A high-performance DC converter suitable for a current source type WPT receiving end system

Abstract

A kind of high-performance DC converter suitable for current source type WPT receiving end system, the present application belongs to the field of wireless power transmission system, the present application includes first switch tube G1, second switch tube G2, third switch tube G3, rectifier filter capacitor C dc , output capacitor C o , inductance L and output load R, the first end of first switch tube G1 and the first end of second switch tube G2 are connected to the positive output end of rectifier circuit, the second end of first switch tube G1 is connected to rectifier filter capacitor C dc ;The first end of second switch tube G2 is connected to the first end of third switch tube G3 and the first end of inductance L respectively, the second end of inductance L is connected to the first end of output capacitor C o And the first end of output load R, the second end of rectifier filter capacitor C dc , the second end of third switch tube G3, the second end of output capacitor C o And the second end of output load R are connected to the negative output end of rectifier circuit.The high-performance DC converter without right half plane zero point is designed to eliminate the right half plane zero point of traditional converter, improve the control performance of system.

Description

TECHNICAL FIELD

[0001] The present application relates to a DC converter, in particular to a high-performance DC converter suitable for a current source type WPT receiving end system, and belongs to the field of wireless power transmission systems. BACKGROUND

[0002] Compared with the traditional contact type wired power supply, the wireless power transmission technology has the advantages of high reliability, high intelligence and high flexibility. At present, the WPT technology has been widely applied to electric vehicles, biological medicine, intelligent inspection robots and intelligent wearable devices and other fields. For the WPT system, the stable and controllable voltage and current at both ends of the load are the basic requirements. The principle diagram of the traditional wireless power transmission system is shown in Figure 1 The receiving end often adds a Buck converter after the rectifier circuit, which can obtain a stable output voltage and dynamically adjust the equivalent impedance of the system to improve the transmission efficiency of the system through the control of the Buck converter.

[0003] Traditional research believes that the control transfer function of the Buck converter has no right half plane zero (RHPz) and is a minimum phase system with good control characteristics. However, in the WPT system, when using S-S, LCC-LCC, LCL-LCL and other compensation networks with constant current output characteristics, the control transfer function of the Buck converter will have a right half plane zero, and at this time the control system is a non-minimum phase system. In the time domain, when the control system is under the action of a step signal, the deviation between the actual value and the expected value of the controlled quantity will first increase and then decrease in the initial stage, and a negative overshoot phenomenon will occur. During the negative overshoot stage, the controller will receive false signals, resulting in an increase in the regulation time of the system and a decrease in the stability of the system, and even a positive feedback will be formed, leading to unstable output.

[0004] The right half plane zero of the non-minimum phase system cannot be directly compensated by the traditional controller, and some existing parameter design criteria and control methods can reduce the negative effects of the non-minimum phase characteristics to a certain extent, thereby improving the control performance of the system. However, these methods cannot essentially eliminate the RHPz of the system, and the system is essentially a non-minimum phase system. Therefore, it is of great significance to analyze and design a converter without RHPz for designing a high-performance wireless power transmission system. SUMMARY

[0005] The present application is proposed to solve the problem of low bandwidth and low stability caused by the right half plane zero of the existing converter, and a high-performance DC converter suitable for a current source type WPT receiving end system is proposed.

[0006] The technical scheme adopted by the present application to solve the above problems is:

[0007] The present application comprises a first switch tube G1, a second switch tube G2, a third switch tube G3, a rectification filter capacitor C dc , an output capacitor C o , an inductor L and an output load R, the first end of the first switch tube G1 and the first end of the second switch tube G2 are connected to the positive output end of the rectification circuit, the second end of the first switch tube G1 is connected to the rectification filter capacitor C dc , the second end of the second switch tube G2 is respectively connected to the first end of the third switch tube G3 and the first end of the inductor L, the second end of the inductor L is connected to the first end of the output capacitor C o and the first end of the output load R, the second end of the rectification filter capacitor C dc , the second end of the third switch tube G3, the second end of the output capacitor C o and the second end of the output load R are connected to the negative output end of the rectification circuit.

[0008] Further, the converter is provided with three working states, which are as follows:

[0009] (1) State 1 [t0 < t ≤ t1] (d1T):

[0010] When t = t0, the first switch tube G1 is off, the second switch tube G2 and the third switch tube G3 are on, the receiving end of the WPT system is short-circuited by the second switch tube G2 and the third switch tube G3, the current i r flows through the second switch tube G2 and the third switch tube G3 for freewheeling, at this time the WPT system does not charge the capacitor C dc , at this time the third switch tube G3 is on, the inductor L flows through the third switch tube G3 for freewheeling, the inductor L and the output capacitor C o provide energy for the load R; in this state, the WPT system neither charges the capacitor C dc nor provides energy for the load;

[0011] (2) State 2 [t1 < t ≤ t2] (d2T):

[0012] When t = t1, the second switch tube G2 is off, the first switch tube G1 and the third switch tube G3 are on; at this time the WPT system charges the capacitor C dc , the inductor L flows through the third switch tube G3 for freewheeling, the inductor L and the output capacitor C o provide energy for the load R;

[0013] (3) State 3 [t2 < t ≤ t3] (d3T):

[0014] When t=t2, the third switch tube G3 is off, and the first switch tube G1 and the second switch tube G2 are on; at this time, the WPT system and the capacitor C dc provide energy for the inductor L and the output capacitor C o and the load.

[0015] Further, the duty cycles in the three states should satisfy the following relationship:

[0016] d1+d2+d3=1 (1)

[0017] In the formula, d1 is the ratio of the working time of state 1 to the period; d2 is the ratio of the working time of state 2 to the period; and d3 is the ratio of the working time of state 3 to the period.

[0018] Further, according to the ampere-second balance of C dc and C o and the volt-second balance of L, the steady-state expression of the output voltage U o is:

[0019]

[0020] In the formula, γ=1+cos(D1π), I s is the maximum value of the input current, D3 is the duty cycle of state 3, and R is the output load.

[0021] Further, modeling analysis is performed on the designed converter, and the transfer function of the duty cycle d1 of the designed converter to the output voltage U o is:

[0022]

[0023] In the formula, C dc and C o are the rectifier filter capacitor and the output capacitor respectively, L is the inductor, D1 and D3 are the duty cycles of state 1 and state 3 respectively, R is the output load, and I s is the maximum value of the input current.

[0024] As can be seen from formula (3), the transfer function of the designed converter to the output voltage does not have a right half plane zero point, and it is a minimum phase system.

[0025] The beneficial effects of the present application are: the right half plane zero point existing in the traditional current source type Buck converter is fundamentally eliminated, the non-minimum phase characteristic is eliminated, the system bandwidth can be effectively improved, and the system stability is enhanced.

[0026] The application adopts a circuit topology design method, and is based on the physical nature of the right half plane zero point of a Buck converter in a wireless power transmission system to design a high-performance DC converter without the right half plane zero point, so as to eliminate the right half plane zero point of a traditional converter and improve the control performance of the system. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a structural schematic diagram of a traditional wireless power transmission system;

[0028] Figure 2 is a structural schematic diagram of a converter of the application;

[0029] Figure 3 is an equivalent circuit model of the application in different states;

[0030] Figure 4 is a key waveform diagram of the converter of the application. DETAILED DESCRIPTION

[0031] DETAILED DESCRIPTION: The embodiment adopts a circuit topology design method, and is based on the physical nature of the right half plane zero point (RHPz) of a Buck converter in a wireless power transmission system to design a high-performance DC converter without the right half plane zero point, so as to eliminate the RHPz of a traditional converter and improve the control performance of the system. The schematic diagram of the designed converter is shown in the figure. Figure 2 C dc is a rectifier filter capacitor, L is a filter inductor, C o is an output filter capacitor, R is an output load, i s is a rectifier input current, U dc is a filter capacitor voltage, U o is an output capacitor voltage, and I L is an inductor current.

[0032] The new circuit topology structure adds a switch tube G1 at the filter capacitor C dc of the traditional Buck circuit, and increases a control degree of freedom.

[0033] The specific structure of the converter is that the first switch tube G1, the second switch tube G2, the third switch tube G3, the rectifier filter capacitor C dc , the output capacitor C o , the inductor L and the output load R are connected, the first end of the first switch tube G1 and the first end of the second switch tube G2 are connected to the positive output end of the rectifier circuit, the second end of the first switch tube G1 is connected to the rectifier filter capacitor C dc , the second end of the second switch tube G2 is respectively connected to the first end of the third switch tube G3 and the first end of the inductor L, and the second end of the inductor L is connected to the output capacitor C othe first end of the rectifier filter capacitor C dc the second end of the output capacitor C o the second end of the rectifier filter capacitor C

[0034] The equivalent circuit diagrams of the designed Buck circuit in different working states are shown in Figure 3 For convenience of analysis, it is defined that the ratio of the working time of the three working states of the designed Buck circuit to the period is d1, d2 and d3 respectively.

[0035] The key waveforms of the designed converter are shown in Figure 4 The analysis of the designed converter in different states is as follows:

[0036] (1) State 1 [t0 < t < t1] (d1T):

[0037] Figure 3 (a) shows the equivalent circuit diagram of state 1. When t = t0, the first switch G1 is off, and the second switch G2 and the third switch G3 are on. The receiving end of the WPT system is short-circuited by the second switch G2 and the third switch G3, and the current i r continues to flow through the second switch G2 and the third switch G3, and at this time the WPT system does not charge the capacitor C dc At this time, the third switch G3 is on, the inductor L continues to flow through the third switch G3, and the inductor L and the output capacitor C o provide energy to the load R. In this state, the WPT system neither charges the capacitor C dc nor provides energy to the load.

[0038] (2) State 2 [t1 < t < t2] (d2T):

[0039] Figure 3 (b) shows the equivalent circuit diagram of state 2. When t = t1, the second switch G2 is off, and the first switch G1 and the third switch G3 are on. At this time, the WPT system charges the capacitor C dc , the inductor L continues to flow through the third switch G3, and the inductor L and the output capacitor C o provide energy to the load R.

[0040] (3) State 3 [t2 < t < t3] (d3T):

[0041] Figure 3 (c) shows the equivalent circuit diagram of state 3. When t = t2, the third switch G3 is off, and the first switch G1 and the second switch G2 are on. At this time, the WPT system and the capacitor C dcFor the inductor L and the output capacitor C o It provides energy to the load.

[0042] The duty cycle under various states should satisfy the following relationship:

[0043] d1+d2+d3=1 (1)

[0044] This circuit has three operating states. To eliminate the right-half-plane zeros in the transfer function, the duty cycle d3 of state 3, which supplies power to the load, should remain constant. If the timing of this state is placed in the second position, changing the duration of the other two states will affect the input current of this state. Thus, even if the duration of state 3 remains constant, changing the duration of the other two states will affect the energy supplied to the load in each cycle. Therefore, the timing of state 3 can only be either the first or third position. To reduce the voltage withstand requirement of the first switching transistor G1, the capacitor C should be... dc Charge first, then discharge. In state 1, the wireless receiver uses the second switch G2 and the third switch G3 for freewheeling, without affecting the capacitor C. dc Charging does not provide energy to the load, resulting in low energy transfer efficiency. Therefore, to improve the system's energy transfer efficiency, the input current in this state should be minimized, and the system's operating timing should be selected as follows: Figure 4 As shown, the working sequence is state 1-state 2-state 3.

[0045] By C dc and C o The output voltage U can be obtained from the ampere-second balance and the volt-second balance of L. o The steady-state expression is:

[0046]

[0047] Here, γ = 1 + cos(D1π), I s Here, D3 represents the maximum input current, D3 represents the duty cycle of state 3, and R represents the output load. The basic idea of ​​the above converter is to introduce an additional circuit state (state 1) so that the input capacitor C... dc Charging time, inductor L and output capacitor C o The energy release time can be controlled independently. This is because only the output capacitor C is in state 3. o The inductor L stores energy, and energy is released in both states 1 and 2. If the duty cycle (d3) in state 3 is kept constant, and only d1 and d2 are adjusted, this circuit can change the input capacitance C. dc The charging time does not affect the output capacitor C. o The time it takes for the inductor L to release energy is used to eliminate the non-minimum phase characteristic of the system.

[0048] Modeling and analyzing the designed converter, the transfer function of the designed converter duty cycle d1 to output voltage U o is obtained as follows:

[0049]

[0050] wherein C dc and C o are rectification filter capacitor and output capacitor respectively, L is inductance, D1 and D3 are duty cycles of state 1 and state 3 respectively, R is output load, I s is the maximum value of input current. It can be seen from equation (3) that the transfer function of the designed converter control to output voltage does not have right half plane zero point, and is a minimum phase system.

[0051] The above merely describes preferred embodiments of the present application and is not intended to limit the present application in any form. Although the present application has been disclosed as above with preferred embodiments, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical contents without departing from the technical solution of the present application, and any simple modification, equivalent replacement and improvement of the above embodiments within the technical solution of the present application and the spirit and principle of the present application are all within the protection scope of the present application.

Claims

1. A high-performance DC converter suitable for a current-source type WPT receiving-end system, characterized in that, The converter comprises a first switch tube , a second switch tube , a third switch tube , a rectification filtering capacitor , an output capacitor , an inductor and an output load , the first end of the first switch tube and the first end of the second switch tube are connected to the positive output end of the rectification circuit, the second end of the first switch tube is connected to the rectification filtering capacitor , the second end of the second switch tube is respectively connected to the first end of the third switch tube and the first end of the inductor , the second end of the inductor is connected to the first end of the output capacitor and the first end of the output load , the second end of the rectification filtering capacitor , the second end of the third switch tube , the second end of the output capacitor and the second end of the output load are connected to the negative output end of the rectification circuit.

2. The high-performance DC converter suitable for a current-source type WPT receiving-end system according to claim 1, characterized in that, The converter is provided with three working states, and the states are as follows: (1) State 1 : When the first switch tube is turned off, the second switch tube and the third switch tube are turned on, the receiving end of the WPT system is short-circuited by the second switch tube and the third switch tube , the current flows through the second switch tube and the third switch tube for freewheeling, at this time, the WPT system does not charge the capacitor ; at this time, the third switch tube is turned on, the inductor flows through the third switch tube for freewheeling, the inductor and the output capacitor provide energy for the load ; in this state, the WPT system neither charges the capacitor nor provides energy for the load (2) State 2 ]: When the second switch tube is turned off, the first switch tube and the third switch tube are turned on; at this time, the WPT system charges the capacitor , the inductor continues to flow through the third switch tube , the inductor and the output capacitor provide energy for the load ; (3) State 3 ]: When the third switch tube is off, the first switch tube and the second switch tube are on; at this time, the WPT system and the capacitor provide energy for the inductor and the output capacitor and the load.

3. The high-performance DC converter suitable for a current-source type WPT receiving-end system according to claim 2, characterized in that, The duty cycles of the three states should satisfy the following relationship: (1) wherein is the ratio of the on-time to the period for state 1 ; is the ratio of the on-time to the period for state 2; The ratio of the working time to the period for state 3.

4. The high-performance DC converter suitable for a current-source type WPT receiving-end system according to claim 2, characterized in that, The output voltage and ampere balance and volt-second balance of the output voltage The steady-state expression for the output voltage (2) wherein , is the maximum value of the input current, is the duty cycle of state 3, is the output load.

5. The high-performance DC converter suitable for a current-source type WPT receiving-end system according to claim 2, characterized in that, Modeling analysis of the designed converter can obtain the duty cycle of the designed converter The transfer function of the output voltage is (3) wherein and are a rectifying filter capacitor and an output capacitor, respectively, is an inductance, and are duty cycles of state 1 and state 3, respectively, is an output load, is a maximum value of the input current; It can be seen from equation (3) that the transfer function of the designed converter control to the output voltage does not have a right half plane zero point, and is a minimum phase system.

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