A three-phase network configuration type inverter control method with adaptive regulation of tie impedance

Abstract

The application discloses a grid-connection impedance self-adaptive regulation grid-connected inverter control method, which comprises the following steps: detecting grid-connected current and output voltage, performing coordinate transformation and power calculation, and obtaining an initial reference value of grid-connected voltage through power synchronous control; obtaining a nonlinear equation set about grid impedance by using collected grid-connected current, output voltage and calculated active and reactive power of the inverter, realizing real-time identification of the grid impedance through genetic algorithm, and then virtually outputting an impedance at an output port of the inverter through a virtual impedance algorithm, so as to self-adaptively regulate the grid-connection impedance between the inverter and the grid to an expected value. The application can self-adaptively regulate the grid-connection impedance between the grid-connected inverter and the grid, thereby ensuring that the grid-connected inverter can reliably and stably operate under strong and weak grid working conditions.

Description

Technical Field

[0001] This invention relates to the field of inverter control, and more specifically, to a control method for a three-phase grid-type inverter with adaptive adjustment of interconnection impedance. Background Technology

[0002] Inverters, serving as the interface between distributed renewable power generation units and the power grid, are core equipment in new power systems. With the increasing penetration of new energy sources and the decreasing proportion of synchronous generator power generation, grid-connected inverters, which provide voltage and frequency support to the grid, are becoming a research hotspot for scholars both domestically and internationally. Currently, many countries and regions have proposed plans for the large-scale application of grid-connected inverters.

[0003] Grid-based inverters typically employ power synchronization technology similar to synchronous generators, using output voltage as the control target. They can provide necessary voltage and frequency support without relying on a large AC power grid. However, due to the intermittent, random, and volatile nature of high-proportion renewable energy generation, grid impedance can exhibit a wide range of variations, posing challenges to the safe, stable, and high-quality operation of grid-based inverters. Actual operation of the ESCRI-SA project in Australia shows that grid-based inverters can operate stably under extremely weak grid conditions with an SCR (short circuit ratio) << 1.5. However, their stability margin decreases with increasing grid strength, and even unstable oscillations may occur. Engineers from NARI Group Corporation and researchers from Aalborg University have provided an intuitive explanation for this phenomenon: the grid-based inverter can be considered equivalent to a voltage source, directly connected in parallel with the equivalent voltage source of the grid through a very small interconnection impedance, thus resulting in poor stability.

[0004] To address the aforementioned stability issues, existing research has focused on reshaping the output impedance by adding impedance adapters, addressing the external characteristics of the inverter ports. This method effectively improves grid-connected stability but increases system hardware costs. Furthermore, some researchers have proposed optimizing control strategies to eliminate the negative resistance characteristic of the inverter's output impedance, thereby ensuring system stability. However, this method does not consider power quality issues under different grid impedances. From the perspective of the interconnection impedance between the grid-connected inverter and the grid, how to adaptively adjust it to ensure the system operates under optimal conditions is a key problem worthy of research and resolution in this field. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a control method for a three-phase grid-type inverter with adaptive adjustment of interconnection impedance, which aims to solve the technical problem that grid-type inverters are difficult to operate reliably and stably under wide-range fluctuations in grid impedance.

[0006] This invention discloses a control method for a three-phase grid-type inverter with adaptive tie impedance adjustment, comprising the following steps:

[0007] Step S1, detect the grid current. i g_x And perform coordinate transformations to obtain αβ coordinate system and dq Grid current in coordinate system i g_m and i g_n Detect output voltage v o_x And perform coordinate transformation to obtain αβ coordinate system and dq Output voltage in coordinate system v o_m and v o_n ; where subscript x express a , b , c , m express α、β , n express d, q ;

[0008] Step S2, according to dq Output voltage in coordinate system v o_n and grid current i g_n Calculate the active power output of the grid-connected inverter. P and reactive power Q ;

[0009] Step S3, based on active power P reactive power Q and active power reference value P ref Reactive power reference value Q ref The amplitude of the output voltage is obtained. V and phase angle θ ;

[0010] Step S4, based on the output voltage amplitude V and phase angle θ Obtain the output voltage reference value before inserting the virtual impedance. v oref0_m ,include α Directional output voltage reference value v oref0_α and β Directional output voltage reference value voref0_β ;

[0011] Step S5, based on the grid current i g_m Corrected output voltage reference value v oref_n Active power P and reactive power Q The power angle between the output voltage and the mains voltage δ Rated voltage amplitude V n and the corrected output voltage reference value v oref_n List the information about the power grid resistance. R g and grid reactance X g The nonlinear equations are solved iteratively using a genetic algorithm to obtain the grid impedance. Z g = R g + jX g The expression for the nonlinear equation system is as follows:

[0012]

[0013] Step S6, Set the target grid impedance Z g_t = R g_t +jX g_t , target grid impedance Z g_t = R g_t +jX g_t Subtract grid impedance Z g = R g + jX g Obtain virtual impedance Z v = R v +jX v ;

[0014] Step S7, virtual impedance Z v The product of the current and the grid-connected current is added to the initial reference value of the grid-connected voltage. v oref0_d and v oref0_qIn this process, the corrected output voltage reference value is obtained. v oref_n ;

[0015] Step S8, adjust the corrected output voltage reference value. v oref_n With output voltage v o_n The error is sent to the voltage controller. G v The voltage is regulated to output a PWM modulation signal, which is then used to generate a PWM control signal through sinusoidal pulse width modulation.

[0016] Furthermore, in step S2 above, there is active power. P and reactive power Q The calculation formula is:

[0017]

[0018]

[0019] in, v o_d for d Shaft output voltage, v o_q for q Shaft output voltage, i g_d for d Axis grid current, i g_q for q Axis grid current.

[0020] Furthermore, step S3 above includes converting active power... P With active power reference value P ref After comparison, multiply by the inertial element m p ω p / ( s + ω p This generates an angular frequency change Δω, which is related to the nominal angular frequency value. ω n Add and multiply by 1 s The phase angle of the output voltage is obtained. θ ,in, m p This is the active power droop coefficient. ω p The corner frequency of the active inertial element; the reactive power Q Reactive power reference value Qref After comparison, multiply by the inertial element n q ω q / ( s + ω q This generates a voltage change ΔV, which is related to the rated voltage amplitude. V n The summation yields the amplitude of the output voltage. V ,in, n q This is the reactive power droop factor. ω p The turning angle frequency of the reactive inertial element.

[0021] Furthermore, in step S4 above, α Directional output voltage reference value v oref0_α and β Directional output voltage reference value v oref0_β The calculation formula is as follows:

[0022] ,

[0023] .

[0024] Furthermore, during the first run to step S5, the corrected output voltage reference value... v oref_n The output voltage reference value before inserting virtual impedance. v oref0_m After the first iteration, when the process reaches step S5, the corrected output voltage reference value is... v oref_n The corrected output voltage reference value obtained in the previous operation step S7. v oref_n .

[0025] Furthermore, in step S6 above, the virtual impedance Z v = R v +jX v The calculation formula is:

[0026] ,

[0027] ,

[0028] in, X g_t andR g_t Target grid impedance Z g_t The reactance and resistance components in the equation.

[0029] Furthermore, the corrected output voltage reference value is obtained according to the following formula. v oref_n

[0030]

[0031] Compared with the prior art, the control method provided by the present invention, through the above-described technical solution conceived in this invention, enables the grid-connected inverter to operate reliably and stably under various grid strengths and operating conditions (such as strong grids, weak grids, inductive grids, and capacitive grids) by adaptively changing the interconnection impedance between the grid-connected inverter and the grid. It can also solve the current sharing problem of multiple inverters connected to the grid, thereby realizing the plug-and-play functionality of the grid-connected inverter in various grids. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the system structure of a three-phase grid inverter under traditional control methods.

[0033] Figure 2 This is a flowchart illustrating a specific implementation of the control method of the present invention.

[0034] Figure 3 This is a schematic diagram of the system structure of a three-phase grid inverter under the control method proposed in this invention.

[0035] Figure 4 The output power simulation waveforms of a three-phase grid-type inverter under strong grid conditions are shown, using both the traditional control method and the control method proposed in this invention.

[0036] Figure 5 The output current simulation waveforms of a three-phase grid-type inverter under strong grid conditions are shown using both the traditional control method and the control method proposed in this invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0038] Figure 1This is a control block diagram of a grid-connected inverter under traditional control methods. The grid-connected inverter includes a DC power supply 1, a three-phase inverter bridge 2, an LC filter 3, and a public power grid 4, which are connected sequentially. The three-phase inverter bridge 2 includes switching transistors. S 1~ S 6 and its freewheeling diode; LC filter 3 includes three sets of filter inductors. L f and filter capacitor C f Public power grid 4 includes three-phase voltage sources. v g and equivalent grid impedance Z g .

[0039] Furthermore, Figure 1 The controller 5 of the grid-connected inverter is also shown, including a power synchronization controller 51 and an output voltage controller 52.

[0040] exist Figure 1 In this structure, the traditional control method is to input an active power reference value to the controller 5. P ref Reactive power reference value Q ref Inverter output voltage angular frequency ω n and its amplitude V n and grid current flowing through the public power grid i g and filter capacitor C f Output voltage v o Controller 5 first performs coordinate transformation on the sampled three-phase current and voltage (from...). abc Coordinate system transformation to dq (Coordinate system), and obtain the active power output of the grid-type inverter according to the instantaneous power calculator 55. P and reactive power Q Then, the reference voltage is obtained through the power synchronization controller 51. v oref_n Finally, the output voltage controller 52 tracks the command value, thus providing voltage support. The three-phase current is sampled by the current sensor 7.

[0041] like Figure 2 and Figure 3 As shown, the control method provided by the present invention includes the following steps:

[0042] Step S1, detect the grid current.i g_x The current sensor 7 was used to collect data and perform coordinate transformation to obtain the following results: αβ coordinate system and dq Grid current in coordinate system i g_m and i g_n ; Detecting output voltage using a voltage sensor v o_x Collect and perform coordinate transformation to obtain αβ coordinate system and dq Output voltage in coordinate system v o_m and v o_n ; where subscript x express a , b , c , m express α、 β , n express d, q .

[0043] Step S2, will dq Output voltage in coordinate system v o_n and grid current i g_n The data is fed into the instantaneous power calculator 55, and the active power output of the grid-type inverter is calculated using the instantaneous power calculation formulas (Formula I and Formula II). P and reactive power Q The instantaneous power is calculated using the following equations I and II:

[0044]

[0045] Step S3, active power P reactive power Q and the corresponding active power reference value P ref Reactive power reference value Q ref The signal is fed into the power synchronization controller 51 to obtain the amplitude of the output voltage. V and phase angle θ .

[0046] Furthermore, in the power synchronization controller 51, the active power P With active power reference value P ref After comparison, multiply by the inertial element m p ωp / ( s + ω p This generates an angular frequency change Δω, which is related to the nominal angular frequency value. ω n Add and multiply by 1 s The phase angle of the output voltage is obtained. θ ,in, m p This is the active power droop coefficient. ω p The corner frequency of the active inertial element; the reactive power Q Reactive power reference value Q ref After comparison, multiply by the inertial element n q ω q / ( s + ω q This generates a voltage change ΔV, which is related to the rated voltage amplitude. V n The summation yields the amplitude of the output voltage. V ,in, n q This is the reactive power droop factor. ω p The turning angle frequency of the reactive inertial element.

[0047] Step S4, based on the output voltage amplitude output by the power synchronization controller 51 V and phase angle θ The output voltage reference value before inserting the virtual impedance is obtained using the voltage reference calculation formulas (Equations III and IV). v oref0_m ,include α Directional output voltage reference value v oref0_α and β Directional output voltage reference value v oref0_β ,

[0048]

[0049] Step S5: In the virtual impedance calculator 54, based on the collected grid current... i g_m Corrected output voltage reference value v oref_n Active power P and reactive power QThe power angle between the output voltage and the grid voltage (i.e., the angle difference between the output voltage and the grid voltage). δ Rated voltage amplitude V n and the corrected output voltage reference value v oref_n List the information about the power grid resistance. R g and grid reactance X g The nonlinear equation system (Equations V, VI, and VII) is solved iteratively using a genetic algorithm to obtain the grid impedance. Z g = R g + jX g ,

[0050]

[0051] Specifically, during the first run to step S5, the corrected output voltage reference value v oref_n The output voltage reference value before inserting virtual impedance. v oref0_m After the first iteration, when the process reaches step S5, the corrected output voltage reference value is... v oref_n The corrected output voltage reference value obtained in the previous operation step S7. v oref_n .

[0052] In one specific embodiment, the genetic algorithm is a basic genetic algorithm.

[0053] Step S6: In the virtual impedance calculator 54, set the target grid impedance. Z g_t = R g_t +jX g_t Under the influence of the target grid impedance, the system can operate stably and have good power quality. The required virtual impedance can be calculated according to the reference formulas (Equation VIII and Equation IX). Z v = R v +jX v ,

[0054]

[0055] Step S7, in the virtual impedance inserter 53, insert the virtual impedance Z vThe product of the current and the grid-connected current is added to the initial reference value of the grid-connected voltage. v oref0_d and v oref0_q In the middle, the corrected output voltage reference value is obtained according to formulas X and XI. v oref_n Formulas X and XI are as follows:

[0056]

[0057] Step S8: In the output voltage controller 52, the corrected output voltage reference value is... v oref_n With output voltage v o_n The error is sent to the voltage controller. G v The voltage-regulated output PWM modulation signal is used to generate the three-phase inverter bridge switching transistors through sinusoidal pulse width modulation. S 1~ S 6's PWM control signal.

[0058] In one specific embodiment, the voltage controller G v It is a PI controller.

[0059] Furthermore, the control method for a three-phase grid-type inverter with adaptive adjustment of interconnection impedance according to the present invention also includes the following steps.

[0060] Step S9: Determine if the device is powered off. If yes, proceed to step S10; otherwise, return to step S1 to continue execution.

[0061] Step S10: Power off.

[0062] like Figure 3 As shown, the above control method adds an adaptive virtual impedance between the power grid and the grid-connected inverter. Z v Virtual impedance Z v The value is adaptively adjusted based on stability requirements and real-time identification of grid impedance.

[0063] Finally, under the power grid operating conditions ( L g = 0.01mH, R g At a current of 0.001Ω, simulations were performed using PLECS to compare three-phase grid inverters employing traditional control methods and the control method proposed in this invention, respectively, to verify the superiority of the control method provided in this invention. t = 5 sWhen the control method is switched from the traditional control method to the method provided by this invention, the following result is obtained: Figure 4 and Figure 5 The simulation results are shown in the comparison chart. Figure 4 Simulation waveforms of active power P and reactive power Q output by a three-phase grid-connected inverter under strong grid conditions, using both conventional control methods and the control method proposed in this invention. Figure 5 To test the output current of a three-phase grid-connected inverter under strong grid conditions using both conventional control methods and the control method proposed in this invention. i g_a Simulation waveform diagram. From Figure 4 and Figure 5 As can be seen, traditional control methods cannot guarantee the stability of grid-connected inverters, while when t After switching from the traditional control method to the control method proposed in this invention within 5 seconds, the output power and current of the grid-connected inverter gradually stabilize from unstable to stable. Clearly, the method provided by this invention enables the grid-connected inverter to operate reliably and stably, thereby achieving plug-and-play functionality in the power grid.

[0064] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A control method for a three-phase grid-type inverter with adaptive tie impedance adjustment, characterized in that, Includes the following steps: Step S1, detect the grid current. i g_x And perform coordinate transformations to obtain αβ coordinate system and dq Grid current in coordinate system i g_m and i g_n Detect output voltage v o_x And perform coordinate transformation to obtain αβ coordinate system and dq Output voltage in coordinate system v o_m and v o_n ; Among them, subscript x express a , b , c , m express α、β , n express d, q ; Step S2, according to dq Output voltage in coordinate system v o_n and grid current i g_n Calculate the active power output of the grid-connected inverter. P and reactive power Q ; Step S3, based on active power P reactive power Q and active power reference value P ref Reactive power reference value Q ref The amplitude of the output voltage is obtained. V and phase angle θ ; Step S4, based on the output voltage amplitude V and phase angle θ Obtain the output voltage reference value before inserting the virtual impedance. v oref0_m ,include α Directional output voltage reference value v oref0_α and β Directional output voltage reference value v oref0_β ; Step S5, based on the grid current i g_m Corrected output voltage reference value v oref_n Active power P and reactive power Q The power angle between the output voltage and the mains voltage δ Rated voltage amplitude V n List the information about the power grid resistance. R g and grid reactance X g The nonlinear equations are solved iteratively using a genetic algorithm to obtain the grid impedance. Z g = R g + jX g The expression for the nonlinear equation system is as follows: ， ， ， in, X g and R g These are the reactance component and resistance component of the grid impedance, respectively. When running to step S5 for the first time, the corrected output voltage reference value is the output voltage reference value before inserting the virtual impedance. When running to step S5 after the first time, the corrected output voltage reference value is the corrected output voltage reference value obtained in the previous run step S7. Step S6, Set the target grid impedance Z g_t = R g_t +jX g_t , target grid impedance Z g_t = R g_t +jX g_t Subtract grid impedance Z g = R g + jX g Obtain virtual impedance Z v = R v +jX v ; Step S7, virtual impedance Z v The product of the current and the grid-connected current is added to the initial reference value of the grid-connected voltage. v oref0_d and v oref0_q In this process, the corrected output voltage reference value is obtained. v oref_n ; Step S8, adjust the corrected output voltage reference value. v oref_n With output voltage v o_n The error is sent to the voltage controller. G v The voltage is regulated to output a PWM modulation signal, which is then used to generate a PWM control signal through sinusoidal pulse width modulation.

2. The control method for a three-phase grid-type inverter with adaptive tie impedance adjustment according to claim 1, characterized in that, The active power in step S2 P and reactive power Q The calculation formula is: in, v o_d for d Shaft output voltage, v o_q for q Shaft output voltage, i g_d for d Axis grid current, i g_q for q Axis grid current.

3. The control method for a three-phase grid-type inverter with adaptive tie impedance adjustment according to claim 2, characterized in that, Step S3 includes converting active power P With active power reference value P ref After comparison, multiply by the inertial element m p ω p / ( s + ω p This generates an angular frequency change Δω, which is related to the nominal angular frequency value. ω n Add and multiply by 1 s The phase angle of the output voltage is obtained. θ ,in, m p This is the active power droop coefficient. ω p The corner frequency of the active inertial element; the reactive power Q Reactive power reference value Q ref After comparison, multiply by the inertial element n q ω q / ( s + ω q This generates a voltage change ΔV, which is related to the rated voltage amplitude. V n The summation yields the amplitude of the output voltage. V ,in, n q This is the reactive power droop factor. ω p The turning angle frequency of the reactive inertial element.

4. The control method for a three-phase grid-type inverter with adaptive tie impedance adjustment according to claim 3, characterized in that, In step S4 α Directional output voltage reference value v oref0_α and β Directional output voltage reference value v oref0_β The calculation formula is as follows: ， 。 5. The control method for a three-phase grid-type inverter with adaptive tie impedance adjustment according to claim 4, characterized in that, In step S6, the virtual impedance Z v = R v +jX v The calculation formula is: ， ， in, X g_t and R g_t Target grid impedance Z g_t The reactance and resistance components in the equation.

6. The control method for a three-phase grid-type inverter with adaptive tie impedance adjustment according to claim 5, characterized in that, The corrected output voltage reference value is obtained according to the following formula. v oref_n ， ， in, v oref0_d For the revised version d Shaft output voltage reference value, v oref0_q For the revised version q Shaft output voltage reference value, initial grid-connected voltage reference value v oref0_d and v oref0_q The output voltage reference value before inserting virtual impedance v oref0_m Obtained by transformation.

7. The control method for a three-phase grid-type inverter with adaptive tie impedance adjustment according to claim 1, characterized in that, The genetic algorithm described is a basic genetic algorithm.

8. The control method for a three-phase grid-type inverter with adaptive tie impedance adjustment according to claim 1, characterized in that, The voltage controller G v It is a PI controller.

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