An inverter parallel control system and method based on high-frequency alternating current small signal synchronization

Abstract

This invention belongs to the field of inverter parallel control and discloses an inverter parallel control system and method based on high-frequency AC small-signal synchronization. Based on the compensation amount and combined with droop control, this invention generates the controlled variable, drooping the high-frequency AC small-signal frequency. Based on the square wave voltage of the same frequency as the high-frequency AC small-signal, and then based on the inverter line voltage, a series resonance and isolated output terminal power frequency voltage are formed to ensure the effective injection of the high-frequency AC small-signal sine wave. Simultaneously, the DC component in the sine wave is isolated, generating the current in the series resonant branch. The current in the series resonant branch and the high-frequency AC small-signal sine wave are converted into the active power of the high-frequency AC small-signal, updating the compensation amount. This invention can achieve balanced control of the controlled variable even in the presence of low-frequency harmonics in the system, avoiding interference from low-frequency harmonics on the AC small-signal synchronization regulation performance, and achieving balanced control of the controlled variable.

Description

Technical Field

[0001] This invention belongs to the field of inverter parallel control, specifically relating to an inverter parallel control system and method based on high-frequency AC small-signal synchronization. Background Technology

[0002] With the rapid development of new energy technologies, inverters have been widely used. Voltage source inverters, which can significantly improve system frequency and voltage stability and enhance power quality, have become a research hotspot. By paralleling voltage source inverters, system capacity can be increased, and modular management can be easily implemented. For parallel inverter systems, achieving balance among the controlled variables of the parallel inverters without relying on communication is a crucial indicator for ensuring the reliable operation of the parallel inverter system.

[0003] Traditional non-communication methods typically inject a low-frequency small AC signal (LF-SACS) into the system. By establishing a droop relationship between the LF-SACS and the controlled variable, the uniformity of the LF-SACS frequency in steady state is used to achieve balanced control of the controlled variable. However, factors such as nonlinear loads, dead time of switching transistors, saturation nonlinearity of magnetic components, and DC-side midpoint potential imbalance can generate a large number of low-frequency harmonics in the system. If low-frequency harmonics with frequencies close to the injected LF-SACS exist in the system, it will cause low-frequency fluctuations in the controlled variable. The frequency of the fluctuation is the frequency difference between the LF-SACS and the harmonics, and the amplitude of the fluctuation is positively correlated with the amplitude of the harmonics, reducing the control performance of the parallel inverter. Therefore, this method has certain limitations in systems with abundant low-frequency harmonics. Summary of the Invention

[0004] The purpose of this invention is to overcome the limitations of low-frequency AC small-signal synchronization methods and provide an inverter parallel control system and method based on high-frequency AC small-signal synchronization, which can avoid the interference of low-frequency harmonics on the AC small-signal synchronization regulation performance and achieve balanced control of the controlled variable.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides an inverter parallel control system based on high-frequency AC small-signal synchronization, comprising:

[0007] The droop controller is used to generate the controlled variable y based on the compensation amount x and the droop control.

[0008] A high-frequency AC small-signal frequency droop module is used to adjust the frequency ω of a high-frequency AC small-signal based on the controlled variable y. ss0By performing droop adjustment, the high-frequency AC small-signal frequency ω after droop adjustment is obtained. ss ;

[0009] A voltage-controlled oscillator is used to adjust the frequency ω of a high-frequency AC small signal after droop adjustment. ss Generate a square wave voltage e at the same frequency. ss ';

[0010] Bandpass filter, used for square wave voltage e ss 'Perform filtering to obtain the sine wave e at the desired high-frequency AC small signal frequency.' ss ;

[0011] Power amplifier, used to amplify sine wave e ss The power;

[0012] The coupling module is used to adjust the frequency ω of the high-frequency AC small signal after drooping. ss This forms a series resonant branch and a series coupling branch, ensuring the high-frequency AC small signal sine wave e ss Effective injection, while isolating the sine wave e ss The DC component in the circuit and the power frequency line voltage at the input terminal generate the current i in the series resonant branch. ss ;

[0013] A multiplier is used to combine the current i of the series resonant branch. ss and high-frequency AC small signal sine wave e ss ;

[0014] A low-pass filter is used to filter the signal output from the multiplier to obtain the active power P of the high-frequency AC small signal. ssf ;

[0015] The active power amplifier module is used to amplify the active power P of a high-frequency AC small signal. ssf The compensation amount x is obtained.

[0016] A further improvement of this invention lies in that, in the high-frequency AC small-signal frequency droop module, the droop-adjusted high-frequency AC small-signal frequency ω is obtained through the following method. ss :

[0017] ω ss =ω ss0 -k ss y

[0018] Where, k ss This is the frequency droop coefficient for high-frequency AC small-signal signals.

[0019] A further improvement of this invention is that, in the active power amplification module, the compensation amount x is obtained through the following method:

[0020] x = Gp p ssf

[0021] Among them, G p It represents the active power amplification factor for high-frequency AC small-signal signals.

[0022] A further improvement of the present invention is that the coupling module includes a series resonant branch and a series coupling branch. The series resonant branch is connected to form a series resonance at the high frequency AC small signal frequency, and the series coupling branch is connected to the inverter line voltage and isolates the power frequency voltage.

[0023] A further improvement of the present invention is that the droop controller is used to receive the current signal and voltage signal of the filter, and output a PWM control signal according to the compensation amount x.

[0024] Secondly, the present invention provides a parallel control method for inverters based on high-frequency AC small-signal synchronization, comprising the following steps:

[0025] Based on the compensation amount x, combined with droop control, the controlled variable y is generated;

[0026] Construct the compensation quantity x and the active power P of the high-frequency AC small signal. ssf The amplification relationship between them, and the frequency ω of the high-frequency AC small signal. ss0 By performing droop adjustment, the high-frequency AC small-signal frequency ω after droop adjustment is obtained. ss ;

[0027] Based on the high-frequency AC small signal frequency ω after droop adjustment ss Generate a square wave voltage e at the same frequency. ss ', square wave voltage e ss 'By performing filtering and power amplification, a good sine wave at the high-frequency AC small-signal frequency is obtained e' ss ;

[0028] Based on the high-frequency AC small signal frequency ω after droop adjustment ss This forms a series resonant branch and a series coupling branch, ensuring the high-frequency AC small signal sine wave e ss Effective injection, while isolating the sine wave e ss The DC component in the circuit and the power frequency line voltage at the output terminal generate the current i in the series resonant branch. ss ;

[0029] Based on the sine wave e of the high-frequency AC small signal ss and the current i in the series resonant branch ss Calculate the active power P of the high-frequency AC small-signal signal. ssf .

[0030] A further improvement of this invention lies in that it addresses the high-frequency AC small-signal frequency ω.ss0 By performing droop adjustment, the high-frequency AC small-signal frequency ω after droop adjustment is obtained. ss The specific methods are as follows:

[0031] ω ss =ω ss0 -k ss y

[0032] Where, k ss This is the frequency droop coefficient for high-frequency AC small-signal signals.

[0033] A further improvement of this invention lies in constructing the compensation amount x and the active power P of the high-frequency AC small signal. ssf The amplification relationship between them is as follows:

[0034] x = G p p ssf

[0035] Among them, G p It represents the active power amplification factor for high-frequency AC small-signal signals.

[0036] A further improvement of this invention lies in ensuring the sinusoidal wave e of the high-frequency AC small signal. ss Effective injection, while isolating the sine wave e ss The DC component in the circuit and the power frequency line voltage component at the output terminal generate the current i in the series resonant branch. ss In the steps,

[0037] Specifically, it includes:

[0038] By creating a series resonance branch at the high-frequency AC small-signal frequency, the sine wave e of the high-frequency AC small signal is guaranteed. ss Effective injection, while simultaneously high-frequency AC small signal sine wave e ss The DC component in the circuit prevents transformer saturation. The transformer is used for electrical isolation, and through a series coupling branch, it isolates the power frequency voltage while also ensuring the sinusoidal waveform of the high-frequency AC small signal. ss Effective injection.

[0039] A further improvement of the present invention is that,

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] This invention generates a controlled variable based on the compensation amount and droop control. The droop adjustment regulates the frequency of the high-frequency AC small signal. Based on the square wave voltage of the same frequency as the high-frequency AC small signal, and then based on the inverter's power frequency line voltage, a series resonance and isolation power frequency voltage are formed. This ensures the effective injection of the high-frequency AC small signal sine wave while isolating the DC component in the sine wave. Current is generated in the series resonant branch, and the current in the series resonant branch and the high-frequency AC small signal sine wave are converted into the active power of the high-frequency AC small signal, updating the compensation amount. This invention can achieve balanced control of the controlled variable even in the presence of low-frequency harmonics in the system, avoiding interference from low-frequency harmonics on the synchronous regulation performance of the AC small signal, and achieving balanced control of the controlled variable. Attached Figure Description

[0042] Figure 1 Block diagram of a parallel inverter system;

[0043] Figure 2 This is a block diagram of the controller of the present invention;

[0044] Figure 3 This is a structural diagram of the coupling module in this invention;

[0045] Figure 4(a) shows the experimental waveform of the fundamental frequency when frequency recovery is performed using the traditional PI control method;

[0046] Figure 4(b) shows the reactive power experimental waveform during frequency recovery using the traditional PI control method.

[0047] Figure 5(a) shows the experimental waveform of the fundamental frequency when frequency recovery is performed by injecting a low-frequency AC small signal.

[0048] Figure 5(b) shows the reactive power experimental waveform when frequency recovery is performed using the injection of a low-frequency AC small signal.

[0049] Figure 6(a) shows the experimental waveform of the fundamental frequency when frequency recovery is performed by injecting a high-frequency AC small signal.

[0050] Figure 6(b) shows the reactive power experimental waveform when frequency recovery is performed using the injection of a high-frequency AC small signal. Detailed Implementation

[0051] To further understand the content of this invention, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments are merely illustrative and not limiting of the invention.

[0052] Figure 1 This is a block diagram of a parallel inverter system. Each inverter includes a DC bus, a switching network, a filter, and a local controller. Each inverter is connected to the PCC terminal and supplies power to the load. Figure 2This is a block diagram of a local controller for a single inverter based on high-frequency AC small-signal synchronization, consisting of a software control module and a hardware small-signal injection and detection module. The coupling module is connected to both ends of the inverter's line voltage (e.g., phases B and C). The given operating condition defined in this invention is a low-voltage, small-scale AC microgrid, where the microgrid's line impedance is purely resistive and very small.

[0053] See Figure 2 A parallel control system for inverters based on high-frequency AC small-signal synchronization includes:

[0054] The droop controller is used to generate the controlled variable y based on the compensation amount x and the droop control; it is used to receive the voltage and current signals from the filter and output the PWM control signal based on the compensation amount x.

[0055] A high-frequency AC small-signal frequency droop module is used to adjust the frequency ω of a high-frequency AC small-signal based on the controlled variable y. ss0 By performing droop adjustment, the high-frequency AC small-signal frequency ω after droop adjustment is obtained. ss ;

[0056] A voltage-controlled oscillator is used to adjust the frequency ω of a high-frequency AC small signal after droop adjustment. ss Generate a square wave voltage e at the same frequency. ss ';

[0057] Bandpass filter, used for square wave voltage e ss 'Perform filtering to obtain the sine wave e at the desired high-frequency AC small signal frequency.' ss ;

[0058] Power amplifier, used to amplify sine wave e ss The power;

[0059] The coupling module is used to determine the frequency ω of the high-frequency AC small signal. ss This forms a series resonant branch and a series coupling branch, ensuring the high-frequency AC small signal sine wave e ss Effective injection, while isolating the sine wave e ss The DC component in the circuit and the power frequency line voltage at the input terminal generate the current i in the series resonant branch. ss ;

[0060] A multiplier is used to combine the current i of the series resonant branch. ss and high-frequency AC small signal sine wave e ss ;

[0061] A low-pass filter is used to filter the signal output from the multiplier to obtain the active power P of the high-frequency AC small signal. ssf ;

[0062] The active power amplifier module is used to amplify the active power P of a high-frequency AC small signal. ssf The compensation amount x is obtained.

[0063] The coupling module includes a series resonant branch and a series coupling branch. The series resonant branch is connected to form a series resonance at the high-frequency AC small-signal frequency, and the series coupling branch is connected to the inverter line voltage and isolates the power frequency voltage.

[0064] See Figure 2 A parallel control method for inverters based on high-frequency AC small-signal synchronization includes the following steps:

[0065] S1, based on the compensation amount x, combined with droop control, generates the controlled variable y.

[0066] S2, construct the compensation amount x and the active power P of the high-frequency AC small signal. ssf The amplification relationship between them, and the frequency ω of the high-frequency AC small signal. ss0 By performing droop adjustment, the high-frequency AC small-signal frequency ω after droop adjustment is obtained. ss The details are as follows:

[0067] ω ss =ω ss0 -k ss y

[0068] x = G p p ssf

[0069] Where, k ss G is the frequency droop factor for high-frequency AC small-signal signals. p It represents the active power amplification factor for high-frequency AC small-signal signals.

[0070] S3, based on the high-frequency AC small signal frequency ω after droop adjustment ss Generate a square wave voltage e at the same frequency. ss ', square wave voltage e ss 'By performing filtering and power amplification, a good sine wave at the high-frequency AC small-signal frequency is obtained e' ss .

[0071] S4, based on the high-frequency AC small signal frequency ω ss This forms a series resonant branch and a series coupling branch, ensuring the high-frequency AC small signal sine wave e ss Effective injection, while isolating the sine wave e ss The DC component in the circuit and the power frequency line voltage at the output terminal generate the current i in the series resonant branch. ss ; .

[0072] S5, based on the sine wave e of the high-frequency AC small signal. ssand the current i in the series resonant branch ss Calculate the active power P of the high-frequency AC small-signal signal. ssf .

[0073] Example:

[0074] This invention proposes a parallel control method for inverters based on high-frequency AC small-signal synchronization. This method can achieve balanced control of the controlled variable even in the presence of low-frequency harmonics in the system. This section uses second-order frequency recovery as an application background for experimental verification.

[0075] Table 1 provides the operating conditions and related parameters.

[0076]

[0077] To test this invention, an inverter parallel experimental platform was built, and the system parameters are shown in Table 1. To demonstrate the effectiveness and superiority of this invention, the performance of different secondary frequency recovery methods in distributing reactive power needs to be compared under this operating condition, as shown in Figures 4-6. Figure 4 shows the secondary frequency recovery using traditional PI control. In Figure 4(a), the fundamental frequency is restored to the rated frequency of 50Hz. However, due to the different integral histories of the PI, the reactive power in Figure 4(b) cannot be evenly distributed. Figure 5 shows the inverter parallel control method based on low-frequency AC small-signal synchronization. Due to the presence of a large number of low-frequency harmonics in the system, the fundamental frequency in Figure 5(a) and the reactive power in Figure 5(b) exhibit low-frequency oscillations, which deteriorate the power quality. Figure 6 shows the inverter parallel control method based on high-frequency AC small-signal synchronization in this invention. Due to the presence of the coupling module, a large number of low-frequency harmonics are isolated. The fundamental frequency in Figure 6(a) is restored to the rated value, and the reactive power in Figure 6(b) is smoothly and evenly distributed.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A parallel control system for inverters based on high-frequency AC small-signal synchronization, characterized in that, include: The droop controller is used to generate the controlled variable y based on the compensation amount x and the droop control. A high-frequency AC small-signal frequency droop module is used to adjust the frequency ω of a high-frequency AC small signal based on the controlled variable y. ss0 By performing droop adjustment, the high-frequency AC small-signal frequency ω after droop adjustment is obtained. ss ; A voltage-controlled oscillator is used to adjust the frequency ω of a small high-frequency AC signal. ss Generate a square wave voltage e at the same frequency. ss '; Bandpass filter, used for square wave voltage e ss 'Perform filtering to obtain the sine wave e at the desired high-frequency AC small signal frequency.' ss ; Power amplifier, used to amplify sine waves e ss The power; The coupling module is used to adjust the frequency ω of the high-frequency AC small signal after droop adjustment. ss This forms a series resonant branch and a series coupling branch, ensuring the high-frequency AC small signal sine wave e ss Effective injection, while isolating the sine wave e ss The DC component in the circuit and the power frequency line voltage at the input terminal generate the current i in the series resonant branch. ss ; A multiplier is used to combine the current i of the series resonant branch. ss and high-frequency AC small signal sine wave e ss ; A low-pass filter is used to filter the signal output from the multiplier to obtain the active power P of the high-frequency AC small signal. ssf ; The active power amplifier module is used to amplify the active power P of a high-frequency AC small signal. ssf The compensation amount x is obtained.

2. The inverter parallel control system based on high-frequency AC small-signal synchronization according to claim 1, characterized in that, In the high-frequency AC small-signal frequency droop module, the droop-adjusted high-frequency AC small-signal frequency ω is obtained through the following method. ss : oh ss =ω ss0 -k ss y Where, k ss This is the frequency droop coefficient for high-frequency AC small-signal signals.

3. The inverter parallel control system based on high-frequency AC small-signal synchronization according to claim 1, characterized in that, active power... In the power amplifier module, the compensation amount x is obtained through the following method: x=G p p ssf Among them, G p It represents the active power amplification factor for high-frequency AC small-signal signals.

4. The inverter parallel control system based on high-frequency AC small-signal synchronization according to claim 1, characterized in that, The coupling module includes a series resonant branch and a series coupling branch. The series resonant branch is connected to form a series resonance at the high-frequency AC small-signal frequency, and the series coupling branch is connected to the inverter line voltage and isolates the power frequency voltage.

5. The inverter parallel control system based on high-frequency AC small-signal synchronization according to claim 1, characterized in that, The droop controller receives the current and voltage signals from the filter and outputs a PWM control signal based on the compensation amount x.

6. A parallel control method for inverters based on high-frequency AC small-signal synchronization, characterized in that, Includes the following steps: Based on the compensation amount x, combined with droop control, the controlled variable y is generated; Construct the compensation quantity x and the active power P of the high-frequency AC small signal. ssf The amplification relationship between them, and the frequency ω of the high-frequency AC small signal. ss0 By performing droop adjustment, the high-frequency AC small-signal frequency ω after droop adjustment is obtained. ss ; Based on the high-frequency AC small signal frequency ω after droop adjustment ss Generate a square wave voltage e at the same frequency. ss ', square wave voltage e ss 'By performing filtering and power amplification, a good sine wave at the high-frequency AC small-signal frequency is obtained e' ss ; Based on the high-frequency AC small signal frequency ω after droop adjustment ss This forms a series resonant branch and a series coupling branch, ensuring the high-frequency AC small signal sine wave e ss Effective injection, while isolating the sine wave e ss The DC component in the circuit and the power frequency line voltage at the output terminal generate the current i in the series resonant branch. ss ; Based on the sine wave e of the high-frequency AC small signal ss and the current i in the series resonant branch ss Calculate the active power P of the high-frequency AC small-signal signal. ssf .

7. The inverter parallel control method based on high-frequency AC small-signal synchronization according to claim 6, characterized in that, For high-frequency AC small signal frequency ω ss0 By performing droop adjustment, the high-frequency AC small-signal frequency ω after droop adjustment is obtained. ss The specific methods are as follows: oh ss =ω ss0 -k ss y Where, k ss This is the frequency droop coefficient for high-frequency AC small-signal signals.

8. The inverter parallel control method based on high-frequency AC small-signal synchronization according to claim 6, characterized in that, Construct the compensation quantity x and the active power P of the high-frequency AC small signal. ssf The amplification relationship between them is as follows: x=G p p ssf Among them, G p It represents the active power amplification factor for high-frequency AC small-signal signals.

9. The inverter parallel control method based on high-frequency AC small-signal synchronization according to claim 6, characterized in that, While ensuring the high-frequency AC small signal sine wave e ss Effective injection, while isolating the sine wave e ss The DC component in the circuit and the power frequency line voltage component at the output terminal generate the current i in the series resonant branch. ss The steps specifically include: By creating a series resonance branch at the high-frequency AC small-signal frequency, the sine wave e of the high-frequency AC small signal is guaranteed. ss Effective injection, while simultaneously high-frequency AC small signal sine wave e ss The DC component in the circuit prevents transformer saturation. The transformer is used for electrical isolation, and through a series coupling branch, it isolates the power frequency voltage while also ensuring the sinusoidal waveform of the high-frequency AC small signal. ss Effective injection.

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