Fractional order control power decoupling network inverter voltage ride-through support method and device

Abstract

The application provides a fractional order control power decoupling grid-connected inverter voltage ride-through support method and device, which is used for an inverter system containing a reactive power ring, an active power ring, a power decoupling ring, a voltage open loop and a current closed loop, generates reference voltage and angle of a voltage and current ring through power decoupling and fractional order control power ring, and increases closed loop control and reference voltage limiting link in the reactive power ring, adopts fractional order control and increases active current limiting link in the voltage and current ring, so that the grid-connected point voltage can be effectively supported and the grid-connected point voltage and current peak can be effectively inhibited, the active power can be maintained, and the active power peak can be reduced when high and low voltage ride-through occurs; when high and low voltage ride-through occurs, the application can better support the grid-connected point voltage, realize accurate control of voltage and current, effectively inhibit the grid-connected point voltage and current peak, maintain the active power to more accurately track the given reference value, reduce the active power peak, and improve the stability of the grid-connected inverter.

Description

Technical Field

[0001] This invention relates to the field of grid-connected inverter control technology, and in particular to a method and apparatus for supporting voltage ride-through of a grid-connected inverter with fractional-order control power decoupling, specifically relating to a grid-connected inverter system with fractional-order control power decoupling. Background Technology

[0002] A grid-tied inverter is a core power conversion device that converts direct current (DC) generated by solar panels or wind turbines into alternating current (AC) that is in phase and frequency with the power grid, and then synchronously injects it into the public power grid. Its core functions are to achieve maximum power point tracking (MPPT) and meet the requirements for safe grid-connected operation.

[0003] Currently, commonly used grid-connected inverters are divided into grid-following inverters (GFL) and grid-forming inverters (GFM). In recent years, the theory of grid-forming inverters has developed rapidly, with significant breakthroughs in both theoretical research and applications in some new energy power generation. Grid-forming inverters share many similarities with grid-following inverters and exhibit superior stability under weak grid conditions, thus attracting widespread attention from scholars both domestically and internationally.

[0004] The ability to autonomously generate a stable voltage and frequency reference is one of the most critical parts of a GFM system. Virtual synchronous generators (VSGs) are the most mainstream and typical control technology implementation method for GFM. However, there is coupling between its active power loop and reactive power loop. At the same time, traditional PID control is difficult to achieve precise control of power, voltage and current when subjected to disturbances, which reduces the stability of grid-connected inverters. In addition, the traditional reactive power loop lacks closed-loop control, which reduces its robustness during operation and limits its grid support effect during high and low voltage ride-throughs. Especially during zero voltage ride-throughs, the voltage support effect is extremely poor, the grid connection point voltage drops to 0, and the active power cannot be maintained at 0. Even after the fault is recovered, it cannot return to the original state.

[0005] This invention proposes a solution to the above-mentioned problems. Summary of the Invention

[0006] This invention proposes a method and apparatus for supporting voltage ride-through in a grid-connected inverter with fractional-order control power decoupling. The system includes a grid-connected inverter system with fractional-order control power decoupling. This system has a simple structure. Through power decoupling and fractional-order control power loops, reference voltages and angles for voltage and current loops are generated. Closed-loop control and reference voltage limiting are added to the reactive power loop. Fractional-order control and active current limiting are added to the voltage and current loops. When high and low voltage ride-throughs occur, this system can better support the grid connection point voltage, achieve precise voltage and current control, effectively suppress voltage and current spikes at the grid connection point, maintain more accurate active power tracking of the given reference value, reduce active power spikes, and improve the stability of the grid-connected inverter.

[0007] The present invention adopts the following technical solution.

[0008] A fractional-order control power decoupling grid-connected inverter voltage ride-through support method is proposed for supporting the high and low voltage ride-through stability of grid-connected inverters (GFM). This method is applicable to inverter systems containing reactive power loops, active power loops, power decoupling loops, voltage open loops, and current closed loops. By generating reference voltages and angles for the voltage and current loops through power decoupling and fractional-order control power loops, and by adding closed-loop control and reference voltage limiting components to the reactive power loop, and employing fractional-order control and adding active current limiting components to the voltage and current loops, this method effectively supports the grid connection point voltage during high and low voltage ride-through, achieving precise voltage and current control, effectively suppressing grid connection point voltage and current spikes, maintaining more accurate active power tracking of the given reference value, reducing active power spikes, and improving the stability of the grid-connected inverter.

[0009] The method employs fractional-order control and decoupling control of the inverter's active and reactive power; compares the real-time values ​​of active and reactive power with reference values; uses fractional-order control in the reactive power loop and adds closed-loop control (inertia control); and derives the voltage loop reference voltage based on the relationship between Pf and QV. and angular frequency When the grid voltage experiences a low / high voltage ride-through, the system actively supports the grid connection point voltage by increasing / decreasing reactive power, and maintains active power tracking the given value by increasing / decreasing the grid connection point current, while simultaneously supporting the grid connection point voltage. Fractional-order control is employed in the voltage and current loops to achieve more precise control of voltage and current. Active current is limited in the current loop to prevent large instantaneous spikes in current and power. The reference voltage output from the power loop to the voltage loop is adjusted based on the grid voltage's rated value. Limiting is implemented to suppress large instantaneous spikes in active power generated during grid voltage dips. The support effect of grid connection point voltage during high and low voltage ride-through is optimized to maintain more accurate active power tracking of the reference value, suppress spikes in active power and grid connection point current generated during grid voltage steps, achieve more precise and stable control of voltage and current, and better realize high and low voltage ride-through.

[0010] A fractional-order control power decoupling grid-connected inverter voltage ride-through support device is provided. This device utilizes the fractional-order control power decoupling grid-connected inverter voltage ride-through support method described above. The device is a grid-connected inverter system comprising a reactive power loop, an active power loop, a power decoupling loop, an open voltage loop, and a closed current loop. The active power loop, reactive power loop, and power decoupling loop employ fractional-order control to jointly achieve power decoupling and output a reference voltage. and angular frequency The voltage open-loop and current closed-loop of the fractional-order control are used as reference values.

[0011] The reactive power loop adopts fractional-order control and adds closed-loop control (inertia control). The small signal generated by the reactive power and active power through the power decoupling loop is added to the output values ​​of the active power loop and the reactive power loop. At the same time, an amplitude limiter is added to the output reference voltage of the reactive power loop.

[0012] Fractional-order control is used in the voltage open-loop and current closed-loop, and a limiting circuit is added to the reference active current.

[0013] like Figure 1 As shown, the grid-connected inverter system is a grid-connected inverter system based on fractional-order control power decoupling, including a main circuit, dq coordinate transformation, active power loop, reactive power loop, voltage open loop, current closed loop, PWM control and power decoupling loop;

[0014] The main circuit is a three-phase full-bridge controlled inverter circuit connected to the power grid, including parasitic resistance. Filter inductor Filter capacitor Line inductance and line impedance The DC voltage is converted by a three-phase inverter and then filtered by an LC filter before being connected to the grid at the grid connection point. For inverter output current, This refers to the grid connection point current.

[0015] The dq coordinate transformation performs voltage and current transformation, and the transformed values ​​are calculated in the open-loop voltage control and closed-loop current control of the fractional-order control. The reactive power loop adopts fractional-order control and adds closed-loop and reference voltage limiting links. The output values ​​in the active power loop and reactive power loop are added to the small-signal values ​​obtained through the small-signal calculation matrix in the power decoupling loop to obtain the reference angle. and reference voltage ;

[0016] The current closed-loop control method includes an active current limiting method; the PWM stage controls the switching of the inverter switching transistors.

[0017] like Figure 2 As shown, the power decoupling loop achieves decoupling control by analyzing the coupling mechanism between active and reactive power; specifically:

[0018] The active power control loop of the virtual synchronous generator (VSG) in the inverter system is expressed by the following formula:

[0019] Formula 1;

[0020] Formula 2;

[0021] Formula 3;

[0022] The reactive power control loop of the inverter system can be expressed by the following formula:

[0023] Formula 4;

[0024] The small-signal model for its control is derived from formulas 1, 2, 3, and 4:

[0025] Formula 5;

[0026] When the inverter system is operating, the voltage phase difference between its converter terminal and the grid node is expressed by the formula:

[0027] Formula 6;

[0028] The state variables of VSG are defined as follows:

[0029] Formula 7;

[0030] The output of VSG is:

[0031] Formula 8;

[0032] Combining equations 5, 7, and 8, we obtain the open-loop state-space model of VSG as follows:

[0033] Formula 9;

[0034] The output matrix of VSG is represented as follows:

[0035] Formula 10;

[0036] The power transmitted through a three-phase line is expressed as:

[0037] Formula 11;

[0038] Expanding linearization formula 11 using a multivariate Taylor series yields the linearized model for power transmission as follows:

[0039] Formula 12;

[0040] The parameters of the linearized power transfer model are:

[0041] Formula 13;

[0042] , , and To linearize the model parameters, coupling elements and and Positive correlation; and their interrelationship leads to mutual coupling between the dynamics of active and reactive power control;

[0043] By ignoring the phase of the grid voltage For higher-order transient disturbances, assuming the small phase difference signal is equal to the small phase signal of the VSG output voltage, then:

[0044] Formula 14;

[0045] Since the control bandwidth of the voltage loop is much wider than that of the power loop, the dynamic characteristics of the voltage loop can be ignored when focusing on the power loop, and it can be assumed that the voltage loop can perfectly follow the reference, i.e.:

[0046] Formula 15;

[0047] Combining formulas 9, 10, 12, 14, and 15, the closed-loop state-space model of VSG is obtained as follows:

[0048] Formula 16;

[0049] Analysis of the VSG state-space model reveals the coupling mechanism between active and reactive power control. This coupling can be eliminated by designing an additional controller.

[0050] The closed-loop system after PQ decoupling is expressed by Equation 17 as follows:

[0051] Formula 17;

[0052] The power control loop uses full-state feedback control of the VSG to eliminate the coupling between active and reactive power control.

[0053] In the full-state feedback control of VSG, the output matrix n of the power control is modified to be the sum of the original VSG control output and the state variable feedback, specifically in the form of:

[0054] Formula 18;

[0055] Combining formulas 9, 12, 14, 15, and 18, the state-space model of the VSG closed-loop system incorporating full-state feedback is obtained as follows:

[0056] Formula 19;

[0057] Formula 19 is the same as Formula 17; by solving them simultaneously, we get:

[0058] Formula 20;

[0059] The parameters in Formula 20 are Figure 2 The values ​​of the small and medium signal operation matrices, and the corresponding Figure 2 The power relationship in the equation is:

[0060] Formula 21;

[0061] By decoupling the control of active and reactive power, more precise and faster control and adjustment of active and reactive power can be achieved, thereby improving the stability and controllability of the grid-type inverter.

[0062] like Figure 2 It includes the active power loop and reactive power loop mentioned above. Its droop control adjusts the inverter's output power by simulating the frequency regulation and voltage regulation characteristics of a synchronous generator to maintain voltage and frequency stability. Its expression is:

[0063] Formula 22;

[0064] Formula 23;

[0065] , These represent the reference and actual values ​​of the inverter's angular velocity, respectively. , These represent the reference value and the actual output power of the inverter, respectively. , These represent the reference value and the actual value of the inverter terminal voltage, respectively. , These represent the reference value and the actual output power of the inverter, respectively. , These represent the active power droop factor and the reactive power droop factor of the inverter, respectively.

[0066] To improve the stability of grid-connected inverters during high and low voltage ride-through and reduce fluctuations and spikes in active and reactive power during fault ride-through, VSG control is adopted, a closed-loop circuit is added to the reactive power loop, a reference voltage amplitude limiting circuit is added, and fractional-order control is used in the reactive power loop, as expressed by the formula:

[0067] Formula 24;

[0068] Formula 25;

[0069] Formula 26;

[0070] Compared to traditional systems, the reactive power loop employs fractional-order control, resulting in more precise control and adjustment of reactive power, improved robustness, and the addition of closed-loop inertia control. This allows for better negative feedback of reactive power, enabling timely adjustments to support the grid connection voltage during high and low voltage ride-throughs. It also ensures that active power tracks the given reference value, maintaining grid active power without needing to reduce active power to support voltage, thus achieving high and low voltage ride-throughs without disconnecting from the grid. Simultaneously, a reference voltage is output from the reactive power loop. A limiting mechanism is added to prevent excessive active power spikes during high- and low-voltage ride-throughs from causing excessive impact on the power grid.

[0071] like Figure 3 It includes the voltage loop and current loop, and the reference voltage of the voltage loop. The voltage loop, derived from the reactive power loop output, is expressed by the formula:

[0072] Formula 27;

[0073] The current loop is expressed by the formula:

[0074] Formula 28;

[0075] Because a reference voltage limiting circuit is added to the reactive power loop, the active voltage in the voltage loop is controlled, and fractional-order control is used in the voltage and current loops. Compared with traditional integer order Fractional-order control enables more precise voltage and current control, enhances robustness against grid disturbances, and improves voltage support, especially during zero-voltage ride-through, enabling the grid connection point voltage to be supported up to 90% without reducing active power. Secondly, by adding an active current limiting circuit to the current loop, the spikes generated by active power during high and low voltage ride-through are further suppressed, while the spikes of the grid connection point current are weakened, reducing the impact on the power grid.

[0076] The implementation steps of the device specifically include the following steps:

[0077] Step 1: Obtain the small-signal operation matrix through the power decoupling loop;

[0078] Step 2: Perform operations on the small signal input with the small signal operation matrix to obtain the reference voltage small signal. With small angle signal ;

[0079] Step 3: Obtain the angle from the active power loop. The small-signal matrix operation yields the angle small signal. Adding them together yields ;

[0080] Step 4: Use fractional-order control and add closed-loop control in the reactive power loop;

[0081] Step 5: Convert the voltage obtained from the reactive power loop. Small signal of reference voltage Add them together to get the reference voltage. ;

[0082] Step 6: Add a reference voltage limiting circuit to the reactive power loop output stage;

[0083] Step 7: Employ fractional-order control in the voltage and current loop. Furthermore, a reference active current limiting circuit is added to the current loop.

[0084] This invention provides a method and apparatus for supporting high and low voltage ride-through stability of a grid-connected inverter with fractional-order control and power decoupling, belonging to the field of grid-connected inverter control. The method performs fractional-order control and decoupling control on the active and reactive power of the grid-connected inverter; compares the real-time values ​​of active and reactive power with reference values; employs fractional-order control in the reactive power loop and adds closed-loop control (inertia control); and derives the voltage loop reference voltage based on the relationship between Pf and QV. and angular frequency When the grid voltage experiences a low (high) voltage ride-through, reactive power increases (decreases) to actively support the grid connection point voltage, while the grid connection point current increases (decreases) to maintain active power tracking the given value, simultaneously supporting the grid connection point voltage. Fractional-order control is employed in the voltage and current loops to achieve more precise control of voltage and current. Active current is limited in the current loop to prevent large instantaneous spikes in current and power. The reference voltage output from the power loop to the voltage loop is based on the grid voltage's rated value. This invention limits the voltage fluctuations to suppress large instantaneous spikes in active power generated during grid voltage dips. It optimizes the support effect of the grid connection point voltage during high- and low-voltage ride-through, maintains more accurate active power tracking of the reference value, suppresses spikes in active power and grid connection point current during grid voltage steps, achieves more precise and stable control of voltage and current, and better facilitates high- and low-voltage ride-through.

[0085] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0086] 1. The active power can be adjusted in a timely manner and accurately track the given reference value during high and low voltage ride-through.

[0087] 2. The voltage support effect at the grid connection point is better during high and low voltage ride-through.

[0088] 3. The active power spike during the high-low voltage transition is smaller.

[0089] 4. The voltage and current spikes at the grid connection point during the high and low voltage transition are effectively suppressed, protecting the power grid from the impact of large voltage and current.

[0090] 5. During zero-voltage ride-through, the active power peak can be controlled within 1.1 times the rated value, and the active power setpoint (full load) can be maintained without disconnecting from the grid, without reducing the active power, and the grid connection point voltage support effect reaches 90%. In addition, after the fault is repaired, it can be quickly adjusted back to the rated value.

[0091] 6. Compared with the traditional network configuration of integer-order PI control, it has better robustness and controllability when subjected to disturbances. Attached Figure Description

[0092] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0093] Appendix Figure 1 This is a schematic diagram of a grid-connected inverter system based on fractional-order control power decoupling in an embodiment of the present invention.

[0094] Appendix Figure 2This is a schematic diagram of the power decoupling loop in an embodiment of the present invention, illustrating the coupling mechanism between active and reactive power.

[0095] Appendix Figure 3 This is a schematic diagram of the voltage loop and current loop in an embodiment of the present invention. Detailed Implementation

[0096] As shown in the figure, a fractional-order control power decoupling grid-connected inverter voltage ride-through support method is used to support the high and low voltage ride-through stability of grid-connected inverters (GFM). This method is applied to inverter systems containing reactive power loops, active power loops, power decoupling loops, voltage open loops, and current closed loops. By generating reference voltages and angles for the voltage and current loops through power decoupling and fractional-order control power loops, and by adding closed-loop control and reference voltage limiting components to the reactive power loop, and by employing fractional-order control and adding active current limiting components to the voltage and current loops, this method effectively supports the grid connection point voltage during high and low voltage ride-through, achieving precise voltage and current control, effectively suppressing voltage and current spikes at the grid connection point, maintaining more accurate active power tracking of the given reference value, reducing active power spikes, and improving the stability of the grid-connected inverter.

[0097] The method employs fractional-order control and decoupling control of the inverter's active and reactive power; compares the real-time values ​​of active and reactive power with reference values; uses fractional-order control in the reactive power loop and adds closed-loop control (inertia control); and derives the voltage loop reference voltage based on the relationship between Pf and QV. and angular frequency When the grid voltage experiences a low / high voltage ride-through, the system actively supports the grid connection point voltage by increasing / decreasing reactive power, and maintains active power tracking the given value by increasing / decreasing the grid connection point current, while simultaneously supporting the grid connection point voltage. Fractional-order control is employed in the voltage and current loops to achieve more precise control of voltage and current. Active current is limited in the current loop to prevent large instantaneous spikes in current and power. The reference voltage output from the power loop to the voltage loop is adjusted based on the grid voltage's rated value. Limiting is implemented to suppress large instantaneous spikes in active power generated during grid voltage dips. The support effect of grid connection point voltage during high and low voltage ride-through is optimized to maintain more accurate active power tracking of the reference value, suppress spikes in active power and grid connection point current generated during grid voltage steps, achieve more precise and stable control of voltage and current, and better realize high and low voltage ride-through.

[0098] A fractional-order control power decoupling grid-connected inverter voltage ride-through support device is provided. This device utilizes the fractional-order control power decoupling grid-connected inverter voltage ride-through support method described above. The device is a grid-connected inverter system comprising a reactive power loop, an active power loop, a power decoupling loop, an open-loop voltage system (voltage loop), and a closed-loop current system (current loop). The active power loop, reactive power loop, and power decoupling loop employ fractional-order control to jointly achieve power decoupling and output a reference voltage. and angular frequency The voltage open-loop and current closed-loop of the fractional-order control are used as reference values.

[0099] The reactive power loop adopts fractional-order control and adds closed-loop control (inertia control). The small signal generated by the reactive power and active power through the power decoupling loop is added to the output values ​​of the active power loop and the reactive power loop. At the same time, an amplitude limiter is added to the output reference voltage of the reactive power loop.

[0100] Fractional-order control is used in the voltage open-loop and current closed-loop, and a limiting circuit is added to the reference active current.

[0101] like Figure 1 As shown, the grid-connected inverter system is a grid-connected inverter system based on fractional-order control power decoupling, including a main circuit, dq coordinate transformation, active power loop, reactive power loop, voltage open loop, current closed loop, PWM control and power decoupling loop;

[0102] The main circuit is a three-phase full-bridge controlled inverter circuit connected to the power grid, including parasitic resistance. Filter inductor Filter capacitor Line inductance and line impedance The DC voltage is converted by a three-phase inverter and then filtered by an LC filter before being connected to the grid at the grid connection point. For inverter output current, This refers to the grid connection point current.

[0103] The dq coordinate transformation performs voltage and current transformation, and the transformed values ​​are calculated in the open-loop voltage control and closed-loop current control of the fractional-order control. The reactive power loop adopts fractional-order control and adds closed-loop and reference voltage limiting links. The output values ​​in the active power loop and reactive power loop are added to the small-signal values ​​obtained through the small-signal calculation matrix in the power decoupling loop to obtain the reference angle. and reference voltage ;

[0104] The current closed-loop control method includes an active current limiting method; the PWM stage controls the switching of the inverter switching transistors.

[0105] like Figure 2 As shown, the power decoupling loop achieves decoupling control by analyzing the coupling mechanism between active and reactive power; specifically:

[0106] The active power control loop of the virtual synchronous generator (VSG) in the inverter system is expressed by the following formula:

[0107] Formula 1;

[0108] Formula 2;

[0109] Formula 3;

[0110] The reactive power control loop of the inverter system can be expressed by the following formula:

[0111] Formula 4;

[0112] The small-signal model for its control is derived from formulas 1, 2, 3, and 4:

[0113] Formula 5;

[0114] When the inverter system is operating, the voltage phase difference between its converter terminal and the grid node is expressed by the formula:

[0115] Formula 6;

[0116] The state variables of VSG are defined as follows:

[0117] Formula 7;

[0118] The output of VSG is:

[0119] Formula 8;

[0120] Combining equations 5, 7, and 8, we obtain the open-loop state-space model of VSG as follows:

[0121] Formula 9;

[0122] The output matrix of VSG is represented as follows:

[0123] Formula 10;

[0124] The power transmitted through a three-phase line is expressed as:

[0125] Formula 11;

[0126] Expanding linearization formula 11 using a multivariate Taylor series yields the linearized model for power transmission as follows:

[0127] Formula 12;

[0128] The parameters of the linearized power transfer model are:

[0129] Formula 13;

[0130] , , and To linearize the model parameters, coupling elements and and Positive correlation; and their interrelationship leads to mutual coupling between the dynamics of active and reactive power control;

[0131] By ignoring the phase of the grid voltage For higher-order transient disturbances, assuming the small phase difference signal is equal to the small phase signal of the VSG output voltage, then:

[0132] Formula 14;

[0133] Since the control bandwidth of the voltage loop is much wider than that of the power loop, the dynamic characteristics of the voltage loop can be ignored when focusing on the power loop, and it can be assumed that the voltage loop can perfectly follow the reference, i.e.:

[0134] Formula 15;

[0135] Combining formulas 9, 10, 12, 14, and 15, the closed-loop state-space model of VSG is obtained as follows:

[0136] Formula 16;

[0137] Analysis of the VSG state-space model reveals the coupling mechanism between active and reactive power control. This coupling can be eliminated by designing an additional controller.

[0138] The closed-loop system after PQ decoupling is expressed by Equation 17 as follows:

[0139] Formula 17;

[0140] The power control loop uses full-state feedback control of the VSG to eliminate the coupling between active and reactive power control.

[0141] In the full-state feedback control of VSG, the output matrix n of the power control is modified to be the sum of the original VSG control output and the state variable feedback, specifically in the form of:

[0142] Formula 18;

[0143] Combining formulas 9, 12, 14, 15, and 18, the state-space model of the VSG closed-loop system incorporating full-state feedback is obtained as follows:

[0144] Formula 19;

[0145] Formula 19 is the same as Formula 17; by solving them simultaneously, we get:

[0146] Formula 20;

[0147] The parameters in Formula 20 are Figure 2 The values ​​of the small and medium signal operation matrices, and the corresponding Figure 2 The power relationship in the equation is:

[0148] Formula 21;

[0149] By decoupling the control of active and reactive power, more precise and faster control and adjustment of active and reactive power can be achieved, thereby improving the stability and controllability of the grid-type inverter.

[0150] like Figure 2 It includes the active power loop and reactive power loop mentioned above. Its droop control adjusts the inverter's output power by simulating the frequency regulation and voltage regulation characteristics of a synchronous generator to maintain voltage and frequency stability. Its expression is:

[0151] Formula 22;

[0152] Formula 23;

[0153] , These represent the reference and actual values ​​of the inverter's angular velocity, respectively. , These represent the reference value and the actual output power of the inverter, respectively. , These represent the reference value and the actual value of the inverter terminal voltage, respectively. , These represent the reference value and the actual output power of the inverter, respectively. , These represent the active power droop factor and the reactive power droop factor of the inverter, respectively.

[0154] To improve the stability of grid-connected inverters during high and low voltage ride-through and reduce fluctuations and spikes in active and reactive power during fault ride-through, VSG control is adopted, a closed-loop circuit is added to the reactive power loop, a reference voltage amplitude limiting circuit is added, and fractional-order control is used in the reactive power loop, as expressed by the formula:

[0155] Formula 24;

[0156] Formula 25;

[0157] Formula 26;

[0158] Compared to traditional systems, the reactive power loop employs fractional-order control, resulting in more precise control and adjustment of reactive power, improved robustness, and the addition of closed-loop inertia control. This allows for better negative feedback of reactive power, enabling timely adjustments to support the grid connection voltage during high and low voltage ride-throughs. It also ensures that active power tracks the given reference value, maintaining grid active power without needing to reduce active power to support voltage, thus achieving high and low voltage ride-throughs without disconnecting from the grid. Simultaneously, a reference voltage is output from the reactive power loop. A limiting mechanism is added to prevent excessive active power spikes during high- and low-voltage ride-throughs from causing excessive impact on the power grid.

[0159] like Figure 3 It includes the voltage loop and current loop, and the reference voltage of the voltage loop. The voltage loop, derived from the reactive power loop output, is expressed by the formula:

[0160] Formula 27;

[0161] The current loop is expressed by the formula:

[0162] Formula 28;

[0163] Because a reference voltage limiting circuit is added to the reactive power loop, the active voltage in the voltage loop is controlled, and fractional-order control is used in the voltage and current loops. Compared with traditional integer order Fractional-order control enables more precise voltage and current control, enhances robustness against grid disturbances, and improves voltage support, especially during zero-voltage ride-through, enabling the grid connection point voltage to be supported up to 90% without reducing active power. Secondly, by adding an active current limiting circuit to the current loop, the spikes generated by active power during high and low voltage ride-through are further suppressed, while the spikes of the grid connection point current are weakened, reducing the impact on the power grid.

[0164] The implementation steps of the device specifically include the following steps:

[0165] Step 1: Obtain the small-signal operation matrix through the power decoupling loop;

[0166] Step 2: Perform operations on the small signal input with the small signal operation matrix to obtain the reference voltage small signal. With small angle signal ;

[0167] Step 3: Obtain the angle from the active power loop. The small-signal matrix operation yields the angle small signal. Adding them together yields ;

[0168] Step 4: Use fractional-order control and add closed-loop control in the reactive power loop;

[0169] Step 5: Convert the voltage obtained from the reactive power loop. Small signal of reference voltage Add them together to get the reference voltage. ;

[0170] Step 6: Add a reference voltage limiting circuit to the reactive power loop output stage;

[0171] Step 7: Employ fractional-order control in the voltage and current loop. Furthermore, a reference active current limiting circuit is added to the current loop.

[0172] The technical solution provided in this example is a grid-connected inverter system based on fractional-order control power decoupling. The system includes a reactive power loop, an active power loop, a power decoupling loop, an open-loop voltage circuit, and a closed-loop current circuit. The active power loop, reactive power loop, and power decoupling loop jointly achieve power decoupling using fractional-order control. Closed-loop control and reference voltage limiting are added to the reactive power loop, and a reference voltage is output. and angular frequency It is used as a reference value in the open-loop voltage and closed-loop current of fractional-order control.

[0173] The above embodiments are one of the implementation methods of the present invention, but the implementation methods of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A fractional-order control power decoupling grid-connected inverter voltage ride-through support method, used for high and low voltage ride-through stability support of grid-connected inverters (GFM), characterized in that: The method is used in inverter systems containing reactive power loops, active power loops, power decoupling loops, voltage open loops, and current closed loops. It generates reference voltages and angles for the voltage and current loops through power decoupling and fractional-order control of the power loop. Furthermore, it adds closed-loop control and reference voltage limiting links to the reactive power loop, and employs fractional-order control and adds active current limiting links to the voltage and current loops. This effectively supports the grid connection point voltage during high and low voltage crossovers, effectively suppresses grid connection point voltage and current spikes, maintains active power, and reduces active power spikes.

2. The fractional-order control power decoupling grid inverter voltage ride-through support method according to claim 1, characterized in that: The method employs fractional-order control and decoupling control of the inverter's active and reactive power; compares the real-time values ​​of active and reactive power with reference values; uses fractional-order control in the reactive power loop and adds closed-loop control; and derives the voltage loop reference voltage based on the relationship between Pf and QV. and angular frequency When the grid voltage experiences a low / high voltage ride-through, the system actively supports the grid connection point voltage by increasing / decreasing reactive power, and maintains active power tracking the given value by increasing / decreasing the grid connection point current, while simultaneously supporting the grid connection point voltage. Fractional-order control is employed in the voltage and current loops. Active current is limited in the current loop to prevent large instantaneous spikes in current and power. The reference voltage output from the power loop to the voltage loop is adjusted based on the grid voltage's rated value. Limiting is implemented to suppress large instantaneous spikes in active power generated during grid voltage dips.

3. A fractional-order control power decoupled grid inverter voltage ride-through support device, using the fractional-order control power decoupled grid inverter voltage ride-through support method as described in claim 2, characterized in that: The device is a grid-connected inverter system comprising a reactive power loop, an active power loop, a power decoupling loop, an open-loop voltage circuit, and a closed-loop current circuit. The active power loop, reactive power loop, and power decoupling loop employ fractional-order control to jointly achieve power decoupling and output a reference voltage. and angular frequency The voltage open-loop and current closed-loop of the fractional-order control are used as reference values.

4. The fractional-order control power decoupling grid inverter voltage ride-through support device according to claim 3, characterized in that: The reactive power loop adopts fractional-order control and adds closed-loop control. The small signal generated by the power decoupling loop is added to the output values ​​of the active power loop and the reactive power loop. At the same time, an amplitude limiter is added to the output reference voltage of the reactive power loop.

5. The fractional-order control power decoupling grid inverter voltage ride-through support device according to claim 4, characterized in that: Fractional-order control is used in the voltage open-loop and current closed-loop, and a limiting circuit is added to the reference active current.

6. The fractional-order control power decoupling grid inverter voltage ride-through support device according to claim 5, characterized in that: The grid-connected inverter system is a grid-connected inverter system based on fractional-order control power decoupling, including a main circuit, dq coordinate transformation, active power loop, reactive power loop, voltage open loop, current closed loop, PWM control and power decoupling loop; The main circuit is a three-phase full-bridge controlled inverter circuit connected to the power grid, including parasitic resistance. Filter inductor Filter capacitor Line inductance and line impedance The DC voltage is converted by a three-phase inverter and then filtered by an LC filter before being connected to the grid at the grid connection point. For inverter output current, This refers to the grid connection point current. The dq coordinate transformation performs voltage and current transformation, and the transformed values ​​are calculated in the open-loop voltage control and closed-loop current control of the fractional-order control. The reactive power loop adopts fractional-order control and adds closed-loop and reference voltage limiting links. The output values ​​in the active power loop and reactive power loop are added to the small-signal values ​​obtained through the small-signal calculation matrix in the power decoupling loop to obtain the reference angle. and reference voltage ; The current closed-loop control method includes an active current limiting method; the PWM stage controls the switching of the inverter switching transistors.

7. The fractional-order control power decoupling grid inverter voltage ride-through support device according to claim 6, characterized in that: The power decoupling loop achieves decoupling control by analyzing the coupling between active and reactive power; specifically: The active power control loop of the virtual synchronous generator (VSG) in the inverter system is expressed by the following formula: Official 1; Official 2; Official 3; The reactive power control loop of the inverter system can be expressed by the following formula: Official 4; The small-signal model for its control is derived from formulas 1, 2, 3, and 4: Official 5; When the inverter system is operating, the voltage phase difference between its converter terminal and the grid node is expressed by the formula: Official 6; The state variables of VSG are defined as follows: Official 7; The output of VSG is: Official 8; Combining equations 5, 7, and 8, we obtain the open-loop state-space model of VSG as follows: Official 9; The output matrix of VSG is represented as follows: Official 10; The power transmitted through a three-phase line is expressed as follows: Official 11; Expanding Equation 11 using a multivariate Taylor series, we obtain the linearized model for power transfer as follows: Official 12; The parameters of the linearized power transfer model are: Official 13; , , and To linearize the model parameters, coupling elements and and Positive correlation; and their interrelationship leads to mutual coupling between the dynamics of active and reactive power control; By ignoring the phase of the grid voltage For higher-order transient disturbances, assuming the small phase difference signal is equal to the small phase signal of the VSG output voltage, then: Official 14; When focusing on the power loop, neglecting the dynamic characteristics of the voltage loop, and assuming that the voltage loop can perfectly follow the reference, we have: Official 15; Combining formulas 9, 10, 12, 14, and 15, the closed-loop state-space model of VSG is obtained as follows: Official 16; The purpose is to eliminate the coupling between active and reactive power control by adding an additional controller; The closed-loop system after PQ decoupling is expressed by Equation 17 as follows: Official 17; The power control loop uses full-state feedback control of the VSG to eliminate the coupling between active and reactive power control.

8. The fractional-order control power decoupling grid inverter voltage ride-through support device according to claim 7, characterized in that: In the full-state feedback control of VSG, the output matrix n of the power control is modified to be the sum of the VSG control output and the state variable feedback, specifically in the form of: Official 18; Combining formulas 9, 12, 14, 15, and 18, the state-space model of the VSG closed-loop system incorporating full-state feedback is obtained as follows: Formula 19; Solving equations 19 and 17 simultaneously yields: Official 20; The parameters in Formula 20 are the values ​​of the small-signal operation matrix, and the corresponding power relationship is: Official 21; By decoupling the control of active and reactive power, more precise and faster control and adjustment of active and reactive power can be achieved, thereby improving the stability and controllability of the grid-type inverter.

9. The fractional-order control power decoupling grid inverter voltage ride-through support device according to claim 8, characterized in that: The active power loop and reactive power loop mentioned above, whose droop control simulates the frequency regulation and voltage regulation characteristics of a synchronous generator, adjust the inverter's output power to maintain voltage and frequency stability. The expression for this is: Official 22; Official 23; , These represent the reference and actual values ​​of the inverter's angular velocity, respectively. , These represent the reference value and the actual output power of the inverter, respectively. , These represent the reference value and the actual value of the inverter terminal voltage, respectively. , These represent the reference value and the actual output power of the inverter, respectively. , These represent the active power droop factor and the reactive power droop factor of the inverter, respectively. VSG control is adopted, and a closed-loop circuit is added to the reactive power loop. A reference voltage amplitude limiting circuit is added, and fractional-order control is used in the reactive power loop, as expressed by the formula: Official 24; Official 25; Official 26; The reactive power loop employs fractional-order control and increases closed-loop inertia control, enabling negative feedback of reactive power. During high and low voltage ride-throughs, adjustments are made to support the grid connection point voltage, ensuring active power can track the given reference value and maintain grid active power. The reactive power loop outputs a reference voltage. A limiting mechanism is added to prevent excessive active power spikes during high- and low-voltage ride-throughs from causing excessive impact on the power grid. Reference voltage of voltage loop The voltage loop from the reactive power loop output is expressed by the formula: Official 27; The current loop is expressed by the formula: Official 28; Fractional-order control is used in the voltage and current loops. By adding an active current limiting circuit to the current loop, the spikes generated by active power during high and low voltage ride-through are further suppressed, while the spikes of the grid connection point current are also weakened.

10. The fractional-order control power decoupling grid inverter voltage ride-through support device according to claim 9, characterized in that: The implementation of the device specifically includes the following steps: Step 1: Obtain the small-signal operation matrix through the power decoupling loop; Step 2: Perform operations on the small signal input with the small signal operation matrix to obtain the reference voltage small signal. With small angle signal ; Step 3: Calculate the angle obtained from the active power loop. The small-signal matrix operation yields the angle small signal. Adding them together yields ; Step 4: Use fractional-order control and add closed-loop control in the reactive power loop; Step 5: Convert the voltage obtained from the reactive power loop. Small signal of reference voltage Add them together to get the reference voltage. ; Step 6: Add a reference voltage limiting circuit to the reactive power loop output stage; Step 7: Employ fractional-order control in the voltage and current loop. Furthermore, a reference active current limiting circuit is added to the current loop.

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