode fault detection method

[0130] In the previous section, an IPT system containing a protective inductor was analyzed, which is protected after a diode failure. However, in the event of a system failure, it becomes critical to identify and repair it. This section will focus on the diagnosis method of rectifier failure. It is relatively rare for a single-channel IPT charging device to have multiple diodes fail at the same time. The system is likely to be processed after a diode failure. Therefore, the proposed single diode fault detection technology for IPT charging equipment is highly practical and significant.

[0131] Due to the intermediate frequency characteristics of wireless charging technology, traditional industrial frequency power electronic fault detection technology has limitations. In order to reduce the hardware standard of fault detection at intermediate frequency, a fault detection method based on eigenvalue DC bias is proposed. The type and location of the fault are determined by measuring the root mean square and DC components of the eigenvalue. According to the qualitative and quantitative analysis of the protection type IPT system in the previous section, the protection inductor current is used to detect the fault type and location of the fault. I 1 as a characteristic quantity after a fault occurs. Monitor the current of the protection inductor I 1. According to the current of the protection inductorI 1Determine the type and location of diode failure in the bridge rectifier.

[0132] Through simulation and theoretical analysis, when a diode fails in an open circuit, there will be an AC component in its characteristic current that cannot be ignored. K ac The theoretical value is not less than 23.7%. When a short circuit occurs, there is no AC component in the theoretical analysis, and the DC threshold coefficient K dc is ±1.

[0133] The single diode fault judgment process is as follows Fig.18 As shown, the sensor is first used to collect the protection inductor current, and the DC component, total RMS value and RMS value of the AC component are obtained through signal processing, and then substituted into formula (20) to calculate the AC and DC threshold coefficients. If the DC component exists, the system rectifier is faulty. Otherwise, the system is normal, and the loop continues to detect whether the DC threshold coefficient exceeds the limit value. When the DC component is detected in the feature quantity, according to K dc The fault location can be determined by the positive or negative value of the signal, and the fault type can be determined by the presence or absence of AC component.

[0134] The fault characteristic quantity of this method will not be affected by the drift of system parameters. It uses the proportion of electrical quantity components after the fault as the basis for judgment and has better stability.

[0135] The specific steps include:

[0136] S1, obtain the current of the protection inductor I 1.

[0137] S2, current for protection inductor I 1 Perform Fourier decomposition to obtain the DC component, AC component and effective value of the current of the protection inductor, and calculate the DC threshold coefficient and the AC threshold coefficient.

[0138] Perform Fourier decomposition to obtain:

[0139] ;

[0140] Its effective value satisfies the relationship of formula (19):

[0141] ;

[0142] The specific proof of (19) will not be repeated here. and is the effective value and phase angle of the kth harmonic component of the protection inductor current. (k = 1, 2, ... ∞)

[0143] The DC threshold coefficient and AC threshold coefficient of the fault characteristic quantity are defined to determine the fault type and location of a single diode, as shown in formula (20):

[0144] ;

[0145] in I 1_dc To protect the DC component of the inductor current, I 1_ac To protect the AC component of the inductor current, I 1_RMS To protect the effective value of the inductor current.

[0146] S3, determining the diode fault type and position of the bridge rectifier according to the DC component, AC component, effective value, DC threshold coefficient and AC threshold coefficient of the current of the protection inductor.

[0147] The specific sub-steps include:

[0148] S31, if the current of the protection inductor has a DC component, it is determined that the bridge rectifier fails and S32 is executed; otherwise, it is determined that the bridge rectifier does not fail and the process ends.

[0149] S32, determining whether the DC threshold coefficient is greater than zero. If the DC threshold coefficient is greater than zero, determining that one of the first diode and the fourth diode of the bridge rectifier is faulty. Otherwise, determining that one of the second diode and the third diode of the bridge rectifier is faulty.

[0150] S33, if the current of the protection inductor has an AC component, it is determined that the bridge rectifier has an open circuit fault, otherwise, it is determined that the bridge rectifier has a short circuit fault.

[0151] In summary, the present invention proposes an inductive power transmission system and a fault detection method with rectifier fault protection, which prevents the entire system from being damaged after a single-tube open-circuit fault occurs in the rectifier, thereby improving the reliability and safety of the system. Through qualitative and quantitative analysis of a single diode fault in the rectifier in a traditional SS-type IPT system, the hazards and impacts of the diode fault on the system are first summarized, and the necessity of the proposed protection method is emphasized. Then, a rectifier protection circuit and a fault detection method of an embodiment of the present invention are proposed, and the feasibility of the method is obtained through simulation results and theoretical deduction. The proposed method will not affect the parameter configuration of the traditional SS-type IPT system, and has the characteristics of low cost and significant protection effect.

[0152] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An inductive power transmission system with rectifier fault protection, characterized in that: The invention comprises an inverter, a primary side compensation network, a primary side coil, a secondary side coil, a secondary side compensation network, a bridge rectifier and a rectifier fault protection circuit, wherein the output end of the inverter is connected to the primary side coil through the primary side compensation network, and the secondary side coil is connected to the bridge rectifier through the secondary side compensation network; the primary side compensation network comprises a primary side series compensation capacitor, and the secondary side compensation network comprises a secondary side series compensation capacitor; the primary side coil and the secondary side coil are coupled; the bridge rectifier comprises a first diode, a second diode, a third diode and a fourth diode, and in the positive half cycle of the bridge rectifier, the first diode and the fourth diode are turned on, and in the negative half cycle of the bridge rectifier, the second diode and the third diode are turned on; the rectifier fault protection circuit comprises a protection inductor, and the rectifier fault protection circuit is connected in parallel to the two input ends of the bridge rectifier; Adjusting the capacitance value of the primary-side series compensation capacitor so that the total input impedance of the inductive power transmission system is weakly inductive; The step of adjusting the capacitance value of the primary-side series compensation capacitor so that the total input impedance of the inductive power transmission system is weakly inductive comprises the following steps: Calculating the resonance value of the primary-side series compensation capacitor; Calculating the adjustment value of the primary-side series compensation capacitor to obtain the actual value of the primary-side series compensation capacitor so that the total input impedance of the inductive power transmission system is weakly inductive; Z in =Re<Z in >+Im<Z in > A=R eq r pro +R eq r s +r pro r s Among them, Z in is the total input impedance of the inductive power transfer system, Re <Z in > for Z in The real part, Im <Z in > for Z in The imaginary part, j represents a complex number, ω0 is the system resonant angular frequency, L p is the self-inductance of the primary coil, C p is the actual value of the primary side series compensation capacitor, C p0 is the resonant value of the primary side series compensation capacitor, ΔC p is the adjustment value of the primary side series compensation capacitor, M is the mutual inductance of the primary side coil and the secondary side coil, L pro is the inductance value of the protection inductor, R eq is the equivalent resistance of the bridge rectifier, r s is the internal resistance of the secondary coil, r pro is the internal resistance of the protection inductor, and A is an auxiliary calculation value.

2. An inductive power transmission system with rectifier fault protection as claimed in claim 1, characterized in that: The inductive power transmission system is a constant current output type inductive power transmission system.

3. A fault detection method for an inductive power transmission system with rectifier fault protection as claimed in claim 1, characterized in that: The capacitance value of the primary-side series compensation capacitor is adjusted so that the impedance angle of the total input impedance of the inductive power transmission system is in the range of (0,10°].

4. A fault detection method for an inductive power transmission system with rectifier fault protection according to any one of claims 1 to 3, characterized in that: Monitoring the current of the protection inductor, and determining the diode fault type and location of the bridge rectifier according to the current of the protection inductor; The method of determining the diode fault type and position of the bridge rectifier according to the current of the protection inductor comprises the following steps: S1, obtaining the current of the protection inductor; S2, performing Fourier decomposition on the current of the protection inductor to obtain a DC component, an AC component and an effective value of the current of the protection inductor, and calculating a DC threshold coefficient and an AC threshold coefficient; The calculation formula for Fourier decomposition of the current of the protection inductor is: Where, I1 is the current of the protection inductor, I 1_dc is the DC component of the current of the protection inductor, I 1_ac(k) is the effective value of the kth harmonic component of the current of the protection inductor, θ k is the phase angle of the kth harmonic component of the current of the protection inductor, k=1,2,…∞, I 1_RMS is the effective value of the current of the protection inductor; The calculation formulas of the DC threshold coefficient and the AC threshold coefficient are: Among them, K dc is the DC threshold coefficient, K ac is the AC threshold coefficient, I 1_ac is the AC component of the current of the protection inductor; S3, determining the diode fault type and position of the bridge rectifier according to the DC component, AC component, effective value, DC threshold coefficient and AC threshold coefficient of the current of the protection inductor.

5. A fault detection method for an inductive power transmission system with rectifier fault protection as claimed in claim 4, characterized in that: The method of determining the diode fault type and position of the bridge rectifier according to the DC component, AC component, effective value, DC threshold coefficient and AC threshold coefficient of the current of the protection inductor comprises the following steps: S31, if the current of the protection inductor has a DC component, it is determined that the bridge rectifier has a fault and S32 is executed; otherwise, it is determined that the bridge rectifier has not a fault and the process ends; S32, determining whether the DC threshold coefficient is greater than zero. If the DC threshold coefficient is greater than zero, determining that one of the first diode and the fourth diode of the bridge rectifier is faulty. Otherwise, determining that one of the second diode and the third diode of the bridge rectifier is faulty. S33, if the current of the protection inductor has an AC component, it is determined that the bridge rectifier has an open circuit fault; otherwise, it is determined that the bridge rectifier has a short circuit fault.

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