Control method of soft switching grid-connected inverter and related equipment

Abstract

The invention relates to the technical field of soft switching grid-connected inverter control, in particular to a control method of a soft switching grid-connected inverter and related equipment. The method comprises the following steps: S1, sampling a three-phase current signal output by a soft switching grid-connected inverter and a three-phase voltage signal of a power grid, and obtaining a three-phase voltage modulation wave signal; performing current direction judgment on the three-phase current signal to obtain a three-phase current direction signal; obtaining a three-phase voltage modulation wave signal finally acting on the converter according to the three-phase voltage modulation wave signal and the three-phase current direction signal; comparing the three-phase voltage modulation wave signal finally acting on the converter with the triangular carrier wave signal to obtain control signals S1-S6 corresponding to main switch tubes S1-S6 of three-phase bridge arms of the soft switching grid-connected inverter; and according to the three-phase current direction signal, judging whether an auxiliary switch action is needed so as to generate a driving signal Sx1-Sx6 corresponding to an auxiliary switch Sx1-Sx6 of a three-phase bridge arm of the soft switching grid-connected inverter. According to the invention, the efficiency and modulation complexity of the inverter are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of soft-switch grid-connected inverter control, and in particular to a control method and related equipment for a soft-switch grid-connected inverter. Background Art

[0002] With the increasing integration of renewable energy sources such as photovoltaics and wind power into power systems, the requirements for inverter performance and efficiency are becoming increasingly stringent. Traditional hard-switching inverters often suffer from high losses, low efficiency, and significant electromagnetic interference. The emergence of soft-switching technology in the early 1980s effectively reduced the losses of hard-switching inverters and improved energy conversion efficiency. This has made soft-switching inverters a long-standing research hotspot in the field of power electronics.

[0003] Soft-switching inverters can be broadly categorized as resonant DC-link soft-switching inverters and resonant pole soft-switching inverters. Dr. Divan first proposed the resonant DC-link soft-switching inverter, which significantly reduces switching losses and improves system efficiency compared to hard-switching circuits. However, this topology results in voltage stress on the switching devices reaching 2.5 times the DC bus voltage. Furthermore, because the auxiliary components are located on the DC bus, they experience significant conduction losses over time, resulting in frequent zero-crossing gaps in the bus voltage and reducing the efficiency of DC voltage utilization.

[0004] The well-known auxiliary resonant pole inverter (ARCP) topology utilizes three high-power resonant inductors, which limits device size reduction and increases system losses. Some new ARCP inverter topologies use only one or two auxiliary commutation inductors to achieve ZVS conduction for all main switches and ZCS switching for all auxiliary switches. However, this approach only allows precise operation of the auxiliary switches at unity power factor. A better solution for achieving precise load-adaptive auxiliary switch operation under arbitrary power factor conditions has yet to be found. Summary of the Invention

[0005] To address the challenges of the prior art, the present invention provides a control method and related equipment for a soft-switching grid-connected inverter. Unlike conventional control methods, the present invention adaptively adjusts the main circuit switching sequence and auxiliary switch operation timing of the soft-switching grid-connected inverter based on the magnitude and direction of the load current, enabling soft switching at any power factor. The specific technical solution is as follows:

[0006] A control method for a soft-switching grid-connected inverter comprises the following steps:

[0007] Step S1, sampling the three-phase current signal i output by the soft-switching grid-connected inverter abc And the three-phase voltage signal v of the power grid abc ;

[0008] Step S2: According to the three-phase current signal i output by the soft-switching grid-connected inverter abc And the three-phase voltage signal v of the power grid abc Get the three-phase voltage modulation wave signal v mabc ;

[0009] Step S3: three-phase current signal i abc Determine the current direction and obtain the three-phase current direction signal flag abc ;

[0010] Step S4: According to the three-phase voltage modulation wave signal v mabc And three-phase current direction signal flag abc The final three-phase voltage modulation wave signal v′ acting on the converter is obtained mabc ;

[0011] Step S5: The three-phase voltage modulation wave signal v′ is finally applied to the converter. mabc Comparing with the triangular carrier signal car, the control signals S1-S6 corresponding to the main switch tubes S1-S6 of the three-phase bridge arm of the soft-switching grid-connected inverter are obtained;

[0012] Step S6: According to the three-phase current direction signal flag abc Determine whether the auxiliary switch action is required to generate the auxiliary switch S of the three-phase bridge arm of the soft switching grid-connected inverter x1 -S x6 The corresponding driving signal S x1 -S x6 .

[0013] Preferably, step S2 specifically includes the following steps:

[0014] Step S21: The three-phase voltage signal v abc The phase signal θ of the three-phase voltage of the power grid is obtained by inputting the phase-locked loop PLL ;

[0015] Step S22: The sampled three-phase current signal i abc The phase signal θ obtained by the phase-locked loop PLL Input the abc / dq conversion module together to obtain the d-axis sampling current I d_adc and q-axis sampling current I q_adc ;

[0016] Step S23: Set the q-axis current reference value I q_ref and q-axis sampling current I q_adc Subtract and get the q-axis current error err q , set the d-axis current reference value I d_ref and d-axis sampling current Id_adc Subtract and get the d-axis current error err d ;

[0017] Step S24: the obtained d-axis current error err d and q-axis current error err q Input the d-axis PI controller and q-axis PI controller respectively to obtain the d-axis voltage modulation wave m d and q-axis voltage modulation wave m q ;

[0018] Step S25: the obtained d-axis voltage modulation wave m d and q-axis voltage modulation wave m q With the phase signal θ PLL Input them together into the dq / abc module to obtain the three-phase voltage modulation wave signal v mabc .

[0019] Preferably, the phase signal θ of the three-phase voltage in step S21 is PLL The specific calculation is as follows:

[0020] θ PLL =G PLL (s)v abc ;

[0021]

[0022] Among them, G PLL (s) is the transfer function of the phase-locked loop, V m is the normalized amplitude of the three-phase grid voltage, K VCO is the sensitivity coefficient of the voltage controlled oscillator, K p_PLL is the phase-locked loop proportional coefficient, K i_PLL is the phase-locked loop integral coefficient.

[0023] Preferably, the d-axis voltage modulation wave m in step S24 d and q-axis voltage modulation wave m q The specific calculation is as follows:

[0024]

[0025] where K p_d and K p_q are the proportional coefficients of the d-axis PI controller and the q-axis PI controller, K i_d and K i_q are the integral coefficients of the d-axis PI controller and the q-axis PI controller respectively.

[0026] Preferably, the three-phase voltage modulation wave signal v in step S25 mabc is calculated as follows:

[0027]

[0028] Among them, v ma 、v mb 、v mc They represent the voltage modulation signals of the a-phase, b-phase and c-phase bridge arms of the soft-switching grid-connected inverter respectively.

[0029] Preferably, the three-phase current direction signal flag in step S3 abc is calculated as follows:

[0030] flag abc =[flag a flag b flag c ] T ;

[0031]

[0032] Among them, flag a 、flag b 、flag c Respectively represent the current direction signals of phase a, phase b, and phase c, flag y Indicates the y-phase current direction signal, i y Represents the Y-phase current signal.

[0033] Preferably, the three-phase voltage modulation wave signal v′ finally applied to the converter in step S4 is mabc is: v′ mabc =[v′ ma v′ mb v′ mc ];

[0034]

[0035] Among them, v′ ma 、v′ mb 、v′ mc They represent the actual voltage modulation signals acting on the a-phase, b-phase, and c-phase bridge arms of the soft-switching grid-connected inverter, respectively. PWM is the amplitude of the sawtooth wave signal.

[0036] Preferably, the control signals S1-S6 corresponding to the main switches S1-S6 of the three-phase bridge arms of the soft-switching grid-connected inverter in step S5 are specifically as follows:

[0037]

[0038] car=t PWM *sawtooth(2πf*t);

[0039] Where f is the switching frequency, and the sawtooth function is used to generate a sawtooth wave with an amplitude of 1 and a period of 1 / f. Indicates S z Negate, S z Represents the control signal of the zth main switch tube.

[0040] Preferably, in step S6, the auxiliary switch S of the three-phase bridge arm of the soft-switching grid-connected inverter x1 -S x6 The corresponding driving signal S x1 -S x6 The details are as follows:

[0041]

[0042] where t c is the auxiliary switch modulation wave, which represents the turn-on time of the auxiliary switch. Indicates flag y Negate, S xz is the driving signal of the zth auxiliary switch.

[0043] An electronic device includes a memory and a processor, wherein the memory is used to store a computer program, and the processor runs the computer program to enable the electronic device to execute the control method of the soft-switching grid-connected inverter.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The control method of the present invention can accurately distinguish all switches in the natural commutation operation of phase A, realize the one-time action of the auxiliary circuit, realize the synchronous auxiliary implementation of ZVS by all main switches, and realize ZCS by all auxiliary switches, thereby improving the efficiency of the converter and reducing the modulation complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly describes the drawings required for the specific embodiments or the description of the prior art. Similar elements or parts are generally identified by similar reference numerals throughout the drawings. Elements or parts in the drawings are not necessarily drawn to scale.

[0047] Figure 1 This is a topological diagram of an implementation example of a soft-switching grid-connected inverter of the present invention.

[0048] Figure 2 It is a schematic diagram of the operating points of the two bridge arms commutation process of an implementation example of a soft-switching grid-connected inverter of the present invention.

[0049] Figure 3 It is a comparison chart of the traditional SPWM modulation strategy and the control method of the present invention.

[0050] Figure 4 It is an implementation logic diagram of the control method of the present invention.

[0051] Figure 5 It is the theoretical waveform of the soft-switching grid-connected inverter after implementing the control method of the present invention.

[0052] Figure 6 This is circuit operation mode 1 of the soft-switching grid-connected inverter after implementing the control method of the present invention.

[0053] Figure 7 This is circuit operation mode 2 of the soft-switching grid-connected inverter after implementing the control method of the present invention.

[0054] Figure 8 This is circuit operation mode 3 of the soft-switching grid-connected inverter after implementing the control method of the present invention.

[0055] Figure 9 This is circuit operation mode 4 of the soft-switching grid-connected inverter after implementing the control method of the present invention.

[0056] Figure 10 This is circuit operation mode 5 of the soft-switching grid-connected inverter after implementing the control method of the present invention.

[0057] Figure 11 This is circuit operation mode 6 of the soft-switching grid-connected inverter after implementing the control method of the present invention.

[0058] Figure 12 It is the simulation waveform of phase a after implementing the control method of the present invention.

[0059] Figure 13 It is the simulation waveform of phase b after implementing the control method of the present invention.

[0060] Figure 14 It is the simulation waveform of phase C after implementing the control method of the present invention.

[0061] Figure 15 It is the grid-connected current and the auxiliary inductor current after the control method of the present invention is implemented.

[0062] Figure 16 It is the experimental waveform of the switching process of S2 and S6 after implementing the control method of the present invention.

[0063] Figure 17 It is the experimental waveform of the switching process of S1 and S5 after implementing the control method of the present invention. DETAILED DESCRIPTION

[0064] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0065] It will be understood that when used in this specification and the appended claims, the terms “comprises” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0066] It should also be understood that the terms used in the present specification are only for the purpose of describing particular embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0067] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0068] To address the complex modulation issues in soft-switching inverters, this paper proposes a control method for soft-switching grid-connected inverters. By detecting the current sector, all A natural commutation processes are adjusted to edge alignment, thereby achieving synchronous assistance for the three-phase circuit through a single action of the auxiliary circuit. This method of adjusting the A natural commutation process through current sector detection ensures the reliability of hard-switching assistance at any power factor.

[0069] The topology of the soft-switching grid-connected inverter of the present invention is as follows: Figure 1 As shown, the positive direction of the physical quantity is represented by an arrow. The circuit includes a DC power supply V dc , the first DC link capacitor C dc1 , the second DC link capacitor C dc2 , the first auxiliary commutation inductor L r1 and the second auxiliary commutation inductor L r2 , the first auxiliary switch tube S x1 , the second auxiliary switch tube S x2 , the third auxiliary switch tube S x3 , the fourth auxiliary switch tube S x4 , the fifth auxiliary switch tube S x5 , the sixth auxiliary switch tube S x6 , the first auxiliary diode Dx1 , the second auxiliary diode D x2 , the third auxiliary diode D x3 , the fourth auxiliary diode D x4 , the fifth auxiliary diode D x5 , the sixth auxiliary diode D x6 , first main switch tube S1, second main switch tube S2, third main switch tube S3, fourth main switch tube S4, fifth main switch tube S5, sixth main switch tube S6, three-phase inductor filter L, three-phase AC power grid v a 、v b 、v c . Usually, the inductor L r1 and L r2 Meet L r1 =L r2 =L r . L r is the inductor value.

[0070] The key feature of the soft-switching inverter is its synchronous auxiliary support for the auxiliary switch during the commutation process. r1 Provides ZVS condition for the three main switches in the inverter upper bridge arm. In each switching cycle, L r1 The auxiliary resonant inductor L r2 A ZVS condition is provided for the three main switches in the low-side bridge, with two auxiliary switches synchronized during each switching cycle. To simplify the analysis, the following assumptions are made: all components operate under ideal conditions. The load inductance is significantly larger than the resonant inductance, so the load current varies minimally during each switching event, allowing it to be approximated as a constant current source. The DC link capacitor is of a sufficiently large value to ensure minimal fluctuations in the DC link midpoint voltage.

[0071] For a three-phase soft-switching grid-connected inverter, the bridge arm state when the upper switch is on is recorded as H, and the bridge arm state when the lower switch is on is recorded as L. For bridge converters, the operation is usually divided into two different modes according to the level and direction of the load current. Figure 2 The two different cases of commutation directions are shown. The upper half plane corresponds to the rising edge transition from the lower switch to the upper switch, while the lower half plane corresponds to the falling edge transition from the upper switch to the lower switch. Mode 1 indicates auxiliary circuit assisted commutation, such as Figure 2 Mode 2 represents natural commutation, as shown in the purple area. Figure 2 The green area in the figure is shown.

[0072] Figure 3 (a) illustrates the generation logic of conventional SPWM using sawtooth wave. It shows that the modulation wave v ma 、v mb and v mcRepresents the duration of the first PWM state in the switching cycle. The amplitude of the sawtooth wave is recorded as t PWM , which represents the time required for the sawtooth wave to count from 0 to the highest point. In order to ensure that the switching state is converted from LHL to HLH at the beginning of the cycle, the modulation wave of phase b can be reversed, that is, t PWM -v mb ,like Figure 3 (b) As shown. In this way, the auxiliary switch S x1 、S x4 and S x5 It is only necessary to adjust the auxiliary inductor L before the end of the switching cycle. r1 and L r2 Pre-charging is performed to assist the natural commutation process of phase A in the three-phase bridge arm. The control method for the soft-switching grid-connected inverter provided by the present invention is based on the current sector alignment of the natural commutation process of phase A. This method modifies the traditional SPWM modulation strategy using only load current direction information, ensuring synchronization of the natural commutation process of all phase A phases. This is assisted by two resonant inductors to enable operation at any power factor.

[0073] The logic block diagram of a control method for a soft-switching grid-connected inverter provided by the present invention is as follows: Figure 4 As shown, the specific steps include:

[0074] Step S1, sampling the three-phase current signal i output by the soft-switching grid-connected inverter abc And the three-phase voltage signal v of the power grid abc ;

[0075] i abc =[i a i b i c ] T ;

[0076] Among them, i a 、i b 、i c They are the a-phase, b-phase and c-phase current signals of the power grid respectively.

[0077] v abc =[v a v b v c ] T ;

[0078] Among them, v a 、v b 、v c They are the a-phase, b-phase, and c-phase voltage signals output by the soft-switching grid-connected inverter respectively.

[0079] Step S2: According to the three-phase current signal i output by the soft-switching grid-connected inverterabc And the three-phase voltage signal v of the power grid abc Get the three-phase voltage modulation wave signal v mabc The specific steps include:

[0080] Step S21: The three-phase voltage signal v abc The phase signal θ of the three-phase voltage of the power grid is obtained by inputting the phase-locked loop PLL .

[0081] Phase signal θ of three-phase voltage PLL The specific calculation is as follows:

[0082] θ PLL =G PLL (s)v abc ;

[0083]

[0084] Among them, G PLL (s) is the transfer function of the phase-locked loop, V m is the normalized amplitude of the three-phase grid voltage, K VCO is the sensitivity coefficient of the voltage controlled oscillator, K p_PLL is the phase-locked loop proportional coefficient, K i_PLL is the phase-locked loop integral coefficient.

[0085] Taking a 380V three-phase power grid as an example, the normalization method is as follows:

[0086]

[0087] Step S22: The sampled three-phase current signal i abc The phase signal θ obtained by the phase-locked loop PLL Input the abc / dq conversion module together to obtain the d-axis sampling current I d_adc and q-axis sampling current I q_adc .

[0088] d-axis sampling current I d_adc and q-axis sampling current I q_adc The calculation is as follows:

[0089]

[0090] Step S23: Set the q-axis current reference value I q_ref and q-axis sampling current I q_adc Subtract and get the q-axis current error err q , set the d-axis current reference value I d_ref and d-axis sampling current I d_adc Subtract and get the d-axis current error err d .

[0091] q-axis current error err q and d-axis current error err d The calculation is as follows:

[0092] err q =I q_ref -I q_adc ;

[0093] err d =I d_ref -I d_adc .

[0094] Step S24: the obtained d-axis current error err d and q-axis current error err q Input the d-axis PI controller and q-axis PI controller respectively to obtain the d-axis voltage modulation wave m d and q-axis voltage modulation wave m q . d-axis voltage modulation wave m d and q-axis voltage modulation wave m q The specific calculation is as follows:

[0095]

[0096] where K p_d and K p_q are the proportional coefficients of the d-axis PI controller and the q-axis PI controller, K i_d and K i_q are the integral coefficients of the d-axis PI controller and the q-axis PI controller respectively.

[0097] Step S25: the obtained d-axis voltage modulation wave m d and q-axis voltage modulation wave m q With the phase signal θ PLL Input them together into the dq / abc module to obtain the three-phase voltage modulation wave signal v mabc .

[0098] Three-phase voltage modulation wave signal v mabc is calculated as follows:

[0099]

[0100] Among them, v ma 、v mb 、v mc They represent the voltage modulation signals of the a-phase, b-phase and c-phase bridge arms of the soft-switching grid-connected inverter respectively.

[0101] Step S3: three-phase current signal i abcDetermine the current direction and obtain the three-phase current direction signal flag abc .

[0102] Three-phase current direction signal flag abc is calculated as follows:

[0103] flag abc =[flag a flag b flag c ] T ;

[0104]

[0105] Among them, flag a 、flag b 、flag c Respectively represent the current direction signals of phase a, phase b, and phase c, flag y Indicates the y-phase current direction signal, i y Represents the Y-phase current signal.

[0106] Step S4: According to the three-phase voltage modulation wave signal v mabc And three-phase current direction signal flag abc The final three-phase voltage modulation wave signal v′ acting on the converter is obtained mabc .

[0107] The three-phase voltage modulation wave signal v′ that finally acts on the converter mabc for:

[0108] v′ mabc =[v′ ma v′ mb v′ mc ];

[0109]

[0110] Among them, v′ ma 、v′ mb 、v′ mc They represent the actual voltage modulation signals acting on the a-phase, b-phase, and c-phase bridge arms of the soft-switching grid-connected inverter, respectively. PWM is the amplitude of the sawtooth wave signal.

[0111] Step S5: The three-phase voltage modulation wave signal v′ is finally applied to the converter. mabc By comparing with the triangular carrier signal car, control signals S1-S6 corresponding to the main switch tubes S1-S6 of the three-phase bridge arm of the soft-switching grid-connected inverter are obtained.

[0112] The control signals S1-S6 corresponding to the main switch tubes S1-S6 of the three-phase bridge arm of the soft-switching grid-connected inverter are as follows:

[0113]

[0114] car=t PWM *sawtooth(2πf*t);

[0115] Where f is the switching frequency, and the sawtooth function is used to generate a sawtooth wave with an amplitude of 1 and a period of 1 / f. Indicates S z Negate, S z Represents the control signal of the zth main switch tube.

[0116] Step S6: According to the three-phase current direction signal flag abc Determine whether the auxiliary switch action is required to generate the auxiliary switch S of the three-phase bridge arm of the soft switching grid-connected inverter x1 -S x6 The corresponding driving signal S x1 -S x6 .

[0117] Auxiliary switch S of the three-phase bridge arm of the soft-switching grid-connected inverter x1 -S x6 The corresponding driving signal S x1 -S x6 The details are as follows:

[0118]

[0119] Among them t c is the auxiliary switch modulation wave, which represents the turn-on time of the auxiliary switch. Indicates flag y Negate, S xz is the driving signal of the zth auxiliary switch.

[0120] The waveforms of the key points of the soft switching grid-connected inverter operation are as follows: Figure 5 The typical working mode of the soft switching grid-connected inverter is as follows. Figure 6-11 The following sections analyze the various operating modes of the circuit. The entire A-phase natural commutation process can be divided into six stages.

[0121] Mode 1: (~t1): such as Figure 6 As shown, in the initial state, the soft-switching grid-connected inverter is in the LHL state, and the circuit operates in steady state. The phase current of phase a flows in the negative direction through the second main switch S2; the phase current of phase b flows in the negative direction through the third main switch S3; and the phase current of phase c flows in the negative direction through the sixth main switch S6. The auxiliary circuit is not open.

[0122] Mode 2: (t1-t2): At time t1, the first auxiliary switch S x1 , the fourth auxiliary switch tube S x4 and the fifth auxiliary switch S x5 Open at the same time, such as Figure 7 As shown. In the first auxiliary commutation inductor L r1 and the second auxiliary commutation inductor L r2 Under the influence of the first auxiliary switch tube S x1 , the fourth auxiliary switch tube S x4 and the fifth auxiliary switch S x5 The three auxiliary switches achieve zero current conduction (ZCS). r1 and the second auxiliary commutation inductor L r2 The inductor current is expressed in V dc / (2L r ) begins to charge at a slope of r1 The charging current gradually replaces the current in the second main switch tube S2 and the sixth main switch tube S6. r2 The current of the third main switch tube S3 replaces the current of the third main switch tube S3. When the current is equal to i a 、i c (For the first auxiliary commutation inductor L r1 ) or i b (For the second auxiliary commutation inductor L r2 ) is the sum of the load currents, the load current is commutated to the auxiliary branch, and the currents in the second main switch tube S2, the third main switch tube S3 and the sixth main switch tube S6 are reduced to zero. Subsequently, the first auxiliary commutation inductor L r1 and the second auxiliary commutation inductor L r2 The charging continues, causing the current in the second main switch tube S2, the third main switch tube S3 and the sixth main switch tube S6 to become positive and gradually increase until the sixth main switch tube S6 is turned off, thus ending this mode. r1 and the second auxiliary commutation inductor L r2 The current that exceeds the load current is called the overcharge current, denoted as I boost , which is determined by the dead time T during the main switch turn-on and turn-off process. d The first auxiliary commutation inductor L r1 and the second auxiliary commutation inductor L r2 Minimum I boost The calculation formula for charging time is as follows:

[0123]

[0124] For the first auxiliary commutation inductor Lr1 and the second auxiliary commutation inductor L r2 The load current I load1 and I load2 is defined as i a +i c and i b I load1 =i a +i c ;I load2 =i b .

[0125] Mode 3: (t2~t3): If Figure 8 As shown, at time t2, the second main switch tube S2, the third main switch tube S3 and the sixth main switch tube S6 are turned off. r1 The current on the second auxiliary commutation inductor L corresponds to the discharge of the parasitic capacitance of the first main switch tube S1 and the fifth main switch tube S5, and charges the parasitic capacitance of the second main switch tube S2 and the sixth main switch tube S6. r2 The current on the MOSFET corresponds to the discharge of the parasitic capacitance of the fourth main switch tube S4 and charges the parasitic capacitance of the third main switch tube S3. r When the charging and discharging of the first auxiliary commutation inductor L is completed, the parasitic diodes of the first main switch tube S1, the fourth main switch tube S4 and the fifth main switch tube S5 are turned on, and this mode ends. r1 The parasitic capacitance of the main switch and the second auxiliary commutation inductor L r2 The resonance process of the a-phase, b-phase circuits and the parasitic capacitance of the b-phase circuit. During the resonance process, the current peak will reach I peak :

[0126]

[0127] Mode 4: (t3~t4): Figure 9 As shown, after the parasitic diodes of the first main switch tube S1, the fourth main switch tube S4 and the fifth main switch tube S5, the switches meet the ZVS condition. r1 and the second auxiliary commutation inductor L r2 Before the current in the circuit is discharged to the same load current, the first, fourth, and fifth main switches S1, S4, and S5 must be turned on simultaneously. Otherwise, the first, fourth, and fifth main switches S1, S4, and S5 will not be able to achieve zero voltage switching. This means that the time t4 must meet the following requirements:

[0128]

[0129] Mode 5: (t4~t5): As Figure 10 As shown, at time t4, the first main switch tube S1, the fourth main switch tube S4 and the fifth main switch tube S5 are turned on. The first auxiliary commutation inductor L r1 and the second auxiliary commutation inductor L r2 The discharge continues, but its current is gradually replaced by the current passing through the first main switch tube S1, the fourth main switch tube S4 and the fifth main switch tube S5. r1 and the second auxiliary commutation inductor L r2 This mode ends when the current decreases to zero. Then, at time t5, the first auxiliary switch S can be turned off under ZCS conditions. x1 , the fourth auxiliary switch tube S x4 and the fifth auxiliary switch S x5 Therefore, t3 to t5 represent the first auxiliary commutation inductor L r1 and the second auxiliary commutation inductor L r2 The linear discharge period of the inductor. The calculation formula for the linear discharge time of the inductor is:

[0130]

[0131] Mode 6: (t5-t6): At t5, the first auxiliary switch S x1 , the fourth auxiliary switch tube S x4 and the fifth auxiliary switch S x5 When the inverter is turned off in ZCS mode, the state of the soft-switching grid-connected inverter changes to HLH. The circuit operates in a stable state; the DC side power supply supplies power to the three-phase load through the first main switch tube S1, the fourth main switch tube S4, and the fifth main switch tube S5.

[0132] Since the HLH-LLH-LHH-LHL commutation process is a natural soft switching commutation process, no assistance is required.

[0133] To verify the above theoretical analysis, a simulation model was constructed in this embodiment. The parameters of the soft-switching inverter used in the simulation are shown in Table 1.

[0134] Table 1 Simulation parameters

[0135] parameter value parameter value <![CDATA[V dc / V]]> 800 f / kHz 80 <![CDATA[L r / μH]]> 4.7 <![CDATA[C dc / μF]]> 204

[0136] Figure 12 、 Figure 13 and Figure 14 The switch drive signals, load current, auxiliary branch current and main switch voltage signals of phases a, b and c during the natural commutation time of A are shown respectively.

[0137] for Figure 12 , the first auxiliary switch tube S x1 The second main switch tube S2 of the lower switch is turned on before it is turned off, and serves as the first auxiliary commutation inductor Lr1 Before the first main switch S1 is turned on, the first auxiliary inductor current i Sx1 Always keep it greater than the load current i a . In the first auxiliary inductor current i Sx1 Under the action of switch S1 voltage U S1 Before the first main switch tube S1 is turned on, the voltage drops to 0, ensuring that the first main switch tube S1 is turned on under ZVS conditions. Figure 13 and Figure 14 , which also shows that the corresponding switch has achieved ZVS turn-on.

[0138] That is to say, in the first auxiliary commutation inductor L r1 and the first auxiliary commutation inductor L r2 With the help of , all A natural commutation actions in the three phases achieve ZVS. At the same time, judging from the auxiliary switch action signals and auxiliary branch currents, all enabled auxiliary branches achieve ZCS switching on and off.

[0139] also, Figure 15 The waveforms of the three-phase load current and the auxiliary inductor current are shown in Figure 1. Figure 15 As can be seen from the figure, when assisting all phase A natural commutation operations, the peak current of the auxiliary inductor is reasonable and does not cause significant losses. On the other hand, combined with the simulation results, even if there are significant differences in the distribution of the inter-phase resonant inductor current, all phase A natural commutation switches can still be assisted.

[0140] In order to further verify the theoretical analysis of the soft-switching inverter, a 3kW grid-connected inverter prototype was built, and the parameters are shown in Table 1. Figure 16 and 17 The switching waveforms of phase a and phase c are shown. Figure 16 It can be seen from the figure that for phase a and phase c, the second main switch tube S2 and the sixth main switch tube S6 under the bridge arm have parasitic capacitances. gs During the falling period, that is, during the falling period of S2 and S6, the voltage V across the second main switch tube S2 and the sixth main switch tube S6 is ds Keeping it at 0, pseudo ZVS shutdown can be achieved. For the first main switch tube S1 and the fifth main switch tube S5 on the bridge arm, when the switch drive signal V gs Before rising, the voltage V ds It drops to zero in advance, indicating that the first main switch tube S1 and the fifth main switch tube S5 on the bridge arm are ZVS turned on, that is, the first auxiliary commutation inductor L r1 ZVS turn-on is achieved with the help of

[0141] Those skilled in the art will appreciate that the modules of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition of each example has been generally described in terms of function in the above description. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0142] In the embodiments provided by the present invention, it should be understood that the division of modules is merely a logical function division, and there may be other division methods in actual implementation, for example, multiple modules can be combined into one module, one module can be split into multiple modules, or some features can be ignored, etc.

[0143] In addition, the functional modules in various embodiments of the present invention may be integrated into a single processing module, or each module may exist physically separately, or two or more modules may be integrated into a single module. The aforementioned integrated modules may be implemented in the form of hardware or software functional modules.

[0144] If the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server or network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, read-only memory (ROM, Read-0nly Memory), random access memory (RAM, Random Access Memory), mobile hard disk, magnetic disk or optical disk, etc., various media that can store program code.

[0145] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.

Claims

1. A control method for a soft-switching grid-connected inverter, characterized in that: The following steps are involved: Step S1, sampling the three-phase current signal i output by the soft-switching grid-connected inverter abc And the three-phase voltage signal v of the power grid abc ; Step S2: According to the three-phase current signal i output by the soft-switching grid-connected inverter abc And the three-phase voltage signal v of the power grid abc Get the three-phase voltage modulation wave signal v mabc ; Step S3: three-phase current signal i abc Determine the current direction and obtain the three-phase current direction signal flag abc ; Step S4: According to the three-phase voltage modulation wave signal v mabc And three-phase current direction signal flag abc The final three-phase voltage modulation wave signal v′ acting on the converter is obtained mabc ; Step S5: The three-phase voltage modulation wave signal v′ is finally applied to the converter. mabc Comparing with the triangular carrier signal car, the control signals S1-S6 corresponding to the main switch tubes S1-S6 of the three-phase bridge arm of the soft-switching grid-connected inverter are obtained; Step S6: According to the three-phase current direction signal flag abc Determine whether the auxiliary switch action is required to generate the auxiliary switch S of the three-phase bridge arm of the soft switching grid-connected inverter x1 -S x6 The corresponding driving signal S x1 -S x6 .

2. The control method of a soft-switching grid-connected inverter according to claim 1, characterized in that: The step S2 specifically includes the following steps: Step S21: The three-phase voltage signal v abc The phase signal θ of the three-phase voltage of the power grid is obtained by inputting the phase-locked loop PLL ; Step S22: The sampled three-phase current signal i abc The phase signal θ obtained by the phase-locked loop PLL Input the abc / dq conversion module together to obtain the d-axis sampling current I d_adc and q-axis sampling current I q_adc ; Step S23: Set the q-axis current reference value I q_ref and q-axis sampling current I q_adc Subtract and get the q-axis current error err q , set the d-axis current reference value I d_ref and d-axis sampling current I d_adc Subtract and get the d-axis current error err d ; Step S24: the obtained d-axis current error err d and q-axis current error err q Input the d-axis PI controller and q-axis PI controller respectively to obtain the d-axis voltage modulation wave m d and q-axis voltage modulation wave m q ; Step S25: the obtained d-axis voltage modulation wave m d and q-axis voltage modulation wave m q With the phase signal θ PLL Input them together into the dq / abc module to obtain the three-phase voltage modulation wave signal v mabc .

3. The control method of a soft-switching grid-connected inverter according to claim 2, characterized in that: The phase signal θ of the three-phase voltage in step S21 PLL The specific calculation is as follows: i PLL =G PLL (s)v abc ; Among them, G PLL (s) is the transfer function of the phase-locked loop, V m is the normalized amplitude of the three-phase grid voltage, K VCO is the sensitivity coefficient of the voltage controlled oscillator, K p_PLL is the phase-locked loop proportional coefficient, K i_PLL is the phase-locked loop integral coefficient.

4. The control method of a soft-switching grid-connected inverter according to claim 1, characterized in that: In step S24, the d-axis voltage modulation wave m d and q-axis voltage modulation wave m q The specific calculation is as follows: where K p_d and K p_q are the proportional coefficients of the d-axis PI controller and the q-axis PI controller, K i_d and K i_q are the integral coefficients of the d-axis PI controller and the q-axis PI controller respectively.

5. The control method of a soft-switching grid-connected inverter according to claim 1, characterized in that: In step S25, the three-phase voltage modulation wave signal v mabc is calculated as follows: Among them, v ma 、v mb 、v mc They represent the voltage modulation signals of the a-phase, b-phase and c-phase bridge arms of the soft-switching grid-connected inverter respectively.

6. The control method of a soft-switching grid-connected inverter according to claim 1, characterized in that: The three-phase current direction signal flag in step S3 abc is calculated as follows: flag abc =[flag a flag b flag c ] T ; Among them, flag a 、flag b 、flag c Respectively represent the current direction signals of phase a, phase b, and phase c, flag y Indicates the y-phase current direction signal, i y Represents the Y-phase current signal.

7. The control method of a soft-switching grid-connected inverter according to claim 7, characterized in that: The three-phase voltage modulation wave signal v′ finally acts on the converter in step S4 mabc for: v′ mabc =[v′ ma v′ mb v′ mc ]; Among them, v′ ma 、v′ mb 、v′ mc They represent the actual voltage modulation signals acting on the a-phase, b-phase, and c-phase bridge arms of the soft-switching grid-connected inverter, respectively. PWM is the amplitude of the sawtooth wave signal.

8. The control method of a soft-switching grid-connected inverter according to claim 8, characterized in that: The control signals S1-S6 corresponding to the main switches S1-S6 of the three-phase bridge arms of the soft-switching grid-connected inverter in step S5 are specifically as follows: car=t PWM *sawtooth(2πf*t); Where f is the switching frequency, and the sawtooth function is used to generate a sawtooth wave with an amplitude of 1 and a period of 1 / f; S z-1 Indicates S z Negate, S z Represents the control signal of the zth main switch tube.

9. The control method of a soft-switching grid-connected inverter according to claim 7, characterized in that: The auxiliary switch S of the three-phase bridge arm of the soft-switching grid-connected inverter in step S6 is x1 -S x6 The corresponding driving signal S x1 -S x6 The details are as follows: where t c is the auxiliary switch modulation wave, which represents the turn-on time of the auxiliary switch. Indicates flag y Negate, S xz is the driving signal of the zth auxiliary switch.

10. An electronic device, characterized in that: The electronic device comprises a memory and a processor, wherein the memory is used to store a computer program, and the processor runs the computer program to enable the electronic device to execute the control method of the soft-switching grid-connected inverter according to any one of claims 1 to 9.

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