Single-stage AC-DC converter soft switching modulation method based on frequency conversion

Abstract

The invention discloses a single-stage AC-DC converter soft switching modulation method based on frequency conversion, and belongs to the field of electronic power, and the method comprises the steps: selecting a full-bridge part of a single-stage AC-DC converter as a modulation mode of dual PWM and phase shift; circuit parameters, such as high-frequency frequency, inductance and the like, of rated working conditions are designed, and soft switching of all switches is achieved; and frequency conversion is adopted in a power frequency period, so that the maximum current ripple is reduced, and the efficiency is improved. Soft switching is realized through circuit parameters and a modulation method, and ripple minimization on the basis of soft switching is realized through a frequency conversion strategy; according to the method, control is simple, independent decoupling control for maintaining output power, alternating current sine output and bus voltage stability is achieved, and for application occasions pursuing high efficiency and high power density, the switching loss can be effectively reduced, the efficiency of the converter is improved, and meanwhile the operation stability and control accuracy of the converter are improved.

Description

Technical Field

[0001] The present invention belongs to the field of power electronics, and more particularly, relates to a single-stage AC-DC converter soft switching modulation method based on frequency conversion. Background Art

[0002] Residential photovoltaic power generation is rapidly developing, representing a huge market both domestically and internationally. Research into more efficient, high-power-density bidirectional AC-DC converters is a prerequisite for the further popularization of household photovoltaic storage. However, microinverters, as AC-DC converters, primarily utilize a two-stage structure, limiting efficiency and size. Totem-pole isolated single-stage AC-DC converters offer significant potential for microinverter applications due to their advantages, such as reduced magnetic and filter component size, a reduced number of switches, and fully soft switching.

[0003] The traditional solution is a two-stage cascade topology of an inverter and an isolated DC-DC. How to organically combine them and maintain soft switching and a small current RMS value under the time-varying voltage during the power frequency cycle, thereby improving the efficiency of the converter, is an extremely challenging problem. Summary of the Invention

[0004] In response to the above defects or improvement needs of the prior art, the present invention provides a single-stage AC-DC converter soft switching modulation method based on frequency conversion, which aims to achieve full-switch soft switching while reducing the current of the AC side switch, thereby improving the efficiency of the converter.

[0005] To achieve the above objectives, according to a first aspect of the present invention, a soft switching modulation method for a single-stage AC-DC converter based on frequency conversion is provided, wherein the single-stage AC-DC converter is a totem pole isolated single-stage AC-DC converter. The method comprises:

[0006] (1) According to the formula Calculate the switching frequency f of each high-frequency switch in the converter s ; According to the reference AC current d-axis component I gd_ref The actual AC current d-axis component i gd The error relationship is calculated by the first proportional integral controller to dynamically calculate the duty cycle d of the switch tubes on each full bridge in the converter; according to V bus With the reference bus voltage V bus_ref The error relationship is calculated by the second proportional integral controller, and the outward shift of the AC side switch tube PWM wave and the DC side switch tube PWM wave is compared. f s * is the reference frequency;

[0007] (2) Calculate the first and second inductors L in the converter under rated operating conditions g1 、L g2The size of i g1_ac <i g1_Δ Among them, L g1 =L g2 =[V g 2 (V bus -V g )] / (2f s PV bus ), P is the reference power of the converter, V g is the AC voltage, θ g is the AC voltage phase, V bus is the bus voltage;

[0008] (3) Through f s , d generates a reference modulation wave, then the modulation wave signal of S1 is the reference modulation wave, and the modulation wave signal of S3 lags the modulation wave signal of S1 by 1 / 2T s , T s =1 / f s , the modulation wave signal of S7 lags behind the modulation wave signal of S1 The modulation wave signal of S9 lags behind the modulation wave signal of S1

[0009] Among them, S1 and S2 are complementary, S3 and S4 are complementary, S7 and S8 are complementary, S9 and S 10 Complementary conduction; S1 and S2 are the upper switch tubes of the first and second high-frequency half-bridges on the AC side, respectively; S3 and S4 are the lower switch tubes of the first and second high-frequency half-bridges, respectively; the midpoints of the bridge arms of the first and second high-frequency half-bridges are connected to the primary like-name terminals and the primary non-like-name terminals of the transformer, respectively; S7 and S8 are the upper switch tubes of the third and fourth high-frequency half-bridges on the DC side, respectively; S9 and S 10 are the lower switch tubes of the third and fourth high-frequency half-bridges respectively, and the midpoints of the bridge arms of the third and fourth high-frequency half-bridges are connected to the secondary side same-name terminal and the secondary side non-same-name terminal of the transformer respectively; L g1 、L g2 are AC inductors, connected to the midpoints of the bridge arms of the first and second high-frequency half bridges respectively.

[0010] According to a second aspect of the present invention, there is provided an electronic device comprising: a computer-readable storage medium and a processor;

[0011] The computer-readable storage medium is used to store executable instructions;

[0012] The processor is configured to read the executable instructions stored in the computer-readable storage medium and execute the method according to the first aspect.

[0013] According to a third aspect of the present invention, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a processor to execute the method according to the first aspect.

[0014] According to a fourth aspect of the present invention, a computer program product is provided, comprising a computer program or instructions, wherein when the computer program or instructions are executed by a processor, the method according to the first aspect is implemented.

[0015] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0016] The method provided by the present invention combines the two-stage topology of the inverter cascade DAB, taking into account the soft switching characteristics of both; soft switching is achieved by using circuit parameters and modulation methods, without any requirements for the control loop and response speed; the adverse effect of the grid-connected current on the soft switching is offset by the current ripple on the AC side inductor, and soft switching of all high-frequency switching tubes is achieved by the switching current of the dual active bridge part; the control is simple, and independent decoupling control is achieved to maintain output power, AC sinusoidal output and bus voltage stability. For applications that require high efficiency and high power density, it can effectively reduce switching losses and improve converter efficiency while improving converter operation stability and control accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a topology diagram of a totem pole isolated AC-DC converter;

[0018] Figure 2 This is a flow chart of a soft switching modulation method for a single-stage AC-DC converter based on frequency conversion provided by an embodiment of the present invention.

[0019] Figure 3 (a) to (f) are schematic diagrams of the waveforms of the DAB part in the converter in working modes A1, A2, B1, B2, C1, and C2 respectively. DETAILED DESCRIPTION

[0020] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is 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 for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0021] The embodiment of the present invention provides a single-stage AC-DC converter soft switching modulation method based on frequency conversion, wherein the single-stage AC-DC converter is a totem pole isolated single-stage AC-DC converter, such as Figure 1As shown, the totem pole isolated single-stage AC-DC converter circuit includes a first high-frequency half-bridge composed of AC side switches S1 and S2, a second high-frequency half-bridge composed of AC side switches S3 and S4, and a low-frequency half-bridge composed of AC side switches S5 and S6. ac The inductance L at the midpoint of the bridge arm formed by the positive electrode and the switching tubes S1 and S2 g1 , connect AC power supply V ac The inductance L at the midpoint of the bridge arm formed by the positive electrode and the switching tubes S3 and S4 g2 , AC power supply V ac The negative electrode is connected to the midpoint of the bridge arm composed of switch tubes S5 and S6, and the capacitor C on the three sets of half-bridge busbars on the primary side c , and the DC power supply V dc The connected output filter capacitor C o The third high-frequency half-bridge composed of DC side switch tubes S7 and S8, DC side switch tubes S9 and S 10 The fourth high-frequency half-bridge is composed of a high-frequency isolation unit connected between the midpoints of the high-frequency full-bridge arms on both sides. The high-frequency isolation unit is composed of a leakage inductance L s And transformer T;

[0022] like Figure 2 As shown, the method provided by the embodiment of the present invention includes:

[0023] (1) According to the formula Calculate the switching frequency f of each high-frequency switch in the converter s , in which, increasing the frequency in some stages within the power frequency cycle is the key to reducing the current stress and the effective value of the current; according to the reference AC current d-axis component I gd_re The actual AC current d-axis component i gd The error relationship is calculated by the first proportional integral controller to dynamically calculate the duty cycle d of the switch tubes on each full bridge in the converter; according to V bus With the reference bus voltage V bus_ref The error relationship is calculated by the second proportional integral controller, and the outward shift of the AC side switch tube PWM wave and the DC side switch tube PWM wave is compared.

[0024] Specifically, a phase-locked module PLL is used to generate the AC voltage V of the totem pole isolated single-stage AC-DC converter. g , get the phase θ of the AC voltage gAt the same time, based on the phase of the AC voltage obtained by the phase-locked loop (PLL), the AC current is passed through the filtering module and the αβ-dq module to obtain the actual AC current d-axis component. When the DC side is a load, the reference AC current d-axis component is dynamically adjusted through the proportional-integral controller according to the error relationship between the DC reference voltage and the DC side voltage. When the DC side is a power supply, the reference AC current d-axis component is calculated based on the reference power of the converter.

[0025] Then, according to the AC voltage phase θ g , calculate the frequency of the operating point, that is, the switching frequency f of the high-frequency switching tube s ;

[0026] According to the error relationship between the reference AC current d-axis component and the actual AC current d-axis component, the duty cycle of the full-bridge upper tube, i.e. d, is dynamically adjusted by the proportional-integral controller;

[0027] According to the actual bus voltage V bus The error relationship with the reference bus voltage is compared with the outward shift of the PWM wave of the AC side switch tube and the PWM wave of the DC side switch tube calculated by the proportional integral controller.

[0028] The method provided by the embodiment of the present invention has three degrees of freedom. The first degree of freedom is the switching frequency f s , used to reduce AC ripple; the second degree of freedom is the external phase shift between the high-frequency full bridges on both sides Used to control the DC bus voltage; the third degree of freedom is the duty cycle d of the PWM wave of the AC side switch tube, which is used to achieve AC sinusoidal output and full-bridge soft switching.

[0029] (2) Calculate the first and second inductors L in the converter under rated operating conditions g1 、L g2 The size of i g1_ac <i g1_Δ Among them, L g1 =L g2 =[V g 2 (V bus -V g )] / (2f s PV bus ), P is the reference power of the converter, V g is the AC voltage, θ g is the AC voltage phase, V bus is the bus voltage; f s * is the reference frequency.

[0030] Specifically, calculate the inductor L in the single-stage AC-DC converter under rated operating conditions g1 and L g2 The size of the two inductors makes the inductance L corresponding to the high-frequency switching cycle at each time point in the power frequency cycle g1 and L g2 The maximum current is positive and the minimum current is negative, so that the current polarity of the switching tubes S1 to S4 in the inverter part meets the soft switching requirements (the current polarity passing through the switching tube when it is turned on is negative, that is, it flows from the source to the drain of the MOSFET), that is, S1-S4 have soft switching in the entire power frequency cycle.

[0031] (3) Through f s , d generates a reference modulation wave, then the modulation wave signal of S1 is the reference modulation wave, and the modulation wave signal of S3 lags the modulation wave signal of S1 by 1 / 2T s , T s =1 / f s , the modulation wave signal of S7 lags behind the modulation wave signal of S1 The modulation wave signal of S9 lags behind the modulation wave signal of S1

[0032] Among them, S1 and S2 are complementary, S3 and S4 are complementary, S7 and S8 are complementary, S9 and S 10 Complementary conduction; S1 and S2 are the upper switch tubes of the first and second high-frequency half-bridges on the AC side, respectively; S3 and S4 are the lower switch tubes of the first and second high-frequency half-bridges, respectively; the midpoints of the bridge arms of the first and second high-frequency half-bridges are connected to the primary like-name terminals and the primary non-like-name terminals of the transformer, respectively; S7 and S8 are the upper switch tubes of the third and fourth high-frequency half-bridges on the DC side, respectively; S9 and S 10 are the lower switch tubes of the third and fourth high-frequency half-bridges respectively, and the midpoints of the bridge arms of the third and fourth high-frequency half-bridges are connected to the secondary side same-name terminal and the secondary side non-same-name terminal of the transformer respectively; L g1 、L g2 are AC inductors, connected to the midpoints of the bridge arms of the first and second high-frequency half bridges respectively.

[0033] Specifically, according to the outward migration The duty cycle of the PWM wave of the AC side switch tube and the duty cycle d and switching frequency f of the PWM wave of the DC side switch tube s Generate the corresponding modulation wave of high-frequency switch tube respectively; in the two low-frequency switch tubes, when the AC voltage v g When the AC voltage v g When it is negative, S5 is turned on and S6 is turned off.

[0034] Among them, the duty cycle of S1, S3, S7 and S9 is d, S1 and S2 are complementary conduction, S3 and S4 are complementary conduction, S7 and S8 are complementary conduction, S9 and S 10 Complementary conduction, the frequency of the driving signal of each high-frequency switch tube is f s By f s The reference modulation wave is generated by summing up d, and the S1 modulation wave signal is taken as the reference modulation wave. The S3 modulation wave signal lags the S1 modulation wave signal by 1 / 2T. s , T s =1 / f s , S7 modulation wave signal lags behind S1 modulation wave signal S9 modulation wave signal lags behind S1 modulation wave signal

[0035] Depending on the working state of the DAB part, the working mode of the converter is based on the degree of freedom Divide by the size relationship of d:

[0036] When 0 <d<0.5, When the working mode is A1, when 0.5 <d<1, When it is working mode A2;

[0037] When 0 <d<0.5, When the working mode is B1, when 0.5 <d<1, When it is working mode B2;

[0038] When 0 <d<0.5, When the working mode is C1, when 0.5 <d<1, It is working mode C2.

[0039] Among them, the three working modes A1, B1 and C1 must exist, and the existence of the other three working modes is determined by the relationship between the DC bus voltage and the AC voltage peak.

[0040] Depend on Figure 3 It can be seen that in the six working modes of the DAB part, the polarity of the switching current of the high-frequency switch is affected by the degree of freedom and d, and the degrees of freedom f s Not relevant.

[0041] Since operating modes A1 and A2 are symmetrical, their soft switching characteristics are the same. The same is true for operating modes B1 and B2, and C1 and C2. Therefore, the soft switching characteristics of the totem pole isolated single-stage AC-DC converter are analyzed below using operating modes A1, B1, and C1 as examples.

[0042] In the parameter design of this modulation strategy, n=V bus / V dc , Lg1 =L g2 =[V g 2 (V bus -V g )] / (2f s PV bus ), where P is the reference power of the converter, V bus is the bus voltage, V dc is the DC voltage, V g is the AC voltage, and n is the transformer ratio.

[0043] For the AC current part:

[0044]

[0045] Among them, i g1_ac For L g1 The power frequency component, i g1_Δ For L g1 pulsating component.

[0046] According to the parameter design, i g1_ac <i g1_Δ , so when S1 and S2 are turned on, the polarity of the AC current flowing through the switch is negative, i g2 The corresponding relationship is similar to that of S3 and S4. Therefore, the AC current part has a positive effect on the soft switching of S1 to S4. This part can be ignored when distinguishing the soft switching in the DAB modal analysis below.

[0047] (1) Working mode A1: 0 <d<0.5,

[0048] Assuming that the steady state is reached within the switching cycle (i.e., high-frequency switching cycle) and that the current is symmetrical, calculate the current at four time points.

[0049]

[0050] Among them, i Ls (t0) and i Ls (t4) = -i Ls (t0) corresponds to the soft switching of S1 and S2, i Ls (t1) and i Ls (t5) = -i Ls (t1) corresponds to the soft switching of S3 and S4, i Ls (t2) and i Ls (t6) = -i Ls (t2) corresponds to the soft switching of S7 and S9, i Ls (t3) and i Ls (t7) = -i Ls(t3) corresponds to S8 and S 10 Therefore, in working mode A1, all switching tubes have soft switching.

[0051] (2) Working mode B1: 0 <d<0.5,

[0052] Assuming that the switching cycle reaches steady state and has symmetry, calculate the current at four time points

[0053]

[0054] Among them, i Ls (t0) and i Ls (t4) = -i Ls (t0) corresponds to the soft switching of S1 and S2, i Ls (t2) and i Ls (t2) = -i Ls (t2) corresponds to the soft switching of S3 and S4, i Ls (t1) and i Ls (t5) = -i Ls (t1) corresponds to the soft switching of S7 and S9, i Ls (t3) and i Ls (t7) = -i Ls (t3) corresponds to S8 and S 10 Therefore, in working mode B1, all switching tubes have soft switching.

[0055] (3) Working mode C1: 0 <d<0.5,

[0056] Assuming that the switching cycle reaches steady state and has symmetry, calculate the current at four time points

[0057]

[0058] Among them, i Ls (t0) and i Ls (t4) = -i Ls (t0) corresponds to the soft switching of S1 and S2, i Ls (t3) and i Ls (t7) = -i Ls (t3) corresponds to the soft switching of S3 and S4, i Ls (t2) and i Ls (t6) = -i Ls (t2) corresponds to the soft switching of S7 and S9, i Ls (t1) and i Ls (t5) = -i Ls (t1) corresponds to S8 and S10 Therefore, in working mode C1, all switch tubes have soft switching.

[0059] The above analysis shows the soft switching characteristics of a totem pole isolated single-stage AC-DC converter using the modulation method provided by an embodiment of the present invention. The adverse effects of the grid-connected current on soft switching are offset by the current ripple on the AC-side inductor, and soft switching of all high-frequency switches is achieved through the switching current of the dual active bridge section.

[0060] An embodiment of the present invention provides an electronic device, comprising: a computer-readable storage medium and a processor;

[0061] The computer-readable storage medium is used to store executable instructions;

[0062] The processor is configured to read the executable instructions stored in the computer-readable storage medium and execute the method described in any one of the above embodiments.

[0063] An embodiment of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a processor to execute the method described in any of the above embodiments.

[0064] An embodiment of the present invention provides a computer program product, including a computer program or instructions, which implements the method described in any of the above embodiments when executed by a processor.

[0065] 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 single-stage AC-DC converter soft switching modulation method based on frequency conversion, wherein the single-stage AC-DC converter is a totem pole isolated single-stage AC-DC converter, characterized in that: The method comprises: (1) According to the formula Calculate the switching frequency f of each high-frequency switch in the converter s ; According to the reference AC current d-axis component I gd_ref The actual AC current d-axis component i gd The error relationship is dynamically calculated by the first proportional integral controller for calculating the duty cycle d of the switch tubes on each full bridge in the converter; according to V bus With reference bus voltage V bus_ref The error relationship is calculated by the second proportional integral controller, and the outward shift of the PWM wave of the AC side switch tube and the PWM wave of the DC side switch tube is compared. f s * is the reference frequency; (2) Calculate the first and second inductors L in the converter under rated conditions g1 , L g2 size to fit i g1_ac <i g1_Δ Among them, L g1 =L g2 =[V g 2 (V bus -V g )] / (2f s PV bus ), P is the reference power of the converter, V g is the AC voltage, θ g is the AC voltage phase, V bus is the bus voltage; (3) Through f s , d generates a reference modulation wave, then the modulation wave signal of S1 is the reference modulation wave, and the modulation wave signal of S3 lags the modulation wave signal of S1 by 1 / 2T s , T s =1 / f s , the modulation wave signal of S7 lags behind the modulation wave signal of S1 The modulation wave signal of S9 lags behind the modulation wave signal of S1 Among them, S1 and S2 are complementary conduction, S3 and S4 are complementary conduction, S7 and S8 are complementary conduction, S9 and S 10 Complementary conduction; S1 and S2 are the upper switch tubes of the first and second high-frequency half-bridges on the AC side, respectively; S3 and S4 are the lower switch tubes of the first and second high-frequency half-bridges, respectively; the midpoints of the bridge arms of the first and second high-frequency half-bridges are connected to the primary same-name end and the primary non-same-name end of the transformer, respectively; S7 and S8 are the upper switch tubes of the third and fourth high-frequency half-bridges on the DC side, respectively; S9 and S 10 are the lower switch tubes of the third and fourth high-frequency half-bridges, respectively, and the midpoints of the bridge arms of the third and fourth high-frequency half-bridges are connected to the secondary side same-name end and the secondary side non-same-name end of the transformer respectively; L g1 , L g2 are AC inductors connected to the midpoints of the bridge arms of the first and second high-frequency half bridges respectively.

2. The method according to claim 1, characterized in that When 0 <d<0.5, When , the converter works in mode A1; When 0.5 <d<1, When , the converter works in mode A2; When 0 <d<0.5, When , the converter works in mode B1; When 0.5 <d<1, When , the converter works in mode B2; When 0 <d<0.5, When , the converter works in C1 mode; When 0.5 <d<1, When , the converter works in mode C2.

3. The method according to claim 1, characterized in that k p , k i are the proportional gain and integral gain of the first proportional-integral controller respectively.

4. The method according to claim 1, characterized in that d=k p `(I gd_re -i gd )+∫(I gd_re -i gd ) i `dt;k p `、k i ` are the proportional gain and integral gain of the second proportional-integral controller respectively.

5. An electronic device, characterized in that: include: A computer readable storage medium and a processor; The computer-readable storage medium is used to store executable instructions; The processor is used to read the executable instructions stored in the computer-readable storage medium and execute the method according to any one of claims 1 to 4.

6. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a processor to execute the method according to any one of claims 1 to 4.

7. A computer program product comprising a computer program or instructions, characterized in that When the computer program or instruction is executed by a processor, the method according to any one of claims 1 to 4 is implemented.

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