EC-WPT system based on frequency switching constant current / constant voltage output and its parameter design method

Abstract

The present invention relates to the technical field of EC-WPT, and specifically discloses an EC-WPT system based on frequency switching constant current / constant voltage output and a parameter design method thereof, which adopts an LC-CLC type resonant network, analyzes the characteristics of the LC-CLC resonant network, provides the conditions for realizing constant current / constant voltage output characteristics and the calculation method of constant current frequency and constant voltage frequency, and provides a system parameter design method. The EC-WPT system and parameter design method proposed in this article have the following advantages: no complex detection and control circuits are required, and the system can achieve constant current / constant voltage output when the load changes; no need to switch circuit topology, only switching the operating frequency is required to achieve switching between constant current and constant voltage working modes; no matter it is a constant current working mode or a constant voltage working mode, the system can achieve a ZPA (zero phase angle) state, reduce reactive power loss, and effectively improve system efficiency; the system has relatively few compensation elements, which can reduce system complexity.

Description

Technical Field

[0001] The present invention relates to the technical field of EC-WPT (electric field coupled wireless power transmission), and in particular to an EC-WPT system based on frequency switching constant current / constant voltage output and a parameter design method thereof. Background Art

[0002] Wireless Power Transfer (WPT) technology combines power electronics technology with modern control theory and technology, and realizes wireless transmission of electric energy through carriers such as magnetic fields, electric fields, microwaves, and lasers. The common wireless charging method is magnetic coupling wireless power transfer (MC-WPT) technology. Electric-field coupling wireless power transfer (EC-WPT) technology has the following advantages: low cost, light weight, and changeable shape of the coupling mechanism; low electromagnetic interference around the coupling mechanism; energy can be transmitted across metal barriers; and the eddy current loss caused on the metal conductors between or around the coupling mechanism is very small. Therefore, the study of EC-WPT technology can complement the advantages of MC-WPT technology and further expand the application field of WPT technology. At present, many achievements have been made in high-frequency inverter design, compensation of coupling mechanism, output voltage regulation control, parallel transmission of energy and signal, resonant topology optimization, and transmission spacing expansion.

[0003] In the actual application of WPT technology, some electrical equipment requires the system to have different constant output characteristics (constant current / constant voltage) in different operating stages, that is, the system output voltage or output current is decoupled from the load. In addition, the system must have the function of switching between constant current and constant voltage modes on demand. For example, when charging lithium batteries wirelessly, this type of battery uses a charging mode of constant current first and then constant voltage during charging. In the initial stage, the system needs to work in constant current mode, and the voltage rises rapidly. When the voltage rises to the rated value, the system needs to switch to constant voltage mode.

[0004] In the relevant research on EC-WPT technology, the existing literature mainly focuses on two methods to achieve constant output of the system. The first method is to set a detection circuit at the output end of the system, and feed back the detected load voltage to the control circuit at the transmitting end to achieve constant output. The second method is to use the characteristics of the resonant network to achieve constant output of the system. Relatively speaking, the latter does not need to set up detection and complex control circuits, and the complexity and cost of the system are lower, which has greater advantages. At present, there are literatures that use double-sided F-CLCL resonant network and T-Π composite resonant network to make the system output voltage not change with the load size. There are also literatures that use parameter design to make the bilateral LC resonant network system have the characteristics of constant output voltage. There are also literatures that use parameter design to make the bilateral LC resonant network system have the characteristics of constant output current. There are also literatures that propose a T-type CLC resonant network that can make the system output voltage constant. The resonant network in the above literature can only make the system realize constant voltage output or constant current output. In order to realize both constant current power supply and constant voltage power supply and mode switching in practical applications, there are also literatures that propose a FF / T variable structure resonant network to realize the switching of the system constant current / constant voltage working mode; there are also literatures that use a variable structure LC-CLCL resonant network to realize the switching of the system constant current / constant voltage working mode; both methods require adding a control switch in the resonant network, and the on and off of the switch needs to be controlled to realize the switching between the constant current and constant voltage working modes. The additional switching devices increase the cost and volume of the system and affect the reliability of the system. Summary of the invention

[0005] The present invention provides an EC-WPT system based on frequency switching constant current / constant voltage output and a parameter design method thereof, and solves the technical problem of how to satisfy the requirement that the system has different constant output characteristics (constant current / constant voltage) of the electrical equipment in different operation stages, that is, the system output voltage or output current is decoupled from the load. In addition, the system also needs to have the function of switching between constant current and constant voltage modes on demand and maintain a high transmission efficiency.

[0006] In order to solve the above technical problems, the present invention provides an EC-WPT system based on frequency switching constant current / constant voltage output, including a transmitting end and a receiving end, wherein the transmitting end is provided with a DC power supply, a high-frequency inverter, an LC resonant network and two energy transmitting plates, and the receiving end is provided with two energy receiving plates, a CLC resonant network, a rectifier filter circuit and an electrical load; when the system requires constant voltage output, the high-frequency inverter is operated at a constant voltage working frequency f cv Output high-frequency inverter signal; when the system requires constant current output, the high-frequency inverter operates at a constant current operating frequency f ccOutput high-frequency inverter signal; the LC resonant network includes an inductor L1 and a capacitor C1, the inductor L1 and the capacitor C1 are connected in series between the two output ends of the high-frequency inverter, and the two ends of the capacitor C1 are respectively connected to the two energy emitting plates; the CLC-Π type resonant network includes an inductor L2, a capacitor C2, and a capacitor C 3x , the two energy receiving plates are connected to the two ends of capacitor C2 respectively. 3x The two ends of are connected to the rectifier filter circuit respectively, and the inductor L2 is connected in series with the capacitor C2 and the capacitor C 3x between;

[0007] make Coupling capacitor C s =(C s1 C s2 ) / (C s1 +C s2 ), C s1 Approximately equal to C 13 , C s2 Approximately equal to C 24 , C 13 is the capacitance formed between the energy emitting plate P1 and the energy receiving plate P3, C 24 The capacitance C is formed between the energy emitting plate P2 and the energy receiving plate P4. 3x Together with the rectifier and filter circuit, it is equivalent to capacitor C3, α=C1 / C s , β=C2 / C s , k=C3 / C2 are the three defined correlation coefficients, then the LC resonant network and the CLC-Π type resonant network satisfy the relationship:

[0008]

[0009] And, the constant voltage working frequency f cv and constant current operating frequency f cc Satisfaction relationship:

[0010]

[0011] Preferably, the system has a constant output voltage and constant output current RMS for:

[0012]

[0013] is the output voltage of the high frequency inverter.

[0014] Preferably, 500kHz <f cc <f cv <2MHz.

[0015] Preferably, the high-frequency inverter adopts a high-frequency full-bridge inverter circuit composed of four MOSFETs.

[0016] Preferably, the rectification and filtering circuit includes a full-bridge rectification circuit composed of four diodes and a filtering capacitor C f .

[0017] The present invention also provides a parameter design method for an EC-WPT system based on frequency switching constant current / constant voltage output, comprising the steps of:

[0018] S1. Set the constant voltage working frequency f according to engineering experience cv The value of

[0019] S2. Determine the constant output current I according to actual requirements L The set value and constant output voltage U L The setting value of the coupling capacitor C is determined according to the coupling mechanism. s size;

[0020] S3, set constant output voltage U L The theoretical value U L_理论值 =U L The set value, constant output current I L Theoretical value I L_理论值 =I L The setting value of

[0021] S4. According to U L_理论值 ,I L_理论值 And the voltage-current relationship of the system is used to calculate the DC input voltage E of the DC power supply. dc The value of

[0022] S5. Calculate C1, C2, C3, L1, L2 and f according to the system voltage, current, capacitance and inductance relationship. cc The value of

[0023] S6. Determine the constant output voltage U L The actual value of U L_实际 Is it equal to the set value? If so, proceed to step S7. If not, further determine U L_实际 The size relationship between it and its set value, if it is judged that U L_实际 If it is less than the set value, increase U L_理论值 And return to step S4, if it is determined that U L_实际 If it is greater than the set value, reduce U L_理论值 And return to step S4;

[0024] S7, determine the constant output current I L The actual value of I L_实际Is it equal to the set value? If so, proceed to step S8. If not, further determine I L_实际 The size relationship between it and its set value, if it is judged that I L_实际 If it is less than the set value, I will be increased. L_理论值 And return to step S4, if it is determined that I L_实际 If it is greater than the set value, I will be reduced. L_理论值 And return to step S4;

[0025] S8, take C 3x The initial value of is C3;

[0026] S9, determine whether the system has reached the zero phase angle state, if so, obtain a set of C1, C2, C 3x , L1, L2 and f cc Parameter value, if otherwise reduce C 3x , until the system reaches the zero phase angle state.

[0027] Further, in step S4, the voltage-current relationship of the system includes:

[0028]

[0029]

[0030]

[0031] Further, in step S5, the voltage, current, capacitance and inductance relationship of the system includes:

[0032]

[0033]

[0034]

[0035]

[0036] The EC-WPT system based on frequency switching constant current / constant voltage output and its parameter design method provided by the present invention adopts LC-CLC resonant network, analyzes the characteristics of LC-CLC resonant network, gives the conditions for realizing constant current / constant voltage output characteristics and the calculation method of constant current frequency and constant voltage frequency, gives the system parameter design method, realizes the switching of constant current / constant voltage working mode by switching frequency, and finally verifies the effectiveness of the system's constant current / constant voltage output characteristics and parameter design method through simulation and experiment. The EC-WPT system and parameter design method proposed in this paper have the following advantages:

[0037] 1) No complex detection and control circuits are required, and the system can achieve constant current / constant voltage output when the load changes;

[0038] 2) No need to switch circuit topology, just switch the operating frequency to achieve the switching between constant current and constant voltage working modes;

[0039] 3) Whether in constant current working mode or constant voltage working mode, the system can achieve ZPA (zero phase angle) state, reduce reactive power loss and effectively improve system efficiency;

[0040] 4) The system has relatively few compensation components, which can reduce system complexity and improve system reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a topology diagram of an EC-WPT system provided by an embodiment of the present invention;

[0042] Figure 2 is an equivalent circuit model diagram of a coupling mechanism provided by an embodiment of the present invention;

[0043] Figure 3 is an equivalent circuit diagram of the EC-WPT system provided by an embodiment of the present invention;

[0044] Figure 4 is a parameter design flow chart of the EC-WPT system provided by an embodiment of the present invention;

[0045] Figure 5 is a curve diagram of phase, output current and voltage changing with operating frequency provided by an embodiment of the present invention;

[0046] Figure 6 is a diagram showing the influence of L1 on output characteristics provided by an embodiment of the present invention;

[0047] Figure 7 is a diagram showing the influence of C1 on output characteristics provided by an embodiment of the present invention;

[0048] Figure 8 is a diagram showing the influence of C2 on output characteristics provided by an embodiment of the present invention;

[0049] Fig. 9 is a diagram showing the influence of L2 on output characteristics provided by an embodiment of the present invention;

[0050] Fig.10 is a diagram showing the influence of C3 on output characteristics provided by an embodiment of the present invention;

[0051] Fig.11 is a simulation waveform diagram of the inverter output voltage and current provided by an embodiment of the present invention;

[0052] Fig.12is R in the constant current mode provided by the embodiment of the present invention L =24Ω, R L =38Ω, R L =48Ω and R in constant voltage mode L =24Ω, R L =38Ω, R L =48Ω when the inverter output voltage and current simulation waveform;

[0053] Fig.13 is a simulation waveform diagram of load current and voltage provided by an embodiment of the present invention;

[0054] Fig.14 is an experimental waveform diagram of the constant current working mode provided by an embodiment of the present invention;

[0055] Fig.15 is an experimental waveform diagram of the constant voltage working mode provided by an embodiment of the present invention;

[0056] Fig.16 It is an experimental waveform diagram corresponding to the switching between constant current / constant current working modes provided by an embodiment of the present invention;

[0057] Fig.17 is a curve diagram of output power and transmission efficiency changing with load provided by an embodiment of the present invention;

[0058] Fig.18 It is a curve diagram of output voltage and output current changing with load provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0059] The following specifically illustrates the implementation mode of the present invention in conjunction with the accompanying drawings. The embodiments are provided for illustrative purposes only and cannot be understood as limiting the present invention. The accompanying drawings are provided for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0060] The embodiment of the present invention provides an EC-WPT system based on frequency switching constant current / constant voltage output, including a transmitting end and a receiving end, wherein the transmitting end is provided with a DC power supply, a high frequency inverter, an LC resonant network and two energy transmitting plates, and the receiving end is provided with two energy receiving plates, a CLC-Π type resonant network, a rectifier filter circuit and an electrical load. The system structure is as follows Figure 1 As shown, where E dcis the DC input voltage; S1-S4 is a high-frequency full-bridge inverter circuit composed of 4 MOSFETs; the primary resonant network is an LC resonant network (including inductor L1 and capacitor C1, inductor L1 and capacitor C1 are connected in series between the two output ends of the high-frequency inverter, and the two ends of capacitor C1 are respectively connected to the two energy emitting plates); the secondary resonant network is a CLC-Π type resonant network composed of two capacitors and one inductor (including inductor L2, capacitor C2, capacitor C 3x , the two energy receiving plates are connected to the two ends of capacitor C2 respectively. 3x The two ends of are connected to the rectifier filter circuit respectively, and the inductor L2 is connected in series with the capacitor C2 and the capacitor C 3x D1-D4 is a full-bridge rectifier circuit composed of 4 diodes; C f is the filter capacitor; R L It is the load equivalent resistance. The DC power source generates an alternating voltage through a high-frequency inverter, which is filtered by the LC resonant network at the transmitting end, and the voltage is pumped up to the high excitation voltage required by the coupling mechanism. When the receiving plate of the coupling mechanism is placed near the transmitting plate, an alternating electric field is generated between the two plates. Under the action of the alternating electric field, a displacement current "flows" through the plates, realizing wireless transmission of electric energy. The rectifier filter converts AC power into DC power to power the battery.

[0061] Figure 1 The four plates of the coupling mechanism shown in the figure are cross-coupled, which can be equivalent to Figure 2 (a) shows the equivalent model of six capacitors. 12 and C 34 The capacitors formed by the plates P1-P2 and P3-P4 are located at the energy transmitting and receiving ends respectively; C 13 and C 24 The capacitors formed by the plates P1-P3 and P2-P4 constitute the energy transmission channel; C 23 and C 14 are the capacitances formed by the plates P2-P3 and P1-P4 respectively; the six-capacitor equivalent model can be further equivalent to Figure 2 (b) Π model. For the tightly coupled parallel coupling mechanism, when the plates on the same side are on the same horizontal plane and far apart, the coupling capacitance C of the plates on the same side is 12 and C 34 is almost zero, and the cross-coupling capacitance C 14 and C 23 Much smaller than the coupling capacitance C between the opposite plates 13 and C 24 At this time, the coupling mechanism can be equivalent to Figure 2 (c) shows the equivalent model of two capacitors, where C s1 Approximately equal to C13 , C s2 is approximately equal to C 24 .

[0062] In Figure 1 the topology shown, the internal resistance of the inductor and the equivalent series resistance of the capacitor are usually small relative to their own impedance. To simplify the analysis, the internal resistance of the inductor and the equivalent series resistance of the capacitor can be ignored, and the system can be equivalently represented as the circuit shown in Figure 3 , where C s =(C s1 C s2 ) / (C s1 +C s2 ). Figure 1 In, since a capacitor C 3x is connected in parallel at the input of the rectifier, the input voltage u o of the rectifier is not a square wave, and the input current i4 is not a sine wave either, and the voltage lags behind the current. Therefore, the rectifier, the filter capacitor, and the load R L can be equivalently represented as a capacitor and a resistor R eq connected in parallel. So when designing the circuit parameters, C 3x <C3 should be considered, where the equivalent resistance R eq satisfies R eq =8R L / π 2 .

[0063] Figure 3 In u in is the output voltage of the inverter. Expanding it by the Fourier trigonometric series formula, we get

[0064]

[0065] where ω is the working angular frequency of the system, which satisfies ω = 2πf with the working frequency f. Since the resonant compensation network of the system can filter out most of the high-order harmonics, the fundamental harmonics approximation (FHA) method can be used to analyze the circuit, and then we can obtain

[0066]

[0067] In vector form, it can be expressed as

[0068]

[0069] Similarly, there is a similar approximate relationship between the input voltage and current and the output voltage and current of the rectifier

[0070]

[0071] In formula (4), U L and I L Respectively, the resistor R L Voltage across the two ends u L The average value and current i L The average value, U o and I o is the equivalent circuit R eq The effective value of the voltage across the two ends and the effective value of the current flowing through.

[0072] In the equivalent circuit Figure 3 In the constant voltage working mode, the operating frequency of the system is f cv , the corresponding operating angular frequency is ω cv , inductors L1 and L2 resonate with capacitors C1 and C2 respectively, that is, the parameter relationship satisfies:

[0073]

[0074] Assume that capacitors C1, C2, C3 and equivalent coupling capacitor C s The relationship between them is:

[0075]

[0076] α=C1 / C s , β=C2 / C s , k=C3 / C2 are the three defined correlation coefficients.

[0077] According to Kirchhoff's voltage law, the following equations can be obtained:

[0078]

[0079] Where X L1 , X c1 , X cs , X c2 , X L2 , X c3 They are L1, C1, C s , C2, L2 and C3 impedance. From equation (7), the input current of the system can be obtained and output voltage The expression is:

[0080]

[0081] From equation (8), it can be seen that when the system satisfies the resonant condition shown in equation (5), the output voltage of the system is independent of the load, and the system can achieve constant voltage output. At the same time, in order to make the system work in the ZPA state when the output voltage is constant, the input impedance of the system should be purely resistive, so the input current The imaginary part of should be 0, that is, the system should satisfy the following relationship:

[0082]

[0083] At the operating frequency f cv When , the inductors L1 and L2 satisfy the resonance condition of equation (5), and the size of the capacitor C3 satisfies expression (9), so L1, L2 and C3 can be expressed as:

[0084]

[0085] From formula (7), we can get the output current The expression is:

[0086]

[0087] Where G1 and G2 are two eq To make the output current independent of the load, the constant current working angular frequency ω cc In this case, G1 should be equal to 0.

[0088] Assume α and β satisfy:

[0089]

[0090] Substituting equation (12), equation (10) and equation (6) into equation (7), we can get two solutions for G1 = 0:

[0091]

[0092] exist Figure 3 The impedance in the equivalent circuit is as follows:

[0093]

[0094] When cc =ω cc1 When , the input impedance Z6 of the system is:

[0095]

[0096] Obviously, the imaginary part of the input impedance is not 0 and the system cannot achieve the ZPA state.

[0097] When cc =ω cc2 When , the input impedance Z6 of the system is:

[0098]

[0099] At this time, the imaginary part of the system input impedance is 0, the system can achieve the ZPA state, and the system output current for:

[0100]

[0101] It can be seen that the output current Only with input voltage The equivalent coupling capacitance C of the coupling mechanism s , constant voltage working frequency ω cv It is related to the capacitance ratio α and has nothing to do with the load, so the system can achieve constant current output.

[0102] According to the analysis and derivation in the previous two sections, if the system is to be able to switch between the constant current / constant voltage operating modes by switching the frequency, the compensation element of the system needs to satisfy the condition in equation (18):

[0103]

[0104] If the compensation parameters satisfy equation (18), the system's constant voltage operating frequency f cv and constant current operating frequency f cc They are as follows:

[0105]

[0106] According to equations (8), (17) and (18), the system's constant output voltage is and constant output current for:

[0107]

[0108] System parameter design process is as follows Figure 4 As shown. At present, the operating frequency of most EC-WPT systems is in the range of 500kHz to 2MHz. If the operating frequency is too high, the dynamic loss and electromagnetic interference of the system will be large; if the frequency is too low, the compensation inductance of the system will be large, and the quality factor and power density of the system will be low. In addition, if the equivalent coupling capacitance of the coupling mechanism is large, the operating frequency can be designed to be smaller. If the equivalent coupling capacitance of the coupling mechanism is too small, the operating frequency must be larger. According to the above analysis and the engineering needs, f is designed to be larger in the range of 500kHz to 2MHz. cv Since the theoretical derivation above is based on the fundamental wave approximation method, when we use the actual required constant output voltage U L Size and constant output current I L When the size is used as a theoretical value to calculate the system component parameters, the actual DC output voltage U L and the actual DC output current I L It is usually not equal to the required size, so U L and I LThe theoretical value of needs to be slightly adjusted; in addition, from the above analysis, it can be seen that C 3x The value of C is smaller than the capacitance value C3 calculated by the equivalent circuit. Therefore, when determining the parameter C 3x When 3x The initial value of is taken as C3. Through simulation and observation of the waveforms of the inverter output voltage and current in constant voltage mode, the system should not be in ZPA state, but in capacitive state. C should be reduced. 3x until the entire system reaches the ZPA state.

[0109] Specifically, refer to Figure 4 , a parameter design method of an EC-WPT system based on frequency switching constant current and constant voltage output provided by an embodiment of the present invention comprises the steps of:

[0110] S1. Set the constant voltage working frequency f according to engineering experience cv The value of

[0111] S2. Determine the constant output current I according to actual requirements L The set value and constant output voltage U L The setting value (I L and U L Respectively represent the load current i L and the voltage across the load u L The coupling capacitance C is determined according to the coupling mechanism. s size;

[0112] S3, set constant output voltage U L The theoretical value U L_理论值 =U L The set value, constant output current I L Theoretical value I L_理论值 =I L The setting value of

[0113] S4. According to U L_理论值 ,I L_理论值 The voltage-current relationship of the system includes equations (3), (4), and (20) to calculate the DC input voltage E of the DC power supply: dc The value of

[0114] S5. Calculate C1, C2, C3, L1, L2 and f according to the system voltage, current, capacitance and inductance relationship including equation (20), equation (18), equation (19) and equation (4). cc The value of

[0115] S6. Determine the constant output voltage U L The actual value of U L_实际Is it equal to the set value? If so, proceed to step S7. If not, further determine U L_实际 The size relationship between it and its set value, if it is judged that U L_实际 If it is less than the set value, increase U L_理论值 And return to step S4, if it is determined that U L_实际 If it is greater than the set value, reduce U L_理论值 And return to step S4;

[0116] S7, determine the constant output current I L The actual value of I L_实际 Is it equal to the set value? If so, proceed to step S8. If not, further determine I L_实际 The size relationship between it and its set value, if it is judged that I L_实际 If it is less than the set value, I will be increased. L_理论值 And return to step S4, if it is determined that I L_实际 If it is greater than the set value, I will be reduced. L_理论值 And return to step S4;

[0117] S8, take C 3x The initial value of is C3;

[0118] S9, determine whether the system has reached the zero phase angle state, if so, obtain a set of C1, C2, C 3x , L1, L2 and f cc Parameter value, if otherwise reduce C 3x , until the system reaches the zero phase angle state.

[0119] The following is a system sensitivity analysis.

[0120] In practical applications, the inverter may deviate due to control circuit errors and cannot accurately reach a certain frequency point. If the system is too sensitive to frequency, it will affect the system's constant current / constant voltage output characteristics. Therefore, the system's sensitivity to the operating frequency must be analyzed.

[0121] Currently, the rated input of lithium batteries is mostly 96V / 2A, 72V / 2A, and 48V / 2A. Therefore, taking the output voltage of 96V in the system constant voltage output mode and the output current of 2A in the constant current mode as an example, the maximum and minimum values ​​of the load resistance are set to 72Ω and 24Ω respectively. Set the equivalent coupling capacitance C of the coupling mechanism s is 0.5nF, the constant voltage operating frequency is 800kHz, according to Figure 4 The flow chart shown in the figure is shown in Table 1. The constant current operating frequency of the system is 706.6kHz. Given the DC input voltage E dc is 47V.

[0122] Table 1 Parameter values ​​of theoretical calculation

[0123]

[0124] Figure 5 The voltage U L 、Current I L And the curve of the system input phase angle changing with the operating frequency. Figure 5 It can be seen that the system has two ZPA operating frequency points, which are the constant current operating frequency and the constant voltage operating frequency, which is consistent with the above theoretical design. In addition, at the constant current frequency f cc In the range of ±4kHz, the system has a good constant current effect; in the constant voltage frequency f cv Within the range of ±5kHz, the system has a good constant voltage effect. Therefore, the inverter can ensure that the system has a good constant current / constant voltage output characteristic within a 0.5% error range.

[0125] In practical applications, when the system is working, the compensation component parameters of the resonant network will inevitably deviate from their theoretical values ​​due to environmental factors such as heat. If the output characteristics of the system are too sensitive to changes in component parameters, when the deviation of component parameters is too large, it will seriously affect the constant current / constant voltage output characteristics of the system. Therefore, it is necessary to analyze the parameter sensitivity of the resonant network.

[0126] The system takes the parameters in Table 1. The influence of the change of each component parameter on the output characteristics is as follows Figure 6 — Fig.10 As shown. When there is no deviation in component parameters, the voltage U L and current I L The theoretical values ​​are about 96V and 2A respectively. The system should be in ZPA state, the input phase angle should be 0°, and U L The allowable deviation is ±2V, I L The allowable deviation of the input phase angle is ±0.2A, and the allowable deviation of the input phase angle is ±10°.

[0127] from Figure 6 It can be seen that in the constant current working mode, the resistor R L The smaller the value, the larger the allowable value range of L1. In the constant voltage working mode, the resistor R L The larger the value, the larger the allowable value range of L1. Comprehensively consider the output voltage U in constant current / constant voltage working modes L , output current I L The allowable deviation of the input phase angle is 12.76uH~13.2uH. Figure 7 It can be concluded that the range of C1 values ​​is 2.992nF to 3.143nF; Figure 8As can be seen from (a), to ensure the constant current output characteristics of the system, C2 can have a larger value range, i.e. 1.452nF to 1.6nF. However, Figure 8 (b) shows that the system constant voltage output is very sensitive to C2, which can only take values ​​between 1.518nF and 1.538nF. Therefore, the value range of C2 is 1.518nF to 1.538nF. Fig. 9 It can be concluded that the range of L2 values ​​is 25.79uH to 26.07uH; Fig.10 It can be concluded that the range of C3 values ​​is 6.36nF to 7.539nF;

[0128] In order to verify the effectiveness of the constant current / constant voltage output characteristics and parameter design of the designed EC-WPT system, according to Figure 1 The circuit topology is shown and the designed parameters are shown in Table 1. The corresponding simulation model is established using the MATLAB / Simulink simulation platform.

[0129] Fig.11 is the system inverter output voltage u in The simulation waveform of current i1 shows that at the moment of switching the operating frequency, the inverter output current has only a slight mutation, and at other switching points, the inverter output current has almost no mutation, and the system reliability is high. Fig.12 is the constant current mode R L =24Ω, R L =38Ω, R L =48Ω and constant voltage mode R L =24Ω, R L =38Ω, R L =48Ω when the inverter output voltage and current simulation waveform diagram, it can be seen from the figure that no matter in the constant current mode or the constant voltage mode, the system is basically in the ZPA state, which is consistent with the above theoretical design.

[0130] Fig.13 is the DC output voltage u L and the DC output current i L Simulation waveform diagram. In 0~0.03s, the operating frequency is 706.6kHz, and the system works in constant current mode; at 0.01s, the load resistance R L Switching from 24Ω to 38Ω, the current i L From 2.11A to 2.06A; at 0.02s, the load resistance R L Switching from 38Ω to 48Ω, the current i LFrom 2.06A to 2.02A; at 0.03s, the operating frequency is switched to 800kHz, the system enters the constant voltage working mode, and the voltage quickly stabilizes at 95.4V after oscillation; at 0.04s, the load resistance R L Switching from 48Ω to 60Ω, the voltage u L From 95.4V to 96.4V; at 0.05s, the load resistance R L Switching from 60Ω to 72Ω, the voltage u L From 96.4V to 97.2V. It can be seen that in the constant current working mode, when the load resistance changes by 50%, the current i L Only 1.8% change occurs; in constant voltage mode, when the load resistance changes by 50%, the voltage u L Only 1.8% change occurs. Therefore, the proposed system has better constant current / constant voltage output characteristics under load changes.

[0131] The following is an experimental verification.

[0132] In order to further verify the above theoretical analysis, based on the simulation verification, Figure 1 The experimental setup was built with the system topology shown and the parameters in Table 2. The power supply provides a 48V DC voltage and a constant current operating frequency f cc =695kHz, constant voltage operating frequency f cv =790kHz. The parameters set in the experiment have a small deviation from the theory, which is because the influence of system internal resistance and parasitic parameters is not considered in the theoretical derivation.

[0133] Table 2 Experimental parameter values

[0134]

[0135] Fig.14 is the inverter output voltage u in constant current working mode in , inverter output current i1, load end output DC voltage u L and current i L The experimental waveform diagram. Fig.14 (a) is R L =25Ω constant current working mode experimental waveform diagram, from the figure can be seen, the current i L is 2.03A, and the inverter output current i1 lags slightly behind the inverter output voltage u in , which is conducive to achieving system zero voltage switching (ZVS), reducing switching losses and improving transmission efficiency. Fig.14 (b) is working in constant current mode, the system input and output change with the load R L The experimental waveform of the change, at the switching point 1, the load R LSwitching from 30Ω to 60Ω, the current i L From 2A to 1.86A, at switching point 2, the load R L Switching from 60Ω to 30Ω, the current i L From 1.86A to 2A. Experimental data show that under large load disturbance, the current i L The voltage is only reduced by 7%, which has better constant current output characteristics.

[0136] Fig.15 (a) is R L =48Ω, experimental waveform in constant voltage working mode, voltage u L The inverter output current i1 is about 97.3V, which slightly lags behind the inverter output voltage u in , to achieve system zero voltage switching (ZVS). Fig.15 (b) is working in constant voltage mode, the system input and output change with the load R L The experimental waveform of the change, at the switching point 1, the load R L Switching from 55Ω to 80Ω, the voltage u L From 97.5V to 99V, at switch point 2, the load R L Switching from 55Ω to 80Ω, the voltage u L From 99V to 97.5V. Experimental data shows that under large load disturbance, the voltage u L The increase is only 1.5%, which has better constant voltage output characteristics.

[0137] Fig.16 is the load R L =48Ω, the system switches between constant current / constant voltage working modes, and the inverter output voltage u in , inverter output current i1, load end output DC voltage u L and current i L Experimental waveform diagram. At switching point 1, the operating frequency of the system changes from f cc Switch to f cv , voltage u L and current i L This is because the system internal resistance and parasitic parameters cause the system to work at a constant current. L As the current increases, the current will decrease slightly; at switching point 2, the operating frequency of the system changes from f cv Switch to f cc At the switching moment of the two working modes, the input current i1 of the system does not have excessive impact, and the system can switch smoothly at any time.

[0138] Fig.17 The output power and transmission efficiency vary with R LThe change curve of R L increases with the increase of L =25Ω, the output power is 103.23W, the transmission efficiency is 77.6%, when R L =32Ω, the output power is 130.69W, the transmission efficiency is 83.78%, when R L =48Ω, the output power is 185.6W, and the transmission efficiency is 87.83%; in the constant voltage working mode, at R L =48Ω, the output power is 197.23W, the efficiency is 87.2%, and the R L =60Ω, the output power is 161.54W, the efficiency is 88.17%, and the R L =70Ω, the output power is 140W and the efficiency is 85.87%. Therefore, the system has a high transmission efficiency whether in constant current mode or constant voltage mode.

[0139] Fig.18 is the current i in the experiment L and voltage u L With load R L The theoretical current i L The size is constant at 2A, the voltage u L The magnitude is constant at 96V, but in reality, the current i L With the load R L The voltage u L With the load R L These errors are mainly caused by three reasons. The first reason is that the above theory is based on the fundamental wave approximation method, and the high-order harmonics will cause a small amount of error when acting on the system; the second reason is that the internal resistance of the system components and some parasitic parameters are not taken into account in the theoretical derivation. The third reason is that when the filter capacitor C f When it is not large enough, the size of the resistor will have a slight effect on the output voltage of the filter circuit.

[0140] In summary, the embodiments of the present invention are centered around the need for the system to have different constant output characteristics (constant current / constant voltage) in different operating stages of electrical equipment, that is, the system output voltage or output current is decoupled from the load, and has the requirement to switch between constant current and constant voltage modes on demand. A constant current / constant voltage EC-WPT system based on an LC-CLC resonant network is proposed, and the switching of the operating mode is achieved by switching the frequency. The parameter conditions for the constant current / constant voltage output of the system under load changes are derived, and a system parameter design method is given. The sensitivity of the system operating frequency and the parameter sensitivity of the resonant network compensation elements are analyzed. It is concluded that the system is insensitive to the operating frequency and the allowable error range of each compensation element is given. Finally, the effectiveness of the constant current / constant voltage output characteristics of the system and the parameter design method are verified through simulation and experiments. The EC-WPT system and parameter design method proposed in this article have the following advantages:

[0141] 1) No complex detection and control circuits are required, and the system can achieve constant current / constant voltage output when the load changes.

[0142] 2) There is no need to switch the circuit topology, only the operating frequency needs to be switched to achieve the switching between constant current and constant voltage working modes.

[0143] 3) Whether in constant current working mode or constant voltage working mode, the system can achieve ZPA state, reduce reactive power loss and effectively improve system efficiency.

[0144] 4) The system has relatively few compensation devices, which can reduce system complexity and improve system reliability.

[0145] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. An EC-WPT system based on frequency switching constant current / constant voltage output includes a transmitting end and a receiving end, wherein the transmitting end is provided with a DC power supply, a high-frequency inverter, an LC resonant network and two energy transmitting plates, and the receiving end is provided with two energy receiving plates, a CLC-Π type resonant network, a rectifier filter circuit and an electrical load; when the system requires constant voltage output, the high-frequency inverter operates at a constant voltage working frequency f cv Output high-frequency inverter signal; when the system requires constant current output, the high-frequency inverter operates at a constant current operating frequency f cc Output high-frequency inverter signal; the LC resonant network includes an inductor L1 and a capacitor C1, the inductor L1 and the capacitor C1 are connected in series between the two output ends of the high-frequency inverter, and the two ends of the capacitor C1 are respectively connected to the two energy emitting plates; the CLC-Π type resonant network includes an inductor L2, a capacitor C2, and a capacitor C 3x , the two energy receiving plates are connected to the two ends of capacitor C2 respectively. 3x The two ends of are connected to the rectifier filter circuit respectively, and the inductor L2 is connected in series with the capacitor C2 and the capacitor C 3x between; characterized in that: make Coupling capacitor C s =(C s1 C s2 ) / (C s1 +C s2 ), C s1 Equal to C 13 , C s2 Equal to C 24 , C 13 is the capacitance formed between the energy emitting plate P1 and the energy receiving plate P3, C 24 The capacitance C is formed between the energy emitting plate P2 and the energy receiving plate P4. 3x Together with the rectifier and filter circuit, it is equivalent to capacitor C3, α=C1 / C s , β=C2 / C s , k=C3 / C2 are the three defined correlation coefficients, then the LC resonant network and the CLC-Π type resonant network satisfy the relationship: And, the constant voltage working frequency f cv and constant current operating frequency f cc Satisfaction relationship:

2. The EC-WPT system based on frequency switching constant current / constant voltage output according to claim 1 is characterized in that: The system's constant output voltage and constant output current for: is the output voltage of the high frequency inverter.

3. The EC-WPT system based on frequency switching constant current / constant voltage output according to claim 1 is characterized in that: 500kHz<f cc <f cv <2MHz。 4. The EC-WPT system based on frequency switching constant current / constant voltage output according to claim 1, characterized in that: The high-frequency inverter adopts a high-frequency full-bridge inverter circuit composed of four MOSFETs.

5. The EC-WPT system based on frequency switching constant current / constant voltage output according to claim 1, characterized in that: The rectifier and filter circuit includes a full-bridge rectifier circuit composed of four diodes and a filter capacitor C f .

6. A parameter design method for an EC-WPT system based on frequency switching constant current / constant voltage output according to any one of claims 2 to 5, characterized in that: Includes steps: S1. Set the constant voltage working frequency f according to engineering experience cv The value of S2. Determine the constant output current I according to actual requirements L The set value and constant output voltage U L The setting value of the coupling capacitor C is determined according to the coupling mechanism. s size; S3, make the DC side constant output voltage U L Theoretical value U L_理论值 =U L The set value, constant output current I L Theoretical value I L_理论值 =I L The setting value of S4. According to U L_理论值 ,I L_理论值 And the voltage-current relationship of the system is used to calculate the DC input voltage E of the DC power supply. dc The value of S5. Calculate C1, C2, C3, L1, L2 and f according to the system voltage, current, capacitance and inductance relationship. cc The value of S6. Determine the constant output voltage U L The actual value of U L_实际 Is it equal to the set value? If so, proceed to step S7. If not, further determine U L_实际 The size relationship between it and its set value, if it is judged that U L_实际 If it is less than the set value, increase U L_理论值 And return to step S4, if it is determined that U L_实际 If it is greater than the set value, reduce U L_理论值 And return to step S4; S7, determine the constant output current I L The actual value of I L_实际 Is it equal to the set value? If so, proceed to step S8. If not, further determine I L_实际 The size relationship between it and its set value, if it is judged that I L_实际 If it is less than the set value, I will be increased. L_理论值 And return to step S4, if it is determined that I L_实际 If it is greater than the set value, I will be reduced. L_理论值 And return to step S4; S8, take C 3x The initial value of is C3; S9, determine whether the system has reached the zero phase angle state, if so, obtain a set of C1, C2, C 3x , L1, L2 and f cc Parameter value, if otherwise reduce C 3x , until the system reaches the zero phase angle state.

7. The parameter design method of the EC-WPT system based on frequency switching constant current / constant voltage output according to claim 6 is characterized in that: In step S4, the voltage-current relationship of the system includes:

8. The parameter design method of the EC-WPT system based on frequency switching constant current / constant voltage output according to claim 6 is characterized in that: In step S5, the voltage, current, capacitance and inductance relationship of the system includes:

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