Grid-connected and off-grid switching method for PMSG (Permanent Magnet Synchronous Generator) converter based on network construction type control

Abstract

The invention discloses a grid-connected and off-grid switching method for a PMSG converter based on network construction type control, and relates to the technical field of grid-connected and off-grid switching of a fan, and the method comprises the steps: building a transient reference power controller in response to a grid-connected instruction; starting the transient reference power controller to pre-synchronize key operation parameters and power grid parameters of the grid construction type PMSG power generation system; judging whether a grid-connected condition of the PMSG power generation system is met or not based on the pre-synchronization state, and if yes, executing a grid-connected action; if not, the key operation parameters of the PMSG power generation system are dynamically adjusted based on the pre-synchronization deviation, and the grid connection action is executed until the key operation parameters reach the pre-synchronization expectation and meet the grid connection condition; the problems of unstable and unsafe grid connection caused by parameter difference are avoided, the problems of poor switching effect and low efficiency caused by single control factor in the prior art are solved, and the reliability, the stability and the switching efficiency of grid connection switching are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of wind turbine on-grid and off-grid switching, and in particular to a PMSG converter on-grid and off-grid switching method based on grid-type control. Background Art

[0002] With the transformation of energy structure and the rapid development of renewable energy, wind power has gradually become an important part of the power grid. Wind turbines based on grid-type control can not only operate normally in grid-connected mode, but also operate safely and stably in off-grid mode during grid failure or maintenance. However, the operating parameters between the inverter and the microgrid are not in a fluctuation range. When the inverter switches from off-grid mode to grid-connected mode, direct grid connection will face the impact problem caused by the voltage, frequency and phase at both ends of the grid connection point not meeting the grid connection requirements, which may cause system crash in severe cases; therefore, it is necessary to control smooth switching, and the control is usually implemented by controlling the input of the V / f controller, so that it is adjusted with the grid voltage as the reference signal, reducing the output voltage of the converter and the voltage and phase difference of the large grid, so as to achieve switching. However, if only the voltage and phase are controlled, more reliable smooth switching cannot be ensured. Due to the incompleteness of the control factors, in the face of demand scenarios with high grid connection conditions, it is difficult to meet the grid connection conditions by controlling only the voltage and phase. For example, when the frequency deviation between the grid and the inverter is large, the grid connection may bring certain current shocks and grid fluctuations, thereby affecting the stability and safety of the grid connection.

[0003] Chinese patent, publication number: CN117811058A, publication date: April 2, 2024, discloses a method and system for switching between on-grid and off-grid operation of a microgrid. The initial control parameters of the droop control mode are calculated according to the grid voltage parameters before switching, and the constant power control mode is switched to the droop control mode to complete the switching of the microgrid from on-grid operation to off-grid operation; the control expected parameters of the droop control mode are calculated according to the grid voltage parameters before switching, and the microgrid parameters are adjusted until the microgrid parameters meet the target requirements, and the droop control mode is switched to the constant power control mode, completing the switching of the microgrid from off-grid operation to on-grid operation. However, this invention only calculates the amplitude expected parameters and frequency expected parameters of the droop control mode according to the grid voltage parameters before switching, and adjusts the microgrid parameters until the microgrid parameters meet the target requirements, and switches from the droop control mode to the constant power control mode, thereby realizing on-grid and off-grid switching; it ignores the influence of the voltage phase on the power transmission of the grid, thereby affecting the grid connection conditions, resulting in poor grid connection reliability and low effect. Summary of the invention

[0004] The purpose of the present invention is to address the problems of poor switching effect and low efficiency caused by a single control factor in existing off-grid and grid-connected technologies; a PMSG converter on-grid and off-grid switching method based on grid-configuration control is proposed, and a transient reference power controller is established to utilize the difference in key parameters between the inverter and the microgrid when the inverter is off-grid, dynamically adjust the key operating parameters of the inverter operation, realize parameter pre-synchronization, detect the difference in each parameter after pre-synchronization to determine whether the grid-connected conditions are met, and if so, execute the grid connection, otherwise continue to adjust the operating parameters of the power generation system until the grid-connected conditions are met; through the transient power reference controller, the problem of unstable and unsafe grid connection caused by parameter differences is avoided, the problem of poor switching effect and low efficiency caused by a single control factor in the prior art is overcome, and the reliability, stability and switching efficiency of the grid-connected switching are significantly improved.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a PMSG converter on-grid and off-grid switching method based on grid-type control, comprising the following steps: establishing a transient reference power controller in response to a grid connection instruction; Starting the transient reference power controller to pre-synchronize key operating parameters of the grid-forming PMSG power generation system with grid parameters; Based on the pre-synchronization state, it is determined whether the grid-connected conditions of the PMSG power generation system are met. If so, the grid-connected action is executed; if not, the key operating parameters of the PMSG power generation system are dynamically adjusted based on the pre-synchronization deviation until the key operating parameters reach the pre-synchronization expectations and meet the grid-connected conditions, and the grid-connected action is executed.

[0006] In this scheme, by establishing a transient reference power controller, before executing grid connection, the key operating parameters (including power, frequency, amplitude, phase) of the power generation system are dynamically adjusted by utilizing the difference between the key parameters of the inverter when it is off-grid and the microgrid, so that the key operating parameters of the power generation system are close to the parameters of the microgrid, and pre-synchronization with the corresponding parameters of the microgrid is achieved, namely, frequency pre-synchronization, phase pre-synchronization, voltage amplitude pre-synchronization and power pre-synchronization; and after pre-synchronization, the adjusted state of each parameter is detected to determine whether the grid connection conditions are met. If not, the parameters are continuously adjusted until the grid connection conditions are met and the grid connection action is executed, thereby minimizing the grid connection impact, thereby achieving smooth switching from the off-grid mode to the grid-connected mode, ensuring stable and safe grid connection of the power generation system, and improving the switching efficiency at the same time, solving the problem of poor switching effect and low efficiency in the prior art due to the single control factor (i.e., the key influencing parameters during off-grid switching are not fully considered), and significantly improving the reliability, stability and switching efficiency of the grid-connected switching.

[0007] Preferably, the step of establishing a transient reference power controller in response to a grid connection instruction comprises the following sub-steps: Based on the grid-connected command received by the PMSG power generation system, the angular frequency and operating phase angle of the inverter are obtained; Compare the angular frequency and the operating phase angle with operating parameters corresponding to the power grid, respectively, to obtain a first frequency difference and a first phase difference between the PMSG power generation system and the power grid; A transient reference power increment is generated based on the first frequency difference and the first phase difference, and a transient reference power controller is established.

[0008] Preferably, generating a transient reference power increment based on the first frequency difference and the first phase difference, and establishing a transient reference power controller, comprises the following sub-steps: Based on a control gain function, the first frequency difference, the first phase difference, and the output power of the PMSG power generation system are used as pre-synchronization targets to generate the transient reference power increment; A control gain coefficient is determined according to the time variation characteristics of the pre-synchronization target under grid-connected conditions, and gain control is performed on the transient reference power increment based on the control gain coefficient to construct the transient reference power controller.

[0009] Preferably, the calculation formula of the transient reference power controller is as follows: Wherein, Δω(t) is the first frequency difference, is the first phase difference, ΔP1(t) is the electromagnetic power output by the PMSG power generation system, g() represents the control gain function, and t represents time.

[0010] Preferably, the calculation formula of the transient reference power controller is as follows: In the formula, g i (i=1,2,3) represents the sub-function of the control gain function g, μ i is the difference coefficient, and its value is set according to the magnitude between the corresponding parameters of the PMSG power generation system and the power grid. a represents the frequency control gain coefficient, b represents the power control gain coefficient, and c represents the phase control gain coefficient.

[0011] Preferably, the step of starting the transient reference power controller to pre-synchronize key operating parameters of the grid-connected PMSG power generation system with grid parameters comprises the following sub-steps: Based on the Pf controller, the angular frequency, operating phase angle and output power of the power grid are used as the adjustment reference, and the angular frequency, phase and power of the PMSG power generation system are adjusted in the direction of the power grid parameters to control the pre-synchronization of the operating state of the PMSG power generation system with the operating state of the power grid.

[0012] Preferably, the step of adjusting the angular frequency, phase and power of the PMSG power generation system toward the grid parameters includes: Based on the Pf controller to simulate the rotor motion of the synchronous generator, the droop control is used to adjust the angular frequency, power and phase of the PMSG power generation system once, and the proportional-integral control is used to adjust the angular frequency, power and phase of the PMSG power generation system twice.

[0013] In this scheme, the output transient reference power is adaptively adjusted through time t. As the time increases, the transient reference power output becomes smaller, so that the key grid-connected parameters in the later stage of pre-synchronization can approach the microgrid more smoothly.

[0014] Preferably, judging whether the grid connection conditions of the PMSG power generation system are met based on the pre-synchronization state includes: acquiring the key operating parameters of the PMSG power generation system that has completed pre-synchronization, and calculating the voltage amplitude difference, the second frequency difference and the second phase difference between the PMSG power generation system and the power grid; Comparing the sum of the voltage amplitude difference and the second frequency difference with the first grid connection condition threshold, and synchronously comparing the second phase difference with the second grid connection condition threshold; If the sum of the voltage amplitude difference and the second frequency difference is less than or equal to the first grid-connection condition threshold and the second phase difference is less than or equal to the second grid-connection condition threshold, the grid-connection condition is met.

[0015] Preferably, the calculation formula of the grid connection condition is as follows: Wherein, F(U,ω) is the sum of the voltage amplitude difference and the second frequency difference, U is the output voltage amplitude of the inverter pre-synchronization, U0 is the grid voltage amplitude, ω is the output angular frequency of the inverter pre-synchronization, ω0 is the grid angular frequency, is the operating phase angle of the inverter pre-synchronization, is the operating phase angle of the power grid, T1 is the first grid-connected condition threshold, and T2 is the second grid-connected condition threshold.

[0016] Preferably, the first grid connection condition threshold and the second grid connection condition threshold include: Based on the pre-synchronization requirements of the key operating parameters of the PMSG power generation system and the grid parameters, the minimum value in the maximum fluctuation range of the key operating parameters is selected as the first grid connection condition threshold; The second grid connection condition threshold is determined based on the phase angle change state of the PMSG power generation system.

[0017] In this solution, the first grid-connected condition threshold is the smallest possible condition threshold, which is set according to the maximum allowable fluctuation range of frequency, voltage and power required by the grid-connected condition; the second grid-connected condition threshold is the phase angle condition threshold. When the grid-connected conditions are met, the smaller the second grid-connected condition threshold is, the smaller the impact on the system will be when connected to the grid.

[0018] Beneficial effects of the present invention: 1. By establishing a transient reference power controller, the key parameters are dynamically adjusted to approach the microgrid parameters by using the difference between the inverter and the microgrid when the inverter is off-grid, until the parameter difference between the power generation system and the microgrid meets the threshold range to achieve pre-synchronization with the corresponding parameters of the microgrid, so as to minimize the impact of grid connection, realize smooth switching from off-grid mode to grid-connected mode, and ensure the stability and safe grid connection of the power generation system; 2. Through the dynamic adjustment of parameters after pre-synchronization and pre-synchronization result detection, the parameters of the power generation system gradually approach the microgrid after each adjustment. The step-by-step process can avoid the adjustment amplitude being too large, causing electrical signal fluctuations to affect the normal operation of the power generation system, or the adjustment amplitude being too small, which will extend the grid-connected switching time and reduce the grid-connected switching efficiency, and significantly improve the on-grid and off-grid switching efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Other features, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings. The drawings are only for the purpose of illustrating preferred embodiments and are not to be considered as limiting the present invention. Also, the same reference symbols are used throughout the drawings to represent the same parts.

[0020] Figure 1 The flowchart is a PMSG converter on-grid and off-grid switching method based on grid-type control in this embodiment.

[0021] Figure 2 This is an overall control block diagram of a networking type control of this embodiment.

[0022] Figure 3 This is a block diagram of voltage amplitude control during the pre-synchronization process of this embodiment.

[0023] Figure 4 This is a frequency-phase control block diagram during the pre-synchronization process of this embodiment.

[0024] Figure 5 This is a block diagram of voltage amplitude control during the pre-synchronization process of this embodiment.

[0025] Figure 6 This is a phase tracking process diagram of a pre-synchronization control of this embodiment.

[0026] Figure 7This is a diagram showing changes in key parameters of a transient process of pre-synchronization control in this embodiment.

[0027] Figure 8 The figure is a schematic diagram comparing the inverter output power changes of a pre-synchronous grid-connected and a direct grid-connected inverter according to the embodiment.

[0028] Fig. 9 The figure is a schematic diagram comparing the grid frequency changes of a pre-synchronous grid connection and a direct grid connection according to the present embodiment. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific implementation method described herein is only an optimal embodiment of the present invention, which is only used to explain the present invention and does not limit the scope of protection of the present invention. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0030] Example 1: Figure 1 As shown, a PMSG converter on-grid and off-grid switching method based on grid-type control includes the following steps: establishing a transient reference power controller in response to a grid connection instruction; Start the transient reference power controller to pre-synchronize the key operating parameters of the grid-connected PMSG power generation system with the grid parameters; judge whether the grid-connected conditions of the PMSG power generation system are met based on the pre-synchronization state, and if so, execute the grid-connected action; if not, dynamically adjust the key operating parameters of the PMSG power generation system based on the pre-synchronization deviation until the key operating parameters reach the pre-synchronization expectations and meet the grid-connected conditions, and then execute the grid-connected action.

[0031] Specifically, establishing a transient reference power controller in response to a grid connection instruction includes the following sub-steps: Based on the grid-connected command received by the PMSG power generation system, the angular frequency and operating phase angle of the inverter are obtained; Compare the angular frequency and the operating phase angle with the operating parameters corresponding to the power grid, respectively, to obtain a first frequency difference and a first phase difference between the PMSG power generation system and the power grid; A transient reference power increment is generated based on the first frequency difference and the first phase difference, and a transient reference power controller is established.

[0032] Specifically, generating a transient reference power increment based on the first frequency difference and the first phase difference, and establishing a transient reference power controller, includes the following sub-steps: Based on the control gain function, the first frequency difference, the first phase difference and the output power of the PMSG power generation system are used as pre-synchronization targets to generate a transient reference power increment; The control gain coefficient is determined according to the time variation characteristics of the pre-synchronization target under the grid-connected condition, and the transient reference power increment is gain controlled based on the control gain coefficient to construct a transient reference power controller.

[0033] Specifically, the calculation formula of the transient reference power controller is as follows: Where Δω(t) is the first frequency difference, is the first phase difference, ΔP1(t) is the electromagnetic power output by the PMSG power generation system, g() represents the control gain function, and t represents time.

[0034] Specifically, the calculation formula of the transient reference power controller is as follows: In the formula, g i (i=1,2,3) represents the sub-function of the control gain function g, μ i is the difference coefficient, and its value is set according to the magnitude between the corresponding parameters of the PMSG power generation system and the power grid. a represents the frequency control gain coefficient, b represents the power control gain coefficient, and c represents the phase control gain coefficient.

[0035] Specifically, starting the transient reference power controller to pre-synchronize the key operating parameters of the grid-type PMSG power generation system with the grid parameters includes the following sub-steps: Based on the Pf controller, the angular frequency, operating phase angle and output power of the power grid are used as the adjustment reference, and the angular frequency, phase and power of the PMSG power generation system are adjusted in the direction of the power grid parameters to control the pre-synchronization of the operating state of the PMSG power generation system with the operating state of the power grid.

[0036] Specifically, the angular frequency, phase and power of the PMSG power generation system are adjusted in the direction of the grid parameters, including: simulating the rotor movement of the synchronous generator based on the Pf controller, using droop control to perform a primary adjustment on the angular frequency, power and phase of the PMSG power generation system, and using proportional-integral control to perform a secondary adjustment on the angular frequency, power and phase of the PMSG power generation system.

[0037] As an implementation method, Figure 2 As shown, based on the Pf controller, the rotor motion of the synchronous generator is simulated to dynamically adjust the angular frequency and power of the PMSG power generation system. The motion equation is as follows: Where H is the inertia time constant, K d is the damping coefficient, P set , P eare the mechanical power input and electromagnetic power output of the virtual synchronous machine, ω is the output angular frequency of the inverter power supply, ω0 is the angular frequency of the power grid, ω ref is the rated angular frequency; First, the droop control is introduced into equation (3) to perform primary frequency modulation on the angular frequency and power of the PMSG power generation system. The primary frequency modulation formula is as follows: In the formula, m p is the droop coefficient, P ref is the power setting value; Secondly, the angular frequency and power of the PMSG power generation system are secondary modulated through the integral link. The secondary frequency modulation formula is as follows: In the formula, k ip is the integral coefficient of secondary frequency modulation; In this embodiment, the primary frequency modulation and the secondary frequency modulation are combined to obtain the Pf link control equation, as shown below: By adjusting the angular frequency and power of the PMSG power generation system, the phase angle is further affected to change, thereby achieving phase adjustment.

[0038] Furthermore, if Figure 3 As shown, when the angular frequency and power of the PMSG power generation system are adjusted, the AC voltage of the PMSG power generation system is adjusted by proportional-integral control of the virtual excitation current, thereby adjusting the voltage amplitude of the PMSG power generation system. The adjustment formula is as follows: In the formula, k pq and k iq are proportional coefficient and integral coefficient respectively, M f is the virtual inductance, i f is the virtual excitation current, D q is the reactive power droop coefficient, Q ref is the reactive power setting value, U ref is the voltage setting value, Q e is the inverter output reactive power, U is the inverter output voltage amplitude, and ΔU is the voltage difference; After automatic voltage regulation, the actual voltage value will always track the set value, so in the process of voltage amplitude pre-synchronization, it is only necessary to adjust the voltage U ref and reactive power setting value Q ref Just change it to the grid value, and keep other parts unchanged, to ensure safe and reliable off-grid switching while improving switching efficiency.

[0039] Furthermore, if Figure 4 As shown in the figure, the PMSG power generation system starts pre-synchronization, and controls the output angular frequency and phase of the PMSG power generation system to approach the grid through the Pf control link (formula (6)). At this time, ΔP1(t) is disturbed and started, and ΔP2(t) is further regulated to make the frequency and phase of the power generation system approach the parameters of the grid. After the PMSG power generation system is pre-synchronized, the detection device detects the difference between the frequency, phase and voltage amplitude of the power generation system and the parameters of the microgrid again. If the grid connection conditions are met, a closing signal is issued, and the power generation system starts to connect to the grid. At this time, the grid control is converted to the grid-following control to reduce the impact of grid connection and enable the power generation system to achieve smooth switching between grid connection and off-grid connection.

[0040] It can be understood that the principle of achieving pre-synchronization by using a transient reference power controller is mainly: adaptively adjust the output transient reference power through time t. As time goes by, the transient reference power output becomes smaller, so that the key grid-connected parameters in the later stage of pre-synchronization can approach the microgrid more smoothly.

[0041] In this embodiment, after confirming that the operating parameters of the power generation system meet the expectations, the grid connection action can be quickly executed. For example, if the voltage amplitude difference, frequency difference, and phase difference between the power generation system and the microgrid meet the safety threshold range, the grid mode is switched immediately. This efficient grid connection method reduces energy loss and time delay in the grid connection process, and improves the energy utilization and operation efficiency of the entire system. After the first pre-synchronization, the key operating parameters of the power generation system are detected. If the difference between each parameter and the microgrid does not meet the threshold range, the transient power reference controller continues to dynamically adjust the parameters of the power generation system according to the difference, and repeats the above steps until the parameter difference between the power generation system and the microgrid meets the threshold range; through pre-synchronization and dynamic adjustment of parameters after pre-synchronization result detection, the parameters of the power generation system gradually approach the microgrid after each adjustment. The step-by-step process can avoid the adjustment amplitude being too large to cause electrical signal fluctuations that affect the normal operation of the power generation system, or the adjustment amplitude being too small to extend the grid connection switching time and reduce the grid connection switching efficiency.

[0042] Specifically, judging whether the grid connection conditions of the PMSG power generation system are met based on the pre-synchronization state includes: Acquire key operating parameters of the PMSG power generation system that has completed pre-synchronization, and calculate the voltage amplitude difference, the second frequency difference, and the second phase difference between the PMSG power generation system and the power grid; Comparing the sum of the voltage amplitude difference and the second frequency difference with the first grid connection condition threshold, and synchronously comparing the second phase difference with the second grid connection condition threshold; If the sum of the voltage amplitude difference and the second frequency difference is less than or equal to the first grid-connection condition threshold and the second phase difference is less than or equal to the second grid-connection condition threshold, the grid-connection condition is met.

[0043] Specifically, the calculation formula for the grid connection condition is as follows: Where, F(U,ω) is the sum of the voltage amplitude difference and the second frequency difference, U is the output voltage amplitude of the inverter pre-synchronization, U0 is the grid voltage amplitude, ω is the output angular frequency of the inverter pre-synchronization, ω0 is the grid angular frequency, is the operating phase angle of the inverter pre-synchronization, is the operating phase angle of the power grid, T1 is the first grid-connected condition threshold, and T2 is the second grid-connected condition threshold.

[0044] Specifically, the first grid connection condition threshold and the second grid connection condition threshold include: Based on the pre-synchronization requirements of the key operating parameters of the PMSG power generation system and the grid parameters, the minimum value in the maximum fluctuation range of the key operating parameters is selected as the first grid connection condition threshold; A second grid connection condition threshold is determined based on a phase angle change state of the PMSG power generation system.

[0045] In this embodiment, the first grid-connected condition threshold is a condition threshold that is as small as possible, and is set according to the maximum allowable fluctuation range of frequency, voltage and power required by the grid-connected condition; the second grid-connected condition threshold is a phase angle condition threshold. When the grid-connected condition is met, the smaller the second grid-connected condition threshold is, the smaller the impact on the system during grid-connected condition is.

[0046] Embodiment 2, as Figure 5 As shown in the figure, first the upper layer issues a grid connection command, the grid-type PMSG power generation system starts pre-synchronization, and the detection device first detects the difference Δω(t) between the angular frequency and the operating phase angle between the inverter and the microgrid. The difference between the two is used to generate a transient reference power increment ΔP2(t) through the g function. The Pf control link of formula (6) is used to change the system output angular frequency and phase to be close to the grid. At this time, ΔP1(t) is activated by interference, and ΔP2(t) is further regulated to make the frequency and phase of the power generation system close to the parameters of the microgrid. Then the voltage U ref and reactive power setting value Q ref The detection device detects the difference between the frequency, phase and voltage amplitude of the power generation system and the parameters of the microgrid again. If the two grid-connected conditions on the left side of the figure are met, a closing signal is issued and the power generation system starts to be grid-connected. At this time, the grid-forming control is converted to the grid-following control to reduce the impact of grid connection and enable the power generation system to achieve smooth switching between grid and off-grid.

[0047] As a specific implementation method, Figure 6 As shown, in the simulation, the upper layer issues a grid-connected command at 20s, after which the inverter starts pre-synchronization control. The results are captured from 21s to 21.3s. The output phase of the inverter during off-grid stable operation lags behind the microgrid. After the pre-synchronization start, the transient power controller begins to play a role. At 21s, the inverter output phase still lags behind the grid phase by about 0.414π. At around 21.3s, the phase is synchronized with the grid. Before the 20th second, the inverter output is in a steady state. At the 20th second, the inverter starts pre-synchronization control. In the pre-synchronization stage, the transient power controller starts and outputs the corresponding transient power compensation ΔP2(t) according to the relationship between the inverter and the grid angular frequency, phase and its own output power difference. Its maximum value reaches 4MW. Figure 7 As shown in the figure, the maximum value of the inverter output frequency is close to 50.04, which corresponds to increasing the reference power set by the inverter so that its output frequency rises to catch up with the grid phase. The pre-synchronization stage ends at around 21.3s, and the transient reference power drops to 0. This verifies the effectiveness of the transient power control pre-synchronization strategy proposed in this study.

[0048] Furthermore, if Figure 8 As shown in the figure, in order to track the grid phase during the pre-synchronization process, the inverter increases the inverter output frequency by increasing the transient reference power, thereby increasing the inverter output power, and the maximum value reaches 15.1MW. In the case of direct grid connection without pre-synchronization, due to the large difference in phase, frequency, and voltage between the inverter and the grid at the moment of grid connection, the overall system is greatly impacted, and the maximum instantaneous power output of the inverter can reach 21.8MW, which is seriously overregulated. It can be seen that this solution can effectively reduce the impact of grid connection, ensure a smoother system transition, and reduce the adverse impact on grid stability.

[0049] Furthermore, if Fig. 9 As shown, in the case of direct grid connection, the overall system is subject to a greater impact, the grid frequency fluctuation time is the longest, about 1.4s, the fluctuation amplitude is the largest, and the lowest point is 49.92Hz. In this embodiment, after the pre-synchronization stage, the impact of the grid connection on the system frequency is greatly reduced, which is reflected in the small fluctuation amplitude of the frequency, and the system frequency recovers to 50Hz faster.

[0050] The beneficial effect of the embodiment is that by establishing a transient reference power controller, the parameters such as power, frequency, phase or voltage amplitude of the power generation system can be adjusted in a targeted and accurate manner to match the corresponding parameters of the microgrid, thereby achieving accurate and efficient pre-synchronization with the microgrid, minimizing the impact current or voltage fluctuation caused by the difference in parameters when connected to the grid, and ensuring the safe and stable operation of the power generation system and the microgrid; at the same time, during the pre-synchronization process, the secondary adjustment of power and frequency is achieved through comprehensive droop control and integral proportional control, and the operating parameters of the power generation system can be more flexibly and quickly adjusted according to the difference between the operating parameters of the power generation system and the microgrid to adapt to different grid-connected scenarios and needs, significantly improving the adaptability of the grid-connected and off-grid switching method; after confirming that the operating parameters of the power generation system meet expectations, the grid-connected action can be quickly executed. For example, if the voltage amplitude difference, frequency difference, and phase difference between the power generation system and the microgrid meet the grid-connected conditions, the grid mode is switched immediately. This efficient grid-connected method reduces energy loss and time delays during the grid-connected process, and improves the energy utilization and operation efficiency of the entire system. In addition, a smooth and efficient grid-connected process can enhance the reliability of the system, ensuring that the power generation system can be connected to the grid in a timely manner when needed and provide a stable power supply, and that the power generation system can be connected to the grid smoothly and quickly, reducing the impact on users and improving their electricity experience.

[0051] The above specific embodiments are preferred embodiments of the present invention, and are not intended to limit the specific implementation scope of the present invention. The scope of the present invention includes but is not limited to the present specific embodiments. All equivalent changes made in accordance with the shape, structure, and method of the present invention are within the protection scope of the present invention.

Claims

1. A PMSG converter on-grid and off-grid switching method based on grid-type control, characterized in that: The steps include: establishing a transient reference power controller in response to a grid connection instruction; Starting the transient reference power controller to pre-synchronize key operating parameters of the grid-forming PMSG power generation system with grid parameters; Based on the pre-synchronization state, it is determined whether the grid-connected conditions of the PMSG power generation system are met. If so, the grid-connected action is executed; if not, the key operating parameters of the PMSG power generation system are dynamically adjusted based on the pre-synchronization deviation until the key operating parameters reach the pre-synchronization expectations and meet the grid-connected conditions, and the grid-connected action is executed.

2. The PMSG converter on-grid and off-grid switching method based on grid-type control according to claim 1 is characterized in that: The step of establishing a transient reference power controller in response to a grid connection instruction comprises the following sub-steps: Based on the grid-connected command received by the PMSG power generation system, the angular frequency and operating phase angle of the inverter are obtained; Compare the angular frequency and the operating phase angle with operating parameters corresponding to the power grid, respectively, to obtain a first frequency difference and a first phase difference between the PMSG power generation system and the power grid; A transient reference power increment is generated based on the first frequency difference and the first phase difference, and a transient reference power controller is established.

3. The PMSG converter on-grid and off-grid switching method based on grid-type control according to claim 2 is characterized in that: Generating a transient reference power increment based on the first frequency difference and the first phase difference, and establishing a transient reference power controller, comprises the following sub-steps: Based on a control gain function, the first frequency difference, the first phase difference, and the output power of the PMSG power generation system are used as pre-synchronization targets to generate the transient reference power increment; A control gain coefficient is determined according to the time variation characteristics of the pre-synchronization target under grid-connected conditions, and gain control is performed on the transient reference power increment based on the control gain coefficient to construct the transient reference power controller.

4. The PMSG converter on-grid and off-grid switching method based on grid-type control according to claim 3 is characterized in that: The calculation formula of the transient reference power controller is as follows: Wherein, Δω(t) is the first frequency difference, is the first phase difference, ΔP1(t) is the electromagnetic power output by the PMSG power generation system, g() represents the control gain function, and t represents time.

5. The PMSG converter on-grid and off-grid switching method based on grid-type control according to claim 4 is characterized in that: The calculation formula of the transient reference power controller is as follows: In the formula, g i (i=1,2,3) represents the sub-function of the control gain function g, μ i is the difference coefficient, and its value is set according to the magnitude between the corresponding parameters of the PMSG power generation system and the power grid. a represents the frequency control gain coefficient, b represents the power control gain coefficient, and c represents the phase control gain coefficient.

6. The PMSG converter on-grid and off-grid switching method based on grid-type control according to claim 1 is characterized in that: The step of starting the transient reference power controller to pre-synchronize the key operating parameters of the grid-connected PMSG power generation system with the grid parameters includes the following sub-steps: Based on the Pf controller, the angular frequency, operating phase angle and output power of the power grid are used as the adjustment reference, and the angular frequency, phase and power of the PMSG power generation system are adjusted in the direction of the power grid parameters to control the pre-synchronization of the operating state of the PMSG power generation system with the operating state of the power grid.

7. The PMSG converter on-grid and off-grid switching method based on grid-type control according to claim 6 is characterized in that: The step of adjusting the angular frequency, phase and power of the PMSG power generation system toward the grid parameters includes: Based on the Pf controller to simulate the rotor motion of the synchronous generator, the droop control is used to adjust the angular frequency, power and phase of the PMSG power generation system once, and the proportional-integral control is used to adjust the angular frequency, power and phase of the PMSG power generation system twice.

8. The method for switching the PMSG converter on and off the grid based on grid-type control according to claim 1 is characterized in that: The determining whether the grid connection condition of the PMSG power generation system is met based on the pre-synchronization state includes: Acquire the key operating parameters of the PMSG power generation system that has completed pre-synchronization, and calculate the voltage amplitude difference, the second frequency difference, and the second phase difference between the PMSG power generation system and the power grid; Comparing the sum of the voltage amplitude difference and the second frequency difference with the first grid connection condition threshold, and synchronously comparing the second phase difference with the second grid connection condition threshold; If the sum of the voltage amplitude difference and the second frequency difference is less than or equal to the first grid-connection condition threshold and the second phase difference is less than or equal to the second grid-connection condition threshold, the grid-connection condition is met.

9. The PMSG converter on-grid and off-grid switching method based on grid-type control according to claim 8, characterized in that: The calculation formula of the grid connection condition is as follows: Wherein, F(U,ω) is the sum of the voltage amplitude difference and the second frequency difference, U is the output voltage amplitude of the inverter pre-synchronization, U0 is the grid voltage amplitude, ω is the output angular frequency of the inverter pre-synchronization, ω0 is the grid angular frequency, is the operating phase angle of the inverter pre-synchronization, is the operating phase angle of the power grid, T1 is the first grid-connected condition threshold, and T2 is the second grid-connected condition threshold.

10. The PMSG converter on-grid and off-grid switching method based on grid-type control according to claim 8, characterized in that: The first grid connection condition threshold and the second grid connection condition threshold include: Based on the pre-synchronization requirements of the key operating parameters of the PMSG power generation system and the grid parameters, the minimum value in the maximum fluctuation range of the key operating parameters is selected as the first grid connection condition threshold; The second grid connection condition threshold is determined based on the phase angle change state of the PMSG power generation system.

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