Control method and system for simulating synchronous condenser operation of grid-connected new energy inverter

Abstract

The application discloses a control method and system for simulating synchronous condenser operation of a new energy grid-connected inverter, and belongs to the technical field of new energy grid-connected inverter control. The method comprises the following steps: obtaining actual active power delivered to a power grid according to three-phase voltage and three-phase current of a grid-connected inverter port, delivering the active power to active frequency control to obtain the phase of internal potential in the grid-connected inverter; obtaining three-phase voltage amplitudes of the grid-connected inverter port through amplitude calculation of the three-phase voltage, and delivering the three-phase voltage amplitudes to strong excitation control to output the amplitude of the internal potential simulating the external characteristic of the synchronous condenser; inputting the phase and the amplitude of the internal potential into internal potential generation calculation to generate three-phase internal potential modulation waves; and delivering the three-phase internal potential modulation waves to space vector modulation (SVPWM) to obtain trigger pulse signals of each switch tube of the grid-connected inverter.

Description

Technical Field

[0001] This invention belongs to the field of control technology for grid-connected inverters for new energy, and specifically relates to a control method for simulating the operation of synchronous condensers in grid-connected inverters for new energy. Background Technology

[0002] With the increasing proportion of renewable energy in power systems using power electronic devices as interfaces, new energy sources should shoulder the responsibility of maintaining power system stability. To avoid the problems of voltage drops at the output ports of grid-connected inverters during grid faults, which limit short-circuit current output and prevent timely relay protection, thus further expanding the fault area, and the greater the voltage drop at the ports during short-circuit transients, the more likely it is to cause power system transient instability, researching control strategies for maintaining port voltage stability in grid-connected inverters during short-circuit faults, improving the transient stability performance of high-proportion renewable energy power systems, and maintaining relay protection operation logic is of significant research importance and value.

[0003] To improve the voltage stability of grid-connected inverter ports during short circuits, there are currently two main approaches. One is to add dynamic reactive power compensation devices, such as synchronous condensers, to enhance the voltage stability of the power system. However, the instantaneous reactive power support of synchronous condensers relies on complex system parameter design and adjustment, and considering initial and maintenance costs, synchronous condensers are difficult to apply in large-scale distributed renewable energy grid connection projects. The other approach is to improve the control method of renewable energy grid-connected inverters. By simulating the inertia and damping characteristics of synchronous generators in the control stage, the grid-connected inverter gives the renewable energy sources similar external characteristics to synchronous generators, enabling them to provide a certain frequency and voltage support to the grid. However, because this control method focuses on simulating the normal operating characteristics of synchronous generators and is limited by the overload capacity of power electronic devices, the voltage at the grid-connected inverter ports still suffers from significant voltage drops and insufficient reactive power supply during short circuits. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a control method and system for simulating the operation of a synchronous condenser in a new energy grid-connected inverter.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A control method for simulating synchronous condenser operation in a new energy grid-connected inverter includes the following steps:

[0007] Power calculations are performed based on the three-phase voltage and output three-phase current at the grid-connected inverter port to obtain the actual active power delivered to the grid.

[0008] The active power actually delivered to the grid is fed into the active frequency loop control to obtain the phase of the internal potential of the grid-connected inverter.

[0009] The amplitude of the three-phase voltage at the grid-connected inverter port is obtained by amplitude calculation, and then the amplitude of the three-phase voltage is sent to the strong excitation control to output the amplitude of the internal potential simulating the external characteristics of the synchronous condenser.

[0010] The phase and amplitude of the internal potential are input into the internal potential generation module to obtain a three-phase internal potential modulation wave.

[0011] The three-phase internal potential modulation wave is transmitted to the space vector modulation (SVPWM) to obtain the trigger pulse signal for each switch of the grid-connected inverter.

[0012] Furthermore, the active frequency control step includes:

[0013] S21, the rated angular frequency ω n The frequency error signal is obtained by subtracting the angular frequency ω generated by the active frequency element;

[0014] S22, multiply the frequency error signal by the droop coefficient D of the active frequency loop. p With the rated angular frequency ω n The product of these amplifies the frequency error signal;

[0015] S23, compare the frequency error signal with the reference active power P ref The summation and subtraction of the actual active power P transmitted to the grid e By adjusting the output frequency to adapt to different actual active power outputs, the resulting signal is connected to the integrator input port. The integrator output signal is the angular frequency ω generated by the active power frequency element. This is achieved by adjusting the integration coefficient 1 / (Jω). n The magnitude of ) changes the time constant of the active frequency loop;

[0016] S24, the angular frequency ω generated by the active frequency element is passed through an integrator to obtain the phase θ of the internal potential.

[0017] Furthermore, the active frequency control equation is as follows:

[0018]

[0019] In the formula, P ref For reference active power; P e J is the actual active power delivered to the grid; J is the moment of inertia of the active frequency control; ω n The rated angular frequency; D p This is the droop factor of the active frequency loop.

[0020] Furthermore, the three-phase voltage amplitude U at the output port of the grid-connected inverter o The calculation equation is as follows:

[0021]

[0022]

[0023] In the formula, u α u β The voltage components of the three-phase voltage at the grid-connected inverter port in the αβ coordinate system.

[0024] Furthermore, the process of strong excitation control includes:

[0025] S31, the rated voltage amplitude U at the output port of the grid-connected inverter. o,ref The voltage amplitude U at the actual grid-connected inverter output port o The difference is calculated to obtain the error signal of the port voltage. This error signal is then multiplied by the amplification factor k0 and transmitted to the input of the integrator. The output of the integrator is the transient value of the internal potential amplitude E. The integrator adjusts the magnitude of the internal potential amplitude E by accumulating the voltage error.

[0026] S32, the voltage amplitude U at the actual grid-connected inverter output port. o After multiplying by the gain factor k1, the result after passing through the inertial element with a set time constant τ, and multiplying by the amplification factor k2, is the voltage amplitude U at the actual grid-connected inverter output port. o The difference is calculated to obtain the voltage amplitude U at the output port of the grid-connected inverter. o The subtransient quantity of the internal potential amplitude E during dynamic changes;

[0027] S33, the internal potential amplitude E is obtained by superimposing the transient quantity of the internal potential amplitude E and the subtransient quantity of the internal potential amplitude E.

[0028] Furthermore, the voltage equation for the synchronous condenser is:

[0029]

[0030] In the formula, x, x′, and x″ represent the equivalent steady-state, transient, and subtransient reactances of the stator, respectively; T′ and T″ represent the time constants corresponding to the transient and subtransient states, respectively; E′ and E″ represent the amplitude components of the internal potential corresponding to the subtransient and transient states, respectively; I L E represents the phase current amplitude. f This represents the amplitude of the no-load excitation phase voltage.

[0031] Furthermore, in strong excitation control, the formula for calculating the gain coefficient k0 is:

[0032]

[0033] Where, τ vτ is the time constant of the voltage loop, which is the value of τ when a short circuit occurs on the grid side. v It can be considered as a transient time constant;

[0034] The formula for calculating the time constant τ is:

[0035] τ=τ v a%

[0036] Where a% is the percentage of the subtransient time constant to the transient control;

[0037] The formula for calculating the gain coefficient k1 is:

[0038]

[0039] The formula for calculating the gain coefficient k2 is:

[0040]

[0041] Where ΔQ represents the increase in reactive power output at the grid-connected inverter port when a short circuit occurs; when the voltage change at the grid-connected inverter port is ΔU o At that time, the output reactive power changes by ΔQ.

[0042] Furthermore, further, the three-phase internal potential e abc The calculation expression is:

[0043]

[0044] In the formula, θ is the phase of the internal potential, and E is the amplitude of the internal potential.

[0045] Furthermore, the grid-connected inverter circuit used in the control method includes: a DC power supply, a three-phase inverter, and a three-phase LC filter; the DC power supply is connected to the DC input terminal of the three-phase inverter, the output terminal of the three-phase inverter is connected to one end of the three-phase filter inductor, the other end of the three-phase filter inductor is connected to one end of the three-phase filter capacitor and the main power grid, and the other end of the three-phase filter capacitor is short-circuited.

[0046] The control system for simulating synchronous condenser operation in a new energy grid-connected inverter includes:

[0047] Power calculation module: Calculates the power based on the three-phase voltage and output three-phase current at the grid-connected inverter port to obtain the actual active power delivered to the grid;

[0048] Internal potential phase calculation module: The active power actually delivered to the grid is fed into the active frequency control to obtain the phase of the internal potential of the grid-connected inverter;

[0049] Internal potential amplitude calculation module: The three-phase voltage amplitude of the grid-connected inverter port is obtained by amplitude calculation, and then the three-phase voltage amplitude is sent to the strong excitation control to output the amplitude of the internal potential simulating the external characteristics of the synchronous condenser.

[0050] Modulation wave generation module: Input the phase and amplitude of the internal potential into the internal potential generation module to obtain a three-phase internal potential modulation wave;

[0051] In addition, the trigger pulse generation module: transmits the three-phase modulation wave to the space vector modulation (SVPWM) to obtain the trigger pulse signals of each switching transistor of the grid-connected inverter.

[0052] The beneficial effects of this invention are:

[0053] 1. When a short-circuit fault occurs on the grid side, the control method of the present invention can be used to quickly restore the three-phase voltage output of the grid-connected inverter port to the rated value.

[0054] 2. In the instant of a short-circuit fault on the grid side, the instantaneous reactive power compensation can be adjusted by designing the control parameters of the strong excitation link, which facilitates the grid connection application of distributed new energy sources. Attached Figure Description

[0055] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0056] Figure 1 This is a schematic diagram of the virtual synchronous condenser control system of the present invention;

[0057] Figure 2 This is a schematic diagram of the potential generation within the grid-connected inverter of the present invention;

[0058] Figure 3 Simulation waveforms comparing the outputs of the control method of this invention and the virtual synchronous generator control method during a power grid short circuit.

[0059] Figure 4 The simulation waveform diagram shows the influence of various coefficients in the variable strong excitation control link of this invention on the internal potential amplitude when the power grid is short-circuited. Detailed Implementation

[0060] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0061] like Figure 1 As shown, the control method for simulating synchronous condenser operation in a new energy grid-connected inverter is described. The main circuit of the applied new energy grid-connected inverter includes a DC power supply U. dc Three-phase inverter, three-phase LC filter; DC power supply U dc Connected to the DC input terminal of the three-phase inverter, and the output terminal of the three-phase inverter is connected to the three-phase filter inductor L. f One end is connected to the three-phase filter inductor L. f The other end is connected to the three-phase filter capacitor C f One end and the large power grid u g Connected, three-phase filter capacitor C f The other end is short-circuited;

[0062] The control method includes the following steps:

[0063] S1, based on the three-phase voltage u at the grid-connected inverter port abc Output three-phase current i abc Perform power calculations to obtain the actual active power P transmitted to the power grid. e ;

[0064] The actual active power P transmitted to the power grid e The calculation equation is as follows:

[0065] P e =u a i a +u b i b +u c i c (1)

[0066] In the formula u a u b u c The three-phase voltage u output from the grid-connected inverter port are respectively abc The voltages of phases A, B, and C; i a i b i c The three-phase output current i of the grid-connected inverter are respectively abc The currents in phases A, B, and C.

[0067] S2 represents the actual active power P transmitted to the power grid.e The voltage is fed into the active frequency control system, and the phase θ of the internal potential of the grid-connected inverter is calculated.

[0068] Figure 2 (a) in the diagram is a schematic diagram of active power control, in which the active frequency control steps include:

[0069] S21, the rated angular frequency ω n The frequency error signal is obtained by subtracting the angular frequency ω generated by the active frequency element;

[0070] S22, multiply the frequency error signal by the droop coefficient D of the active frequency loop. p With the rated angular frequency ω n The product of these amplifies the frequency error signal;

[0071] S23, compare the frequency error signal with the reference active power P ref The summation and subtraction of the actual active power P transmitted to the grid e By adjusting the output frequency to adapt to different actual active power outputs, the resulting signal is connected to the integrator input port. The integrator output signal is the angular frequency ω generated by the active power frequency element. This is achieved by adjusting the integration coefficient 1 / (Jω). n The magnitude of ) can change the time constant of the active frequency loop;

[0072] S24, the angular frequency ω generated by the active frequency element is passed through an integrator to obtain the phase θ of the internal potential.

[0073] The rotor motion equations of the simulated synchronous machine are used to obtain the active frequency control equations.

[0074]

[0075] In the formula, P ref For reference active power; P e J is the actual active power delivered to the grid; J is the moment of inertia of the active frequency control; ω n The rated angular frequency; D p This is the droop factor of the active frequency loop.

[0076] S3 will convert the three-phase voltage u at the grid-connected inverter port. abc The amplitude of the three-phase voltage is obtained through amplitude calculation, and then the amplitude of the three-phase voltage is sent to the strong excitation control to output the amplitude E of the internal potential simulating the external characteristics of the synchronous condenser.

[0077] The three-phase voltage amplitude U at the output port of the grid-connected inverter o The calculation equation is as follows:

[0078]

[0079]

[0080] In the formula, u α u β The voltage components of the three-phase voltage at the grid-connected inverter port in the αβ coordinate system.

[0081] Figure 2 (b) in the diagram is a schematic diagram of strong excitation control. The strong excitation control process includes:

[0082] S31, the rated voltage amplitude U at the output port of the grid-connected inverter. o,ref The voltage amplitude U at the actual grid-connected inverter output port o The difference is calculated to obtain the error signal of the port voltage. This error signal is then multiplied by the amplification factor k0 and transmitted to the input of the integrator. The output of the integrator is the transient quantity of the internal potential amplitude E. The integrator adjusts the magnitude of the internal potential amplitude E by accumulating the voltage error, thereby reducing the voltage amplitude U at the output port of the grid-connected inverter. o With the rated value U o,ref The error, the magnitude of the amplification factor k0, affects the time it takes for the grid-connected inverter to recover to the rated value;

[0083] S32, the voltage amplitude U at the actual grid-connected inverter output port. o After multiplying by the gain factor k1, the result after passing through the inertial element with a set time constant τ, and multiplying by the amplification factor k2, is the voltage amplitude U at the actual grid-connected inverter output port. o The difference is calculated to obtain the voltage amplitude U at the output port of the grid-connected inverter. o The subtransient quantity of the internal potential amplitude E during dynamic changes;

[0084] S33, the internal potential amplitude E is obtained by superimposing the transient quantity of the internal potential amplitude E and the subtransient quantity of the internal potential amplitude E.

[0085] A synchronous condenser is a special type of synchronous motor. Its mathematical model is similar to that of a typical synchronous motor, employing a fifth-order synchronous condenser model, which assumes that the flux linkages of the damping and excitation windings remain constant during the subtransient period. The voltage equation for the synchronous condenser is then obtained as follows:

[0086]

[0087] In the formula, x, x′, and x″ represent the equivalent steady-state, transient, and subtransient reactances of the stator, respectively; T′ and T″ represent the time constants corresponding to the transient and subtransient states, respectively; E′ and E″ represent the amplitude components of the internal potential corresponding to the subtransient and transient states, respectively; I L E represents the phase current amplitude. f This represents the amplitude of the no-load excitation phase voltage.

[0088] Where IL With E f The calculation expressions are as follows:

[0089]

[0090] E f =U o,ref +xI L (6)

[0091] Combining equations (4) and (6), we get

[0092]

[0093] The calculation expressions for each coefficient in equation (7) are as follows:

[0094]

[0095] Its increment expression is:

[0096]

[0097] Where ΔE represents the increment of the internal potential amplitude; ΔU o ΔE1 and ΔE2 represent the increments of the transient and subtransient terms of the internal potential amplitude, respectively. Further analysis shows the influence of the gain coefficients of the subtransient and transient terms of the internal potential amplitude on the internal potential amplitude when a short-circuit voltage drop occurs.

[0098] The transient term ΔE1 is the adjustment term for the port voltage from transient to steady state, and the port voltage increment ΔU o This is negatively correlated with the output phase voltage amplitude U. o trending toward reference value U o,ref Its gain coefficient k0 represents the actual voltage U after the port voltage drops following a short-circuit fault. o The rate of change to the reference value increases with the increase of k0, and the time for the internal potential amplitude increment ΔE to enter steady state after the short circuit decreases.

[0099] The subtransient term ΔE2 is the regulating term that dominates the instantaneous port voltage support when a short circuit occurs. From equation (8), it can be seen that in the time domain, the time constant τ and the gain coefficient k1 are negatively correlated with the internal potential amplitude increment ΔE, and are the dominant factors affecting the attenuation amplitude and attenuation time of the internal potential amplitude increment ΔE. As the gain coefficient k1 and the time constant τ increase, the attenuation amplitude and attenuation time of the subtransient term of the internal potential amplitude increment ΔE increase. The gain coefficient k2 is related to the port voltage increment ΔU. oThe negative correlation determines the magnitude of the increase in internal potential amplitude ΔE during the subtransient phase at the instant of a short circuit. As k2 increases, the magnitude of the increase in internal potential amplitude ΔE during the subtransient phase after a short circuit increases, while the attenuation magnitude and attenuation time constant remain unchanged.

[0100] In the strong excitation control loop, the calculation expressions for the gain coefficients k0, k1, k2, and the time constant τ are as follows:

[0101] Gain coefficient k0:

[0102]

[0103] Where, τ v τ is the time constant of the voltage loop, which is the value of τ when a short circuit occurs on the grid side. v It can be considered as a transient time constant.

[0104] Time constant τ:

[0105] τ=τ v a%

[0106] Where a% is the percentage of the subtransient time constant to the transient control;

[0107] The gain coefficient k1 is:

[0108]

[0109] The gain coefficient k2 is:

[0110]

[0111] Where ΔQ represents the increase in reactive power output at the grid-connected inverter port when a short circuit occurs; Equation (12) represents the change in voltage at the grid-connected inverter port when the voltage change is ΔU. o At that time, the output reactive power changes by ΔQ.

[0112] S4, input the phase θ and amplitude E of the internal potential into the internal potential generation to obtain a three-phase internal potential modulation wave;

[0113] Figure 2 (c) in the diagram is a schematic diagram of internal potential generation, showing the three-phase internal potential modulation wave e. abc The calculation expression is:

[0114]

[0115] In the formula, θ is the phase of the internal potential, and E is the amplitude of the internal potential.

[0116] S5, finally, the three-phase modulation wave is sent to the space vector modulation (SVPWM) to obtain the trigger pulse signal of each switch of the grid-connected inverter.

[0117] like Figure 3 The figure shows a simulation waveform comparison of the output of the control method of this invention and the virtual synchronous generator control method when the power grid is short-circuited.

[0118] In the simulation, the main circuit parameters of the virtual synchronous condenser and the virtual synchronous generator are set as follows, and the phase voltage amplitude is referenced to U. o,ref 256V, filter inductor L f The equivalent line inductance L when a short-circuit fault occurs on the grid side is 150 μH. g The value is 300μH. The control parameters of the virtual synchronous condenser's strong excitation loop are as follows: For every 10% drop in the port voltage during a short circuit, 500kVar of instantaneous reactive power support can be provided. According to equation (12), the gain coefficient k2 of the strong excitation control loop is calculated to be 1.66, and the voltage loop time constant is taken as τ. v =50ms, the subtransient process accounts for 20% of the transient process, so τ = τ v ×a%=10ms, the gain coefficient k0=1 / τ of the strong excitation control loop is obtained. v =20, and the gain coefficient k1 = 166 is calculated according to formula (11).

[0119] Under the above simulation parameters, when a short-circuit fault occurs on the grid side, the simulated waveforms comparing the output three-phase voltages of the control method of this invention and the virtual synchronous generator control method are as follows: Figure 3 As shown in (a), after a short circuit occurs, the three-phase voltage drop at the port of the virtual synchronous generator is large, and the port voltage cannot be restored to the rated value after the short circuit. In contrast, after using the strong excitation control method of the virtual synchronous condenser of the present invention, the drop in the three-phase voltage at the port of the grid-connected inverter is smaller, and it can quickly recover to the rated voltage for operation, maintain the stability of the port voltage at the moment of short circuit, and improve the transient stability of the power system.

[0120] Figure 3 Figure (b) shows a simulation waveform comparing the output three-phase currents of the control method of this invention and the control method of a virtual synchronous generator. When a short-circuit fault occurs on the grid side, the three-phase output current of the control method of this invention increases rapidly, ensuring timely operation of the relay protection. In contrast, the output three-phase current of the virtual synchronous generator is smaller than the three-phase output current of the control method of this invention both at the moment of the short circuit and after the short circuit enters steady state.

[0121] Figure 3(c) in the figure is a simulation waveform comparing the internal potential amplitude of the control method of the present invention and the virtual synchronous generator control method. According to the above simulation settings, at the instant of a three-phase short circuit on the grid side, the internal potential of the control method of the present invention increases rapidly. When a three-phase short circuit occurs on the grid side, it is equivalent to the grid-connected inverter operating independently with line impedance. According to Kirchhoff's voltage law, Uo / E = Lg / (Lg+Lf), and the internal potential voltage E = 384V is calculated when the port voltage recovers to the rated value of 256V after the short circuit and enters a new steady state. In contrast, the internal potential of the virtual synchronous generator rises smoothly when the grid is short-circuited, and the amplitude when entering a new steady state after the short circuit is only 327V.

[0122] Figure 3 Figure (d) shows a simulation waveform comparing the port voltage amplitudes of the control method of this invention and the virtual synchronous generator control method. When a short circuit occurs on the grid side, the grid-connected inverter port voltage of the control method of this invention drops to 195V. At this time, the internal potential of the control method of this invention increases rapidly, causing the port voltage to recover to the rated value and maintaining the voltage stability of the power system. In contrast, the virtual synchronous generator control method fails to cause a rapid increase in internal potential during the short circuit, resulting in a deeper voltage drop, and the port voltage is only 218V when entering the new steady state after the short circuit.

[0123] Figure 3 Figure (e) shows a simulation waveform comparing the amplitude of the filter inductor current under the control method of this invention and the virtual synchronous generator control method. At the instant a short circuit occurs on the grid side, the short-circuit current amplitude of the control method of this invention is 3670A, which is higher than the 3013A under the virtual synchronous generator control method. Furthermore, upon entering the new steady state after the short circuit, the short-circuit current amplitudes under the control method of this invention and the virtual synchronous generator control method are 2650A and 2280A, respectively, indicating that the control method of this invention makes it easier for the relay protection to operate in a timely manner.

[0124] Figure 3Figure (f) shows a simulation waveform comparing the output reactive power of the control method of this invention and the virtual synchronous generator control method. At the instant of a short circuit on the grid side, the voltage at the grid-connected inverter port under the control method of this invention drops to 195V. Based on a 10% drop in port voltage, 500kVar of reactive power support can be provided. Theoretically, the present invention can provide 1191kVar of reactive power support in the subtransient state, which is consistent with the simulation results. Furthermore, the reactive power support at the moment of the short circuit can be adjusted by adjusting the strong excitation coefficient as needed. In comparison, the instantaneous reactive power support of the virtual synchronous generator is smaller at 800kVar, and the instantaneous reactive power support depends on the actual system parameters and is difficult to adjust through control parameters. Moreover, after the short circuit enters a new steady state, the reactive power using the control method of this invention is 1043kvar, higher than the 760kvar of the virtual synchronous generator. Therefore, the virtual synchronous condenser control method introduced in this invention can provide stronger reactive power support after a short circuit compared to the virtual synchronous generator method.

[0125] Figure 4 The simulation waveform diagram shows the influence of various coefficients in the variable strong excitation control link of the present invention on the internal potential when the power grid is short-circuited.

[0126] in, Figure 4 Figure (a) shows the simulation waveform of the effect of the varying gain coefficient k0 on the internal potential in this invention. As the gain coefficient k0 of the transient term increases, the time constant τ of the corresponding voltage loop also increases. v The reduced gain coefficient (k0) allows the voltage to rise to a higher value in a shorter time under the action of the integrator, thus shortening the time for the port voltage to reach steady state. A higher gain coefficient (k0) is beneficial for improving the recovery speed of the voltage amplitude to the rated value when the grid-connected inverter port voltage drops. Therefore, when designing parameters, if only the speed of voltage amplitude recovery is considered, this gain coefficient should be increased.

[0127] Figure 4 (b) in the figure is a simulation waveform diagram of the effect of the change of gain coefficient k1 on the internal potential. As the gain coefficient k1 increases, the decay amplitude and decay time of the internal potential increment ΔE subtransient term increase.

[0128] Figure 4 (c) in the figure is the simulation waveform diagram of the effect of the changing time constant τ on the internal potential in this invention. As the time constant τ increases, the decay amplitude and decay time of the internal potential increment ΔE subtransient term increase.

[0129] Figure 4Figure (d) shows the simulation waveform of the effect of the varying gain coefficient k2 on the internal potential. As the gain coefficient k2 increases, the amplitude of the subtransient instantaneous increment ΔE of the internal potential increases, while the attenuation amplitude and attenuation time constant remain unchanged. However, the gain coefficient k2 amplifies the harmonic components of the port voltage. If its parameters are designed too large, it can easily lead to system instability. Therefore, it is necessary to appropriately increase the coefficients k1 and τ to suppress the risk of system instability. When designing the parameters, the gain coefficient k2 can be determined based on the instantaneous reactive power demand of the grid-connected inverter during a short circuit.

[0130] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0131] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A control method for simulating synchronous condenser operation in a new energy grid-connected inverter, characterized in that, Includes the following steps: Power calculations are performed based on the three-phase voltage and output three-phase current at the grid-connected inverter port to obtain the actual active power delivered to the grid. The active power actually delivered to the grid is fed into the active frequency loop control to obtain the phase of the internal potential of the grid-connected inverter. The amplitude of the three-phase voltage at the grid-connected inverter port is obtained by amplitude calculation, and then the amplitude of the three-phase voltage is sent to the strong excitation control to output the amplitude of the internal potential simulating the external characteristics of the synchronous condenser. The phase and amplitude of the internal potential are input into the internal potential generation module to obtain a three-phase internal potential modulation wave. The three-phase internal potential modulation wave is transmitted to the space vector modulation (SVPWM) to obtain the trigger pulse signal of each switch of the grid-connected inverter; The active frequency loop control includes: S21, the rated angular frequency ω n The frequency error signal is obtained by subtracting the angular frequency ω generated by the active frequency loop; S22, multiply the frequency error signal by the droop coefficient D of the active frequency loop. p With the rated angular frequency ω n The product of these amplifies the frequency error signal; S23, compare the amplified frequency error signal with the reference active power P ref The summation and subtraction of the actual active power P transmitted to the grid e By adjusting the output frequency, it adapts to different actual active power P. e The obtained signal is connected to the input port of the first integrator. The output signal of the first integrator is the angular frequency ω generated by the active frequency loop. By adjusting the integration coefficient 1 / (Jω) n The size of the active frequency loop changes the time constant. S24, the angular frequency ω generated by the active frequency loop can be passed through a second integrator to obtain the phase θ of the internal potential; The process of strong excitation control includes: S31, the rated three-phase voltage amplitude U at the grid-connected inverter port. o,ref The actual three-phase voltage amplitude U at the grid-connected inverter port o The error signal of the port voltage is obtained by subtracting the error signal. This error signal is then multiplied by the amplification factor k0 and transmitted to the input of the third integrator. The output of the third integrator is the transient value of the internal potential amplitude E. The third integrator adjusts the magnitude of the internal potential amplitude E by accumulating the error signal of the port voltage. S32, the actual three-phase voltage amplitude U at the grid-connected inverter port. o After multiplying by the gain factor k1, the result after passing through the inertial element with a set time constant τ, and multiplying by the amplification factor k2, is the actual three-phase voltage amplitude U at the grid-connected inverter port. o The difference is calculated to obtain the three-phase voltage amplitude U at the inverter port. o The subtransient quantity of the internal potential amplitude E during dynamic changes; S33, the internal potential amplitude E is obtained by superimposing the transient quantity of the internal potential amplitude E and the subtransient quantity of the internal potential amplitude E.

2. The control method for simulating synchronous condenser operation of a new energy grid-connected inverter according to claim 1, characterized in that, The equation for the active frequency loop control is: In the formula, P ref For reference active power; P e J is the actual active power transmitted to the grid; J is the moment of inertia of the active frequency loop; ω n The rated angular frequency; D p This is the droop factor of the active frequency loop.

3. The control method for simulating synchronous condenser operation of a new energy grid-connected inverter according to claim 1, characterized in that, The three-phase voltage amplitude U at the grid-connected inverter port o The calculation equation is as follows: In the formula, u α u β Three-phase voltage at the grid-connected inverter port , , Voltage components in the αβ coordinate system.

4. The control method for simulating synchronous condenser operation of a new energy grid-connected inverter according to claim 1, characterized in that, The voltage equation for the synchronous condenser is: In the formula, These are the stator's equivalent steady-state, transient, and subtransient reactances, respectively. These are the time constants corresponding to the transient and subtransient states, respectively. These represent the amplitude components of the internal potential corresponding to the transient and subtransient states, respectively; IL is the amplitude of the phase current; and Ef is the amplitude of the no-load excitation phase voltage.

5. The control method for simulating synchronous condenser operation of a new energy grid-connected inverter according to claim 4, characterized in that, In strong excitation control, the formula for calculating the amplification factor k0 is: in, τ v The time constant of the voltage loop is the time constant when a short circuit occurs on the grid side. τ v It is the transient time constant; The formula for calculating the time constant τ is: Where a% is the percentage of the subtransient time constant to the transient control; The formula for calculating the gain coefficient k1 is: The formula for calculating the gain coefficient k2 is: Where ΔQ represents the increase in reactive power output at the grid-connected inverter port when a short circuit occurs; when the voltage change at the grid-connected inverter port is ΔU o At that time, the output reactive power changes by ΔQ.

6. The control method for simulating synchronous condenser operation of a new energy grid-connected inverter according to claim 1, characterized in that, The three-phase internal potential is e abc The calculation expression is: In the formula, θ is the phase of the internal potential, and E is the amplitude of the internal potential.

7. The control method for simulating synchronous condenser operation of a new energy grid-connected inverter according to claim 1, characterized in that, The grid-connected inverter used in the control method includes: a DC power supply, a three-phase inverter, and a three-phase LC filter; the DC power supply is connected to the DC input terminal of the three-phase inverter, the output terminal of the three-phase inverter is connected to one end of the three-phase filter inductor, the other end of the three-phase filter inductor is connected to one end of the three-phase filter capacitor and the main power grid, and the other end of the three-phase filter capacitor is short-circuited.

8. A control system for simulating synchronous condenser operation of a new energy grid-connected inverter, comprising the method described in any one of claims 1-7, characterized in that, include: Power calculation module: Calculates the power based on the three-phase voltage and output three-phase current at the grid-connected inverter port to obtain the actual active power delivered to the grid; Internal potential phase calculation module: The active power actually delivered to the grid is fed into the active frequency loop control to obtain the phase of the internal potential of the grid-connected inverter; Internal potential amplitude calculation module: The three-phase voltage amplitude of the grid-connected inverter port is obtained by amplitude calculation, and then the three-phase voltage amplitude is sent to the strong excitation control to output the amplitude of the internal potential simulating the external characteristics of the synchronous condenser. Modulation wave generation module: Input the phase and amplitude of the internal potential into the internal potential generation module to obtain a three-phase internal potential modulation wave; In addition, the trigger pulse generation module: transmits the three-phase internal potential modulation wave to the space vector modulation (SVPWM) to obtain the trigger pulse signal of each switch of the grid-connected inverter.

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