A robust control method for inverters with extremely weak grids adapted to next-generation power semiconductors

Abstract

This invention relates to the field of grid-connected inverter control technology, and more particularly to a robust control method for inverters operating in extremely weak grids that is compatible with next-generation power semiconductors. The technical solution includes the following steps: acquiring the three-phase current of the inverter bridge arm inductor and the three-phase voltage of the filter capacitor at the grid connection point PCC; performing coordinate transformation and phase-locked loop processing on the three-phase voltage to obtain the phase angle of the grid-side capacitor voltage. This invention introduces a voltage-supported robust controller designed based on the μ-synthesis method, and combines it with an AC voltage controller to form a dual-path adaptive switching architecture. Without altering the standard vector control core, it effectively suppresses system instability and insufficient voltage support caused by grid-side impedance uncertainty under extremely weak grid conditions, achieving stable operation and rated power injection of the inverter within a wide SCR range. It balances rapid dynamic response under weak grid conditions with high robust stability under extremely weak grid conditions, significantly improving the system's disturbance rejection capability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of grid-connected inverter control, and in particular to a robust control method for an extremely weak grid inverter adapted to next-generation power semiconductors. BACKGROUND

[0002] With the large-scale development and grid-connected penetration of distributed renewable energy sources such as wind power and photovoltaic power, the energy power system is accelerating the transformation towards high efficiency and clean. At the same time, the next-generation power semiconductor devices represented by silicon carbide (SiC) and gallium nitride (GaN) have become the key support for promoting energy efficient conversion due to their core advantages of high frequency, high power density and low loss. The packaging and interconnection forming platform of the next-generation power semiconductor devices needs to be equipped with a voltage source grid-connected inverter (VSC) to realize the interface adaptation of new energy and the grid, and the running stability of the platform directly determines the actual landing effect of the performance of the next-generation power semiconductor devices.

[0003] The short circuit ratio (SCR) of the grid is a core indicator representing the strength of the grid, and SCR≤3 is usually defined as a weak grid, and SCR=1 is defined as an extremely weak grid. When the grid-connected inverter is connected to a weak grid, especially an extremely weak grid, the traditional vector control strategy faces severe stability and performance challenges: on the one hand, the significant increase in grid impedance leads to strong coupling effects between the inverter and the grid through the phase-locked loop (PLL), and the existing controller design often ignores the PLL dynamic characteristics. This simplification can meet the demand in a strong grid, but it will introduce unmodeled dynamics in an extremely weak grid, causing system oscillation or even instability; on the other hand, to maintain basic stability, existing technologies need to significantly limit active power injection, for example, only 0.4-0.6 pu power can be injected in an extremely weak grid with SCR=1, which severely restricts the utilization efficiency of renewable energy.

[0004] Current solutions to the above problems have obvious defects: simply reducing the PLL gain can alleviate the coupling problem, but it will greatly sacrifice the system dynamic response speed; the control scheme based on gain scheduling needs to design dozens of sub-controllers, which has a complex structure and is difficult to implement in engineering; power synchronization control without PLL can improve stability, but it loses the inherent overcurrent protection function of standard vector control, which is incompatible with the current industrial application status; the traditional PI controller can only achieve local stability under certain conditions, and cannot adapt to changes in operating points and uncertainties in grid impedance, making it difficult to provide effective voltage support in an extremely weak grid, which easily leads to system instability. Therefore, the present application proposes a robust control method for an extremely weak grid inverter adapted to next-generation power semiconductors. SUMMARY

[0005] The purpose of the present application is to solve the problem of stability caused by PLL dynamic coupling and uncertainty of grid impedance in the background art, and propose a robust control method for extremely weak grid inverter suitable for next-generation power semiconductors.

[0006] The technical solution of the present application is a robust control method for extremely weak grid inverter suitable for next-generation power semiconductors, comprising the following steps:

[0007] Collecting three-phase currents of the inverter bridge arm inductance and three-phase voltages of the filter capacitor at the point of common coupling (PCC);

[0008] Performing coordinate transformation and phase-locked loop processing on the three-phase voltages to obtain the phase angle of the grid-side capacitor voltage ;

[0009] Based on the coordinate-transformed axis voltage variable, two axis current reference values are obtained through an AC voltage controller and a voltage support robust controller ;The voltage support robust controller is based on a comprehensive method and DK iterative design, used to suppress grid-side impedance uncertainty;

[0010] Performing coordinate transformation on the three-phase currents to obtain axis current variables, calculating the absolute value of the deviation of the axis current variable from the current reference value, and combining the hysteresis comparison logic to adaptively switch the output target axis current reference value; Based on the coordinate-transformed voltage variable, current variable, and target

[0011] axis current reference value, a coordinate-transformed voltage control signal is generated through a current control loop and a voltage feedforward link; Performing inverse coordinate transformation on the voltage control signal to obtain the control signal in the three-phase stationary coordinate system;

[0012] Performing pulse width modulation on the control signal in the three-phase stationary coordinate system to generate switching signals to control the turn-on and turn-off of the inverter power devices.

[0013] Optionally, the coordinate transformation is Park transformation, and the phase angle of the grid-side capacitor voltage

[0014] is calculated by the following formula:

[0015]

[0016] wherein, is a phase-locked loop PI controller; This is the proportional adjustment coefficient of the phase-locked loop. For the integral adjustment coefficient of the phase-locked loop, The rated angular frequency of the grid voltage. For the Laplace operator, After Park transformation Shaft voltage variable.

[0017] Optionally, via AC voltage controller Received The shaft current reference value satisfies:

[0018]

[0019] in, It is a voltage loop PI controller. This is the voltage loop proportional adjustment coefficient. This is the voltage loop integral adjustment coefficient. for Axis grid voltage command signal, After Park transformation Axis voltage variable, For the Laplace operator.

[0020] Optionally, the design process of the voltage-supported robust controller K includes:

[0021] Treating the change in grid-side impedance as a multiplicative uncertainty, a perturbation model is established:

[0022]

[0023] in, For uncertain weighting functions, It is a variable uncertainty function. For the nominal model;

[0024] Design a perturbation weight function With output weight function , The design incorporates features to enhance the suppression of low-frequency disturbances and prevent the amplification of high-frequency noise. The design ensures tracking accuracy at low frequencies and prevents the controller from over-responding to high-frequency dynamics.

[0025] Using the MATLAB Robust Control Toolbox, through The voltage-supported robust controller is obtained by combining the comprehensive method with DK iterative calculation. .

[0026] Optionally, a voltage-supported robust controller can be used. Received Shaft current reference value satisfy:

[0027]

[0028] in, For the set Axis grid voltage command signal, After Park transformation Shaft voltage variable.

[0029] Optionally, the hysteresis comparison logic is as follows:

[0030] Set threshold With hysteresis threshold When the absolute value of the deviation is ≤ At that time, the target The shaft current reference value is the output of the AC voltage controller AVC. Shaft current reference value;

[0031] When the absolute value of the deviation > At that time, the target Shaft current reference value for voltage-supported robust controller Output Shaft current reference value;

[0032] when <Absolute value of deviation≤ At that time, the target The shaft current reference value is from the previous control cycle. Shaft current reference value.

[0033] Optionally, the voltage control signal includes Shaft voltage control signal and Shaft voltage control signal ,satisfy:

[0034]

[0035] in, It is a current loop PI controller; This is the proportional adjustment coefficient for the current loop. This is the integral adjustment coefficient for the current loop; for Shaft current command signal, For the goal Shaft current reference value; , The Park transformation results are respectively , Axis current variable; This refers to the inductance value of the inverter bridge arm. The rated angular frequency of the grid voltage. For the Laplace operator, After Park transformation Axis voltage variable, After Park transformation Shaft voltage variable.

[0036] Optionally, the inverse coordinate transformation in step 6 is a Park inverse transformation, used to convert the voltage control signal in the synchronous rotating coordinate system into a control signal in the three-phase stationary coordinate system.

[0037] Optionally, the parameters of the phase-locked loop PI controller satisfy: 0.5 ≤ ≤1.0, 40≤ ≤60, =100πrad / s.

[0038] Optionally, the short-circuit ratio (SCR) of the extremely weak power grid is 1, the inverter bridge arm inductance is 2mH, and the filter capacitor is 6μF.

[0039] Compared with the prior art, this application includes at least one of the following beneficial technical effects:

[0040] By using the μ synthesis method and the DK iterative design of the voltage support robust controller, the multiplicative uncertainty of grid-side impedance can be effectively suppressed, and the core problems of inverter instability and insufficient voltage support under extremely weak grids with SCR=1 can be completely solved.

[0041] In weak power grids, the AC voltage controller (AVC) ensures rapid dynamic response, while in extremely weak power grids, it automatically switches to a robust controller to provide stable voltage support, thus achieving dual optimization of dynamic response speed and operational stability.

[0042] Without modifying the standard vector control core architecture, only adding a robust controller and an adaptive switching unit can achieve wide SCR range operation, significantly improve grid connection point voltage stiffness, and adapt to the current state of industrial applications;

[0043] It accurately matches the common characteristics of next-generation power semiconductor device packaging and interconnect molding platforms, provides reliable grid-connected interface control support for the platform, ensures rated power injection, and improves the efficiency of new energy utilization.

[0044] In summary, this invention introduces a voltage-supported robust controller designed based on the μ-synthesis method and combines it with an AC voltage controller to form a dual-path adaptive switching architecture. Without altering the standard vector control core, it effectively suppresses system instability and insufficient voltage support caused by grid-side impedance uncertainty under extremely weak power grids. This enables stable operation and rated power injection of the inverter over a wide SCR range, while also balancing rapid dynamic response under weak power grid conditions with high robust stability under extremely weak power grid conditions. This significantly improves the system's disturbance rejection capability and provides a reliable control solution for high-frequency, high-power-density packaging platforms adapted to next-generation power semiconductor devices. Attached Figure Description

[0045] Figure 1 The topology diagram of the three-phase LC grid-connected inverter used in the implementation of this invention is shown below;

[0046] Figure 2 A topology diagram of a three-phase LC grid-connected inverter with variable structure voltage support control based on a robust controller.

[0047] Figure 3 The block diagram for robust control of a grid-connected inverter based on the SISO model is shown.

[0048] Figure 4 The waveforms of the grid connection point voltage and the output current of the grid-connected inverter before and after adopting the control strategy of this invention are shown under the condition that the grid short-circuit ratio is 1 (SCR=1, extremely weak grid). Detailed Implementation

[0049] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0050] Example: This invention proposes a robust control method for inverters operating in extremely weak grids adapted to next-generation power semiconductors. The topology used in this example is as follows. Figure 1 As shown, this topology includes a three-phase full-bridge inverter and inverter arm inductors. Filter capacitor Grid impedance In this embodiment, , , .

[0051] like Figure 2The method of the present invention consists of the following steps:

[0052] Step 1: Collect the inductance of the inverter bridge arm of the inverter system. Three-phase current , , And at the grid connection point PCC, the filter capacitor Three-phase voltage , , ;

[0053] Step 2: Adjust the capacitance of the grid-side filter in the three-phase stationary coordinate system. Three-phase voltage , , After performing the Park transformation, we obtain the coordinates in the synchronous rotating coordinate system. , Axis voltage variable , The , Axis voltage variable , After passing through a phase-locked loop (PLL), the phase angle of the grid-side capacitor voltage is obtained. ;

[0054] Phase angle of grid-side capacitor voltage The calculation formula is shown in equation (1):

[0055]

[0056] In equation (1), It is a phase-locked loop PI controller. This is the proportional adjustment coefficient of the phase-locked loop. This is the integral adjustment coefficient of the phase-locked loop. The rated angular frequency of the grid voltage. This is the Laplace operator. In this embodiment, it is designed... , , .

[0057] Step 3: According to Axis voltage variable Through the AC voltage controller AVC, the result is obtained using equation (2). :

[0058] (2)

[0059] In equation (2), For the set Axis grid voltage command signal, For the Laplace operator, It is a voltage loop PI controller. This is the voltage loop proportional adjustment coefficient. This is the voltage loop integral adjustment coefficient. In this embodiment, , .

[0060] Step 4: According to Axis voltage variable By using the voltage-supported robust controller K, equation (3) is obtained. :

[0061] (3)

[0062] In equation (3), For the set Axis grid voltage command signal, For the Laplace operator, A voltage-supported robust controller designed to account for uncertainties in grid-side impedance.

[0063] Step 4.1: Establish the robust control block diagram of the SISO system as follows: Figure 3 As shown. Treating the change in grid-side impedance as a multiplicative uncertainty, a perturbation model with uncertainty is established, as shown in equation (4):

[0064] (4)

[0065] In equation (4), For perturbation models, For uncertain weighting functions, For a variable, uncertain function, This is the nominal model. Meanwhile, to achieve reference tracking and interference suppression, the perturbation and output weights are designed as follows: and , and All are designed as first-order low-pass filters, with perturbation weights. The gain is designed to be 10 to enhance low-frequency disturbance suppression; output weighting The gain is designed to be 1 to ensure tracking accuracy at low frequencies.

[0066] The relevant weight function is designed using the Robust Control Toolbox in MATLAB software, as shown in equation (5):

[0067] (5)

[0068] Step 4.2: Utilize By employing a comprehensive approach and performing DK iterations using the Robust Control Toolbox in MATLAB, a voltage-supported robust controller for a grid-connected converter model that considers grid-side inductance variations can be obtained. As shown in equation (6):

[0069]

[0070] Step 5: Based on the phase angle of the grid-side capacitor voltage The three-phase current in the three-phase stationary coordinate system , , After performing the Park transformation, the coordinates in the rotating coordinate system are obtained. , Axis current variable , ;

[0071] Step 6: According to Axis current variable With the output of the adaptive switching unit By comparison, using equation (7) we obtain :

[0072] (7)

[0073] according to The values ​​are compared with the set threshold A and hysteresis threshold h in the hysteresis comparison unit, which controls the output of the adaptive switching unit. for or The control logic of the adaptive switching unit is as shown in equation (8):

[0074] (8)

[0075] In equation (8), when When, the adaptive switching unit outputs For AC voltage controller AVC output ;when When, the adaptive switching unit outputs For voltage-supported robust controller K output ;when When, the adaptive switching unit outputs Output for the previous control cycle In this embodiment, the design , .

[0076] Step 7: According to , Axis voltage variable , and current variables , The inverter control signal is obtained through the AC current control loop ACC and the grid-side capacitor voltage feedforward loop, using equation (9). , :

[0077]

[0078] In equation (9), , The settings based on the inverter system capacity , Axis grid current command signal; For the Laplace operator, The rated angular frequency of the grid voltage. It is a current loop PI controller. This is the proportional adjustment coefficient for the current loop. This is the integral adjustment coefficient for the current loop. In this embodiment, it is designed... , , .

[0079] Step 8: Based on the phase angle of the grid-side capacitor voltage Control signals for the inverter , After performing the inverse Park transform, the control signal in the three-phase stationary coordinate system is obtained. , , ;

[0080] Step 9: Control signal , , After pulse width modulation (PWM), switching signals for the power devices in the inverter are generated and then passed through the drive circuit to control the power devices to turn on and off.

[0081] Figure 4 The graphs show the grid connection point voltage and grid-connected inverter output current waveforms before and after applying the control strategy of this invention, under a grid short-circuit ratio of 1 (SCR=1, extremely weak grid). Figure 4 It can be observed that under extremely weak power grid conditions, the AC voltage controller AVC grid connection point voltage and the grid-connected inverter output current are severely distorted and contain a large amount of harmonics. By adopting this invention, after automatically switching to the robust controller, due to the robustness of the robust controller, there is no distortion in the grid connection point voltage and the grid-connected inverter output current after a very short transition process, and the grid-connected inverter can operate stably.

[0082] This invention can accurately adapt to extremely weak power grid scenarios with a short-circuit ratio (SCR) of 1. Through a voltage-support robust controller based on the μ-synthesis method and DK iterative design, it effectively suppresses multiplicative uncertainty in grid-side impedance, completely solving the core problems of inverter oscillation, instability, and insufficient voltage support under extremely weak power grids. Simultaneously, it overcomes the limitation of existing technologies requiring significant restrictions on active power injection in this scenario, maintaining system stability without reducing power output and ensuring rated power injection to improve renewable energy utilization efficiency. It employs a dual-path control architecture consisting of an AC voltage controller (AVC) and a voltage-support robust controller, combined with hysteresis comparison switching logic based on q-axis current deviation and set thresholds A and h. Under weak power grids, it relies on the AVC to ensure rapid dynamic response, while under extremely weak power grids, it automatically switches to the robust controller to achieve stable voltage support. Furthermore, when the deviation is between Ah and A, it maintains the output of the previous cycle, avoiding system fluctuations caused by frequent switching, thus balancing dynamic response speed and operational stability. This method does not require modification of the core of standard vector control. The architecture upgrades functionality solely through the addition of a voltage-supported robust controller and an adaptive switching unit, ensuring full compatibility with existing standard vector control systems. It retains essential industrial applications such as overcurrent protection, making it highly adaptable to current industrial applications. Furthermore, it eliminates the need for dozens of sub-controllers, featuring clear control logic achieved through a combination of mature technologies such as coordinate transformation, controller computation, hysteresis comparison, and pulse width modulation, thus reducing engineering deployment and debugging costs. Simultaneously, it precisely matches the common characteristics of next-generation power semiconductor device packaging and interconnection platforms like SiC and GaN. Stable grid-connected interface control ensures the full realization of the structural design advantages of these platforms, such as optimized parasitic parameters and improved thermal reliability, providing core control technology support for the engineering application of next-generation power semiconductor devices. Moreover, through the synergistic effect and adaptive adjustment of the dual-path controller, it enhances the stability of the voltage at the grid connection point PCC, reduces voltage distortion and fluctuations, mitigates the impact of grid-side disturbances on inverter operation, and significantly improves the overall grid-connected system's anti-disturbance performance.

[0083] The above specific embodiments are merely several optional embodiments of the present invention. Based on the technical solutions of the present invention and the relevant teachings of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A robust control method for a very weak grid inverter adapted to next generation power semiconductors, characterized by, The method comprises the following steps: Collecting three-phase current of the inverter bridge arm inductor and three-phase voltage of the filter capacitor at the grid-connected point PCC; The three-phase voltage is subjected to coordinate transformation and phase-locked loop processing to obtain the phase angle of the grid-side capacitor voltage ; Based on the coordinate transformation The axis voltage variable is controlled by the AC voltage controller And the voltage support robust controller Two Axis current reference values are obtained; the voltage support robust controller Based on The comprehensive method and DK iteration design The three-phase current is coordinate-transformed to obtain The shaft current variable is calculated The absolute value of the deviation of the shaft current variable from the current shaft current reference value is combined with hysteresis comparison logic to adaptively switch output target shaft current reference value; The coordinate-transformed voltage variable, the current variable and the target The axis current reference value generates the coordinate-transformed voltage control signal through the current control loop and the voltage feedforward link. Performing inverse coordinate transformation on the voltage control signal to obtain a control signal in a three-phase stationary coordinate system; Performing pulse width modulation on the control signal in the three-phase stationary coordinate system to generate a switching signal for controlling the turn-on and turn-off of the inverter power device; The voltage supports robust controller The design process includes: Regarding the grid-side impedance change as multiplicative uncertainty, a perturbation model is established: wherein, is an uncertainty weight function, is a variable uncertainty function, is a nominal model; Designing disturbance weight function Designing output weight function , Designing for enhancing the suppression of low-frequency disturbance, Designing for ensuring the tracking accuracy of low-frequency output; The robust controller of the voltage support is obtained by using MATLAB robust control toolbox and through The voltage support robust controller is obtained by using MATLAB robust control toolbox and through ; The hysteresis comparison logic is: Setting threshold With hysteresis threshold When the absolute value of the deviation is less than or equal to The target The axis current reference value is the output of the alternating voltage controller AVC Axis current reference value; When the absolute value of the deviation > At that time, the target Shaft current reference value for voltage-supported robust controller Output Shaft current reference value; When <Deviation absolute value ≤ Target axis current reference value is the axis current reference value of the previous control period. axis current reference value.

2. The robust control method of a very weak grid inverter adapted for next generation power semiconductor according to claim 1, characterized in that, The coordinate transformation is a Park transformation, the phase angle of the grid-side capacitor voltage is calculated by the following equation: wherein, is a phase locked loop PI controller; is a proportional regulation coefficient of the phase locked loop, is an integral regulation coefficient of the phase locked loop, is a grid voltage nominal angular frequency, is a Laplace operator, is a Park-transformed axis voltage variable.

3. The robust control method of a very weak grid inverter adapted for next generation power semiconductor according to claim 1, characterized in that, By an ac voltage controller Obtained The shaft current reference value satisfies: wherein, is a voltage loop PI controller, is a voltage loop proportional gain, is a voltage loop integral gain, is is an axis grid voltage command signal, is a Park-transformed is an axis voltage variable, is a Laplacian operator.

4. The robust control method of a very weak grid inverter adapted for next generation power semiconductor according to claim 1, characterized in that, Robust controller by voltage support obtained Shaft current reference value satisfies: wherein, is set to be the axis grid voltage command signal, is the Park-transformed axis voltage variable, is a voltage support robust controller designed considering grid-side impedance uncertainty factors.

5. The method of claim 1, wherein, The voltage control signal comprises Shaft voltage control signal With Shaft voltage control signal , satisfies: wherein, is a current loop PI controller; is a current loop proportional regulation coefficient, is a current loop integral regulation coefficient; is a shaft current command signal, is a target shaft current reference value; , are respectively Park-transformed , shaft current variables; is an inverter bridge arm inductance value, is a grid voltage nominal angular frequency, is a Laplace operator, is a Park-transformed shaft voltage variable, is a Park-transformed shaft voltage variable.

6. The method of claim 1, wherein, The inverse coordinate transformation in step 6 is Park inverse transformation, which is used to convert the voltage control signal in the synchronous rotating coordinate system into a control signal in the three-phase stationary coordinate system.

7. The robust control method of a very weak grid inverter adapted for next generation power semiconductor according to claim 2, characterized by, The parameters of the phase-locked loop PI controller satisfy: 0.5≤ ≤1.0, 40≤ ≤60, =100π rad / s.

8. The method of claim 1, wherein the method is robust to a very weak grid inverter. The short circuit ratio SCR of the extremely weak power grid is 1, the inverter bridge arm inductor value is 2 mH, and the filter capacitor value is 6 μF.

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