Dynamic voltage restorer and control method based on distribution network state acquisition

Abstract

The present invention provides a dynamic voltage restorer based on distribution network state acquisition and a control method thereof, belonging to the field of smart grid and control technology thereof; in view of the technical defects of the existing technical solutions that the thyristor cannot be reliably segmented and the control switching cannot be quickly and accurately satisfied with the sudden change of load, the present invention proposes a method for voltage sag using an output voltage prediction model, which can accurately predict the output voltage at the next time based on the current moment, and then establishes an adaptive fast switching strategy based on feedback control with strong load adaptability on the basis of high-accuracy prediction, the purpose of the proposed strategy is to ensure that the shutdown process is affected by the sudden change of load power and the current zero crossing, improve the reliability of thyristor shutdown, and realize fast and accurate control of the voltage restorer DVR.

Description

Technical Field

[0001] The present invention belongs to the technical field of smart grid and control thereof, and specifically relates to a dynamic voltage restorer based on distribution network state acquisition and a control method thereof. Background Art

[0002] Dynamic Voltage Restorer (DVR) is a device used to solve dynamic power quality problems such as voltage sag and swell in distribution networks. It eliminates voltage disturbances by injecting a specific series voltage into the power grid to ensure the normal operation of sensitive loads. Its detection module is responsible for real-time collection of power on the system and load side, providing accurate information for the compensation control link. The compensation control unit comprehensively determines the real-time voltage compensation amount based on real-time information, the needs of specific loads, and the compensation capability of the DVR, and performs real-time control.

[0003] The control strategy of DVR is an important part of its research. The existing technology uses parameter fuzzy self-tuning PID control method to control three-phase series transformer-free DVR, which realizes fast and accurate compensation of system voltage sag. In addition, there is also optimization of the capacity and location of DVR in the distribution network based on genetic algorithm to improve economy. There are also studies on the control technology of dynamic voltage restorer of distribution network, including improving the detection algorithm of voltage signal to meet the requirements of compensation instantaneity.

[0004] In terms of the specific implementation of the control strategy, some studies have proposed using proportional integral (PI) and adaptive neural fuzzy inference system (ANFIS) control schemes to improve the voltage quality of the distribution network through simulation and implementation. Another study compared and analyzed two methods based on variable structure control to design nonlinear control of dynamic voltage restorers.

[0005] However, most existing technologies are implemented through end-to-end control or compensation. When faced with sudden changes in load, they cannot achieve high real-time and accuracy, resulting in the inability of switching to adapt to sudden changes in load, which in turn causes large-scale failures in power grid operation. Summary of the invention

[0006] The purpose of the present invention is to solve the above-mentioned problems existing in the prior art and to provide a dynamic voltage restorer based on distribution network status acquisition and a control method thereof.

[0007] In a first aspect, the voltage restorer DVR provided by the present invention comprises the following units:

[0008] Energy storage system: DVR needs an energy storage system to provide the required energy to quickly generate compensation voltage. The energy storage system can be a battery, supercapacitor or other form of energy storage device.

[0009] Control unit: The control unit of the DVR is responsible for monitoring the state of the power grid, detecting sudden changes in voltage load, and controlling the inverter to generate corresponding compensation voltage based on the detection results; the control unit includes detection algorithms, control strategies and actuators.

[0010] Interface circuit: DVR needs to be connected to the power grid and load, so an interface circuit is required to achieve electrical connection. The interface circuit can include a transformer or other types of coupling devices to adapt to different power grid conditions.

[0011] Protection and bypass units: To ensure the safety and reliability of the system, DVRs are usually equipped with protection circuits and bypass mechanisms; these mechanisms can automatically switch when abnormal conditions are detected to protect the system from damage.

[0012] Communication interface: The DVR communication interface exchanges data with the external control system or monitoring system to achieve remote monitoring and control.

[0013] In the second aspect, in the present invention, the control unit of the three-phase DVR of the power grid includes an inverter, an LC filter circuit, a cascaded step-up transformer and a bypass switch, wherein the DC voltage source Udc serves as a power supply for the DVR system.

[0014] The inverter converts the energy in the energy storage system into the required compensation voltage. The inverter uses PWM (pulse width modulation) technology to control the amplitude and phase of the output voltage. Filter circuit In order to reduce the harmonics in the compensation voltage generated by the inverter, the DVR may also include a filter circuit to improve the quality of the compensation voltage.

[0015] Furthermore, the present invention is based on the above-mentioned dynamic voltage restorer based on distribution network state acquisition and its control method provided by the present invention, which specifically includes the following steps:

[0016] Step 1: Determine the load trend and current load voltage u o and load current i o Increasing and decaying trends are divided into different load modes according to the increasing and decaying trends, including synchronous increasing mode, load current increasing and voltage decreasing mode, load voltage decreasing and current increasing mode, and voltage and current synchronous decreasing four modes, which are defined as Mode 1 to Mode 4 respectively.

[0017] Step 2: Establish an output voltage prediction model based on the measurable variables of the DVR, which specifically includes:

[0018] Define the variable err as the difference between the measured output voltage of the DVR at the current time t and the corrected output prediction value:

[0019] err(t)=u o (t)-u oc(t)err(t)=u o (t)-u oc (t)

[0020] Where u o (t) represents the output voltage measured at time k, u oc (t) represents the predicted output voltage after DVR correction at time t;

[0021] A voltage prediction model is further established by fitting the multivariate DVR output voltage. According to the current DVR output voltage at time t, the inverter inductor current and load current, and the inverter output voltage, the DVR output voltage at time t+1 can be predicted. The prediction is made using the following formula:

[0022]

[0023] Where F is the DVR sampling frequency, is the current value of the inverter inductor at the current moment, i β (t)] is the load current value at the current moment, R, L and C are the resistance, inductance and capacitance corresponding to the filter circuit;

[0024] The output voltage u at time k+1 is calculated from the above formula op After (t+1), the output voltage deviation err is used to predict the output voltage u at time k. op (t+1) is corrected, and the predicted output voltage of the DVR after correction at time k+1 is obtained as

[0025] u o (t+1)=u op (t+1)+err(t);

[0026] Step 3: Based on the predicted output voltage and the current load mode, determine whether there is a voltage sag. Specifically, when the difference between the predicted output voltage and the output voltage value at the previous moment exceeds a certain threshold value for n consecutive cycles in the sampling period, it is determined that there is a voltage sag;

[0027] Step 4, when no voltage sag event is detected, controlling the load current to flow through the thyristor bypass branch;

[0028] Step 5, when a voltage sag event is detected, adaptive control of compensation switching is performed based on the load mode in step 1;

[0029] Specifically, when the current load mode belongs to mode 2 or mode 3, the thyristor trigger signal is removed and the current loop is used and activated to filter the inductor current. Linear following load current i β(t)] adjustment. Since the thyristor has not been turned off at this stage, the filter capacitor branch is controlled by bypass. The switching mutation ripple of the inductor will be superimposed on the gradually decreasing thyristor current, reducing the thyristor current to below the holding current. At time t+1, the thyristor is completely turned off, and all the current is commutated to the filter inductor side.

[0030] When the current load mode belongs to mode 1 or mode 4, the current load mutation mode is determined, the current loop control structure is kept unchanged, the deviation value of the current loop is filtered, and whether to switch to the voltage loop is selected based on the comparison result with the threshold current; further, at the next moment, it is determined that the system has successfully switched current, and the current loop is switched to the voltage loop synchronously. The DVR outputs voltage according to the selected compensation strategy and compensation demand, and the DVR system enters the voltage compensation mode.

[0031] Compared with the prior art, the beneficial effects of the present invention are: in view of the technical defects of the prior art that the thyristor cannot be reliably switched and the control input cannot be quickly and accurately met with load mutation, the present invention proposes a method for voltage sag based on an output voltage prediction model, which can accurately predict the output voltage at the next time based on the current moment, and then establishes an adaptive fast switching strategy based on feedback control with strong load adaptability on the basis of high-accuracy prediction. The purpose of the proposed strategy is to ensure that the shutdown process is not affected by load power mutation and current zero crossing, improve the reliability of thyristor shutdown, and realize fast and accurate control of the voltage restorer DVR. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the block diagram of the voltage restorer DVR system for this application;

[0033] Figure 2 A circuit diagram of a control unit provided in an embodiment of the present application;

[0034] Figure 3 This is a flow chart of the control method of this application. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0036] Example 1, see attached Figure 1 The voltage restorer DVR provided by the present invention comprises the following units:

[0037] Energy storage system: DVR needs an energy storage system to provide the required energy to quickly generate compensation voltage. The energy storage system can be a battery, supercapacitor or other form of energy storage device.

[0038] Control unit: The control unit of the DVR is responsible for monitoring the state of the power grid, detecting sudden changes in voltage load, and controlling the inverter to generate corresponding compensation voltage based on the detection results; the control unit includes detection algorithms, control strategies and actuators.

[0039] Interface circuit: DVR needs to be connected to the power grid and load, so an interface circuit is required to achieve electrical connection. The interface circuit can include a transformer or other types of coupling devices to adapt to different power grid conditions.

[0040] Protection and bypass units: To ensure the safety and reliability of the system, DVRs are usually equipped with protection circuits and bypass mechanisms; these mechanisms can automatically switch when abnormal conditions are detected to protect the system from damage.

[0041] Communication interface: The DVR communication interface exchanges data with the external control system or monitoring system to achieve remote monitoring and control.

[0042] Example 2, see attached Figure 2 In the present invention, the control unit of the three-phase DVR of the power grid includes an inverter, an LC filter circuit, a cascaded step-up transformer and a bypass switch, wherein a DC voltage source Udc serves as a power supply for the DVR system.

[0043] The inverter converts the energy in the energy storage system into the required compensation voltage. The inverter uses PWM (pulse width modulation) technology to control the amplitude and phase of the output voltage. Filter circuit In order to reduce the harmonics in the compensation voltage generated by the inverter, the DVR may also include a filter circuit to improve the quality of the compensation voltage.

[0044] Example 3, see the attached specification Figure 3 The present invention is based on the above-mentioned dynamic voltage restorer based on distribution network state acquisition and its control method provided by the present invention, which specifically includes the following steps:

[0045] Step 1: Determine the load trend and current load voltage u o and load current i o Increasing and decaying trends are divided into different load modes according to the increasing and decaying trends, including synchronous increasing mode, load current increasing and voltage decreasing mode, load voltage decreasing and current increasing mode, and voltage and current synchronous decreasing four modes, which are defined as Mode 1 to Mode 4 respectively.

[0046] Step 2: Establish an output voltage prediction model based on the measurable variables of the DVR, which specifically includes:

[0047] Define the variable err as the difference between the measured output voltage of the DVR at the current time t and the corrected output prediction value:

[0048] err(t)=u o (t)-u oc (t)err(t)=u o (t)-u oc (t)

[0049] Where u o (t) represents the output voltage measured at time k, u oc (t) represents the predicted output voltage after DVR correction at time t;

[0050] A voltage prediction model is further established by fitting the multivariate DVR output voltage. According to the current DVR output voltage at time t, the inverter inductor current and load current, and the inverter output voltage, the DVR output voltage at time t+1 can be predicted. The prediction is made using the following formula:

[0051]

[0052] Where F is the DVR sampling frequency, is the current value of the inverter inductor at the current moment, i β (t)] is the load current value at the current moment, R, L and C are the resistance, inductance and capacitance corresponding to the filter circuit;

[0053] The output voltage u at time k+1 is calculated from the above formula op After (t+1), the output voltage deviation err is used to predict the output voltage u at time k. op (t+1) is corrected, and the predicted output voltage of the DVR after correction at time k+1 is obtained as

[0054] u o (t+1)=u op (t+1)+err(t);

[0055] Step 3: Based on the predicted output voltage and the current load mode, determine whether there is a voltage sag. Specifically, when the difference between the predicted output voltage and the output voltage value at the previous moment exceeds a certain threshold value for n consecutive cycles in the sampling period, it is determined that there is a voltage sag;

[0056] Step 4, when no voltage sag event is detected, controlling the load current to flow through the thyristor bypass branch;

[0057] Step 5, when a voltage sag event is detected, adaptive control of compensation switching is performed based on the load mode in step 1;

[0058] Specifically, when the current load mode belongs to mode 2 or mode 3, the thyristor trigger signal is removed and the current loop is used and activated to filter the inductor current. Linear following load current iβ (t)] adjustment. Since the thyristor has not been turned off at this stage, the filter capacitor branch is controlled by bypass. The switching mutation ripple of the inductor will be superimposed on the gradually decreasing thyristor current, reducing the thyristor current to below the holding current. At time t+1, the thyristor is completely turned off, and all the current is commutated to the filter inductor side.

[0059] When the current load mode belongs to mode 1 or mode 4, the current load mutation mode is determined, the current loop control structure is kept unchanged, the deviation value of the current loop is filtered, and whether to switch to the voltage loop is selected based on the comparison result with the threshold current; further, at the next moment, it is determined that the system has successfully switched current, and the current loop is switched to the voltage loop synchronously. The DVR outputs voltage according to the selected compensation strategy and compensation demand, and the DVR system enters the voltage compensation mode.

[0060] Some embodiments of the present application further provide a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the system functions described in the method embodiments are executed.

[0061] Some embodiments of the present application also provide an electronic device, characterized in that it includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the system execution method can be implemented when the processor executes the program.

[0062] The above are only embodiments of the present application and are not intended to limit the scope of protection of the present application. For those skilled in the art, the present application may have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings.

[0063] The above are only specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

[0064] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0065] In the description of the present invention, unless otherwise specified, the terms "upper", "lower", "left", "right", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they cannot be understood as limitations on the present invention.

[0066] Finally, it should be explained that the above technical solution is only one implementation method of the present invention. For those skilled in the art, it is easy to make various types of improvements or modifications based on the application methods and principles disclosed in the present invention, and it is not limited to the method described in the above specific implementation method of the present invention. Therefore, the method described above is only preferred and does not have a restrictive meaning.

Claims

1. A dynamic voltage restorer control method based on distribution network state acquisition, characterized in that The voltage restorer DVR includes an energy storage system, a control unit, an interface circuit, a protection and bypass unit, and a communication interface. The dynamic voltage restorer and the control method thereof are used to perform the following steps: Step 1: Determine the load trend and current load voltage u o and load current i o Increase and decay trends are divided into different load modes according to the increase and decay trends; specifically, there are four modes: synchronous increase mode, load current increase and voltage reduction mode, load current reduction and voltage increase mode, and voltage and current synchronous reduction mode, which are defined as mode 1 to mode 4 respectively; Step 2: Establish an output voltage prediction model based on the measurable variables of the DVR, which specifically includes: Define the variable err as the difference between the measured output voltage of the DVR at the current time t and the corrected output prediction value: err(t)=u o (t)-u oc (t); Where u o (t) represents the output voltage measured at time t, u oc (t) represents the predicted output voltage after DVR correction at time t; A voltage prediction model is established by fitting the multivariate DVR output voltage. According to the current DVR output voltage, inverter inductor current, load current and inverter output voltage at time t, the output voltage u of the DVR at time t+1 can be predicted. op (t+1), predicted by the following formula: Where F is the DVR sampling frequency, is the current value of the inverter inductor at the current moment, i β (t)] is the load current value at the current moment, R, L and C are the resistance, inductance and capacitance corresponding to the filter circuit; The output voltage u at time t+1 is calculated from the above formula op After (t+1), the output voltage error value err predicted at time t is used to predict the output voltage u op (t+1) is corrected, and the predicted output voltage of the DVR after correction at time t+1 is obtained as: u o (t+1)=u op (t+1)+err(t); Step 3: Based on the predicted output voltage and the current load mode, determine whether there is a voltage sag at present; specifically, when the difference between the predicted output voltage and the output voltage value at the previous moment exceeds a certain threshold value for n consecutive cycles in the sampling period, it is determined that there is a voltage sag at present; Step 4, when no voltage sag event is detected, controlling the load current to flow through the thyristor bypass branch; Step 5, when a voltage sag event is detected, adaptive control of compensation switching is performed based on the load mode in step 1; The adaptive control in step 5 includes, when the current load mode belongs to mode 2 or mode 3, removing the thyristor trigger signal, and using and activating the current loop to filter the inductor current Linear following load current i β (t)] adjustment. Since the thyristor has not been turned off at this stage, the filter capacitor branch is controlled by bypass. The switching mutation ripple of the inductor will be superimposed on the gradually decreasing thyristor current, reducing the thyristor current to below the holding current. At time t+1, the thyristor is completely turned off, and all the current is commutated to the filter inductor side. The adaptive control in step 5 includes, when the current load mode belongs to mode 1 or mode 4, determining the current load mutation mode, keeping the current loop control structure unchanged, filtering the deviation value of the current loop, and choosing whether to switch to the voltage loop according to the comparison result with the threshold current; further judging that the system has successfully switched at the next moment, synchronously switching from the current loop to the voltage loop, the DVR outputs the voltage according to the selected compensation strategy and compensation demand, and the DVR system enters the voltage compensation mode.

2. The control method according to claim 1, characterized in that: The DVR is a three-phase DVR.

3. The control method according to claim 1, characterized in that The control unit comprises an inverter, an LC filter circuit, a cascaded step-up transformer and a bypass switch, wherein a DC voltage source is used as a power supply for the DVR system.

4. An electronic device, characterized in that: The invention comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor can implement the control method described in any one of claims 1 to 3 when executing the program.

5. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, wherein the program, when executed by a processor, can implement the control method described in any one of claims 1 to 3.

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