A method for suppressing secondary harmonic current of a phase-shifted full-bridge converter

Abstract

This invention discloses a method for suppressing second harmonic current in a phase-shifted full-bridge converter. Firstly, a series virtual impedance is introduced at the output of the phase-shifted full-bridge converter. This virtual impedance passes through a bandpass filter and is then connected to the feedback loop. This improves the output impedance of the phase-shifted full-bridge converter at its characteristic frequency while maintaining characteristics in other frequency bands. Secondly, notch filters are added to the voltage and current feedback branches, effectively reducing the second harmonic components of the sampled voltage and current. This reduces the impact of the second harmonic in the sampled voltage and current values ​​on the voltage and current dual-loop control. This method effectively reduces the impact of the second harmonic current on the load side of the phase-shifted full-bridge converter, thereby reducing the interference of the second harmonic current in the inductor current of the phase-shifted full-bridge converter on the current loop control and reducing the electrical stress on the power devices and filter components of the phase-shifted full-bridge converter.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, and relates to phase-shifted full-bridge converters, specifically to a method for suppressing second harmonic current in a phase-shifted full-bridge converter. Background Technology

[0002] With the increasing depletion of traditional energy resources such as coal and oil, the country has been vigorously supporting the development of new energy technologies in recent years, which have been widely applied in various fields such as automobiles, ships, and consumer electronics. Two-stage single-phase converters, as the core component of AC-DC conversion, play an indispensable and crucial role in new energy applications.

[0003] A two-stage single-phase converter consists of a front-end DC-DC converter and a rear-end single-phase inverter. The phase-shifted full-bridge converter is one of the most common topologies of DC-DC converters. However, the inherent characteristics of a single-phase inverter can lead to a large second harmonic component in its input current, which further affects the performance and stability of the front-end phase-shifted full-bridge converter.

[0004] The second harmonic component in the input current of a single-phase inverter is provided by the phase-shifted full-bridge converter and the bus capacitor, resulting in the presence of a second harmonic component in the output filter inductor current of the phase-shifted full-bridge converter. This has two main effects.

[0005] 1. At present, in order to improve the response capability of phase-shifted full-bridge converter to load changes, the mainstream control method is to use a dual-loop control system with voltage outer loop and current inner loop. The current inner loop monitors the inductor current in real time, which causes the second harmonic component in the inductor current to have a significant impact on the current inner loop control.

[0006] 2. Second harmonic current increases the effective current value of power devices and filter inductors, thereby increasing the current stress on them, affecting their service life, and in severe cases, causing device damage.

[0007] Therefore, in the design of phase-shifted full-bridge converters, effective measures need to be taken to suppress the effects of second harmonic currents.

[0008] Currently widely used methods include increasing the bus capacitance, connecting an LC notch filter in parallel at the output of the phase-shifted full-bridge converter, and using a notch filter in the voltage outer loop. These methods mainly have two problems:

[0009] 1. To achieve good suppression, the bus capacitor or LC notch filter needed is very large, which does not meet the miniaturization requirements of today's equipment.

[0010] 2. Current methods for suppressing second harmonic current are mainly aimed at single-loop voltage control systems, and their effectiveness in mainstream dual-loop voltage and current control systems is limited.

[0011] How to minimize the second harmonic current on the output side of a phase-shifted full-bridge converter remains a concern for those skilled in the art. Summary of the Invention

[0012] To address the shortcomings of existing technologies and the need for improvement, this invention provides a method for suppressing the second harmonic current in a dual-loop controlled phase-shifted full-bridge converter. The aim is to reduce the second harmonic current component in the inductor current of the phase-shifted full-bridge converter, thereby ensuring the reliable and stable operation of the phase-shifted full-bridge converter.

[0013] The technical solution adopted by this invention to solve its technical problem is: a method for suppressing the second harmonic current of a phase-shifted full-bridge converter, based on the operating condition that there is a second harmonic current on the load side of the phase-shifted full-bridge converter, wherein the input voltage V of the phase-shifted full-bridge converter... in After the input capacitor C in A full-bridge IGBT is connected, wherein the left arm of the full-bridge IGBT consists of IGBTD1 and IGBTD2, and the right arm consists of IGBTD3 and IGBTD4, with an input voltage V. in The positive terminal is connected to the collectors of IGBTD1 and IGBTD3, and the input voltage V in The negative terminal is connected to the emitters of IGBTD2 and IGBTD4, and the emitter of IGBTD3 is connected to the DC blocking capacitor C1 and the resonant inductor L. r The emitter of IGBTD1 is connected to the same transformer T. r The two input terminals on the primary side, transformer T r The two output terminals on the secondary side are rectified by a rectifier bridge composed of diodes D1, D2, D3, and D4. The positive output of the rectifier bridge is then filtered by inductor L. f Connect capacitor C bus The positive terminal of the rectifier bridge is connected to the negative terminal of the capacitor C. bus The negative terminal, capacitor C bus With dummy load R d Parallel connection, current source I inv With dummy load R d Parallel connection, used to simulate load-side current; includes the following steps:

[0014] S1, the phase-shifted full-bridge converter uses dual-loop voltage and current control. The control system includes an outer-loop voltage PI controller G. v (s) and the current inner loop PI controller G i (s), the sampled output voltage v bus and inductor current i L The feedback loops are connected to voltage and current PI controllers respectively; where the voltage outer loop PI controller G... v The transfer function of (s) is In the formula, kpv is the proportional coefficient of the voltage outer-loop PI controller, kpi is the integral coefficient of the voltage outer-loop PI controller, and G is the current inner-loop PI controller. i The transfer function of (s) is kpi is the proportional coefficient of the current inner loop PI controller, and kii is the integral coefficient of the current inner loop PI controller.

[0015] S2, the sampled output voltage v bus After passing through the first notch filter G N1 (s) and voltage reference value v ref The difference is calculated, and the result is passed through the voltage outer loop PI controller G. v (s) Obtain the current inner loop PI controller G i (s) current reference value i ref The first notch filter G N1 The transfer function of (s) is In the formula, ω0 is the characteristic angular frequency, Q N1 These are the characteristic coefficients;

[0016] S3, the sampled inductor current i L After passing through the second notch filter G N2 (s) and the current reference value i of the inner current loop PI controller ref Find the difference, and the result of the difference is d. y Among them, the second notch filter G N2 The transfer function of (s) is In the formula, ω0 is the characteristic angular frequency, Q N2 These are the characteristic coefficients;

[0017] S4, the inductor current i L After passing through bandpass filter G BPF (s), multiplied by the series virtual impedance r s And divide by the input voltage V of the phase-shifted full-bridge converter. in The result obtained is the difference d described in S3. y The difference is taken to obtain the change in duty cycle d. s The signal is sent to the PWM modulation module to generate a PWM signal; where the bandpass filter G... BPF The transfer function of (s) is In the formula, ω0 is the characteristic angular frequency, Q BPF These are the characteristic coefficients;

[0018] S5, the PWM signal controls the on / off state of power devices IGBTD1~IGBTD4, and the DC voltage v is obtained after transformation by transformer Tr and rectification by rectifier bridge. rec v rec The output voltage v is obtained after filtering by the output LC filter.bus .

[0019] Furthermore, in steps S2 and S3, the first notch filter G N1 (s) and second notch filter G N2 The characteristic angular frequency ω0 of (s) is set as the frequency of the second harmonic current, and the characteristic coefficient Q is... N1 and Q N2 The value can be adjusted.

[0020] Furthermore, the series virtual impedance r in step S4 s Its setting value can be adjusted.

[0021] Furthermore, in step S4, the bandpass filter G BPF The characteristic angular frequency ω0 of (s) is set as the frequency of the second harmonic current, and the characteristic coefficient Q is... BPF The value can be adjusted.

[0022] Furthermore, the aforementioned transformer T r The primary-to-secondary ratio is set to 1:2.

[0023] This invention is used to reduce the second harmonic current in the output filter inductor current of a phase-shifted full-bridge converter when there is a second harmonic current on the load side. This reduces the interference of the second harmonic current in the inductor current on the current loop control and reduces the electrical stress on the power devices and filter devices of the phase-shifted full-bridge converter.

[0024] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0025] 1. It eliminates the need for additional hardware circuits such as bus capacitors or LC filter circuits, simplifying the circuit structure, greatly saving equipment space, and providing a foundation for equipment miniaturization.

[0026] 2. By selecting appropriate values ​​for the characteristic coefficients QN1 and QN2 of the first notch filter GN1(s) and the second notch filter GN2(s), the series virtual impedance r is determined. s By selecting appropriate values ​​for the characteristic coefficient QBPF of the bandpass filter GBPF(s), the second harmonic current component of the output filter inductor current of the phase-shifted full-bridge converter can be greatly reduced. In the embodiments of the present invention, compared with the traditional method, the second harmonic current component of the output filter inductor current of the phase-shifted full-bridge converter is reduced by about 90%.

[0027] 3. The control method is simple, effective, and easy to implement. Attached Figure Description

[0028] Figure 1 This is a flowchart of the suppression method of the present invention;

[0029] Figure 2 This is the basic topology of the phase-shifted full-bridge converter in an embodiment of the present invention;

[0030] Figure 3 This is a control block diagram of the phase-shifting full-bridge converter according to an embodiment of the present invention;

[0031] Figure 4 Control block diagram of a proportional phase-shifting full-bridge converter;

[0032] Figure 5 The waveforms of the phase-shifted full-bridge converter without preprocessing are shown in the embodiments and comparative examples of the present invention.

[0033] Figure 6 The following are comparison waveforms of the inductor current after low-pass filtering in the phase-shifted full-bridge converters of the embodiments and comparative examples of the present invention. 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] In this invention, the terms "first," "second," etc. (if present) in the invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0036] Figure 1 This is a flowchart of the method for suppressing the second harmonic current of a phase-shifted full-bridge converter (hereinafter referred to as the second harmonic current suppression method) in an embodiment of the present invention. See also... Figure 1 , combined Figures 2-6 The second harmonic current suppression method in this embodiment will be described in detail.

[0037] This embodiment is based on Figure 2 The basic topology of the phase-shifted full-bridge converter shown is as follows: Figure 3 The control block diagram shown is available for reference. Figure 2 and Figure 3 right Figure 1 The execution process of each of the shown operation procedures will be explained.

[0038] See Figure 2 The basic topology of the phase-shifted full-bridge converter in this embodiment is explained below: Input voltage V in (Internal resistance is R) p_vin After passing through the input capacitor C in (Internal resistance is R)p_Cin The IGBT is connected to a full-bridge IGBT, wherein the left bridge arm is composed of IGBTD1 and IGBTD2, and the right bridge arm is composed of IGBTD3 and IGBTD4, with an input voltage V. in The positive terminal is connected to the collectors of IGBTD1 and IGBTD3, and the input voltage V in The negative terminal is connected to the emitters of IGBTD2 and IGBTD4, and the emitter of IGBTD3 is connected to the DC blocking capacitor C1 and the resonant inductor L. r The emitter of IGBTD1 is connected to the same transformer T. r The two input terminals on the primary side, transformer T r The two output terminals on the secondary side are rectified by a rectifier bridge composed of diodes D1, D2, D3, and D4. The positive output of the rectifier bridge is then filtered by inductor L. f Connect capacitor C bus (Internal resistance is R) p_Cbus The positive terminal of the rectifier bridge is connected to the negative terminal of the capacitor C. bus The negative terminal, capacitor C bus With dummy load R d Parallel connection, current source I inv With dummy load R d Parallel connection is used to simulate the load-side current (including DC current component and second harmonic current component).

[0039] The parameter settings for each component of the phase-shifted full-bridge converter are as follows: Input voltage V in Set to 200V, internal resistance R p_vin Set to 1mR; input capacitor C in Set to 1000uF, internal resistance R p_Cin The current is set to 4.2mR; the DC blocking capacitor C1 is set to 30uF; the resonant inductor L... r Set to 2.5uH; Transformer T r The primary-to-secondary turns ratio is set to 1:2; the filter inductor L f Set to 600uH; Capacitor C bus Set to 1000uF, equivalent internal resistance R p_Cbus Set to 10mR; dummy load R d Set to 100k; Current source I inv The DC component is set to 40A, and the amplitude of the second harmonic current component is set to 40A.

[0040] Step S1: The phase-shifted full-bridge converter uses dual-loop control of voltage and current. The control system includes a voltage outer-loop PI controller G. v (s) and the current inner loop PI controller G i (s), the sampled output voltage v bus and inductor current iL The feedback loops are then connected to voltage and current PI controllers respectively.

[0041] Among them, the voltage outer loop PI controller G v The transfer function of (s) is In the formula, kpv is the proportional coefficient of the voltage outer-loop PI controller, and kpi is the integral coefficient of the voltage outer-loop PI controller. Specifically, the voltage outer-loop PI controller G... v The proportional gain kpv of (s) is set to 0.15, and the integral gain kpi is set to 2.5, resulting in the voltage outer loop PI controller G. v The transfer function of (s) .

[0042] Among them, the inner loop PI controller G i The transfer function of (s) is In the formula, kpi is the proportional coefficient of the current inner-loop PI controller, and kii is the integral coefficient of the current inner-loop PI controller. Specifically, the current inner-loop PI controller G... i The proportional coefficient kpi of (s) is set to 0.0015, and the integral coefficient kii is set to 2, thus obtaining the current inner-loop PI controller G. i The transfer function of (s) is .

[0043] Step S2: The control system acquires the output voltage v of the phase-shifted full-bridge converter. bus Output voltage v bus After passing through the first notch filter G N1 (s) is filtered, with reference voltage v ref Subtract v bus After passing through the first notch filter G N1 (s) The filtered result is fed into the outer loop PI controller G. v (s), to obtain the current inner loop PI controller G i (s) reference value i ref .

[0044] The first notch filter G N1 The transfer function of (s) is In the formula, ω0 is the characteristic angular frequency, Q N1 The characteristic coefficient is Q. Specifically, the characteristic angular frequency ω0 is set to the angular frequency of the second harmonic current of the load, which is 2*π*100, and the characteristic coefficient Q is... N1 Setting it to 10, the first notch filter G is calculated. N1 The transfer function of (s) is .

[0045] Specifically, the reference voltage v ref Set the target output voltage to 360V.

[0046] Step S3: The control system acquires the inductor current i of the phase-shifted full-bridge converter. L Inductor current i L After passing through the second notch filter G N2 (s) Filtering is performed, and the current inner loop PI controller G mentioned in step S2 is used. i (s) reference value i ref Subtract inductor current i L After passing through the second notch filter G N2 (s) The result after filtering is the difference result d. y .

[0047] Among them, the second notch filter G N2 The transfer function of (s) is In the formula, ω0 is the characteristic angular frequency, Q N2 The characteristic coefficient is Q. Specifically, the characteristic angular frequency ω0 is set to the angular frequency of the second harmonic current of the load, which is 2*π*100, and the characteristic coefficient Q is... N2 The second notch filter G is calculated by setting it to 10. N2 The transfer function of (s) is .

[0048] Step S4, the inductor current i of the phase-shifted full-bridge converter L After passing through bandpass filter G BPF (s) Filtering, multiplied by the series virtual impedance r s And divide by the input voltage V of the phase-shifted full-bridge converter. in The result obtained is the difference d obtained in step S3. y The difference is taken to obtain the change in duty cycle d. s Send it to the PWM modulation module to generate Figure 2 The four PWM signals shown are PWM1 to PWM4.

[0049] Among them, the bandpass filter G BPF The transfer function of (s) is In the formula, ω0 is the characteristic angular frequency, Q BPF The characteristic coefficient is Q. Specifically, the characteristic angular frequency ω0 is set to the angular frequency of the second harmonic current of the load, which is 2*π*100, and the characteristic coefficient Q is... BPF The value is set to 100, and the bandpass filter G is calculated. BPF The transfer function of (s) is .

[0050] Specifically, the series virtual impedance r s Set it to 2.5.

[0051] Specifically, the input voltage V of the phase-shifted full-bridge converter inSet to 200V.

[0052] Step S5, see Figure 2 Four PWM signals, PWM1 to PWM4, control the on / off state of four IGBT modules (IGBTD1 to IGBTD4) respectively, generating alternating voltage. This alternating voltage is then transformed by transformer Tr and rectified by diodes D1 to D4 in the rectifier bridge to obtain a DC voltage v. rec ;v rec The output voltage v is obtained after filtering by the output LC filter. bus .

[0053] Among them, the duty cycle change d mentioned in steps S4 and S5 s to the DC voltage v rec The process of change can be equivalent to: Figure 3 The duty cycle change d shown s Multiply by the input voltage V of the phase-shifted full-bridge converter in The DC voltage v is obtained rec The process.

[0054] Specifically, transformer T r The primary-to-secondary ratio is set to 1:2.

[0055] Specifically, the LC filter includes an inductor L f and capacitor C bus Inductor L f The inductance is set to 600uH, and the capacitor C bus The capacitance is set to 1000uF, and the equivalent internal resistance is set to 10mR.

[0056] To verify the practicality of the second harmonic current suppression method in this embodiment, based on Figure 2 The basic topology of the phase-shifted full-bridge converter shown is as follows: Figure 3 The control block diagram shown demonstrates the simulation analysis of the second harmonic current component in the inductor current of a phase-shifted full-bridge converter under the operating conditions of a load-side DC current component of 40A and a second harmonic current amplitude of 40A. Under the same operating conditions, a traditional single-voltage-loop controlled second harmonic current suppression method for phase-shifted full-bridge converters is used as a comparative example to simulate the second harmonic current component in the inductor current of the phase-shifted full-bridge converter, and the simulation results are compared with those of the embodiment of this invention. The simulation analysis process and results are explained.

[0057] The basic topology and component parameters of the comparative phase-shifted full-bridge converter are the same as those in the embodiment of this invention; the control block diagram of the comparative phase-shifted full-bridge converter is as follows: Figure 4 It is shown that, with Figure 3The control block diagrams of the embodiments of the present invention shown differ as follows: the inner loop PI controller for current is removed; the inductor current I is removed. L Feedback loop through the second notch filter; voltage outer loop PI controller G V The output of (s) is no longer subtracted, but is directly used as d in step S2. y Output voltage v bus No longer passing through the first notch filter G N1 (s) is not filtered, but directly transformed by the sampling transform coefficients Hv and compared with the reference voltage v. ref Find the difference.

[0058] The remaining steps in the control block diagram for the proportional model and the specific implementation of each step are the same as those in the embodiments of the present invention.

[0059] Figure 5 and Figure 6 The diagram shows a comparison of the inductor current waveforms of phase-shifted full-bridge converters in embodiments and comparative examples of the present invention. Figure 5 The waveform of the inductor current without preprocessing. Figure 6 The waveform of the inductor current after being filtered by a low-pass filter with a cutoff frequency of 1kHz is shown to facilitate the removal of the influence of high-frequency components and to quantitatively calculate the second harmonic component. Figure 5 and Figure 6 The waveforms shown are as follows: the dashed waveform is the inductor current waveform of the comparative example, and the solid waveform is the inductor current waveform of the embodiment.

[0060] in accordance with Figure 6 The data shown indicates that the peak-to-peak value of the second harmonic component of the inductor current in the phase-shifted full-bridge converter is calculated to be... .

[0061] The peak-to-peak value of the second harmonic component of the inductor current in the comparative phase-shifted full-bridge converter is:

[0062] .

[0063] The calculated peak-to-peak ratio of the second harmonic component of the inductor current in the embodiment and the comparative example is as follows: .

[0064] Simulation results show that the second harmonic component of the inductor current of the phase-shifted full-bridge converter in this embodiment is only about 10% of that in the comparative example, which confirms the effectiveness of the second harmonic current suppression method proposed in this patent.

[0065] Those skilled in the art will readily understand 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 within the scope of protection of the present invention.

Claims

1. A method for suppressing second harmonic current in a phase-shifted full-bridge converter, based on the condition that second harmonic current exists on the load side of the phase-shifted full-bridge converter, characterized in that: The input voltage V of the phase-shifted full-bridge converter in Through input capacitor C in A full-bridge IGBT is connected, wherein the left arm of the full-bridge IGBT consists of IGBTD1 and IGBTD2, and the right arm consists of IGBTD3 and IGBTD4, with an input voltage V. in The positive terminal is connected to the collectors of IGBTD1 and IGBTD3, and the input voltage V in The negative terminal is connected to the emitters of IGBTD2 and IGBTD4, and the emitter of IGBTD3 is connected to the DC blocking capacitor C1 and the resonant inductor L. r The emitter of IGBTD1 is connected to the same transformer T. r Primary input terminal, transformer T r The secondary side output is rectified by a rectifier bridge composed of diodes D1 to D4, and the positive output of the rectifier bridge passes through a filter inductor L. f Connect capacitor C bus The positive terminal of the rectifier bridge is connected to the negative terminal of the capacitor C. bus The negative terminal, capacitor C bus With dummy load R d Parallel connection, current source I inv With dummy load R d Parallel simulation of load-side current; including the following steps S1, the phase-shifted full-bridge converter uses dual-loop voltage and current control, and the sampled output voltage v bus and inductor current i L The feedback loop is then connected to the outer voltage loop PI controller G. v (s) and the current inner loop PI controller G i (s), where the voltage outer loop PI controller G v The transfer function of (s) is In the formula, kpv is the proportional coefficient of the voltage outer-loop PI controller, kpi is the integral coefficient of the voltage outer-loop PI controller, and G is the current inner-loop PI controller. i The transfer function of (s) is kpi is the proportional coefficient of the current inner loop PI controller, and kii is the integral coefficient of the current inner loop PI controller. S2, Output voltage v bus After passing through the first notch filter G N1 (s) and voltage reference value v ref The difference is calculated, and the difference is passed through the voltage outer loop PI controller G. v (s) Obtain the current inner loop PI controller G i (s) current reference value i ref The first notch filter G N1 The transfer function of (s) is In the formula, ω0 is the characteristic angular frequency, Q N1 These are the characteristic coefficients; S3, inductor current i L After passing through the second notch filter G N2 (s) and current reference value i ref Find the difference to get d y The second notch filter G N2 The transfer function of (s) is In the formula, ω0 is the characteristic angular frequency, Q N2 These are the characteristic coefficients; S4, inductor current i L After passing through bandpass filter G BPF (s), multiplied by the series virtual impedance r s And divided by the input voltage V in The result obtained is the same as d y The difference is used to obtain the change in duty cycle d. s The signal is sent to the PWM modulation module to generate a PWM signal; where the bandpass filter G... BPF The transfer function of (s) In the formula, ω0 is the characteristic angular frequency, Q BPF These are the characteristic coefficients; S5, the PWM signal controls the on / off state of IGBTD1~IGBTD4, and after transformation by transformer Tr and rectification by rectifier bridge, a DC voltage v is obtained. rec v rec The output voltage v is obtained after filtering by the output LC filter. bus .

2. The method for suppressing the second harmonic current of a phase-shifted full-bridge converter according to claim 1, characterized in that, The first notch filter G in steps S2 and S3 N1 (s) and second notch filter G N2 The characteristic angular frequency of (s) is set to the frequency of the second harmonic current, and the characteristic coefficient Q is... N1 and Q N2 Adjustable.

3. The method for suppressing the second harmonic current of a phase-shifted full-bridge converter according to claim 2, characterized in that, The series virtual impedance r in step S4 s The setting is adjustable.

4. The method for suppressing the second harmonic current of a phase-shifted full-bridge converter according to claim 3, characterized in that, In step S4, the bandpass filter G BPF The characteristic angular frequency of (s) is set to the frequency of the second harmonic current, and the characteristic coefficient Q is... BPF Adjustable.

5. A method for suppressing second harmonic current in a phase-shifted full-bridge converter according to claim 1, 2, 3, or 4, characterized in that, The transformer T r The primary-to-secondary ratio is set to 1:2.

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