Active control method and system for fault ride-through of network construction type photovoltaic converter

Abstract

The invention discloses an active control method and system for fault ride-through of a network construction type photovoltaic converter. The method comprises the following steps: acquiring a converter-side output modulation voltage measurement value, a converter-side output current measurement value, a grid-side output voltage measurement value, a capacitor voltage measurement value, a converter output angular frequency, a converter-side filter inductor and a filter capacitor of the photovoltaic power generation system; the method comprises the following steps: determining an on state of a fault control mode and whether to enter a low-voltage ride-through control flow or not based on a difference between a grid-side output voltage measurement value and a first preset threshold value, and determining whether the low-voltage ride-through control flow comprises a first stage executed by a sliding mode control module; and the second stage is executed by a power grid voltage feedforward control module, a Park inverse transformation module, an active damping control module and a space vector pulse width modulation (SPWM) module. According to the active control method and system for fault ride-through of the network construction type photovoltaic converter provided by the embodiment of the invention, the accuracy and real-time performance of fault ride-through control of the photovoltaic converter are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic power generation, and in particular to a method and system for actively controlling fault ride-through of a grid-type photovoltaic converter. Background Art

[0002] With the growing global demand for renewable energy and the continuous advancement of photovoltaic power generation technology, photovoltaic power generation is becoming increasingly important in the global energy structure. Grid-connected photovoltaic inverters play a key role in photovoltaic power generation systems by converting the direct current generated by photovoltaic modules into alternating current for use in the power grid.

[0003] When a grid fault occurs, such as a voltage sag or frequency deviation, traditional inverters or converters will automatically disconnect from the grid because they cannot adapt to the drastic changes in the grid. This may cause power supply interruptions or even equipment damage or failure, which will not only increase the cost of repairing and replacing equipment, but may also affect the normal operation of the photovoltaic power generation system.

[0004] Due to the diversity and complexity of grid fault conditions, photovoltaic power plants need to be able to quickly and accurately adjust their output power to support grid voltage stability. Existing photovoltaic converter fault ride-through control methods are difficult to provide accurate and timely voltage support to the grid during fault ride-through. Summary of the invention

[0005] The present invention provides a grid-type photovoltaic converter fault ride-through active control method and system to solve the technical problem that the existing photovoltaic converter fault ride-through control method is difficult to provide accurate and timely voltage support to the power grid during the fault ride-through period.

[0006] In order to solve the above technical problems, an embodiment of the present invention provides a method and system for active control of fault ride-through of a grid-connected photovoltaic inverter.

[0007] The method is applied to a grid-type photovoltaic converter fault ride-through active control system composed of a sliding mode control module, a grid voltage feedforward control module, a Park inverse transformation module, an active damping control module and a space vector pulse width modulation (SPWM) module, and the method comprises:

[0008] Collect the measured values ​​of the inverter-side output modulation voltage, the inverter-side output current, the grid-side output voltage, the capacitor voltage, the inverter output angular frequency, the inverter-side filter inductance and filter capacitance of the photovoltaic power generation system;

[0009] Determine the on state of the fault control mode based on the difference between the grid-side output voltage measurement value and the first preset threshold value; when the on state of the fault control mode is off, maintain the control state of the photovoltaic power generation system, otherwise enter the low voltage ride through control process, the low voltage ride through control process includes a first stage executed by the sliding mode control module, and a second stage executed by the grid voltage feedforward control module, the Park inverse transformation module, the active damping control module and the space vector pulse width modulation SPWM module;

[0010] During the execution of the first stage, based on the output modulation voltage measurement value of the converter side, the output current measurement value of the converter side, the grid side output voltage measurement value, the capacitor voltage measurement value, the converter output angular frequency, the converter side filter inductor and the filter capacitor, the converter voltage loop and current loop control parameters are obtained;

[0011] The converter voltage loop and current loop control parameters include an updated d-axis reference value of the converter side output current, an updated q-axis reference value of the converter side output current, an updated d-axis reference value of the converter side output modulation voltage, and an updated q-axis reference value of the converter side output modulation voltage, so as to control the inner loop output of the converter;

[0012] After the first stage is completed, the converter voltage loop and current loop control parameters are input into the second stage for execution, so as to perform fault ride-through control on the grid-connected photovoltaic converter.

[0013] As one of the preferred solutions, the converter voltage loop and current loop control parameters are obtained based on the converter side output modulation voltage measurement value, the converter side output current measurement value, the grid side output voltage measurement value, the capacitor voltage measurement value, the converter output angular frequency, the converter side filter inductor and the filter capacitor, including:

[0014] Obtaining a first orthogonal dq-axis positive and negative sequence component of the converter side output modulation voltage measurement value, a second orthogonal dq-axis positive and negative sequence component of the converter side output current measurement value, a second orthogonal d-axis component of the converter side output current measurement value, and a second orthogonal q-axis component of the converter side output current measurement value;

[0015] Obtaining a third orthogonal dq-axis positive and negative sequence component of the grid-side output voltage measurement value, a fourth orthogonal dq-axis positive and negative sequence component of the capacitor voltage measurement value, a fourth orthogonal d-axis component of the capacitor voltage measurement value, and a fourth orthogonal q-axis component of the capacitor voltage measurement value;

[0016] Obtaining a first DC component of the active power output by the converter and a second DC component of the reactive power output by the converter based on a linear algebraic relationship between the first orthogonal dq axis positive and negative sequence components and the second orthogonal dq axis positive and negative sequence components;

[0017] Acquire a fifth orthogonal dq-axis positive and negative sequence component of a converter-side output current reference value based on a linear relationship among the first DC component, the second DC component and the third orthogonal dq-axis positive and negative sequence component;

[0018] Calculate the improved convergence rate based on the difference between the capacitor voltage measurement value and the reference value, and the difference between the converter side output current measurement value and the reference value;

[0019] Based on the linear relationship among the converter output angular frequency, the converter side filter inductance, the filter capacitor, the fourth orthogonal d-axis component, the fourth orthogonal q-axis component, the second orthogonal d-axis component, the second orthogonal q-axis component and the improved approach rate, the converter voltage loop and current loop control parameters are calculated.

[0020] As one of the preferred schemes, the first orthogonal dq axis positive and negative sequence components, the second orthogonal dq axis positive and negative sequence components, the third orthogonal dq axis positive and negative sequence components, and the fourth orthogonal dq axis positive and negative sequence components all include an orthogonal d axis positive sequence component, an orthogonal d axis negative sequence component, an orthogonal q axis positive sequence component, and an orthogonal q axis negative sequence component.

[0021] As one of the preferred schemes, the obtaining of the first orthogonal dq-axis positive and negative sequence component of the converter side output modulation voltage measurement value, the second orthogonal dq-axis positive and negative sequence component of the converter side output current measurement value, the second orthogonal d-axis component of the converter side output current measurement value, and the second orthogonal q-axis component of the converter side output current measurement value includes:

[0022] The output modulation voltage measurement value of the converter side is processed by using a phase-locked loop technology based on a dual second-order generalized integrator to obtain the first orthogonal dq-axis positive and negative sequence components of the output modulation voltage measurement value of the converter side;

[0023] Processing the output current measurement value of the converter side by using a phase-locked loop technology based on a dual second-order generalized integrator to obtain a second orthogonal dq-axis positive and negative sequence component of the output current measurement value of the converter side, a second orthogonal d-axis component of the output current measurement value of the converter side, and a second orthogonal q-axis component of the output current measurement value of the converter side;

[0024] The obtaining of the third orthogonal dq-axis positive and negative sequence components of the grid-side output voltage measurement value, the fourth orthogonal dq-axis positive and negative sequence components of the capacitor voltage measurement value, the fourth orthogonal d-axis component of the capacitor voltage measurement value, and the fourth orthogonal q-axis component of the capacitor voltage measurement value includes:

[0025] The grid-side output voltage measurement value is processed by using a phase-locked loop technology based on a dual second-order generalized integrator to obtain a third orthogonal dq-axis positive and negative sequence component of the grid-side output voltage measurement value;

[0026] The capacitor voltage measurement value is processed using a phase-locked loop technology based on a double second-order generalized integrator to obtain a fourth orthogonal dq-axis positive and negative sequence component of the capacitor voltage measurement value, a fourth orthogonal d-axis component of the capacitor voltage measurement value, and a fourth orthogonal q-axis component of the capacitor voltage measurement value.

[0027] As one of the preferred solutions, the specific method of obtaining the first DC component of the active power output by the converter and the second DC component of the reactive power output by the converter based on the linear algebraic relationship between the first orthogonal dq axis positive and negative sequence components and the second orthogonal dq axis positive and negative sequence components includes:

[0028]

[0029] Among them, P b is the first DC component, Q b is the second DC component, is the orthogonal d-axis positive-sequence component of the first orthogonal dq-axis positive- and negative-sequence components, is the orthogonal d-axis negative-sequence component of the first orthogonal dq-axis positive- and negative-sequence components, is the orthogonal q-axis positive-sequence component of the first orthogonal dq-axis positive-sequence component, is the orthogonal q-axis negative-sequence component of the first orthogonal dq-axis positive- and negative-sequence components, is the orthogonal d-axis positive-sequence component of the second orthogonal dq-axis positive- and negative-sequence components, is the orthogonal d-axis negative-sequence component of the second orthogonal dq-axis positive- and negative-sequence components, is the orthogonal q-axis positive-sequence component of the second orthogonal dq-axis positive- and negative-sequence components, It is the orthogonal q-axis negative-sequence component of the second orthogonal dq-axis positive and negative-sequence components.

[0030] As one of the preferred solutions, the specific method of obtaining the fifth orthogonal dq-axis positive and negative sequence component of the converter side output current reference value based on the linear relationship between the first DC component, the second DC component and the third orthogonal dq-axis positive and negative sequence component includes:

[0031]

[0032] in, is the orthogonal d-axis positive sequence component of the output current reference value of the converter side, is the orthogonal q-axis positive sequence component of the output current reference value of the converter side, is the orthogonal d-axis negative sequence component of the output current reference value of the converter side, is the orthogonal q-axis negative sequence component of the output current reference value of the converter side, is the orthogonal d-axis positive-sequence component of the third orthogonal dq-axis positive- and negative-sequence components, is the orthogonal q-axis positive-sequence component of the third orthogonal dq-axis positive- and negative-sequence components, P b is the first DC component, Q b is the second DC component.

[0033] As one of the preferred solutions, the preset capacitor voltage dq-axis component reference value includes a preset capacitor voltage d-axis component reference value and a preset capacitor voltage q-axis component reference value, and the improved convergence rate includes a first improved convergence rate parameter, a second improved convergence rate parameter, a third improved convergence rate parameter and a fourth improved convergence rate parameter;

[0034] The calculation of the improved approach rate based on the difference between the capacitor voltage measurement value and the reference value, and the difference between the converter side output current measurement value and the reference value, comprises:

[0035] Taking the difference between the preset capacitor voltage d-axis component reference value and the fourth orthogonal d-axis component as a first sliding surface parameter, taking the saturation function value of the first sliding surface parameter as a first saturated sliding surface parameter, and calculating the first improved approach rate parameter based on a linear relationship between the first sliding surface parameter and the first saturated sliding surface parameter;

[0036] Taking the difference between the preset capacitor voltage q-axis component reference value and the fourth orthogonal q-axis component as a second sliding surface parameter, taking the saturation function value of the second sliding surface parameter as a second saturated sliding surface parameter, and calculating the second improved convergence rate parameter based on a linear relationship between the second sliding surface parameter and the second saturated sliding surface parameter;

[0037] taking the difference between the orthogonal d-axis positive sequence component of the converter-side output current reference value and the second orthogonal d-axis component as a third sliding surface parameter, taking the saturation function value of the third sliding surface parameter as a third saturated sliding surface parameter, and calculating the third improved approach rate parameter based on the linear relationship between the third sliding surface parameter and the third saturated sliding surface parameter;

[0038] The difference between the orthogonal d-axis positive-sequence component of the converter-side output current reference value and the second orthogonal q-axis component is used as a fourth sliding surface parameter, the saturation function value of the fourth sliding surface parameter is used as a fourth saturated sliding surface parameter, and based on the linear relationship between the fourth sliding surface parameter and the fourth saturated sliding surface parameter, the fourth improved convergence rate parameter is calculated.

[0039] As one of the preferred solutions, the converter voltage loop and current loop control parameters include an updated d-axis reference value of the converter side output current, an updated q-axis reference value of the converter side output current, an updated d-axis reference value of the converter side output modulation voltage, and an updated q-axis reference value of the converter side output modulation voltage;

[0040] The step of calculating the converter voltage loop and current loop control parameters based on the linear relationship between the converter output angular frequency, the converter side filter inductor, the filter capacitor, the fourth orthogonal d-axis component, the fourth orthogonal q-axis component, the second orthogonal d-axis component, the second orthogonal q-axis component and the improved approach rate comprises:

[0041]

[0042] Among them, i md is the updated d-axis reference value of the converter side output current, i mq is the updated q-axis reference value of the converter output current, i od is the second orthogonal d-axis component, i oq is the second orthogonal q-axis component, u cq is the fourth orthogonal q-axis component, u cd is the fourth orthogonal d-axis component, ω is the output angular frequency of the converter, C f is the filter capacitor, is the first improved approach rate parameter, is the second improved convergence rate parameter, u md is the updated d-axis reference value of the output modulation voltage on the converter side, u mq is the updated q-axis reference value of the output modulation voltage on the converter side, L f1 is the converter side filter inductor, is the third improved approach rate parameter, is the fourth improved approach rate parameter.

[0043] As one preferred solution, the method of determining the activation state of the fault control mode based on the difference between the grid-side output voltage measurement value and the first preset threshold value includes:

[0044] When the grid-side output voltage measurement value is less than or equal to the first preset threshold, the fault control mode is turned on; otherwise, the fault control mode is turned off.

[0045] Another embodiment of the present invention provides an active control system for fault ride-through of a grid-type photovoltaic converter, the system comprising a sliding mode control module, a grid voltage feedforward control module, a Park inverse transformation module, an active damping control module and a space vector pulse width modulation (SPWM) module. When the system executes the computer program, it implements the active control method for fault ride-through of a grid-type photovoltaic converter as described above.

[0046] Compared with the prior art, the embodiments of the present invention have the following advantages:

[0047] (1) A grid-connected photovoltaic converter fault ride-through active control system is constructed by a sliding mode control module, a grid voltage feedforward control module, a Park inverse transformation module, an active damping control module, and a space vector pulse width modulation (SPWM) module. An improved sliding mode controller is used in the sliding mode control module to replace the traditional PI control, and the sign function is replaced by a saturation function. The improved approach rate of the sliding mode control is calculated, and the adverse effects of chattering are eliminated.

[0048] (2) Based on the measured value of the output modulation voltage on the converter side, the measured value of the output current on the converter side, the measured value of the output voltage on the grid side, the measured value of the capacitor voltage, the output angular frequency of the converter, the filter inductance and the filter capacitance on the converter side, the updated d-axis reference value of the output current on the converter side, the updated q-axis reference value of the output current on the converter side, the updated d-axis reference value of the output modulation voltage on the converter side and the updated q-axis reference value of the output modulation voltage on the converter side are calculated to control the inner loop output of the converter, thereby improving the accuracy of the converter control and the real-time performance of the fault ride-through control of the photovoltaic converter;

[0049] (3) A grid voltage feedforward control module is formed by multiplying the grid-side output voltage measurement value and the preset voltage feedforward control coefficient, and an active damping control module is formed by multiplying the capacitor voltage measurement value and the preset active damping feedforward coefficient, which further improves the accuracy of converter control and the real-time performance of fault ride-through control of the photovoltaic converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 A schematic diagram of obtaining an improved approach rate in one embodiment of the present invention;

[0051] Figure 2 A schematic diagram of obtaining control parameters of a voltage loop and a current loop of a converter in one embodiment of the present invention;

[0052] Figure 3The present invention is a flowchart of an active control system for fault ride-through of a grid-connected photovoltaic inverter in one embodiment of the present invention. DETAILED DESCRIPTION

[0053] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] In the description of this application, the terms "first", "second", "third", etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", "third", etc. may explicitly or implicitly include one or more of the feature. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0055] In the description of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be a connection between the two elements. The terms "vertical", "horizontal", "left", "right", "upper", "lower" and similar expressions used herein are only for illustrative purposes, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0056] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood by specific circumstances.

[0057] Step S1: Collect the inverter side output modulation voltage measurement value, the inverter side output current measurement value, the grid side output voltage measurement value, the capacitor voltage measurement value, the inverter output angular frequency, the inverter side filter inductance and filter capacitance of the photovoltaic power generation system.

[0058] In the event of a severe voltage drop in the power grid, the grid-connected photovoltaic power generation system can maintain connection with the power grid and continue to provide power support to the grid, effectively avoiding the occurrence of large-scale power outages.

[0059] The grid-type photovoltaic inverter monitors the voltage, current and other parameters of the power grid in real time to determine whether the power grid has a fault. Once a power grid fault is detected, the fault ride-through control strategy is immediately activated. Through the coordinated control strategy, the photovoltaic inverter can achieve rapid response and stable control during the power grid fault. Therefore, before performing fault ride-through control on the photovoltaic inverter, it is necessary to first collect the voltage, current and other parameters of the photovoltaic power generation system.

[0060] Specifically, voltage sensors and current sensors are set at the nodes of the photovoltaic power generation system to collect the output modulation voltage measurement value, the output current measurement value, the grid-side output voltage measurement value, the capacitor voltage measurement value, the inverter output angular frequency, and the inverter side filter inductance and filter capacitance of the photovoltaic power generation system.

[0061] Step S2: determining the on state of the fault control mode based on the grid-side output voltage measurement value, and determining whether to enter the low voltage ride through control process.

[0062] By implementing the fault ride-through control strategy, the grid-connected inverter can continue to provide power support to the grid during a grid fault, maintain the continuity of power supply, and reduce the duration and scope of power outages. The grid-connected photovoltaic inverter fault ride-through control technology is one of the important means to improve the stability and reliability of photovoltaic power generation systems.

[0063] Specifically, when the measured value of the grid-side output voltage is less than or equal to the first preset threshold, the fault control mode is turned on, the low voltage ride-through control process is entered, and steps S3 to S9 are executed; otherwise, the fault control mode is turned off, and the control state of the photovoltaic power generation system is maintained.

[0064] It should be noted that the low voltage ride-through control process includes a first stage executed by a sliding mode control module, and a second stage executed by a grid voltage feedforward control module, a Park inverse transformation module, an active damping control module and a space vector pulse width modulation SPWM module. The first preset threshold is a manually preset value. In this embodiment, the first preset threshold is 0.5pu. As other implementation methods, the implementer can choose it at will. This application does not impose any special restrictions on this. Pu is used to describe the relationship between the actual voltage and the nominal voltage. For example, if the nominal voltage of a circuit is 400V, and the actual measured voltage is 320V, then the voltage pu value of the circuit is 0.8.

[0065] Step S3: Use a phase-locked loop technology based on a dual second-order generalized integrator to obtain the first orthogonal dq-axis positive and negative sequence components of the output modulation voltage measurement value on the converter side, the second orthogonal dq-axis positive and negative sequence components of the output current measurement value on the converter side, the second orthogonal d-axis component of the output current measurement value on the converter side, and the second orthogonal q-axis component of the output current measurement value on the converter side.

[0066] It should be noted that, as an embodiment of the present application, the use of a phase-locked loop technology based on a biquad generalized integrator to process the target signal includes:

[0067] The target signal is used as the input of the abc / αβ transformation module to output the target α-axis component and the target β-axis component; the target α-axis component and the target β-axis component are used as the input of the DSOGIQ module to output the target α-axis positive-sequence component and the target β-axis positive-sequence component; the target α-axis positive-sequence component and the target β-axis positive-sequence component are used as the input of the αβ / dq transformation module to output the target orthogonal d-axis component and the target orthogonal q-axis component; the target orthogonal d-axis component and the target orthogonal q-axis component are used as the input of the positive and negative sequence separation module respectively to output the target orthogonal d-axis positive-sequence component and the target orthogonal d-axis negative-sequence component, the target orthogonal q-axis positive-sequence component and the target orthogonal q-axis negative-sequence component.

[0068] A phase-locked loop technology based on a double second-order generalized integrator is used to process the output modulation voltage measurement value on the converter side to obtain the first orthogonal dq-axis positive and negative sequence components of the output modulation voltage measurement value on the converter side; a phase-locked loop technology based on a double second-order generalized integrator is used to process the output current measurement value on the converter side to obtain the second orthogonal dq-axis positive and negative sequence components of the output current measurement value on the converter side, the second orthogonal d-axis component of the output current measurement value on the converter side, and the second orthogonal q-axis component of the output current measurement value on the converter side.

[0069] It should be noted that the first orthogonal dq-axis positive and negative sequence components of the output modulation voltage measurement value on the converter side and the second orthogonal d-axis component of the output current measurement value on the converter side both include an orthogonal d-axis positive sequence component, an orthogonal d-axis negative sequence component, an orthogonal q-axis positive sequence component and an orthogonal q-axis negative sequence component.

[0070] Step S4: Obtain the first DC component of the converter output active power and the second DC component of the converter output reactive power based on the linear algebraic relationship between the first orthogonal dq-axis positive and negative sequence components of the converter side output modulation voltage measurement value and the second orthogonal dq-axis positive and negative sequence components of the converter side output current measurement value.

[0071] According to the expressions of output active power and output reactive power in the converter LVRT control strategy when the voltage unbalance drops, the first DC component of the converter output active power and the second DC component of the converter output reactive power are calculated:

[0072]

[0073] Among them, P b is the first DC component of the converter output active power, Q b The second DC component of the converter output reactive power, is the orthogonal d-axis positive sequence component of the output modulation voltage measurement value of the converter side, is the orthogonal d-axis negative sequence component of the output modulation voltage measurement value of the converter side, is the orthogonal q-axis positive sequence component of the output modulation voltage measurement value of the converter side, is the orthogonal q-axis negative sequence component of the output modulation voltage measurement value of the converter side, is the orthogonal d-axis positive sequence component of the output current measurement value on the converter side, is the orthogonal d-axis negative sequence component of the output current measurement value on the converter side, is the orthogonal q-axis positive sequence component of the output current measurement value on the converter side, It is the orthogonal q-axis negative sequence component of the output current measurement value on the converter side.

[0074] Step S5: using a phase-locked loop technology based on a dual second-order generalized integrator to obtain the third orthogonal dq-axis positive and negative sequence components of the grid-side output voltage measurement value, the fourth orthogonal dq-axis positive and negative sequence components of the capacitor voltage measurement value, the fourth orthogonal d-axis component of the capacitor voltage measurement value, and the fourth orthogonal q-axis component of the capacitor voltage measurement value.

[0075] A phase-locked loop technology based on a double second-order generalized integrator is used to process the grid-side output voltage measurement value to obtain the third orthogonal dq-axis positive and negative sequence components of the grid-side output voltage measurement value; a phase-locked loop technology based on a double second-order generalized integrator is used to process the capacitor voltage measurement value to obtain the fourth orthogonal dq-axis positive and negative sequence components of the capacitor voltage measurement value, the fourth orthogonal d-axis component of the capacitor voltage measurement value, and the fourth orthogonal q-axis component of the capacitor voltage measurement value.

[0076] It should be noted that the fourth orthogonal dq-axis positive and negative sequence components of the capacitor voltage measurement value and the fourth orthogonal d-axis component of the capacitor voltage measurement value both include an orthogonal d-axis positive sequence component, an orthogonal d-axis negative sequence component, an orthogonal q-axis positive sequence component and an orthogonal q-axis negative sequence component.

[0077] Step S6: Obtain the fifth orthogonal dq-axis positive and negative sequence components of the converter side output current reference value based on the linear relationship between the first DC component of the converter output active power, the second DC component of the converter output reactive power and the third orthogonal dq-axis positive and negative sequence components of the grid-side output voltage measurement value.

[0078] It should be noted that the current injected by the converter into the grid should not contain negative sequence current components, that is, the orthogonal d-axis negative sequence component and the orthogonal q-axis negative sequence component of the converter side output current reference value are both 0. Under this condition, when the converter is running at full power, the fifth orthogonal dq-axis positive and negative sequence components of the converter side output current reference value are calculated:

[0079]

[0080] in, is the orthogonal d-axis positive sequence component of the output current reference value of the converter side, is the orthogonal q-axis positive sequence component of the output current reference value of the converter side, is the orthogonal d-axis negative sequence component of the output current reference value of the converter side, is the orthogonal q-axis negative sequence component of the output current reference value of the converter side, is the orthogonal d-axis positive sequence component of the grid-side output voltage measurement value, is the orthogonal q-axis positive sequence component of the grid-side output voltage measurement value, P b is the first DC component of the converter output active power, Q b The second DC component of the reactive power is output by the converter.

[0081] Step S7: Calculate the improvement convergence rate based on the difference between the capacitor voltage measurement value and the reference value, and the difference between the converter-side output current measurement value and the reference value.

[0082] The sliding mode variable structure controller is to eliminate the error between the system state variable and the reference value. The input of the sliding mode controller is defined as the difference between the system variable and the reference value. The preset capacitor voltage dq-axis component reference value includes the preset capacitor voltage d-axis component reference value and the preset capacitor voltage q-axis component reference value. Therefore, the sliding surface of the sliding mode variable structure controller for active control of fault ride-through of the grid-type photovoltaic converter is defined as the deviation between the actual value and the reference value of the capacitor voltage and the output current on the converter side:

[0083]

[0084] Among them, s1 is the first sliding surface parameter, u cd is the fourth orthogonal d-axis component of the capacitor voltage measurement, is the reference value of the d-axis component of the preset capacitor voltage; s2 is the second sliding surface parameter, u cq is the fourth orthogonal q-axis component of the capacitor voltage measurement, is the reference value of the q-axis component of the preset capacitor voltage; s3 is the third sliding surface parameter, i md is the second orthogonal d-axis component of the output current measurement value on the converter side, is the orthogonal d-axis positive sequence component of the output current reference value of the converter side; s4 is the fourth sliding surface parameter, i mq is the second orthogonal q-axis component of the output current measurement value on the converter side, It is the orthogonal q-axis positive sequence component of the output current reference value on the converter side.

[0085] Furthermore, the saturation function is used to improve the sliding mode control rate:

[0086]

[0087] Among them, sat() is the saturation function, is the first improved approach rate parameter, is the second improved approach rate parameter, is the third improved approach rate parameter, is the fourth improved approaching rate parameter, s1 is the first sliding surface parameter, s2 is the second sliding surface parameter, s3 is the third sliding surface parameter, s4 is the fourth sliding surface parameter, σ1, σ2, σ3, σ4, μ1, μ2, μ3, and μ4 are all artificially preset approaching rate coefficients.

[0088] It should be noted that the improved convergence rate includes a first improved convergence rate parameter, a second improved convergence rate parameter, a third improved convergence rate parameter and a fourth improved convergence rate parameter. The calculation of the saturation function is a well-known technology and will not be elaborated in this application.

[0089] For details, see Figure 1 , Figure 1It is a schematic diagram showing the acquisition of improved approach rate in one embodiment of the present invention.

[0090] Step S8: Calculate the converter voltage loop and current loop control parameters based on the converter output angular frequency, converter side filter inductance, filter capacitor, the fourth orthogonal d-axis component of the capacitor voltage measurement value, the fourth orthogonal q-axis component of the capacitor voltage measurement value, the second orthogonal d-axis component of the converter side output current measurement value, the second orthogonal q-axis component of the converter side output current measurement value and the improved linear relationship of the convergence rate.

[0091] The converter voltage loop and current loop control parameters include an updated d-axis reference value of the converter side output current, an updated q-axis reference value of the converter side output current, an updated d-axis reference value of the converter side output modulation voltage, and an updated q-axis reference value of the converter side output modulation voltage.

[0092] The converter voltage loop and current loop control parameters are calculated according to the fourth orthogonal q-axis component of the capacitor voltage measurement value, the second orthogonal d-axis component of the converter side output current measurement value, the second orthogonal q-axis component of the converter side output current measurement value and the improved approach rate:

[0093]

[0094] Among them, i md is the updated d-axis reference value of the converter side output current, i mq is the updated q-axis reference value of the converter output current, i od is the second orthogonal d-axis component, i oq is the second orthogonal q-axis component, u cq is the fourth orthogonal q-axis component, u cd is the fourth orthogonal d-axis component, ω is the converter output angular frequency, C f is the filter capacitor, is the first improved approach rate parameter, is the second improved approach rate parameter, u md is the updated d-axis reference value of the output modulation voltage on the converter side, u mq is the updated q-axis reference value of the output modulation voltage on the converter side, L f1 is the filter inductor on the converter side, is the third improved approach rate parameter, is the fourth improved approach rate parameter.

[0095] For details, see Figure 2 , Figure 2 It is a schematic diagram showing the acquisition of the voltage loop and current loop control parameters of the converter in one embodiment of the present invention.

[0096] Step S9: input the converter voltage loop and current loop control parameters into the second stage of the low voltage ride through control process for execution, so as to perform fault ride through control on the grid-connected photovoltaic converter.

[0097] Specifically, the second stage is composed of a grid voltage feedforward control module, a Park inverse transformation module, an active damping control module and a space vector pulse width modulation SPWM module. The grid voltage feedforward control module is composed of multiplying the grid-side output voltage measurement value and the preset voltage feedforward control coefficient, and the active damping control module is composed of multiplying the capacitor voltage measurement value and the preset active damping feedforward coefficient.

[0098] It should be noted that the preset voltage feedforward control coefficient and the preset active damping feedforward coefficient are both artificially preset values, and this application does not impose any special restrictions on this.

[0099] A person skilled in the art can understand that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program, and the program can be stored in a computer-readable storage medium, and when the program is executed, it can include the processes of the embodiments of the above-mentioned methods. The storage medium can be a disk, an optical disk, a read-only memory (ROM) or a random access memory (RAM), etc.

[0100] Another embodiment of the present invention provides an active control system for fault ride-through of a grid-type photovoltaic inverter, the system comprising a sliding mode control module, a grid voltage feedforward control module, a Park inverse transformation module, an active damping control module and a space vector pulse width modulation (SPWM) module, the system executing the steps in an active control method for fault ride-through of a grid-type photovoltaic inverter as described in the above embodiment.

[0101] For details, see Figure 3 , Figure 3 The figure shows a flow chart of an active control system for fault ride-through of a grid-connected photovoltaic inverter in one embodiment of the present invention. Figure 3 in,i md is the updated d-axis reference value of the converter side output current, i mq is the updated q-axis reference value of the converter output current, u md is the updated d-axis reference value of the output modulation voltage on the converter side, u mq is the updated q-axis reference value of the output modulation voltage on the converter side, ω is the converter output angular frequency, C f is the filter capacitor, L f1 is the filter inductance on the converter side, u m is the measured value of the output modulation voltage on the converter side, i mis the output current measurement value of the converter side, u o is the measured value of the grid-side output voltage, u c is the capacitor voltage measurement value, k u is the preset voltage feedforward control coefficient, k c is the preset active damping feedforward coefficient, and t1 is the first preset threshold.

[0102] Correspondingly, another embodiment of the present invention provides a computer-readable storage medium, which includes a stored computer program, wherein when the computer program is running, the device where the computer-readable storage medium is located is controlled to execute the steps in a method for active control of fault crossing of a grid-connected photovoltaic inverter as in the above embodiment.

[0103] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for active control of fault ride-through of a grid-connected photovoltaic converter, characterized in that: The method is applied to a grid-type photovoltaic converter fault ride-through active control system composed of a sliding mode control module, a grid voltage feedforward control module, a Park inverse transformation module, an active damping control module and a space vector pulse width modulation (SPWM) module, and the method comprises: Collect the measured values ​​of the inverter-side output modulation voltage, the inverter-side output current, the grid-side output voltage, the capacitor voltage, the inverter output angular frequency, the inverter-side filter inductance and filter capacitance of the photovoltaic power generation system; Determine the on state of the fault control mode based on the difference between the grid-side output voltage measurement value and the first preset threshold value; when the on state of the fault control mode is off, maintain the control state of the photovoltaic power generation system, otherwise enter the low voltage ride through control process, the low voltage ride through control process includes a first stage executed by the sliding mode control module, and a second stage executed by the grid voltage feedforward control module, the Park inverse transformation module, the active damping control module and the space vector pulse width modulation SPWM module; During the execution of the first stage, based on the output modulation voltage measurement value of the converter side, the output current measurement value of the converter side, the grid side output voltage measurement value, the capacitor voltage measurement value, the converter output angular frequency, the converter side filter inductor and the filter capacitor, the converter voltage loop and current loop control parameters are obtained; The converter voltage loop and current loop control parameters include an updated d-axis reference value of the converter side output current, an updated q-axis reference value of the converter side output current, an updated d-axis reference value of the converter side output modulation voltage, and an updated q-axis reference value of the converter side output modulation voltage, so as to control the inner loop output of the converter; After the first stage is completed, the converter voltage loop and current loop control parameters are input into the second stage for execution, so as to perform fault ride-through control on the grid-connected photovoltaic converter.

2. A grid-connected photovoltaic converter fault ride-through active control method according to claim 1, characterized in that: The step of obtaining the converter voltage loop and current loop control parameters based on the converter side output modulation voltage measurement value, the converter side output current measurement value, the grid side output voltage measurement value, the capacitor voltage measurement value, the converter output angular frequency, the converter side filter inductor and the filter capacitor comprises: Obtaining a first orthogonal dq-axis positive and negative sequence component of the converter side output modulation voltage measurement value, a second orthogonal dq-axis positive and negative sequence component of the converter side output current measurement value, a second orthogonal d-axis component of the converter side output current measurement value, and a second orthogonal q-axis component of the converter side output current measurement value; Obtaining a third orthogonal dq-axis positive and negative sequence component of the grid-side output voltage measurement value, a fourth orthogonal dq-axis positive and negative sequence component of the capacitor voltage measurement value, a fourth orthogonal d-axis component of the capacitor voltage measurement value, and a fourth orthogonal q-axis component of the capacitor voltage measurement value; Obtaining a first DC component of the active power output by the converter and a second DC component of the reactive power output by the converter based on a linear algebraic relationship between the first orthogonal dq axis positive and negative sequence components and the second orthogonal dq axis positive and negative sequence components; Acquire a fifth orthogonal dq-axis positive and negative sequence component of a converter-side output current reference value based on a linear relationship among the first DC component, the second DC component and the third orthogonal dq-axis positive and negative sequence component; Calculate the improved convergence rate based on the difference between the capacitor voltage measurement value and the reference value, and the difference between the converter side output current measurement value and the reference value; Based on the linear relationship among the converter output angular frequency, the converter side filter inductance, the filter capacitor, the fourth orthogonal d-axis component, the fourth orthogonal q-axis component, the second orthogonal d-axis component, the second orthogonal q-axis component and the improved approach rate, the converter voltage loop and current loop control parameters are calculated.

3. A method for active control of fault ride-through of a grid-connected photovoltaic converter according to claim 2, characterized in that: The first orthogonal dq axis positive and negative sequence components, the second orthogonal dq axis positive and negative sequence components, the third orthogonal dq axis positive and negative sequence components, and the fourth orthogonal dq axis positive and negative sequence components all include an orthogonal d axis positive sequence component, an orthogonal d axis negative sequence component, an orthogonal q axis positive sequence component, and an orthogonal q axis negative sequence component.

4. The active control method for fault ride-through of a grid-connected photovoltaic converter according to claim 2, characterized in that: The method of obtaining the first orthogonal dq axis positive and negative sequence component of the converter side output modulation voltage measurement value, the second orthogonal dq axis positive and negative sequence component of the converter side output current measurement value, the second orthogonal d axis component of the converter side output current measurement value, and the second orthogonal q axis component of the converter side output current measurement value includes: The output modulation voltage measurement value of the converter side is processed by using a phase-locked loop technology based on a dual second-order generalized integrator to obtain the first orthogonal dq-axis positive and negative sequence components of the output modulation voltage measurement value of the converter side; Processing the output current measurement value of the converter side by using a phase-locked loop technology based on a dual second-order generalized integrator to obtain a second orthogonal dq-axis positive and negative sequence component of the output current measurement value of the converter side, a second orthogonal d-axis component of the output current measurement value of the converter side, and a second orthogonal q-axis component of the output current measurement value of the converter side; The obtaining of the third orthogonal dq-axis positive and negative sequence components of the grid-side output voltage measurement value, the fourth orthogonal dq-axis positive and negative sequence components of the capacitor voltage measurement value, the fourth orthogonal d-axis component of the capacitor voltage measurement value, and the fourth orthogonal q-axis component of the capacitor voltage measurement value includes: The grid-side output voltage measurement value is processed by using a phase-locked loop technology based on a dual second-order generalized integrator to obtain a third orthogonal dq-axis positive and negative sequence component of the grid-side output voltage measurement value; The capacitor voltage measurement value is processed using a phase-locked loop technology based on a double second-order generalized integrator to obtain a fourth orthogonal dq-axis positive and negative sequence component of the capacitor voltage measurement value, a fourth orthogonal d-axis component of the capacitor voltage measurement value, and a fourth orthogonal q-axis component of the capacitor voltage measurement value.

5. The active control method for fault ride-through of a grid-connected photovoltaic converter according to claim 3, characterized in that: The specific method of obtaining the first DC component of the active power output by the converter and the second DC component of the reactive power output by the converter based on the linear algebraic relationship between the first orthogonal dq-axis positive and negative sequence components and the second orthogonal dq-axis positive and negative sequence components includes: Among them, P b is the first DC component, Q b is the second DC component, is the orthogonal d-axis positive-sequence component of the first orthogonal dq-axis positive-sequence component, is the orthogonal d-axis negative-sequence component of the first orthogonal dq-axis positive- and negative-sequence components, is the orthogonal q-axis positive-sequence component of the first orthogonal dq-axis positive-sequence component, is the orthogonal q-axis negative-sequence component of the first orthogonal dq-axis positive- and negative-sequence components, is the orthogonal d-axis positive-sequence component of the second orthogonal dq-axis positive- and negative-sequence components, is the orthogonal d-axis negative-sequence component of the second orthogonal dq-axis positive- and negative-sequence components, is the orthogonal q-axis positive-sequence component of the second orthogonal dq-axis positive- and negative-sequence components, It is the orthogonal q-axis negative-sequence component of the second orthogonal dq-axis positive and negative-sequence components.

6. The active control method for fault ride-through of a grid-connected photovoltaic converter according to claim 3, characterized in that: The specific method of obtaining the fifth orthogonal dq-axis positive and negative sequence component of the converter side output current reference value based on the linear relationship between the first DC component, the second DC component and the third orthogonal dq-axis positive and negative sequence component includes: in, is the orthogonal d-axis positive sequence component of the output current reference value of the converter side, is the orthogonal q-axis positive sequence component of the output current reference value of the converter side, is the orthogonal d-axis negative sequence component of the output current reference value of the converter side, is the orthogonal q-axis negative sequence component of the output current reference value of the converter side, is the orthogonal d-axis positive-sequence component of the third orthogonal dq-axis positive- and negative-sequence components, is the orthogonal q-axis positive-sequence component of the third orthogonal dq-axis positive- and negative-sequence components, P b is the first DC component, Q b is the second DC component.

7. A method for active control of fault ride-through of a grid-connected photovoltaic converter according to claim 6, characterized in that: The preset capacitor voltage dq-axis component reference value includes a preset capacitor voltage d-axis component reference value and a preset capacitor voltage q-axis component reference value, and the improved approach rate includes a first improved approach rate parameter, a second improved approach rate parameter, a third improved approach rate parameter and a fourth improved approach rate parameter; The calculation of the improved approach rate based on the difference between the capacitor voltage measurement value and the reference value, and the difference between the converter side output current measurement value and the reference value, comprises: Taking the difference between the preset capacitor voltage d-axis component reference value and the fourth orthogonal d-axis component as a first sliding surface parameter, taking the saturation function value of the first sliding surface parameter as a first saturated sliding surface parameter, and calculating the first improved approach rate parameter based on a linear relationship between the first sliding surface parameter and the first saturated sliding surface parameter; Taking the difference between the preset capacitor voltage q-axis component reference value and the fourth orthogonal q-axis component as a second sliding surface parameter, taking the saturation function value of the second sliding surface parameter as a second saturated sliding surface parameter, and calculating the second improved convergence rate parameter based on a linear relationship between the second sliding surface parameter and the second saturated sliding surface parameter; taking the difference between the orthogonal d-axis positive sequence component of the converter-side output current reference value and the second orthogonal d-axis component as a third sliding surface parameter, taking the saturation function value of the third sliding surface parameter as a third saturated sliding surface parameter, and calculating the third improved approach rate parameter based on the linear relationship between the third sliding surface parameter and the third saturated sliding surface parameter; The difference between the orthogonal d-axis positive-sequence component of the converter-side output current reference value and the second orthogonal q-axis component is used as a fourth sliding surface parameter, the saturation function value of the fourth sliding surface parameter is used as a fourth saturated sliding surface parameter, and based on the linear relationship between the fourth sliding surface parameter and the fourth saturated sliding surface parameter, the fourth improved convergence rate parameter is calculated.

8. The active control method for fault ride-through of a grid-connected photovoltaic converter according to claim 7, characterized in that: The converter voltage loop and current loop control parameters include an updated d-axis reference value of the converter side output current, an updated q-axis reference value of the converter side output current, an updated d-axis reference value of the converter side output modulation voltage, and an updated q-axis reference value of the converter side output modulation voltage; The step of calculating the converter voltage loop and current loop control parameters based on the linear relationship between the converter output angular frequency, the converter side filter inductor, the filter capacitor, the fourth orthogonal d-axis component, the fourth orthogonal q-axis component, the second orthogonal d-axis component, the second orthogonal q-axis component and the improved approach rate comprises: Among them, i md is the updated d-axis reference value of the converter side output current, i mq is the updated q-axis reference value of the converter output current, i od is the second orthogonal d-axis component, i oq is the second orthogonal q-axis component, u cq is the fourth orthogonal q-axis component, u cd is the fourth orthogonal d-axis component, ω is the output angular frequency of the converter, C f is the filter capacitor, is the first improved approach rate parameter, is the second improved convergence rate parameter, u md is the updated d-axis reference value of the output modulation voltage on the converter side, u mq is the updated q-axis reference value of the output modulation voltage on the converter side, L f1 is the converter side filter inductor, is the third improved approach rate parameter, is the fourth improved approach rate parameter.

9. The active control method for fault ride-through of a grid-connected photovoltaic converter according to claim 1, characterized in that: The step of determining the start state of the fault control mode based on the difference between the grid-side output voltage measurement value and the first preset threshold value includes: When the grid-side output voltage measurement value is less than or equal to the first preset threshold, the fault control mode is turned on; otherwise, the fault control mode is turned off.

10. A grid-type photovoltaic converter fault ride-through active control system, characterized in that: The system includes a sliding mode control module, a grid voltage feedforward control module, a Park inverse transformation module, an active damping control module and a space vector pulse width modulation (SPWM) module. When the system executes the computer program, it implements a grid-type photovoltaic inverter fault ride-through active control method as described in any one of claims 1 to 9.

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