Active capacitor based on full-bridge inverter

Abstract

The application discloses a kind of active capacitances based on full-bridge inverter, the active capacitance includes series impedance network, full-bridge inverter and control circuit;The series impedance network includes series inductance and series capacitance, and the series inductance is connected in series with series capacitance;The full-bridge inverter includes first bridge arm, second bridge arm and DC voltage source, and the first bridge arm and second bridge arm are powered by DC voltage source, and the switching node of the first bridge arm is connected to the switching node of second bridge arm both ends of series impedance network;The control circuit samples active capacitance both ends voltage and active capacitance input current in real time, and the output voltage of full-bridge inverter is controlled by closed loop control algorithm to control first bridge arm and second bridge arm, so as to adjust the input current of active capacitance, reach the purpose of adjusting the capacitance value of active capacitance.The application greatly improves the performance of variable capacitor, reduces the cost and volume of variable capacitor.

Description

Technical Field

[0001] This invention relates to the technical field of active devices, and in particular to an active capacitor based on a full-bridge inverter. Background Technology

[0002] In applications such as resonant converters and wireless power transfer, tuning capacitors are essential components. In many applications, variable capacitors are typically used for tuning to improve the flexibility of the resonant network and enhance topology performance. However, existing variable capacitor technologies applicable to resonant networks, such as controllable switched capacitors and controllable capacitor arrays, have significant shortcomings. Controllable switched capacitors suffer from significant current waveform distortion and large inrush current, while controllable capacitor arrays have drawbacks such as discontinuous capacitance values, a large number of switches, and a large number of fixed capacitors. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings and deficiencies of existing technologies and proposes an active capacitor based on a full-bridge inverter. By adjusting the duty cycle of the full-bridge inverter, its equivalent fundamental voltage is adjusted, thereby changing the input current of the active capacitor and achieving the purpose of adjusting the capacitance value. This not only solves the problems of significant current distortion and large inrush current in controllable switched capacitors, but also addresses the issues of discontinuous capacitance values, large number of switches, and large number of fixed capacitors in controllable capacitor arrays. It achieves a variable capacitor with superior performance compared to existing technologies, while reducing cost and size. This invention significantly improves the performance of variable capacitors and reduces their cost and size.

[0004] To achieve the above objectives, the technical solution provided by this invention is as follows: an active capacitor based on a full-bridge inverter, wherein the active capacitor includes a series impedance network, a full-bridge inverter, and a control circuit; the series impedance network includes a series inductor and a series capacitor, wherein the series inductor and the series capacitor are connected in series; the full-bridge inverter includes a first bridge arm, a second bridge arm, and a DC voltage source, wherein the first bridge arm and the second bridge arm are powered by the DC voltage source, and the switching nodes of the first bridge arm and the second bridge arm are connected to the two ends of the series impedance network; the control circuit samples the voltage across the active capacitor and the input current of the active capacitor in real time, and controls the first bridge arm and the second bridge arm through a closed-loop control algorithm to adjust the output voltage of the full-bridge inverter, thereby adjusting the input current of the active capacitor and achieving the purpose of adjusting the capacitance value of the active capacitor.

[0005] Furthermore, the capacitance value C of the active capacitor ACT Controlled by the output voltage duty cycle of the full-bridge inverter, the capacitor value and the duty cycle satisfy the following equation:

[0006]

[0007] In the formula, j is the imaginary unit, ω CZ is the operating frequency of the active capacitor. ACT V is the impedance of the active capacitor. C V is the voltage phasor across the active capacitor. AB C is the output voltage phasor of the full-bridge inverter; E V is the equivalent capacitance of the series impedance network. DC is the DC voltage source voltage; D is the duty cycle of the full-bridge inverter output voltage.

[0008] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0009] 1. Compared with controllable switched capacitors, the current waveform of this invention is undistorted.

[0010] 2. Compared with controllable switched capacitors, the present invention has no surge current.

[0011] 3. Compared with controllable capacitor arrays, the capacitance value of the present invention can be continuously adjusted.

[0012] 4. Compared with controllable capacitor arrays, the circuit of this invention is simple and requires fewer switching devices.

[0013] 5. Compared with controllable capacitor arrays, the present invention requires fewer capacitors, only one capacitor is needed. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of an embodiment of the present invention.

[0015] Figure 2 This is a simulation model diagram of the active capacitor main circuit according to an embodiment of the present invention.

[0016] Figure 3 This is a block diagram of active capacitor control according to an embodiment of the present invention.

[0017] Figure 4 This is a simulation model diagram of the active capacitor control circuit according to an embodiment of the present invention.

[0018] Figure 5 This is a simulation waveform diagram of the voltage across the active capacitor and the input current in an embodiment of the present invention.

[0019] Figure 6 This is a graph showing the relationship between the capacitance value and duty cycle of the active capacitor in an embodiment of the present invention. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0021] like Figure 1As shown, this embodiment discloses an active capacitor based on a full-bridge inverter, including a series impedance network, a full-bridge inverter, and a control circuit. The series impedance network includes a series inductor and a series capacitor, which are connected in series. The full-bridge inverter includes bridge arm 1, bridge arm 2, and a DC voltage source. Bridge arm 1 and bridge arm 2 are powered by the DC voltage source. The switching nodes of bridge arm 1 and bridge arm 2 are connected to the two ends of the series impedance network. The control circuit samples the voltage V across the active capacitor in real time. C and the input current I of the active capacitor C By controlling the duty cycle D of the full-bridge inverter's output voltage through a closed-loop algorithm, the fundamental component I of the full-bridge inverter's output voltage is changed. AB This adjusts the input current I of the active capacitor. C This achieves the purpose of adjusting the capacitance value of the active capacitor.

[0022] In the above active capacitor, according to Kirchhoff's laws, the input current of the active capacitor can be expressed as:

[0023]

[0024] In the formula, I C V is the input current phasor of the active capacitor; C Z is the voltage phasor across the active capacitor. S The impedance of the series impedance network is the sum of the series inductor impedance and the series capacitor impedance; V AB Let V be the fundamental phasor of the output voltage of the full-bridge inverter, and V C With V AB The frequencies and phases are the same. Fourier decomposition of the output voltage of the full-bridge inverter yields its fundamental phasor as:

[0025]

[0026] In the formula, V DC is the voltage of the DC voltage source; D is the duty cycle of the output voltage of the full-bridge inverter.

[0027] Properly design the series capacitor so that the series impedance network operates at the active capacitor's angular frequency ω. C The process exhibits capacitive properties. For ease of explanation, a process variable C is introduced. E , representing the equivalent capacitance of the series impedance network. The impedance Z of the series impedance network can then be expressed as... S Represented as:

[0028]

[0029] That is, let the capacitance value C of the series capacitor be S satisfy

[0030]

[0031] According to the definition of impedance, the impedance Z of an active capacitor is... ACT It can be represented as:

[0032]

[0033] The capacitance value C of the active capacitor is then... ACT It can be represented as:

[0034]

[0035] Due to V C With V AB Since they are in phase, the coefficient α is a real number. The capacitance value of the active capacitor can be adjusted by changing the duty cycle of the full-bridge inverter through the control circuit.

[0036] like Figure 2 As shown, the simulation model of the main circuit of the active capacitor is based on Figure 1 The system consists of a series inductor, a series capacitor, bridge arm 1, bridge arm 2, a DC voltage source, and a control circuit. The operating frequency of the active capacitor is ω. C =2π×10 5 rad / s; the inductance value of the series inductor is L S =200μH; Let the equivalent capacitance of the series impedance network be C. E =1.0μF, then according to equation (4), the capacitance value C of the series capacitor can be obtained. S =12.5nF; Voltage V of the DC voltage source DC =100V; A sinusoidal voltage source is connected across the active capacitor to simulate the application environment. The voltage amplitude of the sinusoidal voltage source is 80V, and the angular frequency is 2π×10⁻⁶. 5 rad / s.

[0037] like Figure 3 As shown, the control strategy for an active capacitor is as follows: First, the desired capacitance value of the active capacitor is given. Desired capacitance value With the expected impedance modulus The relationship between capacitance value C ACT With impedance mode |Z ACT The relationship is consistent, therefore the desired impedance modulus can be calculated using equation (6). Then, the desired input current is calculated based on the voltage across the active capacitor. With actual input current I C Subtraction yields the current error E C The current is then fed into a PID controller and compensated to obtain the duty cycle D. Finally, after passing through the full-bridge inverter gain, an excitation is applied to the series impedance network to generate the current response I. CThe steps for tuning the control parameters are as follows:

[0038] The transfer function of a PID controller can be expressed as:

[0039]

[0040] In the simulation model, the ramp voltage amplitude of the PWM generator module is set to 1V, then the gain of the full-bridge inverter can be expressed as:

[0041]

[0042] The transfer function of a series impedance network can be expressed as:

[0043]

[0044] By employing the zero-pole cancellation method, the two zeros of the PID controller cancel out the double poles of the series impedance network, thus obtaining...

[0045]

[0046] Setting K I =2.00000, then K P =6.32626×10 -6 ,K D =5.00270×10 -12 .

[0047] like Figure 4 As shown, the control circuit includes a voltage and current RMS value calculation module, a phase difference calculation module, a current expected value calculation module, a PID control module, and a PWM generation module. The input quantities of the control circuit include the expected capacitance value of the active capacitor. Voltage V across the active capacitor C The sampled value, the active capacitor input current I C The sampled values; the output of the control circuit is the control signal for the two arms of the full-bridge inverter.

[0048] Set the desired capacitance value of the active capacitor The steady-state waveforms of the voltage across the active capacitor, the input current to the active capacitor, and the output voltage of the full-bridge inverter are as follows: Figure 5 As shown. The voltage across the active capacitor lags the input current of the active capacitor by 87.48°. Active capacitor input current Substituting into equation (5), the impedance Z of the active capacitor can be obtained. ACT =8.0∠-87.48°Ω, substituting into equation (6) yields the capacitance value C of the active capacitor. ACT=198.8nF. The capacitance value error is less than 0.6%, exhibiting excellent accuracy. The error mainly comes from the internal resistance of the series impedance network, therefore there is still room for optimization.

[0049] The relationship between the capacitance value of the active capacitor and the duty cycle of the full-bridge inverter output voltage is shown in the curve below. Figure 6 As shown, the theoretical results obtained by equation (6) are in agreement with the simulation results, proving the correctness of the theoretical derivation of this invention.

[0050] Based on the above analysis, the active capacitor based on the full-bridge inverter provided by this invention can completely replace the traditional controllable switched capacitor and controllable capacitor array. The advantages of this invention are obvious and it is worth promoting.

[0051] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An active capacitor based on a full-bridge inverter, characterized in that: The active capacitor includes a series impedance network, a full-bridge inverter, and a control circuit. The series impedance network includes a series inductor and a series capacitor, which are connected in series. The full-bridge inverter includes a first bridge arm, a second bridge arm, and a DC voltage source. The first and second bridge arms are powered by the DC voltage source, and the switching nodes of the first and second bridge arms are connected to the two ends of the series impedance network. The control circuit samples the voltage across the active capacitor and the input current of the active capacitor in real time, and uses a closed-loop control algorithm to control the first and second bridge arms to adjust the output voltage of the full-bridge inverter, thereby adjusting the input current of the active capacitor and achieving the purpose of adjusting the capacitance value of the active capacitor. The capacitance value C of the active capacitor ACT Controlled by the output voltage duty cycle of the full-bridge inverter, the capacitor value and the duty cycle satisfy the following equation: In the formula, j is the imaginary unit, ω C Z is the operating frequency of the active capacitor. ACT V is the impedance of the active capacitor. C V is the voltage phasor across the active capacitor. AB C is the output voltage phasor of the full-bridge inverter; E V is the equivalent capacitance of the series impedance network; DC is the DC voltage source voltage; D is the duty cycle of the full-bridge inverter output voltage.

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