A method for suppressing starting surge current of an inductively coupled energy transmission system

Abstract

The present invention provides a method for suppressing the starting impact current of an inductively coupled energy transmission system. First, a mathematical model of the inductively coupled energy transmission system is established, and the starting time t of the system is calculated and set. s , select the appropriate triangular carrier frequency f, and then start the s The duty cycle D is changed according to the law of the nonlinear saturation function and compared with the triangular carrier to obtain the switching function d. When the switching function d is at a logic high level, the high-frequency inverter adopts a phase shift control with a phase shift angle of 0°. When the switching function d is at a logic low level, the high-frequency inverter stops working, thereby suppressing the starting impact current of the inductively coupled energy transmission system. When the duty cycle D changes according to the law of the nonlinear saturation function, the system oscillation time is significantly shortened and the amplitude is reduced.

Description

Technical Field

[0001] This invention belongs to the field of wireless power transmission, and specifically relates to a method for suppressing the starting inrush current of an inductively coupled energy transmission system. Background Art

[0002] Inductive coupling power transfer system is a new type of power supply method that transmits electrical energy to the load in a non-contact manner through the principle of electromagnetic induction. Due to its advantages such as no physical connection required, safety, reliability and environmental friendliness, this technology has been widely used in low-power applications such as electronic products and medical equipment, as well as high-power applications such as electric vehicles and rail transportation.

[0003] In high-power applications, inductively coupled power transfer systems need to transmit significant power to the load. This results in a large inrush current during startup, which can severely damage the bidirectional controllable power switching devices in the high-frequency inverter, causing the system to malfunction. Therefore, it is essential to effectively suppress the inrush current of inductively coupled power transfer systems.

[0004] Existing soft-start control methods for inductively coupled power transfer systems mainly fall into three categories: phase-shift control, frequency conversion control, and adding a pre-charge circuit. K. Hata, T. Imura, H. Fujimoto, et al., in their paper "Soft-start control method for in-motion charging of electric vehicles based on transient analysis of wireless power transfer system [C]. 2018 IEEE Energy Conversion Congress and Exposition, 2018, 2009-2015," employed phase-shift control for soft starting. By adjusting the phase shift angle, the input voltage of the high-frequency inverter is gradually increased from a small value to the rated input voltage, thus suppressing the starting inrush current. However, when the phase shift angle is large, the bidirectional controllable power switching device cannot achieve soft switching, resulting in significant switching losses, causing the bidirectional controllable power switching device to overheat and even be damaged. In their paper "Analysis and parameter optimization of start-up process for LLC resonant converter [J]. IEEE Trans on Power Electronics, 2015, 30(12): 7113-7122," R. Chang, B. Liu, and S. Duan employ frequency conversion control for soft start-up. By adjusting the operating frequency of the high-frequency inverter, the system impedance gradually decreases, and the output current of the high-frequency inverter gradually increases, thereby preventing large inrush currents during startup. However, this method generates a significant amount of reactive power, reducing system efficiency. Furthermore, for inductively coupled energy transfer systems exhibiting frequency splitting, it can easily lead to system instability. Chinese invention patent CN202011224629.6, "Electromagnetic Induction Wireless Power Transfer System and its Start-up Current Inrush Suppression Method," uses an additional pre-charging circuit to pre-charge the secondary-side filter capacitor to suppress the startup inrush current. However, this method adds an extra pre-charging circuit, resulting in high engineering costs. Summary of the Invention

[0005] To effectively suppress the inrush current during the startup process of the aforementioned inductively coupled energy transfer system, this invention proposes a method for suppressing the startup inrush current of an inductively coupled energy transfer system.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A method for suppressing inrush current during startup in an inductively coupled energy transfer system includes the following steps:

[0008] Step 1: Establish a mathematical model of the inductively coupled energy transfer system, and calculate and set the start-up time t of the inductively coupled energy transfer system. s ;

[0009] Step 2: Based on the turn-on time t of the bidirectional controllable power switching device in the high-frequency inverter r With turn-off time t f Select a suitable triangular carrier frequency f;

[0010] Step 3: The duty cycle D changes according to a nonlinear saturation function. When the start-up time t is reached... s At that time, the duty cycle D equals 1;

[0011] Step 4: The duty cycle D is compared with the triangular carrier wave to obtain the switching function d. When the switching function d is at a logic high level, the high-frequency inverter adopts phase shift control with a phase shift angle of 0°. When the switching function d is at a logic low level, the high-frequency inverter stops working.

[0012] Furthermore, in step 1, the inductively coupled energy transfer system is based on a series-to-series compensation circuit, and the start-up time of the inductively coupled energy transfer system of the series-to-series compensation circuit satisfies the following formula:

[0013]

[0014] Among them, L p For the self-inductance of the transmitting coil, r p This is the equivalent resistance value of the loss on the original side.

[0015] Furthermore, in step 2, the carrier frequency f satisfies the following formula:

[0016]

[0017] Among them, t r t f These represent the turn-on and turn-off times of the bidirectional controllable power switching devices in the high-frequency inverter.

[0018] Furthermore, the expression for the nonlinear saturation function in step 3 is:

[0019]

[0020] Where t represents time and π is the mathematical constant pi.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] 1. During startup, the phase shift angle is 0°, which enables zero-voltage turn-on of the bidirectional controllable power switching device and reduces the heat generation of the bidirectional controllable power switching device;

[0023] 2. The high-frequency inverter uses a fixed operating frequency, which will not cause system instability and reduce reactive power loss during startup.

[0024] 3. No additional pre-charging circuit is required, resulting in low engineering costs. Attached Figure Description

[0025] Figure 1 This is the circuit topology of an inductively coupled energy transfer system;

[0026] Figure 2 This is a schematic diagram of the drive signal of the high-frequency inverter under the present invention;

[0027] Figure 3 This is a control block diagram for implementing the method of the present invention;

[0028] Figure 4 The waveform of the transmitting coil current without using any soft-start method;

[0029] Figure 5 The transmitting coil current waveform obtained using the method of the present invention;

[0030] Figure 6 This is a schematic diagram of zero-voltage conduction of a high-frequency inverter using the method of the present invention between 0.7 and 0.9 ms.

[0031] Figure 7 This is a schematic diagram of zero-voltage turn-on of a high-frequency inverter using the method of the present invention between 4.1 and 4.12 ms;

[0032] Figure 8 The waveform of the transmitting coil current when the duty cycle D changes according to the ramp-up law.

[0033] In the diagram, 1 is the duty cycle D, 2 is the triangular carrier wave, 3 is the switching function d, 4 is the phase-shift control with a phase angle of 0°, 100 is the primary side of the inductively coupled energy transfer system, 101 is the DC voltage source, 102 is the high-frequency inverter, 103 is the equivalent resistance of the primary side loss, 104 is the primary side compensation capacitor, 105 is the transmitting coil, 200 is the secondary side of the inductively coupled energy transfer system, 201 is the receiving coil, 202 is the secondary side compensation capacitor, 203 is the equivalent resistance of the secondary side loss, 204 is the rectifier filter circuit, 205 is the load, and 120 is the mutual inductance M between the primary side transmitting coil and the secondary side receiving coil. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0035] like Figure 1 As shown, the embodiment of the inductively coupled energy transfer system of the present invention is based on a series-to-series compensation circuit and consists of a primary side 100 and a secondary side 200 of the inductively coupled energy transfer system. The primary side 100 of the inductively coupled energy transfer system consists of a DC voltage source 101, a high-frequency inverter 102, a primary side loss equivalent resistance 103, a primary side compensation capacitor 104, and a transmitting coil 105. The secondary side 200 of the inductively coupled energy transfer system consists of a receiving coil 201, a secondary side compensation capacitor 202, a secondary side loss equivalent resistance 203, a rectifier filter circuit 204, and a load 205. The inductively coupled energy transfer system also includes a mutual inductance M120 between the primary side transmitting coil and the secondary side receiving coil. The high-frequency inverter 102 consists of first to fourth bidirectional controllable power switching devices S1, S2, S3, and S4, and the drive signals for the first to fourth bidirectional controllable power switching devices S1, S2, S3, and S4 are g1, g2, g3, and g4, respectively. The rectifier and filter circuit consists of diodes D1, D2, D3, and D4 (first to fourth) and a filter capacitor. The voltage of the DC voltage source 101 on the primary side is expressed as V. dc The output voltage of the high-frequency inverter 102 is expressed as V. ab The current of the transmitting coil 105 is expressed as I. p The equivalent resistance of the primary side loss is 103, expressed as r. p Primary-side compensation capacitor 104 capacitance value C p The self-inductance of the transmitting coil 105 is represented as L. p The self-inductance of the secondary-side receiving coil 201 is represented as L. s The capacitance value of the secondary compensation capacitor 202 is expressed as C. s The equivalent resistance of the secondary side loss is denoted as r. s The capacitance value of the filter capacitor is expressed as C. o The resistance of the load 205 is represented by R, and the input voltage of the rectifier filter circuit 204 is represented by V. cd The current of the receiving coil 201 is expressed as I. s .

[0036] The positive and negative terminals of the DC voltage source 101 on the primary side are connected to the collectors of the first bidirectional controllable power switch S1 and the third bidirectional controllable power switch S3, and the emitters of the second bidirectional controllable power switch S2 and the fourth bidirectional controllable power switch S4, respectively. The emitter of the first bidirectional controllable power switch S1 is connected to the collector of the second bidirectional controllable power switch S2 as one output terminal of the high-frequency inverter 102, and the emitter of the second bidirectional controllable power switch S2 is connected to the collector of the fourth bidirectional controllable power switch S4 as the other output terminal of the high-frequency inverter 102.

[0037] The cathodes of the first diode D1 and the third diode D3, and the anodes of the second diode D2 and the fourth diode D4 are connected to the positive and negative terminals of the filter capacitor, respectively. The anode of the first diode D1 and the cathode of the second diode D2 are connected as one input terminal of the rectifier filter circuit, and the anode of the third diode D3 and the cathode of the fourth diode D4 are connected as the other input terminal of the rectifier filter circuit.

[0038] like Figure 2 The diagram shows the drive signals of the high-frequency inverter according to the present invention. Within the switching function d = 1, the high-frequency inverter 102 operates using a phase-shift control method with a phase-shift angle of 0°; within the switching function d = 0, the high-frequency inverter 102 stops operating. g1, g2, g3, and g4 are the drive signals for the first to fourth bidirectional controllable power switching devices S1, S2, S3, and S4, respectively.

[0039] like Figure 3 The diagram shown is a control block diagram for implementing the method of this invention. The duty cycle D1 changes according to a nonlinear saturation function. The duty cycle D1 is compared with the triangular carrier wave 2 to obtain the switching function d3, where d=1 represents a logic high level and d=0 represents a logic low level. Combined with the phase shift control 4 with a phase shift angle of 0°, the driving signals g1, g2, g3, and g4 for the first to fourth bidirectional controllable power switching devices S1, S2, S3, and S4 are obtained.

[0040] Figure 3 Startup time t in s Design according to the following method.

[0041] according to Figure 1 The mathematical model of the inductively coupled energy transfer system yields the transmitting coil current I. p With the high-frequency inverter output voltage V ab The ratio G p The expression is:

[0042]

[0043] Where, s is the Laplace differential operator, r p 、L p 、C p These represent the equivalent resistance of the loss on the primary side, the self-inductance of the transmitting coil, and the capacitance of the compensation capacitor, respectively. m Let ω be the reflection impedance, ω be the system resonant angular frequency, and r be the reflection impedance. s 、L s These represent the equivalent resistance of the secondary side losses and the self-inductance of the receiving coil, R. e Let be the AC equivalent resistance, M be the mutual inductance between the transmitting coil and the receiving coil, k be the coupling factor between the transmitting coil and the receiving coil, Q1 and Q2 be the quality factors of the primary and secondary circuits respectively, and ζ1 and ζ2 be the reciprocals of the quality factors Q1 and Q2 respectively.

[0044] Considering the coupling factor k = 0, the transmitting coil current I p The expression for the unit step response is:

[0045]

[0046] Where, t is time, ω d is the damped oscillation frequency.

[0047] transmitting coil current I p The expression for the error between the actual response and the steady-state output is:

[0048]

[0049] Among them, I p (t) represents the transmitting coil current at time t, I p (∞) represents the transmitting coil current in steady state, and δ represents the allowable range of transmitting coil current fluctuation error.

[0050] The quality factor Q1 of the primary-side circuit takes a high value, generally Q1>100, therefore, (ζ1 / 2) 2 <<1. Taking δ = 0.02, then, according to the above formula, the system startup time t can be calculated. s Configure as follows:

[0051]

[0052] Figure 3 Regarding the selection of the carrier frequency f: Theoretically, the higher the carrier frequency f, the smoother the process of the DC voltage source injecting energy into the inductively coupled energy transfer system. However, if the carrier frequency f is too high, it will cause the bidirectional controllable power switch device to fail to turn on and off normally. Therefore, according to the datasheet regarding the turn-on time t of the bidirectional controllable power switch device... r With turn-off time tf The carrier frequency f satisfies the following expression:

[0053]

[0054] Figure 3 In this context, the expression for the nonlinear saturation function is:

[0055]

[0056] Where t represents time and π is the mathematical constant pi.

[0057] In this embodiment, the DC voltage source voltage V dc =100V, the self-inductance L of the primary side transmitting coil was measured. p =22.14μH, capacitance C of the primary-side compensation capacitor p =1.27μF, loss equivalent resistance r p =0.033Ω, self-inductance L of the secondary side receiving coil s =980μH, capacitance C of the secondary compensation capacitor s =28.7nF, equivalent resistance value r s =0.495Ω, capacitance C of the filter capacitor o =1000μF, resistive load resistance R = 6Ω, mutual inductance between transmitting and receiving coils M = 15μH. Therefore, the start-up time t is selected. s =5.25ms. Additionally, the triangular carrier frequency f = 30kHz was selected.

[0058] like Figure 4 The waveform of the transmitting coil current is shown without any soft-start control. The starting inrush current can reach 281A.

[0059] like Figure 5 The figure shows the transmitting coil current waveform using the method of the present invention, at the start-up time t. s The maximum starting current is 41.4A, which is nearly 7 times lower than that of an inductively coupled energy transfer system without soft-start control.

[0060] like Figure 6 This is a schematic diagram of zero-voltage turn-on of a high-frequency inverter using the method of this invention between 0.7 and 0.9 ms, as shown below. Figure 7 The diagram shows a zero-voltage turn-on of a high-frequency inverter using the method of this invention between 4.1 and 4.12 ms. The high-frequency inverter achieves zero-voltage turn-on during startup, which reduces switching losses during startup.

[0061] like Figure 8 This is the waveform of the transmitting coil current when the duty cycle D changes according to a ramp-up pattern. At the start-up time t...s Within this range, the suppression effect of the starting current is consistent with the suppression effect of the duty cycle D changing according to a nonlinear saturation function. However, the starting time t... s After that, the system needs to undergo a certain amount of oscillation before it reaches a steady state.

[0062] In summary, the startup inrush current suppression method of this invention can effectively suppress the inrush current during the startup process of an inductively coupled energy transmission system, effectively solving the problems of overheating or reactive power loss of bidirectional controllable power switching devices that may occur during startup, and with low engineering cost. Furthermore, compared to when the duty cycle D changes according to a ramp-up pattern, the system can reach steady state without oscillation, resulting in superior control performance.

[0063] It will be easily understood by those skilled in the art that the above description is merely 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 scope of protection of the present invention.

Claims

1. A method for suppressing startup impact current of an inductively coupled energy transmission system, characterized in that: The steps include: Step 1: Establish a mathematical model of the inductively coupled energy transmission system, calculate and set the start-up time t of the inductively coupled energy transmission system s ; The inductively coupled energy transmission system is based on a series-series compensation circuit, and the startup time of the inductively coupled energy transmission system of the series-series compensation circuit satisfies the following formula: ， Among them, L p is the self-inductance of the transmitting coil, r p is the loss equivalent resistance value of the primary side; Step 2: According to the opening time t of the bidirectional controllable power switch device in the high-frequency inverter r With the turn-off time t f , select a suitable triangular carrier frequency f; The carrier frequency f satisfies the following formula: ， Among them, t r ,t f They are the turn-on time and turn-off time of the bidirectional controllable power switch device in the high-frequency inverter respectively; Step 3: The duty cycle D changes according to the law of nonlinear saturation function. When the start time t is reached, s When , the duty cycle D is equal to 1; The expression of the nonlinear saturation function is: ， Among them, t represents time, π is pi; Step 4: Compare the duty cycle D with the triangular carrier to obtain the switching function d; when the switching function d is at a logic high level, the high-frequency inverter adopts a phase shift control with a phase shift angle of 0°; when the switching function d is at a logic low level, the high-frequency inverter stops working.

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