Control method and device for heterogeneous grid-connected system with wide short-circuit ratio and power variation

Abstract

The application discloses a control method and device for a wide short-circuit ratio and power change heterogeneous grid-connected system, and the method comprises the following steps: applying follow-grid type control and network type control to follow-grid type control systems and network type control systems in the heterogeneous grid-connected system; the follow-grid type control comprises the following steps: calculating the strength of the power grid based on the voltage drop amount; adjusting the numerical value of the virtual inductance reference value based on the output power scale value of the controlled current source and the strength of the power grid, and calculating the virtual inductance compensation value; calculating the compensation voltage term based on the virtual inductance compensation value; the network type control comprises the following steps: obtaining the dynamic damping based on the change rate of the actual output active power of the virtual synchronous generator; and adding the dynamic damping to the swing equation of the virtual synchronous generator. By adopting the technical scheme, the dynamic virtual inductance and damping are introduced in the control, so that the low-frequency oscillation of the system can be overcome more rapidly, and the operation stability is improved.

Description

Technical Field

[0001] This invention relates to the field of power electronics and grid-connected control technology, and in particular to a control method and apparatus for a heterogeneous grid-connected system with wide short-circuit ratio and power variation. Background Technology

[0002] In recent years, heterogeneous grid-connected systems (HGCS), which are composed of a hybrid of grid-following (GFL) and grid-forming (GFM) control, have gradually attracted attention.

[0003] Heterogeneous grid-connected systems combine the advantages of both types of control and are expected to operate stably across the entire power grid. GFLs use phase-locked loops (PLLs) to synchronize grid voltage and control output current, offering advantages such as fast response and high power density. GFMs simulate the voltage source characteristics of synchronous generators, autonomously establishing voltage and frequency, giving them a natural advantage in weak grids and islanded operation.

[0004] However, there are certain problems in practical applications. Under strong grid conditions, grid-type control is prone to low-frequency oscillation (LFO) (usually 1 to 10 Hz) due to insufficient damping of its active power loop. Under weak grid conditions, when the grid impedance increases, the negative damping characteristics caused by passively tracking the voltage and frequency of the grid can easily lead to low-frequency oscillations in the system.

[0005] In existing technologies, the problems existing in grid-based control and grid-following control are usually overcome by introducing fixed virtual inductance and fixed damping. However, these methods are static open-loop designs and cannot adapt to real-time changes in grid strength and dynamic fluctuations in inverter output power in grid-based control and grid-following control, resulting in weak system operation stability. Summary of the Invention

[0006] Purpose of the invention: The present invention provides a control method and apparatus for a heterogeneous grid-connected system with wide short-circuit ratio and power variation, aiming to address the weakness of existing heterogeneous grid-connected systems in resisting low-frequency oscillations under wide short-circuit ratio conditions.

[0007] Technical Solution: This invention provides a control method for a heterogeneous grid-connected system with wide short-circuit ratio and power variation, comprising: the heterogeneous grid-connected system includes a grid-following control system, a grid-building control system, a grid impedance, and a power grid; the grid-following control system and the grid-building control system are coupled at a common coupling point and connected to the power grid through the grid impedance; both the grid-following control system and the grid-building control system include a converter and a filter; the common coupling point is located at the coupling point between the filter capacitor and the three-phase line; grid-following control and grid-building control are respectively applied to the grid-following control system and the grid-building control system, wherein: the grid-following control includes: acquiring the three-phase voltage at the common coupling point, converting the three-phase voltage at the coupling point to obtain d-axis voltage and q-axis voltage, and obtaining the voltage component at the coupling point through voltage magnitude calculation; comparing the voltage component at the coupling point with the grid voltage reference value to obtain the voltage drop; calculating the current grid short-circuit ratio based on the voltage drop, and thereby estimating the grid strength. The strength of the grid is considered; the per-unit value of the output power of the controlled current source is calculated based on the actual output power of the controlled current source; the per-unit value of the output power of the controlled current source and the strength of the grid are considered together, and the virtual inductance reference value is numerically adjusted to obtain the virtual inductance compensation value; in the current loop control of the grid-connected control, the corresponding compensation voltage term is calculated based on the virtual inductance compensation value, and the reference value of the grid-connected control voltage modulation signal used to control the converter switching tube is calculated; the grid-connected control includes: dynamic damping is obtained by combining the rate of change of the actual output active power of the virtual synchronous generator with the damping gain coefficient; in the grid-connected control, the dynamic damping is added to the swing equation of the virtual synchronous generator to calculate the virtual rotor angular frequency; the voltage phase angle of the virtual synchronous generator is calculated based on the virtual rotor angular frequency and used for the voltage loop and current loop control of the grid-connected control, and the reference value of the grid-connected control voltage modulation signal used to control the converter switching tube is calculated.

[0008] Specifically, the sum of the squares of the d-axis voltage and the q-axis voltage is calculated, and the positive square root of the sum of the squares is calculated to obtain the voltage components at the coupling point.

[0009] Specifically, the voltage component at the coupling point is subtracted from the reference value of the grid voltage to obtain the voltage sag transient; the voltage sag transient is filtered for noise, the absolute value of the output is taken, and multiplied by the per-unit coefficient to obtain the voltage sag amount.

[0010] Specifically, the ratio between the critical voltage drop threshold of a strong power grid and the voltage drop amount is calculated. The strength of the power grid is inferred based on the calculated ratio. The larger the ratio, the stronger the power grid, and the smaller the ratio, the weaker the power grid. The calculation of the per-unit value of the output power of the controlled current source based on the actual output power of the controlled current source includes: calculating the ratio between the actual output power of the controlled current source and the reference value of the output power of the controlled current source, and using the calculated ratio as the per-unit value of the output power of the controlled current source.

[0011] Specifically, the per-unit value of the controlled current source output power is positively correlated with the direction of adjustment of the virtual inductance reference value; the strength of the power grid is negatively correlated with the direction of adjustment of the virtual inductance reference value.

[0012] Specifically, the d-axis compensation voltage is calculated based on the synchronous rotating coordinate system angular frequency, virtual inductance compensation value, and q-axis current; the q-axis compensation voltage is also calculated based on the synchronous rotating coordinate system angular frequency, virtual inductance compensation value, and d-axis current; the three-phase current at the common coupling point is collected and converted to obtain the q-axis current and d-axis current; the d-axis compensation voltage and q-axis compensation voltage are substituted into the voltage equation of the current loop to calculate the reference value of the grid-type control voltage modulation signal.

[0013] Specifically, the rate of change of the actual output active power of the virtual synchronous generator is calculated, a Laplace transform is performed, and then a low-pass filter is used to filter out high-frequency noise to obtain dynamic damping.

[0014] Specifically, the actual output active power of the virtual synchronous generator is filtered out by a high-pass filter to remove the DC component, and the power oscillation signal is extracted. The dynamic damping is then obtained by combining the damping gain coefficient.

[0015] Specifically, the voltage amplitude correction of the virtual synchronous generator is subtracted from the dynamic damping to obtain the voltage amplitude signal of the virtual synchronous generator, which is then used for voltage loop and current loop control in grid-type control.

[0016] This invention also provides a control device for a heterogeneous grid-connected system with wide short-circuit ratio and power variation, comprising a grid-following control unit and a grid-building control unit for the heterogeneous grid-connected system, wherein: the heterogeneous grid-connected system includes a grid-following control system, a grid-building control system, a grid impedance, and a grid; the grid-following control system and the grid-building control system are coupled at a common coupling point and connected to the grid through the grid impedance; both the grid-following control system and the grid-building control system include a converter and a filter, and the common coupling point is located at the coupling point between the filter capacitor and the three-phase line; the grid-following control unit and the grid-building control unit are used to apply grid-following control and grid-building control to the grid-following control system and the grid-building control system, respectively, wherein: the grid-following control of the grid-following control unit includes: acquiring the three-phase voltage at the common coupling point, converting the three-phase voltage at the coupling point to obtain d-axis voltage and q-axis voltage, and obtaining the voltage component at the coupling point through voltage magnitude calculation; comparing the voltage component at the coupling point with the grid voltage reference value to obtain the voltage drop; based on the power... The voltage drop is used to calculate the current grid short-circuit ratio and thus infer the grid strength. The per-unit output power of the controlled current source is calculated based on its actual output power. Considering both the per-unit output power of the controlled current source and the grid strength, the virtual inductance reference value is numerically adjusted to calculate the virtual inductance compensation value. In the current loop control of the grid-following control, the corresponding compensation voltage term is calculated based on the virtual inductance compensation value, thereby calculating the reference value for the grid-following control voltage modulation signal used to control the converter switching transistors. The grid-following control of the grid-following control unit includes: obtaining dynamic damping based on the rate of change of the actual output active power of the virtual synchronous generator, combined with the damping gain coefficient; in the grid-following control, the dynamic damping is additionally added to the swing equation of the virtual synchronous generator to calculate the virtual rotor angular frequency; the voltage phase angle of the virtual synchronous generator is calculated based on the virtual rotor angular frequency and used for the voltage loop and current loop control of the grid-following control, thereby calculating the reference value for the grid-following control voltage modulation signal used to control the converter switching transistors.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: dynamic virtual inductance and damping are introduced in both network-type control and follow-network-type control, which can more quickly overcome the low-frequency oscillations of the system and improve the operational stability. Attached Figure Description

[0018] Figure 1 A schematic diagram of the structure and control flow of the heterogeneous grid-connected system provided by the present invention; Figure 2 A schematic diagram illustrating the calculation process of the network-type control provided by this invention; Figure 3 A schematic diagram illustrating the current loop voltage calculation process for grid-type control provided by the present invention; Figure 4 A schematic diagram illustrating the voltage amplitude signal calculation process for network-type control provided by the present invention; Figure 5 Simulation waveforms for applying fixed parameter control in a power surge scenario; Figure 6 The simulation waveform diagram shows the control method provided by this invention applied in a power surge scenario. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0020] See Figure 1 This is a schematic diagram of the structure and control process of the heterogeneous grid-connected system provided by the present invention.

[0021] In this embodiment of the invention, the heterogeneous grid-connected system includes a grid-connected control system, a grid-connected control system, a grid impedance, and a power grid. The grid-connected control system and the grid-connected control system are coupled at a common coupling point (PCC point) and connected to the power grid through the grid impedance. Both the grid-connected control system and the grid-connected control system include a converter and a filter. The common coupling point is located at the coupling point between the filter capacitor and the three-phase line.

[0022] Figure 1 In the diagram, a symbol suffix of 1 indicates a root-network control system, while a symbol suffix of 2 indicates a structural network control system.

[0023] In practice, the grid-type control system and the network-type control system are relatively independent, coupled to a common coupling point, and connected to the power grid through the power grid impedance.

[0024] In real-time applications, in both grid-based and network-connected control systems, the converter can deliver DC power U... dc1 (U) dc2 ) and three-phase AC voltage e a1 e b1 and e c1 (e) a2 e b2 and e c2 The converter performs the conversion, and includes multiple sub-modules that function as switching transistors; the filter includes an inductor L. f1 (L) f2 ) and capacitor C f1 (C) f2 ); Grid impedance Z g Including inductor L g and resistance R g The power grid includes three-phase u ga u gb and u gc Voltage v at the common coupling pointa1 v b1 and v c1 (v) a2 v b2 and v c2 ), current i a1 i b1 and i c1 (i a2 i b2 and i c2 The current flowing through the load (on the grid resistance side) i la1 i lb1 and i lc1 (i la2 i lb2 and i lc2 ).

[0025] In practical implementation, the short-circuit ratio (SCR) refers to the system short-circuit capacity divided by the equipment capacity, reflecting the grid's support capability for the equipment. A higher SCR indicates a stronger grid system, where equipment switching has less impact on the system, resulting in stable operation. Conversely, a lower SCR indicates a weaker grid system, with higher risks of system harmonics and low-frequency oscillations, leading to less stable operation. The heterogeneous grid-connected system provided by this invention is designed for a wide range of SCRs, covering both strong and weak grids.

[0026] In this embodiment of the invention, the following network control system and the network construction control system are respectively subject to following network control and network construction control.

[0027] In practice, a following-type control is applied to the following-type control system, and a construction-type control is applied to the construction-type control system. Since the following-type control system and the construction-type control system are relatively independent, they can be applied simultaneously or not.

[0028] See Figure 2 This is a schematic diagram of the calculation process for the network-type control provided by the present invention.

[0029] In this embodiment of the invention, the grid-type control includes: acquiring the three-phase voltage at the common coupling point, converting the three-phase voltage at the coupling point into d-axis voltage and q-axis voltage, and obtaining the voltage component at the coupling point through voltage magnitude calculation.

[0030] In a specific embodiment, the three-phase voltage v at the coupling point with the common coupling point of the network control system a1 v b1 and v c1 (v) abc1 After Clark and Park transformations, the d-axis and q-axis voltages can be obtained.

[0031] In this embodiment of the invention, the sum of the square of the d-axis voltage and the square of the q-axis voltage is calculated, and the positive square root of the sum of the squares is calculated to obtain the voltage component at the coupling point.

[0032] In practical implementation, the voltage component at the coupling point is obtained by calculating the voltage magnitude, which can characterize the voltage amplitude at the common coupling point. The formula for calculating the voltage component v at the coupling point is as follows: v=(v d1 +v q1 ) 1 / 2 , Among them, v d1 and v q1 These represent the d-axis voltage and q-axis voltage of the mesh control system, respectively.

[0033] In this embodiment of the invention, the voltage component at the coupling point is compared with the reference value of the grid voltage to obtain the voltage drop.

[0034] In practice, by comparing the voltage component at the coupling point with the reference value of the grid voltage, the degree of voltage drop can be determined, i.e., the amount of voltage drop.

[0035] In this embodiment of the invention, the voltage component at the coupling point is subtracted from the reference value of the grid voltage to obtain the voltage sag transient quantity; the voltage sag transient quantity is filtered for noise, the absolute value of the output is taken, and multiplied by the per-unit coefficient to obtain the voltage sag quantity.

[0036] In practical implementation, the coupling point voltage component v and the grid voltage reference value v g The voltage sag transient is obtained by subtracting the values. This transient is then filtered for noise (filter formula 1 / (0.02s+1), where s represents the Laplace operator), and its absolute value (|u|) is multiplied by the per-unit coefficient K. v (The reciprocal of the reference value, which can be the rated mains voltage or a voltage reference value), yields the voltage drop Δv, which can characterize the percentage of voltage drop.

[0037] In this embodiment of the invention, the current short-circuit ratio of the power grid is calculated based on the voltage drop, and the strength of the power grid is then deduced from this.

[0038] In practice, the voltage sag Δv is inversely related to the grid short-circuit ratio (SCR), i.e., Δv ≈ 1 / SCR. Under strong grid conditions, when the SCR is 10, Δv ≈ 0.1; under weak grid conditions, when the SCR is 1.5, Δv ≈ 0.67. Therefore, the current grid short-circuit ratio can be calculated from the voltage sag, and the strength of the grid can be inferred from this.

[0039] In this embodiment of the invention, the ratio between the critical voltage drop threshold of a strong power grid and the voltage drop amount is calculated. The strength of the power grid is inferred based on the calculated ratio. The larger the ratio, the stronger the power grid, and the smaller the ratio, the weaker the power grid.

[0040] In practice, the critical voltage drop threshold for a strong power grid is typically set at 10% of the reference voltage, or 0.1 per unit. However, this can be adjusted based on the specific application scenario; 0.1 is used as an example here. Therefore, calculating 0.1 / Δv, a strong power grid is defined as Δv ≈ 0.1, while a weak power grid is defined as Δv ≈ 0.67 (i.e., the ratio decreases).

[0041] In this embodiment of the invention, the per-unit value of the output power of the controlled current source is calculated based on the actual output power of the controlled current source.

[0042] In this embodiment of the invention, the actual output power P of the controlled current source is calculated. e1 Compared with the controllable current source output power reference value P rated The ratio between them is used as the per-unit value of the output power of the controlled current source.

[0043] In this embodiment of the invention, the virtual inductance reference value is numerically adjusted by considering the per-unit value of the output power of the controlled current source and the strength of the power grid, thereby calculating the virtual inductance compensation value.

[0044] In this embodiment of the invention, the per-unit value of the output power of the controlled current source is positively correlated with the direction of adjustment of the virtual inductance reference value; the strength of the power grid is negatively correlated with the direction of adjustment of the virtual inductance reference value.

[0045] In practical implementation, the distance between the dominant pole of the PLL causing oscillations and the virtual axis (i.e., the magnitude of negative damping) in grid-controlled phase-locked loop (PLL) is positively correlated with the active power output (actual output power of the controlled current source). To ensure the damping ratio stability of the entire system across the full power range, the required compensation inductance must be proportionally amplified with the active power; that is, the active power and the virtual inductance reference value are positively correlated. Under strong grid conditions, the grid provides strong support for equipment, and its operation is less affected. Therefore, the virtual inductance reference value can be reduced accordingly. Under weak grid conditions, the grid operation is easily affected, leading to oscillation problems, requiring a corresponding increase in the virtual inductance reference value.

[0046] In practical implementation, the virtual inductance compensation value L is calculated according to the following formula. CSVI : L CSVI =L base (1-0.1 / △v)(P e1 / P rated ), Among them, L baseThis represents the virtual inductance reference value.

[0047] Among them, L CSVI With (P) e1 / P rated The (1-0.1 / △v) term is positively correlated with the power grid strength. When △v≈0.1, it is a strong power grid, and the (1-0.1 / △v) term is 0. When △v≈0.67, it is a weak power grid, and the (1-0.1 / △v) term is close to 1, which shows that the power grid strength is negatively correlated with the direction of the adjustment of the virtual inductance reference value.

[0048] In this embodiment of the invention, in the current loop control of the grid-following control, the corresponding compensation voltage term is calculated based on the virtual inductance compensation value to overcome the negative damping characteristics caused by the passive tracking of the grid voltage, thereby calculating the grid-following control voltage modulation signal reference value for controlling the converter switching transistor (grid-following control system).

[0049] In practical implementation, the corresponding compensation voltage term is calculated based on the virtual inductance compensation value, which can overcome the negative damping characteristics caused by the passive tracking of the grid voltage by the grid-following control, thereby overcoming the low-frequency oscillation of the system.

[0050] See Figure 3 This is a schematic diagram of the calculation process of the grid-type control current loop voltage provided by the present invention.

[0051] In this embodiment of the invention, the d-axis compensation voltage is calculated based on the synchronous rotating coordinate system angular frequency, the virtual inductance compensation value, and the q-axis current; the q-axis compensation voltage is also calculated based on the synchronous rotating coordinate system angular frequency, the virtual inductance compensation value, and the d-axis current.

[0052] In this embodiment of the invention, the three-phase current at the common coupling point (with the grid-type control system) is collected and converted into the q-axis current i. q1 and d-axis current i d1 .

[0053] In practical implementation, the d-axis compensation voltage v c-d and q-axis compensation voltage v c-q The calculation formula is as follows: v c-d =ω1L CSVI i q1 ;v c-q =ω1L CSVI i d1 , Where ω1 represents the angular frequency of the synchronous rotating coordinate system.

[0054] In this embodiment of the invention, the d-axis compensation voltage and the q-axis compensation voltage are substituted into the voltage equation of the current loop to calculate the reference value of the grid-type control voltage modulation signal.

[0055] In specific implementation, such as Figure 3 As shown, the reference values ​​of the d-axis and q-axis currents in the rotating coordinate system (i d1 * and i q1 * ), respectively compared with the measured d-axis and q-axis currents (i d1 and i q1 The difference between the current and q axes is calculated to obtain the current error signal, which is then fed into a PI controller to obtain the corresponding voltage compensation component. The measured d-axis and q-axis currents (i...) are then analyzed. d1 and i q1 ) respectively and ω1L f (Due to inductance L) f Multiplying the dq-axis current (and the physical coupling at the d-axis) yields a voltage signal; the calculation result is then compared with the d-axis voltage v in the corresponding logic calculator. d1 d-axis compensation voltage v c-d Perform calculations, and compare them with the q-axis voltage v. q1 and q-axis compensation voltage v c-q Calculations are performed to obtain the reference value e of the d-axis voltage modulation signal. d1 * and q-axis voltage modulation signal reference value e q1 * .

[0056] In specific implementation, such as Figure 1 The grid-based control process shown uses the three-phase voltage v at the common point coupling point acquired by the phase-locked loop (PLL). abc1 Tracking the power grid phase angle θ PLL , using θ PLL The actual output three-phase current i collected abc1 Convert the direct current i to the dq rotating coordinate system d1 and i q1 The actual current i d1 and i q1 With a given current reference value i d1 * and i q1 * The current loop receives the calculated virtual inductance compensation value and performs dynamic voltage compensation (to counteract the negative resistance effect of the phase-locked loop under weak power grid conditions). The dq-axis voltage reference value e output by the current loop is... d1 * and e q1 * After inverse transformation, it reverts to three-phase AC quantity (e) a1 * e b1 * and e c1 *Finally, the current is fed into the PWM generator to drive the power switching transistor and inject current into the power grid.

[0057] In this embodiment of the invention, the network-type control includes: obtaining dynamic damping by combining the rate of change of the actual output active power of the virtual synchronous generator with the damping gain coefficient.

[0058] In practical implementation, the rate of change of the actual output active power of the virtual synchronous generator can, to a certain extent, characterize the disturbances and oscillations of the power grid. In order to accurately suppress oscillations, the dynamic rate of change of active power fluctuations is captured in real time, and dynamic damping is calculated accordingly. By tracking the changes in active power, the virtual rotor angular frequency and voltage amplitude signal in the grid-type control are corrected.

[0059] In this embodiment of the invention, during the theoretical derivation process, the rate of change of the actual output active power of the virtual synchronous generator is calculated, a Laplace transform is performed, and then a low-pass filter is used to filter out high-frequency noise to obtain dynamic damping.

[0060] In practical implementation, and during the theoretical derivation, the dynamic damping is calculated as follows: D DD (t)=K d (dP e2 (t) / dt), Among them, D DD (t) represents the dynamic damping D at time t. DD K d P represents the damping gain coefficient. e2 (t) represents the actual active power P output by the virtual synchronous generator at time t. e2 .

[0061] In practice, a Laplace transform is performed: D DD (s)=K d sP e2 (s), where s represents the Laplace operator, and a first-order low-pass filter is cascaded after the differential stage (the low-pass filter formula is: ω). c / (s+ω c ), ω c (This refers to the filter's cutoff angular frequency) High-frequency attenuation, blocking high-frequency noise.

[0062] In practice, the result of the merger is: D DD =K d (ω c / (s+ω c ))P e2 .

[0063] See Figure 4This is a schematic diagram of the voltage amplitude signal calculation process for the network-type control provided by the present invention.

[0064] In this embodiment of the invention, unlike the theoretical derivation process described above, in actual calculations, based on the rate of change of the actual output active power of the virtual synchronous generator, and combined with the damping gain coefficient conversion to obtain dynamic damping, the dynamic damping can be calculated in the following way: the actual output active power of the virtual synchronous generator is filtered out of the DC component through a high-pass filter to extract the power oscillation signal, and the dynamic damping is obtained by combining the damping gain coefficient conversion.

[0065] In practical implementation, when the system encounters strong grid load disturbances or power surges, it will generate low-frequency oscillations of 1 to 10 Hz, affecting the actual output active power P of the virtual synchronous generator. e2 A high-pass filter (filter formula: s / (s+15)) is applied to filter out the DC component and extract the power oscillation signal, which is then multiplied by the damping gain coefficient K. d This generates a dynamic damping component D. DD .

[0066] In this embodiment of the invention, the voltage amplitude correction of the virtual synchronous generator is subtracted from the dynamic damping to obtain the voltage amplitude signal of the virtual synchronous generator, which is then used for voltage loop and current loop control in grid-type control.

[0067] In practical implementation, the virtual synchronous generator outputs a reactive power reference value Q. ref2 The actual reactive power output Q of the virtual synchronous generator e2 The reactive power deviation is obtained by subtracting the reactive power deviation and inputting it into the PI controller for calculation to obtain the voltage amplitude correction of the virtual synchronous generator. The voltage amplitude correction of the virtual synchronous generator is then subtracted from the dynamic damping to obtain the voltage amplitude signal E0 of the virtual synchronous generator.

[0068] In practical implementation, based on the traditional reactive power PI controller, the voltage amplitude signal of the virtual synchronous generator is corrected by dynamic damping, which can further overcome the oscillation effect of rapid changes in active power on the system.

[0069] In this embodiment of the invention, in the grid-type control, dynamic damping is added to the swing equation of the virtual synchronous generator to calculate the virtual rotor angular frequency; the voltage phase angle of the virtual synchronous generator is calculated based on the virtual rotor angular frequency and used for the voltage loop and current loop control of the grid-type control, thereby calculating the grid-type control voltage modulation signal reference value for controlling the converter switching transistors (grid-type control system).

[0070] In practical implementation, dynamic damping is added to the swing equation of the virtual synchronous generator, and the swing equation is as follows: J(dω² / dt)=P ref2 -P e2 -(D p0 +D DD (ω2-ω0), Where J represents the virtual moment of inertia, ω2 represents the virtual rotor angular frequency, and P ref2 P represents the reference value of the active power output of the virtual synchronous generator. e2 D represents the actual active power output of the virtual synchronous generator. p0 D represents the foundation damping coefficient. DD ω0 represents dynamic damping, and ω0 represents the rated angular frequency.

[0071] In practical implementation, in the oscillation equation, the change in power will lead to the change in rotor speed, which in turn will cause the output to change and oscillate. Increasing dynamic damping can resist this change in rotor speed, making the system tend to be stable. Moreover, dynamic damping is related to the change in power, which can more effectively improve the stability of the system and overcome system oscillation.

[0072] In practical implementation, the virtual rotor angular frequency ω2 calculated from the oscillation equation can be further used to calculate the virtual phase angle θ. VSG .

[0073] In specific implementation, such as Figure 4 The network-type control process shown acquires the three-phase AC voltage V in real time. abc2 and three-phase alternating current i abc2 The signal is fed into a second-order VSG controller (i.e., the power outer loop), and the virtual phase angle θ inside the system is calculated by introducing the swing equation of dynamic damping. VSG Input to voltage loop; three-phase AC voltage V abc2 Based on virtual phase angle θ VSG After conversion, the dq-axis voltage v is obtained. d2 and v q2 The signal is fed into the voltage loop; dynamic damping is introduced into the voltage loop to calculate the voltage amplitude signal of the virtual synchronous generator. After calculation, the voltage loop outputs the dq-axis current reference value i. d2 * and i q2 * The current loop corresponds to the actual dq-axis current i d2 and i q2 (by three-phase alternating current i) abc2 (The converted value) is used for tracking adjustment, and the dq-axis voltage reference value e is output. d2 * and e q2* Combined with virtual phase angle θ VSG The dq axis voltage reference value e d2 * and e q2 * Inverse transformation into three-phase AC quantity (e a2 * e b2 * and e c2 * Finally, the switching transistor is controlled by a PWM generator, and it appears as an AC voltage source to the outside world.

[0074] See Figure 5 The waveform diagram is a simulation waveform of fixed parameter control applied under a power surge scenario; see reference. Figure 6 The waveform diagram is a simulation waveform diagram of the control method provided by the present invention applied under a power change scenario.

[0075] Figure 5 and Figure 6 The parameters for the application scenario shown are: GFM rated power 100kW, GFL rated power 60kW; DC bus voltage 1500V; mains voltage 380V / 50Hz; filter parameters: L f =2mH, C f =10μF; Basic damping coefficient D p0 =1591.55Ws, virtual inertia J=44.52Ws².

[0076] Set the grid-side inductance L g =5mH (strong grid), GFM output power 0.5pu (50kW). At t=1s, the active power of the load (grid-side resistance) increases by 50kW, from the original 50kW to 100kW. Figure 5 The simulation waveform uses traditional fixed damping (no dynamics); the GFM output frequency exhibits a low-frequency oscillation of approximately 7.8Hz, which decays slowly over time, with a settling time exceeding 1 second; Figure 6 To employ the control method provided by this invention (enabling dynamic damping, K) d The simulated waveform (=0.8) shows that the frequency oscillation completely decays within 0.6s, indicating good dynamic response.

[0077] This invention also provides a control device for a heterogeneous grid-connected system with wide short-circuit ratio and power variation, comprising a grid-following control unit and a grid-building control unit for the heterogeneous grid-connected system, wherein: the heterogeneous grid-connected system includes a grid-following control system, a grid-building control system, a grid impedance, and a grid; the grid-following control system and the grid-building control system are coupled at a common coupling point and connected to the grid through the grid impedance; both the grid-following control system and the grid-building control system include a converter and a filter, and the common coupling point is located at the coupling point between the filter capacitor and the three-phase line; the grid-following control unit and the grid-building control unit are used to apply grid-following control and grid-building control to the grid-following control system and the grid-building control system, respectively, wherein: the grid-following control of the grid-following control unit includes: acquiring the three-phase voltage at the common coupling point, converting the three-phase voltage at the coupling point to obtain d-axis voltage and q-axis voltage, and obtaining the voltage component at the coupling point through voltage magnitude calculation; comparing the voltage component at the coupling point with the grid voltage reference value to obtain the voltage drop; based on the power... The voltage drop is used to calculate the current grid short-circuit ratio and thus infer the grid strength. The per-unit output power of the controlled current source is calculated based on its actual output power. Considering both the per-unit output power of the controlled current source and the grid strength, the virtual inductance reference value is numerically adjusted to calculate the virtual inductance compensation value. In the current loop control of the grid-following control, the corresponding compensation voltage term is calculated based on the virtual inductance compensation value, thereby calculating the reference value for the grid-following control voltage modulation signal used to control the converter switching transistors. The grid-following control of the grid-following control unit includes: obtaining dynamic damping based on the rate of change of the actual output active power of the virtual synchronous generator, combined with the damping gain coefficient; in the grid-following control, the dynamic damping is additionally added to the swing equation of the virtual synchronous generator to calculate the virtual rotor angular frequency; the voltage phase angle of the virtual synchronous generator is calculated based on the virtual rotor angular frequency and used for the voltage loop and current loop control of the grid-following control, thereby calculating the reference value for the grid-following control voltage modulation signal used to control the converter switching transistors.

[0078] In specific implementations, the control device for a heterogeneous grid-connected system with wide short-circuit ratio and power variation provided by the present invention, wherein the methods, steps or functions executed by the execution unit can refer to the control method for a heterogeneous grid-connected system with wide short-circuit ratio and power variation provided by the present invention.

Claims

1. A control method for a heterogeneous grid-connected system with wide short-circuit ratio and power variation, characterized in that, include: The heterogeneous grid-connected system includes a grid-connected control system, a grid-structured control system, a grid impedance, and a grid. The grid-connected control system and the grid-structured control system are coupled at a common coupling point and connected to the grid through the grid impedance. Both the grid-connected control system and the grid-structured control system include a converter and a filter. The common coupling point is located at the coupling point between the filter capacitor and the three-phase line. For the following network control system and the network-forming control system, respectively apply the following control and the network-forming control: The network-following control includes: The three-phase voltage at the common coupling point is collected and converted into d-axis and q-axis voltages. The voltage components at the coupling point are obtained by calculating the voltage magnitude. The voltage components at the coupling point are compared with the grid voltage reference value to obtain the voltage drop. The current grid short-circuit ratio is calculated based on the voltage drop, and the grid strength is inferred from this. The per-unit value of the output power of the controlled current source is calculated based on the actual output power of the controlled current source. The virtual inductance reference value is adjusted by taking into account the level of the per-unit value of the output power of the controlled current source and the grid strength, so as to calculate the virtual inductance compensation value. In the current loop control of grid-based control, the corresponding compensation voltage term is calculated based on the virtual inductance compensation value, thereby calculating the reference value of the grid-based control voltage modulation signal used to control the converter switching transistors. The network-type control includes: Dynamic damping is obtained by converting the actual output active power of the virtual synchronous generator into a value based on the rate of change of the damping gain coefficient. In grid-type control, dynamic damping is added to the swing equation of the virtual synchronous generator to calculate the virtual rotor angular frequency. Based on the virtual rotor angular frequency, the voltage phase angle of the virtual synchronous generator is calculated and used for the voltage loop and current loop control of the grid-type control, thereby calculating the reference value of the grid-type control voltage modulation signal used to control the converter switching transistors.

2. The control method for a heterogeneous grid-connected system with wide short-circuit ratio and power variation according to claim 1, characterized in that, The calculation of the coupling point voltage component through the voltage modulus includes: Calculate the sum of the squares of the d-axis voltage and the q-axis voltage, and then calculate the positive square root of the sum of the squares to obtain the voltage components at the coupling point.

3. The control method for a heterogeneous grid-connected system with wide short-circuit ratio and power variation according to claim 2, characterized in that, The obtained voltage drop includes: The voltage sag transient is obtained by subtracting the voltage component at the coupling point from the grid voltage reference value. The voltage sag transient is then filtered for noise, and the absolute value of the output is taken and multiplied by a per-unit coefficient to obtain the voltage sag amount.

4. The control method for a heterogeneous grid-connected system with wide short-circuit ratio and power variation according to claim 3, characterized in that, The determination of the strength of the power grid, and the inference thereof, includes: Calculate the ratio between the critical voltage drop threshold of a strong power grid and the voltage drop amount. Based on the calculated ratio, infer the strength of the power grid. The larger the ratio, the stronger the power grid; the smaller the ratio, the weaker the power grid. The calculation of the per-unit value of the output power of the controlled current source based on the actual output power of the controlled current source includes: Calculate the ratio between the actual output power of the controlled current source and the reference value of the output power of the controlled current source, and use the calculated ratio as the per-unit value of the output power of the controlled current source.

5. The control method for a heterogeneous grid-connected system with wide short-circuit ratio and power variation according to claim 4, characterized in that, The virtual inductance compensation value is calculated by means of: The per-unit value of the output power of the controlled current source is positively correlated with the direction of adjustment of the virtual inductance reference value; the strength of the power grid is negatively correlated with the direction of adjustment of the virtual inductance reference value.

6. The control method for a heterogeneous grid-connected system with wide short-circuit ratio and power variation according to claim 5, characterized in that, The calculation of the corresponding compensation voltage term based on the virtual inductance compensation value includes: The d-axis compensation voltage is calculated based on the synchronous rotating coordinate system angular frequency, virtual inductance compensation value, and d-axis current; the q-axis compensation voltage is calculated based on the synchronous rotating coordinate system angular frequency, virtual inductance compensation value, and d-axis current; the three-phase current at the common coupling point is collected and converted to obtain the q-axis current and d-axis current. Substitute the d-axis compensation voltage and q-axis compensation voltage into the voltage equation of the current loop to calculate the reference value of the grid-type control voltage modulation signal.

7. The control method for a heterogeneous grid-connected system with wide short-circuit ratio and power variation according to claim 1, characterized in that, The dynamic damping, derived by converting the rate of change of the actual output active power of the virtual synchronous generator into a damping gain coefficient, includes: The rate of change of the actual output active power of the virtual synchronous generator is calculated, a Laplace transform is performed, and then a low-pass filter is used to filter out high-frequency noise to obtain dynamic damping.

8. The control method for a heterogeneous grid-connected system with wide short-circuit ratio and power variation according to claim 1, characterized in that, The dynamic damping, derived by converting the rate of change of the actual output active power of the virtual synchronous generator into a damping gain coefficient, includes: The actual output active power of the virtual synchronous generator is filtered out by a high-pass filter to remove the DC component, and the power oscillation signal is extracted. The dynamic damping is then obtained by combining the damping gain coefficient.

9. The control method for a heterogeneous grid-connected system with wide short-circuit ratio and power variation according to claim 7 or 8, characterized in that, The dynamic damping is obtained by combining the damping gain coefficient, and then includes: The voltage amplitude correction of the virtual synchronous generator is subtracted from the dynamic damping to obtain the voltage amplitude signal of the virtual synchronous generator, which is then used for voltage loop and current loop control in grid-type control.

10. A control device for a heterogeneous grid-connected system with wide short-circuit ratio and power variation, characterized in that, This includes grid-following control units and grid-building control units for heterogeneous grid-connected systems, wherein: The heterogeneous grid-connected system includes a grid-connected control system, a grid-structured control system, a grid impedance, and a grid. The grid-connected control system and the grid-structured control system are coupled at a common coupling point and connected to the grid through the grid impedance. Both the grid-connected control system and the grid-structured control system include a converter and a filter. The common coupling point is located at the coupling point between the filter capacitor and the three-phase line. The following control unit and the constructing control unit are used to apply following control and constructing control to the following control system and the constructing control system, respectively, wherein: The network-following control unit includes the following network-following control: The three-phase voltage at the common coupling point is collected and converted into d-axis and q-axis voltages. The voltage component at the coupling point is obtained by calculating the voltage modulus. The voltage component at the coupling point is compared with the grid voltage reference value to obtain the voltage drop. The current grid short-circuit ratio is calculated based on the voltage drop, and the grid strength is inferred from this. The per-unit value of the output power of the controlled current source is calculated based on the actual output power of the controlled current source. The virtual inductance reference value is adjusted by considering the per-unit value of the output power of the controlled current source and the grid strength, thereby calculating the virtual inductance compensation value. In the current loop control of grid-following control, the corresponding compensation voltage term is calculated based on the virtual inductance compensation value, thereby calculating the grid-following control voltage modulation signal reference value used to control the converter switching transistors. The network-type control of the network-type control unit includes: Based on the rate of change of the actual output active power of the virtual synchronous generator, dynamic damping is obtained by combining the damping gain coefficient. In grid-type control, the dynamic damping is added to the swing equation of the virtual synchronous generator to calculate the virtual rotor angular frequency. Based on the virtual rotor angular frequency, the voltage phase angle of the virtual synchronous generator is calculated and used for the voltage loop and current loop control of the grid-type control, thereby calculating the reference value of the grid-type control voltage modulation signal used to control the converter switching transistors.

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