High-performance direct-current converter suitable for current source type WPT receiving end system

Abstract

A high-performance DC converter suitable for a current source type WPT receiving end system belongs to the field of wireless power transmission systems, and comprises a first switch tube G1, a second switch tube G2, a third switch tube G3, a rectification filter capacitor Cdc, an output capacitor Co, an inductor L and an output load R, the first end of the first switching tube G1 and the first end of the second switching tube G2 are connected with the positive output end of the rectifying circuit, and the second end of the first switching tube G1 is connected with the rectifying and filtering capacitor Cdc; the second end of the second switch tube G2 is connected with the first end of a third switch tube G3 and the first end of an inductor L. The second end of the inductor L is connected with the first end of an output capacitor Co and the first end of an output load R. The second end of the rectification filter capacitor Cdc, the second end of the third switch tube G3, the second end of the output capacitor Co and the second end of the output load R are connected with the negative output end of the rectification circuit. By designing the high-performance direct-current converter without the right half plane zero point, the right half plane zero point of a traditional converter is eliminated, and the control performance of the system is improved.

Description

Technical Field

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

[0002] Compared with traditional contact wired power supply, wireless power transmission technology has the advantages of high reliability, high intelligence and high flexibility. At present, WPT technology has been widely used in electric vehicles, biomedicine, intelligent inspection robots and smart wearable devices. For the WPT system, the voltage and current at both ends of the load must be stable and controllable. The schematic diagram of the traditional wireless power transmission system is as follows: Figure 1 As shown, the receiving end often adds a Buck converter after the rectifier circuit. By controlling the Buck converter, on the one hand, a stable output voltage can be obtained, and on the other hand, the equivalent impedance of the system can be dynamically adjusted to improve the transmission efficiency of the system.

[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. In the WPT system, when the compensation network with constant current output characteristics such as SS, LCC-LCC, LCL-LCL is used, the control transfer function of the Buck converter will have a right half plane zero, and the control system is a non-minimum phase system. The right half plane zero is manifested in the time domain as follows: when the control system is under the action of a step signal, the deviation between the actual value of the controlled quantity and the expected value will increase first and then decrease in the initial stage, resulting in a negative overshoot phenomenon. In the negative overshoot stage, the controller will receive an erroneous signal, resulting in an increase in the system's adjustment time, a decrease in the system's stability, and even a positive feedback, resulting in unstable output.

[0004] The zero point of the right half plane in the non-minimum phase system cannot be directly compensated by the traditional controller. Some existing parameter design criteria and control methods can reduce the negative impact of its non-minimum phase characteristics to a certain extent, thereby improving the control performance of the system. However, these methods cannot eliminate the RHPz of the system in essence, and the system is still a non-minimum phase system in essence. Therefore, analyzing and designing a converter without RHPz is of great significance to the design of high-performance wireless power transmission systems. Summary of the invention

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

[0006] The technical solution adopted by the present invention to solve the above problems is:

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

[0008] Furthermore, the converter has three working states, as follows:

[0009] (1) State 1 [t0<t≤t1] (d1T):

[0010] When t=t0, the first switch tube G1 is turned off, the second switch tube G2 and the third switch tube G3 are turned on, and the receiving end of the WPT system is short-circuited by the second switch tube G2 and the third switch tube G3. r The second switch tube G2 and the third switch tube G3 are used for freewheeling. At this time, the WPT system will not dc At this time, the third switch tube G3 is turned on, and the inductor L is freewheeling through the third switch tube G3, and the inductor L and the output capacitor C o Provide energy to the load R; in this state, the WPT system neither supplies energy to the capacitor C dc Charging, nor providing energy to the load;

[0011] (2) State 2 [t1<t≤t2] (d2T):

[0012] When t=t1, the second switch tube G2 is turned off, and the first switch tube G1 and the third switch tube G3 are turned on; at this time, the WPT system supplies power to the capacitor C dc The inductor L is charged, and the third switch tube G3 is used for freewheeling. The inductor L and the output capacitor C o Provide energy to load R;

[0013] (3) State 3 [t2<t≤t3] (d3T):

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

[0015] Furthermore, the duty cycle in the three states should satisfy the following relationship:

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

[0017] Where d1 is the ratio of the working time to the cycle in state 1; d2 is the ratio of the working time to the cycle in state 2; d3 is the ratio of the working time to the cycle in state 3.

[0018] Furthermore, by C dc and C o The ampere-second balance of and the volt-second balance of L can be obtained as the output voltage U o The steady-state expression 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] Furthermore, by modeling and analyzing the designed converter, the effect of the designed converter duty cycle d1 on the output voltage U can be obtained. o The transfer function is:

[0022]

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

[0024] It can be seen from equation (3) that the transfer function from the designed converter control to the output voltage does not have a right half plane zero and is a minimum phase system.

[0025] The beneficial effects of the present invention are: fundamentally eliminating the right half plane zero point existing in the traditional current source Buck converter, eliminating its non-minimum phase characteristic, and effectively improving the system bandwidth and enhancing the system stability.

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

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

[0028] Figure 2 It is a schematic diagram of the overall structure of the converter of the present invention;

[0029] Figure 3 is the equivalent circuit model of the present invention under different states;

[0030] Figure 4 It is the key waveform diagram of the converter of the present invention. DETAILED DESCRIPTION

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

[0032] The new circuit topology is based on the traditional Buck circuit, with the filter capacitor C dc A switch tube G1 is added to increase a degree of control freedom.

[0033] The specific structure of the converter is as follows: a first switch tube G1, a second switch tube G2, a third switch tube G3, a rectifier filter capacitor C dc , output capacitor C o , inductor L and 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 rectifier circuit, and 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 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 output load R, the rectifier filter capacitor C dc The second end of the third switch tube G3, the second end of the output capacitor C o The second end of and the second end of the output load R are connected to the negative output end of the rectifier circuit.

[0034] After adding the new switch tube, the equivalent circuit diagrams of the designed Buck circuit in different working states are as follows: Figure 3 For the convenience of analysis, the ratios of the working time to the cycle of the three working states of the designed Buck circuit are specified as d1, d2 and d3 respectively.

[0035] The key waveforms of the designed converter are as follows: Figure 4 As shown, the different states of the designed converter are analyzed 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 tube G1 is turned off, and the second switch tube G2 and the third switch tube G3 are turned on. The receiving end of the WPT system is short-circuited by the second switch tube G2 and the third switch tube G3, and the current i r The second switch tube G2 and the third switch tube G3 are used for freewheeling. At this time, the WPT system will not dc At this time, the third switch tube G3 is turned on, and the inductor L is freewheeling through the third switch tube G3. The inductor L and the output capacitor C o Provide energy to load R. In this state, the WPT system neither supplies energy to capacitor C dc It does not charge nor provide 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 tube G2 is turned off, and the first switch tube G1 and the third switch tube G3 are turned on. At this time, the WPT system provides capacitor C dc The inductor L is charged, and the third switch tube G3 is used for freewheeling. 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 tube G3 is turned off, and the first switch tube G1 and the second switch tube G2 are turned on. At this time, the WPT system and the capacitor C dcis the inductor L and the output capacitor C o and provide energy to the load.

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

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

[0044] This circuit has three working states. In order to eliminate the right half plane zero in the transfer function, the duty cycle d3 of state 3 for powering the load should be kept unchanged. 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. In this way, even if the duration of state 3 remains unchanged, changing the duration of the other two states will affect the energy for powering the load in each cycle. Therefore, the timing of state 3 can only be the first or third. In order to reduce the withstand voltage requirement for the first switch tube G1, the capacitor C dc First charge and then discharge. In state 1, the wireless receiving end uses the second switch tube G2 and the third switch tube G3 for freewheeling, and does not charge the capacitor C dc Charging does not provide energy to the load, and the energy transmission efficiency is low. Therefore, in order to improve the energy transmission efficiency of the system, the input current in this state should be minimized, and the system working sequence 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 ampere-second balance of and the volt-second balance of L can be obtained as the output voltage U o The steady-state expression is:

[0046]

[0047] Here 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. The basic idea of ​​the above converter is to introduce an additional circuit state (state 1) so that the input capacitor C dc The charging time and inductor L and output capacitor C o The time of releasing energy can be controlled independently. o The input capacitor C is stored in the circuit and the inductor L stores energy. The energy is released in both state 1 and state 2. If the duty cycle (d3) of state 3 is maintained unchanged, only d1 and d2 are adjusted. This circuit can achieve the change of input capacitance C dc The charging time does not affect the output capacitance C o And the time for the inductor L to release energy, thus eliminating the non-minimum phase characteristics of the system.

[0048] By modeling and analyzing the designed converter, we can obtain the effect of the designed converter duty cycle d1 on the output voltage U o The transfer function is:

[0049]

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

[0051] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement made to the above embodiments without departing from the content of the technical solution of the present invention, based on the technical essence of the present invention, within the spirit and principles of the present invention, still fall within the protection scope of the technical solution of the present invention.

Claims

1. A high-performance DC converter suitable for a current source type WPT receiving end system, characterized in that: The converter includes a first switch tube G1, a second switch tube G2, a third switch tube G3, a rectifier filter capacitor C dc , output capacitor C o , inductor L and 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 rectifier circuit, and 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 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 o The first end of the output load R, the rectifier filter capacitor C dc The second end of the third switch tube G3, the second end of the output capacitor C o The second end of and the second end of the output load R are connected to the negative output end of the rectifier circuit.

2. According to claim 1, a high-performance DC converter suitable for a current source type WPT receiving end system is characterized in that: The converter has three working states, as follows: (1) State 1 [t0<t≤t1] (d1T): When t=t0, the first switch tube G1 is turned off, the second switch tube G2 and the third switch tube G3 are turned on, and the receiving end of the WPT system is short-circuited by the second switch tube G2 and the third switch tube G3. r The second switch tube G2 and the third switch tube G3 are used for freewheeling. At this time, the WPT system will not dc At this time, the third switch tube G3 is turned on, and the inductor L is freewheeling through the third switch tube G3, and the inductor L and the output capacitor C o Provide energy to the load R; in this state, the WPT system neither supplies energy to the capacitor C dc Charging, nor providing energy to the load; (2) State 2 [t1<t≤t2] (d2T): When t=t1, the second switch tube G2 is turned off, and the first switch tube G1 and the third switch tube G3 are turned on; at this time, the WPT system supplies power to the capacitor C dc The inductor L is charged, and the third switch tube G3 is used for freewheeling. The inductor L and the output capacitor C o Provide energy to load R; (3) State 3 [t2<t≤t3] (d3T): When t=t2, the third switch tube G3 is turned off, and the first switch tube G1 and the second switch tube G2 are turned on; at this time, the WPT system and the capacitor C dc is the inductor L and the output capacitor C o and provide energy to the load.

3. A high-performance DC converter suitable for a current source type WPT receiving end system according to claim 2, characterized in that: The duty cycle in the three states should satisfy the following relationship: d1+d2+d3=1 (1) Where d1 is the ratio of the working time of state 1 to the cycle; d2 is the ratio of the working time of state 2 to the cycle; d3 is the ratio of the working time of state 3 to the cycle.

4. A high-performance DC converter suitable for a current source type WPT receiving end system according to claim 2, characterized in that: By C dc and C o The ampere-second balance of and the volt-second balance of L can be obtained as the output voltage U o The steady-state expression is: 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.

5. A high-performance DC converter suitable for a current source type WPT receiving end system according to claim 2, characterized in that: By modeling and analyzing the designed converter, we can obtain the effect of the designed converter duty cycle d1 on the output voltage U o The transfer function is: In the formula, C dc and C o are the rectifier filter capacitor and the output capacitor, L is the inductor, D1 and D3 are the duty cycles of state 1 and state 3, R is the output load, I s is the maximum value of the input current; It can be seen from equation (3) that the transfer function from the designed converter control to the output voltage does not have a right half plane zero and is a minimum phase system.

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