Charge quantity control circuit and control method of soft switching grid-connected inverter

Abstract

The invention discloses a charge quantity control circuit and control method of a soft switching grid-connected inverter, and belongs to the technical field of control of power electronic converters, the charge quantity control circuit comprises a soft switching control module and a charge quantity control module, and when the soft switching grid-connected inverter adopts average current control, the digital operand is large, and the control accuracy is high. And the dynamic response effect is not ideal. For the soft switching grid-connected inverter, effective closed-loop control of the soft switching grid-connected inverter is realized based on the relational expression between the bridge arm output charge quantity and the conduction time by taking the bridge arm output charge quantity as the control quantity. According to the invention, the digital operation of the soft-switching grid-connected inverter can be effectively simplified, the dynamic response capability of the soft-switching grid-connected inverter is enhanced, the control is simple, and the realization is easy.

Description

Technical Field

[0001] The present invention belongs to the field of power electronics technology, in particular to the field of control technology of power electronic converters, and specifically relates to a charge control circuit and a control method of a soft-switch grid-connected inverter. Background Art

[0002] As a key device that connects photovoltaic power generation components with the power grid and realizes efficient and high-quality power generation, grid-connected inverters are widely used in new power systems. It is necessary to further improve and realize the high efficiency and compactness of high-frequency grid-connected inverters. However, grid-connected inverters operating at high frequencies have the disadvantages of high switching losses and low conversion efficiency. It can be considered to break through the operating frequency constraints by operating the inductor current in critical conduction mode (CRM) and using soft switching technology to reduce switching losses, further realize the high efficiency and lightweight of grid-connected inverters. The Chinese invention patent with the authorization announcement number "CN102035425B" proposes a control method suitable for the inverter circuit of a single inverter, which can realize the zero voltage opening of the device, reduce the system loss and improve the system efficiency. The reference "G.Son, Z.Huang, Q.Li and F.C.Lee.Analysis and Control of Critical Conduction Mode High-Frequency Single-Phase Transformerless PV Inverter. IEEE Transactions on Power Electronics. 2021, 36 (11)" combines trajectory tracking with average current control, and calculates the conduction time of the switch tube based on the average current control, thereby realizing the control of the grid-connected current and the full range of CRM. However, this scheme requires a ZCD circuit and adjusts the control according to the switching cycle, and the control implementation is relatively complicated. To address this problem, a Chinese invention patent application with publication number "CN113852266A" proposes a fully digital soft switching control circuit for a single-phase grid-connected inverter. This circuit is based on a control scheme with a fixed control frequency, which reduces the performance requirements of the digital controller to a certain extent.

[0003] However, the above schemes all have problems such as large amount of digital calculation and urgent need to optimize the dynamic response performance. Traditional single-cycle control, which is widely used in the fields of active power factor correction (PFC) and DC-DC converters, has the advantages of simple control, small amount of calculation and fast dynamic response, but as a nonlinear algorithm, it also has certain shortcomings. Traditional single-cycle control requires a constant switching frequency and cannot be directly applied to soft-switching grid-connected inverters with changing switching frequency and inductor current in critical conduction mode. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a charge control circuit for a soft-switching grid-connected inverter, including a soft-switching control module and a charge control module. Based on the relationship between the output charge of the bridge arm and the conduction time, the output of the grid-connected current controller is controlled to be the output charge of the bridge arm, and the conduction time and the switching period are calculated and sent to the modulator to realize effective closed-loop control of the soft-switching grid-connected inverter. The present invention can effectively simplify the digital operation of the soft-switching grid-connected inverter, enhance the dynamic response capability of the soft-switching grid-connected inverter, and has simple control and easy implementation, and has broad application prospects in the field of power electronic converters.

[0005] In order to achieve the above object, the technical solution of the present invention is:

[0006] A charge control circuit for a soft-switching grid-connected inverter, wherein the grid-connected inverter comprises an inverter module and a filter module, wherein the input end of the inverter module is connected in parallel to a DC power supply U dc The output end of the inverter module is connected in parallel with the input end of the filter module, and the output end of the filter module is connected in parallel with the AC power grid u g The filtering module includes a first inductor, a first capacitor, and a second inductor. The first end of the first inductor is the first input end of the filtering module. The second end of the first inductor is connected to the first end of the first capacitor and the first end of the second inductor. The second end of the second inductor is the first output end of the filtering module. The second end of the first capacitor is the second input end and the second output end of the filtering module.

[0007] The charge quantity control circuit of the soft-switching grid-connected inverter comprises a soft-switching control module and a charge quantity control module.

[0008] The soft switch control module includes a first voltage sensor, a current sensor, a second voltage sensor, a current regulator, a first subtractor, a first multiplier, a phase lock, a modulator, and a first divider.

[0009] The first voltage sensor samples the DC power supply U dc The second voltage sensor samples the voltage of the AC power grid u g The output end of the second voltage sensor is connected to the input end of the phase lock, the output end of the phase lock is connected to the first input end of the first multiplier and the first input end of the modulator respectively, and the second input end of the first multiplier is connected to the grid current reference value I ref The output terminal of the first multiplier outputs the grid current reference value i ref and connected to the positive input terminal of the first subtractor; the current sensor samples the current i of the first inductorL1 The output end of the current sensor is connected to the negative input end of the first subtractor, the output end of the first subtractor is connected to the input end of the current regulator, and the output end of the current regulator is connected to the charge control module; the dividend input end and the divisor input end of the first divider are connected to the charge control module, the second input end of the modulator is connected to the output end of the first divider, and the third input end of the modulator is connected to the charge control module. The modulator obtains the driving signal required by the grid-connected inverter according to the phase of the first input end and the signals of the second input end and the third input end.

[0010] The charge control module includes a second multiplier, a first scaler, a first adder, a second scaler, a third multiplier, a second divider, a first square root extractor, a second adder, a fourth multiplier, a third scaler, a second subtractor, a fifth multiplier, and a third divider.

[0011] The output end of the first voltage sensor is connected to the first input end of the fourth multiplier and the input end of the third proportional device respectively; the first input end of the second multiplier is connected to the dead time t dead The second input terminal of the second multiplier is connected to the reset current I set The output end of the second multiplier is connected to the input end of the first scaler, the output end of the first scaler is connected to the first input end of the first adder, and the second input end of the first adder is connected to the bridge arm output charge Q output by the output end of the current regulator. inv The output of the first adder is connected to the input of the second scaler, the output of the second scaler is connected to the first input of the third multiplier, the output of the third multiplier is connected to the dividend input of the second divider, the divisor input of the second divider is connected to the output of the fourth multiplier, the output of the second divider is connected to the input of the first square rooter, and the output of the first square rooter outputs the conduction time t on The first input terminal of the second adder is connected to the dividend input terminal of the first divider, and the second input terminal of the second adder is connected to the output terminal of the third divider to output the off time t off , the third input terminal of the second adder is connected to the dead time t dead, the output end of the second adder is respectively connected to the divisor input end of the first divider and the third input end of the modulator; the output end of the second voltage sensor is respectively connected to the second input end of the third multiplier, the divisor input end of the third divider and the negative input end of the second subtractor, the output end of the third proportional device is connected to the positive input end of the second subtractor, and the output end of the second subtractor is connected to the second input end of the fourth multiplier; the first input end of the fifth multiplier is connected to twice the inductance of the first inductor 2L1, the second input end of the fifth multiplier is connected to the output end of the first multiplier, and the output end of the fifth multiplier is connected to the dividend input end of the third divider.

[0012] Furthermore, the gain k1 of the first proportional device is a constant of 0.5; the gain k2 of the second proportional device is four times the first inductance L1 divided by the voltage U of the DC power supply. dc ,Right now The gain k3 of the third proportional device is a constant of 0.5.

[0013] Furthermore, the third input terminal of the second adder and the first input terminal of the second multiplier are connected to the dead time t dead for The second input terminal t of the second adder off The value of Wherein, L1 represents the inductance of the first inductor, C represents the capacitance of the first capacitor, and u g represents the voltage of the AC grid, i ref The output terminal of the first multiplier represents the grid-connected current reference value including phase information.

[0014] Furthermore, the output end of the current regulator is the bridge arm output charge Q inv , which is related to the conduction time t of the output of the first square root generator on The following relationship exists:

[0015]

[0016] where u g represents the voltage of the AC grid, i L1 represents the current of the first inductor, L1 represents the inductance of the first inductor, U dc represents the voltage of the DC power supply, and C1 represents the capacitance of the first capacitor.

[0017] Furthermore, the output of the above modulator includes a first drive signal and a second drive signal, the first drive signal and the second drive signal complement each other at high frequency, and the switching period of the first drive signal and the second drive signal is the value of the third input terminal of the current modulator, the duty cycle of the first drive signal in this switching period is the value of the second input terminal of the current modulator, and the duty cycle of the second drive signal in this switching period is the difference between 1 and the second input terminal of the current modulator; the modulator determines the AC power grid u connected to the grid-connected inverter at this time according to the value of the first input terminal and 0. g The polarity of the inverter module is determined, and the first drive signal and the second drive signal are sent to the switch tube in the inverter module according to different inverter topologies.

[0018] Furthermore, when the connected AC power grid u g In the positive half cycle, when the first driving signal is at a high level, the inverter module makes the current i of the first inductor L1 When the second driving signal is at a high level, the inverter module causes the current i of the first inductor to increase. L1 When the AC power grid u connected g In the negative half cycle, when the first driving signal is at a high level, the inverter module makes the current i of the first inductor L1 When the second driving signal is at a high level, the inverter module makes the current i of the first inductor L1 Increase.

[0019] The present invention also provides a charge control method for a soft-switch grid-connected inverter, which is applied to the charge control circuit of the soft-switch grid-connected inverter, comprising: step S1, sampling the DC power supply U dc The voltage of the AC grid u g The voltage and current of the first inductor i L1 ; Step S2, the grid current reference value i ref and the current i of the first inductor L1 L1 The error input to the current regulator, the current of the first inductor i L1 Closed-loop regulation is performed, and the output bridge arm of the current regulator outputs the charge Q inv ; Step S3, calculate the conduction time t required to achieve charge control on , turn-off time t off ; Step S4, calculate the duty cycle and switching period required to realize charge control and output them to the modulator; Step S5, obtain the first drive signal and the second drive signal in the modulator and send them to the switch tube in the inverter module, end this control cycle, and wait for the next control cycle.

[0020] Furthermore, the switching period T = t on +t off +t dead , duty cycle D = t on / T.

[0021] The beneficial effects of the present invention are:

[0022] (1) The present invention enables the soft-switching grid-connected inverter to operate in a critical conduction mode, and can effectively simplify digital operations of the soft-switching grid-connected inverter by calculating and adjusting the output charge of the bridge arm and the conduction time of the switch tube.

[0023] (2) The present invention does not affect the soft switching performance of the grid-connected inverter when the inductor current is in the critical conduction mode, has the characteristics of high efficiency and low loss, and can effectively enhance the dynamic response capability of the soft switching grid-connected inverter.

[0024] (3) The control logic of the present invention is simple, easy to program and implement, does not require additional hardware circuits, and has the technical advantage of low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention is a schematic diagram of a charge control circuit of a soft-switching grid-connected inverter.

[0026] FIG. 2( a ) is a schematic circuit diagram of an inverter module of the present invention using a full-bridge circuit topology.

[0027] FIG. 2( b ) is a circuit diagram of an inverter module of the present invention adopting a single-phase neutral point clamping topology.

[0028] Figure 3 It is a second-order model of a grid-connected inverter in a critical conduction mode when the charge control circuit of the present invention is adopted.

[0029] Figure 4 The present invention is a flowchart of a specific implementation of a method for controlling the charge amount of a soft-switching grid-connected inverter.

[0030] FIG5(a) is a schematic diagram of steady-state waveforms when the charge control circuit of the soft-switching grid-connected inverter disclosed in the present invention is used.

[0031] FIG5( b ) is a schematic diagram of steady-state waveforms when the full digital soft switching control circuit of the grid-connected inverter of patent application “CN113852266A” is used.

[0032] FIG6( a ) is a schematic diagram of a dynamic response waveform when the charge control circuit of the soft-switching grid-connected inverter disclosed in the present invention is used.

[0033] FIG6( b ) is a schematic diagram of the dynamic response waveform when the full digital soft switching control circuit of the grid-connected inverter of the patent application “CN113852266A” is adopted. DETAILED DESCRIPTION

[0034] The technical solution of the present invention will be described in detail below in conjunction with the accompanying drawings.

[0035] The present invention provides a charge control circuit for a soft-switch grid-connected inverter. Figure 1 shown.

[0036] The grid-connected inverter comprises an inverter module 1 and a filter module 2. The input end of the inverter module 1 is connected in parallel with a DC power supply U dc The output end of the inverter module 1 is connected in parallel to the input end of the filter module 2, and the output end of the filter module 2 is connected in parallel to the AC power grid u g The filtering module 2 includes a first inductor L1, a first capacitor C1, and a second inductor L2. The first end of the first inductor L1 is the first input end of the filtering module 2. The second end of the first inductor L1 is connected to the first end of the first capacitor C1 and the first end of the second inductor L2. The second end of the second inductor L2 is the first output end of the filtering module 2. The second end of the first capacitor is the second input end and the second output end of the filtering module 2.

[0037] The charge quantity control circuit of the soft-switch grid-connected inverter comprises a soft-switch control module 3 and a charge quantity control module 4 .

[0038] The soft switch control module 3 includes a first voltage sensor 31, a current sensor 32, a second voltage sensor 33, a current regulator 34, a first subtractor 35, a first multiplier 36, a phase lock 37, a modulator 38, and a first divider 39. The first voltage sensor 31 samples the DC power supply U dc The second voltage sensor 33 samples the voltage of the AC power grid u g The output end of the second voltage sensor 33 is connected to the input end of the phase lock 37, the output end of the phase lock 37 is connected to the first input end of the first multiplier 36 and the first input end of the modulator 38 respectively, and the second input end of the first multiplier 36 is connected to the grid current reference value I ref The output terminal of the first multiplier 36 outputs the grid current reference value i ref and connected to the positive input terminal of the first subtractor 35; the current sensor 32 samples the current i of the first inductor L1 L1The output end of the current sensor 32 is connected to the negative input end of the first subtractor 35, the output end of the first subtractor 35 is connected to the input end of the current regulator 34, and the output end of the current regulator 34 is connected to the charge control module 4; the dividend input end and the divisor input end of the first divider 39 are connected to the charge control module 4, the second input end of the modulator 38 is connected to the output end of the first divider 39, and the third input end of the modulator 38 is connected to the charge control module 4. The modulator 38 obtains the driving signal required by the grid-connected inverter according to the phase of the first input end and the signals of the second input end and the third input end.

[0039] The charge control module 4 includes a second multiplier 41, a first proportional device 42, a first adder 43, a second proportional device 44, a third multiplier 45, a second divider 46, a first square root device 47, a second adder 48, a fourth multiplier 49, a third proportional device 410, a second subtractor 411, a fifth multiplier 412, and a third divider 413. The output end of the first voltage sensor 31 is respectively connected to the first input end of the fourth multiplier 49 and the input end of the third proportional device 410; the first input end of the second multiplier 41 is connected to the dead time t dead The second input terminal of the second multiplier 41 is connected to the reset current I set The output end of the second multiplier 41 is connected to the input end of the first scaler 42, the output end of the first scaler 42 is connected to the first input end of the first adder 43, and the second input end of the first adder 43 is connected to the bridge arm output charge Q outputted by the output end of the current regulator 34. inv The output end of the first adder 43 is connected to the input end of the second scaler 44, the output end of the second scaler 44 is connected to the first input end of the third multiplier 45, the output end of the third multiplier 45 is connected to the dividend input end of the second divider 46, the divisor input end of the second divider 46 is connected to the output end of the fourth multiplier 49, the output end of the second divider 46 is connected to the input end of the first square root 47, and the output end of the first square root 47 outputs the conduction time t on The first input terminal of the second adder 48 is connected to the dividend input terminal of the first divider 39, and the second input terminal of the second adder 48 is connected to the output terminal of the third divider 413 to output the off time t off The third input terminal of the second adder 48 is connected to the dead time t deadThe output end of the second adder 48 is respectively connected to the divisor input end of the first divider 39 and the third input end of the modulator 38; the output end of the second voltage sensor 33 is respectively connected to the second input end of the third multiplier 45, the divisor input end of the third divider 413 and the negative input end of the second subtractor 411, the output end of the third proportional device 410 is connected to the positive input end of the second subtractor 411, and the output end of the second subtractor 411 is connected to the second input end of the fourth multiplier 49; the first input end of the fifth multiplier 412 is connected to twice the inductance 2L1 of the first inductor L1, the second input end of the fifth multiplier 412 is connected to the output end of the first multiplier 36, and the output end of the fifth multiplier 412 is connected to the dividend input end of the third divider 413.

[0040] Optionally, when the soft-switching grid-connected inverter adopts the soft-switching control module 3 and the charge control module 4, the gain k1 of the first proportional device 42 can be a constant of 0.5; the gain k2 of the second proportional device 44 can be four times the first inductance value L1 divided by the voltage U of the DC power supply. dc ,Right now The gain k3 of the third scaler 410 may be a constant of 0.5.

[0041] Optionally, the third input terminal of the second adder 48 and the first input terminal of the second multiplier (41) are connected to the dead time t dead Can The second input terminal of the second adder 48 receives the off time t off The value can be i ref The output of the first multiplier 36 represents the grid-connected current reference value including the phase information.

[0042] More specifically, the output end of the current regulator 34 is the bridge arm output charge Q inv , which is converted into the conduction time t through the following calculation on , and as the output of the first square root generator 47:

[0043]

[0044] where u g represents the voltage of the AC grid, i L1 represents the current of the first inductor, L1 represents the inductance of the first inductor, U dc represents the voltage of the DC power supply, and C1 represents the capacitance of the first capacitor.

[0045] Furthermore, the output of the modulator 38 includes a first drive signal PWM_a and a second drive signal PWM_s, the first drive signal PWM_a and the second drive signal PWM_s are complementary high-frequency actions, and the switching period of the first drive signal PWM_a and the second drive signal PWM_s is the value of the third input terminal of the current modulator 38, the duty cycle of the first drive signal PWM_a in this switching period is the value of the second input terminal of the current modulator 38, and the duty cycle of the second drive signal PWM_a in this switching period is the difference between 1 and the second input terminal of the current modulator 38; the modulator 38 determines the AC power grid u to which the grid-connected inverter is connected at this time according to the size of the value of the first input terminal and 0. g The polarity of the first drive signal PWM_a and the second drive signal PWM_s are sent to the corresponding specific switch tubes in the inverter module 1 according to different inverter topologies, as shown in Figures 2(a) and 2(b) and their detailed descriptions. g In the positive half cycle, when the first driving signal PWM_a is at a high level, the inverter module 1 makes the current i of the first inductor L1 L1 When the second driving signal PWM_s is at a high level, the inverter module 1 makes the current i of the first inductor L1 L1 When the AC power grid u connected g In the negative half cycle, when the first driving signal PWM_a is at a high level, the inverter module 1 makes the current i of the first inductor L1 L1 When the second driving signal PWM_s is at a high level, the inverter module 1 makes the current i of the first inductor L1 decrease. L1 The first drive signal PWM_a and the second drive signal PWM_s work together to enable the grid-connected inverter to operate in a critical conduction mode, which can achieve zero-voltage switching of the switching device, reduce switching losses, and further improve the overall working efficiency of the inverter.

[0046] For different inverter topologies, the above preferred technical solutions, especially when the soft-switch grid-connected inverter adopts the charge control circuit of the present invention, need to be adjusted in a targeted manner. FIG2 shows a circuit topology applicable to some inverter modules 1 of the present invention. When the full-bridge circuit topology shown in FIG2(a) is adopted, in order to ensure that the circuit topology shown in FIG2(a) works normally, when the AC power grid connected to the inverter module 1 is in the positive half cycle, the first drive signal PWM_a should be used as the drive signal of the first switch tube S1, the second drive signal PWM_s should be used as the drive signal of the second switch tube S2, the drive signal of the fourth switch tube S4 is high, and the drive signal of the third switch tube S3 is low; when the AC power grid connected to the inverter module 1 is in the negative half cycle, the first drive signal PWM_a should be used as the drive signal of the second switch tube S2, the second drive signal PWM_s should be used as the drive signal of the first switch tube S1, the drive signal of the third switch tube S3 is high, and the drive signal of the fourth switch tube S4 is low.

[0047] When the single-phase midpoint clamped topology shown in FIG2(b) is adopted, when the AC power grid connected to the inverter module 1 is in the positive half cycle, the first drive signal PWM_a should be used as the drive signal of the fifth switch tube S5, the second drive signal PWM_s should be used as the drive signal of the seventh switch tube S7, the drive signal of the sixth switch tube S6 is high level, and the drive signal of the eighth switch tube S8 is low level; when the AC power grid connected to the inverter module 1 is in the negative half cycle, the first drive signal PWM_a should be used as the drive signal of the eighth switch tube S8, the second drive signal PWM_s should be used as the drive signal of the sixth switch tube S6, the drive signal of the seventh switch tube S7 is high level, and the drive signal of the fifth switch tube S5 is low level.

[0048] Figure 3 The figure shows a second-order model of a grid-connected inverter in critical conduction mode when the charge control circuit of the present invention is adopted, where s is the output charge Q of the bridge arm. inv Perform differential calculation, i L1 (s) is the current of the first inductor L1 obtained in the frequency domain, i c (s) is the current of the first capacitor C1 obtained in the frequency domain, u c (s) is the voltage of the first capacitor C1 obtained in the frequency domain, is divided by the capacitance C1 of the first capacitor and integrated, u g (s) is the AC power grid u obtained in the frequency domain g The voltage, is divided by the inductance value L2 of the second inductor and integrated, i g (s) is the grid current obtained in the frequency domain.

[0049] Figure 4The figure shows a specific implementation flow chart of a charge control method of a soft-switching grid-connected inverter of the present invention, and each cycle includes the following steps.

[0050] Step S1, at the beginning of each digital control cycle, sampling the DC power supply U dc The voltage of the AC grid u g The voltage and current of the first inductor i L1 ;

[0051] Step S2: set the grid current reference value i ref and the current i of the first inductor L1 L1 The error is input to the current regulator 34. The current regulator 34 adjusts the current i of the first inductor based on the proportional gain and integral gain parameters. L1 Closed-loop regulation is performed, and the current regulator 34 outputs the bridge arm output charge Q inv ;

[0052] Optionally, the current regulator 34 is a PI regulator.

[0053] Step S3, based on the above sampling and the bridge arm output charge Q inv , calculate the on-time t required to achieve charge control on , turn-off time t off ;

[0054] More specifically, the on-time t on The calculation formula is as follows:

[0055]

[0056] Among them, u g represents the voltage of the AC grid, i L1 represents the current of the first inductor, L1 represents the inductance of the first inductor, U dc represents the voltage of the DC power supply, and C1 represents the capacitance of the first capacitor.

[0057] Turn-off time t off The calculation formula is as follows:

[0058]

[0059] Among them, i ref It is the reference value of grid current.

[0060] Step S4, calculating the duty cycle and switching period required to realize charge quantity control and outputting them to the modulator 38;

[0061] Furthermore, the switching period T = t on +t off +tdead , duty cycle D = t on / T;

[0062] Step S5, obtaining the first drive signal and the second drive signal in the modulator 38 and sending them to the switch tube in the inverter module 1, ending the current control cycle and waiting for the next control cycle.

[0063] Optionally, a charge control method for a soft-switching grid-connected inverter of the present invention is implemented in a digital controller.

[0064] The single-phase midpoint clamped topology shown in FIG2(b) was verified by building a corresponding experimental platform in MATLAB, and the experimental results of the grid-connected inverter in critical conduction mode when the charge control scheme proposed in the present invention and the average current control scheme based on full digital soft switching proposed in the patent application "CN113852266A" were obtained, as shown in FIG5 and FIG6, where FIG5(a) is a steady-state waveform when the grid-connected inverter adopts the charge control circuit of the soft switching grid-connected inverter disclosed in the present invention, and FIG5(b) is a steady-state waveform when the full digital soft switching control circuit of the grid-connected inverter of the patent application "CN113852266A" is adopted. It can be seen that when the charge control circuit of the soft switching grid-connected inverter disclosed in the present invention is adopted, the grid-connected current i g The waveform quality is good, similar to that of FIG5(b) when the full digital soft switch control circuit of the grid-connected inverter of the patent application "CN113852266A" is used, and there is no obvious distortion. When FIG5(a) uses the charge control circuit, the grid current i g The total harmonic distortion rate of the grid current is 2.35%. When the full digital soft switch control circuit is used in Figure 5(b), the grid current i g The total harmonic distortion rate of the grid-connected current is 2.15%. The analysis results of the total harmonic distortion rate of the grid-connected current of the two are basically the same. Figure 6 (a) is the dynamic response waveform when the charge control circuit of the soft-switching grid-connected inverter disclosed by the present invention is adopted, and Figure 6 (b) is the dynamic response waveform when the full digital soft-switching control circuit of the grid-connected inverter of the patent application "CN113852266A" is adopted. The grid-connected current reference value I ref The grid reference current I ref When a step change is performed, the grid current i is g There will be a more obvious overshoot oscillation phenomenon, and when the charge control circuit shown in Figure 6 (a) is used, the corresponding grid current i g The overshoot is small, which indicates that the charge control circuit of the soft-switching grid-connected inverter proposed in the present invention further enhances the dynamic performance of the grid-connected inverter. The above experimental results verify the effectiveness of the technical solution of the present invention.

[0065] The embodiments are only for illustrating the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A charge control circuit for a soft-switching grid-connected inverter, the grid-connected inverter comprising an inverter module (1) and a filter module (2), the input end of the inverter module (1) being connected in parallel with a DC power supply U dc The output end of the inverter module (1) is connected in parallel to the input end of the filter module (2), and the output end of the filter module (2) is connected in parallel to the AC power grid u g The filtering module (2) comprises a first inductor, a first capacitor, and a second inductor, wherein the first end of the first inductor is the first input end of the filtering module (2), the second end of the first inductor is connected to the first end of the first capacitor and the first end of the second inductor, the second end of the second inductor is the first output end of the filtering module (2), and the second end of the first capacitor is the second input end and the second output end of the filtering module (2); It is characterized in that The charge quantity control circuit of the soft-switch grid-connected inverter comprises a soft-switch control module (3) and a charge quantity control module (4); the soft-switch control module (3) comprises a first voltage sensor (31), a current sensor (32), a second voltage sensor (33), a current regulator (34), a first subtractor (35), a first multiplier (36), a phase lock (37), a modulator (38), and a first divider (39); the first voltage sensor (31) samples the DC power supply U dc The second voltage sensor (33) samples the voltage of the AC power grid u g The output end of the second voltage sensor (33) is connected to the input end of the phase lock (37), the output end of the phase lock (37) is respectively connected to the first input end of the first multiplier (36) and the first input end of the modulator (38), and the second input end of the first multiplier (36) is connected to the grid current reference value I ref The output terminal of the first multiplier (36) outputs the grid current reference value i ref and connected to the positive input terminal of the first subtractor (35); the current sensor (32) samples the current i of the first inductor L1 The output end of the current sensor (32) is connected to the negative input end of the first subtractor (35), the output end of the first subtractor (35) is connected to the input end of the current regulator (34), and the output end of the current regulator (34) is connected to the charge control module (4); the dividend input end and the divisor input end of the first divider (39) are connected to the charge control module (4), the second input end of the modulator (38) is connected to the output end of the first divider (39), the third input end of the modulator (38) is connected to the charge control module (4), and the modulator (38) obtains the driving signal required by the grid-connected inverter according to the phase of the first input end and the signals of the second input end and the third input end; The charge quantity control module (4) comprises a second multiplier (41), a first proportional device (42), a first adder (43), a second proportional device (44), a third multiplier (45), a second divider (46), a first square root device (47), a second adder (48), a fourth multiplier (49), a third proportional device (410), a second subtractor (411), a fifth multiplier (412), and a third divider (413); the output end of the first voltage sensor (31) is respectively connected to the first input end of the fourth multiplier (49) and the input end of the third proportional device (410); the first input end of the second multiplier (41) is connected to the dead time t dead The second input terminal of the second multiplier (41) is connected to a reset current I set The output end of the second multiplier (41) is connected to the input end of the first scaler (42), the output end of the first scaler (42) is connected to the first input end of the first adder (43), and the second input end of the first adder (43) is connected to the bridge arm output charge Q outputted from the output end of the current regulator (34). inv The output end of the first adder (43) is connected to the input end of the second scaler (44), the output end of the second scaler (44) is connected to the first input end of the third multiplier (45), the output end of the third multiplier (45) is connected to the dividend input end of the second divider (46), the divisor input end of the second divider (46) is connected to the output end of the fourth multiplier (49), the output end of the second divider (46) is connected to the input end of the first square rooter (47), and the output end of the first square rooter (47) outputs the conduction time t on The first input terminal of the second adder (48) is connected to the dividend input terminal of the first divider (39), and the second input terminal of the second adder (48) is connected to the output terminal of the third divider (413) to output the off time t off The third input terminal of the second adder (48) is connected to the dead time t dead , the output end of the second adder (48) is respectively connected to the divisor input end of the first divider (39) and the third input end of the modulator (38); the output end of the second voltage sensor (33) is respectively connected to the second input end of the third multiplier (45), the divisor input end of the third divider (413) and the negative input end of the second subtractor (411); the output end of the third proportional device (410) is connected to the positive input end of the second subtractor (411); the output end of the second subtractor (411) is connected to the second input end of the fourth multiplier (49); the first input end of the fifth multiplier (412) is connected to twice the first inductance 2L1, the second input end of the fifth multiplier (412) is connected to the output end of the first multiplier (36), and the output end of the fifth multiplier (412) is connected to the dividend input end of the third divider (413).

2. The charge control circuit of the soft-switching grid-connected inverter according to claim 1, characterized in that: The gain k1 of the first proportional device (42) is a constant of 0.5; the gain k2 of the second proportional device (44) is four times the first inductance value L1 divided by the voltage U of the DC power supply. dc ,Right now The gain k3 of the third proportional device (410) is a constant of 0.

5.

3. The charge control circuit of the soft-switching grid-connected inverter according to claim 2, characterized in that: The third input terminal of the second adder (48) and the first input terminal of the second multiplier (41) are connected to the dead time t dead for The second input terminal of the second adder (48) receives the off time t off The value of Wherein, L1 represents the inductance of the first inductor, C1 represents the capacitance of the first capacitor, and u g represents the voltage of the AC grid, i ref The output terminal of the first multiplier (36) represents a grid-connected current reference value including phase information.

4. The charge control circuit of the soft-switching grid-connected inverter according to claim 3, characterized in that: The output end of the current regulator (34) is the bridge arm output charge quantity Q inv , which is equal to the conduction time t of the output terminal of the first square root generator (47). on The following relationship exists: where u g represents the voltage of the AC grid, i L1 represents the current of the first inductor, L1 represents the inductance of the first inductor, U dc represents the voltage of the DC power supply, and C1 represents the capacitance of the first capacitor.

5. The charge control circuit of the soft-switching grid-connected inverter according to claim 1, characterized in that: The modulator (38) outputs a first drive signal and a second drive signal, wherein the first drive signal and the second drive signal complement each other and operate at a high frequency, and the switching period of the first drive signal and the first drive signal is the value of the third input terminal of the current modulator (38), the duty cycle of the first drive signal in this switching period is the value of the second input terminal of the current modulator (38), and the duty cycle of the second drive signal in this switching period is the difference between 1 and the second input terminal of the current modulator (38); the modulator (38) determines the AC grid u to which the grid-connected inverter is connected at this time according to the difference between the value of the first input terminal and 0. g The polarity of the inverter module (1) is determined, and the first drive signal and the second drive signal are sent to the switch tube in the inverter module (1) according to different inverter topologies.

6. The charge control circuit of the soft-switching grid-connected inverter according to claim 5, characterized in that: When the connected AC power grid u g In the positive half cycle, when the first driving signal is at a high level, the inverter module (1) causes the current i of the first inductor to L1 When the second driving signal is at a high level, the inverter module (1) causes the current i of the first inductor to increase. L1 When the AC power grid u connected g In the negative half cycle, when the first driving signal is at a high level, the inverter module (1) causes the current i of the first inductor to L1 When the second driving signal is at a high level, the inverter module (1) causes the current i of the first inductor to decrease. L1 Increase.

7. A method for controlling the charge amount of a soft-switching grid-connected inverter, characterized in that: A charge control circuit for a soft-switching grid-connected inverter as claimed in any one of claims 1 to 6, comprising: Step S1, sampling the DC power supply U dc The voltage of the AC grid u g The voltage and current of the first inductor i L1 ; Step S2: set the grid current reference value i ref and the current i of the first inductor L1 L1 The error is input into the current regulator (34) to adjust the current i of the first inductor. L1 Closed-loop regulation is performed, and the output bridge arm of the current regulator (34) outputs the charge Q inv ; Step S3, calculating the on-time t required to achieve charge control on , turn-off time t off ; Step S4, calculating the duty cycle and switching period required to realize charge quantity control and outputting them to the modulator (38); Step S5, obtaining the first drive signal and the second drive signal in the modulator (38) and sending them to the switch tube in the inverter module (1), ending the current control cycle and waiting for the next control cycle.

8. The charge control method of the soft-switching grid-connected inverter according to claim 7, characterized in that: The duty cycle and switching period required for charge control satisfy the following equation: Switching period T = t on +t off +t dead , duty cycle D = t on / T.

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