Transient overvoltage suppression control method and device for open-winding motor interface grid-connected system

Abstract

The application discloses a kind of open-winding motor interface grid-connected system transient overvoltage suppression control methods, comprising: real-time monitoring power grid fault clearing signal, grid-connected point voltage and frequency detection value, in combination with power grid fault clearing time and voltage recovery time, identify and divide into electromagnetic transient impulse and electromechanical transient oscillation stage;Electromagnetic transient impulse stage utilizes the transient reactive power absorption characteristics of open-winding synchronous motor itself, inhibits overvoltage peak, electromechanical transient oscillation stage with system frequency as feedback, generates additional excitation control quantity and is superimposed to excitation given, inhibits overvoltage oscillation;When grid-connected point voltage amplitude and rate of change recover to within preset threshold, Crowbar circuit is disconnected, and system control is switched from transient operation mode to steady-state operation mode;The voltage vector required by converter is calculated and combined with SVPWM to generate the driving signal of each bridge arm switching device in the converter to exert control on the system, realizing transient overvoltage suppression.

Description

Technical Field

[0001] This application relates to the field of motor control technology, and in particular to a transient overvoltage suppression control method and device for an open-winding motor interface grid-connected system. Background Technology

[0002] With the increasing proportion of new energy equipment in the power system, the penetration rate of new energy sources, represented by wind and solar power, has been rising year by year in recent years. Their large-scale integration has brought severe challenges to the safe and stable operation of the power grid. Traditional low-voltage ride-through (LVRT) technology injects reactive current into the grid through converter control during grid voltage dips to support the voltage at the grid connection point and prevent the unit from disconnecting due to protection actions. However, when the grid fault is quickly cleared, the large amount of capacitive reactive current injected due to LVRT has a certain response delay and cannot stop immediately after the fault is cleared, resulting in reactive power excess and causing transient overvoltage in the system. This transient overvoltage phenomenon not only triggers the overvoltage protection mechanism of new energy units, leading to a new round of grid disconnection accidents, but also poses a significant threat to the insulation safety of power electronic devices. Therefore, requiring new energy power plants with LVRT capabilities to also possess transient overvoltage suppression capabilities after fault clearance has become an important direction in current research on new energy grid integration.

[0003] Scholars have already confirmed the superiority of open-winding synchronous motor interface converter grid-connected topologies in enhancing active support capabilities during faults. However, the feasibility of this grid-connected topology, designed to enhance low-voltage ride-through capability, directly relates to the generation of transient overvoltages and the effectiveness of its own physical mechanisms in suppressing transient overvoltages during the transient process after grid fault clearance. Intuitively, a synchronous motor in a strongly excited state during a fault may experience LC resonance due to its high internal potential at the moment the fault is cleared, leading to dangerous electromagnetic transient overvoltage impacts. On the other hand, after the grid short-circuit fault is cleared, the synchronous motor can transform into a powerful reactive power absorption source and oscillation damper thanks to its rapid excitation regulation capability and inherent damping characteristics. This complex, time-evolving dual effect necessitates research into its grid transient overvoltage suppression characteristics.

[0004] To fundamentally solve this problem, improvements have been made to the system topology, resulting in grid-connected systems with open-winding motor interfaces. This topology provides new energy devices with active support capabilities and enhances the ability to suppress transient overvoltages after fault clearance. To promote the adoption of this topology, it is necessary to design corresponding transient overvoltage suppression and smooth transition control strategies for the transient process after fault clearance. Summary of the Invention

[0005] The purpose of this application is to provide a transient overvoltage suppression control method and device for an open-winding motor interface grid-connected system, so as to solve the technical problem of suppressing transient overvoltages in the power grid caused by short-circuit fault clearing.

[0006] According to a first aspect of the embodiments of this application, a transient overvoltage suppression control method for an open-winding motor interface grid-connected system is provided, comprising: Real-time monitoring of power grid fault clearing signals, grid connection point voltage detection values, and frequency detection values; Based on the fault clearing time corresponding to the power grid fault clearing signal and the voltage recovery time corresponding to the recovery of the grid connection point voltage detection value to the preset voltage safety constraint range, the electromagnetic transient impact stage and the electromechanical transient oscillation stage are identified. The control methods for the synchronous motor excitation and converter in transient and steady-state operation modes generate reference voltage vectors for the d and q axes of the converter and reference electrical angles for the converter. The control method for the transient operation mode includes: during the electromagnetic transient impact phase, utilizing the transient reactive power absorption characteristics of the open-winding synchronous motor connected in series at the converter port to suppress transient overvoltage peaks; during the electromechanical transient oscillation phase, using the frequency detection value as a feedback signal to generate an additional excitation control quantity and superimposing it onto the excitation input, providing damping to suppress transient overvoltage oscillations. The control method for the steady-state operation mode includes: continuously monitoring the grid connection point voltage detection value and its rate of change; when the grid connection point voltage detection value recovers to a preset lower voltage limit and the rate of change is lower than a set threshold, controlling the Crowbar circuit to disconnect, and synchronously switching the excitation control of the synchronous motor and the converter control from the transient operation mode to the steady-state operation mode, completing a smooth transition from transient overvoltage suppression to steady-state grid connection. Based on the d-axis and q-axis reference voltage vectors and the reference electrical angle of the converter, the required voltage vector of the converter is calculated, and the drive signals of each bridge arm switching device in the converter are generated in combination with SVPWM to apply control to the system.

[0007] According to a second aspect of the embodiments of this application, a transient overvoltage suppression control device for an open-winding motor interface grid-connected system is provided, characterized in that it comprises: The data acquisition module is used to monitor power grid fault clearing signals, grid connection point voltage detection values, and frequency detection values ​​in real time. The stage identification module is used to identify the electromagnetic transient impact stage and the electromechanical transient oscillation stage based on the fault clearing time corresponding to the power grid fault clearing signal and the voltage recovery time corresponding to the recovery of the grid connection point voltage detection value to the preset voltage safety constraint range. The generation module is used to generate the d-axis and q-axis reference voltage vectors and the reference electrical angle of the converter through the control methods of the synchronous motor excitation and the converter in transient and steady-state operation modes. The control method in the transient operation mode includes: during the electromagnetic transient impact stage, using the transient reactive power absorption characteristics of the open-winding synchronous motor connected in series at the converter port to suppress the transient overvoltage peak; during the electromechanical transient oscillation stage, using the frequency detection value as a feedback signal to generate an additional excitation control quantity and superimposing it on the excitation setpoint input to provide damping to suppress transient overvoltage oscillations for the system. The control method in the steady-state operation mode includes: continuously monitoring the grid connection point voltage detection value and its rate of change; when the grid connection point voltage detection value recovers to the preset lower voltage limit and the rate of change is lower than the set threshold, controlling the Crowbar circuit to disconnect, and synchronously switching the excitation control of the synchronous motor and the converter control from the transient operation mode to the steady-state operation mode to complete the smooth transition from transient overvoltage suppression to steady-state grid connection. The control module is used to calculate the voltage vector required by the converter based on the d-axis and q-axis reference voltage vectors and the converter reference electrical angle, and to generate drive signals for each bridge arm switching device in the converter in combination with SVPWM, so as to apply control to the system.

[0008] According to a third aspect of the embodiments of this application, an electronic device is provided, comprising: One or more processors; Memory, used to store one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors perform the method as described in the first aspect.

[0009] The technical solutions provided by the embodiments of this application may include the following beneficial effects: As can be seen from the above embodiments, this application adopts a technical means of connecting an open-winding synchronous motor and a converter in series to the power grid, and implementing transient overvoltage suppression in stages. This overcomes the technical problem of transient overvoltage caused by the clearing of short-circuit faults in traditional new energy grid-connected systems, thereby achieving transient overvoltage suppression. By combining the time of power grid fault clearing with the voltage recovery time at the grid connection point to identify the electromagnetic transient and electromechanical transient stages, the technical problems of unclear division of transient overvoltage stages and insufficient control targeting are overcome, thereby achieving corresponding suppression control for different transient stages. By utilizing the transient reactive power absorption characteristics of the open-winding synchronous motor in the electromagnetic transient stage and using synchronous motor excitation damping control in the electromechanical transient stage, the technical problem that a single suppression method cannot simultaneously address overvoltage peak suppression and oscillation attenuation is overcome, thereby comprehensively improving the transient overvoltage suppression effect. By controlling the Crowbar circuit to disconnect and the control mode to switch through voltage recovery judgment conditions, the technical problem of the inability to smoothly switch between transient suppression and steady-state operation stages is overcome, thereby achieving a smooth system transition.

[0010] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0011] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0012] Figure 1 This is the topology of an open-winding motor interface grid-connected system according to an embodiment of the present invention.

[0013] Figure 2 This is a flowchart of a transient overvoltage suppression control method for an open-winding motor interface grid-connected system according to an embodiment of the present invention.

[0014] Figure 3 This is a block diagram of transient control for an open-winding motor interface grid-connected system according to an embodiment of the present invention.

[0015] Figure 4 This is a control block diagram of an excitation regulation method for an open-winding synchronous motor with additional phase compensation according to an embodiment of the present invention.

[0016] Figure 5 This is a control block diagram of the method for controlling the switching of the recovery steady-state operation mode according to an embodiment of the present invention.

[0017] Figure 6 This is a comparison of the simulation results of transient overvoltage suppression in a grid-connected system of a non-open-winding synchronous motor according to an embodiment of the present invention and a grid-connected system of an open-winding synchronous motor with additional phase compensation excitation regulation.

[0018] Figure 7 This is a comparison chart of simulation results of grid connection point voltage and reactive power operation before and after applying the transient overvoltage suppression method according to an embodiment of the present invention.

[0019] Figure 8 This is a block diagram of a transient overvoltage suppression control device for an open-winding motor interface grid-connected system according to an embodiment of the present invention. Detailed Implementation

[0020] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0021] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0022] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0023] Figure 1 The topology of the open-winding motor interface grid-connected system studied in this embodiment of the invention includes a new energy power generation device and a DC / AC three-phase inverter I, a Crowbar switching circuit and an open-winding synchronous motor II, and an AC power grid III. The DC side of the three-phase inverter is connected to photovoltaic or energy storage to realize the DC-AC conversion of new energy. The stator windings of the open-winding synchronous motor are connected to the converter through a parallel Crowbar circuit, and the other three terminals are connected to the power grid. The motor operates without load in the synchronous condenser state. The power grid can be regarded as a three-phase ideal voltage source.

[0024] Compared with the traditional topology of new energy grid-connected systems, Figure 1The open-winding synchronous motor introduced into the topology can withstand short-circuit currents that are many times higher than the overload capacity of the converter when a short-circuit fault occurs in the power grid. At the same time, it can spontaneously absorb excess reactive power from the power grid when the fault is cleared, which is beneficial for transient overvoltage suppression. However, the introduction of the open-winding motor will also slightly increase the topological complexity and operating losses of the system.

[0025] Figure 2 This is a flowchart of a transient overvoltage suppression control method for an open-winding motor interface grid-connected system according to an embodiment of the present invention; as follows: Figure 2 As shown, the method includes the following steps: S1: Real-time monitoring of grid fault clearing signals, grid connection point voltage detection values, and frequency detection values.

[0026] Specifically, in order to accurately identify the transient phase of the power grid and achieve transient overvoltage suppression control, the fault clearing signal output by the power grid protection device is collected in real time through the system control unit, and the three-phase voltage amplitude at the grid connection point and the actual operating frequency of the power grid are collected simultaneously.

[0027] This step allows us to obtain real-time electrical parameters at the grid connection point, providing fundamental monitoring data for subsequent transient phase identification and overvoltage suppression control.

[0028] S2: Based on the fault clearing time corresponding to the power grid fault clearing signal and the voltage recovery time corresponding to the recovery of the grid connection point voltage detection value to the preset voltage safety constraint range, identify the electromagnetic transient impact stage and the electromechanical transient oscillation stage.

[0029] Specifically, in order to clarify the meaning of the corresponding critical moments, the transient overvoltage process is divided into stages, with the triggering time of the power grid fault clearing signal as the starting point. The starting point is the moment when the voltage amplitude at the grid connection point returns to the preset voltage amplitude safety constraint range. The dividing point is the moment when the rate of change of the voltage amplitude at the grid connection point returns to the preset safety constraint range of the voltage change rate. The transient process is divided into an electromagnetic transient impact stage and an electromechanical transient oscillation stage at the end of the transient process.

[0030] The electromagnetic transient impact stage is The electromechanical transient oscillation stage is Among them, the safe constraint range for voltage amplitude is 0.9pu-1.1pu, and the safe constraint range for voltage change rate is within 0.1pu / s.

[0031] Grid connection point voltage variation rate The calculation formula is as follows: ; In the formula, This refers to the voltage amplitude of the power grid. For time.

[0032] This step provides a timing basis for subsequently dividing the transient overvoltage process into stages and implementing corresponding overvoltage suppression methods.

[0033] S3: Using the control methods of the synchronous motor excitation and converter in transient and steady-state operation modes, generate the d-axis and q-axis reference voltage vectors and the converter reference electrical angle; Specifically, such as Figure 3 The diagram shown is a transient control block diagram of an open-winding motor interface grid-connected system according to an embodiment of the present invention. The system is generally divided into synchronous motor excitation control (…). Figure 3 (a) in the context of converter control Figure 3 The system comprises two parts (b) of the above. Module 1 is an open-winding synchronous motor, Module 2 is an AC power grid, Module 3 is a detection device that detects the three-phase voltage of the power grid (3-1), the three-phase current of the power grid (3-2), and the rotor speed of the synchronous motor (3-3), respectively. Module 4 is a three-phase current coordinate transformation module, Module 5 is a speed outer loop controller, Module 6 is a d-axis current inner loop controller, Module 7 is a q-axis current inner loop controller, Module 8 is a two-phase rotating / stationary coordinate inverse transformation module, Module 9 is an SVPWM modulation module, Module 10 is a converter, Module 11 is a synchronous motor excitation reactive power outer loop controller, and Module 12 is an excitation current inner loop controller. Excitation control uses PI control by subtracting the system reactive power setpoint from the reactive power, and outputs the excitation current setpoint. Then, based on the given excitation current and the actual excitation current... The differential is used for PI control to output the synchronous motor excitation voltage. The converter control acquires the actual rotor electrical angular velocity of the synchronous motor. , compared with a given reference electric angular velocity The difference is used to obtain the speed deviation. The deviation is input into the speed PI regulator, which outputs a reference value for the q-axis stator current. Then, the actual q-axis stator current after Park transformation is collected. , and the q-axis current reference value The difference is used to obtain the q-axis current deviation. The deviation is input into the q-axis current PI regulator, which outputs a reference value for the q-axis stator voltage. .

[0034] S31: The control method for the transient operation mode includes: during the electromagnetic transient impact stage, using the transient reactive power absorption characteristics of the open-winding synchronous motor connected in series at the converter port to suppress the transient overvoltage peak; during the electromechanical transient oscillation stage, using the frequency detection value as a feedback signal to generate an additional excitation control quantity and superimposing it on the excitation given input to provide damping to the system to suppress transient overvoltage oscillation.

[0035] During the electromagnetic transient impact phase, the transient reactive power absorption characteristics of the open-winding synchronous motor connected in series at the converter port are utilized to suppress transient overvoltage peaks. Specifically, this includes: A1: Reactive power feedback control is performed on the excitation voltage of the open-winding synchronous motor. The excitation voltage of the synchronous motor is generated by a proportional-integral (PI) controller, which adjusts the voltage according to the deviation between the system reactive power reference value and the system reactive power actual value. Specifically, in order to achieve rapid tracking and zero steady-state error regulation of the system reactive power, while ensuring stable control of the excitation current, and forming a complete closed-loop control link from reactive power command to excitation voltage, this embodiment performs PI control based on the difference between the system reactive power setpoint and the actual system reactive power value (e.g., Figure 3 Module 11), output excitation current setpoint The calculation formula is: ; In the formula, and These are the proportional coefficient and integral coefficient of the reactive power PI regulator, respectively. The given value for system reactive power; This represents the actual value of the system's reactive power.

[0036] PI control is performed based on the difference between the given value of the excitation current of the open-winding synchronous motor and the actual value of the excitation current (e.g., ...). Figure 3 Module 12) outputs the synchronous motor excitation voltage. The calculation formula is: ; In the formula, and These are the proportional coefficient and integral coefficient of the excitation current PI regulator, respectively; i f This is the actual value of the excitation current.

[0037] This step enables rapid tracking of the system's reactive power command, eliminates reactive power steady-state deviation, provides accurate current setpoints for subsequent excitation current inner-loop control, and improves the dynamic and steady-state performance of the system's reactive power response.

[0038] A2: The converter performs vector control on the rotor speed of the open-winding synchronous motor. The d-axis current setpoint of the converter is set to 0, and the control of the q-axis current setpoint adopts a proportional-integral (PI) control structure. This controller calculates based on the deviation between the rotor speed setpoint and the actual electrical angular velocity of the synchronous motor rotor. Specifically, in order to achieve speed tracking and torque control of an open-winding synchronous motor, the actual rotor electrical angular velocity of the open-winding synchronous motor is collected. , compared with a given reference electric angular velocity The difference is used to obtain the speed deviation. The deviation is input into the speed PI regulator (e.g., Figure 3 Module 5) outputs the reference value of the q-axis stator current. The calculation formula is: ; In the formula, and These are the proportional coefficient and integral coefficient of the speed PI regulator, respectively.

[0039] Control strategy adopted The vector control method directly sets the reference value of the d-axis stator current. It is 0, that is: ; This step eliminates the coupling between the d-axis and q-axis components of the stator current, ensuring that the motor's electromagnetic torque is determined solely by the q-axis stator current, thus simplifying the torque control logic.

[0040] Acquire the actual d-axis stator current after Park transformation (like Figure 3 (Module 4), and the d-axis current reference value The difference is used to obtain the d-axis current deviation. The deviation is input into the d-axis current PI regulator (e.g., Figure 3 Module 6) outputs the reference value of the d-axis stator voltage. The calculation formula is: ; In the formula, and These are the proportional and integral coefficients of the d-axis current PI regulator, respectively.

[0041] Acquire the actual q-axis stator current after Park transformation (like Figure 3 (Module 4), and q-axis current reference value The difference is used to obtain the q-axis current deviation. The deviation is input into the q-axis current PI regulator (e.g., Figure 3Module 7) outputs the reference value of the q-axis stator voltage. The calculation formula is: ; In the formula, and These are the proportional and integral coefficients of the q-axis current PI regulator, respectively.

[0042] The output of the dq-axis current PI regulator will be used as the input for the subsequent inverse Park transform (e.g., Figure 3 Module 8) provides a voltage reference signal (e.g., for the converter's SVPWM modulation) Figure 3 (Module 9) ultimately realizes vector control of the open-winding synchronous motor.

[0043] A3: Analysis of the transient reactive power absorption characteristics of a split-winding synchronous motor.

[0044] Specifically, in order to reveal the spontaneous reactive power absorption mechanism of open-winding synchronous motors under transient overvoltage, it is necessary to conduct a theoretical analysis of the transient reactive power characteristics of the motor, so as to provide theoretical support for subsequent transient overvoltage suppression strategies.

[0045] Based on the fundamental theory of synchronous motors, the formula for calculating the reactive power of an open-winding synchronous motor is as follows: ; When a transient overvoltage occurs at the grid connection point, the synchronous motor excitation lags: ; The motor enters underexcitation operation state: ; In the formula, This refers to the reactive power at the synchronous motor port. For the direct-axis synchronous reactance of the synchronous motor; This is a reference value for the synchronous motor excitation voltage after a transient overvoltage occurs.

[0046] This step demonstrates that open-winding synchronous motors can adaptively absorb transient reactive power based on the overvoltage amplitude at the grid connection point. The higher the grid connection point voltage, the greater the transient reactive power absorbed by the synchronous motor, thereby suppressing the peak value of transient overvoltage.

[0047] During the electromechanical transient oscillation phase, the system frequency detection value is used as a feedback signal to generate an additional excitation control quantity, which is then superimposed on the excitation setpoint input to provide damping for the system to suppress transient overvoltage oscillations. Specifically, this includes: Specifically, in order to suppress transient overvoltage oscillations, additional damping control needs to be introduced to accelerate the decay of oscillations by providing additional positive damping, thereby suppressing the continuous oscillation of transient overvoltages.

[0048] Based on the reactive power calculation formula and excitation voltage calculation formula of open-winding synchronous motor: ; ; ; The closed-loop transfer function can be obtained by rearranging the functions: ; In the formula, This is the complex frequency domain expression for the excitation voltage; This is the reactive power proportionality coefficient; and These are the proportional coefficient and integral coefficient of the reactive power closed-loop excitation PI regulator, respectively. For the complex frequency domain expression of the reference reactive power; This is the complex frequency domain expression for the grid voltage coupling term; This is the complex frequency domain expression for the grid connection point voltage; It is a complex frequency variable.

[0049] Both sides ride at the same time s After simplification, the characteristic equation of the system can be obtained: ; Compared to the standard second-order system form: ; The comparison shows that: , ; In the formula, The damping ratio; It is the natural oscillation angular frequency.

[0050] The damping ratio is calculated as follows: ; Therefore, the inherent low-damping characteristic of this reactive power closed loop can cause system oscillations, requiring additional damping control to suppress them. In this embodiment, the system frequency deviation is selected as the signal for feedback power oscillation, and its output is superimposed on the excitation control as an additional excitation control signal. The additional excitation control signal is generated from the system frequency deviation signal through the following processing: the system frequency deviation signal is input into a controller composed of a transient gain element and a lead / lag element cascaded together, and then multiplied by a proportional coefficient.

[0051] Specifically, such as Figure 4 The diagram shown is a control block diagram of an excitation regulation method for an open-winding synchronous motor with added phase compensation according to an embodiment of the present invention, wherein module 13 is the phase compensation stage. The system frequency deviation is... As a signal reflecting power oscillations, the output is used as an additional signal through a phase compensation circuit. This is superimposed on the excitation control to suppress transient overvoltage oscillations.

[0052] Select system frequency deviation As a signal reflecting power oscillations: ; Design a phase compensation circuit (such as...) Figure 4 Module 13), whose output serves as an additional signal. Superimposed on excitation control: ; In the formula, This is the proportionality coefficient; For transient gain circuitry; For leading / lagging links; The time constant of the transient gain stage; , These are the lead time constant and lag time constant for the lead / lag elements, respectively.

[0053] This step allows for dynamic adjustment of the excitation based on the system frequency deviation during the electromechanical transient oscillation phase of transient overvoltage, generating an electrical torque in phase with the speed deviation to provide positive damping for the system and increase the equivalent damping coefficient. This effectively suppresses electromechanical transient oscillations and accelerates oscillation decay.

[0054] S32: The control method under the steady-state operation mode includes: continuously monitoring the grid connection point voltage detection value and its rate of change; when the grid connection point voltage detection value recovers to the preset lower voltage limit and the rate of change is lower than the set threshold, controlling the Crowbar circuit to disconnect, and synchronously switching the excitation control of the synchronous motor and the converter control from the transient operation mode to the steady-state operation mode, completing the smooth transition from transient overvoltage suppression to steady-state grid connection, including the following sub-steps: C1: When a transient overvoltage occurs in the power grid, in order to limit the overvoltage of the converter and the bypass inrush current and protect the power devices, the Crowbar circuit is in a closed state. The converter uses rotor speed vector control to operate the synchronous motor. The excitation voltage of the synchronous motor is adjusted according to the reactive power feedback of the power grid, so that the system operates in transient operation mode. Specifically, when a transient overvoltage fault occurs in the power grid, the system operates in transient operation mode, and the converter uses rotor speed vector control to operate the synchronous motor, which generates the converter d-axis and q-axis reference voltage vectors and the converter reference electrical angle accordingly. To ensure that the system does not become unstable during transient operation, this embodiment adopts a rotor speed vector control method to achieve steady-state operation of the synchronous motor, providing a stable voltage reference vector and electrical angle reference for converter modulation.

[0055] The calculation formula for using rotor speed vector control of synchronous motor operation in a converter is as follows: ; In the formula, , These are the d-axis and q-axis reference voltage vectors of the converter, respectively. , These are the proportional and integral coefficients of the speed ring, respectively.

[0056] The formula for calculating the converter reference electrical angle is as follows: ; In the formula, The reference electrical angle for the converter; Electrical angular velocity is used to compensate for frequency deviation; This is the initial value of the reference electrical angle for the converter.

[0057] This step enables reliable operation during transient processes and provides a reliable voltage reference vector and electrical angle reference for subsequent converter SVPWM modulation.

[0058] C2: When the transient overvoltage fault is cleared, the voltage amplitude at the grid connection point recovers to the preset upper voltage limit and the voltage change rate is lower than the set threshold. After the steady-state operation is restored, the control Crowbar circuit is disconnected, and the converter control is switched to droop control of the active and reactive power at the grid connection point, so that the system operates in steady-state operation mode. Specifically, such as Figure 5 The diagram shown is a control block diagram of the method for controlling the switching of the recovery steady-state operation mode according to an embodiment of the present invention. Module 14 is a grid power calculation unit, module 15 is an active power outer loop controller, module 16 is a reactive power outer loop controller, module 17 is a speed / position signal processing unit, and module 18 is a three-phase voltage modulation wave generation unit. When the detected voltage value at the grid connection point recovers to the preset lower voltage limit and the rate of change is lower than a set threshold, the Crowbar circuit is disconnected, and the converter control strategy is switched from vector control of the rotor speed of the split-winding synchronous motor to droop control of the power at the grid connection point.

[0059] When the voltage amplitude recovers to the safe constraint range (0.9pu-1.1pu) and the voltage change rate recovers to the safe constraint range (0.1pu / s), the system detects the end of the transient process and controls the grid-connected system to switch to steady-state control mode. At this time, in order to switch the open-winding synchronous motor interface grid-connected system from transient operation mode to steady-state operation mode, it is necessary to control the Crowbar circuit to be disconnected, forming a structure in which the converter is connected to the grid through the open-winding synchronous motor interface, and the power of the grid connection point is directly controlled by the converter. At the same time, the phase compensation link in the synchronous motor excitation system is removed; The converter control strategy has been switched from vector control of the rotor speed of the split-winding synchronous motor to droop control of the power at the grid connection point, including: The expressions for the droop control law of active and reactive power at the grid connection point are: ; In the formula, The active power droop factor (e.g.) Figure 5 Module 15). The reactive power droop factor (e.g.) Figure 5 Module 16). The electrical angular velocity of the converter output voltage; This represents the amplitude of the converter's output voltage. The output reference voltage amplitude of the converter; This is a reference value for active power. This represents the actual value of active power.

[0060] The amplitude of the converter output voltage is determined by directing the voltage vector to the d-axis. Transformed into the reference voltage vector in the dq coordinate system , and reference electrical angle .

[0061] The formulas for calculating the d-axis and q-axis reference voltage vectors for active and reactive power droop control of the converter are as follows: ; The formula for calculating the converter reference electrical angle is as follows: ; This step enables a smooth transition and steady-state operation of the system after the transient fault is cleared. It also provides a reliable voltage reference vector and electrical angle reference for subsequent converter SVPWM modulation, thereby improving the operational reliability of the system after fault recovery.

[0062] S4: Based on the d-axis and q-axis reference voltage vectors and the reference electrical angle of the converter, calculate the required voltage vector of the converter and combine it with SVPWM to generate the drive signals for each bridge arm switching device in the converter to apply control to the system, including the following sub-steps: S41: Based on the d-axis and q-axis reference voltage vectors of the converter, the Park transformation is used to convert them into voltage components in a two-phase stationary coordinate system to obtain the converter reference voltage vector. Specifically, the motor d-axis and q-axis reference voltage vectors generated according to the converter power control method , and converter reference electrical angle The voltage components are converted to a two-phase stationary coordinate system using the Park transformation (e.g., ...). Figure 3 As shown in module 8, the converter reference voltage vector is obtained; specifically, it is calculated using the following formula: ; In the formula, , For the converter in α / The reference voltage vector required for the β axis.

[0063] S42: Based on the converter reference voltage vector, execute the SVPWM algorithm to generate the PWM pulse signal required by the converter, and then generate the drive signal of each bridge arm switching device in the converter to apply control to the system; Specifically, based on the converter reference voltage vector, the SVPWM algorithm (such as...) is executed. Figure 3 As shown in module 9, it mainly includes sector determination of the reference voltage vector, calculation of the action time of non-zero and zero vectors in each sector, and determination of the vector switching point of each sector. Finally, a triangular carrier signal of a certain frequency is used to compare with the vector switching point of each sector, so as to generate the PWM pulse signal required by the converter.

[0064] Figure 6 The figure shows a comparison of the simulation results of transient overvoltage suppression in a grid-connected system of a non-open-winding synchronous motor and a grid-connected system of an open-winding synchronous motor with additional phase compensation excitation regulation. Figure 6 (a) in the figure is the grid-connected voltage waveform when the motor excitation only uses reactive PI control. Figure 6 (b) in the figure represents motor excitation based on reactive power PI control, with the addition of a control based on... Phase-compensated grid connection point voltage waveform. From Figure 6 As can be seen from (a) above, when relying solely on reactive power PI control, the voltage overshoot at the grid connection point is significant during fault recovery, accompanied by obvious periodic fluctuations; while from... Figure 6 As can be seen in (b) of the paper, the introduction of the proposed... After phase-compensated excitation control, the system response speed is greatly improved, the voltage overshoot is effectively reduced, and the voltage fluctuation during the fault recovery phase is suppressed. The effect of transient overvoltage suppression and the dynamic recovery performance of the system are significantly optimized.

[0065] Figure 7 This is a comparison chart of simulation results of grid connection point voltage and reactive power operation before and after applying the transient overvoltage suppression method according to an embodiment of the present invention. Figure 7 (a) in the figure is the grid connection point voltage waveform without the application of transient overvoltage suppression method. Figure 7 (b) in the figure shows the grid connection point voltage waveform under the applied transient overvoltage suppression method. Figure 7 (c) in the figure shows the reactive power waveform at the grid connection point without the application of transient overvoltage suppression methods. Figure 7 Figure (d) shows the reactive power waveform at the grid connection point under the transient overvoltage suppression method. The initial active power is 1 p.u., and the reactive power is 0 p.u. A short-circuit fault occurs at 20 s, causing the grid voltage to drop to 0.4 p.u. The fault is cleared after 0.1 s. The PCC voltage and reactive power waveforms are compared with those without the transient control strategy. Figure 7 As shown in (a) and (b), after a short-circuit fault occurs in the power grid, the grid voltage drops to 0.4 pu. After the fault is cleared, the PCC voltage without the transient control strategy increases to 1.11 pu, while the PCC voltage with the transient overvoltage suppression strategy increases to 1.06 pu. Simulation results show that the proposed transient overvoltage suppression strategy has a good transient overvoltage suppression effect on the PCC voltage. Figure 7 As can be seen from (c) and (d) in the figure, when the fault is cleared, the operating condition without the transient control strategy cannot absorb the excess reactive power of the PCC in time. However, the operating condition with the transient overvoltage suppression strategy can absorb the excess reactive power of the PCC through parameter improvement and the phase-advancing conversion of the synchronous motor, thereby achieving transient overvoltage suppression.

[0066] Through the above embodiments of the present invention, a transient overvoltage suppression control strategy is studied for an open-winding motor interface grid-connected system topology, in which an open-winding synchronous motor is connected in series with a new energy power generation converter and then connected to the AC grid. By real-time monitoring of grid fault clearing signals, grid connection point voltage and frequency detection values, the electromagnetic transient impact and electromechanical transient oscillation stages are divided. A staged control method is designed to suppress overvoltage peaks using the transient reactive power absorption characteristics of the open-winding synchronous motor connected in series with the converter port, and to suppress overvoltage oscillations using synchronous motor excitation damping control. Based on the constraints of grid connection point voltage amplitude and voltage change rate, a smooth transition method is designed for the simultaneous switching of Crowbar circuit disconnection and synchronous motor excitation and converter control modes, thereby realizing the transient overvoltage suppression exit method. Through the above transient overvoltage suppression control method, transient overvoltage suppression of the proposed topology is achieved.

[0067] This application introduces a synchronous motor between the new energy converter and the power grid. From the perspective of the grid port, its grid-connected topology has the transient reactive power regulation characteristics of a synchronous motor, which solves the technical problem of poor transient overvoltage suppression effect of traditional power electronic converters after grid fault clearance, and improves the transient operation stability and voltage support capability of the grid-connected system.

[0068] Figure 8 This is a block diagram illustrating a transient overvoltage suppression control device for an open-winding motor interface grid-connected system according to an exemplary embodiment. (Refer to...) Figure 8 The device includes: The data acquisition module 1 is used to monitor in real time the power grid fault clearing signal, the voltage detection value at the grid connection point, and the frequency detection value. The stage identification module 2 is used to identify the electromagnetic transient impact stage and the electromechanical transient oscillation stage based on the fault clearing time corresponding to the power grid fault clearing signal and the voltage recovery time corresponding to the recovery of the grid connection point voltage detection value to the preset voltage safety constraint range. The generation module 3 is used to generate the d-axis and q-axis reference voltage vectors and the reference electrical angle of the converter through the control methods of the synchronous motor excitation and the converter in transient and steady-state operation modes. The control method in the transient operation mode includes: during the electromagnetic transient impact stage, using the transient reactive power absorption characteristics of the open-winding synchronous motor connected in series at the converter port to suppress the transient overvoltage peak; during the electromechanical transient oscillation stage, using the frequency detection value as a feedback signal to generate an additional excitation control quantity and superimposing it on the excitation setpoint input to provide damping to suppress transient overvoltage oscillations for the system. The control method in the steady-state operation mode includes: continuously monitoring the grid connection point voltage detection value and its rate of change; when the grid connection point voltage detection value recovers to the preset lower voltage limit and the rate of change is lower than the set threshold, controlling the Crowbar circuit to disconnect, and synchronously switching the excitation control of the synchronous motor and the converter control from the transient operation mode to the steady-state operation mode to complete the smooth transition from transient overvoltage suppression to steady-state grid connection. The control module 4 is used to calculate the voltage vector required by the converter based on the d-axis and q-axis reference voltage vectors and the converter reference electrical angle, and to generate drive signals for each bridge arm switching device in the converter in combination with SVPWM, so as to apply control to the system.

[0069] Regarding the apparatus in the above embodiments, the specific manner in which each module performs its operation has been described in detail in the embodiments related to the method, and will not be elaborated upon here.

[0070] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can be referred to in the description of the method embodiments. The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this application according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0071] Accordingly, this application also provides an electronic device, comprising: one or more processors; a memory for storing one or more programs; and when the one or more programs are executed by the one or more processors, causing the one or more processors to implement the transient overvoltage suppression control method for open-winding motor interface grid-connected systems as described above.

[0072] Accordingly, this application also provides a computer-readable storage medium storing computer instructions that, when executed by a processor, implement the transient overvoltage suppression control method for an open-winding motor interface grid-connected system as described above.

[0073] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of this application are indicated by the claims.

[0074] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A transient overvoltage suppression control method for a grid-connected system with an open-winding motor interface, characterized in that, include: Real-time monitoring of power grid fault clearing signals, grid connection point voltage detection values, and frequency detection values; Based on the fault clearing time corresponding to the power grid fault clearing signal and the voltage recovery time corresponding to the recovery of the grid connection point voltage detection value to the preset voltage safety constraint range, the electromagnetic transient impact stage and the electromechanical transient oscillation stage are identified. By using the synchronous motor excitation and converter control methods in transient and steady-state operation modes, the d-axis and q-axis reference voltage vectors and the converter reference electrical angle are generated. The control method for the transient operation mode includes: during the electromagnetic transient impact stage, utilizing the transient reactive power absorption characteristics of the open-winding synchronous motor connected in series at the converter port to suppress the transient overvoltage peak; during the electromechanical transient oscillation stage, using the frequency detection value as a feedback signal to generate an additional excitation control quantity and superimposing it on the excitation setpoint input to provide damping to suppress transient overvoltage oscillations; the control method for the steady-state operation mode includes: continuously monitoring the grid connection point voltage detection value and its rate of change; when the grid connection point voltage detection value recovers to the preset voltage lower limit and the rate of change is lower than the set threshold, controlling the Crowbar circuit to disconnect, and synchronously switching the excitation control of the synchronous motor and the converter control from the transient operation mode to the steady-state operation mode, completing a smooth transition from transient overvoltage suppression to steady-state grid connection; Based on the d-axis and q-axis reference voltage vectors and the reference electrical angle of the converter, the required voltage vector of the converter is calculated, and the drive signals of each bridge arm switching device in the converter are generated in combination with SVPWM to apply control to the system.

2. The transient overvoltage suppression control method for an open-winding motor interface grid-connected system according to claim 1, characterized in that, The grid connection point voltage detection values ​​include the three-phase voltage amplitude and voltage change rate at the grid connection point; the frequency detection values ​​include the system rated frequency, actual frequency, and frequency deviation value.

3. The transient overvoltage suppression control method for an open-winding motor interface grid-connected system according to claim 1, characterized in that, Based on the fault clearing time corresponding to the grid fault clearing signal and the voltage recovery time corresponding to the recovery of the grid connection point voltage detection value to the preset voltage safety constraint range, the electromagnetic transient impact stage and the electromechanical transient oscillation stage are identified, including: The fault clearing time corresponding to the power grid fault clearing signal and the voltage recovery time corresponding to the recovery of the grid connection point voltage detection value to the preset voltage safety constraint range are obtained. Taking the fault clearing time as the starting point and the voltage recovery time as the ending point, the electromagnetic transient impact stage and the electromechanical transient oscillation stage are divided. The time period from the fault clearing time to the voltage recovery time is the electromagnetic transient impact stage, and the time period from the voltage recovery time to the present is the electromechanical transient oscillation stage.

4. The transient overvoltage suppression control method for an open-winding motor interface grid-connected system according to claim 1, characterized in that, During the electromagnetic transient impact phase, the transient reactive power absorption characteristics of the open-winding synchronous motor connected in series at the converter port are utilized to suppress transient overvoltage peaks, including: The excitation voltage of the open-winding synchronous motor is controlled by reactive power feedback. The excitation voltage of the synchronous motor is generated by a proportional-integral (PI) controller, which adjusts the voltage according to the deviation between the system reactive power reference value and the actual system reactive power value. The converter performs vector control on the rotor speed of the open-winding synchronous motor. The d-axis current setpoint of the converter is set to 0, and the control of the q-axis current setpoint adopts a proportional-integral (PI) control structure. The controller calculates based on the deviation between the rotor speed setpoint and the actual electrical angular velocity of the synchronous motor rotor. Analysis of the transient reactive power absorption characteristics of a split-winding synchronous motor.

5. The transient overvoltage suppression control method for an open-winding motor interface grid-connected system according to claim 1, characterized in that, The frequency detection value is used as a feedback signal to generate an additional excitation control quantity, which is then superimposed on the excitation setpoint input to provide damping for the system to suppress transient overvoltage oscillations, including: The system frequency deviation is selected as the feedback power oscillation signal, and its output is superimposed on the excitation control as an additional excitation control signal. The additional excitation control signal is generated by the system frequency deviation signal through the following processing: the system frequency deviation signal is input into a controller composed of a transient gain element and a lead / lag element cascaded together, and then multiplied by a proportional coefficient.

6. The transient overvoltage suppression control method for an open-winding motor interface grid-connected system according to claim 1, characterized in that, Continuously monitor the grid connection point voltage and its rate of change. When the grid connection point voltage recovers to the preset lower voltage limit and the rate of change is lower than the set threshold, control the Crowbar circuit to disconnect, and synchronously switch the excitation control of the synchronous motor and the converter control from transient operation mode to steady-state operation mode, completing a smooth transition from transient overvoltage suppression to steady-state grid connection, including: When a transient overvoltage occurs in the power grid, the Crowbar circuit is in a closed state, and the converter uses rotor speed vector control to operate the synchronous motor. The excitation voltage of the synchronous motor is adjusted according to the reactive power feedback of the power grid, so that the system operates in transient operation mode. When the transient overvoltage fault is cleared, and the voltage amplitude at the grid connection point recovers to the preset upper voltage limit and the voltage change rate is lower than the set threshold, after the steady-state operation is restored, the control Crowbar circuit is disconnected, and the converter control is switched to droop control of the active and reactive power at the grid connection point, so that the system operates in steady-state mode.

7. The transient overvoltage suppression control method for an open-winding motor interface grid-connected system according to claim 1, characterized in that, Based on the d-axis and q-axis reference voltage vectors of the converter and the reference electrical angle of the converter, the required voltage vector of the converter is calculated and combined with SVPWM to generate drive signals for each bridge arm switching device in the converter, so as to apply control to the system, including: Based on the d-axis and q-axis reference voltage vectors of the converter, the Park transformation is used to convert them into voltage components in a two-phase stationary coordinate system, thus obtaining the converter reference voltage vector. Based on the converter reference voltage vector, the SVPWM algorithm is executed to generate the PWM pulse signal required by the converter, and then the drive signal of each bridge arm switching device in the converter is generated to control the system.

8. A transient overvoltage suppression and control device for an open-winding motor interface grid-connected system, characterized in that, include: The data acquisition module is used to monitor power grid fault clearing signals, grid connection point voltage detection values, and frequency detection values ​​in real time. The stage identification module is used to identify the electromagnetic transient impact stage and the electromechanical transient oscillation stage based on the fault clearing time corresponding to the power grid fault clearing signal and the voltage recovery time corresponding to the recovery of the grid connection point voltage detection value to the preset voltage safety constraint range. The generation module is used to generate the d-axis and q-axis reference voltage vectors and the reference electrical angles of the converter by means of synchronous motor excitation and control methods of the converter in transient and steady-state operation modes. The control method for the transient operation mode includes: during the electromagnetic transient impact stage, utilizing the transient reactive power absorption characteristics of the open-winding synchronous motor connected in series at the converter port to suppress the transient overvoltage peak; during the electromechanical transient oscillation stage, using the frequency detection value as a feedback signal to generate an additional excitation control quantity and superimposing it on the excitation setpoint input to provide damping to suppress transient overvoltage oscillations; the control method for the steady-state operation mode includes: continuously monitoring the grid connection point voltage detection value and its rate of change; when the grid connection point voltage detection value recovers to the preset voltage lower limit and the rate of change is lower than the set threshold, controlling the Crowbar circuit to disconnect, and synchronously switching the excitation control of the synchronous motor and the converter control from the transient operation mode to the steady-state operation mode, completing a smooth transition from transient overvoltage suppression to steady-state grid connection; The control module is used to calculate the voltage vector required by the converter based on the d-axis and q-axis reference voltage vectors and the converter reference electrical angle, and to generate drive signals for each bridge arm switching device in the converter in combination with SVPWM, so as to apply control to the system.

9. An electronic device, characterized in that, include: One or more processors; Memory, used to store one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the method as described in any one of claims 1-7.

10. A computer-readable storage medium storing computer instructions thereon, characterized in that, When executed by the processor, this instruction implements the steps of the method as described in any one of claims 1-7.

Images