A soft switching modulation method for single-stage AC-DC converter based on frequency conversion

Abstract

The application discloses a single-stage AC-DC converter soft switching modulation method based on frequency conversion, and belongs to the field of electronic power. The method selects the full-bridge part of the single-stage AC-DC converter as a modulation mode of double PWM plus phase shifting. Circuit parameters of a rated working condition, such as a high-frequency frequency, an inductance, etc. are designed to realize soft switching of all switches. Frequency conversion is adopted in a power frequency cycle to reduce the maximum current ripple and improve the efficiency. The soft switching is realized through the circuit parameters and the modulation method, and the ripple is minimized on the basis of the soft switching realized through the frequency conversion strategy. The method is simple to control, realizes independent decoupling control of maintaining output power, AC sine output and bus voltage stability, and can effectively reduce switching loss, improve converter efficiency, and improve the stability and control accuracy of the converter operation for the application occasions pursuing high efficiency and high power density.

Description

Technical Field

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

[0002] The residential photovoltaic (PV) power generation industry is developing rapidly and has a huge market both domestically and internationally. Researching more efficient and high-power-density bidirectional AC-DC converters is a prerequisite for the further popularization of residential PV and energy storage. However, micro-inverters, as a type of AC-DC converter, mainly adopt a two-stage structure, which limits efficiency and size. Totem-pole isolated single-stage AC-DC converters, with their advantages of reduced magnetic and filter component size, fewer switches, and fully soft-switching, show great potential in micro-inverter applications.

[0003] The traditional approach involves cascading an inverter and an isolated DC-DC converter. The challenge lies in how to organically combine these two topologies while maintaining soft switching and a small effective current value under time-varying voltage conditions during the power frequency cycle, thereby improving the converter's efficiency. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a soft-switching modulation method for a single-stage AC-DC converter based on frequency conversion, which aims to achieve full-switching 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, and the method includes:

[0006] (1) According to the formula Calculate the switching frequency of each high-frequency switch in the converter. f s According to the reference alternating current d Axial components I gd_ref With actual alternating current d Axial components i gd The error relationship is determined by the first proportional-integral controller dynamically calculating the duty cycle of each switch on the full-bridge in the converter. d ;according to V bus With reference bus voltage V bus_ref The error relationship is calculated by the second proportional-integral controller, comparing the outward shift of the AC-side switching transistor PWM wave with that of the DC-side switching transistor PWM wave. d φ ,f s * is the reference frequency;

[0007] (2) the size of the first and second inductances in the converter under rated operating conditions is calculated L g1 , L g2 to meet ; wherein, L g1 = L g2 [ V g 2 ( V bus - V g )] / (2 f 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) the reference modulation wave is generated by f s , d ; then S the modulation wave signal of 1 is the reference modulation wave, S the modulation wave signal of 3 lags behind the modulation wave signal of 1 by S 1 / 2 T s , T s =1 / f s , S the modulation wave signal of 7 lags behind the modulation wave signal of 1 by S 1 / 2 d φ T s , S the modulation wave signal of 9 lags behind the modulation wave signal of 1 by S 1 / 2 d φ T s +1 / 2 T s ;

[0009] wherein, S 1 and S 2 are complementary on, S 3 and S 4 are complementary on, S 7 and S 8 are complementary on, S 9 and S 10 complementary on; S 1, S 2 are respectively first and second high-frequency half-bridge upper switch tubes on the alternating current side, S 3, S 4 are respectively first and second high-frequency half-bridge lower switch tubes, bridge arm midpoints of the first and second high-frequency half-bridges are connected to the primary side same name end and the primary side non-same name end of the transformer respectively, S 7, S 8 are respectively third and fourth high-frequency half-bridge upper switch tubes on the direct current side, S 9, S 10 third and fourth high-frequency half-bridge lower switch tubes, bridge arm midpoints 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 is an alternating current inductor, connected to the bridge arm midpoints of the first and second high-frequency half-bridges respectively.

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

[0011] The computer readable storage medium is configured 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 application, a computer readable storage medium is provided, the computer readable storage medium stores computer instructions, the computer instructions are configured to enable the processor to execute the method according to the first aspect.

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

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

[0016] The method provided by this invention combines a two-stage topology of inverter cascaded with DAB, taking into account the soft-switching characteristics of both. Soft switching is achieved using circuit parameters and modulation methods, without requiring specific control loops or response speeds. The adverse effects of grid-connected current on soft switching are offset by the current ripple on the AC-side inductor, and soft switching of all high-frequency switching transistors is achieved through the switching current of the dual active bridge section. The control is simple, achieving independent decoupled control to maintain output power, AC sinusoidal output, and bus voltage stability. For applications requiring high efficiency and high power density, this method can effectively reduce switching losses and improve converter efficiency while enhancing converter operation stability and control accuracy. Attached Figure Description

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

[0018] Figure 2 A flowchart of a frequency-conversion-based soft-switching modulation method for a single-stage AC-DC converter provided in an embodiment of the present invention.

[0019] Figure 3 (a) to (f) are waveform diagrams of the DAB part of the converter in operating modes A1, A2, B1, B2, C1, and C2, respectively. Detailed Implementation

[0020] 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.

[0021] This invention provides a soft-switching modulation method for a single-stage AC-DC converter based on frequency conversion. The single-stage AC-DC converter is a totem-pole isolated single-stage AC-DC converter, such as... Figure 1 As shown, the totem-pole isolated single-stage AC-DC converter circuit includes AC-side switching transistors. S 1. S The first high-frequency half-bridge consists of two transistors, with AC-side switching transistors... S 3. S The second high-frequency half-bridge consists of 4 transistors, with AC-side switching transistors... S 5. S A low-frequency half-bridge consisting of 6 components is connected to an AC power supply. V ac Positive electrode and switching transistor S 1. S The inductance at the midpoint of the bridge arm composed of 2 Lg1 , connecting alternating current power supply V ac positive electrode and switch tube S 3、 S 4 inductance of bridge arm midpoint L g2 , alternating current power supply V ac negative electrode connected to switch tube S 5、 S 6 capacitor on the primary side of three groups of half-bridge bus composed of bridge arm midpoint C c , and direct current power supply V dc connected output filter capacitor C o , direct current side switch tube S 7、 S 8 third high frequency half-bridge composed of, direct current side switch tube S 9、 S 10 fourth high frequency half-bridge composed of, and connected between the two sides of high frequency full bridge bridge arm midpoint high frequency isolation unit, high frequency isolation unit by leakage inductance L s and transformer T composed of;

[0022] As Figure 2 shown, the method provided by the embodiment of the application comprises:

[0023] (1) according to the formula , the switching frequency of each high frequency switch tube in the converter is calculated f s , wherein the increase of the frequency in part of the power frequency cycle is the key to reduce current stress and reduce current effective value; according to the error relationship between the reference alternating current d axis component I gd_re and the actual alternating current d axis component i gd , the duty ratio of each full bridge upper switch tube in the converter is dynamically calculated by the first proportional integral controller d ; according to the error relationship between V bus and the reference bus voltage V bus_ref , the shift of the alternating current side switch tube PWM wave compared with the direct current side switch tube PWM wave is calculated by the second proportional integral controller d φ .

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

[0025] Then, the frequency of the operating point, i.e., the switching frequency of the high-frequency switch tube, is calculated according to the phase of the AC voltage θ g f 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 upper tube of the full-bridge is dynamically adjusted through a proportional-integral controller, i.e., d ;

[0027] According to the error relationship between the actual bus voltage V bus and the reference bus voltage, the phase shift of the AC side switch tube PWM wave and the DC side switch tube PWM wave is calculated through a proportional-integral controller d φ .

[0028] The method provided by the embodiment has three degrees of freedom, the first degree of freedom being the switching frequency f s for reducing AC ripples; the second degree of freedom being the phase shift between the high-frequency full-bridges on the two sides d φ for controlling the DC bus voltage; and the third degree of freedom being the duty cycle of the AC side switch tube PWM wave d for realizing AC sinusoidal output and full-bridge soft switching.

[0029] (2) The sizes of the first and second inductors L g1 , L g2 in the converter under rated operating conditions are calculated so as to meet ; wherein, L g1 =​L g2 [ V g 2 ( V bus - V g )] / (2 f 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, the sizes of the inductances L g1 and L g2 in the single-stage AC-DC converter under the rated operating condition are calculated, and the two inductance sizes are such that the maximum value of the current of the inductances L g1 and L g2 at each time point in the high-frequency switching period corresponding to the power frequency period is positive, and the minimum value is negative, so that the current polarity of the switching tubes S1-S4 in the inverter part meets the soft switching requirement (the current polarity passing through the switching tube at the switching-on time is negative, that is, from the source to the drain of the mosfet), that is, S1-S4 all have soft switching in the whole power frequency period.

[0031] (3) the reference modulation wave is generated through f s , d , S 1 the modulation wave signal is the reference modulation wave, S 3 the modulation wave signal lags behind S 1 the modulation wave signal by T s , T s =1 / f s , S 7 the modulation wave signal lags behind S 1 the modulation wave signal by d φ T s ,S The modulation wave signal of 9 is delayed. S 1 modulated wave signal d φ T s +1 / 2 T s ;

[0032] in, S 1 and S 2 complementary conduction, S 3 and S 4. Complementary conduction, S 7 and S 8 complementary conduction, S 9 and S 10 Complementary conduction; S 1. S 2 are the upper switching transistors of the first and second high-frequency half-bridges on the AC side, respectively. S 3. S 4 are the lower switching transistors 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 side terminals of the transformer and the transformer, respectively. S 7. S 8 are the upper switching transistors of the third and fourth high-frequency half-bridges located on the DC side. S 9. S 10 These are the lower switching transistors of the third and fourth high-frequency half-bridges, respectively. The midpoints of the bridge arms of the third and fourth high-frequency half-bridges are connected to the same-name terminal and the non-same-name terminal of the secondary side of the transformer, respectively. L g1 , L g2 The inductors are AC inductors, which are connected to the midpoints of the arms of the first and second high-frequency half-bridges, respectively.

[0033] Specifically, based on the relocation compared to d φ The duty cycle of the PWM wave on the AC side and the duty cycle d and switching frequency of the PWM wave on the DC side. f s Each generates a corresponding modulation wave for the high-frequency switching transistor; among the two low-frequency switching transistors, when the AC voltage... v g When it is the right time, S 5. Shutdown S 6. When AC voltage is turned on. v g When it is negative, S 5. Activation S 6. Turn off.

[0034] in, S 1.S 3. S 7 and S The duty cycle of 9 is 9 d , S 1 and S 2 complementary conduction, S 3 and S 4. Complementary conduction, S 7 and S 8 complementary conduction, S 9 and S 10 Complementary conduction, the frequency of the drive signal for each high-frequency switch is... f s .pass f s The reference modulation wave is generated by d, and the value is taken as follows. S 1. The modulated wave signal is the reference modulated wave. S 3. Modulation signal hysteresis S 1 modulated wave signal 1 / 2 T s , T s =1 / f s , S 7. Modulation signal hysteresis S 1 Modulated wave signal d φ T s , S 9. Modulation signal hysteresis S 1 Modulated wave signal d φ T s +1 / 2 T s .

[0035] Depending on the operating state of the DAB section, the converter's operating mode varies according to the degrees of freedom. d φ and d Divide by size relationship:

[0036] When 0 < d <0.5, d < d φ When the working mode is A1, and 0.5 < d <1,1- d < d φ The current working mode is A2;

[0037] When 0 < d <0.5, d φ< d <0.5- d φ When the working mode is B1, and 0.5 < d <1, d φ <1- d <0.5- d φ The current working mode is B2;

[0038] When 0 < d <0.5, d >0.5- d φ When the operating mode is C1, and 0.5 < d <1,1- d >0.5- d φ The current working mode is C2.

[0039] Among them, the three operating modes A1, B1 and C1 must exist, while the existence of the other three operating modes depends on the relationship between the magnitude of the DC bus voltage and the peak value of the AC voltage.

[0040] Depend on Figure 3 It can be seen that, in the six operating modes of the DAB section, the polarity of the switching current of the high-frequency switch is subject to the degree of freedom. d φ and d The impact, and degrees of freedom f s Irrelevant.

[0041] Since operating modes A1 and A2 are symmetrical, their soft-switching characteristics are the same. The same applies to operating modes B1 and B2, and C1 and C2. Therefore, the soft-switching characteristics of the totem-pole isolated single-stage AC-DC converter will be 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 , L g1 = L g2 =[ V g 2 ( V bus - V g )] / (2 f s PV bus ),in,P for the reference power of the transformer, V bus for the bus voltage, V dc for the DC voltage, V g for the AC voltage, n for the transformer ratio.

[0043] For the AC current part:

[0044]

[0045]

[0046] wherein, is L g1 the power frequency component of is L g1 the pulsating component of

[0047] According to the parameter design, Therefore, the current polarity of the AC current flowing through the switch when S1 and S2 are turned on is negative, i g2 The corresponding relationship of S3 and S4 is the same, so the AC current part has a positive help for the soft switching of S 1 S 4, and the following part can not be considered when distinguishing DAB mode analysis soft switching.

[0048] (1) Working mode A1: 0 d <0.5, d < d φ

[0049] Assuming that the steady state is reached within the switching period (i.e. the high-frequency switching period), which has symmetry, the currents at the four time points

[0050] (1)

[0051] (2)

[0052] (3)

[0053] (4)

[0054] wherein, i Ls ( t 0) and i Ls ( t4)=- i Ls ( t 0) corresponds to S 1, S 2 soft switch, i Ls ( t 1) and i Ls ( t 5)=- i Ls ( t 1) corresponds to S 3, S 4 soft switch, i Ls ( t 2) and i Ls ( t 6)=- i Ls ( t 2) corresponds to S 7 and S 9 soft switch, i Ls ( t 3) and i Ls ( t 7)=- i Ls ( t 3) corresponds to S 8 and S 10 soft switch, so that the working mode A1, all switch tubes have soft switch.

[0055] (2) working mode B1: 0 d <0.5, d φ < d <0.5- d φ

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

[0057] (5)

[0058] (6)

[0059] (7)

[0060] (8)

[0061] where,i Ls ( t 0) and i Ls ( t 4)=- i Ls ( t 0) corresponds to S 1, S 2 soft switch, i Ls ( t 2) and i Ls ( t 2)=- i Ls ( t 2) corresponds to S 3, S 4 soft switch, i Ls ( t 1) and i Ls ( t 5)=- i Ls ( t 1) corresponds to S 7 and S 9 soft switch, i Ls ( t 3) and i Ls ( t 7)=- i Ls ( t 3) corresponds to S 8 and S 10 soft switch, so that when the working mode B1, all the switch tubes have soft switch.

[0062] (3) working mode C1: 0 d <0.5 ，d >0.5- d φ

[0063] Assuming that the switch cycle reaches steady state, with symmetry, the current at four time points

[0064] (9)

[0065] (10)

[0066] (11)

[0067] (12)

[0068] wherein, i Ls ( t 0) and i Ls ( t 4)- i Ls ( t 0) corresponds to S 1, S 2 soft switch, i Ls ( t 3) and i Ls ( t 7)- i Ls ( t 3) corresponds to S 3, S 4 soft switch, i Ls ( t 2) and i Ls ( t 6)- i Ls ( t 2) corresponds to S 7 and S 9 soft switch, i Ls ( t 1) and i Ls ( t 5)- i Ls ( t 1) corresponds to S 8 and S 10 soft switch, so that in the working mode C1, all switch tubes have soft switch.

[0069] The soft switch characteristics of the totem-pole isolated single-stage AC-DC converter using the modulation mode provided by the embodiment of the application are analyzed above, the current ripple on the AC side inductor offsets the adverse effect of the grid-connected current on the soft switch, and the soft switch of all high-frequency switch tubes is realized through the switching current of the dual active bridge part.

[0070] The embodiment of the application provides an electronic device, including: a computer readable storage medium and a processor.

[0071] The computer readable storage medium is used for storing executable instructions.

[0072] The processor is configured to read the executable instructions stored in the computer readable storage medium and execute the method according to any one of the above embodiments.

[0073] An embodiment of the present application provides a computer readable storage medium storing computer instructions, the computer instructions being configured to cause a processor to execute the method according to any one of the above embodiments.

[0074] An embodiment of the present application provides a computer program product comprising computer programs or instructions, the computer programs or instructions being configured to cause a processor to execute the method according to any one of the above embodiments.

[0075] Those skilled in the art will easily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A soft switching modulation method based on variable frequency for a single-stage AC-DC converter, the single-stage AC-DC converter being a totem-pole isolated single-stage AC-DC converter, characterized in that, The method comprises: (1) According to the formula the switching frequency of each high-frequency switch tube in the converter is calculated f s ; according to the error relationship between the reference alternating current d axis component I gd_ref and the actual alternating current d axis component i gd , the duty ratio of each full-bridge upper switch tube in the converter is dynamically calculated by a first proportional-integral controller d ; according to the error relationship between V bus and the reference bus voltage V bus_ref , the phase shift of the alternating side switch tube PWM wave compared with the outer shift of the direct current side switch tube PWM wave is calculated by a second proportional-integral controller d φ , f s * is the reference frequency; (2) calculating the size of the first and second inductances in the converter under the rated operating condition so as to meet L g1 , L g2 ; wherein, L g1 = L g2 [ V g 2 (2 V bus - V g )] / (2 f 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) by f s , d The reference modulation wave is generated, then S The modulation wave signal of 1 is the reference modulation wave, S The modulation wave signal of 3 lags behind S The modulation wave signal of 1 by 1 / 2 T s , T s =1 / f s , S The modulation wave signal of 7 lags behind S The modulation wave signal of 1 d φ T s , S The modulation wave signal of 9 lags behind S The modulation wave signal of 1 d φ T s +1 / 2 T s ; wherein, S 1 and S 2 are complementary on, S 3 and S 4 are complementary on, S 7 and S 8 are complementary on, S 9 and S 10 complementary on; S 1, S 2 are respectively upper switch tubes of first and second high-frequency half-bridges on the alternating current side, S 3, S 4 are respectively lower switch tubes of the first and second high-frequency half-bridges, the bridge arm midpoints of the first and second high-frequency half-bridges being connected to the same name end and the non-same name end of the primary side of the transformer respectively, S 7, S 8 are respectively upper switch tubes of third and fourth high-frequency half-bridges on the direct current side, S 9, S 10 lower switch tubes of the third and fourth high-frequency half-bridges, the bridge arm midpoints of the third and fourth high-frequency half-bridges being connected to the same name end and the non-same name end of the secondary side of the transformer respectively; L g1 , L g2 are alternating current inductors connected to the bridge arm midpoints of the first and second high-frequency half-bridges respectively.

2. The method of claim 1, wherein, When 0 < t < 0.5, d <0.5, d d φ The working mode of the converter is A1.​ When 0.5 d <1, 1- d d φ The working mode of the converter is A2;​ when 0 < t < 0.5, d <0.5, d φ when 0 < t < 0.5, d <0.5- d φ when 0 < t < 0.5, When 0.5 d <1, d φ <1- d <0.5- d φ The working mode of the converter is B2. When 0 < t < 0.5, d <0.5, d >0.5- d φ The working mode of the converter is C1. When 0.5 d <1, 1- d >0.5- d φ The operating mode of the converter is C2.

3. The method of claim 1, wherein, ; k p 、 k i Kp and Ki are the proportional gain and integral gain of the first proportional-integral controller, respectively.

4. The method of claim 1, wherein, ; k p `, k i `respectively the proportional gain and the integral gain of the second proportional-integral controller.

5. An electronic device, comprising: comprises: a computer readable storage medium and a processor; the computer readable storage medium is configured to store executable instructions; the processor is configured to read the executable instructions stored in the computer readable storage medium and execute the method according to any one of claims 1-4.

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

7. A computer program product comprising computer programs or instructions, characterized in that, The computer program or instructions, when executed by the processor, implement the method according to any one of claims 1-4.

Images