Single-phase Inverter Parallel Control Device and Control Method

Abstract

The present invention discloses a parallel control device and a control method for a single-phase inverter. The control device includes: a common load, an inverter controlled unit, and a control and drive unit. Among them, the control and drive unit is used to collect a first voltage signal across the common load and the main circuit current signal of the corresponding inverter controlled unit, calculate the power to obtain the active power signal and the reactive power signal output by the corresponding inverter, generate a PWM signal based on the active power signal and the reactive power signal, and control the on-off of the power switching tubes in the corresponding inverter through the PWM signal. During the process of generating the PWM signal, the present invention enables the present invention to solve the problem of large overshoot of the output voltage in the island mode by means of voltage-current double closed-loop control, active power-voltage amplitude control, and virtual impedance setting, and improves the system dynamic performance, the inverter power distribution accuracy, and the output voltage quality.

Description

Technical Field

[0001] The present invention relates to the technical field of inverter control, and particularly to a single-phase inverter parallel control device and a control method. Background Art

[0002] Most distributed power generation and energy storage devices are finally connected to the public grid through inverters and are connected to the user side in the island mode. However, parallel connection of multiple inverters is often required to improve capacity, redundancy, and safety. A key technology for inverter parallel connection is the use of droop control. Domestic and foreign experts and scholars have carried out a series of studies on improving droop control strategies based on traditional droop control. Common methods include: decoupling matrix method, virtual impedance method, and adaptive droop coefficient method, etc. However, the problems of large overshoot of the output voltage of the inverter, low power distribution accuracy, and large voltage overshoot at the moment of parallel connection in the island mode have not been effectively solved by the above methods.

[0003] In addition, for the droop control method of inverter parallel connection, it is required that the voltage adjustment time at the moment of inverter parallel connection is short. The traditional droop control method cannot meet this requirement, that is, the dynamic performance of the system is poor, and at the same time, the output voltage quality is also reduced.

[0004] Therefore, the existing inverter parallel control methods have problems such as large voltage overshoot at the moment of parallel connection, low output voltage accuracy, low power distribution accuracy, low output voltage quality, and poor system dynamic performance of the inverter. Summary of the Invention

[0005] The present invention aims to at least solve one of the technical problems in the related art to some extent. For this reason, an object of the present invention is to provide a single-phase inverter parallel control device to solve the problem of large overshoot of the output voltage in the island mode by the traditional droop control method, and improve the system dynamic performance, inverter power distribution accuracy, and output voltage quality.

[0006] The second object of the present invention is to provide a single-phase inverter parallel control method.

[0007] To achieve the above object, the present invention is realized through the following technical solutions:

[0008] A single-phase inverter parallel control device includes:

[0009] A common load;

[0010] Several groups of inverter controlled units, each group of inverter controlled units including: a DC power supply, an inverter, a parallel switch, a filter inductor and a filter capacitor, wherein, the positive and negative terminals of the DC power supply are connected to the positive and negative input terminals of the inverter, the first output terminal of the inverter is connected to the first end of the filter inductor, the second end of the filter inductor and the first end of the parallel switch are both connected to the first end of the filter capacitor, and the second output terminal of the inverter is connected to the second end of the filter capacitor; the second ends of the parallel switches in each group of inverter controlled units are connected to form a first node, and the second ends of the filter capacitors in each group of inverter controlled units are connected to form a second node, and both ends of the common load are respectively connected to the first node and the second node;

[0011] Several groups of control and drive units, each group of control and drive units being connected to the common load and the corresponding inverter controlled unit, each group of control and drive units being configured to collect a first voltage signal across the common load and a main circuit current signal of the corresponding inverter controlled unit, and perform power calculation to obtain an active power signal and a reactive power signal output by the corresponding inverter, and generate a PWM signal according to the active power signal and the reactive power signal, and control the on / off of the power switch tubes in the corresponding inverter through the PWM signal.

[0012] Optionally, each group of control and drive units includes:

[0013] A sensor assembly, the sensor assembly including:

[0014] A voltage sensor, connected in parallel with the common load, the voltage sensor being configured to collect the first voltage signal across the common load;

[0015] A current sensor, connected in series between the corresponding filter inductor and the inverter, the current sensor being configured to collect the main circuit current signal of the corresponding inverter controlled unit;

[0016] A DSP control and power calculation module, connected to the voltage sensor and the current sensor respectively, the DSP control and power calculation module being configured to perform digital processing on the first voltage signal and the main circuit current signal and perform power calculation to obtain an active power signal and a reactive power signal output by the corresponding inverter.

[0017] Optionally, each group of control and drive units further includes an active power voltage amplitude control module, the active power voltage amplitude control module including:

[0018] An amplitude error feedforward sub-module, connected to the corresponding voltage sensor, the amplitude error feedforward sub-module being configured to process a given rated voltage signal and the first voltage signal to obtain a voltage feedforward signal;

[0019] The active voltage droop sub-module is connected to the active power signal output terminal of the DSP control and power calculation module. The active voltage droop sub-module is used to determine the active voltage droop coefficient and perform gain processing on the active power signal through the active voltage droop coefficient.

[0020] Optionally, each set of control and drive units further includes a reactive power-frequency control module, and the reactive power-frequency control module includes:

[0021] A grid frequency setting sub-module for setting the rated voltage angular frequency of the output voltage of the corresponding inverter;

[0022] The reactive power-frequency droop sub-module is connected to the reactive power signal output terminal of the DSP control and power calculation module. The reactive power-frequency droop sub-module is used to determine the reactive power-frequency droop coefficient and perform gain processing on the reactive power signal through the reactive power-frequency droop coefficient.

[0023] Optionally, each set of control and drive units further includes an integration module, and the integration module includes:

[0024] The active voltage integration sub-module is respectively connected to the amplitude error feed-forward sub-module and the active voltage droop sub-module. The active voltage integration sub-module is used to integrate the voltage feed-forward signal and the gain-processed active power signal to obtain a second voltage signal;

[0025] The reactive voltage integration sub-module is respectively connected to the grid frequency setting sub-module and the reactive power-frequency droop sub-module. The reactive voltage integration sub-module is used to integrate the rated voltage angular frequency and the gain-processed reactive power signal to obtain a third voltage signal.

[0026] Optionally, each set of control and drive units further includes:

[0027] A voltage synthesis module is respectively connected to the active voltage integration sub-module and the reactive voltage integration sub-module. The voltage synthesis module is used to synthesize the second voltage signal and the third voltage signal to obtain a fourth voltage signal;

[0028] A voltage feedback module is connected to the corresponding voltage sensor. The voltage feedback module is used to perform gain processing on the first voltage signal to obtain a fifth voltage signal;

[0029] A virtual impedance module is connected to the corresponding current sensor. The virtual impedance module is used to calculate a sixth voltage signal according to the corresponding main circuit current signal.

[0030] Optionally, each set of control and drive units further includes a voltage-current dual-loop control module, and the voltage-current dual-loop control module includes:

[0031] A voltage PI control sub-module, which is respectively connected to the voltage synthesis module, the voltage feedback module and the virtual impedance module. The voltage PI control sub-module is used to perform PI control on the error signal between the signal obtained by subtracting the fourth voltage signal from the sixth voltage signal and the fifth voltage signal, and output a seventh voltage signal;

[0032] A current P control module, which is respectively connected to the voltage PI control sub-module and the corresponding current sensor. The current P control module is used to perform proportional control on the seventh voltage signal according to the main circuit current signal, and output an eighth voltage signal.

[0033] Optionally, each set of control and drive units further includes a drive module, and the drive module includes:

[0034] A PWM generation sub-module, which is connected to the current P control module. The PWM generation sub-module is used to generate a PWM signal according to the eighth voltage signal, and perform on-off control on the power switch tubes in the corresponding inverter through the PWM signal;

[0035] A protection switch, which is respectively connected to the DSP control and power calculation module, the PWM generation sub-module and the power switch tubes. When the DSP control and power calculation module detects that the corresponding main circuit current is greater than a preset current threshold, it controls the protection switch to disconnect.

[0036] Optionally, the common load is a pure resistor, and the virtual impedance in the virtual impedance module is a pure resistor impedance.

[0037] To achieve the above object, a second aspect of the present invention provides a parallel control method for a single-phase inverter, and the method includes:

[0038] Collect the first voltage signal at both ends of the common load and the main circuit current signal of the inverter controlled unit, and perform power calculation to obtain the active power signal and reactive power signal output by the corresponding inverter;

[0039] Determine the rated voltage feedforward signal, perform gain processing on the active power signal, and integrate according to the voltage feedforward signal and the gain-processed active power signal to obtain a second voltage signal;

[0040] Given the rated voltage angular frequency of the output voltage of the corresponding inverter, perform gain processing on the reactive power signal, and integrate according to the rated voltage angular frequency and the gain-processed reactive power signal to obtain a third voltage signal;

[0041] The second voltage signal and the third voltage signal are combined to obtain a fourth voltage signal, the first voltage signal is subjected to gain processing to obtain a fifth voltage signal, and a sixth voltage signal is calculated through a virtual impedance and the main circuit current signal;

[0042] PI control is performed on the error signal between the signal obtained by subtracting the fourth voltage signal and the sixth voltage signal and the fifth voltage signal, and a seventh voltage signal is output, and proportional control is performed on the seventh voltage signal according to the main circuit current signal, and an eighth voltage signal is output;

[0043] A PWM signal is generated according to the eighth voltage signal, and the power switch tubes in the corresponding inverter are controlled to be turned on and off through the PWM signal.

[0044] The present invention has at least the following technical effects:

[0045] In the present invention, the first voltage signal across the common load and the main circuit current signal of the controlled unit of the inverter are collected, and the active power signal and the reactive power signal output by the corresponding inverter are obtained through power calculation. Then, a PWM signal is obtained according to the active power signal and the reactive power signal, and the power switch tubes in the inverter are controlled to be turned on and off through the PWM signal. Among them, a voltage feedforward signal is introduced in the process of obtaining the PWM signal according to the active power signal and the reactive power signal to improve the output voltage accuracy and ensure the output voltage quality. And through the processing of the active voltage droop coefficient and the reactive frequency droop coefficient, the dynamic performance of the system can be improved, and by setting the virtual impedance, the power distribution accuracy of the inverter can be improved, and the double-loop voltage and current control can solve the problem of large voltage overshoot during paralleling.

[0046] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. Description of the Drawings

[0047] Figure 1 It is a structural block diagram of a parallel control device for a single-phase inverter provided by an embodiment of the present invention;

[0048] Figure 2 It is a topological diagram of a parallel controlled circuit of a single-phase inverter provided by an embodiment of the present invention;

[0049] Figure 3 It is a topological diagram of a control drive unit circuit provided by an embodiment of the present invention;

[0050] Figure 4 It is a flowchart of a parallel control method for a single-phase inverter provided by an embodiment of the present invention;

[0051] Figure 5 The waveform diagram of the effective value of the output voltage of two single-phase inverters connected in parallel provided by an embodiment of the present invention;

[0052] Figure 6 The waveform diagram of the instantaneous voltage of the inverter at the moment when two single-phase inverters provided by an embodiment of the present invention are paralleled;

[0053] Figure 7 The waveform diagram of the active power of two single-phase inverters connected in parallel provided by an embodiment of the present invention. Detailed implementation manners

[0054] The following details this embodiment. The examples of the embodiment are shown in the accompanying drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0055] The following describes the single-phase inverter parallel control device and control method of this embodiment with reference to the accompanying drawings.

[0056] Figure 1 The structural block diagram of the single-phase inverter parallel control device provided by an embodiment of the present invention. As Figure 1 shown, the single-phase inverter parallel control device includes: a common load 10, several groups of inverter controlled units 20, and several groups of control and drive units 30.

[0057] Among them, as Figure 2 shown, each group of inverter controlled units 20 includes: a DC power supply DG, an inverter N, a parallel switch S, a filter inductor L, and a filter capacitor C. Among them, the positive and negative terminals of the DC power supply DG are connected to the positive and negative input terminals of the inverter N. The first output terminal of the inverter N is connected to the first end of the filter inductor L. The second end of the filter inductor L and the first end of the parallel switch S are both connected to the first end of the filter capacitor C. The second output terminal of the inverter N is connected to the second end of the filter capacitor C. The second ends of the parallel switches S in each group of inverter controlled units 20 are connected to form a first node, and the second ends of the filter capacitors C in each group of inverter controlled units 20 are connected to form a second node. Both ends of the common load 10, that is, the load R, are respectively connected to the first node and the second node.

[0058] Each group of control and drive units 30 is connected to the common load 10 and the corresponding inverter controlled unit 20. Each group of control and drive units 30 is used to collect the first voltage signal across the common load 10, i.e., both ends of the load R, and the main circuit current signal of the corresponding inverter controlled unit 20, and perform power calculation to obtain the active power signal and reactive power signal output by the corresponding inverter N, and generate a PWM (Pulse Width Modulation Wave) signal according to the active power signal and reactive power signal, and control the on and off of the power switch tubes in the corresponding inverter N through the PWM signal.

[0059] Specifically, Figure 2 is the equivalent circuit diagram of multiple single-phase inverters in parallel. As Figure 2 shown, several groups of inverter controlled units 20 include: input DC power supplies DG1 to DGi, filter inductors L 1 to L i , filter capacitors C 1 to C i , first parallel switches S 1 to the i-th parallel switch S i , inverters N 1 to inverter N i and the common load 10, i.e., the load R. Among them, the filter capacitors C 1 to C i are non-polar capacitors, and the common load 10 is a pure resistive load. Among them, i takes a value greater than 1 and is an integer.

[0060] Taking two single-phase inverters as an example, the DC power supplies DG1 and DG2 in the main circuit can be powered on first, and then the control and drive unit 30 is powered on, and the first parallel switch S 1 of the first inverter N 1 is in the normally closed state, and the second parallel switch S 2 of the second inverter N 2 is in the off state. At this time, both inverters N 1 and N 2 are working normally. Then, the second parallel switch S 2 of the second inverter N 2 can be closed, that is, the second inverter N 2 is paralleled with the first inverter N 1 , and the various indicators of the system are observed through an oscilloscope, such as the voltage change at the load end during the paralleling instant. Among them, the second parallel switch S 2During the experiment implementation, the anti-series connection of two metal-oxide-semiconductor field-effect transistors and / or insulated-gate bipolar transistors is carried out, and their on-off is controlled by the DSP (Digital Signal Processing) in the control drive unit 30, so that the parallel connection of multiple single-phase inverters can be realized.

[0061] Furthermore, the voltage feedback signal across the load R can be collected by the control drive unit 30 of each group, and the corresponding main circuit current signal, that is, the current signal flowing through the filter inductor L, can be collected, and then input into the DSP for digital processing, and the active power signal and reactive power signal of the corresponding inverter output can be obtained through power calculation, so as to facilitate the generation of PWM signals in the later stage, and the on-off control of power switch devices such as switching tubes in the corresponding inverters can be carried out through the PWM signals.

[0062] Such as Figure 3 shown, each group of control drive units 30 includes: a sensor assembly 31 and a DSP control and power calculation module 32, and the sensor assembly 31 includes a voltage sensor 311 and a current sensor 312.

[0063] In this embodiment, the voltage sensor 311 is connected in parallel with the common load 10, and the voltage sensor 311 is used to collect the first voltage signal across the common load 10; the current sensor 312 is connected in series between the filter inductor L and the inverter in the corresponding inverter controlled unit 20, and the current sensor 312 is used to collect the main circuit current signal of the corresponding inverter controlled unit 20; the DSP control and power calculation module 32 is respectively connected to the voltage sensor 311 and the current sensor 312, and the DSP control and power calculation module 32 is used to perform digital processing on the first voltage signal and the main circuit current signal and perform power calculation to obtain the active power signal and reactive power signal of the corresponding inverter output.

[0064] Specifically, the output voltage of the inverter N i i.e., the first voltage signal V i and the current i i of the filter inductor L Li can be detected in real time, and the active power signal P i and the reactive power signal Q i can be obtained through real-time calculation by the DSP control and power calculation module 32.

[0065] Such as Figure 3 shown, each group of control drive units 30 further includes an active power voltage amplitude control module 33, and the active power voltage amplitude control module 33 includes: an amplitude error feedforward sub-module 331 and an active voltage droop sub-module 332.

[0066] Among them, the amplitude error feedforward sub-module 331 is connected to the corresponding voltage sensor 311, and the amplitude error feedforward sub-module 331 is used to process the given rated voltage signal E * and the first voltage signal to obtain a voltage feedforward signal; the active voltage droop sub-module 332 is connected to the active power signal output terminal of the DSP control and power calculation module 32, and the active voltage droop sub-module 332 is used to determine the active voltage droop coefficient m i , and through the active voltage droop coefficient m i perform gain processing on the active power signal P i .

[0067] Specifically, an active power voltage amplitude control module 33 can be set in the control drive unit 30, and this module involves the amplitude error feedforward and the active participation regulation part. Among them, the amplitude error feedforward sub-module 331 is specifically used to introduce the feedback of the error signal between the real-time detected inverter output voltage, that is, the first voltage signal, and the given reference voltage amplitude, that is, the rated voltage signal E * . It can cancel the drop of the inverter output voltage caused by the droop effect and the load effect, stabilize the output voltage within a certain range, and improve the output voltage accuracy and voltage quality. Among them, the active voltage droop sub-module 332 is specifically used for the selection of the active voltage droop coefficient m i . It affects the tracking speed of the amplitude and the dynamic performance of the output voltage and the change degree of the active power when the load voltage amplitude fluctuates after the inverter is switched on and off. At the same time, it makes the inverter have an amplitude droop characteristic and affects the overall corresponding performance of the active power voltage amplitude control module 33.

[0068] In this embodiment, the amplitude error feedforward sub-module 331 satisfies the formula K(E * -V i ) = m i P i , where K is the amplification gain, E * is the given rated voltage signal, V i is the real-time output voltage value of each inverter, that is, the first voltage signal value, m i is the active voltage droop coefficient, and P i is the active power obtained in real time by the DSP control and power calculation module 32 corresponding to each inverter. In this embodiment, the control method of amplitude error feedforward can reduce or eliminate calculation errors, noise and interference, so as to stabilize the accuracy of the output voltage.

[0069] As Figure 3 shown, each group of control drive units 30 further includes a reactive power frequency control module 34, and the reactive power frequency control module 34 includes a grid frequency given sub-module 341 and a reactive power frequency droop sub-module 342.

[0070] Among them, the grid frequency setting sub-module 341 is used to set the rated voltage angular frequency ω of the output voltage of the corresponding inverter. * ; The reactive power-frequency droop sub-module 342 is connected to the reactive power signal output terminal of the DSP control and power calculation module 32. The reactive power-frequency droop sub-module 342 is used to determine the reactive power-frequency droop coefficient n. i and perform gain processing on the reactive power signal through the reactive power-frequency droop coefficient n. i

[0071] Please continue to refer to Figure 3 , Each set of control and drive units 30 further includes an integration module 35. The integration module 35 includes an active voltage integration sub-module 351 and a reactive voltage integration sub-module 352.

[0072] Among them, the active voltage integration sub-module 351 is respectively connected to the amplitude error feedforward sub-module 331 and the active voltage droop sub-module 332. The active voltage integration sub-module 351 is used to integrate the voltage feedforward signal and the gain-processed active power signal to obtain a second voltage signal; the reactive voltage integration sub-module 352 is respectively connected to the grid frequency setting sub-module 341 and the reactive power-frequency droop sub-module 342. The reactive voltage integration sub-module 352 is used to integrate the rated voltage angular frequency ω * and the gain-processed reactive power signal to obtain a third voltage signal.

[0073] In this embodiment, compared with the traditional droop control method where only an integration link is added after the reactive power-frequency droop, an integration link 1 / s is also introduced after the active power-amplitude droop, so that the output of the active power of each inverter is not affected by the requirement that the parallel inverters must have equivalent impedances.

[0074] Furthermore, each set of control and drive units 30 further includes a voltage synthesis module 36, a voltage feedback module 37, and a virtual impedance module 38. Among them, the voltage synthesis module 36 is respectively connected to the active voltage integration sub-module 351 and the reactive voltage integration sub-module 352. The voltage synthesis module 36 is used to synthesize the second voltage signal and the third voltage signal to obtain a fourth voltage signal; the voltage feedback module 37 is connected to the corresponding voltage sensor 311. The voltage feedback module 37 is used to perform gain processing on the first voltage signal to obtain a fifth voltage signal; the virtual impedance module 38 is connected to the corresponding current sensor 312. The virtual impedance module 38 is used to calculate a sixth voltage signal according to the corresponding main circuit current signal.

[0075] Among them, the calculation formula of the voltage synthesis module 36 is: In the formula, u ref is the synthesized reference voltage signal, that is, the fourth voltage signal, Ei The voltage amplitude obtained for active-voltage droop, ω and are respectively the angular frequency and the pre-synchronization phase value corresponding to the voltage signal obtained for reactive-frequency droop.

[0076] In this embodiment, the virtual impedance module 38 sets a reasonable virtual impedance value, which can improve the power distribution accuracy of inverters in parallel under resistive line impedance, and at the same time solve the problems of stability, proportional power distribution, and circulating current between parallel inverters due to the existence of line impedance and impedance differences. Specifically, in this embodiment, by introducing a purely resistive virtual impedance, the voltage equalization accuracy can be significantly improved, the coupling between active voltage and reactive frequency can be reduced, and due to the existence of voltage error feedforward, adding a purely resistive virtual impedance does not need to consider the voltage drop caused thereby.

[0077] Please continue to refer to Figure 3 , each set of control and drive units 30 further includes a voltage-current double-loop control module 39, and the voltage-current double-loop control module 39 includes a voltage PI control sub-module 391 and a current P control module 392.

[0078] Among them, the voltage PI control sub-module 391 is respectively connected to the voltage synthesis module 36, the voltage feedback module 37, and the virtual impedance module 38. The voltage PI control sub-module 391 is used to perform PI control on the error signal between the signal obtained by subtracting the fourth voltage signal from the sixth voltage signal and the fifth voltage signal, and output a seventh voltage signal; the current P control module 392 is respectively connected to the voltage PI control sub-module 391 and the corresponding current sensor 312. The current P control module 392 is used to perform proportional control on the seventh voltage signal according to the main circuit current signal, and output an eighth voltage signal.

[0079] Specifically, the value of the sixth voltage signal obtained by multiplying the virtual impedance value by the current sampled by the inverter in real time can be subtracted from u ref that is, the value of the fourth voltage signal to obtain a voltage signal value, and then perform PI control on the error between this voltage signal value and the fifth voltage signal value output by the voltage feedback module 37 to obtain a seventh voltage signal. The current P control module 392 then performs P control on the seventh voltage signal according to the obtained main circuit current signal, and externally sends out the output result.

[0080] In this embodiment, after adding virtual impedance and double-loop voltage-current control, the equivalent output impedance of the inverter is:

[0081]

[0082] Among them, Z(s) is the output impedance of the inverter itself before adding virtual impedance, R D is the added virtual impedance value, G inv(s) is the closed-loop transfer function of the inverter, and K vp and K vi are the coefficients of PI control respectively, and K p is the P control coefficient, and K pwm is the equivalent inverter proportional coefficient.

[0083] In this embodiment, the transfer function of the added voltage outer loop is:

[0084]

[0085] Select K vp and K vi according to the crossover frequency of this transfer function designed to be 15 - 20 times the power frequency, and make the phase margin of the phase-frequency characteristic curve satisfy within 30 degrees to 60 degrees; among them, the value of K p is obtained by comparing the current inner loop transfer function with the second-order standard oscillation link.

[0086] It should be noted that the virtual impedance module 38 selects the virtual impedance according to when the phase-frequency characteristic curve in the Bode diagram of Z v (s) enters the error band of plus or minus 1 degree near the fundamental frequency. The optimal virtual impedance value can make the imaginary part of the Z v (s) function be 0, so that the equivalent output impedance of the inverter after adding the virtual impedance is purely resistive, and the power decoupling effect is the best.

[0087] The following is a simulation example of two single-phase full-bridge inverters:

[0088] Table 1 Simulation parameters

[0089] DC power supply voltage <![CDATA[V dc = 360V]]> Rated voltage signal amplitude <![CDATA[E * = 230V]]> Rated voltage angular frequency <![CDATA[ω * = 314 rad / s]]> Filter parameter L = 3.6 mH, C = 4.7 uF Fundamental frequency <![CDATA[f * = 50Hz]]> Switching frequency <![CDATA[f s = 50 kHz]]> <![CDATA[Inverter N i Parameters]]> <![CDATA[K = 1, K e = 60, K p = 0.1087, K vp = 0.032, K vi = 20]]> Active voltage droop coefficient <![CDATA[m i = 0.001804 V / W]]> Reactive frequency droop coefficient <![CDATA[n i = 0.003977 (rad / s) / Var]]> Common load R = 41.5 Ω

[0090] Suppose the added virtual impedance is R D , then the function of the inverter output impedance at the fundamental frequency after adding the virtual impedance can be solved as:

[0091]

[0092] Let the imaginary part of Z v (jω) be 0, and solve to get R D = 38.3Ω. At this time, the equivalent output impedance of the inverter after adding the virtual impedance is purely resistive, and the power decoupling effect is the best. It should be noted that due to the existence of voltage error feedforward, there is no need to consider the influence of adding the virtual impedance on the voltage drop of the inverter output voltage.

[0093] In this embodiment, after the virtual impedance module 38 outputs a signal, voltage-current double closed-loop control is introduced, which can effectively improve the overshoot of the AC voltage output by the inverter, thereby avoiding the paralysis of the system caused by excessive instantaneous power during parallel operation in the island mode. Among them, adding a current loop can achieve accurate tracking and equal sharing of the current of each inverter.

[0094] Please continue to refer to Figure 3 , each set of control and drive units 30 further includes a drive module 40, and the drive module 40 includes a PWM generation sub-module 401 and a protection switch 402.

[0095] Among them, the PWM generation sub-module 401 is connected to the current P control module 392. The PWM generation sub-module 401 is used to generate a PWM signal according to the eighth voltage signal, and perform on-off control of the power switch tube in the corresponding inverter through the PWM signal; the protection switch 402 is respectively connected to the DSP control and power calculation module 32, the PWM generation sub-module 401 and the power switch tube. When the DSP control and power calculation module 32 detects that the main circuit current in the corresponding one is greater than the preset current threshold, it can control the protection switch 402 to disconnect.

[0096] In this embodiment, the DSP control and power calculation module 32 obtains in real time the signal detected by the current sensor 312. Once this signal exceeds the set current threshold, the drive signal, that is, the PWM signal, is immediately cut off to play a role in protecting the system.

[0097] It should be noted that the protection switch 402 can be a circuit breaker, specifically an anti-series structure of two switching tubes, which can withstand positive and negative voltages. When the current flowing through the filter inductor is too large, it is controlled to open by the DSP control and power calculation module 32 to play a role in protecting the inverter parallel system.

[0098] Furthermore, the present invention also provides a single-phase inverter parallel control method, as Figure 4 shown, the method includes:

[0099] Step S1: Collect the first voltage signal at both ends of the common load and the main circuit current signal of the inverter controlled unit, and perform power calculation to obtain the active power signal and reactive power signal output by the corresponding inverter.

[0100] Step S2: Determine the rated voltage feedforward signal, perform gain processing on the active power signal, and integrate according to the voltage feedforward signal and the gain-processed active power signal to obtain a second voltage signal.

[0101] Step S3: Given the rated voltage angular frequency of the output voltage of the corresponding inverter, perform gain processing on the reactive power signal, and integrate according to the rated voltage angular frequency and the gain-processed reactive power signal to obtain a third voltage signal.

[0102] Step S4: Synthesize the second voltage signal and the third voltage signal to obtain a fourth voltage signal, perform a gain process on the first voltage signal to obtain a fifth voltage signal, and calculate a sixth voltage signal through a virtual impedance and the main circuit current signal.

[0103] Step S5: Perform PI control on the error signal between the signal obtained by subtracting the sixth voltage signal from the fourth voltage signal and the fifth voltage signal, and output a seventh voltage signal, and perform proportional control on the seventh voltage signal according to the main circuit current signal, and output an eighth voltage signal.

[0104] Step S6: Generate a PWM signal according to the eighth voltage signal, and perform on-off control on the power switching tubes in the corresponding inverter through the PWM signal.

[0105] Specifically, the output currents i L1 , i L2 and voltages V 1 , V 2 of two inverters can be detected respectively, and the real-time active power P i and reactive power Q i values can be calculated. The output signals of the voltage sensors corresponding to each inverter are processed by the DSP control and power calculation module to obtain the effective value RMS, and then amplified by K e times after subtracting from the rated voltage signal, and sent to the active voltage droop sub-module. In this step, in addition to inputting the real-time active power P i to the active power voltage amplitude control module, the reactive power Q i is also input to the reactive power frequency control module, and after being processed by the integration module, voltage synthesis is performed.

[0106] Among them, the PQ droop controllers of the active power voltage amplitude control module and the reactive power frequency control module can be designed respectively as:

[0107] E i = E * - m i P i (4)

[0108] ω i = ω * + n i Q i (5)

[0109] Further, the DSP control and power calculation module can perform arithmetic processing on the value of the virtual impedance module and the output signal of the current sensor, then subtract the arithmetic result from the voltage synthesis signal, and send the final result of the voltage feedback to the voltage-current double-loop control and drive module to output a PWM signal, so as to control the on-off of the power switch tube in the corresponding inverter through the PWM signal.

[0110] Furthermore, the present invention also simulates the parallel control method of the single-phase inverter in this embodiment. The instance simulation process is as follows: Design the effective value of the inverter output voltage to be 230V and the total active power to be 1275W. Inverter N 2 always works. At 1 second, inverter N 1 is incorporated into the system. Observe the external characteristics of the output voltage of the two inverters and the power sharing situation.

[0111] Figure 5 This is the waveform diagram of the effective value of the output voltage of two single-phase inverters connected in parallel provided by the embodiment of the present application. Figure 6 This is the instantaneous voltage waveform diagram of the inverter at the moment of parallel connection. It can be seen from the waveform diagram that at startup, the system adjustment time is short, the dynamic performance is good, the voltage is always stable at the rated output voltage. At the moment of parallel connection, the voltage overshoot is small, the instantaneous waveform of the output voltage does not distort, and it quickly stabilizes to the rated value of the output voltage. Figure 7 This is the waveform diagram of the active power of two single-phase inverters connected in parallel provided by the embodiment of the present application. The active power sharing effect is good, the difference in the shared power does not exceed 10W, and the dynamic performance is good and the stability is high.

[0112] Since the line impedance in the low-voltage microgrid is mainly resistive, the anti-droop control method is adopted in this embodiment. This method utilizes the droop characteristics of active power-voltage (P-E) and reactive power-frequency (Q-f) when the line impedance is resistive, which is very similar to the traditional droop control of active power-frequency (P-f) and reactive power-voltage (Q-E), and is easy to implement, and has advantages such as small loss and small frequency change. Similarly, there is also an active power balance problem in the anti-droop control when the line impedance is unbalanced. However, through the active power-voltage amplitude control module in the present invention, the error value between the given rated voltage E * and the actually detected load terminal voltage is fed back into the system for adjustment, and at the same time, an amplification coefficient K e is added, so that the value of m i P i is always a constant. Therefore, the problem of the active power distribution accuracy of each inverter can be well improved, and at the same time, the voltage drop value is no longer affected by the output impedance of the inverter, and it has strong robustness.

[0113] In summary, the present invention collects the first voltage signal across the common load and the main circuit current signal of the inverter control unit, calculates the power to obtain the corresponding active power signal and reactive power signal output by the inverter, then obtains the PWM signal based on the active power signal and the reactive power signal, and controls the on / off of the power switching tubes in the inverter through the PWM signal. Among them, a voltage feedforward signal is introduced in the process of obtaining the PWM signal based on the active power signal and the reactive power signal to improve the output voltage accuracy and stability, ensure the output voltage quality, improve the problem of poor output voltage quality in the island mode, and through the processing of the active voltage droop coefficient and the reactive frequency droop coefficient, the dynamic performance of the inverter parallel system can be improved, and by setting the virtual impedance, the power distribution accuracy of the inverter can be improved, and the dual-loop voltage and current control can reduce the voltage adjustment time and overshoot at the moment of inverter paralleling.

[0114] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0115] Although the content of the present invention has been introduced in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the present invention. After those skilled in the art have read the above content, various modifications and alternatives to the present invention will be obvious. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims

1. A single-phase inverter parallel control device, characterized in that, it includes: A common load; Several groups of inverter controlled units, each group of inverter controlled units includes: a DC power supply, an inverter, a parallel switch, a filter inductor and a filter capacitor. Wherein, the positive and negative terminals of the DC power supply are connected to the positive and negative input terminals of the inverter, the first output terminal of the inverter is connected to the first end of the filter inductor, the second end of the filter inductor and the first end of the parallel switch are both connected to the first end of the filter capacitor, and the second output terminal of the inverter is connected to the second end of the filter capacitor; the second ends of the parallel switches in each group of inverter controlled units are connected to have a first node, the second ends of the filter capacitors in each group of inverter controlled units are connected to have a second node, and both ends of the common load are respectively connected to the first node and the second node; Several groups of control and drive units, each group of control and drive units is connected to the common load and the corresponding inverter controlled unit. Each group of control and drive units is used to collect the first voltage signal across the common load and the main circuit current signal of the corresponding inverter controlled unit, and perform power calculation to obtain the active power signal and reactive power signal output by the corresponding inverter, and generate a PWM signal according to the active power signal and reactive power signal, and control the on and off of the power switch tube in the corresponding inverter through the PWM signal, Each group of control and drive units further includes an integration module, and the integration module includes: An active voltage integration sub-module, which is respectively connected to the amplitude error feed-forward sub-module and the active voltage droop sub-module in each control and drive unit. The active voltage integration sub-module is used to integrate the voltage feed-forward signal obtained by the amplitude error feed-forward sub-module and the active power signal after gain processing obtained by the active voltage droop sub-module to obtain a second voltage signal; A reactive voltage integration sub-module, which is respectively connected to the grid frequency setting sub-module and the reactive frequency droop sub-module in each control and drive unit. The reactive voltage integration sub-module is used to integrate the rated voltage angular frequency obtained by the grid frequency setting sub-module and the reactive power signal after gain processing obtained by the reactive frequency droop sub-module to obtain a third voltage signal; A voltage synthesis module, which is respectively connected to the active voltage integration sub-module and the reactive voltage integration sub-module. The voltage synthesis module is used to synthesize the second voltage signal and the third voltage signal to obtain a fourth voltage signal; A voltage feedback module, which is connected to the corresponding voltage sensor in each control and drive unit. The voltage feedback module is used to perform gain processing on the first voltage signal collected by the voltage sensor to obtain a fifth voltage signal; A virtual impedance module, which is connected to the corresponding current sensor in each control and drive unit. The virtual impedance module is used to calculate a sixth voltage signal according to the main circuit current signal collected by the current sensor; A voltage-current double-loop control module, and the voltage-current double-loop control module includes: The voltage PI control sub-module is respectively connected to the voltage synthesis module, the voltage feedback module and the virtual impedance module. The voltage PI control sub-module is used to perform PI control on the error signal between the signal obtained by subtracting the fourth voltage signal from the sixth voltage signal and the fifth voltage signal, and output a seventh voltage signal; The current P control module is respectively connected to the voltage PI control sub-module and the corresponding current sensor. The current P control module is used to perform proportional control on the seventh voltage signal according to the main circuit current signal, output an eighth voltage signal, and generate a PWM signal according to the eighth voltage signal.

2. The single-phase inverter parallel control device according to claim 1, characterized in that, Each set of control and drive units includes: The sensor assembly, and the sensor assembly includes: A voltage sensor, which is connected in parallel with the common load. The voltage sensor is used to collect the first voltage signal across the common load; A current sensor, which is connected in series between the corresponding filter inductor and the inverter. The current sensor is used to collect the main circuit current signal of the corresponding inverter controlled unit; The DSP control and power calculation module is respectively connected to the voltage sensor and the current sensor. The DSP control and power calculation module is used to perform digital processing on the first voltage signal and the main circuit current signal and perform power calculation to obtain the active power signal and reactive power signal output by the corresponding inverter.

3. The single-phase inverter parallel control device according to claim 2, characterized in that, Each set of control and drive units further includes an active power voltage amplitude control module, and the active power voltage amplitude control module includes: The amplitude error feed-forward sub-module is connected to the corresponding voltage sensor. The amplitude error feed-forward sub-module is used to process the given rated voltage signal and the first voltage signal to obtain a voltage feed-forward signal; The active voltage droop sub-module is connected to the output terminal of the active power signal of the DSP control and power calculation module. The active voltage droop sub-module is used to determine the active voltage droop coefficient and perform gain processing on the active power signal through the active voltage droop coefficient.

4. The single-phase inverter parallel control device according to claim 3, characterized in that, Each set of control and drive units further includes a reactive power frequency control module, and the reactive power frequency control module includes: The grid frequency setting sub-module is used to set the rated voltage angular frequency of the output voltage of the corresponding inverter; The reactive power frequency droop sub-module is connected to the output terminal of the reactive power signal of the DSP control and power calculation module. The reactive power frequency droop sub-module is used to determine the reactive power frequency droop coefficient and perform gain processing on the reactive power signal through the reactive power frequency droop coefficient.

5. The single-phase inverter parallel control device according to claim 4, characterized in that, Each set of control and drive units further includes a drive module, and the drive module includes: A PWM generation sub-module, connected to the current P control module, is configured to generate a PWM signal according to the eighth voltage signal and control the on / off of the power switch tube in the corresponding inverter through the PWM signal; A protection switch, respectively connected to the DSP control and power calculation module, the PWM generation sub-module and the power switch tube. When the DSP control and power calculation module detects that the corresponding main circuit current is greater than a preset current threshold, it controls the protection switch to disconnect.

6. The single-phase inverter parallel control device according to claim 1, characterized in that, the common load is a pure resistor, and the virtual impedance in the virtual impedance module is a pure resistor impedance.

7. A single-phase inverter parallel control method based on the single-phase inverter parallel control device according to any one of claims 1-6, characterized in that, it includes: Collecting the first voltage signal across the common load and the main circuit current signal of the inverter controlled unit, and performing power calculation to obtain the active power signal and reactive power signal output by the corresponding inverter; Determining the rated voltage feedforward signal, performing gain processing on the active power signal, and integrating the voltage feedforward signal and the gain-processed active power signal to obtain a second voltage signal; Giving the rated voltage angular frequency of the output voltage of the corresponding inverter, performing gain processing on the reactive power signal, and integrating the rated voltage angular frequency and the gain-processed reactive power signal to obtain a third voltage signal; Synthesizing the second voltage signal and the third voltage signal to obtain a fourth voltage signal, performing gain processing on the first voltage signal to obtain a fifth voltage signal, and calculating a sixth voltage signal through the virtual impedance and the main circuit current signal; Performing PI control on the error signal obtained by subtracting the sixth voltage signal from the fourth voltage signal and the fifth voltage signal, and outputting a seventh voltage signal, and performing proportional control on the seventh voltage signal according to the main circuit current signal, and outputting an eighth voltage signal; Generating a PWM signal according to the eighth voltage signal, and controlling the on / off of the power switch tube in the corresponding inverter through the PWM signal.

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