Virtual synchronous machine low voltage ride through control method based on power angle coefficient flexible adjustment

Abstract

This application provides a low-voltage ride-through control method for a virtual synchronous machine based on flexible adjustment of the power angle coefficient. The method includes: obtaining the current-limiting circle of the virtual synchronous machine based on grid voltage, maximum short-circuit current, and equivalent reactance; obtaining the constant reactive power characteristic circle of the virtual synchronous machine based on grid voltage, reactive power, and equivalent reactance; obtaining the first boundary point representing the intersection of the current-limiting circle and the constant reactive power characteristic circle, based on the non-negativity constraint of the active power angle, the current-limiting circle, and the constant reactive power characteristic circle, and obtaining the internal potential power angle in conjunction with the power angle coefficient; obtaining the internal potential amplitude based on grid voltage, internal potential power angle, equivalent reactance, and maximum short-circuit current; and controlling the virtual synchronous machine based on the internal potential power angle and internal potential amplitude. This method meets national standards for reactive power support requirements and equipment overcurrent capacity constraints, achieving optimal allocation of active and reactive power output, thereby improving the inverter capacity utilization rate of the virtual synchronous machine and the fault ride-through reliability of the power system.

Description

Technical Field

[0001] This application relates to the field of power system grid connection and fault control technology, specifically to a low-voltage ride-through control method for a virtual synchronous machine based on flexible adjustment of the power angle coefficient. Background Technology

[0002] With the increasing penetration rate of renewable energy generation, the inertia and damping level of the power grid have significantly decreased, posing a severe challenge to the stable operation of the power system. Virtual Synchronous Generator (VSG) technology, by simulating the rotor motion equations and voltage regulation characteristics of a synchronous generator, provides the necessary inertial support and damping capabilities to the power grid, enabling inverters to possess frequency and voltage characteristics similar to synchronous generators. This improves the frequency stability of microgrids and high-proportion renewable energy systems, and has therefore attracted widespread attention. However, limited by the overcurrent withstand capability of power electronic semiconductor devices (typically 1.2 to 1.5 times the rated current), excessive fault current can easily trigger converter protection actions or even grid disconnection, further exacerbating system operational risks. Therefore, effective current limiting measures must be applied to the VSG to ensure equipment safety and system stability during faults.

[0003] Currently, common VSG current limiting methods mainly include virtual impedance methods, current limiter methods, and methods that limit voltage reference values. Virtual impedance methods limit current by increasing the equivalent output impedance, but may affect steady-state power regulation and dynamic response. Current limiter methods directly apply amplitude limits to the current loop, but are prone to waveform distortion and control mode switching shocks. Currently, current limiting control strategies often use a fixed power angle to set voltage commands, achieving maximum voltage support while keeping the power angle unchanged before and after the fault. While these methods can achieve reactive power support at the current power angle, the active power output is limited by the fixed power angle, making flexible adjustment difficult and unable to meet the differentiated active power requirements in actual operation. Furthermore, these methods lack coordinated optimization of the potential amplitude and phase during the fault period, which may lead to a decrease in system dynamic performance or a deterioration in stability. Summary of the Invention

[0004] This application addresses the problems existing in the prior art by providing a low-voltage ride-through control method for a virtual synchronous machine based on flexible adjustment of the power angle coefficient, which can balance current safety limits and flexible power regulation during grid faults. Under the premise of meeting the national standards for reactive power support requirements and equipment overcurrent capacity constraints, this method achieves the optimal allocation of active and reactive power output, thereby improving the utilization rate of the inverter capacity of the virtual synchronous machine and the fault ride-through reliability of the power system.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: A low-voltage ride-through control method for a virtual synchronous machine based on flexible adjustment of the power angle coefficient, comprising: Collect grid voltage; obtain the reactive power output of the virtual synchronous machine based on the grid voltage; The power angle coefficient, equivalent reactance, and maximum short-circuit current of the virtual synchronous machine are obtained respectively. The current-limiting circle of the virtual synchronous machine is obtained based on the grid voltage, maximum short-circuit current, and equivalent reactance; the constant reactive power characteristic circle of the virtual synchronous machine is obtained based on the grid voltage, reactive power, and equivalent reactance. Based on the non-negative power angle constraint of active power, the first boundary point is obtained according to the current limiting circle and the constant reactive power characteristic circle; the first boundary point represents the intersection of the current limiting circle and the constant reactive power characteristic circle that satisfy the non-negative power angle constraint. The internal potential power angle is obtained based on the power angle coefficient and the first boundary point; the internal potential amplitude is obtained based on the grid voltage, internal potential power angle, equivalent reactance, and maximum short-circuit current. The virtual synchronous machine is controlled based on the internal potential power angle and the internal potential amplitude.

[0006] In some embodiments, the virtual synchronous machine is controlled based on the internal potential power angle and the internal potential amplitude, including: Obtain the normal operating angle of the virtual synchronizer; The reference phase angle is obtained based on the normal operating power angle and the internal potential power angle. The active power output of the virtual synchronous machine is obtained based on the grid voltage; The output voltage phase angle of the virtual synchronous machine is obtained based on the reference phase angle and active power. The output voltage amplitude of the virtual synchronous machine is obtained based on the reactive power and internal potential amplitude. The output internal potential of the virtual synchronous machine is obtained based on the output voltage phase angle and output voltage amplitude.

[0007] In some embodiments, the current-limiting circle of the virtual synchronous machine is obtained based on the grid voltage, maximum short-circuit current, and equivalent reactance, including: The first center is obtained based on the grid voltage. The horizontal axis of the first center is the grid voltage, and the vertical axis of the first center is 0. The first center represents the center of the current-limiting circle. The first radius is obtained by multiplying the maximum short-circuit current by the equivalent reactance. The first radius represents the radius of the current-limiting circle. The flow-limiting circle is obtained based on the first center and the first radius.

[0008] In some embodiments, the constant reactive power characteristic circle of the virtual synchronous machine is obtained based on the grid voltage, reactive power, and equivalent reactance, including: The second center is obtained based on the grid voltage. The horizontal axis of the second center is half of the grid voltage, and the vertical axis of the second center is 0. The second center represents the center of the constant reactive power characteristic circle. The first intermediate term is obtained by multiplying reactive power and equivalent reactance, and the second intermediate term is obtained by squaring half of the grid voltage. The second radius is obtained by summing the first and second intermediate terms and taking the square root. The second radius represents the radius of the constant reactive power characteristic circle. The constant reactive power characteristic circle is obtained based on the second center and the second radius.

[0009] In some embodiments, the internal potential power angle is obtained based on the power angle coefficient and the first boundary point, including: The first power angle is obtained based on the first boundary point, and the first power angle represents the internal potential power angle of the virtual synchronous machine corresponding to the first boundary point. The internal potential power angle is obtained by multiplying the power angle coefficient by the first power angle.

[0010] In some embodiments, the internal potential amplitude is: ; In the formula, The magnitude of the internal potential. This is the grid voltage. The internal potential power angle, The equivalent reactance of the virtual synchronous machine. This is the maximum short-circuit current.

[0011] In some embodiments, the virtual synchronizer includes a power calculator and a power outer loop; The power calculator is used to obtain the active and reactive power output of the virtual synchronous machine based on the grid voltage; The power outer loop is used to obtain the reference phase angle based on the normal operating power angle and the internal potential power angle, to obtain the output voltage phase angle of the virtual synchronous machine based on the reference phase angle and active power, to obtain the output voltage amplitude of the virtual synchronous machine based on the reactive power and the internal potential amplitude, and to obtain the output internal potential of the virtual synchronous machine based on the output voltage phase angle and the output voltage amplitude.

[0012] In some embodiments, the power outer loop includes an active frequency loop, a reactive voltage loop, and a voltage synthesizer; The active frequency loop is used to obtain the reference phase angle based on the normal operating power angle and the internal potential power angle, and to obtain the output voltage phase angle of the virtual synchronous machine based on the reference phase angle and the active power. The reactive voltage loop is used to obtain the output voltage amplitude of the virtual synchronous machine based on the reactive power and internal potential amplitude. The voltage synthesizer is used to obtain the output internal potential of the virtual synchronous machine based on the output voltage phase angle and output voltage amplitude.

[0013] In some embodiments, the virtual synchronous machine further includes a voltage-current inner loop, a pulse width modulator, and an inverter; The voltage-current inner loop is used to obtain the modulation voltage based on the output internal potential; A pulse width modulator is used to obtain a pulse modulated wave based on a modulation voltage; The inverter is installed on the power grid. The inverter is used to obtain three-phase AC power based on pulse modulation waves, and the three-phase AC power is connected to the power grid.

[0014] In some embodiments, controlling the virtual synchronizer based on the internal potential power angle and the internal potential amplitude further includes: The modulation voltage is obtained based on the output internal potential; The pulse modulation wave is obtained based on the modulation voltage; Three-phase alternating current is obtained based on pulse modulation waves, and the three-phase alternating current is connected to the power grid.

[0015] Compared with the prior art, this application has the following advantages: This application fully considers the inverter current limiting capability limitations of virtual synchronous machines in low voltage ride-through scenarios, the reactive power support requirements of national standards, and the system power output requirements. Combining the characteristics of power angle, voltage, and power, it introduces an adaptive power angle coefficient to establish the relationship between internal potential, power angle, and power by constructing the feasible region of the internal potential of the virtual synchronous machine. Combined with power outer loop blocking, phase compensation, and amplitude switching control strategies, it achieves the maximum capacity output of the inverter, forming a low voltage ride-through control method for virtual synchronous machines that takes into account national standard compliance, current limiting safety, and flexible power adjustment. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the low-voltage ride-through control method for a virtual synchronous machine based on flexible adjustment of the power angle coefficient in the embodiments of this application. Figure 2 This is a schematic diagram of the process of controlling the virtual synchronous machine based on the internal potential power angle and internal potential amplitude in an embodiment of this application; Figure 3 This is a schematic diagram of the structure of the virtual synchronous machine grid-connected system simulation model in the embodiments of this application; Figure 4 This is a control block diagram of the power outer loop in an embodiment of this application; Figure 5 This is a simplified schematic diagram of the simulation model of the virtual synchronous machine grid-connected system in the embodiments of this application; Figure 6 This is a diagram showing the current-limiting circle after a fault in the embodiments of this application, and the equivalent circuit vector diagram of the virtual synchronous machine considering the current-limiting capability. Figure 7 This is a schematic diagram of the feasible region of the internal potential of the virtual synchronizer after a fault in an embodiment of this application. Figure 8 In this embodiment of the application, the voltage drops to 0.4. pu ,and k Simulated waveform of active power output by the virtual synchronous machine when =1; Figure 9 In this embodiment of the application, the voltage drops to 0.4. pu ,and k When =1, the simulated waveform of reactive power output by the virtual synchronous machine; Figure 10 In this embodiment of the application, the voltage drops to 0.4. pu ,and k When =1, the simulated voltage waveform of the grid connection point of the virtual synchronous machine; Figure 11 In this embodiment of the application, the voltage drops to 0.4. pu ,and k Simulated waveform of short-circuit current of virtual synchronous machine when =1; Figure 12 In this embodiment of the application, the voltage drops to 0.4. pu ,and k When =1, the power angle simulation waveform diagram; Figure 13 In this embodiment of the application, the voltage drops to 0.4. pu ,and k Simulated waveform of active power output by the virtual synchronous machine when = 0.5; Figure 14 In this embodiment of the application, the voltage drops to 0.4. pu ,and k Simulated waveform of reactive power output by the virtual synchronous machine when =0.5; Figure 15 In this embodiment of the application, the voltage drops to 0.4. pu ,and k Simulated waveform of the grid connection point voltage of the virtual synchronous machine when =0.5; Figure 16 In this embodiment of the application, the voltage drops to 0.4. pu ,and k Simulated waveform of short-circuit current of virtual synchronous machine when =0.5; Figure 17 In this embodiment of the application, the voltage drops to 0.4. pu ,and k The waveform diagram of the power angle simulation when =0.5.

[0017] The attached figures are labeled as follows: 10, power calculator; 20, power outer loop; 21, active frequency loop; 22, reactive voltage loop; 23, voltage synthesizer; 30, voltage and current inner loop; 40, pulse width modulator; 50, inverter; 60, current limiting circle; 70, constant reactive characteristic circle. Detailed Implementation

[0018] To clearly illustrate the technical features of this solution, the implementation methods of this application will be described in detail below with reference to the accompanying drawings and embodiments. This will allow for a full understanding and implementation of how this application uses technical means to solve technical problems and achieve corresponding technical effects. The embodiments of this application and the various features within them can be combined with each other without conflict, and the resulting technical solutions are all within the protection scope of this application.

[0019] To address the problems in the background technology, there is an urgent need for a virtual synchronous machine control method that can balance current safety limits and flexible power adjustment during grid faults. Under the premise of meeting the national standards for reactive power support requirements and equipment overcurrent capacity constraints, it can achieve the optimal allocation of active and reactive power output, thereby improving the utilization rate of the inverter capacity of the virtual synchronous machine and the fault ride-through reliability of the power system.

[0020] It is worth noting that during normal operation of the power system, the grid voltage is monitored in real time. In actual operation, the three-phase voltage of the grid is monitored in real time. When a voltage dip is detected and the subsequent voltage drop is lower than the dip threshold, a grid fault is determined, triggering the virtual synchronous machine low-voltage ride-through control method based on flexible adjustment of the power angle coefficient proposed in this application. Typically, the grid voltage dip threshold is set to 0.9. pu , pu Per-unit values ​​are a dimensionless method of representing relative values. When... hour, The voltage per unit value of the grid after the fault occurs. The grid fault triggers the low voltage ride-through control method of the virtual synchronous machine based on flexible adjustment of the power angle coefficient proposed in this application.

[0021] See Figure 1 This application proposes a low-voltage ride-through control method for a virtual synchronous machine based on flexible adjustment of the power angle coefficient, comprising: Collect grid voltage; obtain the reactive power output of the virtual synchronous machine at the grid connection point based on the grid voltage; when the grid voltage drops and triggers low voltage ride-through control, the reactive power injected by the inverter into the grid is obtained according to formula (1) according to national standard requirements: (1) In the formula: This represents the required reactive power that the inverter injects into the grid. The allowable apparent power after a grid fault; in equation (1): (2) In the formula: This is the grid voltage. This is the rated voltage amplitude. Rated apparent power, This is the voltage drop factor.

[0022] The power angle coefficient, equivalent reactance, and maximum short-circuit current of the virtual synchronous machine are obtained respectively. Considering the current limiting capability limitation of the virtual synchronous machine, the current limiting circle of the virtual synchronous machine is obtained based on the grid voltage, maximum short-circuit current and equivalent reactance; See Figure 5 This is a simplified schematic diagram of a virtual synchronous machine grid-connected system in a power system. The output current of this grid-connected system is determined by the difference between the virtual internal potential and the grid voltage. The output current of the grid-connected system is: (3) In the formula: For the output current of the grid-connected system, The internal potential amplitude of the virtual synchronous machine. The power angle of the output voltage of the virtual synchronous machine. The imaginary unit, The equivalent reactance of the virtual synchronous machine. , The angular frequency of the power grid. This is the equivalent inductance of the virtual synchronous machine.

[0023] To ensure that the fault current, i.e., the output current of the grid-connected system, is less than the maximum short-circuit current of the virtual synchronous machine after a fault occurs, and to prevent the inverter from being damaged by overcurrent, it is necessary to limit the vector trajectory of the virtual internal potential; that is, the vector trajectory of the virtual internal potential must fall within the current-limiting circle. In some embodiments, the current-limiting circle of the virtual synchronous machine is obtained based on the grid voltage, the maximum short-circuit current, and the equivalent reactance, including: The first center is determined based on the grid voltage. The horizontal coordinate of the first center is the grid voltage, and the vertical coordinate is 0. Therefore, the first center is the grid voltage vector. The first center represents the center of the current-limiting circle; The first radius is obtained by multiplying the maximum short-circuit current by the equivalent reactance; that is, the first radius is the voltage drop corresponding to the maximum short-circuit current. , The maximum short-circuit current is represented by the first radius, which characterizes the radius of the current-limiting circle. The current-limiting circle is obtained by drawing a circle with the first center and the first radius. See [link to relevant documentation]. Figure 6 , Figure 6 middle, The voltage of the power grid before the fault. This represents the inverter output current before the fault. This represents the virtual internal potential of the virtual synchronizer before the fault.

[0024] Considering the mandatory requirements of national standards for reactive power support during faults, the constant reactive power characteristic circle of the virtual synchronous machine is obtained based on grid voltage, reactive power, and equivalent reactance. In some embodiments, obtaining the constant reactive power characteristic circle of the virtual synchronous machine based on grid voltage, reactive power, and equivalent reactance includes: The second center is determined based on the grid voltage. The horizontal coordinate of the second center is half of the grid voltage, and the vertical coordinate is 0. Therefore, the second center is... The second center represents the center of the constant reactive power characteristic circle; the first intermediate term is obtained by multiplying the reactive power by the equivalent reactance. The second intermediate term is obtained by squaring half of the grid voltage. The second radius is obtained by summing the first and second intermediate terms and taking the square root. The second radius represents the radius of the constant reactive power characteristic circle; the constant reactive power characteristic circle is obtained based on the second center and the second radius.

[0025] Specifically: taking the direction of the grid voltage as Establishing a rectangular coordinate system around the axes, the coordinates of the endpoint of the internal potential of the virtual synchronous machine can be expressed as follows: The angle between the internal potential of the virtual synchronous machine and the grid voltage is the power angle of the output voltage of the virtual synchronous machine. The internal potential amplitude of a virtual synchronous machine can be expressed as: (4) The coordinate expression for the reactive power output by the virtual synchronous machine is: (5) In the formula: The reactive power output of the virtual synchronous machine; Equation (5) is simplified to obtain equation (6): (6) Therefore, when the equivalent reactance of the virtual synchronous machine The reactive power output of the virtual synchronous machine is a constant value. When known, the vector trajectory of the internal potential of the virtual synchronous machine is a constant reactive power characteristic circle, that is, the constant reactive power characteristic circle is obtained by drawing a circle with the second center as the center and the second radius as the radius. See [link to relevant documentation]. Figure 7 Considering the mandatory requirements of national standards for reactive power support during fault periods, i.e., reactive power output during fault periods must strictly meet the requirements of national standards, that is... Therefore, the range of the internal potential of the virtual synchronous machine is outside the constant reactive power characteristic circle.

[0026] Based on the non-negative power angle constraint of active power, the first boundary point is obtained according to the current limiting circle and the constant reactive power characteristic circle; the first boundary point represents the intersection of the current limiting circle and the constant reactive power characteristic circle that satisfy the non-negative power angle constraint. According to the vector expression of active power: (7) In the formula: This represents the active power output by the virtual synchronizer. Equation (6) shows that when... hour, The virtual synchronous machine outputs active power to the grid to meet the active power maintenance requirements during fault periods. Therefore, it is necessary to impose a non-negative power angle constraint on the internal potential of the virtual synchronous machine. Figure 7 It is evident that the terminal point of the internal potential of the virtual synchronous machine must be located at... The axis and upper half-plane are designed to ensure the output of active power of the virtual synchronizer.

[0027] In summary, considering the current-limiting capability limitations of the virtual synchronous machine, the mandatory requirements of national standards for reactive power support during faults, and the non-negative power angle constraint of active power, the feasible region of the internal potential of the virtual synchronous machine during a fault is as follows: Figure 6 As shown, the feasible region is within the current-limiting circle, outside the constant reactive power characteristic circle, and... The region defined by the three axes above the axis satisfies the inverter's current limiting capability and the national standard requirements for reactive power support, while also ensuring the positive output characteristics of active power.

[0028] according to Figure 7 The feasible region shown includes the current-limiting circle 60, the constant reactive power characteristic circle 70, and... The part corresponding to the axis is the constraint boundary of the feasible region. The current-limiting circle 60 and the constant reactive power characteristic circle 70 are at... The intersection point above the axis is the first boundary point. By combining equations (3) and (5), the first boundary point can be obtained. The corresponding internal potential coordinates of the virtual synchronizer. First boundary point. The internal potential of the corresponding virtual synchronous machine lies on the current-limiting circle, which satisfies the inverter's maximum current-limiting capability to fully utilize the inverter's capacity. Furthermore, the corresponding reactive power strictly meets the minimum reactive power support value required by national standards, maximizing the output of active power. Simultaneously, the first boundary point... The internal potential and work angle corresponding to the point take the maximum value.

[0029] In addition, another boundary point and a second boundary point of the feasible region For the current limiting circle and The intersection of the positive and negative axes, the second boundary point. The corresponding virtual synchronous machine has an internal potential power angle of 0, which is the point that meets the current limiting requirements and has the maximum reactive power output. At this time, the inverter output voltage reaches its maximum value and the active power output is 0.

[0030] In summary, the range of variation of the internal potential and power angle of the virtual synchronous machine within the feasible region is: , The internal potential power angle of the virtual synchronous machine corresponding to the first boundary point covers the entire constrained range from the reactive power maximization output point to the active power maximization output point, providing a clear range of values ​​for subsequent virtual internal potential parameter optimization.

[0031] Based on the angle coefficient and the first boundary point Obtaining the internal potential power angle; in some embodiments, obtaining the internal potential power angle based on the power angle coefficient and the first boundary point includes: obtaining the first power angle based on the first boundary point. The first power angle represents the internal potential power angle of the virtual synchronous machine corresponding to the first boundary point; the internal potential power angle is obtained by multiplying the power angle coefficient and the first power angle.

[0032] The vector trajectory of the virtual internal potential falls at the first boundary point. Second boundary point On the current-limiting arc between the two points, all vectors of the internal potential of the virtual synchronous machine within this range can strictly satisfy the current-limiting capability limit of the virtual synchronous machine, the mandatory requirements of national standards for reactive power support during faults, and the non-negative power angle constraint of active power, and can achieve the maximum capacity output of the inverter. Simultaneously, by adjusting the power angle of the internal potential of the virtual synchronous machine... It can achieve coordinated allocation of active and reactive power—power angle. The larger the value, the closer the active power output is to the constraint limit; the power angle The smaller the value, the closer the reactive power output is to the maximum support capacity.

[0033] To achieve smooth control of the power angle, a power angle coefficient is defined. , The power angle of the internal potential of the virtual synchronous machine during actual operation From the first boundary point The internal potential power angle of the corresponding virtual synchronous machine With the power angle coefficient The product of these factors determines the power angle of the internal potential of the virtual synchronous machine. for: (8) By adjusting the power angle coefficient The values, the internal potential and power angle of the virtual synchronizer The adjustment of the power angle can achieve the coordinated distribution of active and reactive power. The larger the value, the closer the active power output is to the constraint limit; the power angle The smaller the value, the closer the reactive power output is to the maximum support capacity.

[0034] The internal potential amplitude is obtained from the grid voltage, internal potential angle, equivalent reactance, and maximum short-circuit current; from... Figure 7 As seen in the text, when the grid voltage drop and the power angle of the virtual synchronous machine are constant, the internal potential amplitude of the virtual synchronous machine can be determined by the maximum voltage drop generated by the maximum short-circuit current. That is, the virtual internal potential vector trajectory falls on the first boundary point. Second boundary point On the current-limiting arc between the two points, to ensure the inverter's maximum output capacity, the internal potential amplitude of the virtual synchronous machine is: (9) In the formula, The internal potential amplitude of the virtual synchronous machine. This is the grid voltage. The internal potential power angle of the virtual synchronous machine. The equivalent reactance of the virtual synchronous machine. This is the maximum short-circuit current of the virtual synchronous machine.

[0035] The virtual synchronous machine is controlled based on the internal potential power angle and internal potential amplitude. When controlling the virtual synchronous machine based on the internal potential power angle and internal potential amplitude, the active frequency loop and reactive voltage loop are interlocked, and the internal potential amplitude is controlled. As a control command for the reactive voltage loop, the voltage setpoint of the reactive voltage loop is... Switch to internal potential amplitude and the internal potential power angle As the control command for the active frequency loop, the internal potential power angle is... The compensation angle for active and reactive power output .

[0036] See Figure 3 In some embodiments, the virtual synchronizer includes a power calculator 10 and a power outer loop 20; The power calculator 10 is used to obtain the active and reactive power output of the virtual synchronous machine based on the grid voltage; The power outer loop 20 is used to obtain the reference phase angle based on the normal operating power angle and the internal potential power angle, to obtain the output voltage phase angle of the virtual synchronous machine based on the reference phase angle and active power, to obtain the output voltage amplitude of the virtual synchronous machine based on the reactive power and the internal potential amplitude, and to obtain the output internal potential of the virtual synchronous machine based on the output voltage phase angle and the output voltage amplitude.

[0037] See also Figure 4 In some embodiments, the power outer loop 20 includes an active frequency loop 21, a reactive voltage loop 22, and a voltage synthesizer 23. The active frequency loop 21 is used to obtain the reference phase angle based on the normal operating power angle and the internal potential power angle, and to obtain the output voltage phase angle of the virtual synchronous machine based on the reference phase angle and the active power. The reactive voltage loop 22 is used to obtain the output voltage amplitude of the virtual synchronous machine based on the reactive power and internal potential amplitude; Voltage synthesizer 23 is used to obtain the output internal potential of the virtual synchronous machine based on the output voltage phase angle and output voltage amplitude.

[0038] Figure 3 middle, The voltage of the constant voltage source is... For the inductance of the filter circuit, For the capacitors in the filter circuit, The output internal potential of the virtual synchronous machine; Figure 4 middle, For the complex variable in the Laplace transform, Rated active power, The phase of the power loop output voltage after phase compensation. For rated reactive power, the mathematical model of the active frequency loop of the virtual synchronous machine used in this application is as follows: (10) In the formula, The output voltage phase angle of the virtual synchronous machine. For time, for The differential, The input mechanical power for the virtual synchronizer. The active power output by the virtual synchronizer. For rotational inertia, The damping coefficient is... The rated angular frequency; The mathematical model of the reactive voltage loop of the virtual synchronous machine used in this application is as follows: (11) In the formula, The output voltage amplitude of the virtual synchronous machine. The rated internal potential of the virtual synchronous machine, This is the reactive voltage loop droop factor. This is a reference value for reactive power. This refers to the reactive power output of the virtual synchronous machine.

[0039] After a fault occurs, in order to prevent the system from oscillating due to the phase angle adjustment of the power outer loop of the virtual synchronous machine, and to ensure that the amplitude of the virtual internal potential remains stable with the initial phase, it is necessary to perform a blocking operation on the power outer loop controlled by the virtual synchronous machine. By setting both the active power difference and reactive power difference input in the power outer loop to 0, the virtual synchronous machine can maintain the stable power angle before the fault during the fault period, ensuring that the amplitude and phase of the virtual internal potential remain unchanged.

[0040] See Figure 2 In some embodiments, the virtual synchronous machine is controlled based on the internal potential power angle and the internal potential amplitude, including: Obtain the normal operating angle of the virtual synchronizer Normal operating power angle This is also the power angle for compensating the phase of the voltage phase at the grid connection point of the virtual synchronous machine's internal potential phase tracking. The reference phase angle is obtained based on the normal operating power angle and the internal potential power angle, as described above. The internal potential power angle is then... The power angle serves as a compensation angle for active and reactive power output. ,Right now Phase compensation injection is performed during the fault, with the reference phase angle being: (12) In the formula, Used as the reference phase angle; The active power output of the virtual synchronous machine is obtained based on the grid voltage; The output voltage phase angle of the virtual synchronous machine is obtained based on the reference phase angle and active power. The output voltage amplitude of the virtual synchronous machine is obtained based on the reactive power and internal potential amplitude, as described above, and the voltage setpoint of the reactive voltage loop is set accordingly. Switch to internal potential amplitude ,Right now Amplitude switching is performed during the fault period; The output internal potential of the virtual synchronous machine is obtained based on the output voltage phase angle and output voltage amplitude.

[0041] During a fault, amplitude switching and phase compensation injection enable the internal potential of the virtual synchronous machine to be changed to the target value quickly and accurately. This suppresses overcurrent and meets the active and reactive power output requirements, while also avoiding the problem that the mechanical inertia of the virtual synchronous machine hinders the output from quickly reaching a steady state.

[0042] See Figure 3 In some embodiments, the virtual synchronous machine further includes a voltage-current inner loop 30, a pulse width modulator 40, and an inverter 50; The voltage-current inner loop 30 is used to obtain the modulation voltage based on the output internal potential; Pulse width modulator 40 is used to obtain a pulse modulated wave based on the modulation voltage; Inverter 50 is installed on the power grid. Inverter 50 is used to obtain three-phase AC power according to pulse modulation wave, and the three-phase AC power is connected to the power grid.

[0043] In some embodiments, controlling the virtual synchronizer based on the internal potential power angle and the internal potential amplitude further includes: The modulation voltage is obtained based on the output internal potential; The pulse modulation wave is obtained based on the modulation voltage; Three-phase alternating current is obtained based on pulse modulation waves, and the three-phase alternating current is connected to the power grid.

[0044] Experimental Example Building such Figure 3 The virtual synchronous machine grid-connected system simulation model shown is set to have the grid voltage drop to 0.4. pu The maximum allowable current of the inverter in a virtual synchronous machine, which is also the maximum short-circuit current of the virtual synchronous machine, is 1.5. pu Power angle coefficient k Take values ​​of 0.5 and 1 respectively, see [reference]. Figures 8-17 .

[0045] Simulation results show that the output current of the virtual synchronizer did not exceed the current limiting threshold under both operating conditions, i.e., it did not exceed the maximum short-circuit current of the virtual synchronizer, thus satisfying the current-carrying constraint; the power angle coefficient... k When the value is 0.5, the internal potential power angle stabilizes at 8.41°, and the power angle coefficient is... k When the value is 1, the internal potential power angle stabilizes at 16.82°, with small fluctuations and no oscillations; power control is precise. k When the value is 1, the maximum active power output is 0.92. pu The minimum requirement for reactive power matching according to national standards is 0.3. pu , k When the value is 0.5, the active and reactive power output of the virtual synchronous machine is balanced. This shows that the control method proposed in this application can strictly meet the current limiting requirements, ensure the stability of the power angle, and achieve flexible control of active and reactive power, thus verifying the effectiveness and practicality of the method.

[0046] In summary, this application proposes a low-voltage ride-through control method that considers the current-limiting capacity limitations of virtual synchronous machines, the mandatory requirements of national standards for reactive power support during faults, and the constraints on active power output. This method constructs a feasible region, introduces a power angle coefficient to achieve flexible power adjustment, and combines power outer-loop blocking with a phase compensation-replication switching control strategy. This solves the problems of rigid power distribution and easy power angle instability during low-voltage ride-through in traditional virtual synchronous machines, providing a reliable control scheme for fault ride-through in renewable energy power plants.

[0047] Those skilled in the art will understand that embodiments of this application can be provided as methods, apparatus (systems), or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of this application can be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0048] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce an instruction that executes via the processor of the computer or other programmable data processing apparatus to create an instruction for implementing the flowchart. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0049] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0050] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0051] Finally, it should be noted that the above content is only used to illustrate the technical solution of this application, and is not intended to limit the scope of protection of this application. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of this application shall not depart from the substance and scope of the technical solution of this application.

Claims

1. A low-voltage ride-through control method for a virtual synchronous machine based on flexible adjustment of the power angle coefficient, characterized in that, include: Collect the grid voltage; obtain the reactive power output of the virtual synchronous machine based on the grid voltage; The power angle coefficient, the maximum short-circuit current, and the equivalent reactance of the virtual synchronous machine are obtained respectively. The current-limiting circle of the virtual synchronous machine is obtained based on the grid voltage, the maximum short-circuit current, and the equivalent reactance; the constant reactive power characteristic circle of the virtual synchronous machine is obtained based on the grid voltage, the reactive power, and the equivalent reactance. Based on the non-negative power angle constraint of active power, a first boundary point is obtained according to the current limiting circle and the constant reactive power characteristic circle; the first boundary point represents the intersection point of the current limiting circle and the constant reactive power characteristic circle that satisfies the non-negative power angle constraint. The internal potential power angle is obtained based on the power angle coefficient and the first boundary point; the internal potential amplitude is obtained based on the grid voltage, the internal potential power angle, the equivalent reactance, and the maximum short-circuit current. The virtual synchronous machine is controlled based on the internal potential power angle and the internal potential amplitude.

2. The low-voltage ride-through control method for a virtual synchronous machine based on flexible adjustment of the power angle coefficient according to claim 1, characterized in that, Controlling the virtual synchronous machine based on the internal potential power angle and the internal potential amplitude includes: Obtain the normal operating power angle of the virtual synchronizer; The reference phase angle is obtained based on the normal operating power angle and the internal potential power angle; The active power output by the virtual synchronous machine is obtained based on the grid voltage; The output voltage phase angle of the virtual synchronizer is obtained based on the reference phase angle and the active power. The output voltage amplitude of the virtual synchronous machine is obtained based on the reactive power and the internal potential amplitude. The output internal potential of the virtual synchronizer is obtained based on the output voltage phase angle and the output voltage amplitude.

3. The low-voltage ride-through control method for a virtual synchronous machine based on flexible adjustment of the power angle coefficient according to claim 2, characterized in that, The step of obtaining the current-limiting circle of the virtual synchronous machine based on the grid voltage, the maximum short-circuit current, and the equivalent reactance includes: The first center is obtained based on the grid voltage. The horizontal coordinate of the first center is the grid voltage, and the vertical coordinate of the first center is 0. The first center represents the center of the current-limiting circle. The first radius is obtained by multiplying the maximum short-circuit current by the equivalent reactance, and the first radius represents the radius of the current-limiting circle; The flow-limiting circle is obtained based on the first center and the first radius.

4. The low-voltage ride-through control method for a virtual synchronous machine based on flexible adjustment of the power angle coefficient according to claim 3, characterized in that, The constant reactive power characteristic circle of the virtual synchronous machine is obtained based on the grid voltage, the reactive power, and the equivalent reactance, including: The second center is obtained based on the grid voltage. The horizontal coordinate of the second center is half of the grid voltage, and the vertical coordinate of the second center is 0. The second center represents the center of the constant reactive power characteristic circle. The first intermediate term is obtained by multiplying the reactive power and the equivalent reactance, and the second intermediate term is obtained by squaring half of the grid voltage. The second radius is obtained by summing the first intermediate term and the second intermediate term and taking the square root. The second radius represents the radius of the constant reactive power characteristic circle. The constant reactive power characteristic circle is obtained based on the second center and the second radius.

5. The low-voltage ride-through control method for a virtual synchronous machine based on flexible adjustment of the power angle coefficient according to claim 4, characterized in that, The internal potential power angle is obtained based on the power angle coefficient and the first boundary point, including: The first power angle is obtained based on the first boundary point, and the first power angle represents the internal potential power angle of the virtual synchronous machine corresponding to the first boundary point. The internal potential power angle is obtained by multiplying the power angle coefficient by the first power angle.

6. The low-voltage ride-through control method for a virtual synchronous machine based on flexible adjustment of the power angle coefficient according to claim 5, characterized in that, The amplitude of the internal potential is: ； In the formula, The magnitude of the internal potential. This is the grid voltage. The internal potential power angle, The equivalent reactance of the virtual synchronous machine. This is the maximum short-circuit current.

7. The low-voltage ride-through control method for a virtual synchronous machine based on flexible adjustment of the power angle coefficient according to claim 2, characterized in that, The virtual synchronizer includes a power calculator and a power outer loop; The power calculator is used to obtain the active power and reactive power output by the virtual synchronous machine based on the grid voltage; The power outer loop is used to obtain a reference phase angle based on the normal operating power angle and the internal potential power angle, to obtain the output voltage phase angle of the virtual synchronous machine based on the reference phase angle and the active power, to obtain the output voltage amplitude of the virtual synchronous machine based on the reactive power and the internal potential amplitude, and to obtain the output internal potential of the virtual synchronous machine based on the output voltage phase angle and the output voltage amplitude.

8. The low-voltage ride-through control method for a virtual synchronous machine based on flexible adjustment of the power angle coefficient according to claim 7, characterized in that, The power outer loop includes an active frequency loop, a reactive voltage loop, and a voltage synthesizer; The active frequency loop is used to obtain a reference phase angle based on the normal operating power angle and the internal potential power angle, and to obtain the output voltage phase angle of the virtual synchronous machine based on the reference phase angle and the active power. The reactive voltage loop is used to obtain the output voltage amplitude of the virtual synchronous machine based on the reactive power and the internal potential amplitude. The voltage synthesizer is used to obtain the output internal potential of the virtual synchronous machine based on the output voltage phase angle and the output voltage amplitude.

9. The low-voltage ride-through control method for a virtual synchronous machine based on flexible adjustment of the power angle coefficient according to claim 7, characterized in that, The virtual synchronous machine also includes a voltage and current inner loop, a pulse width modulator, and an inverter; The voltage-current inner loop is used to obtain the modulation voltage based on the output internal potential; The pulse width modulator is used to obtain a pulse modulation wave according to the modulation voltage; The inverter is installed on the power grid and is used to obtain three-phase AC power according to the pulse modulation wave. The three-phase AC power is connected to the power grid.

10. The low-voltage ride-through control method for a virtual synchronous machine based on flexible adjustment of the power angle coefficient according to claim 9, characterized in that, Controlling the virtual synchronizer based on the internal potential power angle and the internal potential amplitude further includes: The modulation voltage is obtained based on the output internal potential; A pulse modulation wave is obtained based on the modulation voltage; Three-phase alternating current is obtained based on the pulse modulation wave, and the three-phase alternating current is connected to the power grid.

Images