Low voltage ride through control method and device for open winding motor interface grid-connected system

Abstract

The invention discloses a low voltage ride through control method and device for an open winding motor interface grid-connected system, and the method comprises the steps: firstly obtaining a power grid dispatching power given value, and calculating a system apparent power given value and a power factor angle given value; secondly, designing a three-droop structure system power control method for droop of the motor excitation voltage by the apparent power and droop of the converter voltage phase and amplitude by the power factor angle according to the apparent power of the system and the given value of the power factor angle; thirdly, designing a low-voltage ride-through method for compensating amplitude droop and phase droop channels of the converter to suppress transient overcurrent at the instant of a power grid fault according to the short-circuit current safety constraint of the converter and the reactive power support requirement of the power grid; and finally, calculating a voltage vector required by the inverter and generating a driving signal of each bridge arm switching device in the inverter in combination with SVPWM so as to apply control to the system and realize low voltage ride through.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of motor control, and particularly relates to a low-voltage ride-through control method and device for an open-winding motor interface grid-connected system. BACKGROUND

[0002] With the gradual increase of new energy equipment in the power system, in recent years, the penetration rate of new energy represented by wind energy and solar energy has shown a trend of rising year by year. The large-scale access of new energy brings severe challenges to the safe and stable operation of the power grid. The grid connection rules require new energy units to have low-voltage ride-through capability, that is, to maintain uninterrupted operation of new energy units during power grid faults, so as to maintain the safe and stable operation of the power system. However, due to the limited overload capacity of power electronic devices, the overcurrent at the moment of short-circuit fault of the power grid is easy to cause damage to the devices, which poses a great threat to the safety and stability of the system. At present, grid-connected converters are widely concerned due to their active disturbance and active support characteristics. They have voltage and frequency support capabilities, which solve the problem that traditional follow-network type control is easy to be off-grid and unstable in weak power grids due to the lack of support capability. However, when the power grid is subjected to a large disturbance, the power angle curve and fixed active and reactive power reference values controlled by the power outer loop will cause a large power angle instability and high short-circuit current, which will cause the power electronic devices to be broken down and then damage the equipment.

[0003] Some scholars have also studied the improvement of grid-connected topology to enhance the transient support capability of new energy converters. The idea of adding devices for reactive power support in the grid-connected system is more flexible. Common reactive power compensation devices include shunt capacitors / reactors, static var compensators (SVCs), static synchronous compensators (STATCOMs), and synchronous compensators. The traditional capacitor / reactor has a fixed reactance value, which may interact with the grid impedance to cause resonance risk. The voltage support capability of SVC in a weak power grid will deteriorate significantly, and a large-capacity SVC requires multiple sets of shunt reactors / capacitors, which increases the land area requirement and may cause cascading stability problems. As for STATCOM, high switching frequency increases power loss, requires an additional cooling system, and has high maintenance costs. In addition, the impedance characteristics in the sub / super synchronous frequency band will interact adversely with wind turbines. Installing a synchronous power source can enhance the strength and synchronization characteristics of the power grid, but the cost of installing a synchronous compensator in engineering is high, and it cannot be configured to a lower voltage level, which limits the support capability of new energy units.

[0004] To fundamentally solve this problem, the topology structure of the system is improved, and a device with an open-winding motor interface grid-connected system is provided, which provides the possibility for new energy devices to have active support capability and improve overload capability. In order to popularize this topology, a corresponding low-voltage ride-through control strategy needs to be designed for the topology structure. SUMMARY

[0005] The purpose of the embodiments of the present application is to provide a low voltage ride through control method and device for an open-winding motor interface grid-connected system, so as to solve the technical problem of limited overload capacity of a new energy converter power generation device when a short-circuit fault occurs in a power grid.

[0006] According to a first aspect of the embodiments of the present application, a low voltage ride through control method for an open-winding motor interface grid-connected system is provided, characterized in that the method comprises: obtaining active power and reactive power given values given by power grid dispatching; calculating system apparent power given values and power factor angle given values according to the active power and reactive power given values; designing a three-droop structure system power control method of apparent power versus motor excitation voltage droop and power factor angle versus converter voltage phase and amplitude droop according to the system apparent power given values, power factor angle given values and reactive power given values, the method taking motor excitation voltage and converter d, q axis reference voltage vectors as direct control targets, and achieving expected active power and reactive power given values by actively constructing a system voltage vector triangle corresponding to the power given values; designing a low voltage ride through control method for a new energy converter according to safety constraint conditions of converter short-circuit current and reactive power support requirements of the power grid, the method compensating a converter amplitude droop and phase droop channel at a power grid fault moment, indirectly suppressing current flowing through a motor stator by reducing a reactance voltage drop on the motor, and thereby realizing low voltage ride through; generating converter d, q axis reference voltage vectors and a converter reference electric angle through the three-droop structure system power control method and the low voltage ride through control method; calculating voltage vectors required by an inverter according to the converter d, q axis reference voltage vectors and the converter reference electric angle, and combining SVPWM to generate driving signals of each bridge arm switching device in the inverter, so as to exert control on the system.

[0007] According to a second aspect of the embodiments of the present application, a low voltage ride through control device for an open-winding motor interface grid-connected system is provided, characterized in that the device comprises: an acquisition and obtaining module configured to obtain active power and reactive power given values given by power grid dispatching; a first calculation module configured to calculate system apparent power given values and power factor angle given values according to the active power and reactive power given values; The first design module is configured to design a three-droop structure system power control method of active power versus motor excitation voltage droop, power factor angle versus converter voltage phase and amplitude droop according to the system apparent power given value, power factor angle given value and reactive power given value, the method taking the motor excitation voltage and the converter d, q axis reference voltage vector as direct control targets, and achieving the expected active power and reactive power given values by actively constructing a system voltage vector triangle corresponding to the power given value; The second design module is configured to design a low voltage ride through control method of the new energy converter according to the safety constraint condition of the converter short-circuit current and the grid reactive power support demand, the method compensating the converter amplitude droop and phase droop channel at the grid fault moment, indirectly suppressing the current flowing through the motor stator by reducing the reactance voltage drop on the motor, and thus realizing low voltage ride through. The generation module is configured to generate the converter d, q axis reference voltage vector and the converter reference electric angle through the three-droop structure system power control method and the low voltage ride through control method. The control module is configured to calculate the voltage vector required by the inverter according to the converter d, q axis reference voltage vector and the converter reference electric angle, and generate the driving signal of each bridge arm switching device in the inverter in combination with the SVPWM to exert control on the system.

[0008] According to a third aspect of the embodiments of the present application, an electronic device is provided, including: one or more processors; a memory configured 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 according to the first aspect.

[0009] The technical solutions provided by the embodiments of the present application can have the following beneficial effects: As known from the above embodiments, the present application adopts the technical means of connecting the open-winding synchronous motor and the new energy converter in series and then connecting them to the power grid, overcomes the technical problem of insufficient overload capacity of the traditional new energy converter power generation device under short-circuit fault of the power grid, and thus realizes low voltage ride through. By designing a system power control method with three-droop structure of motor excitation voltage, converter voltage phase and transformer voltage amplitude, the technical problem of no matching transient power control strategy of the converter for the open-winding synchronous motor interface new energy power generation device is overcome, and thus the power of the converter and the open-winding motor can be flexibly adjusted when the power grid has a short-circuit fault. By designing a transient overcurrent suppression method of instantaneous compensation of the voltage phase-amplitude of the new energy converter, the technical problem of easy damage of the new energy converter power generation device by high times short-circuit current when the power grid has a short-circuit fault is overcome, and thus low voltage ride through is realized.

[0010] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the application, as claimed. BRIEF DESCRIPTION OF DRAWINGS

[0011] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the application and serve to explain the principles of the application, in which, like reference numerals designate corresponding parts throughout the several views.

[0012] Figure 1 Topological structure of an open-winding motor interface grid-connected system according to an embodiment of the application.

[0013] Figure 2 Flow chart of a low-voltage ride-through control method of an open-winding motor interface grid-connected system according to an embodiment of the application.

[0014] Figure 3 Control block diagram of a three-sag structure system power control method according to an embodiment of the application.

[0015] Figure 4 Control block diagram of a low-voltage ride-through control method of a new energy converter according to an embodiment of the application.

[0016] Figure 5 Result diagram of a simulation case of a voltage phase-amplitude compensation link not being added to a converter according to an embodiment of the application.

[0017] Figure 6 Result diagram of a simulation case of a voltage phase-amplitude compensation link being added to a converter according to an embodiment of the application.

[0018] Figure 7 Block diagram of a low-voltage ride-through control device of an open-winding motor interface grid-connected system according to an embodiment of the application. DETAILED DESCRIPTION

[0019] The exemplary embodiments will be described in detail herein below with reference to the drawings. In the following description, unless otherwise indicated, like numbers in the figures indicate contact elements or features that are the same or similar. There can be many alterations to the embodiments described herein without departing from the scope of the application. Thus, the exemplary embodiments described herein should be understood not to limit but to explain the scope of the application. The scope of the application is limited only by the claims.

[0020] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting thereof. As used in this application and the appended claims, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term "and / or," as used herein, refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0021] It should be understood that, although the terms first, second, third, etc. can be used herein to describe various information, but these information should not be limited to these terms. These terms are only used to distinguish information of the same type from each other. For example, without departing from the scope of the application, the first information can also be referred to as the second information, and similarly, the second information can also be referred to as the first information. Depending on the context, the word "if" as used herein can be interpreted as "when" or "upon" or "in response to determining".

[0022] Figure 1 The topology of the open-winding motor interface grid-connected system studied in the embodiments of the application includes a new energy power generation device and a DC / AC three-phase inverter I, an open-winding synchronous motor II and an alternating current grid III, wherein the new energy power generation device and the DC / AC three-phase inverter are connected to photovoltaic or energy storage on the DC side, realizing new energy direct-current conversion; the open-winding synchronous motor stator winding 3 terminals are connected to the converter, and the other 3 terminals are connected to the grid, and the motor runs in the motor state without load; the grid can be regarded as a three-phase ideal voltage source.

[0023] Compared with the topology of the conventional new energy grid-connected system, Figure 1 The winding impedance of the open-winding synchronous motor introduced in the topology can be used as a filter of the output port of the converter, thereby reducing the system cost to a certain extent; at the same time, the new energy converter can have similar inertia response capability to the synchronous motor at the transient state, thereby improving the problem of insufficient inertia of the grid; when the short-circuit fault occurs in the grid, the short-circuit current can be borne at a higher multiple compared with the overload capability of the converter. However, when the open-winding motor is introduced, the topology complexity and operating loss of the system will also increase slightly.

[0024] Figure 2 A flowchart of a low-voltage ride-through control method of an open-winding motor interface grid-connected system according to the embodiments of the application; as shown in Figure 2 The method comprises the following steps: S1: obtaining the active power and reactive power given values given by the grid dispatching; Specifically, the active power given value issued by the dispatching center through automatic generation control is received in real time, and the reactive power given value issued by the dispatching center through the automatic voltage control system is received synchronously. Through this step, the basic data source is provided for the subsequent method design.

[0025] S2: Calculate the system apparent power given value and the power factor angle given value according to the active power and reactive power given values; Specifically, the system apparent power given value and the power factor angle given value are calculated by the following formulas, respectively. ; In the formulas, S ref is the system apparent power given value; P ref is the grid dispatch active power given value; Q ref is the grid dispatch reactive power given value; φ ref is the power factor angle given value.

[0026] Through this step, a basis is provided for subsequent transfer of active and reactive power control to apparent power and power factor angle control.

[0027] S3: Design a three-droop structure system power control method of apparent power droop to motor excitation voltage and power factor angle droop to converter voltage phase and amplitude according to the system apparent power given value, the power factor angle given value and the reactive power given value, which takes the motor excitation voltage and the converter d, q axis reference voltage vector as the direct control target, and achieves the expected active power and reactive power given values by actively constructing a system voltage vector triangle corresponding to the power given value. The power control method block diagram is shown in Figure 3 The following sub-steps are included: S31: The system apparent power given value S is drooped, and the droop coefficient is k 1, to obtain the excitation voltage u f ; Specifically, by analyzing the voltage vector relationship among the converter, the motor and the grid and the active and reactive power, it can be obtained that the system apparent power and the motor voltage amplitude meet the droop relationship control rate, and the motor voltage is determined by the excitation voltage. Therefore, the droop control is adopted to indirectly realize accurate control of the motor excitation voltage by controlling the system apparent power. According to the droop relationship between the system apparent power and the motor excitation voltage, the input of the excitation voltage u f is formed, and the calculation formula of the input of the excitation voltage u f is as follows: ; ; In the formulas,S X is the system apparent power md X is the motor d X is the shaft reactance s X is the motor stator reactance f X is the motor excitation reactance U g X is the grid voltage

[0028] S32: power factor angle given value φ Droop, droop coefficient is k 2, and a phase synchronization link and an accurate tracking link are added to the forward channel of the phase differential of the converter, to obtain the converter phase θ 1; Specifically, through analysis of the voltage vector relationship among the converter, the motor and the grid and active power and reactive power, it is found that the system power factor angle and the converter voltage phase meet the droop relationship control rate, so that droop control is adopted to indirectly realize accurate control of the converter voltage phase.

[0029] According to the voltage phase jump caused by the grid fluctuation, a converter voltage phase synchronization link is added to ensure that the system voltage vector phase relationship remains synchronous, including: The converter voltage phase synchronization link additional amount is calculated by the following formula: ; In the formula, θ com X is the converter voltage phase synchronization link additional amount θ 0 is the initial phase difference between the converter voltage phase and the grid voltage phase θ X is the fault transient phase difference between the converter voltage phase and the grid voltage phase According to the droop relationship between the grid power factor angle and the converter voltage phase and the phase synchronization link and the accurate tracking link, the input value of the converter voltage phase is constituted, and the calculation formula of the input value of the converter voltage phase and amplitude is as follows: ; In the formula, θ 1 is the phase difference between the converter and the grid voltage According to the difference between the system reactive power given value and the system reactive power, PI control is performed (such as Figure 3 module 9 in the figure), which is added to the forward channel of the phase differential of the converter, to ensure the accuracy and rapidity of the system operating power, including: The additional amount of the converter voltage accurate tracking link is calculated by the following formula: ; In the formula, θq The additional amount for the converter voltage phase to be accurately tracked; k pq And k iq The proportional coefficient and the integral coefficient of the PI regulator for the additional amount of the converter phase to be accurately tracked, respectively; Q ref The given value of the system reactive power; Q The actual value of the system reactive power; S33: The given value of the power factor angle φ Droop, droop coefficient k 3, and the forward channel additional phase synchronization link of the converter voltage amplitude droop, the converter voltage amplitude U vsc ; Specifically, by analyzing the voltage vector relationship among the converter, the motor and the power grid and the active and reactive power, it can be obtained that the system power factor angle and the converter voltage amplitude meet the droop relationship control rate, and therefore the droop control is adopted to indirectly realize the accurate control of the converter voltage amplitude by controlling the power factor angle of the power grid; According to the voltage phase jump of the power grid fluctuation, an additional converter voltage phase synchronization link is added, including: The additional amount of the converter voltage phase synchronization link is calculated by the following formula: ; In the formula, θ com The additional amount of the converter voltage phase synchronization link; Δ θ 0 is the initial phase difference between the converter voltage phase and the power grid voltage phase; Δ θ is the fault transient phase difference between the converter voltage phase and the power grid voltage phase; According to the droop relationship between the system power factor angle and the converter voltage phase and amplitude, the input value of the converter voltage amplitude is formed, and the calculation formula of the input value of the converter voltage amplitude is as follows: ; In the formula, U vsc The converter voltage amplitude; S34: The given value of the excitation voltage u f Indirectly control the voltage of the open-winding synchronous motor U s The converter voltage phase θ 1 and the converter voltage amplitude U vsc Direct control, actively build a system voltage vector triangle, and then realize the control of the system power; Specifically, according to the vector relationship of the converter voltage, the synchronous motor voltage and the grid voltage, a system voltage vector triangle is actively constructed, and then the control of the system power is realized, including: The system steady-state voltage calculation formula is as follows: ; In the formula, U vsc is the converter voltage, U s is the open-winding synchronous motor voltage, U g is the grid voltage, E 0 is the open-winding synchronous motor induced internal potential, j is the imaginary unit, I is the current flowing through the grid connection point, X s is the motor stator reactance, and ω is the motor rotor speed, md is the motor d-axis inductance, I f is the excitation current of the open-winding synchronous motor; The system steady-state current calculation formula is as follows: ; The system steady-state power calculation formula is as follows: ; In the formula, P 、 Q are the system active power and reactive power respectively.

[0030] Through the three-inclined structure system power control method, the converter and the motor can be coordinated and controlled as a whole, the device is controlled, and the system power instruction can be quickly and accurately responded.

[0031] S4: According to the safety constraint condition of the converter short-circuit current and the reactive power support demand of the grid, a low voltage ride through control method of the new energy converter is designed, which compensates the amplitude droop and phase droop channels of the converter at the moment of grid fault, indirectly suppresses the current flowing through the motor stator by reducing the reactance voltage drop of the motor, and realizes low voltage ride through, including the following sub-steps: S41: The motor stator current and the grid voltage are collected, and the grid connection point reactive power is calculated; Specifically, the motor stator current is collected by using a three-phase current sensor I , the grid voltage is collected by using a voltage sensor U g , and the grid connection point reactive power is calculated as follows: ; In the formula, Q out1the reactive power at the grid-connection point before the fault, U g1 the three-phase voltage of the power grid before the fault, I 1 the three-phase current of the motor stator before the fault, φ 1 the power factor angle at the grid-connection point before the fault; the reactive power after the short-circuit fault of the power grid is calculated according to the following formula: ; in the formula, Q out2 the reactive power at the grid-connection point after the fault, U g2 the three-phase voltage of the power grid after the fault, I 2 the three-phase current of the motor stator after the fault, the current, φ 2 the power factor angle at the grid-connection point after the fault.

[0032] S42: calculating the phase difference between the system converter voltage and the grid voltage after the fault transient compensation according to the constraint of the reactive power at the grid-connection point and the rated current of the converter; Specifically, if the converter short-circuit current capacity constraint and the device reactive power support are to be met at the same time, the calculation formula of the power factor angle at the grid-connection point after the fault φ 2 is as follows: ; in the formula, I gmax is the maximum short-circuit current capacity that the converter can withstand.

[0033] S43: calculating the compensation amount of the phase and amplitude of the converter voltage according to the relationship between the phase difference between the converter voltage and the grid voltage after the fault transient and the power factor angle and the droop of the phase and amplitude of the converter voltage, and adding the compensation amount to the given forward channel of the phase and amplitude of the converter voltage; Specifically, the calculation formula of the power factor angle and the phase of the converter voltage is as follows: ; in the formula, θ 1ref is the given value of the phase of the converter voltage after the low-voltage control method is added; The calculation formula of the compensation value of the phase of the converter voltage is as follows: ; in the formula, θ 1com is the compensation value of the phase of the converter voltage after the fault transient (such as module 1 in Figure 4 k d1 and k i1 ​Kvp and Kvi are the proportional coefficient and integral coefficient of the converter voltage amplitude compensation PI regulator respectively. The calculation formula of the power factor angle and the converter voltage amplitude is as follows: In the formula, θ vscref Vref is the given value of the converter voltage amplitude after the low-voltage control method is added; The calculation formula of the converter voltage amplitude compensation value is as follows: In the formula, U vsccom Vcomp is the compensation value of the instantaneous converter voltage amplitude in the fault (such as Figure 4 the module 2 in the middle), k p2 Kvp and Kvi are the proportional coefficient and integral coefficient of the converter voltage amplitude compensation PI regulator respectively. k i2 Kvp and Kvi are the proportional coefficient and integral coefficient of the converter voltage amplitude compensation PI regulator respectively.

[0034] The overload capacity and current tolerance of the device in the fault can be improved by the low-voltage ride-through control method, and the power grid reactive power support capacity can be improved under the premise of meeting the safety constraints of the converter.

[0035] S5: generating the converter d, q-axis reference voltage vector and the converter reference electric angle through the three droop structure system power control method and the low-voltage ride-through control method; Specifically, the calculation formula of the converter d, q-axis reference voltage vector calculation is as follows: In the formula, U md ref U md ref Kvp and Kvi are the proportional coefficient and integral coefficient of the converter voltage amplitude compensation PI regulator respectively. The calculation formula of the converter reference electric angle is as follows: In the formula, ωt Vref is the given value of the converter voltage amplitude after the low-voltage control method is added;

[0036] Through this step, the basis for the subsequent converter SVPWM is provided.

[0037] S6: calculating the voltage vector required by the inverter according to the converter d, q-axis reference voltage vector and the converter reference electric angle, and combining the SVPWM to generate the driving signal of each bridge arm switching device in the inverter to exert control on the system, including the following sub-steps: ​​​​S61: generating motor d, q axis reference voltage vector according to the converter power control method u md ref 、 u mq ref and converter reference electric angle ωt , using Park transformation to convert into voltage components in two-phase stationary coordinate system (as shown in module 10 in Figure 3 , obtaining inverter reference voltage vector; Specifically, it is calculated by the following formula: ; In the formula, u mα ref 、 u mβ ref is the reference voltage vector required by the inverter in α-β axis.

[0038] S62: according to the inverter reference voltage vector, performing SVPWM algorithm (as shown in module 11 in Figure 3 , mainly including sector judgment of reference voltage vector, calculation of non-zero vector and zero vector action time in each sector and determination of each sector vector switching point, finally using a certain frequency of triangular carrier signal to compare with each sector vector switching point, so as to generate PWM pulse signal required by the converter.

[0039] Figure 5 and Figure 6 shows the simulation waveform diagram of the input power grid active power of 1p.u. and the reactive power of 0.3p.u. at the initial moment. At 2s, when the grid voltage drops to 0.6p.u., without adding converter phase-amplitude compensation control, the simulation waveform diagram of the open-winding motor interface grid-connected system is shown in Figure 5 , it can be seen that at this time, the system instantaneous current overflows seriously, and the converter output power overshoot is larger, and the response speed is slower. At this time, the converter needs to be compensated in amplitude and phase, and the system output current needs to be suppressed. As can be seen from Figure 6 , after adding the VSC voltage phase-amplitude compensation method, the instantaneous overcurrent is effectively suppressed, the grid-connected current does not exceed 1.15 times the rated grid-connected current throughout the process, and the power response speed is faster, which meets the design requirements, and has good current limiting capability.

[0040] According to the above embodiment of the present application, for a kind of open-winding motor interface grid-connected system topology, open-winding synchronous motor is connected in series with new energy power generation converter and is connected with AC power grid, and its power transient control strategy is researched.Through the design of system apparent power given value, power factor angle given value, the three droop relationships of apparent power to open-winding synchronous motor excitation voltage droop, power factor angle to converter voltage phase and amplitude droop are designed, and converter control method is formed;Through the constraint condition of converter short-circuit current and the demand of device reactive power support, the transient overcurrent suppression method of new energy converter voltage phase-amplitude instantaneous compensation is designed, and then low voltage ride through method is realized.Through the above low voltage ride through control method, the transient support capability of the designed new topology is realized.

[0041] The present application introduces a synchronous motor between new energy converter and power grid, from the grid port, its grid connection essence is motor, solves the technical problem of low short-circuit current capacity of traditional power electronic converter, and realizes the improvement of grid safety and stability and active support capability.

[0042] Figure 7 It is a block diagram of a kind of open-winding motor interface grid-connected system low voltage ride through control device according to an exemplary embodiment. Refer to Figure 7 , the device includes: Acquisition acquisition module 1 is used to obtain the active power and reactive power given value given by grid dispatching; First calculation module 2 is used to calculate system apparent power given value and power factor angle given value according to the active power and reactive power given value; First design module 3 is used to design the three droop structure system power control method of apparent power to motor excitation voltage droop, power factor angle to converter voltage phase and amplitude droop according to the system apparent power given value, power factor angle given value and reactive power given value, which takes motor excitation voltage and converter d, q axis reference voltage vector as direct control target, and reaches the expected active power, reactive power given value by actively constructing system voltage vector triangle corresponding to power given value; Second design module 4 is used to design the low voltage ride through control method of new energy converter according to the safety constraint condition of converter short-circuit current and the demand of grid reactive power support, which compensates converter amplitude droop and phase droop channel at the moment of grid fault, indirectly suppresses the current flowing through motor stator by reducing the reactance voltage drop on motor, so as to realize low voltage ride through; Generation module 5 is used to generate converter d, q axis reference voltage vector and converter reference electric angle through the three droop structure system power control method and low voltage ride through control method; The control module 6 is configured to calculate the voltage vector required by the inverter according to the d-q axis reference voltage vector of the converter and the reference electric angle of the converter, and generate the driving signals of the switching devices of each bridge arm of the inverter in combination with the SVPWM to exert control on the system.

[0043] As to the apparatus in the above embodiments, the specific manner in which each module performs operations has been described in detail in the embodiments of the method, and will not be described in detail here.

[0044] For the apparatus embodiments, since they basically correspond to the method embodiments, the relevant parts are described in the part of the method embodiments. The apparatus embodiments described above are merely illustrative, wherein the units described as separate components can or can not be physically separate, and the components displayed as units can or can not be physical units, i.e., can be located in one place, or can be distributed on multiple network units. Some or all of the modules can be selected to achieve the purposes of the present application according to actual needs. Those skilled in the art can understand and implement without creative labor.

[0045] Correspondingly, the present application also provides an electronic device, comprising: one or more processors; a memory for storing 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 open-winding motor interface grid-connected system low-voltage ride-through control method as described above.

[0046] Correspondingly, the present application also provides a computer readable storage medium having computer instructions stored thereon, which are executed by a processor to implement the open-winding motor interface grid-connected system low-voltage ride-through control method as described above.

[0047] Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The application is intended to cover any variations, uses, or adaptations of the application following, in general, the principles of the application and including such departures from the present disclosure as come within known or customary practice in the art to which the application pertains. The specification and examples are to be regarded as illustrative only, and the true scope and spirit of the application is indicated by the appended claims.

[0048] It should be understood that the present application is not limited to the precise construction that has been described above and illustrated in the accompanying drawings, and that various modifications and changes can be made by those skilled in the art without departing from the scope of the present application. The scope of the present application is limited only by the appended claims.

Claims

1. A low-voltage ride-through control method for an open-winding motor interface grid-connected system, characterized in that, include: Obtain the active and reactive power setpoints provided by the power grid dispatching system; Based on the given active power and reactive power values, calculate the system apparent power setpoint and power factor angle setpoint; Based on the system apparent power setpoint, power factor angle setpoint, and reactive power setpoint, a three-droop structure system power control method is designed, where apparent power droops with respect to motor excitation voltage, and power factor angle droops with respect to converter voltage phase and amplitude. This method takes the motor excitation voltage and the converter d-axis and q-axis reference voltage vectors as direct control targets, and actively constructs the system voltage vector triangle corresponding to the power setpoint to achieve the expected active and reactive power setpoints. Based on the safety constraints of the converter short-circuit current and the reactive power support requirements of the power grid, a low-voltage ride-through control method for new energy converters is designed. This method compensates for the amplitude droop and phase droop of the converter during the instant of a power grid fault. By reducing the reactance voltage drop on the motor, it indirectly suppresses the current flowing through the motor stator, thereby achieving low-voltage ride-through. The power control method and low voltage ride-through control method of the three-droop structure system are used to generate the d-axis and q-axis reference voltage vectors and the reference electrical angle of the converter. Based on the d-axis and q-axis reference voltage vectors and the reference electrical angle of the inverter, the voltage vector required by the inverter is calculated, and the drive signals of each bridge arm switching device in the inverter are generated in combination with SVPWM to apply control to the system.

2. The low-voltage ride-through control method for an open-winding motor interface grid-connected system according to claim 1, characterized in that, Based on the given active and reactive power values, calculate the system apparent power setpoint and power factor angle setpoint, including: The apparent power setpoint and power factor angle setpoint of the system are calculated using the following formulas respectively; ； In the formula: S ref This is the system apparent power setpoint; P ref The active power setpoint for power grid dispatch; Q ref The reactive power setpoint for power grid dispatching; φ ref This is the given value for the power factor angle.

3. The low-voltage ride-through control method for an open-winding motor interface grid-connected system according to claim 1, characterized in that, Based on the system's apparent power setpoint, power factor angle setpoint, and reactive power setpoint, a three-droop structure system power control method is designed, where apparent power droops with respect to motor excitation voltage, and power factor angle droops with respect to converter voltage phase and amplitude. This method includes: For the system apparent power setpoint S Sagging, sagging coefficient is k 1. Obtain the excitation voltage u f ; For the power factor angle given value φ Sagging, sagging coefficient is k 2. Furthermore, a phase synchronization and accurate tracking circuit is added to the forward path of the converter phase differential to obtain the converter phase. θ 1; For the power factor angle given value φ Sagging, Sagging Factor k 3. A phase synchronization element is added to the forward path where the converter voltage amplitude is drooping to obtain the converter voltage amplitude. U vsc ; Through excitation voltage u f Indirect control of open-winding synchronous motor voltage U s Converter voltage phase θ 1 and converter voltage amplitude U vsc Direct control actively constructs the system voltage vector triangle, thereby achieving system power control.

4. The low-voltage ride-through control method for an open-winding motor interface grid-connected system according to claim 3, characterized in that, The additional amount of the phase synchronization element is calculated using the following formula: ； In the formula, θ com Additional quantity for the voltage phase synchronization stage of the converter; Δ θ 0 represents the initial phase difference between the converter voltage phase and the grid voltage phase; Δ θ The instantaneous phase difference between the converter voltage phase and the grid voltage phase during a fault; The additional amount for accurate tracking is obtained using the following formula: ； In the formula, θ q Additional parameters for accurate voltage phase tracking of the converter; k pq and k iq These are the proportional and integral coefficients of the PI regulator, which are additional factors for accurate phase tracking of the converter. Q ref The reactive power setpoint for power grid dispatching; Q This refers to the reactive power of the power grid.

5. The low-voltage ride-through control method for an open-winding motor interface grid-connected system according to claim 3, characterized in that, Actively constructing the system voltage vector triangle to achieve system power control is accomplished through the following calculation formula: The steady-state voltage of the system is obtained by the following formula: ； In the formula: U vsc For converter voltage, U s For open-winding synchronous motor voltage, U g This is the grid voltage. E 0 represents the induced internal electromotive force of an open-winding synchronous motor. j The imaginary unit, I X is the current flowing through the grid connection point. s L is the stator reactance of the motor, ω is the rotor speed of the motor, and L is the stator reactance of the motor. md The d-axis inductance of the motor. I f This is the excitation current of an open-winding synchronous motor; The steady-state current of the system is obtained by the following formula: ； The steady-state power of the system is obtained by the following formula: ； In the formula: P and Q are the active power and reactive power of the system, respectively.

6. The low-voltage ride-through control method for an open-winding motor interface grid-connected system according to claim 1, characterized in that, Based on the safety constraints of the converter's short-circuit current and the reactive power support requirements of the power grid, a low-voltage ride-through control method for new energy converters is designed, including: (1) Collect the three-phase stator current of the motor and the three-phase voltage of the power grid, and calculate the reactive power at the grid connection point; (2) Based on the reactive power at the grid connection point and the rated current constraint of the converter, calculate the phase difference between the converter voltage and the grid voltage after instantaneous fault compensation; (3) Based on the phase difference between the instantaneous converter voltage and the grid voltage during the fault, and the relationship between the power factor angle and the phase and amplitude droop of the converter voltage, calculate the compensation amount of the converter voltage phase and amplitude, and add the compensation amount to the forward path of the given converter voltage phase and amplitude.

7. The low-voltage ride-through control method for an open-winding motor interface grid-connected system according to claim 6, characterized in that, (1) The formula for calculating the reactive power at the grid connection point is as follows: ； In the formula, Q out1 The reactive power at the grid connection point before the fault. U g1 The three-phase voltage of the power grid before the fault. I 1 represents the three-phase stator current of the motor before the fault. φ 1 represents the power factor angle at the grid connection point before the fault; The formula for calculating reactive power after a short-circuit fault in the power grid is as follows: ； In the formula, Q out2 This refers to the reactive power at the grid connection point after a fault. U g2 The three-phase voltage of the power grid after the fault. I 2 represents the three-phase stator current and current rating of the motor after the fault. φ 2 represents the power factor angle at the grid connection point after the fault; (2) The formula for calculating the phase difference between the converter voltage and the grid voltage after the instantaneous fault compensation is as follows: To simultaneously satisfy the converter's short-circuit current capacity constraint and reactive power support, the power factor angle at the grid connection point after a fault must be... φ The formula for calculating 2 is as follows: ； In the formula, I gmax This ensures that the converter can withstand the maximum short-circuit current capacity. (3) The calculation formula for the compensation amount of the voltage phase and amplitude of the converter is as follows: The formulas for calculating the power factor angle and the converter voltage phase are as follows: ； In the formula, θ 1ref This is the setpoint value for the converter voltage phase after the low-voltage control method is added; The formula for calculating the converter voltage phase compensation value is as follows: ； In the formula, θ 1com This is the compensation value for the converter voltage phase during a fault. k d1 and k i1 These are the proportional and integral coefficients of the converter voltage phase compensation PI regulator, respectively. The formulas for calculating the power factor angle and the converter voltage amplitude are as follows: ； In the formula, θ vscref This is the setpoint value for the converter voltage amplitude after the low-voltage control method is added; The formula for calculating the voltage amplitude compensation value of the converter is as follows: ； In the formula, U vsccom This is the compensation value for the instantaneous converter voltage amplitude during a fault. k p2 and k i2 These are the proportional coefficient and integral coefficient of the PI regulator for voltage amplitude compensation in the converter, respectively.

8. The low-voltage ride-through 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 inverter and the reference electrical angle of the inverter, the required voltage vector of the inverter is calculated and combined with SVPWM to generate drive signals for each bridge arm switching device in the inverter, so as to apply control to the system, including: Based on the d-axis and q-axis reference voltage vectors of the inverter, the Park transformation is used to convert them into voltage components in a two-phase stationary coordinate system, thus obtaining the inverter reference voltage vector. Based on the inverter 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 inverter is generated to control the system.

9. A low-voltage ride-through control device for an open-winding motor interface grid-connected system, characterized in that, include: The data acquisition module is used to acquire the active and reactive power setpoints given by the power grid dispatching system. The first calculation module is used to calculate the system apparent power setpoint and power factor angle setpoint based on the active power and reactive power setpoints. The first design module is used to design a three-droop structure system power control method based on the system apparent power setpoint, power factor angle setpoint, and reactive power setpoint. This method has the apparent power drooping with respect to the motor excitation voltage, the power factor angle drooping with respect to the converter voltage phase and amplitude, and takes the motor excitation voltage and the converter d-axis and q-axis reference voltage vectors as direct control targets. By actively constructing the system voltage vector triangle corresponding to the power setpoint, the expected active power and reactive power setpoints are achieved. The second design module is used to design a low-voltage ride-through control method for new energy converters based on the safety constraints of the converter short-circuit current and the reactive power support requirements of the power grid. This method compensates for the amplitude droop and phase droop of the converter at the moment of power grid fault, and indirectly suppresses the current flowing through the stator of the motor by reducing the reactance voltage drop on the motor, thereby achieving low-voltage ride-through. The generation module is used to generate the converter's d-axis and q-axis reference voltage vectors and the converter's reference electrical angles through the power control method and low-voltage ride-through control method of the three-droop structure system. The control module is used to calculate the voltage vector required by the inverter based on the d-axis and q-axis reference voltage vectors of the inverter and the reference electrical angle of the inverter, and to generate drive signals for each bridge arm switching device in the inverter in combination with SVPWM, so as to apply control to the system.

10. 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 1-8.

Images