Hybrid synchronous control method for parallel inverter system and related device

Abstract

The invention discloses a parallel inverter system hybrid synchronous control method and a related device, and the method comprises the steps: calculating the reactive output power and the active output power of an inverter according to the output voltage and the output current of the inverter, and then calculating a current reference value of voltage loop PI control and a current reference value of current loop PI control; and finally, the PWM module generates a modulation signal to control the operation of the inverter. The hybrid synchronous control method for the parallel inverter system provided by the invention breaks through the bottleneck that the existing hybrid synchronous control method is only suitable for a grid-connected inverter system, has higher stability margin on a wide-range short-circuit ratio system, and can achieve positive response to system frequency and voltage support requirements at the same time; a new way is provided for friendly grid connection and efficient consumption of new energy, and the technical problems that an existing hybrid synchronous control strategy is only suitable for a grid-connected inverter system under the rated frequency, and the application scene is limited are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a hybrid synchronous control method and related devices for a parallel inverter system. Background Art

[0002] A parallel inverter system is a large inverter system formed by connecting multiple inverters together to convert DC power into AC power. Inverter control strategies are mainly divided into two categories: Grid-Following (GFL) mode and Grid-Forming (GFM) mode.

[0003] The GFL mode controlled inverter plays a role similar to a controlled current source in the power system. Although the GFL mode control can achieve power tracking of a given output, it cannot operate independently and actively increase power output to support the grid frequency, which weakens the system inertia. At the same time, the use of the phase-locked loop also greatly affects the dynamic stability of the system, showing capacitive negative damping behavior near the base frequency band of the converter output impedance. The capacitive negative damping behavior will interact with the inductive weak grid, which is prone to harmonic instability.

[0004] The grid-forming (GFM) inverter has the primary frequency regulation capability of a traditional generator, and the classic control algorithms include droop control and virtual synchronous generator control. The inverter in this mode can achieve power balance and frequency regulation by adjusting its own power output, but its synchronization stability problem limits its application in power systems. The GFM mode has stronger stability in weak grids because it synchronizes with the grid frequency through a power self-synchronization loop, which can provide the necessary frequency and voltage support for weak grids. However, GFM is prone to output power oscillations and is difficult to maintain stability in strong grids with high short circuit ratios (SCR).

[0005] It can be seen that both the GFL mode and the GFM mode are difficult to meet the stability requirements. However, the two modes are complementary in terms of stability, so the control strategy for the combination of the two modes has begun to attract attention. This hybrid method aims to effectively utilize the advantages of the grid-building and grid-following control strategies to cover the disadvantages of each other in control. At present, the research on hybrid synchronous control strategies is mainly divided into two categories: mode switching strategy and hybrid synchronous control strategy. The mode switching strategy is based on the measurement of the short-circuit ratio. It adopts a switch-like form to switch the converter between the GFL mode and the GFM mode according to the current detected system short-circuit ratio. The inverter works in the GFM mode under a weak grid and in the GFL mode under a strong grid. However, under this control strategy, the mode switching of the inverter will rely on the accurate detection of the system short-circuit ratio. At the same time, the repeated switching of the inverter control mode will lead to increased costs and may cause system power fluctuations and instability. The hybrid synchronous control strategy will improve the frequent mode switching or the degree of dependence on the system's short-circuit ratio. The hybrid synchronous control strategy itself will be more adaptable to a wide range of short-circuit ratio stability, and will exhibit the operating characteristics of both GFL and GFM during operation. However, the current research on the hybrid synchronous control strategy is only applicable to grid-connected operation at rated frequency, and the application scenarios are limited. Therefore, how to break through the defect that the existing hybrid synchronous control strategy is only applicable to grid-connected inverter systems at rated frequency and the application scenarios are limited is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0006] The present invention provides a hybrid synchronous control method and related devices for a parallel inverter system, which are used to solve the technical problem that the existing hybrid synchronous control strategy is only applicable to grid-connected inverter systems at rated frequency and has limited application scenarios.

[0007] In view of this, a first aspect of the present invention provides a hybrid synchronous control method for a parallel inverter system, comprising:

[0008] Calculating reactive output power and active output power of the inverter according to the measured output voltage and output current of the inverter;

[0009] Performing droop control on the reactive output power and the active power to obtain an output voltage reference value;

[0010] Calculating a first dq-axis current reference value based on the output voltage reference value and the output voltage;

[0011] Calculating a reactive power setting value and an active power setting value of the inverter according to the measured output voltage and output frequency of the inverter;

[0012] Calculating a second dq-axis current reference value based on the reactive power setting value and the active power setting value;

[0013] synthesizing a current reference value of the inverter according to the first dq-axis current reference value and the second dq-axis current reference value;

[0014] The current reference value of the inverter is input into the current loop PI controller, the output of the current loop PI controller is converted into the abc coordinate system through coordinate transformation, and a modulation signal is generated through a PWM module to control the inverter.

[0015] Optionally, the calculation formula for calculating the reactive output power and the active output power of the inverter is:

[0016]

[0017]

[0018] in, is the active output power of the inverter, is the reactive output power of the inverter, is the d-axis component of the inverter output voltage in the dq coordinate system, is the q-axis component of the inverter output voltage in the dq coordinate system, is the d-axis component of the inverter output current in the dq coordinate system, is the q-axis component of the inverter's output current in the dq coordinate system.

[0019] Optionally, calculating a first dq-axis current reference value based on the output voltage reference value and the output voltage includes:

[0020] Based on the output voltage phase angle generated by drooping control of the reactive output power and the active power, the output voltage reference value is transformed into the dq coordinate system, and the first dq axis current reference value is calculated by the voltage loop PI controller according to the output voltage reference value in the dq coordinate system and the output voltage in the dq coordinate system.

[0021] Optionally, the calculation formula of the first dq-axis current reference value is:

[0022]

[0023] in, is the first dq axis current reference value, is the transfer function of the PI controller, is the representation of the output voltage reference value in the dq coordinate system, It is the representation of the output voltage of the inverter in the dq coordinate system.

[0024] Optionally, the calculation formulas for the reactive power setting value and the active power setting value of the inverter are:

[0025]

[0026] in, is the active power setting value of the inverter, is the reactive power setting value of the inverter, is the output frequency of the inverter, is the rated frequency, is the output voltage of the inverter, is the active power reference value, is the reactive power reference value, m is the active power droop coefficient, and n is the reactive power droop coefficient.

[0027] Optionally, the calculation formula of the second dq-axis current reference value is:

[0028]

[0029]

[0030] in, is the second dq axis current reference value, is the d-axis component of the second dq-axis current reference value, is the q-axis component of the second dq-axis current reference value, is the d-axis component of the inverter output voltage in the dq coordinate system.

[0031] A second aspect of the present invention provides a hybrid synchronous control device for a parallel inverter system, comprising:

[0032] An output power calculation module, used to calculate the reactive output power and active output power of the inverter according to the measured output voltage and output current of the inverter;

[0033] A droop control module, used for performing droop control on the reactive output power and the active power to obtain an output voltage reference value;

[0034] A first current reference value calculation module, configured to calculate a first dq-axis current reference value based on the output voltage reference value and the output voltage;

[0035] A power calculation module is used to calculate a reactive power setting value and an active power setting value of the inverter according to the measured output voltage and output frequency of the inverter;

[0036] a second current reference value calculation module, configured to calculate a second dq-axis current reference value based on the reactive power setting value and the active power setting value;

[0037] a synthesis module, configured to synthesize a current reference value of the inverter according to the first dq-axis current reference value and the second dq-axis current reference value;

[0038] A control module is used to input the current reference value of the inverter into the current loop PI controller, convert the output of the current loop PI controller to the abc coordinate system through coordinate transformation and generate a modulation signal through the PWM module to control the inverter

[0039] Optionally, in the output power calculation module, a calculation formula for calculating the reactive output power and the active output power of the inverter is:

[0040]

[0041]

[0042] in, is the active output power of the inverter, is the reactive output power of the inverter, is the d-axis component of the inverter output voltage in the dq coordinate system, is the q-axis component of the inverter output voltage in the dq coordinate system, is the d-axis component of the inverter output current in the dq coordinate system, is the q-axis component of the inverter's output current in the dq coordinate system.

[0043] Optionally, the first current reference value calculation module is specifically used to:

[0044] Based on the output voltage phase angle generated by drooping control of the reactive output power and the active power, the output voltage reference value is transformed into the dq coordinate system, and the first dq axis current reference value is calculated by the voltage loop PI controller according to the output voltage reference value in the dq coordinate system and the output voltage in the dq coordinate system.

[0045] Optionally, the calculation formula of the first dq-axis current reference value is:

[0046]

[0047] in, is the first dq axis current reference value, is the transfer function of the PI controller, is the representation of the output voltage reference value in the dq coordinate system, It is the representation of the output voltage of the inverter in the dq coordinate system.

[0048] Optionally, the calculation formulas for the reactive power setting value and the active power setting value of the inverter are:

[0049]

[0050] in, is the active power setting value of the inverter, is the reactive power setting value of the inverter, is the output frequency of the inverter, is the rated frequency, is the output voltage of the inverter, is the active power reference value, is the reactive power reference value, m is the active power droop coefficient, and n is the reactive power droop coefficient.

[0051] Optionally, the calculation formula of the second dq-axis current reference value is:

[0052]

[0053]

[0054] in, is the second dq axis current reference value, is the d-axis component of the second dq-axis current reference value, is the q-axis component of the second dq-axis current reference value, is the d-axis component of the inverter output voltage in the dq coordinate system.

[0055] A third aspect of the present invention provides a hybrid synchronous control method device for a parallel inverter system, the device comprising a processor and a memory:

[0056] The memory is used to store program code and transmit the program code to the processor;

[0057] The processor is used to execute the hybrid synchronous control method of the parallel inverter system described in any one of the first aspects according to the instructions in the program code.

[0058] A fourth aspect of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium is used to store program code, and the program code is used to execute the hybrid synchronous control method for a parallel inverter system described in any one of the first aspects.

[0059] It can be seen from the above technical solutions that the hybrid synchronous control method for the parallel inverter system provided by the present invention has the following advantages:

[0060] The hybrid synchronous control method of the parallel inverter system provided by the present invention first calculates the reactive output power and active output power of the inverter according to the output voltage and output current of the inverter, and then calculates the current reference value of the voltage loop PI control and the current reference value of the current loop PI control, and finally generates a modulation signal through the PWM module to control the operation of the inverter. For the inverter parallel system under the island, whether it is a strong grid or a weak grid, each inverter of the system can accurately share the load before and after the load changes, and the output is stable; for the inverter parallel system under the grid-connected condition, whether it is a strong grid or a weak grid, the power support of each inverter can follow the frequency change of the system, and has a stable active support capability. The hybrid synchronous control method of the parallel inverter system provided by the present invention breaks through the bottleneck that the existing hybrid synchronous control method is only applicable to the grid-connected inverter system, has a higher stability margin on the wide range short-circuit ratio system, and can actively respond to the system frequency and voltage support requirements, providing a new way for the friendly grid connection and efficient consumption of new energy, and solving the technical problem that the existing hybrid synchronous control strategy is only applicable to the grid-connected inverter system under the rated frequency and the application scenario is limited. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0062] Figure 1 A schematic flow chart of a hybrid synchronous control method for a parallel inverter system provided in an embodiment of the present invention;

[0063] Figure 2 A control block diagram of a hybrid synchronous control method for a parallel inverter system provided in an embodiment of the present invention;

[0064] Figure 3 Bode plots of traditional grid-type inverters at different short-circuit ratios;

[0065] Figure 4 The Bode plots of the traditional grid-connected inverter under different short-circuit ratios;

[0066] Figure 5 Bode diagrams of inverters under different short-circuit ratios in the hybrid synchronous control method of the parallel inverter system provided in the present invention;

[0067] Figure 6 A schematic diagram of the output frequency and output active power of the simulation platform under the isolated island weak power grid provided in an embodiment of the present invention;

[0068] Figure 7 A schematic diagram of the output frequency and output active power of the simulation platform under the isolated island strong power grid provided in an embodiment of the present invention;

[0069] Figure 8 A schematic diagram of the output frequency and output active power of the simulation platform under the grid-connected weak power grid provided in an embodiment of the present invention;

[0070] Fig. 9 A schematic diagram of the output frequency and output active power of the simulation platform under the grid-connected strong power grid provided in an embodiment of the present invention;

[0071] Fig.10 A physical experiment circuit diagram constructed using three inverters, three DC power supplies and a load based on the RTU-BOX 204 experimental platform provided in an embodiment of the present invention;

[0072] Fig.11 The output current and voltage diagram of the physical experiment inverter provided in the embodiment of the present invention;

[0073] Fig.12 Provides a physical experiment inverter output power and frequency diagram for the embodiment of the present invention;

[0074] Fig.13 It is a structural schematic diagram of a hybrid synchronous control device for a parallel inverter system provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0075] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0076] For easier understanding, see Figure 1 and Figure 2 The present invention provides an embodiment of a method for suppressing reverse polarity voltage of an offshore wind power DC submarine cable, comprising:

[0077] Step 101: Calculate reactive output power and active output power of the inverter according to the measured output voltage and output current of the inverter.

[0078] It should be noted that, in the present invention, the output current and output voltage of the inverter are first measured by a voltage and current measuring device, and the reactive output power and active output power of the inverter are calculated based on the measured output voltage and output current of the inverter. In one embodiment, the calculation formula for calculating the reactive output power and active output power of the inverter is:

[0079]

[0080]

[0081] in, is the active output power of the inverter, is the reactive output power of the inverter, is the d-axis component of the inverter output voltage in the dq coordinate system, is the q-axis component of the inverter output voltage in the dq coordinate system, is the d-axis component of the inverter output current in the dq coordinate system, is the q-axis component of the inverter's output current in the dq coordinate system.

[0082] Step 102: Perform droop control on reactive output power and active power to obtain an output voltage reference value.

[0083] It should be noted that after calculating the reactive output power and active output power of the inverter, the reactive output power and active power are controlled to obtain the output voltage reference value. and output voltage phase angle The expression of droop control is:

[0084]

[0085] in, is the output angular frequency reference value, is the output voltage reference value, is the voltage rating, is the angular frequency rating, m is the active power droop coefficient, n is the reactive power droop coefficient, is the active power reference value, is the reactive power reference value.

[0086] Step 103: Calculate a first dq-axis current reference value based on the output voltage reference value and the output voltage.

[0087] It should be noted that the output voltage phase angle generated by the droop control of reactive output power and active power is It is used to convert the output voltage from abc to dq and used as the conversion angle of the inverter to reduce the capacitive negative damping (CND) impact caused by the phase-locked loop. Perform dq transformation and obtain the first dq axis current reference value through the voltage loop PI controller The calculation formula of the first dq axis current reference value is:

[0088]

[0089] in, is the first dq axis current reference value, is the transfer function of the PI controller, is the representation of the output voltage reference value in the dq coordinate system, It is the representation of the output voltage of the inverter in the dq coordinate system.

[0090] Step 104: Calculate the reactive power setting value and the active power setting value of the inverter according to the measured output voltage and output frequency of the inverter.

[0091] It should be noted that measuring the output frequency of the inverter , based on the measured inverter output voltage ( and The output voltage is The projection components on the d and q axes in the dq coordinate system) and the output frequency , calculate the reactive power setting value of the inverter and active power setting value . Figure 2 middle, is the output angular frequency of the inverter, Output three-phase current for the inverter. for Current components in the dq coordinate system.

[0092] The calculation formula for the inverter's reactive power setting value and active power setting value is:

[0093]

[0094] in, is the active power setting value of the inverter, is the reactive power setting value of the inverter, is the output frequency of the inverter, is the rated frequency, is the output voltage of the inverter, is the active power reference value, is the reactive power reference value, is the voltage rating, m is the active power droop coefficient, and n is the reactive power droop coefficient.

[0095] Step 105: Calculate a second dq-axis current reference value based on the reactive power setting value and the active power setting value.

[0096] It should be noted that the second dq axis current reference value The calculation formula is:

[0097]

[0098]

[0099] in, is the second dq axis current reference value, is the d-axis component of the second dq-axis current reference value, is the q-axis component of the second dq-axis current reference value.

[0100] Step 106 : synthesize a current reference value of the inverter according to the first dq-axis current reference value and the second dq-axis current reference value.

[0101] It should be noted that the first dq axis current reference value and the second dq axis current reference value Perform equal synthesis to obtain the current reference value of the inverter The current reference value of the synthetic inverter The formula is:

[0102]

[0103] Step 107: Input the current reference value of the inverter into the current loop PI controller, convert the output of the current loop PI controller into the abc coordinate system through coordinate transformation, and generate a modulation signal through the PWM module to control the inverter.

[0104] It should be noted that the current reference value of the inverter is obtained by synthesis in step 106. After that, the inverter current reference value and The deviation is passed through the current loop PI controller, and the voltage value in the dq coordinate system output by the current loop PI controller is transformed into the abc coordinate system, and then the modulation signal is generated through the PWM module to control the inverter.

[0105] The hybrid synchronous control method of the parallel inverter system provided by the present invention first calculates the reactive output power and active output power of the inverter according to the output voltage and output current of the inverter, and then calculates the current reference value of the voltage loop PI control and the current reference value of the current loop PI control, and finally generates a modulation signal through the PWM module to control the operation of the inverter. For the inverter parallel system under the island, whether it is a strong grid or a weak grid, each inverter of the system can accurately share the load before and after the load changes, and the output is stable; for the inverter parallel system under the grid-connected condition, whether it is a strong grid or a weak grid, the power support of each inverter can follow the frequency change of the system, and has a stable active support capability. The hybrid synchronous control method of the parallel inverter system provided by the present invention breaks through the bottleneck that the existing hybrid synchronous control method is only applicable to the grid-connected inverter system, has a higher stability margin on the wide range short-circuit ratio system, and can actively respond to the system frequency and voltage support requirements, providing a new way for the friendly grid connection and efficient consumption of new energy, and solving the technical problem that the existing hybrid synchronous control strategy is only applicable to the grid-connected inverter system under the rated frequency and the application scenario is limited.

[0106] In order to verify the technical effect achieved by the hybrid synchronous control method of the parallel inverter system provided by the present invention, the present invention provides simulation and physical experiments for verification, and the specific implementation steps are as follows:

[0107] Firstly, the traditional grid-following and grid-building control inverter models are established.

[0108] The traditional grid-following control inverter model is:

[0109]

[0110]

[0111] in, To consider the impedance model of the grid-following control inverter of the filter circuit, For the grid-following control inverter impedance model, is the LC filter inductor, is the LC filter capacitor, is the passive damping resistor, is the transfer function of the PI controller in the current loop of the grid-following control mode, For the phase-locked loop, is the inverter modulation voltage amplitude, is the current amplitude, is the initial angle of the grid current, is the initial angle of the grid voltage, is the set of PWM gain and signal delay, j is the imaginary unit, is the decoupling term of the current controller, is the angular frequency rating.

[0112] Based on the impedance stability criterion, is the impedance model of the power grid, if If sufficient phase margin is met, the inverter in the grid-following control mode is small-signal stable, that is, the phase difference between the amplitude-frequency curve of the inverter output impedance and the grid impedance at all intersection frequencies must be less than 180°. Considering that the impedance of the grid is inductive, the area where the phase-frequency curve of the inverter output impedance is less than -90° is considered to be an unstable dangerous area, which is called capacitive negative damping. Figure 3 For different short circuit ratios and The Bode plot of Figure 3 It can be seen from the figure that when the short-circuit ratio is less than 2, the positive-sequence impedance of the inverter in the grid-following control mode will interact with the grid impedance in the capacitive negative damping region, resulting in inverter instability.

[0113] The traditional grid-connected control inverter model is:

[0114]

[0115]

[0116] in, In order to consider the impedance model of the grid-type control inverter of the filter circuit, To construct the grid-controlled inverter impedance model, is the transfer function of the PI controller in the voltage loop of the network control mode, is the transfer function of the PI controller in the current loop of the network control mode, is the inverter modulation voltage amplitude, is the current amplitude, is the initial angle of the grid current, is the initial angle of the grid voltage, is the set of PWM gain and signal delay, j is the imaginary unit, is the rated voltage, , , and are the active and reactive droop coefficients respectively.

[0117] Likewise, if If sufficient phase margin is met, the inverter in the grid-type control mode will be small-signal stable. Figure 4 For different short circuit ratios and Bode plot. Compared with the grid-following control mode, the capacitive negative damping region of the positive sequence impedance of the inverter in the grid-building control mode is concentrated around 50Hz. When the short-circuit ratio is greater than 8, the positive sequence impedance of the inverter in the grid-building control mode will interact with the grid impedance in the capacitive negative damping region, resulting in inverter instability.

[0118] Then, the hybrid synchronous control method for the parallel inverter system provided in the present invention is used to execute steps 101 to 107 to control the inverter. The impedance model corresponding to the hybrid synchronous control method for the parallel inverter system provided in the present invention is:

[0119]

[0120]

[0121] in, is the impedance model corresponding to the hybrid synchronous control method of the parallel inverter system provided in the present invention, n is a constant coefficient, and its value is 0.5, The impedance model corresponding to the hybrid synchronous control method of the parallel inverter system provided in the present invention when the filter circuit is considered.

[0122] Figure 5 Given The Bode diagram of , proves the correctness of the impedance model corresponding to the hybrid synchronous control method of the parallel inverter system provided in the present invention. Figure 5 It can be seen from the Bode plot that the hybrid synchronous control method for the parallel inverter system adopted by the present invention can be stable over a wide range of short-circuit ratios, and there is almost no unstable region in the phase margin. The inverter of the hybrid synchronous control method for the parallel inverter system adopted by the present invention has good small signal stability in the range of short-circuit ratios of 1 to 100.

[0123] In order to verify the effectiveness of the hybrid synchronous control method of the parallel inverter system adopted by the present invention, a parallel three-phase AC inverter parallel system is built in MATLAB / Simulink, with a rated voltage level of 220V, a rated frequency of 50Hz, a maximum active power value of 20kW, and different inverter support capabilities. The simulation will be verified under the conditions of SCR=1 and SCR=5 with different line impedance values.

[0124] Embodiment 1:

[0125] Build a three-phase island microgrid consisting of three inverters.

[0126] The system's initial load is 45kW, 15kW load is connected in 1s, and the load is restored in 2s.

[0127] When the island short circuit ratio SCR=1, Figure 6Figure 2 shows the output frequency diagram (Figure a) and output active power diagram (Figure b) of the three-machine parallel inverter. Figure 7 The output frequency diagram (Figure a) and output active power diagram (Figure b) of the three-machine parallel inverter when the island short circuit ratio SCR=5.

[0128] Depend on Figure 6 and Figure 7 It can be seen from the simulation image that in the inverter parallel system under the island, no matter it is a strong grid or a weak grid, each inverter in the system can accurately share the load before and after the load changes, and the output is stable, indicating that the control strategy is effective.

[0129] Embodiment 2:

[0130] Build a three-phase grid-connected system consisting of three inverters.

[0131] Output power setting value of each inverter =15kW. The system initial frequency is set to the rated frequency, the system frequency drops to 49.9Hz at 1s and recovers at 2s.

[0132] Figure 8 The output frequency diagram (Figure a) and output active power diagram (Figure b) of the three-machine parallel inverter when the short-circuit ratio SCR of the grid-connected system is 1. Fig. 9 The output frequency diagram (Figure a) and output active power diagram (Figure b) of the three-machine parallel inverter when the short-circuit ratio SCR of the grid-connected system is 5.

[0133] Depend on Figure 8 and Fig. 9 It can be seen from the simulation images that in the inverter parallel system under grid-connected conditions, whether it is a strong grid or a weak grid, the power support of each inverter in the system can follow the frequency change of the system and has stable active support capability. The control strategy is effective.

[0134] The feasibility of this method in parallel inverters is proved by experiments based on the RTU-BOX 204 experimental platform. Three inverters, three DC power supplies and loads are used. The circuit diagram is shown in Fig.10 As shown in the figure, the DSP-based Rtunit controller compiles the program and runs as a controller, and the inverter switching frequency is 10kHz.

[0135] The inverter output current and voltage are as follows Fig.11 As shown, the output power and frequency are shown in Fig.12 .from Fig.11 and Fig.12 It can be seen that the system output voltage and current are stable, the output power is stable, it can respond in power when the system load is switched, and the dynamic performance is good when the load is cut in.

[0136] For easier understanding, see Fig.13 The present invention provides an embodiment of a hybrid synchronous control device for a parallel inverter system, comprising:

[0137] An output power calculation module, used to calculate the reactive output power and active output power of the inverter according to the measured output voltage and output current of the inverter;

[0138] A droop control module is used to perform droop control on reactive output power and active power to obtain an output voltage reference value;

[0139] A first current reference value calculation module, used for calculating a first dq-axis current reference value based on the output voltage reference value and the output voltage;

[0140] A power calculation module is used to calculate a reactive power setting value and an active power setting value of the inverter according to the measured output voltage and output frequency of the inverter;

[0141] A second current reference value calculation module, used for calculating a second dq-axis current reference value based on a reactive power setting value and an active power setting value;

[0142] A synthesis module, used for synthesizing a current reference value of the inverter according to the first dq-axis current reference value and the second dq-axis current reference value;

[0143] The control module is used to input the current reference value of the inverter into the current loop PI controller, convert the output of the current loop PI controller into the abc coordinate system through coordinate transformation, and generate a modulation signal through the PWM module to control the inverter.

[0144] In one embodiment, in the output power calculation module, the calculation formula for calculating the reactive output power and active output power of the inverter is:

[0145]

[0146]

[0147] in, is the active output power of the inverter, is the reactive output power of the inverter, is the d-axis component of the inverter output voltage in the dq coordinate system, is the q-axis component of the inverter output voltage in the dq coordinate system, is the d-axis component of the inverter output current in the dq coordinate system, is the q-axis component of the inverter's output current in the dq coordinate system.

[0148] In one embodiment, the first current reference value calculation module is specifically used for:

[0149] Based on the output voltage phase angle generated by droop control of reactive output power and active power, the output voltage reference value is transformed into the dq coordinate system, and the first dq axis current reference value is calculated by the voltage loop PI controller according to the output voltage reference value in the dq coordinate system and the output voltage in the dq coordinate system.

[0150] In one embodiment, the calculation formula of the first dq axis current reference value is:

[0151]

[0152] in, is the first dq axis current reference value, is the transfer function of the PI controller, is the representation of the output voltage reference value in the dq coordinate system, It is the representation of the output voltage of the inverter in the dq coordinate system.

[0153] In one embodiment, the calculation formulas for the reactive power setting value and the active power setting value of the inverter are:

[0154]

[0155] in, is the active power setting value of the inverter, is the reactive power setting value of the inverter, is the output frequency of the inverter, is the rated frequency, is the output voltage of the inverter, is the active power reference value, is the reactive power reference value, m is the active power droop coefficient, and n is the reactive power droop coefficient.

[0156] In one embodiment, the calculation formula of the second dq-axis current reference value is:

[0157]

[0158]

[0159] in, is the second dq axis current reference value, is the d-axis component of the second dq-axis current reference value, is the q-axis component of the second dq-axis current reference value, is the d-axis component of the inverter output voltage in the dq coordinate system.

[0160] The present invention also provides an embodiment of a hybrid synchronous control device for a parallel inverter system, the device comprising a processor and a memory:

[0161] The memory is used to store the program code and transmit the program code to the processor;

[0162] The processor is used to execute any one of the implementation methods of the aforementioned hybrid synchronous control method for parallel inverter systems according to the instructions in the program code.

[0163] The present invention also provides an embodiment of a computer-readable storage medium, which is used to store program codes, and the program codes are used to execute any one of the aforementioned embodiments of the hybrid synchronous control method of the parallel inverter system.

[0164] The present invention also provides an embodiment of a computer program product including instructions, which, when executed on a computer, enables the computer to execute any one of the aforementioned embodiments of the hybrid synchronous control method for a parallel inverter system.

[0165] The hybrid synchronous control device, equipment, computer-readable storage medium and computer program product including instructions for the parallel inverter system provided in the present invention are all used to execute the hybrid synchronous control method for the parallel inverter system provided in the present invention. The principles and technical effects achieved are the same as those of the hybrid synchronous control method for the parallel inverter system provided in the present invention, and will not be repeated here.

[0166] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A hybrid synchronous control method for a parallel inverter system, characterized in that: include: Calculating reactive output power and active output power of the inverter according to the measured output voltage and output current of the inverter; Performing droop control on the reactive output power and the active power to obtain an output voltage reference value; Calculating a first dq-axis current reference value based on the output voltage reference value and the output voltage; Calculating a reactive power setting value and an active power setting value of the inverter according to the measured output voltage and output frequency of the inverter; Calculating a second dq-axis current reference value based on the reactive power setting value and the active power setting value; synthesizing a current reference value of the inverter according to the first dq-axis current reference value and the second dq-axis current reference value; The current reference value of the inverter is input into the current loop PI controller, the output of the current loop PI controller is converted into the abc coordinate system through coordinate transformation, and a modulation signal is generated through a PWM module to control the inverter.

2. The hybrid synchronous control method of a parallel inverter system according to claim 1, characterized in that: The calculation formula for calculating the reactive output power and active output power of the inverter is: in, is the active output power of the inverter, is the reactive output power of the inverter, is the d-axis component of the inverter output voltage in the dq coordinate system, is the q-axis component of the inverter output voltage in the dq coordinate system, is the d-axis component of the inverter output current in the dq coordinate system, is the q-axis component of the inverter's output current in the dq coordinate system.

3. The hybrid synchronous control method of a parallel inverter system according to claim 1, characterized in that: The calculating a first dq-axis current reference value based on the output voltage reference value and the output voltage comprises: Based on the output voltage phase angle generated by drooping control of the reactive output power and the active power, the output voltage reference value is transformed into the dq coordinate system, and the first dq axis current reference value is calculated by the voltage loop PI controller according to the output voltage reference value in the dq coordinate system and the output voltage in the dq coordinate system.

4. The hybrid synchronous control method of a parallel inverter system according to claim 3, characterized in that: The calculation formula of the first dq axis current reference value is: in, is the first dq axis current reference value, is the transfer function of the PI controller, is the representation of the output voltage reference value in the dq coordinate system, It is the representation of the output voltage of the inverter in the dq coordinate system.

5. The hybrid synchronous control method of a parallel inverter system according to claim 1, characterized in that: The calculation formulas for the reactive power setting value and the active power setting value of the inverter are: in, is the active power setting value of the inverter, is the reactive power setting value of the inverter, is the output frequency of the inverter, is the rated frequency, is the output voltage of the inverter, is the active power reference value, is the reactive power reference value, m is the active power droop coefficient, and n is the reactive power droop coefficient.

6. The hybrid synchronous control method of a parallel inverter system according to claim 5, characterized in that: The calculation formula of the second dq axis current reference value is: in, is the second dq axis current reference value, is the d-axis component of the second dq-axis current reference value, is the q-axis component of the second dq-axis current reference value, is the d-axis component of the inverter output voltage in the dq coordinate system.

7. A hybrid synchronous control device for a parallel inverter system, characterized in that: include: An output power calculation module, used to calculate the reactive output power and active output power of the inverter according to the measured output voltage and output current of the inverter; A droop control module, used for performing droop control on the reactive output power and the active power to obtain an output voltage reference value; A first current reference value calculation module, configured to calculate a first dq-axis current reference value based on the output voltage reference value and the output voltage; A power calculation module is used to calculate a reactive power setting value and an active power setting value of the inverter according to the measured output voltage and output frequency of the inverter; a second current reference value calculation module, configured to calculate a second dq-axis current reference value based on the reactive power setting value and the active power setting value; a synthesis module, configured to synthesize a current reference value of the inverter according to the first dq-axis current reference value and the second dq-axis current reference value; The control module is used to input the current reference value of the inverter into the current loop PI controller, convert the output of the current loop PI controller into the abc coordinate system through coordinate transformation, and generate a modulation signal through a PWM module to control the inverter.

8. The hybrid synchronous control device for a parallel inverter system according to claim 7, characterized in that: In the output power calculation module, the calculation formula for calculating the reactive output power and active output power of the inverter is: in, is the active output power of the inverter, is the reactive output power of the inverter, is the d-axis component of the inverter output voltage in the dq coordinate system, is the q-axis component of the inverter output voltage in the dq coordinate system, is the d-axis component of the inverter output current in the dq coordinate system, is the q-axis component of the inverter's output current in the dq coordinate system.

9. A hybrid synchronous control device for a parallel inverter system, characterized in that: The device comprises a processor and a memory: The memory is used to store program code and transmit the program code to the processor; The processor is used to execute the hybrid synchronous control method of the parallel inverter system according to any one of claims 1 to 6 according to the instructions in the program code.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium is used to store program codes, and the program codes are used to execute the hybrid synchronous control method for a parallel inverter system according to any one of claims 1 to 6.

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