Power self-synchronization control system and method of grid-connected converter with adaptive grid strength

Abstract

This invention discloses a grid-adaptive power self-synchronization control system and method for grid-connected converters. It replaces the actual voltage value with a virtual electromotive force (EMF) value calculated by the controller. The system includes: calculating virtual power based on the actual current and virtual EMF at the grid connection point; superimposing the virtual active power with the grid-connected state and grid-side phase or a self-determined phase after active power synchronization modulation to obtain a phase command; superimposing the virtual reactive power with the virtual EMF d-axis amplitude and a given voltage reference after reactive power synchronization modulation to obtain the virtual EMF d-axis amplitude; obtaining the virtual EMF q-axis amplitude after the actual current is decomposed based on the phase command and filtered by a notch filter; and outputting the virtual EMF d- and q-axis amplitudes as a converter modulation command via PWM modulation. This invention significantly improves the stability of grid-connected converters when connected to strong grids while retaining the strong active support capability of grid-connected control under weak grid conditions.

Description

Technical Field

[0001] This invention relates to the technical field of grid-connected stability control of new energy sources, and in particular to a grid-connected converter power self-synchronization control system and method that is adaptive to grid strength. Background Technology

[0002] Compared to traditional grid-based control, grid-based control can provide full-process voltage source support for the large power grid, ensuring that the grid-based converter can build its own AC output voltage without relying on an external AC system. This plays a key role in enhancing the operating characteristics of the power grid and achieving high renewable energy targets.

[0003] Grid-based control exhibits good stability under weakly synchronous grids. However, as grid strength increases, the risk of instability surges, and voltage and current oscillations occur at the common coupling point, posing a serious threat to new energy grid-connected systems. It is urgent to address the problem of poor adaptability of grid-based control to real-world complex grid scenarios.

[0004] In terms of control performance, grid-based control should not only provide sufficient voltage and frequency active support strength under different grid strengths and different grid disturbance forms, but also improve the rapid response capability of grid events, shorten the active and reactive power response delay of control, obtain more accurate power values, and study grid-based control strategies with grid strength adaptive capabilities. In terms of control structure, grid-based control should not only simplify the control structure and highlight the characteristics of rapid response, but also improve the applicability of complex grid scenarios, achieve the same bidirectional converter control structure and unified control parameters, and eliminate the need to readjust the control loop when the power flow direction is switched.

[0005] Currently, grid-based control is mostly based on existing methods such as droop control, virtual synchronous machine, power synchronization control, virtual oscillator, and phase-locked loop-based grid-based control. These methods add controller damping links and introduce passive damping to improve stability in a single power grid scenario. However, due to one-sided model design or complex control structure, it is not yet possible to simultaneously meet the requirements of having power grid strength adaptive capability and being suitable for bidirectional converters. Summary of the Invention

[0006] The primary objective of this invention is to address the shortcomings of existing technologies by providing a grid-strength adaptive power self-synchronization control system for grid-connected converters. This system retains the strong active support capability of grid-connected control under weak grid conditions while significantly improving the stability of grid-connected converters when connected to strong grids.

[0007] The second objective of this invention is to provide a grid-connected converter power self-synchronization control method that is adaptive to grid strength.

[0008] The first objective of this invention is achieved through the following technical solution: a grid-adaptive power self-synchronization control system for grid-connected converters, comprising:

[0009] The power calculation module is used to calculate the power based on the d-axis amplitude v of the virtual electromotive force. sd Virtual potential q-axis amplitude v sq The actual current vector i at the common coupling point o The virtual active power P at the grid connection point is output. pcc and virtual reactive power Q pcc ;

[0010] The reference phase command module is used to determine and select the first reference phase ω based on whether the grid converter is in inverter or rectifier mode. pcc t, second reference phase ω ref t or third reference phase ω dc t is used as the reference phase ω0t;

[0011] The active power synchronization module is used to synchronize the virtual active power P. pcc The phase error θ is calculated and summed with the reference phase ω0t to obtain the phase command ω. s t;

[0012] The reactive power synchronization module is used to synchronize the virtual reactive power Q. pcc The virtual AC voltage amplitude E is calculated.

[0013] The AC voltage modulation module is used to calculate the d-axis command, i.e., the virtual electromotive force d-axis amplitude v, based on the virtual AC voltage amplitude E. sd ;

[0014] The current notch modulation module is used to adjust the current vector i at the common coupling point. o The q-axis command, i.e., the virtual potential q-axis amplitude v, is calculated. sq ;

[0015] The PWM modulation module is used to adjust the amplitude of the virtual electromotive force d-axis, v. sd Virtual potential q-axis amplitude v sq and phase command ω s t Synthetic converter modulation command.

[0016] Furthermore, the power calculation module performs the following operations:

[0017] The actual current vector i at the common coupling point o Based on phase command ω s After performing the Parker transformation, the actual current d-axis amplitude i is obtained. od and the actual current q-axis amplitude i oq Then, based on the actual current d-axis amplitude i od Actual current q-axis amplitude i oq Virtual potential d-axis amplitude v sdand virtual potential q-axis amplitude v sq Calculate the virtual active power P at the grid connection point. pcc and virtual reactive power Q pcc Among them, P pcc and Q pcc The calculation formula is:

[0018]

[0019] Furthermore, the reference phase command module performs the following operations:

[0020] First reference phase ω pcc The method for calculating t is as follows: the actual voltage vector v at the common coupling point is... o Based on the actual voltage phase ω at the common coupling point pcc After performing the Parker transformation, the actual voltage d-axis amplitude v is obtained. od And the actual voltage q-axis amplitude v oq v oq With respect to the phase voltage q-axis reference value v oqref The difference is calculated, and after entering the phase voltage PI controller, ω is obtained. pcc t, ω pcc t returns feedback to v after the points accumulation process. o The expression for the phase voltage PI controller in the Parker transformation stage is:

[0021]

[0022] In the formula, s represents the Laplace operator, t represents time, and k represents the time interval. vop k represents the phase voltage proportionality coefficient. voi Represents the phase voltage integral coefficient;

[0023] Second reference phase ω ref The method for calculating t is as follows: given the active support frequency f ref ω was calculated ref The expression for t is:

[0024]

[0025] Third reference phase ω dc The calculation method for t is: through the DC side voltage V of the grid converter. dc and DC voltage reference V dcref ω was calculated dc The expression for t is:

[0026] ω dc t = k dc (V dcref -V dc )

[0027] In the formula, k dc This represents the DC voltage proportionality coefficient;

[0028] The first reference phase ω is selected based on whether the grid converter is in inverter or rectifier mode. pcc t, second reference phase ω ref t and the third reference phase ω dc One of the terms t is used as the reference phase ω0t, as follows:

[0029] When the grid-connected converter is in inverter mode, if it is in the grid connection switching process, the converter phase is required to catch up with the grid phase. The first reference phase is used as the reference phase ω0t, that is, let ω0t = ω pcc If the converter is in stable operation after grid connection, it is required to play an active support role. The second reference phase is used as the reference phase ω0t, that is, let ω0t = ω ref t; When the grid converter is in rectification mode, a specified voltage is required to be output on the DC side, using the third reference phase ω. dc Let t be the reference phase ω0t, that is, let ω0t = ω dc t.

[0030] Furthermore, the active power synchronization module performs the following operations:

[0031] Active power reference P ref P output by the power calculation module pcc The difference is calculated, and the phase error θ is obtained after entering the active power synchronous integral controller. θ is then summed with ω0t output by the reference phase command module to obtain the phase command ω. s t, ω s t feedback back to i o The Parker transform stage, fed forward to v sd v sq The expression for the active power synchronous integral controller in the Parker inverse transform stage is:

[0032]

[0033] In the formula, k pi This represents the synchronous integral coefficient of active power.

[0034] Furthermore, the reactive power synchronization module performs the following operations:

[0035] Reactive power reference Q ref Q output by the power calculation module pcc The difference is calculated, and after entering the reactive power synchronous proportional controller, a virtual AC voltage e is obtained. e is superimposed on the AC voltage amplitude reference E. ref The virtual AC voltage amplitude E is obtained, and its expression is:

[0036] E = e + E ref =k qi (Q ref -Q pcc )+E ref

[0037] In the formula, k qi This represents the reactive power synchronization ratio coefficient.

[0038] Furthermore, the AC voltage modulation module performs the following operations:

[0039] Connect E and v sd After the difference is calculated, it enters the AC voltage PI controller and is compared with the d-axis component of the notch current output by the current notch modulation module. dn Differential calculation, superimposed AC voltage amplitude d-axis reference V dref Get v sd v sd Feedback is sent to the power calculation module and the reactive power synchronization module, v sd The expression is:

[0040]

[0041] In the formula, k vp k represents the AC voltage proportionality coefficient. vi This represents the integral coefficient of AC voltage.

[0042] Furthermore, the current notch modulation module performs the following operations:

[0043] will i oq After inputting into the notch filter, the q-axis component i of the notch current is obtained. qn And invert it, and compare it with the AC voltage amplitude q-axis reference V. qref After superposition, we get v sq v sq Feedback is sent to the power calculation module, based on the actual current vector i at the common coupling point. o The q-axis command, i.e., the virtual potential q-axis amplitude v, is calculated. sq ;change i od After inputting the notch filter, i is obtained dn And it is sent to the AC voltage modulation module, i dn i qn and v sq The expressions are as follows:

[0044]

[0045] v sq =V qref -i qn

[0046] In the formula, ω t Let ζ be the target notch frequency and ζ be the damping ratio.

[0047] Furthermore, the PWM modulation module performs the following operations:

[0048] v sd and v sq Based on ω s t undergoes a Parker transform to obtain a three-phase modulated wave v sabc Perform PWM modulation.

[0049] The second objective of this invention is achieved through the following technical solution: a grid-adaptive power self-synchronization control method for grid-connected converters, wherein, when executing the steps of the method, the processor calls the power calculation module, reference phase command module, active power synchronization module, reactive power synchronization module, AC voltage modulation module, current notch modulation module, and PWM modulation module in the aforementioned grid-adaptive power self-synchronization control system for grid-connected converters, so as to realize the corresponding functions in each module.

[0050] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0051] 1. This invention has the ability to adapt to grid strength, while retaining the strong active support capability of grid-type control under weak grid conditions, and greatly improving the stability of grid-type converters when connected to strong grids.

[0052] 2. This invention introduces a notch filter to replace the virtual admittance commonly used in traditional mesh control, which improves the ability to suppress subsynchronous oscillations and low-frequency oscillations while completely avoiding the instability risk caused by the uncertainty of the virtual admittance value.

[0053] 3. This invention eliminates the LPF filtering stage commonly added to the power channel in traditional network control, thereby reducing control complexity and simplifying the design and debugging complexity of the system.

[0054] 4. This invention has good applicability to complex power grid scenarios, and is also applicable to bidirectional converters under both strong and weak power grids. Furthermore, the bidirectional converter parameters are uniformly tuned, and there is no need to readjust the control parameters when the power flow direction is switched. Attached Figure Description

[0055] Figure 1 This is a control structure framework diagram of the system of the present invention in Example 1.

[0056] Figure 2 The figure shows the experimental results of the inverter-mode grid converter being connected to the high-voltage power grid in Example 1.

[0057] Figure 3 The figure shows the experimental results of the inverter-mode grid converter being connected to a weak power grid in Example 1.

[0058] Figure 4 The figure shows the experimental results of the reference change of the output power of the in-situ grid converter in the grid-connected inverter mode of the strong power grid in Example 1.

[0059] Figure 5 The figure shows the experimental results of the reference change of the output power of the in-situ grid converter in the weak grid grid-connected inverter mode in Example 1.

[0060] Figure 6 This is a diagram showing the experimental results of the grid converter in rectification mode connected to a strong power grid in Example 1.

[0061] Figure 7 This is a diagram showing the experimental results of the grid converter in rectification mode connected to a weak power grid in Example 1.

[0062] Figure 8 The figure shows the experimental results of the reference change of the output power of the grid converter in the strong grid-connected rectification mode in Example 1.

[0063] Figure 9 The figure shows the experimental results of the reference change of the output power of the grid converter in the weak grid rectifier mode in Example 1. Detailed Implementation

[0064] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0065] Example 1

[0066] like Figure 1 As shown, this embodiment discloses a grid-strength adaptive power self-synchronization control system for grid-connected converters. Figure 1 In the middle, v g It is the grid voltage vector, R g It is the resistance of the power grid line, L g It is the inductance of the power grid line, PCC is the point of common coupling, L f It is the filter inductor of the grid converter, i dc It is the DC-side current of the grid converter, V dc It is the DC side voltage of the grid converter, C dc It is the DC-side filter capacitor of the grid converter.

[0067] This control system operates on a grid-connected converter connected in parallel with the power grid. It consists of control modules including a power calculation module, a reference phase command module, an active power synchronization module, a reactive power synchronization module, an AC voltage modulation module, a current notch modulation module, and a PWM modulation module. The function and implementation of each control module are as follows:

[0068] a. Power calculation module, its functions and implementation are as follows:

[0069] The actual current vector i at the common coupling point o Based on phase command ω s The actual current d-axis amplitude i is obtained by decomposing t into dq. od and the actual current q-axis amplitude i oq Then, based on the actual current d-axis amplitude i od Actual current q-axis amplitude i oq Virtual potential d-axis amplitude v sd and virtual potential q-axis amplitude v sq Calculate the virtual active power P at the grid connection point. pcc and virtual reactive power Q pcc Among them, P pcc and Q pcc The calculation formula is:

[0070]

[0071] b. The reference phase command module, its functions and implementation are as follows:

[0072] Calculate the first reference phase ω pcc t or second reference phase ω ref t or third reference phase ω dc t, depending on whether the grid converter is in inverter or rectifier mode, select one of them as the reference phase ω0t;

[0073] First reference phase ω pcc The method for calculating t is as follows: the actual voltage vector v at the common coupling point is... o Based on the actual voltage phase ω at the common coupling point pcc After performing the Parker transformation, the actual voltage d-axis amplitude v is obtained. od And the actual voltage q-axis amplitude v oq v oq With respect to the phase voltage q-axis reference value v oqref The difference is calculated, and after entering the phase voltage PI controller, ω is obtained. pcc t, ω pcc t is fed back to v after the points are awarded. o The expression for the phase voltage PI controller in the Parker transformation stage is:

[0074]

[0075] In the formula, s represents the Laplace operator, t represents time, and k represents the time interval. vop k represents the phase voltage proportionality coefficient. voi Represents the phase voltage integral coefficient;

[0076] Second reference phase ω refThe method for calculating t is as follows: given the active support frequency f ref ω was calculated ref The expression for t is:

[0077]

[0078] Third reference phase ω dc The calculation method for t is: through the DC side voltage V of the grid converter. dc and DC voltage reference V dcref ω was calculated dc The expression for t is:

[0079] ω dc t = k dc (V dcref -V dc )

[0080] In the formula, k dc This represents the DC voltage proportionality coefficient;

[0081] The first reference phase ω is selected based on whether the grid converter is in inverter or rectifier mode. pcc t, second reference phase ω ref t and the third reference phase ω dc One of the terms t is used as the reference phase ω0t, as follows:

[0082] When the grid-connected converter is in inverter mode, if it is in the grid connection switching process, the converter phase is required to catch up with the grid phase. The first reference phase is used as the reference phase ω0t, that is, let ω0t = ω pcc If the converter is in stable operation after grid connection, it is required to play an active support role. The second reference phase is used as the reference phase ω0t, that is, let ω0t = ω ref t; When the grid converter is in rectification mode, a specified voltage is required to be output on the DC side, using the third reference phase ω. dc Let t be the reference phase ω0t, that is, let ω0t = ω dc t.

[0083] c. Active power synchronization module, whose functions and implementation methods are as follows:

[0084] Active power reference P ref P output by the power calculation module pcc The difference is calculated, and the phase error θ is obtained after entering the active power synchronous integral controller. θ is then summed with ω0t output by the reference phase command module to obtain the phase command ω. s t, ω s t feedback back to i o The Parker transform stage, fed forward to v sd vsq The expression for the active power synchronous integral controller in the Parker inverse transform stage is:

[0085]

[0086] In the formula, k pi This represents the synchronous integral coefficient of active power.

[0087] d. Reactive power synchronization module, whose functions and implementation methods are as follows:

[0088] Reactive power reference Q ref Q output by the power calculation module pcc The difference is calculated, and after entering the reactive power synchronous proportional controller, a virtual AC voltage e is obtained. e is superimposed on the AC voltage amplitude reference E. ref The virtual AC voltage amplitude E is obtained, and its expression is:

[0089] E = e + E ref =k qi (Q ref -Q pcc )+E ref

[0090] In the formula, k qi This represents the reactive power synchronization ratio coefficient.

[0091] e. AC voltage modulation module, its function and implementation method are as follows:

[0092] Connect E and v sd After the difference is calculated, it enters the AC voltage PI controller and is compared with the d-axis component of the notch current output by the current notch modulation module. dn Differential calculation, superimposed AC voltage amplitude d-axis reference V dref Get v sd v sd Feedback is sent to the power calculation module and the reactive power synchronization module, v sd The expression is:

[0093]

[0094] In the formula, k vp k represents the AC voltage proportionality coefficient. vi This represents the integral coefficient of AC voltage.

[0095] f. Current notch modulation module, its function and implementation are as follows:

[0096] will i oq After inputting into the notch filter, the q-axis component i of the notch current is obtained. qn And invert it, and compare it with the AC voltage amplitude q-axis reference V. qref After superposition, we get vsq v sq Feedback is sent to the power calculation module, based on the actual current vector i at the common coupling point. o The q-axis command, i.e., the virtual potential q-axis amplitude v, is calculated. sq ;change i od After inputting the notch filter, i is obtained dn And it is sent to the AC voltage modulation module, i dn i qn and v sq The expressions are as follows:

[0097]

[0098] v sq =V qref -i qn

[0099] In the formula, ω t Let ζ be the target notch frequency and ζ be the damping ratio.

[0100] g. The PWM modulation module, its function and implementation are as follows:

[0101] v sd and v sq Based on ω s The three-phase modulated wave v is obtained by performing the Park inverse transform on t. sabc Perform PWM modulation.

[0102] To verify the effectiveness of the control system proposed in this embodiment, an experiment was conducted using a system consisting of a grid-connected bidirectional converter (hereinafter referred to as the grid-connected converter) and a simulated power grid as the experimental object. The experimental parameters are shown in Table 1.

[0103] Table 1 Experimental parameters

[0104] symbol variable name Value <![CDATA[P ref ]]> Active power reference 1000W <![CDATA[L f ]]> Converter filter inductor 1mH <![CDATA[v oqref ]]> Phase voltage q-axis reference 0 <![CDATA[v dcref ]]> DC voltage reference 800V <![CDATA[Q ref ]]> Reactive power reference 0 <![CDATA[E ref ]]> Virtual voltage amplitude reference 311V <![CDATA[V dref ]]> AC voltage amplitude d-axis reference 311V <![CDATA[V qref ]]> AC voltage amplitude q-axis reference 0 <![CDATA[V g ]]> Rated voltage amplitude of power grid 311V

[0105] a) Testing of grid-connected converter in inverter mode connected to the power grid

[0106] In the experimental test, the power grid frequency f = 55 Hz, and the power grid phase... The short-circuit ratio (SCR) is 40.91 (for a high-voltage power grid). The experimental results are as follows: Figure 2 As shown, under the proposed grid strength adaptive power self-synchronization control system for grid-connected converters, the grid-connected converter exhibits strong stability after being connected to a strong grid in inverter mode. At t = 0.05–0.1 s, the grid-connected converter is in inverter islanded operation mode, with switch S2 closed and switches S1 and S3 open, ω0t = ω reft plays an active supporting role; t = 0.1~0.15s, the grid-connected converter is in inverter-grid switching mode, switch S1 is closed, and switches S2 and S3 are open, ω0t = ω pcc At time t, the converter phase successfully catches up with the grid phase; after t = 0.15s, the grid-connected converter is in inverter-grid-stable mode, switch S2 is closed, and switches S1 and S3 are open, ω0t = ω ref The proposed control system plays an active supporting role. During the grid connection switching process, the proposed control system successfully restored the grid connection voltage and current to stability within only 0.02s (i.e., one grid cycle), while the power curve overshoot was small, achieving grid-connected converter friendly connection to the strong grid under unity power factor.

[0107] b. Testing of grid-connected converters in inverter mode connected to a weak power grid

[0108] In the experimental test, the power grid frequency f = 55 Hz, and the power grid phase... Short-circuit ratio (SCR) = 0.56 (weak grid), experimental results are as follows: Figure 3 As shown, under the proposed grid strength adaptive power self-synchronization control system for grid-connected converters, the grid-connected converter maintains strong stability after being connected to a weak grid in inverter mode. At t = 0.05–0.1 s, the grid-connected converter is in inverter islanded operation mode, with switch S2 closed and switches S1 and S3 open, ω0t = ω ref t plays an active supporting role; t = 0.1~0.15s, the grid-connected converter is in inverter-grid switching mode, switch S1 is closed, and switches S2 and S3 are open, ω0t = ω pcc At time t, the converter phase successfully catches up with the grid phase; after t = 0.15s, the grid-connected converter is in inverter-grid-stable mode, switch S2 is closed, and switches S1 and S3 are open, ω0t = ω ref The proposed control system plays an active supporting role. During the grid connection switching process, the proposed control system successfully restored the grid connection voltage and current to stability within only 0.04s (i.e., 2 grid cycles), while the power curve overshoot was small. It achieved friendly grid connection of the grid-connected converter to the weak grid under unity power factor, maintaining the inherent advantages of traditional grid-connected control methods.

[0109] c. Test of reference change in output power of grid-connected converter under strong grid inverter mode

[0110] In the experimental test, the grid frequency f = 50 Hz, the short-circuit ratio SCR = 40.91 (strong grid), and the active power reference P at t = 0.15 s. ref The experimental results were as follows: The power was increased from 1000W to 2000W. Figure 4As shown, under the proposed grid strength adaptive grid converter power self-synchronization control system, after the grid converter in inverter mode is stably connected to the strong grid, the active power reference P is increased. ref The actual output power of the converter quickly follows the reference and exhibits strong stability, playing a proactive supporting role. After changing the power reference, the proposed control system successfully restores the grid-connected voltage and current to stability within only 0.02s (i.e., one grid cycle), while the power curve overshoot is small, demonstrating rapid power command following characteristics even under strong grid conditions.

[0111] d. Test of reference change in output power of grid-connected converter under weak grid inverter mode

[0112] In the experimental test, the grid frequency f = 50 Hz, the short-circuit ratio SCR = 0.56 (weak grid), and the active power reference P at t = 0.15 s. ref The experimental results were as follows: The power was increased from 1000W to 2000W. Figure 5 As shown, under the proposed grid strength adaptive grid converter power self-synchronization control system, after the grid converter in inverter mode is stably connected to the weak grid, the active power reference P is increased. ref The actual output power of the converter quickly follows the reference and exhibits strong stability, playing a proactive supporting role. After changing the power reference, the proposed control system successfully restores the grid-connected voltage and current to stability within only 0.02s (i.e., one grid cycle), while the power curve overshoot is small, demonstrating the expected fast power command following characteristics under weak grid conditions.

[0113] e. Testing of grid-connected converters in rectification mode connected to the power grid

[0114] In the experimental test, the grid frequency f = 50 Hz, the short-circuit ratio SCR = 40.91 (strong grid), and the reference voltage V of the DC side of the grid converter. dcref =800V, experimental results are as follows Figure 6 As shown, under the proposed grid strength adaptive power self-synchronization control system for grid-connected converters, the grid-connected converters connected to a strong grid exhibit strong stability in rectification mode. After grid connection at t=0s, the grid-connected converter is in rectification mode, requiring a specified DC output voltage. Switch S3 is closed, while switches S1 and S2 are open, and ω0t = ω dc During grid connection, the proposed control system successfully restored the grid-side voltage and current to stability within only 0.02s (i.e., one grid cycle), while the DC-side output voltage quickly reached the target value. The power curve overshoot was small, achieving a fast, stable, and accurate DC-side dynamic response under strong AC grid conditions.

[0115] f. Testing of grid-connected converters in rectification mode integrated into the high-voltage power grid

[0116] In the experimental test, the grid frequency f = 50 Hz, the short-circuit ratio SCR = 0.56 (weak grid), and the DC side voltage reference V of the grid converter was used. dcref =800V, experimental results are as follows Figure 7 As shown, under the proposed grid strength adaptive power self-synchronization control system for grid-connected converters, the grid-connected converters connected to a weak grid exhibit strong stability in rectification mode. After grid connection at t=0s, the grid-connected converter is in rectification mode, requiring a specified DC output voltage. Switch S3 is closed, while switches S1 and S2 are open, and ω0t = ω dc During grid connection, the proposed control system successfully restored the grid-side voltage and current to stability within only 0.1s (i.e., 5 grid cycles), while the DC-side output voltage quickly reached the target value. The power curve overshoot was small, achieving fast, stable, and accurate DC-side dynamic response under weak AC grid conditions.

[0117] g. Test of reference change in output power of grid-connected converter under strong grid rectification mode

[0118] In the experimental test, the grid frequency f = 50 Hz, the short-circuit ratio SCR = 40.91 (strong grid), and the reference voltage V of the DC side of the grid converter. dcref =800V, active power reference P at t=1s ref The experimental results were as follows: The power was increased from 1000W to 2000W. Figure 8 As shown, under the proposed grid strength adaptive grid converter power self-synchronization control system, after the grid converter is stably connected to the strong grid in rectification mode, the active power reference P is increased. ref The actual output power of the converter on the DC side quickly follows the reference and exhibits strong stability. After changing the power reference, the proposed control system successfully restores the grid-connected voltage and current, as well as the DC-side output voltage, to stability within only 0.02s (i.e., one grid cycle), demonstrating rapid power command following characteristics even under strong grid conditions.

[0119] h. Test of reference change in output power of grid-connected converter under weak grid rectifier mode

[0120] In the experimental test, the grid frequency f = 50 Hz, the short-circuit ratio SCR = 0.56 (weak grid), and the DC side voltage reference V of the grid converter was used. dcref =800V, active power reference P at t=1s ref The experimental results were as follows: The power was increased from 1000W to 2000W. Figure 9 As shown, under the proposed grid strength adaptive grid converter power self-synchronization control system, after the grid converter is stably connected to the weak grid in rectification mode, the active power reference P is increased. refThe actual output power of the converter on the DC side quickly follows the reference and exhibits strong stability. After changing the power reference, the proposed control system successfully restores the grid-connected voltage and current, as well as the DC-side output voltage, to stability within only 0.16s (i.e., 8 grid cycles), demonstrating rapid power command following characteristics even under weak grid conditions.

[0121] Example 2

[0122] This embodiment discloses a grid-strength adaptive power self-synchronization control method for grid-connected converters. When executing the steps of this method, the processor calls the power calculation module, reference phase command module, active power synchronization module, reactive power synchronization module, AC voltage modulation module, current notch modulation module, and PWM modulation module in the grid-strength adaptive power self-synchronization control system described in Embodiment 1 to realize the corresponding functions of each module, including the following steps:

[0123] Step 1, use the power calculation module to calculate based on v sd v sq The actual current vector i at the common coupling point o The virtual active power P at the grid connection point is obtained after calculation. pcc and virtual reactive power Q pcc ;

[0124] Step 2: Using the reference phase command module, select the first reference phase ω based on whether the grid converter is in inverter or rectifier mode. pcc t, second reference phase ω ref t or third reference phase ω dc t is used as the reference phase ω0t: When the grid-connected converter is in inverter mode, if it is in the process of grid connection switching, switch S1 is closed and switches S2 and S3 are open, let ω0t = ω pcc t; If the system is in stable operation after grid connection, switch S2 is closed, and switches S1 and S3 are open. Let ω0t = ω ref When the grid converter is in rectification mode, switch S3 is closed, and switches S1 and S2 are open. Let ω0t = ω dc t;

[0125] Step 3, using the active power synchronization module, according to P pcc The phase error θ is calculated and summed with ω0t to obtain the phase command ω. s t;

[0126] Step 4, use a reactive power synchronization module, according to Q pcc and v sd The virtual AC voltage amplitude E is calculated.

[0127] Step 5: Using the current notch modulation module, based on the actual current vector i at the common coupling point... o The q-axis command, i.e., the virtual potential q-axis amplitude v, is calculated. sq and obtain i dn ;

[0128] Step 6, using the AC voltage modulation module, according to i dn The d-axis command, i.e., the d-axis amplitude of the virtual AC voltage E, is calculated from the virtual AC voltage amplitude E. sd ;

[0129] Step 7: Using the PWM modulation module, based on the virtual electromotive force d-axis amplitude v sd Virtual potential q-axis amplitude v sq and phase command ω s t Synthetic converter modulation command.

[0130] In the description of Embodiment 1, it should be noted that the terms "Step 1", "Step 2", "Step 3", "Step 4", "Step 5", "Step 6", and "Step 7" are only used to describe the interaction relationship and relative inheritance process of the various control modules in this invention. They are not unique in description and should not be construed as indicating or implying relative importance, nor should they be construed as limiting this embodiment.

[0131] Example 3

[0132] This embodiment discloses a non-transitory computer-readable medium storing instructions that, when executed by a processor, perform the steps of the grid strength adaptive grid converter power self-synchronization control method according to Embodiment 2.

[0133] In this embodiment, the non-transitory computer-readable medium can be a disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), USB flash drive, portable hard drive, etc.

[0134] Example 4

[0135] This embodiment discloses a computing device, including a processor and a memory for storing processor-executable programs. When the processor executes the program stored in the memory, it implements the grid strength adaptive grid converter power self-synchronization control method described in Embodiment 2.

[0136] The computing device described in this embodiment may be a desktop computer, laptop computer, smartphone, PDA handheld terminal, tablet computer, programmable logic controller (PLC), or other terminal device with processor function.

[0137] The above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Therefore, any changes made in accordance with the shape and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A grid-connected converter power self-synchronization control system adaptive to grid strength, characterized in that, include: The power calculation module is used to calculate the power based on the d-axis amplitude v of the virtual electromotive force. sd Virtual potential q-axis amplitude v sq and the actual current vector i at the common coupling point o The virtual active power P at the grid connection point is output. pcc and virtual reactive power Q pcc ; The reference phase command module is used to determine and select the first reference phase ω based on whether the grid converter is in inverter or rectifier mode. pcc t, second reference phase ω ref t or third reference phase ω dc t is used as the reference phase ω0t; The active power synchronization module is used to synchronize the virtual active power P. pcc The phase error θ is calculated and summed with the reference phase ω0t to obtain the phase command ω. s t; The reactive power synchronization module is used to synchronize the virtual reactive power Q. pcc The virtual AC voltage amplitude E is calculated. The AC voltage modulation module is used to calculate the d-axis command, i.e., the virtual electromotive force d-axis amplitude v, based on the virtual AC voltage amplitude E. sd ; The current notch modulation module is used to adjust the current vector i at the common coupling point. o The q-axis command, i.e., the virtual potential q-axis amplitude v, is calculated. sq ; The PWM modulation module is used to adjust the amplitude of the virtual electromotive force d-axis, v. sd Virtual potential q-axis amplitude v sq and phase command ω s t Synthetic converter modulation command; The reference phase command module performs the following operations: First reference phase ω pcc The method for calculating t is as follows: the actual voltage vector v at the common coupling point is... o Based on the actual voltage phase ω at the common coupling point pcc After performing the Parker transformation, the actual voltage d-axis amplitude v is obtained. od And the actual voltage q-axis amplitude v oq v oq With respect to the phase voltage q-axis reference value v oqref The difference is calculated, and after entering the phase voltage PI controller, ω is obtained. pcc t, ω pcc t returns feedback to v after the points accumulation process. o The expression for the phase voltage PI controller in the Parker transformation stage is: In the formula, s represents the Laplace operator, t represents time, and k represents the time interval. vop k represents the phase voltage proportionality coefficient. voi Represents the phase voltage integral coefficient; Second reference phase ω ref The method for calculating t is as follows: given the active support frequency f ref ω was calculated ref The expression for t is: Third reference phase ω dc The calculation method for t is: through the DC side voltage V of the grid converter. dc and DC voltage reference V dcref ω was calculated dc The expression for t is: ω dc t=k dc (V dcref -V dc ) In the formula, k dc This represents the DC voltage proportionality coefficient; The first reference phase ω is selected based on whether the grid converter is in inverter or rectifier mode. pcc t, second reference phase ω ref t and the third reference phase ω dc One of the terms t is used as the reference phase ω0t, as follows: When the grid-connected converter is in inverter mode, if it is in the grid connection switching process, the converter phase is required to catch up with the grid phase. The first reference phase is used as the reference phase ω0t, that is, let ω0t = ω pcc t; If the converter is in stable operation after grid connection, it is required to play an active support role. The second reference phase is used as the reference phase ω0t, that is, let ω0t = ω ref t; When the grid converter is in rectification mode, a specified voltage is required to be output on the DC side, using the third reference phase ω. dc Let t be the reference phase ω0t, that is, let ω0t = ω dc t.

2. The grid-adaptive power self-synchronization control system for grid converters according to claim 1, characterized in that, The power calculation module performs the following operations: The actual current vector i at the common coupling point o Based on phase command ω s After performing the Parker transformation, the actual current d-axis amplitude i is obtained. od and the actual current q-axis amplitude i oq Then, based on the actual current d-axis amplitude i od Actual current q-axis amplitude i oq Virtual potential d-axis amplitude v sd and virtual potential q-axis amplitude v sq Calculate the virtual active power P at the grid connection point. pcc and virtual reactive power Q pcc ; Among them, P pcc and Q pcc The calculation formula is:

3. The grid-adaptive power self-synchronization control system for grid converters according to claim 2, characterized in that, The active power synchronization module performs the following operations: Active power reference P ref P output by the power calculation module pcc The difference is calculated, and the phase error θ is obtained after entering the active power synchronous integral controller. θ is then summed with ω0t output by the reference phase command module to obtain the phase command ω. s t, ω s t feedback back to i o The Parker transform stage, fed forward to v sd v sq The expression for the active power synchronous integral controller in the Parker inverse transform stage is: In the formula, k pi This represents the synchronous integral coefficient of active power.

4. The grid-adaptive power self-synchronization control system for grid converters according to claim 3, characterized in that, The reactive power synchronization module performs the following operations: Reactive power reference Q ref Q output by the power calculation module pcc The difference is calculated, and after entering the reactive power synchronous proportional controller, a virtual AC voltage e is obtained. e is superimposed on the AC voltage amplitude reference E. ref The virtual AC voltage amplitude E is obtained, and its expression is: E=e+E ref =k qi (Q ref -Q pcc )+E ref In the formula, k qi This represents the reactive power synchronization ratio coefficient.

5. A grid-connected converter power self-synchronization control system adaptive to grid strength according to claim 4, characterized in that, The AC voltage modulation module performs the following operations: Connect E and v sd After the difference is calculated, it enters the AC voltage PI controller and is compared with the d-axis component of the notch current output by the current notch modulation module. dn Differential calculation, superimposed AC voltage amplitude d-axis reference V dref Get v sd v sd Feedback is sent to the power calculation module and the reactive power synchronization module, v sd The expression is: In the formula, k vp k represents the AC voltage proportionality coefficient. vi This represents the integral coefficient of AC voltage.

6. A grid-connected converter power self-synchronization control system adaptive to grid strength according to claim 5, characterized in that, The current notch modulation module performs the following operations: will i oq After inputting into the notch filter, the q-axis component i of the notch current is obtained. qn And invert it, and compare it with the AC voltage amplitude q-axis reference V. qref After superposition, we get v sq v sq Feedback is sent to the power calculation module, based on the actual current vector i at the common coupling point. o The q-axis command, i.e., the virtual potential q-axis amplitude v, is calculated. sq ;change i od After inputting the notch filter, i is obtained dn And it is sent to the AC voltage modulation module, i dn i qn and v sq The expressions are as follows: v sq =V qref -i qn In the formula, ω t Let ζ be the target notch frequency and ζ be the damping ratio.

7. A grid-connected converter power self-synchronization control system adaptive to grid strength according to claim 6, characterized in that, The PWM modulation module performs the following operations: v sd and v sq Based on ω s t undergoes a Parker transform to obtain a three-phase modulated wave v sabc Perform PWM modulation.

8. A grid-connected converter power self-synchronization control method adaptive to grid strength, characterized in that, When executing the steps in the method, the processor calls the power calculation module, reference phase command module, active power synchronization module, reactive power synchronization module, AC voltage modulation module, current notch modulation module and PWM modulation module in the grid strength adaptive grid converter power self-synchronization control system according to any one of claims 1-7, so as to realize the corresponding functions in each module.

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