Capacitor type selection method and device of unified power quality conditioner and computer equipment

Abstract

The invention relates to a capacitor type selection method and device of a unified power quality conditioner and computer equipment, and relates to the technical field of power electronics, and the method comprises the steps: obtaining modulation wave functions of space vector pulse width modulation of input and output AC ports when the unified power quality conditioner is in a preset operation condition; the operation conditions comprise rated and limit conditions; obtaining first current values of the input and output AC ports; obtaining a modulation wave value corresponding to each modulation wave function, and obtaining a first capacitance current average value of each capacitor in each switching period based on the modulation wave value and each first current value; based on the first capacitance current average value of each capacitor, determining a second capacitance current average value flowing through each capacitor in a fundamental wave period; based on the first capacitance current average value and the second capacitance current average value, obtaining a capacitance current instantaneous value of each capacitor in a fundamental wave period; and processing the current instantaneous value of each capacitor based on a preset mode to determine the minimum capacitance value of each capacitor so as to realize the type selection of each capacitor.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a capacitor selection method, device and computer equipment for a unified power quality conditioner. Background Art

[0002] With the large-scale access of distributed energy such as photovoltaics, DC loads such as electric vehicle charging piles, and nonlinear and impact loads in low-voltage distribution networks, the harmonic content and imbalance of low-voltage feeder currents have increased significantly, affecting the safe and stable operation of the power grid. In response to the power quality problem, a variety of governance devices have been proposed and applied, such as unified power quality conditioners (UPQC), especially transformerless unified power quality conditioners; transformerless UPQC includes a DC port, wherein the DC port is connected to a common DC bus composed of a first DC side capacitor and a second DC side capacitor in series, i.e., a DC link.

[0003] It can be seen that the DC side capacitor is an important part of the DC link of the transformerless UPQC, which affects the fluctuation of the DC bus voltage and thus affects the stability of the output voltage. Therefore, the reasonable design of the DC side capacitor is related to the stability of the output voltage through the transformerless UPQC. Summary of the invention

[0004] Based on this, it is necessary to provide a capacitor selection method, device, computer equipment, computer-readable storage medium and computer program product for a unified power quality conditioner that can design capacitors for a transformerless UPQC in response to the above technical problems.

[0005] In a first aspect, the present application provides a capacitor selection method for a unified power quality conditioner, comprising:

[0006] When the unified power quality conditioner is in a preset operating condition, obtaining modulation wave functions of space vector pulse width modulation corresponding to the input AC port and the output AC port of each phase of the unified power quality conditioner, respectively; wherein the preset operating condition includes a rated condition and a limit condition;

[0007] Acquire first current values ​​respectively corresponding to the input AC port and the output AC port of each phase;

[0008] Obtaining a modulation wave value corresponding to each of the modulation wave functions, and obtaining a first capacitor current average value of each capacitor in each switching cycle within a fundamental wave cycle based on the modulation wave value and each of the first current values;

[0009] Determine an average value of a second capacitor current flowing through each of the capacitors in one fundamental wave period based on an average value of the first capacitor current of each of the capacitors;

[0010] Based on the first capacitor current average value and the second capacitor current average value, acquiring the instantaneous value of the capacitor current of each of the capacitors within one fundamental wave period;

[0011] The instantaneous value of each capacitor current is processed based on a preset method to determine the minimum capacitance value of each capacitor; and the selection of each capacitor in the unified power quality conditioner is determined based on each minimum capacitance value.

[0012] In one embodiment, the obtaining of the first current values ​​respectively corresponding to the input AC port and the output AC port of each phase includes:

[0013] Based on the input current amplitude of the input AC port, the output current amplitude of the output AC port, the angle at which the input AC port current leads the input AC port voltage, the angle at which the load voltage lags behind the output AC port voltage, the angle at which the load current lags behind the load voltage, and the angle that changes with time, of each phase of the unified power quality conditioner, the first current values ​​corresponding to the input AC port and the output AC port of each phase are obtained; wherein the load is electrically connected to the output AC port of the unified power quality conditioner.

[0014] In one of the embodiments, before the unified power quality conditioner is in a preset operating condition, the method further includes:

[0015] Among multiple operating conditions of the unified power quality conditioner, determining that the power grid electrically connected to the unified power quality conditioner, the operating condition in which the corresponding power grid voltage has the lowest positive sequence component is the limit condition; wherein the power grid is electrically connected to the input AC port of the unified power quality conditioner;

[0016] The unified power quality conditioner is operated based on the extreme operating condition, and the input current amplitude of the input AC port of each phase of the unified power quality conditioner is obtained; the input current amplitude is used to obtain the first current value of the corresponding input AC port.

[0017] In one embodiment, the step of obtaining modulation wave functions of space vector pulse width modulation corresponding to input AC ports and output AC ports of each phase of the unified power quality conditioner includes:

[0018] Obtaining the sinusoidal pulse width modulation wave functions corresponding to the input AC port and the output AC port of each phase of the unified power quality conditioner under the sinusoidal pulse width modulation modulation mode;

[0019] Determine an input zero-sequence component based on the sinusoidal pulse width modulation wave function of each of the input AC ports; and determine an output zero-sequence component based on the sinusoidal pulse width modulation wave function of each of the output AC ports;

[0020] Based on the sum of the sinusoidal pulse width modulation wave function of each input AC port and the input zero-sequence component, the modulation wave function of the space vector pulse width modulation corresponding to each input AC port is determined; and based on the sum of the sinusoidal pulse width modulation wave function of each output AC port and the output zero-sequence component, the modulation wave function of the space vector pulse width modulation corresponding to each output AC port is determined.

[0021] In one embodiment, determining the average value of the second capacitor current flowing through each capacitor in one fundamental wave period based on the average value of the first capacitor current of each capacitor includes:

[0022] In one fundamental wave cycle, an average value of the second capacitor current flowing through each capacitor in one fundamental wave cycle is determined based on an integration calculation of the average value of the first capacitor current of each capacitor.

[0023] In one embodiment, obtaining the instantaneous value of the capacitor current of each capacitor within one fundamental wave period based on the first capacitor current average value and the second capacitor current average value includes:

[0024] Based on the difference between the first capacitor current average value and the second capacitor current average value corresponding to each capacitor, the instantaneous value of the capacitor current of each capacitor within one fundamental wave period is obtained.

[0025] In one embodiment, the processing of the instantaneous value of each capacitor current based on a preset method to determine the minimum capacitance value of each capacitor includes:

[0026] Based on time integration of the instantaneous value of each capacitor current, the corresponding charge amount of the capacitor charging and discharging is obtained, and then based on the capacitor definition formula and the preset capacitor voltage ripple requirement, the minimum capacitance value of each capacitor is determined.

[0027] In a second aspect, the present application also provides a capacitor selection device for a unified power quality conditioner, comprising:

[0028] A data acquisition module, used for acquiring modulation wave functions of space vector pulse width modulation corresponding to input AC ports and output AC ports of each phase of the unified power quality conditioner respectively when the unified power quality conditioner is in a preset operating condition; wherein the preset operating condition includes a rated condition and a limit condition;

[0029] The data acquisition module is also used to acquire the first current values ​​corresponding to the input AC port and the output AC port of each phase respectively;

[0030] A data processing module, used for obtaining a modulation wave value corresponding to each of the modulation wave functions, and obtaining a first capacitor current average value of each capacitor in each switching cycle within a fundamental wave cycle based on the modulation wave value and each of the first current values;

[0031] The data processing module is further used to determine an average value of a second capacitor current flowing through each of the capacitors in one fundamental wave period based on an average value of the first capacitor current of each of the capacitors;

[0032] The data processing module is further used to obtain the instantaneous value of the capacitor current of each of the capacitors within one fundamental wave period based on the first capacitor current average value and the second capacitor current average value;

[0033] The capacitor selection module is used to process the instantaneous value of each capacitor current based on a preset method to determine the minimum capacitance value of each capacitor; and determine the selection of each capacitor in the unified power quality conditioner based on each minimum capacitance value.

[0034] In a third aspect, the present application further provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the following steps are implemented:

[0035] When the unified power quality conditioner is in a preset operating condition, obtaining modulation wave functions of space vector pulse width modulation corresponding to the input AC port and the output AC port of each phase of the unified power quality conditioner, respectively; wherein the preset operating condition includes a rated condition and a limit condition;

[0036] Acquire first current values ​​respectively corresponding to the input AC port and the output AC port of each phase;

[0037] Obtaining a modulation wave value corresponding to each of the modulation wave functions, and obtaining a first capacitor current average value of each capacitor in each switching cycle within a fundamental wave cycle based on the modulation wave value and each of the first current values;

[0038] Determine an average value of a second capacitor current flowing through each of the capacitors in one fundamental wave period based on an average value of the first capacitor current of each of the capacitors;

[0039] Based on the first capacitor current average value and the second capacitor current average value, acquiring the instantaneous value of the capacitor current of each of the capacitors within one fundamental wave period;

[0040] The instantaneous value of each capacitor current is processed based on a preset method to determine the minimum capacitance value of each capacitor; and the selection of each capacitor in the unified power quality conditioner is determined based on each minimum capacitance value.

[0041] In a fourth aspect, the present application further provides a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the following steps are implemented:

[0042] When the unified power quality conditioner is in a preset operating condition, obtaining modulation wave functions of space vector pulse width modulation corresponding to the input AC port and the output AC port of each phase of the unified power quality conditioner, respectively; wherein the preset operating condition includes a rated condition and a limit condition;

[0043] Acquire first current values ​​respectively corresponding to the input AC port and the output AC port of each phase;

[0044] Obtaining a modulation wave value corresponding to each of the modulation wave functions, and obtaining a first capacitor current average value of each capacitor in each switching cycle within a fundamental wave cycle based on the modulation wave value and each of the first current values;

[0045] Determine an average value of a second capacitor current flowing through each of the capacitors in one fundamental wave period based on an average value of the first capacitor current of each of the capacitors;

[0046] Based on the first capacitor current average value and the second capacitor current average value, acquiring the instantaneous value of the capacitor current of each of the capacitors within one fundamental wave period;

[0047] The instantaneous value of each capacitor current is processed based on a preset method to determine the minimum capacitance value of each capacitor; and the selection of each capacitor in the unified power quality conditioner is determined based on each minimum capacitance value.

[0048] In a fifth aspect, the present application further provides a computer program product, including a computer program, which implements the following steps when executed by a processor:

[0049] When the unified power quality conditioner is in a preset operating condition, obtaining modulation wave functions of space vector pulse width modulation corresponding to the input AC port and the output AC port of each phase of the unified power quality conditioner, respectively; wherein the preset operating condition includes a rated condition and a limit condition;

[0050] Acquire first current values ​​respectively corresponding to the input AC port and the output AC port of each phase;

[0051] Obtaining a modulation wave value corresponding to each of the modulation wave functions, and obtaining a first capacitor current average value of each capacitor in each switching cycle within a fundamental wave cycle based on the modulation wave value and each of the first current values;

[0052] Determine an average value of a second capacitor current flowing through each of the capacitors in one fundamental wave period based on an average value of the first capacitor current of each of the capacitors;

[0053] Based on the first capacitor current average value and the second capacitor current average value, acquiring the instantaneous value of the capacitor current of each of the capacitors within one fundamental wave period;

[0054] The instantaneous value of each capacitor current is processed based on a preset method to determine the minimum capacitance value of each capacitor; and the selection of each capacitor in the unified power quality conditioner is determined based on each minimum capacitance value.

[0055] The present application provides a capacitor selection method, device, computer equipment, computer-readable storage medium and computer program product for a unified power quality conditioner. The capacitor selection method for a unified power quality conditioner comprises: obtaining, when the unified power quality conditioner is in a preset operating condition, a modulation wave function of space vector pulse width modulation corresponding to the input AC port and the output AC port of each phase of the unified power quality conditioner; wherein the preset operating condition includes a rated condition and an extreme condition; obtaining first current values ​​corresponding to the input AC port and the output AC port of each phase; obtaining a modulation wave value corresponding to each modulation wave function; and obtaining a modulation wave value corresponding to each modulation wave function based on the modulation wave value and each first current. The method comprises the following steps: determining a first capacitor current average value of each capacitor in each switching cycle within a fundamental cycle; determining a second capacitor current average value flowing through each capacitor in a fundamental cycle based on the first capacitor current average value of each capacitor; obtaining the instantaneous value of the capacitor current of each capacitor within a fundamental cycle based on the first capacitor current average value and the second capacitor current average value; processing the instantaneous value of each capacitor current based on a preset method to determine the minimum capacitance value of each capacitor; determining the selection of each capacitor in the unified power quality conditioner through each minimum capacitance value; thereby obtaining a capacitor selection that is more in line with the application scenario of UPQC for power quality management, which is beneficial to ensuring the power supply quality of the power grid for the load. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the drawings required for use in the embodiments of the present application or related technical descriptions will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0057] Figure 1A circuit structure diagram of a unified power quality conditioner in one embodiment;

[0058] Figure 2 A schematic diagram of a flow chart of a method for selecting capacitors for a unified power quality conditioner in one embodiment;

[0059] Figure 3 A schematic diagram of a flow chart of a method for selecting capacitors for a unified power quality conditioner in another embodiment;

[0060] Figure 4 A schematic diagram of a flow chart of a method for selecting capacitors for a unified power quality conditioner in another embodiment;

[0061] Figure 5 1 is a voltage and current phasor diagram of the grid side and the load side of a transformerless UPQC in one embodiment;

[0062] Figure 6 A schematic diagram of three level combinations including level P of a transformerless UPQC in one embodiment;

[0063] Figure 7 is a schematic diagram of a comparison result of a modulation wave and a carrier wave and a corresponding first DC capacitor current in an embodiment;

[0064] Figure 8 A schematic diagram of a flow chart of a method for selecting capacitors for a unified power quality conditioner in yet another embodiment;

[0065] Fig. 9 is a simulation waveform diagram of the first DC capacitor voltage under rated working conditions in one embodiment;

[0066] Fig.10 is a simulation waveform diagram of the first DC capacitor voltage under extreme working conditions in an embodiment;

[0067] Fig.11 A structural block diagram of a capacitor selection device for a unified power quality conditioner in one embodiment;

[0068] Fig.12 FIG. 4 is a diagram showing the internal structure of a computer device in one embodiment. DETAILED DESCRIPTION

[0069] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0070] In recent years, with the large-scale access of distributed energy such as photovoltaics, DC loads such as electric vehicle charging piles, and nonlinear and impact loads in low-voltage distribution networks, the harmonic content and imbalance of low-voltage feeder currents have increased significantly, affecting the safe and stable operation of the power grid. Therefore, power quality management has become a research hotspot. In related technologies, devices for managing power quality include: passive filters, dynamic voltage restorers (Dynamic Voltage Restorer, DVR), active power filters (Active Power Filter, APF), and unified power quality conditioners (Unified Power Quality Conditioner, UPQC). Among them, UPQC has the ability to solve a variety of power quality problems such as current harmonics and load imbalance, and is a comprehensive power quality management device.

[0071] In the related art, UPQC is generally composed of a parallel APF and a series APF, which are connected to each other through a common DC bus containing DC capacitors. The series APF is responsible for compensating the voltage fundamental wave, voltage harmonics, etc., and the parallel APF is responsible for compensating the current harmonics, reactive current, unbalanced current, etc. However, the general UPQC topology requires an industrial frequency transformer to achieve voltage compensation, which is expensive and bulky. Therefore, a method such as Figure 1 The transformerless UPQC shown has two AC ports (an input AC port and an output AC port) and one DC port, the input AC port is connected to the power grid, the output AC port is connected to the load, and the DC port is connected to a common DC bus composed of a first DC side capacitor and a second DC side capacitor in series, i.e., a DC link.

[0072] Among them, the DC side capacitor is an important part of the DC link of the transformerless unified power quality conditioner, which affects the fluctuation of the DC bus voltage and thus affects the stability of the output voltage. In the relevant technology, there is no design of DC side capacitors for UPQC and power grid abnormal scenarios, and there is also no design of DC side capacitors in a transformerless UPQC with two AC ports.

[0073] Based on this, in an exemplary embodiment, Figure 2 As shown in the figure, a unified capacitor selection method for power quality conditioners is provided. Figure 1The circuit structure of the unified power quality conditioner in is used as an example to illustrate. In the relevant steps of the capacitor selection method for the unified power quality conditioner provided in this application, some data processing steps involved can be implemented through a terminal or a server connected to the terminal in communication, wherein the terminal can be but not limited to various personal computers, laptops, smart phones, tablet computers, etc., and the server can be an independent physical server, or a server cluster or distributed system composed of multiple physical servers, or a cloud server providing cloud computing services.

[0074] For details, please refer to Figure 1 and Figure 2 The capacitor selection method for a unified power quality conditioner provided in the present application includes the following steps 101 to 106. Among them:

[0075] Step 101, when the unified power quality conditioner is in a preset operating condition, obtain the modulation wave function of the space vector pulse width modulation corresponding to the input AC port and the output AC port of each phase of the unified power quality conditioner; wherein the preset operating condition includes the rated condition and the limit condition.

[0076] The rated operating condition refers to the operating condition under which the unified power quality conditioner operates according to the operating parameters specified during design; the limit operating condition refers to the worst operating condition among multiple harsh operating conditions that the unified power quality conditioner is in. Harsh operating conditions may include, for example, three-phase voltage amplitude drop, single-phase ground fault, two-phase short circuit fault, and two-phase ground fault.

[0077] The capacitor is, for example, Figure 1 C shown in dc1 and C dc2 . That is, the DC side capacitor in the transformerless UPQC.

[0078] Exemplarily, the unified power quality conditioner is controlled to operate in a pre-selected operating condition, that is, to operate in a rated condition or an extreme condition, and then, during the operation of the unified power quality conditioner, the modulation wave function of the space vector pulse width modulation (SVPWM) corresponding to the input AC port and the output AC port of each phase is obtained. The present application does not limit the method for obtaining the modulation wave function of the space vector pulse width modulation, and an optional acquisition method will be provided later.

[0079] Step 102: Obtain first current values ​​corresponding to the input AC port and the output AC port of each phase respectively.

[0080] Exemplarily, when the unified power quality conditioner is controlled to operate in a preselected operating condition, first current values ​​corresponding to the input AC port and the output AC port of each phase are obtained to calculate the current flowing through the capacitor in the unified power quality conditioner.

[0081] Step 103, obtaining the modulation wave value corresponding to each modulation wave function, and obtaining the first capacitor current average value of each capacitor in each switching cycle within a fundamental wave cycle based on the modulation wave value and each first current value.

[0082] Exemplarily, for each modulation wave function of space vector pulse width modulation, the corresponding modulation wave value is obtained, and based on the value of each modulation wave value and the first current value corresponding to each input AC port and output AC port obtained by executing step 102, the first capacitor current average value of each capacitor in each single switching cycle is determined.

[0083] Step 104 : determining an average value of a second capacitor current flowing through each capacitor in one fundamental wave period based on an average value of the first capacitor current of each capacitor.

[0084] For example, after calculating the first capacitor current average value of each capacitor in each single switching cycle, the second capacitor current average value flowing through each capacitor in a fundamental cycle can be further calculated, that is, the DC component of the current flowing through the capacitor in a fundamental cycle can be obtained.

[0085] Step 105 : acquiring instantaneous values ​​of capacitor currents of each capacitor within a fundamental wave period based on the first capacitor current average value and the second capacitor current average value.

[0086] Exemplarily, by using a preset calculation method, correlation calculation is performed on the first capacitor current average value and the second capacitor current average value corresponding to each capacitor, so that the instantaneous value of the capacitor current of each capacitor within a fundamental wave period can be obtained.

[0087] Step 106, processing the instantaneous value of each capacitor current based on a preset method to determine the minimum capacitance value of each capacitor; and determining the selection of each capacitor in the unified power quality conditioner based on each minimum capacitance value.

[0088] Exemplarily, after obtaining the instantaneous value of the capacitor current of each capacitor, the instantaneous value of the capacitor current can be processed by a preset processing method to obtain the minimum capacitance value corresponding to each capacitor; after knowing the minimum capacitance value of each capacitor, the selection type corresponding to each capacitor can be determined based on this, that is, the selection type of each capacitor in the unified power quality conditioner can be determined through each minimum capacitance value.

[0089] In the capacitor selection method of the unified power quality conditioner, when the unified power quality conditioner is in a preset operating condition, the modulation wave function of the space vector pulse width modulation corresponding to the input AC port and the output AC port of each phase of the unified power quality conditioner is obtained; wherein the preset operating condition includes the rated condition and the limit condition; the first current values ​​corresponding to the input AC port and the output AC port of each phase are obtained; the modulation wave value corresponding to each modulation wave function is obtained, and based on the modulation wave value and each first current value, the first capacitor current average value of each capacitor under each switching cycle within a fundamental cycle is obtained; based on the first capacitor current average value of each capacitor, the second capacitor current average value flowing through each capacitor under a fundamental cycle is determined; based on the first capacitor current average value and the second capacitor current average value, the instantaneous value of the capacitor current of each capacitor within a fundamental cycle is obtained; the instantaneous value of each capacitor current is processed based on a preset method to determine the minimum capacitance value of each capacitor; the selection of each capacitor in the unified power quality conditioner is determined by each minimum capacitance value; thereby obtaining a capacitor selection that is more in line with the application scenario of UPQC for power quality management, which is conducive to ensuring the power supply quality of the power grid for the load.

[0090] In an exemplary embodiment, the above step 102 is performed to obtain the first current values ​​corresponding to the input AC port and the output AC port of each phase, which can be selectively performed as follows: based on the input current amplitude of the input AC port, the output current amplitude of the output AC port, the angle by which the input AC port current leads the input AC port voltage, the angle by which the load voltage lags behind the output AC port voltage, the angle by which the load current lags behind the load voltage, and the angle that changes with time, of each phase of the unified power quality conditioner, obtain the first current values ​​corresponding to the input AC port and the output AC port of each phase; wherein the load is electrically connected to the output AC port of the unified power quality conditioner.

[0091] For example, the input current amplitude of the input AC port can be expressed as I in ; The output current amplitude of the output AC port can be expressed as I out ; The angle at which the input AC port current leads the input AC port voltage can be expressed as β; The angle at which the load voltage lags behind the output AC port voltage can be expressed as γ; The angle at which the load current lags behind the load voltage can be expressed as The angle that changes with time can be represented as θ.

[0092] The specific calculation method of the first current values ​​corresponding to the input AC port and the output AC port of each phase will be shown in the relevant embodiments below.

[0093] In an exemplary embodiment, please refer to Figure 1 and Figure 3, when the operating condition of the unified power quality conditioner in step 101 is an extreme condition, before executing step 101, when the unified power quality conditioner is in a preset operating condition, it also includes steps 107 and 108, wherein:

[0094] Step 107, determining, among multiple operating conditions of the unified power quality conditioner, a power grid electrically connected to the unified power quality conditioner, and an operating condition corresponding to a power grid voltage with the lowest positive sequence component as an extreme operating condition; wherein the power grid is electrically connected to an input AC port of the unified power quality conditioner;

[0095] Step 108, operating the unified power quality conditioner based on the extreme operating condition, and obtaining the input current amplitude of the input AC port of each phase of the unified power quality conditioner; the input current amplitude is used to obtain the first current value of the corresponding input AC port.

[0096] in, Figure 3 The article provides a capacitor selection method when the unified power quality conditioner is in an extreme severe working condition. The extreme working condition is the worst working condition among multiple severe working conditions in which the unified power quality conditioner is in.

[0097] Exemplarily, when the unified power quality conditioner is operated under various severe operating conditions, the positive sequence component of the grid voltage corresponding to the grid electrically connected to the unified power quality conditioner can be obtained, and the operating condition when the grid voltage has the lowest positive sequence component is taken as the extreme condition. Then, in the process of operating the unified power quality conditioner based on the extreme condition, the input current amplitude of the input AC port of each phase of the unified power quality conditioner is obtained, and the output current amplitude of the output AC port of each phase of the unified power quality conditioner can be further obtained, so as to facilitate the subsequent calculation of the first current values ​​corresponding to each input AC port and output AC port. That is, the execution of step 107 and step 108 can lay the foundation for the subsequent execution of steps 101 and 102, and provide some data required for the execution of steps 101 and 102.

[0098] In an exemplary embodiment, the above step 101 is performed to obtain the modulation wave function of the space vector pulse width modulation corresponding to the input AC port and the output AC port of each phase of the unified power quality conditioner, which can be achieved by executing steps 111 to 113, wherein:

[0099] Step 111, obtaining the sinusoidal pulse width modulation wave functions corresponding to the input AC port and the output AC port of each phase under the sinusoidal pulse width modulation modulation mode of the unified power quality conditioner;

[0100] Step 112, determining an input zero-sequence component based on a sinusoidal pulse width modulation wave function of each input AC port; and determining an output zero-sequence component based on a sinusoidal pulse width modulation wave function of each output AC port;

[0101] Step 113, based on the sum of the sinusoidal pulse width modulation wave function of each input AC port and the input zero-sequence component, determine the modulation wave function of the space vector pulse width modulation corresponding to each input AC port; and based on the sum of the sinusoidal pulse width modulation wave function of each output AC port and the output zero-sequence component, determine the modulation wave function of the space vector pulse width modulation corresponding to each output AC port.

[0102] Exemplarily, under rated operating conditions, when the grid voltage is normal, the phases of the modulation waves of the input AC port and the output AC port are artificially made the same, and then, first, the sinusoidal pulse width modulation wave functions corresponding to the input AC port and the output AC port of each phase of the unified power quality conditioner under the modulation mode of sinusoidal pulse width modulation are obtained, and then, based on the obtained sinusoidal pulse width modulation wave functions of each input AC port, the corresponding zero-sequence component is calculated to obtain the input zero-sequence component; and, based on the obtained sinusoidal pulse width modulation wave functions of each output AC port, the corresponding zero-sequence component is calculated to obtain the output zero-sequence component; then, by superimposing the sinusoidal pulse width modulation wave functions of each input AC port with the input zero-sequence component, the modulation wave function of the space vector pulse width modulation corresponding to each input AC port can be obtained, and, by superimposing the sinusoidal pulse width modulation wave functions of each output AC port with the output zero-sequence component, the modulation wave function of the space vector pulse width modulation corresponding to each output AC port can be obtained.

[0103] In an exemplary embodiment, the above step 104 is performed to determine the average value of the second capacitor current flowing through each capacitor in a fundamental wave cycle based on the average value of the first capacitor current of each capacitor. It can be specifically performed as follows: within a fundamental wave cycle, based on the integration calculation of the average value of the first capacitor current of each capacitor, to determine the average value of the second capacitor current flowing through each capacitor in a fundamental wave cycle.

[0104] Exemplarily, after obtaining the first capacitor current average value of each capacitor, the current average value (second capacitor current average value) within a fundamental wave cycle, ie, the DC component of the current flowing through the capacitor, may be calculated by integration.

[0105] In an exemplary embodiment, the above step 105 is performed to obtain the instantaneous value of the capacitor current of each capacitor within a fundamental wave period based on the first capacitor current average value and the second capacitor current average value, which can be specifically performed as follows: based on the difference between the first capacitor current average value and the second capacitor current average value corresponding to each capacitor, the instantaneous value of the capacitor current of each capacitor within a fundamental wave period is obtained.

[0106] Exemplarily, the instantaneous value of the capacitor current of each capacitor within a cycle may be obtained by performing a difference operation on the first capacitor current average value and the second capacitor current average value corresponding to each capacitor that have been acquired.

[0107] In an exemplary embodiment, the above step 106 is performed based on a preset method to process the instantaneous value of each capacitor current to determine the minimum capacitance value of each capacitor. It can be specifically performed as follows: based on the time integration of the instantaneous value of each capacitor current, the corresponding capacitor charge and discharge charge is obtained, and then based on the capacitor definition formula and the preset capacitor voltage ripple requirement, the minimum capacitance value of each capacitor is determined.

[0108] For example, when the instantaneous value of the capacitor current within a fundamental cycle of each capacitor is obtained, the charge amount of the capacitor charge and discharge can be obtained by time integration of the instantaneous value of the capacitor current, and then the theoretical minimum capacitance value is calculated according to the capacitor definition formula and the capacitor voltage ripple requirement. The capacitor definition formula is C=Q / U.

[0109] The capacitor selection method for the unified power quality conditioner provided in this application is also a DC side capacitor design method suitable for rated working conditions of transformerless UPQC. The design of the DC side capacitor needs to meet the requirements of capacitor voltage ripple. The first and second DC side capacitors (such as Figure 1 C dc1 and C dc2 ) are theoretically consistent, so during design, you can choose to consider only one of them. Exemplarily, a design for the first DC side capacitor is also provided.

[0110] The topology of transformerless UPQC is as follows: Figure 1 As shown, the design steps of DC side capacitor under rated working conditions are as follows Figure 4 As shown. Under rated working conditions, the input and output AC port currents both reach 1p.u., and the instantaneous current value is obtained by calculating the average current flowing through the DC capacitor in a switching cycle and a fundamental wave cycle, subtracting them, and then integrating the time to obtain the change in capacitor charge. The capacitor voltage ripple can then be calculated based on the capacitor definition formula.

[0111] The specific design steps may include the following steps S1 to S6, wherein:

[0112] Step S1, calculating the function corresponding to the three-phase modulation wave of the input and output AC ports under the space vector pulse width modulation (SVPWM) mode.

[0113] The principle of SVPWM modulation is to superimpose a zero-sequence component on the modulation wave of sinusoidal pulse width modulation (SPWM) to obtain a higher DC voltage utilization rate. Under rated conditions, the grid voltage is normal, and the control part artificially makes the phase of the modulation wave of the input and output AC ports the same, so we can get:

[0114]

[0115] Wherein, mx,in,SPWM (x = a, b, c) and mx,out,SPWM (x = a, b, c) represent the modulation wave functions of the input and output AC ports under the SPWM modulation mode, respectively. The subscripts "in" and "out" correspond to the input and output AC ports, respectively. Min and Mout are the amplitudes of the three-phase modulation waves of the input and output AC ports, respectively (approximately equal to 1 p.u. under rated conditions), and θ is the angle (radian) that changes with time.

[0116] The zero sequence component is calculated as:

[0117]

[0118] In the formula, m 0,in and m 0,out is the superimposed zero-sequence component, and the max() and min() functions are the functions for taking the maximum and minimum values ​​respectively.

[0119] By superimposing this zero-sequence component on the SPWM modulation wave, the modulation wave function of the input and output AC ports under the SVPWM mode can be obtained.

[0120]

[0121] Step S2, calculating the three-phase rated current of the input and output AC ports.

[0122] Under rated operating conditions, the current of the input and output AC ports is the rated value of 1p.u. However, due to the existence of the filter, the current phase is inconsistent with the voltage of the corresponding port (the fundamental voltage output by each port according to the modulation wave). The specific voltage and current phasor diagram is as follows: Figure 5 As shown in the figure. g 、i g is the voltage and current on the grid side, u in 、i in is the input AC port voltage and current, when the filter capacitor branch is ignored g and i in Same, u Lin and u Rin is the voltage drop across the filter inductor and its parasitic resistance; uL 、i L is the load side voltage and current, u out and i out is the output AC port voltage and current, when the filter capacitor branch is ignored L and i out Same, u Lout and u Rout is the voltage drop across the filter inductor and its parasitic resistance.

[0123] The expression of input AC port current can be written as:

[0124]

[0125] In the formula, I in is the current amplitude, θ is the angle that changes with time (in radians), and β is the angle at which the input AC port current leads the input AC port voltage.

[0126] The expression of the output AC port current can be written as:

[0127]

[0128] In the formula, I out is the current amplitude, θ is the angle that changes with time (in radians), γ is the angle at which the load voltage lags behind the output AC port voltage, It is the angle that the load current lags behind the load voltage, that is, the power factor angle.

[0129] According to the voltage and current phasor diagram, the above leading and lagging angles can be calculated under the premise of known port voltage and current amplitude:

[0130]

[0131] In the formula, u Lin is the inductor voltage drop of the input AC port filter, u Rin Its parasitic resistance voltage drop, u g is the grid voltage; u Lout is the inductor voltage drop of the output AC port filter, u Rout Its parasitic resistance voltage drop, u out is the fundamental component of the output AC port voltage.

[0132] Step S3, calculating the current average value of each switching cycle within a fundamental wave cycle.

[0133] The switching states of the transformerless UPQC and the corresponding levels of the input and output AC ports are shown in Table 1, which includes level P, level OU, level OL, and level N.

[0134] Table 1

[0135]

[0136] First, preprocess the three-phase modulation wave function of the input and output AC ports: when the value of the modulation wave is greater than 0, no change is made; when the value of the modulation wave is less than 0, it is changed to 0. This is because what needs to be calculated is the current flowing through the first DC capacitor, and no matter for the input or output AC port, as long as the output level is P, there will be current flowing through the first DC capacitor. Take phase a as an example, Figure 6 As shown, the level combinations included are PP, P-OL, OL-P ( Figure 6 The current direction in is just a special case. There are other situations in practice, which are not given here due to space limitations).

[0137] The value of the modulation wave corresponds to the duty cycle. When its value is greater than 0, the port level switches between OL and P at high frequency; when its value is less than 0, the port level switches between OU and N at high frequency. Since the three-phase modulation waves are 120° apart, there will only be two situations in which two phases are positive and one phase is negative, or one phase is positive and two phases are negative. According to the above preprocessing method, it becomes two phases positive and one phase is 0, or one phase is positive and two phases are 0. Figure 7 As shown, two special cases are given where phases a and b are positive and phase a is positive. That is, Figure 7 The case where two phases of modulation wave are greater than 0 is taken as an example of phases a and b, and the case where one phase of modulation wave is greater than 0 is taken as an example of phase a. Figure 7 It can be seen that when the level of a phase is P, the first DC capacitor current includes the current of this phase, so the average value of the capacitor current in a single switching cycle is:

[0138]

[0139] Where θ is the angle corresponding to the current switching cycle, and sign() is defined as

[0140] Step S4, calculating the average current value within a fundamental wave period, that is, the DC component of the current flowing through the capacitor, by integration.

[0141] The average current value within a fundamental cycle can be written as an integral and then averaged form:

[0142]

[0143] The calculation formula for the average value of the capacitor current in the above single switching cycle is applicable to all switching cycles in the fundamental cycle, so the integral formula is discretized and converted into the form of integrating and summing the average current values ​​of each switching cycle:

[0144]

[0145] In the formula, f s is the switching frequency, f is the fundamental frequency, and Δθ is the angle element. From this formula, the average value of the current flowing through the first DC capacitor within one fundamental cycle can be calculated, which represents the DC component of the capacitor current.

[0146] Step S5, subtracting the calculation results of step S3 and step S4 to obtain the instantaneous value of the capacitor current without a DC component within one fundamental wave period.

[0147] The result of subtracting the two equations is: C (θ) = i Ts,ave (θ)-I T,ave .

[0148] Step S6, time-integrating the instantaneous value of the capacitor current to obtain the charge amount of the capacitor, and then calculating the theoretical minimum capacitance value according to the capacitance definition formula and the capacitor voltage ripple requirement.

[0149] The charge function of a DC capacitor is:

[0150]

[0151] Where ω is the fundamental angular frequency.

[0152] From this we can get the peak-to-peak value of the charge change: Q C,pp =Q Cmax -Q Cmin；

[0153] In the formula, Q Cmax and Q Cmin Q C The maximum and minimum values ​​of (θ).

[0154] Assume that the capacitor voltage ripple requirement is less than U C,pp , then according to the capacitance definition C = Q / U, the DC capacitance value should satisfy:

[0155] In addition, the present application also provides another DC side capacitor design method suitable for transformerless UPQC under extreme working conditions. When an abnormality occurs in the power grid, the input AC port current will change, while the output AC port current will not change due to the compensation of UPQC. Considering the situation where the grid voltage drops, the input AC port current will rise sharply, thereby increasing the current flowing into the first and second DC capacitors, thereby exacerbating the fluctuation of the DC side voltage, and further affecting the load voltage quality. Therefore, the DC capacitor is designed under extreme working conditions in order to ensure that the capacitor voltage ripple requirements can still be met under abnormal conditions of the power grid, to ensure the stability of the DC side voltage and the normal power supply of the load.

[0156] The design principle is to ensure that the DC side capacitor can meet the capacitor voltage ripple requirements when the grid voltage is abnormal. The design steps under extreme conditions are as follows: Figure 8 Compared with the design steps under rated conditions, the first two steps are added: selecting the extreme conditions and calculating the current amplitude under the extreme conditions, and the subsequent steps remain unchanged.

[0157] Among them, Figure 8 As shown, the extreme operating conditions of the transformerless UPQC are first selected.

[0158] For 0.4kV low-voltage distribution network, when the grid voltage is abnormal, especially when the grid voltage drops, the positive sequence component of the voltage decreases, and the input AC port current must increase to ensure sufficient active power supply. Therefore, the selection principle of the extreme working condition is that the positive sequence component of the 0.4kV grid voltage is the lowest. Voltage drops are divided into symmetrical drops and asymmetrical drops, which are mostly caused by symmetrical faults and asymmetrical faults of the upper line.

[0159] Symmetrical faults are three-phase grounding faults. Under normal circumstances, the transformerless UPQC only responds to three-phase voltage drops with an amplitude of 0.5pu to 1p.u. after the drop, that is, the minimum positive sequence component of the voltage is 0.5pu.

[0160] Asymmetric faults include single-phase grounding faults, two-phase short-circuit faults, and two-phase grounding faults. Take a typical 220kV / 10.5kV / 0.4kV three-level line as an example, where the 220kV / 10.5kV transformer uses YNd11 wiring, the 10.5kV / 0.4kV transformer uses Dyn11 wiring, the neutral point of the 220kV and 0.4kV systems is directly grounded, and the neutral point of the 10.5kV system is not grounded. Considering the worst case, ignoring any impedance, after fault analysis and positive and negative sequence decomposition, we can get:

[0161] After a single-phase grounding fault occurs in a 220kV line (taking phase a as an example), the amplitude of the positive sequence component of the 0.4kV line phase voltage becomes 2 / 3p.u., the phase remains unchanged, the amplitude of the negative sequence component is 1 / 3p.u., and the phase leads the positive sequence component by 60°, that is:

[0162]

[0163] Where U a1 and U a2 They are the positive-sequence and negative-sequence components of phase a voltage respectively. Phase b and phase c can be inferred by analogy using the three-phase symmetry relationship.

[0164] After a two-phase short circuit fault occurs in a 220kV line (taking phase bc as an example), the amplitude of the positive sequence component of the 0.4kV line phase voltage becomes 0.5pu, the phase remains unchanged, the amplitude of the negative sequence component is 0.5pu, and the phase leads the positive sequence component by 120°, that is:

[0165]

[0166] After a two-phase grounding fault occurs in a 220kV line (taking phase bc as an example), the amplitude of the positive sequence component of the 0.4kV line phase voltage becomes 1 / 3 p.u., the phase remains unchanged, the amplitude of the negative sequence component is 1 / 3 p.u., and the phase leads the positive sequence component by 120°, that is:

[0167]

[0168] In summary, when a two-phase grounding fault occurs in a 220kV line, the positive sequence component of the phase voltage of the 0.4kV line is the lowest, which is 1 / 3p.u., so this situation is selected as the extreme operating condition.

[0169] Then, calculate the current amplitude under the extreme conditions.

[0170] After a two-phase grounding fault occurs in the 220kV line, the amplitude of the positive sequence component of the 0.4kV line phase voltage becomes 1 / 3p.u. According to the control method of the transformerless UPQC, the input AC port current is always a three-phase symmetrical sine wave, which interacts with the positive sequence component of the grid voltage to generate power. If the load is a rated pure resistive load, that is, the load side requires 1p.u. of active power, and the grid side needs to input 1p.u. of active power without considering the device and line losses, the amplitude of the input AC port current will reach 3p.u. (assuming that the distribution line can withstand such a large current in a short time).

[0171] The subsequent steps are consistent with the capacitor design method under rated conditions.

[0172] It can be seen that the capacitor selection method for the unified power quality conditioner provided in this application has the following beneficial effects: This application takes into account the influence of the dual-port current of the transformerless UPQC on the DC side capacitor voltage, and designs the capacitor through accurate current calculation and voltage ripple requirements. The capacitor design method under extreme working conditions proposed in this application is more in line with the application scenario of UPQC for power quality management, and can also ensure the load power supply quality under abnormal power grid conditions.

[0173] That is, the present application proposes a DC side capacitor design method that takes into account rated operating conditions and extreme operating conditions, and calculates the lower limit of the DC side capacitor value by calculating the instantaneous value of the capacitor current and the limitations of the capacitor voltage ripple requirements.

[0174] The following is a detailed description with reference to specific embodiments.

[0175] Embodiment 1 is provided; Embodiment 1 corresponds to a DC side capacitor design method considering rated working conditions. Taking a 100kVA transformerless UPQC as an example, the main circuit parameters are shown in Table 2, and the parasitic resistance is calculated as 5% of the impedance.

[0176] Table 2

[0177]

[0178] The three-phase SPWM modulation wave of the input AC port is:

[0179]

[0180] The three-phase SPWM modulation wave of the output AC port is:

[0181]

[0182] Where U m is the phase voltage amplitude, V dc is the DC bus voltage. The phases of the three-phase SPWM modulation waves at the input and output AC ports are still the same, and the SVPWM modulation wave can be obtained after the zero-sequence component is superimposed.

[0183] The β angle is calculated through the voltage and current phasor diagram, and the three-phase current of the input AC port is:

[0184]

[0185] The γ angle is calculated through the voltage and current phasor diagram. At the same time, since it is a pure resistive load, is 0, then the three-phase current of the output AC port is:

[0186]

[0187] according to Figure 4 The steps shown are to calculate the average value of the capacitor current in each switching cycle, then integrate to obtain the average value of the capacitor current in a fundamental cycle, subtract to obtain the instantaneous value of the capacitor current without DC component, and finally obtain the peak-to-peak value of the capacitor charge change: Q C,pp =0.08C.

[0188] The capacitor voltage ripple is generally required not to exceed 2% of the capacitor voltage, that is, 0.01pu DC side voltage, so the lower limit of the DC side capacitor is:

[0189]

[0190] Embodiment 2 is provided; Embodiment 2 corresponds to a DC side capacitor design method considering extreme working conditions. Taking a 100kVA transformerless UPQC as an example, the main circuit parameters are still as shown in Table 2, and the parasitic resistance is calculated as 5% of the impedance.

[0191] Taking the case of a two-phase grounding fault of ab in a 220kV line as an example, the three-phase SPWM modulation wave of the input AC port is:

[0192]

[0193] The three-phase SPWM modulation wave of the output AC port is:

[0194]

[0195] After superposition of zero-sequence components, the SVPWM modulation wave can be obtained.

[0196] Under extreme conditions, the β angle is calculated through the voltage and current phasor diagram, and the three-phase current of the input AC port is:

[0197]

[0198] The γ angle is calculated through the voltage and current phasor diagram. At the same time, since it is a pure resistive load, is 0, then the three-phase current of the output AC port is:

[0199]

[0200] according to Figure 8 The steps shown are to calculate the average value of the capacitor current in each switching cycle, then integrate to obtain the average value of the capacitor current in a fundamental cycle, subtract to obtain the instantaneous value of the capacitor current without DC component, and finally obtain the peak-to-peak value of the capacitor charge change: Q C,pp =0.437C.

[0201] The capacitor voltage ripple is generally required not to exceed 2% of the capacitor voltage, that is, 0.01pu DC side voltage, so the lower limit of the DC side capacitor is:

[0202]

[0203] The application of the method in the above embodiment is further explained below in conjunction with a specific simulation example. MATLAB / Simulink 2021a software is used to perform simulation verification on the system.

[0204] Simulation Example 1, refer to Figure 4 and Fig. 9, which is the first simulation example of this application, and the simulation parameters are shown in Table 3. This example provides a simulation verification of the effectiveness of the DC side capacitor design method under rated conditions, as follows:

[0205] Table 3

[0206] Simulation parameters Numeric Device rated capacity <![CDATA[S N =100kVA]]> Power supply side node line voltage <![CDATA[u g =380V,f=50Hz]]> Input AC port LCL filter <![CDATA[L in1 =46μH,C in =10μF,L in2 =9μH]]> Load side node line voltage <![CDATA[u L =380V,f=50Hz]]> Load power <![CDATA[P load =100kW]]> Output AC port LC filter <![CDATA[L out =46μH,C out =10μF]]> DC port voltage <![CDATA[V dc =750V]]> DC link capacitor <h2 style=";text-align:left;direction:ltr"><![CDATA[C <h2 style=";text-align:left;direction:ltr"> dc <h2 style=";text-align:left;direction:ltr"> <10.7mF]]><h2 style=";text-align:left;direction:ltr"> Switching frequency <![CDATA[f sw =40kHz]]>

[0207] As attached Fig. 9 As shown, it is the voltage V of the first DC capacitor dc1 The horizontal axis is time t, in seconds (s), and the vertical axis is capacitor voltage, in pu (1p.u represents 750V). This simulation waveform shows that the peak-to-peak value of the capacitor voltage is around 0.0085pu, which means that when the DC side capacitor is designed according to the rated working conditions, the capacitor voltage ripple can be limited to the required 0.01pu range.

[0208] Simulation Example 2, refer to Figure 8 and Fig.10 , which is the second simulation example of this application, and the simulation parameters are shown in Table 4. This example provides simulation verification of the effectiveness of the DC side capacitor design method under extreme working conditions, as follows:

[0209] Table 4

[0210]

[0211] As attached Fig.10 As shown, the voltage V of the first DC capacitor dc1 The horizontal axis is time t, in seconds (s), and the vertical axis is capacitor voltage, in pu (1p.u. represents 750V). This simulation waveform shows that the peak-to-peak value of the capacitor voltage fluctuation is around 0.008pu, which means that when the DC side capacitor is designed according to the extreme working conditions, when the power grid experiences a severe sag, the capacitor voltage ripple can still be limited to the required 0.01pu range to ensure the power supply quality of the load.

[0212] It should be understood that, although the various steps in the flowcharts involved in the above-mentioned embodiments are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps does not have a strict order restriction, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above-mentioned embodiments can include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0213] Based on the same inventive concept, the embodiment of the present application also provides a capacitor selection device for a unified power quality conditioner for implementing the capacitor selection method for the unified power quality conditioner involved above. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above method, so the specific limitations in the embodiments of one or more capacitor selection devices for unified power quality conditioners provided below can refer to the limitations of the capacitor selection method for unified power quality conditioners above, and will not be repeated here.

[0214] In an exemplary embodiment, Fig.10 As shown, a capacitor selection device 800 for a unified power quality conditioner is provided, comprising: a data acquisition module 81, a data processing module 82 and a capacitor selection module 83, wherein:

[0215] The data acquisition module 81 is used to obtain the modulation wave function of the space vector pulse width modulation corresponding to the input AC port and the output AC port of each phase of the unified power quality conditioner when the unified power quality conditioner is in a preset operating condition; wherein the preset operating condition includes a rated condition and an extreme condition;

[0216] The data acquisition module 81 is also used to acquire the first current values ​​corresponding to the input AC port and the output AC port of each phase respectively;

[0217] The data processing module 82 is used to obtain the modulation wave value corresponding to each modulation wave function, and obtain the first capacitor current average value of each capacitor in each switching cycle within a fundamental wave cycle based on the modulation wave value and each first current value;

[0218] The data processing module 82 is further used to determine an average value of a second capacitor current flowing through each capacitor in a fundamental wave cycle based on an average value of the first capacitor current of each capacitor;

[0219] The data processing module 82 is further used to obtain the instantaneous value of the capacitor current of each capacitor within a fundamental wave period based on the first capacitor current average value and the second capacitor current average value;

[0220] The capacitor selection module 83 is used to process the instantaneous value of each capacitor current based on a preset method to determine the minimum capacitance value of each capacitor; and determine the selection of each capacitor in the unified power quality conditioner through each minimum capacitance value.

[0221] In an exemplary embodiment, the data acquisition module 81 is used to obtain the first current values ​​corresponding to the input AC port and the output AC port of each phase, specifically for: based on the input current amplitude of the input AC port, the output current amplitude of the output AC port, the angle of the input AC port current leading the input AC port voltage, the angle of the load voltage lagging the output AC port voltage, the angle of the load current lagging the load voltage, and the angle changing with time of each phase of the unified power quality conditioner, to obtain the first current values ​​corresponding to the input AC port and the output AC port of each phase; wherein the load is electrically connected to the output AC port of the unified power quality conditioner.

[0222] In an exemplary embodiment, the capacitor selection device 800 of the unified power quality conditioner also includes an extreme operating condition determination module, which is used to determine, among multiple operating conditions of the unified power quality conditioner, that the power grid electrically connected to the unified power quality conditioner, the corresponding power grid voltage has the lowest positive sequence component and is the extreme operating condition; wherein the power grid is electrically connected to the input AC port of the unified power quality conditioner; the data acquisition module 81 is also used to operate the unified power quality conditioner based on the extreme operating conditions, and obtain the input current amplitude of the input AC port of each phase of the unified power quality conditioner; the input current amplitude is used to obtain the first current value of the corresponding input AC port.

[0223] In an exemplary embodiment, the data acquisition module 81 is used to obtain the modulation wave functions of the space vector pulse width modulation corresponding to the input AC port and the output AC port of each phase of the unified power quality conditioner, and is specifically used to: obtain the sinusoidal pulse width modulation wave functions corresponding to the input AC port and the output AC port of each phase of the unified power quality conditioner under the modulation mode of sinusoidal pulse width modulation; determine the input zero-sequence component based on the sinusoidal pulse width modulation wave function of each input AC port; and, determine the output zero-sequence component based on the sinusoidal pulse width modulation wave function of each output AC port; determine the modulation wave function of the space vector pulse width modulation corresponding to each input AC port based on the sum of the sinusoidal pulse width modulation wave function of each input AC port and the input zero-sequence component; and, determine the modulation wave function of the space vector pulse width modulation corresponding to each output AC port based on the sum of the sinusoidal pulse width modulation wave function of each output AC port and the output zero-sequence component.

[0224] In an exemplary embodiment, the data processing module 82 is used to determine the average value of the second capacitor current flowing through each capacitor in a fundamental wave cycle based on the average value of the first capacitor current of each capacitor, and is specifically used to: within a fundamental wave cycle, based on the integration calculation of the average value of the first capacitor current of each capacitor, to determine the average value of the second capacitor current flowing through each capacitor in a fundamental wave cycle.

[0225] In an exemplary embodiment, the data processing module 82 is used to obtain the instantaneous value of the capacitor current of each capacitor within a fundamental wave period based on the first capacitor current average value and the second capacitor current average value, and is specifically used to obtain the instantaneous value of the capacitor current of each capacitor within a fundamental wave period based on the difference between the first capacitor current average value and the second capacitor current average value corresponding to each capacitor.

[0226] In an exemplary embodiment, the data processing module 82 is used to process the instantaneous value of each capacitor current based on a preset method to determine the minimum capacitance value of each capacitor, specifically for: based on the time integration of the instantaneous value of each capacitor current, obtaining the corresponding capacitor charging and discharging charge, and then based on the capacitor definition formula and the preset capacitor voltage ripple requirement, determining the minimum capacitance value of each capacitor.

[0227] Each module in the capacitor selection device of the unified power quality conditioner can be implemented in whole or in part by software, hardware and a combination thereof. Each module can be embedded in or independent of a processor in a computer device in the form of hardware, or can be stored in a memory in a computer device in the form of software, so that the processor can call and execute operations corresponding to each module.

[0228] In an exemplary embodiment, a computer device is provided. The computer device may be a terminal, and its internal structure diagram may be as shown in FIG. Fig.11 As shown. The computer device includes a processor, a memory, an input / output interface, a communication interface, a display unit and an input device. The processor, the memory and the input / output interface are connected through a system bus, and the communication interface, the display unit and the input device are connected to the system bus through the input / output interface. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The input / output interface of the computer device is used to exchange information between the processor and an external device. The communication interface of the computer device is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner can be implemented through WIFI, a mobile cellular network, near field communication (Near Field Communication, NFC) or other technologies. When the computer program is executed by the processor, a capacitor selection method for a unified power quality conditioner is implemented. The display unit of the computer device is used to form a visually visible picture, which can be a display screen, a projection device or a virtual reality imaging device. The display screen can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device can be a touch layer covering the display screen, or a button, trackball or touchpad set on the computer device shell, or an external keyboard, touchpad or mouse.

[0229] Those skilled in the art will understand that Fig.11 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components.

[0230] In an exemplary embodiment, a computer device is provided, including a memory and a processor, wherein a computer program is stored in the memory, and when the processor executes the computer program, the following steps are implemented:

[0231] When the unified power quality conditioner is in a preset operating condition, a modulation wave function of space vector pulse width modulation corresponding to an input AC port and an output AC port of each phase of the unified power quality conditioner is obtained; wherein the preset operating condition includes a rated condition and an extreme condition;

[0232] Obtaining first current values ​​corresponding to the input AC port and the output AC port of each phase respectively;

[0233] Obtaining a modulation wave value corresponding to each modulation wave function, and obtaining a first capacitor current average value of each capacitor in each switching cycle within a fundamental wave cycle based on the modulation wave value and each first current value;

[0234] Based on the average value of the first capacitor current of each capacitor, determine the average value of the second capacitor current flowing through each capacitor in one fundamental wave cycle;

[0235] Based on the first capacitor current average value and the second capacitor current average value, obtaining the instantaneous value of the capacitor current of each capacitor within a fundamental wave period;

[0236] The instantaneous value of each capacitor current is processed based on a preset method to determine the minimum capacitance value of each capacitor; and the selection of each capacitor in the unified power quality conditioner is determined through each minimum capacitance value.

[0237] In one embodiment, a computer readable storage medium is provided, on which a computer program is stored, and when the computer program is executed by a processor, the following steps are implemented:

[0238] When the unified power quality conditioner is in a preset operating condition, a modulation wave function of space vector pulse width modulation corresponding to an input AC port and an output AC port of each phase of the unified power quality conditioner is obtained; wherein the preset operating condition includes a rated condition and an extreme condition;

[0239] Obtaining first current values ​​corresponding to the input AC port and the output AC port of each phase respectively;

[0240] Obtaining a modulation wave value corresponding to each modulation wave function, and obtaining a first capacitor current average value of each capacitor in each switching cycle within a fundamental wave cycle based on the modulation wave value and each first current value;

[0241] Based on the average value of the first capacitor current of each capacitor, determine the average value of the second capacitor current flowing through each capacitor in one fundamental wave cycle;

[0242] Based on the first capacitor current average value and the second capacitor current average value, obtaining the instantaneous value of the capacitor current of each capacitor within a fundamental wave period;

[0243] The instantaneous value of each capacitor current is processed based on a preset method to determine the minimum capacitance value of each capacitor; and the selection of each capacitor in the unified power quality conditioner is determined through each minimum capacitance value.

[0244] In one embodiment, a computer program product is provided, comprising a computer program, which, when executed by a processor, implements the following steps:

[0245] When the unified power quality conditioner is in a preset operating condition, a modulation wave function of space vector pulse width modulation corresponding to an input AC port and an output AC port of each phase of the unified power quality conditioner is obtained; wherein the preset operating condition includes a rated condition and an extreme condition;

[0246] Obtaining first current values ​​corresponding to the input AC port and the output AC port of each phase respectively;

[0247] Obtaining a modulation wave value corresponding to each modulation wave function, and obtaining a first capacitor current average value of each capacitor in each switching cycle within a fundamental wave cycle based on the modulation wave value and each first current value;

[0248] Based on the average value of the first capacitor current of each capacitor, determine the average value of the second capacitor current flowing through each capacitor in one fundamental wave cycle;

[0249] Based on the first capacitor current average value and the second capacitor current average value, obtaining the instantaneous value of the capacitor current of each capacitor within a fundamental wave period;

[0250] The instantaneous value of each capacitor current is processed based on a preset method to determine the minimum capacitance value of each capacitor; and the selection of each capacitor in the unified power quality conditioner is determined through each minimum capacitance value.

[0251] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant regulations.

[0252] Those of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile memory and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited to this. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, an artificial intelligence (AI) processor, etc., but are not limited to this.

[0253] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0254] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A method for selecting capacitors for a unified power quality conditioner, characterized in that: The method comprises: When the unified power quality conditioner is in a preset operating condition, obtaining modulation wave functions of space vector pulse width modulation corresponding to the input AC port and the output AC port of each phase of the unified power quality conditioner, respectively; wherein the preset operating condition includes a rated condition and a limit condition; Acquire first current values ​​respectively corresponding to the input AC port and the output AC port of each phase; Obtaining a modulation wave value corresponding to each of the modulation wave functions, and obtaining a first capacitor current average value of each capacitor in each switching cycle within a fundamental wave cycle based on the modulation wave value and each of the first current values; Determine an average value of a second capacitor current flowing through each of the capacitors in one fundamental wave period based on an average value of the first capacitor current of each of the capacitors; Based on the first capacitor current average value and the second capacitor current average value, acquiring the instantaneous value of the capacitor current of each of the capacitors within one fundamental wave period; The instantaneous value of each capacitor current is processed based on a preset method to determine the minimum capacitance value of each capacitor; and the selection of each capacitor in the unified power quality conditioner is determined based on each minimum capacitance value.

2. The method according to claim 1, characterized in that The obtaining of first current values ​​respectively corresponding to the input AC port and the output AC port of each phase includes: Based on the input current amplitude of the input AC port, the output current amplitude of the output AC port, the angle at which the input AC port current leads the input AC port voltage, the angle at which the load voltage lags behind the output AC port voltage, the angle at which the load current lags behind the load voltage, and the angle that changes with time, of each phase of the unified power quality conditioner, the first current values ​​corresponding to the input AC port and the output AC port of each phase are obtained; wherein the load is electrically connected to the output AC port of the unified power quality conditioner.

3. The method according to claim 2, characterized in that Before the unified power quality conditioner is in a preset operating condition, the method further includes: Among multiple operating conditions of the unified power quality conditioner, determining that the power grid electrically connected to the unified power quality conditioner, the operating condition in which the corresponding power grid voltage has the lowest positive sequence component is the limit condition; wherein the power grid is electrically connected to the input AC port of the unified power quality conditioner; The unified power quality conditioner is operated based on the extreme operating condition, and the input current amplitude of the input AC port of each phase of the unified power quality conditioner is obtained; the input current amplitude is used to obtain the first current value of the corresponding input AC port.

4. The method according to claim 1, characterized in that The step of obtaining modulation wave functions of space vector pulse width modulation corresponding to input AC ports and output AC ports of each phase of the unified power quality conditioner includes: Obtaining the sinusoidal pulse width modulation wave functions corresponding to the input AC port and the output AC port of each phase of the unified power quality conditioner under the sinusoidal pulse width modulation modulation mode; Determine an input zero-sequence component based on the sinusoidal pulse width modulation wave function of each of the input AC ports; and determine an output zero-sequence component based on the sinusoidal pulse width modulation wave function of each of the output AC ports; Based on the sum of the sinusoidal pulse width modulation wave function of each input AC port and the input zero-sequence component, the modulation wave function of the space vector pulse width modulation corresponding to each input AC port is determined; and based on the sum of the sinusoidal pulse width modulation wave function of each output AC port and the output zero-sequence component, the modulation wave function of the space vector pulse width modulation corresponding to each output AC port is determined.

5. The method according to claim 1, characterized in that The step of determining an average value of a second capacitor current flowing through each of the capacitors in one fundamental wave period based on the average value of the first capacitor current of each of the capacitors includes: In one fundamental wave cycle, an average value of the second capacitor current flowing through each capacitor in one fundamental wave cycle is determined based on an integration calculation of the average value of the first capacitor current of each capacitor.

6. The method according to claim 1, characterized in that The step of obtaining the instantaneous value of the capacitor current of each capacitor within one fundamental wave period based on the first capacitor current average value and the second capacitor current average value includes: Based on the difference between the first capacitor current average value and the second capacitor current average value corresponding to each capacitor, the instantaneous value of the capacitor current of each capacitor within one fundamental wave period is obtained.

7. The method according to claim 1, characterized in that The processing of the instantaneous value of each capacitor current based on a preset method to determine the minimum capacitance value of each capacitor includes: Based on time integration of the instantaneous value of each capacitor current, the corresponding charge amount of the capacitor charging and discharging is obtained, and then based on the capacitor definition formula and the preset capacitor voltage ripple requirement, the minimum capacitance value of each capacitor is determined.

8. A capacitor selection device for a unified power quality conditioner, characterized in that: The device comprises: A data acquisition module, used for acquiring modulation wave functions of space vector pulse width modulation corresponding to input AC ports and output AC ports of each phase of the unified power quality conditioner respectively when the unified power quality conditioner is in a preset operating condition; wherein the preset operating condition includes a rated condition and a limit condition; The data acquisition module is also used to acquire the first current values ​​corresponding to the input AC port and the output AC port of each phase respectively; A data processing module, used for obtaining a modulation wave value corresponding to each of the modulation wave functions, and obtaining a first capacitor current average value of each capacitor in each switching cycle within a fundamental wave cycle based on the modulation wave value and each of the first current values; The data processing module is further used to determine an average value of a second capacitor current flowing through each of the capacitors in one fundamental wave period based on an average value of the first capacitor current of each of the capacitors; The data processing module is further used to obtain the instantaneous value of the capacitor current of each of the capacitors within one fundamental wave period based on the first capacitor current average value and the second capacitor current average value; The capacitor selection module is used to process the instantaneous value of each capacitor current based on a preset method to determine the minimum capacitance value of each capacitor; and determine the selection of each capacitor in the unified power quality conditioner based on each minimum capacitance value.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 6 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 6 are implemented.

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