A fault ride-through control method for a hybrid grid system

Abstract

This invention relates to the field of power electronic converter control technology, specifically to a fault ride-through control method for a hybrid grid system, comprising: S1: calculating the corresponding reference frequency and reference voltage amplitude based on point of common coupling data; S2: calculating the corresponding active power reference value and reactive power reference value for each GFL converter using reverse droop control; S3: calculating the additional reactive power required for each GFL converter and updating the reactive power reference value for each GFL converter; S4: calculating the corresponding reference frequency and reference voltage for each GFM converter using direct droop control; S5: designing a current loop to generate a modulation control signal to drive the operation of the corresponding GFL converter; S6: designing voltage and current loops to generate modulation control signals to drive the operation of the corresponding GFM converter. This invention can meet the needs of power systems with a high proportion of renewable energy sources in scenarios such as fault ride-through optimization, stable operation control, relay protection configuration, and power grid planning and design.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter control technology, specifically to a fault ride-through control method for a hybrid grid system. Background Technology

[0002] In power systems related to new energy grid connection, grid-connected (GFM) converters play an irreplaceable role in weak grid connection scenarios due to their ability to independently support voltage and frequency; while grid-following (GFL) converters are widely used in distributed generation systems due to their advantages of simple control structure and controllable cost.

[0003] However, when a hybrid system containing both GFM and GFL converters encounters a grid fault, the fault ride-through (FRT) problem becomes prominent. Under fault-induced voltage dips, the current control of the GFM converter is prone to transient stability conflicts. Existing solutions, such as mode switching, may result in non-seamless transitions, while current saturation strategies create a contradiction between enhanced transient stability and overcurrent limitation. Furthermore, existing research largely focuses on optimizing the fault ride-through performance of a single type of converter, neglecting the synergistic potential between GFL and GFM converters. This leads to significant frequency deviations during faults and excessively long recovery times after faults in hybrid systems, making it difficult to meet grid specifications for the point of common coupling (PCC). In addition, the impact of different grid short-circuit ratios and fault durations on system stability further exacerbates the complexity of fault ride-through.

[0004] Therefore, there is an urgent need for a fault ride-through strategy that can achieve coordinated control of GFM converters and GFL converters and adapt to multiple operating conditions, so as to improve the fault response capability and operational stability of the hybrid system. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, the technical problem this invention aims to solve is: how to provide a fault ride-through control method for a grid-connected hybrid system that can track the voltage drop status and dynamic changes in converter operating parameters during grid faults in real time, accurately reflect the collaborative operation characteristics of GFM and GFL converters, and then quickly achieve reactive power collaborative allocation and precise fault current regulation based on a hierarchical control architecture and sliding mode control technology, without the need for complex mode switching and electromagnetic transient modeling, taking into account both system stability and grid compliance, and meeting the needs of scenarios such as fault ride-through optimization, stable operation control, relay protection configuration, and grid planning and design for power systems with a high proportion of renewable energy.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A fault ride-through control method for a hybrid grid system includes:

[0008] S1: Calculate the corresponding reference frequency and reference voltage amplitude based on the common connection point data of the hybrid grid system;

[0009] S2: Based on the reference frequency and reference voltage amplitude of the grid-connected hybrid system, the corresponding active power reference value and reactive power reference value are calculated for each GFL converter using reverse droop control.

[0010] S3: Calculate the additional reactive power required for each GFL converter based on the total reactive power of the GFL converter and the total reactive power of the GFM converter, and update the reactive power reference value for each GFL converter.

[0011] S4: Based on the reference frequency and reference voltage amplitude of the grid-connected hybrid system, the corresponding reference frequency and reference voltage are calculated for each GFM converter using direct droop control;

[0012] S5: Based on the active power reference value and the updated reactive power reference value of each GFL converter, design a current loop to generate modulation control signals to drive the operation of the corresponding GFL converter;

[0013] S6: Based on the reference frequency and reference voltage of each GFM converter, design voltage loops and current loops to generate modulation control signals to drive the operation of the corresponding GFM converter.

[0014] Preferably, in step S1, the reference frequency and reference voltage amplitude of the grid-connected hybrid system are calculated using a proportional-integral regulator;

[0015] The formula is expressed as:

[0016] ;

[0017] ;

[0018] In the formula: and Indicates the reference frequency and reference voltage amplitude of the grid-connected hybrid system; and Indicates the nominal frequency and nominal voltage of the point of common coupling; and Indicates the measured frequency and measured voltage at the point of common coupling; and This indicates the proportional gain and integral gain of the proportional-integral controller.

[0019] Preferably, in step S2, the active power reference value and reactive power reference value of the GFL converter are calculated using the following formula:

[0020] ;

[0021] ;

[0022] In the formula: and Indicates the first Active power reference value and reactive power reference value of the GFL converter; and Indicates the first Active and reactive power of a GFL converter with constant input; and Indicates the reference frequency and the first The frequency measured by the phase-locked loop of the GFL converter; and Indicates the reference voltage amplitude and the first The measured terminal voltage of a GFL converter; , Indicates the first The droop slope of the GFL converter. and The slope is the downward slope.

[0023] Preferably, in step S3, the additional reactive power required for each GFL converter is calculated based on the total reactive power of the GFL converter and the total reactive power of the GFM converter.

[0024] The formula is expressed as:

[0025] ;

[0026] In the formula: Indicates the first Additional reactive power of one GFL converter; Indicates total reactive power; Indicates the first The reactive power of a GFL converter with constant input; Indicates the first The reactive power of a constant input GFM converter; , These represent the number of GFL converters and GFM converters, respectively.

[0027] The reactive power reference value is updated based on the additional reactive power required to supplement each GFL converter.

[0028] The formula is expressed as:

[0029] ;

[0030] In the formula: This represents the updated reactive power reference value for each GFL converter. Indicates the first Reference value for reactive power of a GFL converter.

[0031] Preferably, in step S4, the reference frequency and reference voltage of the GFM converter are calculated using the following formula:

[0032] ;

[0033] ;

[0034] In the formula: , Indicates the first Reference frequency and reference voltage of the GFM converter; and Indicates the first Active and reactive power of a constant input GFM converter; and Indicates the reference frequency and reference voltage amplitude; , Indicates the first The droop slope of the GFM converter.

[0035] Preferably, step S5 specifically includes the following processing steps:

[0036] S501: Design a current loop for each GFL converter;

[0037] S502: Calculate the reference current based on the active power reference value and the updated reactive power reference value of the GFL converter;

[0038] S503: The calculated reference current is used as the input of the current loop, and the current loop output control voltage is controlled by the sliding mode current controller;

[0039] S504: Inputs the control voltage output from the current loop to the PWM modulator and outputs the corresponding modulation control signal;

[0040] S505: Controls the operating state of the switching devices in the GFL converter through the modulation control signal output by the PWM modulator.

[0041] Preferably, in step S502, the reference current is calculated using the following formula:

[0042] ;

[0043] In the formula: Indicates the reference current; and The measured voltage at the GFL converter terminal in the dq coordinate system; and This indicates the active power reference value and the updated reactive power reference value of the GFL converter; This represents the voltage vector in the dq coordinate system. express The exchange component voltage vector.

[0044] Preferably, step S6 specifically includes the following processing steps:

[0045] S601: Design voltage and current loops for each GFM converter;

[0046] S602: The reference frequency and reference voltage of the GFM converter are used as the input of the voltage loop, and the voltage loop output reference current is controlled by the sliding mode voltage controller.

[0047] S603: The reference current output from the voltage loop is used as the input to the current loop, and the current loop output control voltage is controlled by the sliding mode current controller.

[0048] S604: Inputs the control voltage output from the current loop to the PWM modulator and outputs the corresponding modulation control signal;

[0049] S605: Controls the operating state of the switching devices in the GFM converter through the modulation control signal output by the PWM modulator.

[0050] Preferably, in step S602, the formula for calculating the voltage loop output reference current is expressed as follows:

[0051] ;

[0052] ;

[0053] ;

[0054] In the formula: This represents the reference current of the GFM converter output from the voltage loop; Indicates a capacitor filter; and This represents the current flowing through the capacitor filter; Indicates the switching gain of the controller; The sliding surface of the voltage loop is indicated; This represents the equivalent control current vector in the dq coordinate system; dq represents the reference voltage vector in the dq coordinate system; dt represents differentiation; This represents the actual current vector of the capacitor filter branch in the dq coordinate system; Represents the synchronous angular velocity in the dq coordinate system; This represents the integral gain of the voltage controller in the dq coordinate system. This represents the voltage vector in the dq coordinate system. express The exchange component voltage vector; This represents the switching compensation current vector in the dq coordinate system; It is a symbolic function;

[0055] The sliding surface of the voltage loop is calculated using the following formula:

[0056] ;

[0057] In the formula: This represents the integral gain of the controller.

[0058] Preferably, in step S603, the sliding surface of the current loop is calculated using the following formula:

[0059] ;

[0060] In the formula: and This represents the sliding surface of the current loop and its integral gain. This represents the actual measured current vector in the dq coordinate system; This represents the reference current vector in the dq coordinate system;

[0061] The control law of the current loop is calculated using the following formula:

[0062] ;

[0063] ;

[0064] ;

[0065] In the formula: Indicates the control power of the current loop; This indicates a positive switching gain; This represents the equivalent control voltage vector in the dq coordinate system; and This indicates the parameters of the core passive components in the output-side filter circuit of the converter. Represents the synchronous angular velocity in the dq coordinate system; This represents the voltage vector in the dq coordinate system.

[0066] Compared with existing technologies, the fault ride-through control method for hybrid grid systems in this invention has the following advantages:

[0067] The fault ride-through control method (strategy) for hybrid grid systems provided by this invention has significant advantages. First, through a three-layer collaborative architecture of monitoring and control layer, main control layer, and secondary control layer, deep cooperation between GFM converters and GFL converters is achieved, with no significant frequency fluctuations during faults. Compared to pure GFL converter systems, the recovery time after a fault is shortened by 70%-80%, and stable operation can be maintained even if the fault duration is extended to 0.4s. The collaborative control effect is significant, and the control stability is greatly improved. Second, the secondary control layer dynamically allocates additional reactive power based on grid specifications, ensuring that the system's reactive power output meets the dynamic voltage support standard during faults. This completely solves the problem of insufficient grid specification compliance during fault ride-through in existing hybrid systems, adapting to the operating specifications of different regional grids. Furthermore, by integrating sliding mode control technology and differentiated droop control strategies, the system can adapt to a wide range of operating conditions, including short-circuit ratios of 1.12 to 7 and fault durations of 0.2s to 0.4s. It has good adaptability to grid parameter changes, converter parameter uncertainties, and fault type fluctuations, exhibiting outstanding robustness and adaptability to multiple operating scenarios. Finally, the fault ride-through control method of the present invention does not require significant changes to the existing converter hardware structure. Performance improvement can be achieved simply by optimizing the control strategy. Moreover, a single GFM converter can significantly improve the system's fault ride-through performance. It is highly practical and has controllable deployment costs. At the same time, through the precise design of PI regulation and sliding mode control and the dynamic reactive power allocation algorithm, the control accuracy is high and the response speed is fast, meeting the real-time requirements of fault ride-through. Attached Figure Description

[0068] To make the objectives, technical solutions, and advantages of the invention clearer, the invention will now be described in further detail with reference to the accompanying drawings, wherein:

[0069] Figure 1 This is a logic block diagram of the fault ride-through control method for a hybrid grid system.

[0070] Figure 2 This is a schematic diagram of the control loop for a GFL converter.

[0071] Figure 3 This is a schematic diagram of the control loop of a GFM converter. Detailed Implementation

[0072] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but only to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0073] The following detailed explanation illustrates the specific implementation methods:

[0074] Example:

[0075] This embodiment discloses a fault ride-through control method for a hybrid grid system.

[0076] like Figure 1 As shown, a fault ride-through control method for a hybrid grid system includes:

[0077] S1: At the monitoring and control layer, the corresponding reference frequency and reference voltage amplitude are calculated based on the common connection point data of the hybrid network system.

[0078] S2: At the main control layer, based on the reference frequency and reference voltage amplitude of the grid-connected hybrid system, reverse droop control is used to calculate the corresponding active power reference value and reactive power reference value for each GFL converter.

[0079] S3: In the secondary control layer, calculate the additional reactive power required for each GFL converter based on the total reactive power of the GFL converter and the total reactive power of the GFM converter, and update the reactive power reference value for each GFL converter.

[0080] S4: In the main control layer, based on the reference frequency and reference voltage amplitude of the grid-connected hybrid system, direct droop control is used to calculate the corresponding reference frequency and reference voltage for each GFM converter;

[0081] S5: Based on the active power reference value and the updated reactive power reference value of each GFL converter, design a current loop to generate modulation control signals to drive the operation of the corresponding GFL converter;

[0082] S6: Based on the reference frequency and reference voltage of each GFM converter, design voltage loops and current loops to generate modulation control signals to drive the operation of the corresponding GFM converter.

[0083] To better illustrate the technical solution of the present invention, this embodiment will be described in more detail through the following parts.

[0084] I. Data Acquisition for Hybrid System Operation

[0085] In this embodiment, the acquired point of common coupling (PCC) data includes nominal frequency and nominal voltage. Simultaneously, measured operating data such as frequency, terminal voltage, active power, and reactive power of the GFM and GFL converters are also acquired.

[0086] It should be noted that the measured frequency and voltage of the common coupling point are collected through the synchronous phasor measurement unit; the active power, reactive power and terminal voltage of the GFL / GFM converter are collected through the photovoltaic power station sensors and the distribution automation terminal; at the same time, the nominal frequency of the power grid (50Hz) and the nominal voltage (380V) are obtained to ensure the real-time and continuous data, providing basic data support for subsequent control.

[0087] II. Proportional-Integral (PI) Controller

[0088] In this embodiment, the reference frequency and reference voltage amplitude of the grid-connected hybrid system are calculated by a proportional-integral regulator.

[0089] The formula is expressed as:

[0090] ;

[0091] ;

[0092] In the formula: and Indicates the reference frequency and reference voltage amplitude of the grid-connected hybrid system; and Indicates the nominal frequency and nominal voltage of the point of common coupling; and Indicates the measured frequency and measured voltage at the point of common coupling; and This indicates the proportional gain and integral gain of the proportional-integral regulator, ensuring appropriate dynamic response and steady-state accuracy when regulating frequency and voltage.

[0093] III. Calculation of Reference Values ​​for GFL Converters

[0094] In this embodiment, based on the reference frequency and reference voltage combined with the measured frequency and terminal voltage of the GFL converter, the active power reference value and reactive power reference value are calculated through reverse droop control.

[0095] Specifically, the active power reference value and reactive power reference value of the GFL converter are calculated using the following formula:

[0096] ;

[0097] ;

[0098] In the formula: and Indicates the first The active and reactive power outputs of the GFL converter in reverse droop, i.e., the active power reference value and the reactive power reference value. and Indicates the first Active and reactive power of a GFL converter with constant input; and Indicates the reference frequency and the first The frequency measured by the phase-locked loop of the GFL converter; and Indicates the reference voltage amplitude and the first The measured terminal voltage of a GFL converter; , Indicates the first The droop slope of the GFL converter. and The slope is the reverse downward slope, and its value must be determined based on the maximum frequency and voltage variation, as well as the rated power of each converter.

[0099] IV. Reference Value Update for GFL Converters

[0100] In this embodiment, the secondary control layer calculates the additional reactive power that the GFL converter needs to supplement based on the reactive power requirements of the power grid specifications and the reactive power contributions of the GFM converter and GFL converter, updates its reactive power reference value, and realizes reactive power coordination between the two types of converters.

[0101] Specifically:

[0102] Calculate the additional reactive power required for each GFL converter based on the total reactive power of the GFL converter and the total reactive power of the GFM converter.

[0103] The formula is expressed as:

[0104] ;

[0105] In the formula: Indicates the first The additional reactive power provided by a GFL converter in an FRT scenario; This represents the total reactive power required by power grid specifications. Indicates the first The reactive power of a GFL converter with constant input; Indicates the first The reactive power of a constant input GFM converter; , These represent the number of GFL converters and GFM converters, respectively.

[0106] The reactive power reference value is updated based on the additional reactive power required to supplement each GFL converter.

[0107] The formula is expressed as:

[0108] ;

[0109] In the formula: This represents the reactive power reference for each GFL converter, i.e., the updated reactive power reference value. Indicates the first Reference value for reactive power of a GFL converter.

[0110] V. Calculation of Reference Values ​​for GFM Converters

[0111] In this embodiment, a reference frequency and a reference voltage are generated by direct droop control based on a reference benchmark and the measured active and reactive power of the GFM converter.

[0112] Specifically, the reference frequency and reference voltage of the GFM converter are calculated using the following formulas:

[0113] ;

[0114] ;

[0115] In the formula: , Indicates the first The frequency and voltage outputs of the GFM converter are directly drooping, i.e., the reference frequency and reference voltage; and Indicates the first The active and reactive power outputs of the GFM converter are directly drooping. and Indicates the first Active and reactive power of a constant input GFM converter; and Indicates the reference frequency and reference voltage amplitude; , Indicates the first The droop slope of the GFM converter.

[0116] VI. Control circuit of GFL converter

[0117] Combination Figure 2As shown, the control loop of the GFL converter is designed through the following steps:

[0118] S501: Design a current loop for each GFL converter;

[0119] S502: Calculate the reference current based on the active power reference value and the updated reactive power reference value of the GFL converter;

[0120] S503: The calculated reference current is used as the input of the current loop, and the current loop output control voltage is controlled by the sliding mode current controller;

[0121] S504: Inputs the control voltage output from the current loop to the PWM modulator and outputs the corresponding modulation control signal;

[0122] S505: Controls the operating state of the switching devices in the GFL converter through the modulation control signal output by the PWM modulator.

[0123] Specifically, the reference current is calculated using the following formula:

[0124] ;

[0125] In the formula: Indicates the reference current; and The measured voltage at the GFL converter terminal in the dq coordinate system; and This indicates the active power reference value and the updated reactive power reference value of the GFL converter; This represents the voltage vector in the dq coordinate system, derived from the voltage along the d-axis ( ) and q-axis voltage ( Composed of, i.e. =[ , ]T (column vector form); express The exchange component voltage vector, composed of the q-axis voltage ( ) and d-axis voltage ( Composed of, i.e. =[ , T (column vector form), its essence is to... The d and q components are swapped in order.

[0126] VII. Control Circuit of GFM Converter

[0127] Combination Figure 3 As shown, the control loop of the GFM converter is designed through the following steps:

[0128] S601: Design voltage and current loops for each GFM converter;

[0129] S602: The reference frequency and reference voltage of the GFM converter are used as inputs to the voltage loop. The voltage loop output reference current is controlled by the sliding mode voltage controller. The reference frequency is the core input of microgrid control. Its calculation is essentially to coordinate the active power output of the GFL converter and the GFM converter by dynamically correcting the frequency reference, so as to achieve frequency stability and reasonable power distribution during normal operation and fault ride-through of the microgrid, and ensure that the requirements of the power grid specifications are met.

[0130] S603: The reference current output from the voltage loop is used as the input to the current loop, and the current loop output control voltage is controlled by the sliding mode current controller.

[0131] S604: Inputs the control voltage output from the current loop to the PWM modulator and outputs the corresponding modulation control signal;

[0132] S605: Controls the operating state of the switching devices in the GFM converter through the modulation control signal output by the PWM modulator.

[0133] Specifically, the formula for calculating the voltage loop output reference current is as follows:

[0134] ;

[0135] ;

[0136] ;

[0137] In the formula: This represents the reference current of the GFM converter output from the voltage loop; Indicates a capacitor filter; and This represents the current flowing through the capacitor filter; Indicates the switching gain of the controller; The sliding surface of the voltage loop is indicated; This represents the equivalent control current vector in the dq coordinate system; dq represents the reference voltage vector in the dq coordinate system; dt represents differentiation; This represents the actual current vector of the capacitor filter branch in the dq coordinate system; Represents the synchronous angular velocity in the dq coordinate system; This represents the integral gain of the voltage controller in the dq coordinate system. This represents the voltage vector in the dq coordinate system. express The exchange component voltage vector; This represents the switching compensation current vector in the dq coordinate system; It is a symbolic function;

[0138] The sliding surface of the voltage loop is calculated using the following formula:

[0139] ;

[0140] In the formula: This represents the integral gain of the controller.

[0141] Specifically, the sliding surface of the current loop is calculated using the following formula:

[0142] ;

[0143] In the formula: and This represents the sliding surface of the current loop and its integral gain. The sliding surface and its derivative must be set to zero to obtain equivalent input control. This represents the actual measured current vector in the dq coordinate system; This represents the reference current vector in the dq coordinate system;

[0144] The control law of the current loop is calculated using the following formula:

[0145] ;

[0146] ;

[0147] ;

[0148] In the formula: Indicates the control power of the current loop; This indicates a positive switching gain; This represents the equivalent control voltage vector in the dq coordinate system; (resistance) and (Inductance) represents the parameters of the core passive component in the output-side filter circuit of the converter; Represents the synchronous angular velocity in the dq coordinate system; This represents the voltage vector in the dq coordinate system.

[0149] The fault ride-through control method (strategy) for hybrid grid systems provided by this invention has significant advantages. First, through a three-layer collaborative architecture of monitoring and control layer, main control layer, and secondary control layer, deep cooperation between GFM converters and GFL converters is achieved, with no significant frequency fluctuations during faults. Compared to pure GFL converter systems, the recovery time after a fault is shortened by 70%-80%, and stable operation can be maintained even if the fault duration is extended to 0.4s. The collaborative control effect is significant, and the control stability is greatly improved. Second, the secondary control layer dynamically allocates additional reactive power based on grid specifications, ensuring that the system's reactive power output meets the dynamic voltage support standard during faults. This completely solves the problem of insufficient grid specification compliance during fault ride-through in existing hybrid systems, adapting to the operating specifications of different regional grids. Furthermore, by integrating sliding mode control technology and differentiated droop control strategies, the system can adapt to a wide range of operating conditions, including short-circuit ratios of 1.12 to 7 and fault durations of 0.2s to 0.4s. It has good adaptability to grid parameter changes, converter parameter uncertainties, and fault type fluctuations, exhibiting outstanding robustness and adaptability to multiple operating scenarios. Finally, the fault ride-through control method of this invention does not require significant modifications to the existing converter hardware structure. Performance improvement can be achieved solely through control strategy optimization, and a single GFM converter can significantly improve the system's fault ride-through performance. It is highly practical, with controllable deployment costs. Furthermore, through precise design of PI regulation and sliding mode control, and a dynamic reactive power allocation algorithm, it achieves high control accuracy and fast response speed, meeting the real-time requirements of fault ride-through. The fault ride-through control method (strategy) for hybrid grid systems provided by this invention has significant advantages. First, through a three-layer collaborative architecture of monitoring control layer, main control layer, and secondary control layer, deep cooperation between GFM converter and GFL converter is achieved, with no significant frequency fluctuations during faults. Compared to a pure GFL converter system, the recovery time after a fault is shortened by 70%-80%, and stable operation can be maintained even if the fault duration is extended to 0.4s. The collaborative control effect is significant, and the control stability is greatly improved. Secondly, the secondary control layer dynamically allocates additional reactive power based on grid specifications, ensuring that the system's reactive power output meets dynamic voltage support standards during faults. This completely solves the problem of insufficient grid specification compliance during fault ride-through in existing hybrid systems and adapts to the grid operation specifications of different regions. In addition, by integrating sliding mode control technology and differentiated droop control strategies, the system can adapt to a wide range of operating conditions, including short-circuit ratios of 1.12 to 7 and fault durations of 0.2s to 0.4s. It has good adaptability to grid parameter changes, converter parameter uncertainties, and fault type fluctuations, and has the advantages of outstanding robustness and adaptability to multiple operating scenarios.Finally, the fault ride-through control method of the present invention does not require significant changes to the existing converter hardware structure. Performance improvement can be achieved simply by optimizing the control strategy. Moreover, a single GFM converter can significantly improve the system's fault ride-through performance. It is highly practical and has controllable deployment costs. At the same time, through the precise design of PI regulation and sliding mode control and the dynamic reactive power allocation algorithm, the control accuracy is high and the response speed is fast, meeting the real-time requirements of fault ride-through.

[0150] This invention enables the integrated grid hybrid system to operate stably in scenarios with short-circuit ratio (SCR) of 1.12 to 7 and fault duration of 0.2s to 0.4s through the coordinated action of the monitoring control layer, the main control layer and the secondary control layer.

[0151] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A fault ride-through control method for a hybrid grid system, characterized in that, include: S1: Calculate the corresponding reference frequency and reference voltage amplitude based on the common connection point data of the hybrid grid system; S2: Based on the reference frequency and reference voltage amplitude of the grid-connected hybrid system, the corresponding active power reference value and reactive power reference value are calculated for each GFL converter using reverse droop control. S3: Calculate the additional reactive power required for each GFL converter based on the total reactive power of the GFL converter and the total reactive power of the GFM converter, and update the reactive power reference value for each GFL converter. S4: Based on the reference frequency and reference voltage amplitude of the grid-connected hybrid system, the corresponding reference frequency and reference voltage are calculated for each GFM converter using direct droop control; S5: Based on the active power reference value and the updated reactive power reference value of each GFL converter, design a current loop to generate modulation control signals to drive the operation of the corresponding GFL converter; S6: Based on the reference frequency and reference voltage of each GFM converter, design voltage loops and current loops to generate modulation control signals to drive the operation of the corresponding GFM converter.

2. The fault ride-through control method for a hybrid interconnected network system as described in claim 1, characterized in that: In step S1, the reference frequency and reference voltage amplitude of the grid-connected hybrid system are calculated using a proportional-integral regulator. The formula is expressed as: ； ； In the formula: and Indicates the reference frequency and reference voltage amplitude of the grid-connected hybrid system; and Indicates the nominal frequency and nominal voltage of the point of common coupling; and Indicates the measured frequency and measured voltage at the point of common coupling; and This indicates the proportional gain and integral gain of the proportional-integral controller.

3. The fault ride-through control method for a hybrid interconnected network system as described in claim 1, characterized in that: In step S2, the active power reference value and reactive power reference value of the GFL converter are calculated using the following formula: ； ； In the formula: and Indicates the first Active power reference value and reactive power reference value of the GFL converter; and Indicates the first Active and reactive power of a GFL converter with constant input; and Indicates the reference frequency and the first The frequency measured by the phase-locked loop of the GFL converter; and Indicates the reference voltage amplitude and the first The measured terminal voltage of a GFL converter; , Indicates the first The droop slope of the GFL converter. and The slope is the downward slope.

4. The fault ride-through control method for a hybrid interconnected network system as described in claim 1, characterized in that: In step S3, the additional reactive power required for each GFL converter is calculated based on the total reactive power of the GFL converter and the total reactive power of the GFM converter. The formula is expressed as: ； In the formula: Indicates the first Additional reactive power of one GFL converter; Indicates total reactive power; Indicates the first The reactive power of a GFL converter with constant input; Indicates the first The reactive power of a constant input GFM converter; , These represent the number of GFL converters and GFM converters, respectively. The reactive power reference value is updated based on the additional reactive power required to supplement each GFL converter. The formula is expressed as: ； In the formula: This represents the updated reactive power reference value for each GFL converter. Indicates the first Reference value for reactive power of a GFL converter.

5. The fault ride-through control method for a hybrid interconnected network system as described in claim 1, characterized in that: In step S4, the reference frequency and reference voltage of the GFM converter are calculated using the following formulas: ； ； In the formula: , Indicates the first Reference frequency and reference voltage of the GFM converter; and Indicates the first Active and reactive power of a constant input GFM converter; and Indicates the reference frequency and reference voltage amplitude; , Indicates the first The droop slope of the GFM converter.

6. The fault ride-through control method for a hybrid interconnected network system as described in claim 1, characterized in that: Step S5 specifically includes the following processing steps: S501: Design a current loop for each GFL converter; S502: Calculate the reference current based on the active power reference value and the updated reactive power reference value of the GFL converter; S503: The calculated reference current is used as the input of the current loop, and the current loop output control voltage is controlled by the sliding mode current controller; S504: Inputs the control voltage output from the current loop to the PWM modulator and outputs the corresponding modulation control signal; S505: Controls the operating state of the switching devices in the GFL converter through the modulation control signal output by the PWM modulator.

7. The fault ride-through control method for a hybrid grid system as described in claim 6, characterized in that: In step S502, the reference current is calculated using the following formula: ； In the formula: Indicates the reference current; and The measured voltage at the GFL converter terminal in the dq coordinate system; and This indicates the active power reference value and the updated reactive power reference value of the GFL converter; This represents the voltage vector in the dq coordinate system. express The exchange component voltage vector.

8. The fault ride-through control method for a hybrid interconnected network system as described in claim 1, characterized in that: Step S6 specifically includes the following processing steps: S601: Design voltage and current loops for each GFM converter; S602: The reference frequency and reference voltage of the GFM converter are used as the input of the voltage loop, and the voltage loop output reference current is controlled by the sliding mode voltage controller. S603: The reference current output from the voltage loop is used as the input to the current loop, and the current loop output control voltage is controlled by the sliding mode current controller. S604: Inputs the control voltage output from the current loop to the PWM modulator and outputs the corresponding modulation control signal; S605: Controls the operating state of the switching devices in the GFM converter through the modulation control signal output by the PWM modulator.

9. The fault ride-through control method for a hybrid interconnected network system as described in claim 8, characterized in that: In step S602, the formula for calculating the voltage loop output reference current is expressed as follows: ； ； ； In the formula: This represents the reference current of the GFM converter output from the voltage loop; Indicates a capacitor filter; and This represents the current flowing through the capacitor filter; Indicates the switching gain of the controller; The sliding surface of the voltage loop is indicated; This represents the equivalent control current vector in the dq coordinate system; dq represents the reference voltage vector in the dq coordinate system; dt represents differentiation; This represents the actual current vector of the capacitor filter branch in the dq coordinate system; Represents the synchronous angular velocity in the dq coordinate system; This represents the integral gain of the voltage controller in the dq coordinate system. This represents the voltage vector in the dq coordinate system. express The exchange component voltage vector; This represents the switching compensation current vector in the dq coordinate system; It is a symbolic function; The sliding surface of the voltage loop is calculated using the following formula: ； In the formula: This represents the integral gain of the controller.

10. The fault ride-through control method for a hybrid grid system as described in claim 8, characterized in that: In step S603, the sliding surface of the current loop is calculated using the following formula: ； In the formula: and This represents the sliding surface of the current loop and its integral gain. This represents the actual measured current vector in the dq coordinate system; This represents the reference current vector in the dq coordinate system; The control law of the current loop is calculated using the following formula: ； ； ； In the formula: Indicates the control power of the current loop; This indicates a positive switching gain; This represents the equivalent control voltage vector in the dq coordinate system; and This indicates the parameters of the core passive components in the output-side filter circuit of the converter. Represents the synchronous angular velocity in the dq coordinate system; This represents the voltage vector in the dq coordinate system.

Images