Network construction type SVG pre-charging control method based on super capacitor and ANPC structure

Abstract

The invention relates to a grid-connected reactive power compensation control technology, and aims to provide a network construction type SVG pre-charging control method based on a super capacitor and an ANPC structure. The method comprises the following steps: charging a super capacitor from an alternating current power grid side through an uncontrolled rectifier and a charging resistor, and introducing reactive power-voltage droop control and active power-frequency droop control with phase calibration until the voltage rises to a specified value, the SVG can simulate the active power-frequency droop characteristic in the synchronous generator through phase following; and when the super capacitor is boosted to a specified value, active power-frequency droop control and reactive power-voltage droop control are switched, and the output is directly imported into a virtual impedance voltage control link to generate a modulation wave for controlling a switching tube of the network construction type SVG. According to the method, the difficult-to-avoid problem of current impact during starting in the pre-charging process of the networking type SVG is solved, and the SVG starting time is shortened by controlling the charging speed; and the problem of easy instability of following net type control is avoided, and the operation stability is enhanced.

Description

TECHNICAL FIELD

[0001] The application relates to the fields of power electronics and grid-connected reactive power compensation control, and particularly relates to a grid-connected SVG pre-charging control method based on an ANPC structure. BACKGROUND

[0002] With the large-scale access of renewable energy, the structure and operation characteristics of the power grid have undergone profound changes, and the traditional power grid support means is facing unprecedented challenges. Among them, the output of wind power and photovoltaic power is affected by nature, and the power fluctuates greatly in a short time, which is easy to break the power balance of the power grid. The traditional converter lacks active voltage support capability, and may be disconnected from the grid when the voltage drops, so the voltage stability problem is particularly prominent, which is an important factor restricting the safe and reliable operation of the power system.

[0003] The grid-connected SVG (static var generator) becomes the core equipment for solving the problem of power grid voltage stability because it has the ability of active and rapid voltage support, fault ride-through and dynamic reactive power regulation. The active neutral point clamped three-level (ANPC) structure becomes one of the key technical routes of the grid-connected SVG because it can effectively solve the problems of midpoint voltage imbalance, high switching loss and uneven device stress of the traditional three-level topology. Because of its better midpoint voltage control, lower switching loss, higher power density and more mature control scheme, it is well suited to the grid-connected SVG scenarios that require high transient voltage support, high power density and flexible active / reactive power regulation, such as high proportion of new energy access scenarios, weak grid scenarios, etc.

[0004] To further improve the transient response speed and fault support capability of the grid-connected SVG, the industry generally adopts a composite topology of "power electronic converter + energy storage unit". Compared with energy storage batteries, the super capacitor in such a composite topology has the characteristics of high power density, high charging and discharging efficiency, long cycle life and excellent low temperature performance, and has become the preferred solution for the energy storage unit of the grid-connected SVG. However, unlike common energy storage batteries, the DC side voltage of the grid-connected SVG based on super capacitors will change with the super capacitor voltage, which also requires pre-charging operation of the grid-connected SVG before entering the steady-state operation mode. The common practice is to charge the super capacitor through an additional super capacitor charger before use, but this increases the additional cost of the grid-connected SVG. Some researchers have proposed directly charging the DC side through the power electronic converter, but due to the large capacitance of the super capacitor, the charging time is relatively long. In addition, the grid-connected SVG is often used in weak grid scenarios, and the two-stage charging using grid-connected control will cause current impact, system instability and other problems when switching control strategies, causing equipment damage or system failure.

[0005] Therefore, it is necessary to propose a new scheme to solve the above problems. SUMMARY

[0006] The technical problem solved by the present application is to overcome the deficiencies in the prior art and provide a network configuration type SVG pre-charging control method based on super capacitor and ANPC structure.

[0007] To solve the technical problem, the solution of the present application is:

[0008] A network configuration type SVG pre-charging control method based on super capacitor and ANPC structure is provided, comprising:

[0009] The super capacitor is located at the DC side of the network configuration type SVG with ANPC structure, and in the charging process, all the switching tubes are controlled to be in the blocking state, and the super capacitor is charged from the AC grid side through uncontrolled rectification and charging resistance; the reactive power-voltage droop control and the active power-frequency droop control with phase calibration are introduced, the reference phase of the network configuration type SVG follows the phase of the AC grid side, so that the network configuration type SVG can simulate the active power-frequency (P-f) droop characteristic in the synchronous generator until the voltage of the super capacitor rises to a predetermined value;

[0010] When the voltage of the super capacitor rises to the predetermined value, the bypass charging resistance is bypassed, the active power-frequency droop control and the reactive power-voltage droop control are switched, and the outputs of the two controls are directly introduced into the virtual impedance voltage control link to generate a modulation wave, which is used to control the switching tubes of the network configuration type SVG after PWM modulation.

[0011] As a preferred scheme of the present application, before the voltage rises to the predetermined value, the reference phase of the network configuration type SVG is calculated based on the output of the active power-frequency droop control, and then the phase is calibrated to follow the phase of the AC grid side; at the same time, the output of the reactive power-voltage droop control is zero, and the calibrated reference phase is used as the input of the virtual impedance voltage control link to generate a modulation wave which does not control the switching tube and is only used for pre-synchronization.

[0012] As a preferred scheme of the present application, specifically comprising:

[0013] Before the voltage of the super capacitor rises to the predetermined value :

[0014] In each control cycle in the charging process, the operating parameters on both sides of the network configuration type SVG are continuously collected;

[0015] The phase of the AC grid side is obtained according to the phase-locked loop principle ;

[0016] The actual active power output by the SVG and the active power reference value As input, output SVG reference frequency through active power-frequency droop control , calculate SVG reference phase through integration ;

[0017] Subtract SVG reference phase from grid-side phase , then multiply by phase calibration coefficient to obtain output phase calibration , which is compensated back to active power-frequency droop to enable SVG reference phase to follow grid-side phase , and generate SVG phase angle after synchronization ;

[0018] Output zero SVG voltage reference value through reactive power-voltage control, input the SVG phase angle to a virtual impedance voltage control link to generate a modulation wave; sequentially through AC current inner loop control, Park transformation, phase-to-phase voltage balancing processing and PWM modulation, the modulation wave is pre-synchronized but not used to control the switch tube in the SVG;

[0019] When the voltage of the super capacitor rises to a predetermined value :

[0020] Close the bypass switch of the charging resistor across the super capacitor; simultaneously switch the active power-frequency droop control and the reactive power-voltage droop control; that is, set the phase calibration to zero, and no longer compensate the SVG reference phase ; at the same time, calculate the SVG voltage reference value according to the actual reactive power output by the SVG and the reactive power reference value ;

[0021] Input the real-time acquired SVG reference phase and the SVG voltage reference value to a virtual impedance voltage control link to generate a modulation wave, which is used to control the switch tube in the grid-forming SVG after modulation.

[0022] As a preferred scheme of the present application, the operating parameters at least include: the voltage of the super capacitor , and the SVG output voltage v g and current i0, and the grid-side three-phase voltage v s .

[0023] As a preferred scheme of the present application, the predetermined value of the voltage rise of the super capacitor should not exceed ; wherein, is the effective value of the phase voltage of the AC side.

[0024] As a preferred scheme of the present application, in the active power-frequency droop control link, the active power and frequency transfer function used is as follows:

[0025]

[0026] In the formula, is the transfer function of the active power-frequency droop control; s is a complex variable in the transfer function; is the droop coefficient.

[0027] As a preferred scheme of the present application, the DC side super capacitor voltage is monitored in each control period until the normal working voltage is reached, and then the control mode of the grid-connected SVG is switched to a preset stable operation control mode; the value of the normal working voltage should be greater than a predetermined voltage rise value in the charging process .

[0028] As a preferred scheme of the present application, the grid-connected SVG is based on an active neutral point clamped three-level structure (i.e. ANPC structure), each phase of which is composed of a filter inductor, a DC side voltage division capacitor group, a super capacitor, a main switch tube and two neutral point clamping switch tubes; the DC side voltage division capacitor group is composed of two capacitors with the same capacity and parameters connected in series, the super capacitor is connected after the voltage division capacitor, and a charging resistor is connected between the main switch tube and the voltage division capacitor to limit the charging current; each switch tube is synchronously selected as an IGBT or an IGCT.

[0029] The present application further provides a device for implementing the pre-charging control method of the grid-connected SVG based on the super capacitor and the ANPC structure, comprising:

[0030] A power grid parameter monitoring module, which continuously acquires the operation parameters of the two sides of the grid-connected SVG in each control period;

[0031] A power calculation module, which calculates the actual active power and the actual reactive power according to the operation parameters of the grid-connected SVG;

[0032] A phase-locked loop control module, which calculates the phase of the AC power grid side according to the phase-locked loop principle ;

[0033] An active power-frequency droop control module, which outputs the SVG reference frequency based on the active power and frequency transfer function, and obtains the SVG reference phase through integral calculation;

[0034] The phase calibration module will calibrate the SVG reference phase. Phase with grid side As input, perform differential calibration and output phase calibration. To compensate for active power-frequency droop control, so that the SVG reference phase Able to follow the phase of the grid side ;

[0035] Reactive power-voltage droop control module, based on the actual reactive power output of SVG. and reactive power reference value Calculate SVG voltage reference value ;

[0036] A virtual impedance voltage control module is used to generate a modulated wave; this occurs when the voltage in the supercapacitor rises to a predetermined value. Previously, it followed the phase of the grid side. SVG phase angle And the voltage value is zero as input; the voltage of the supercapacitor rises to a predetermined value. Then, the actual outputs of the active power-frequency droop control module and the reactive power-voltage droop control module are used as inputs;

[0037] The modulation wave processing and modulation module is used to achieve pre-synchronization of the modulation wave and control of the switching transistors through AC current inner loop control, Park transformation, phase-to-phase and phase-to-phase voltage equalization processing and PWM modulation.

[0038] The present invention also provides a computer device, comprising: at least one processor, and a memory communicatively connected to the at least one processor, wherein the memory stores instructions that are executed by the at least one processor, the instructions being executed by the at least one processor to cause the at least one processor to perform the aforementioned grid-type SVG pre-charge control method based on supercapacitor and ANPC structure.

[0039] The present invention also provides a computer-readable storage medium storing computer instructions for causing the computer to execute the aforementioned network-based SVG pre-charge control method based on supercapacitors and ANPC structures.

[0040] Compared with the prior art, the technical advantages of the present invention are:

[0041] 1. This method monitors the DC-side supercapacitor voltage in real time and uses uncontrolled rectification and active power-frequency droop control unit to charge the DC-side voltage of the grid-type SVG from 0V to the normal operating voltage. This pre-charging method solves the problem of unavoidable current surge during startup in the pre-charging process of the grid-type SVG.

[0042] 2. This invention charges the DC side of the grid-type SVG by uncontrolled rectification and active power-frequency droop control. The active power input to the grid can be controlled by adjusting the active power reference value, thereby controlling the charging speed of the DC side supercapacitor and shortening the start-up time of the grid-type SVG.

[0043] 3. The active power-frequency droop control adopted in this invention is also a grid-type control. Therefore, in the process of switching from active power-frequency droop control in the charging state to grid-type SVG stable operation control, the problem of switching between the two control modes of grid-following control and grid-type control in traditional technology is avoided; the problem of instability of grid-following control under weak grid conditions is avoided, further enhancing the operational stability of grid-type SVG; for this reason, this invention can also extend the operating life of supercapacitors and reduce the cost of use. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the network-type SVG main circuit topology based on the ANPC structure in an embodiment of the present invention.

[0045] Figure 2 This is the overall control flowchart in an embodiment of the present invention.

[0046] Figure 3 This is a control block diagram for the active power-frequency droop control of a grid-type SVG in an embodiment of the present invention.

[0047] Figure 4 This is a graph showing the change in active power during charging in an embodiment of the present invention.

[0048] Figure 5 This is a diagram showing the voltage variation of the supercapacitor in an embodiment of the present invention. Detailed Implementation

[0049] First, it should be noted that this invention relates to circuit control technology, which is an application of computer technology in the field of electronic circuit technology. The implementation of this invention involves the application of multiple software functional modules. The applicant believes that, after carefully reading the application documents and accurately understanding the implementation principles and objectives of this invention, and in conjunction with existing known technologies, those skilled in the art can fully utilize their software programming skills to implement this invention. The aforementioned software functional modules include, but are not limited to: a power grid parameter monitoring module, a power calculation module, a phase-locked loop control module, an active power-frequency droop control module, a phase calibration module, a reactive power-voltage droop control module, a virtual impedance voltage control module, a modulation wave processing and modulation module, etc. All modules mentioned in this application fall within this scope, and the applicant will not list them all further.

[0050] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0051] I. Overview of the Implementation Schemes of the Invention

[0052] 1. Topology description of network-type SVG

[0053] The mesh-type SVG in this invention is based on an active neutral-point clamped three-level structure, i.e., an ANPC structure. For example... Figure 1 As shown, this ANPC network consists of three phases (a, b, c). Each phase comprises a filter inductor, a DC-side voltage divider capacitor bank, a supercapacitor, a main switch, and a neutral point clamping switch. The DC-side voltage divider capacitor bank consists of two capacitors with identical capacitance and parameters connected in series. The supercapacitor is connected after the voltage divider capacitor. Both the main switch and the neutral point clamping switch are IGBTs or IGCTs, and each phase requires two switches for neutral point clamping, which can be either IGBTs or IGCTs. A pre-charging resistor is connected between the main switch and the voltage divider capacitor to limit the charging current. When all switches are in the latched state, this ANPC structure temporarily becomes an uncontrolled rectifier circuit. During charging, the supercapacitor can be charged from the AC grid side through uncontrolled rectification and the charging resistor.

[0054] As an example, the grid-type SVG in this invention has three phases sharing the same set of voltage-degrading capacitors and supercapacitors on the DC side, and the AC output terminal connected to the power grid through a filter inductor. The entire system adopts a star connection to realize the interaction between the three phases and the power grid.

[0055] 2. Control methods for network-type SVG

[0056] Based on the aforementioned grid-type SVG, this invention proposes a pre-charging control method for grid-type SVG based on supercapacitors and ANPC structures. The overall control flow is as follows: Figure 2 As shown.

[0057] This control method synchronizes the grid phase in advance by monitoring the AC side voltage phase; it reduces the current surge during control mode switching by combining active power-frequency droop control; and it controls the amount of active power input and charging speed of the grid-type SVG from the grid side by using active power-frequency droop control, thereby adapting to weak grid environments and avoiding system instability.

[0058] The basic principle is as follows: The supercapacitor is located on the DC side of the grid-type SVG in the ANPC structure. During charging, all switches are kept in a locked state. The supercapacitor is charged from the AC grid side through uncontrolled rectification and charging resistors. Reactive power-voltage droop control and active power-frequency droop control with phase calibration are introduced. By having the grid-type SVG reference phase follow the AC grid phase, the grid-type SVG can simulate the active power-frequency (Pf) droop characteristics of a synchronous generator until the voltage rises to a predetermined value. In this process, the grid-type SVG reference phase is calculated based on the output of the active power-frequency droop control, and then phase-calibrated to follow the AC grid phase. The output of the reactive power-voltage droop control is set to zero, and together with the calibrated reference phase, it serves as the input to the virtual impedance voltage control loop. The generated modulation wave does not control the switches but is only used for pre-synchronization. When the voltage of the supercapacitor rises to a predetermined value, the charging resistor is bypassed, and the active power-frequency droop control and reactive power-voltage droop control are switched. The outputs of the two controls are directly fed into the virtual impedance voltage control loop to generate a modulation wave, which is then modulated by PWM and used to control the switching transistors of the grid-type SVG.

[0059] To make it easier to understand, we will use a control cycle as an example below.

[0060] When charging begins, the bypass switches S1 and S2 of the charging resistor are disconnected; the supercapacitor is charged from the AC grid side through the uncontrolled rectifier and the charging resistor, while keeping all switching transistors in the locked state.

[0061] (1) Monitoring of power grid parameters

[0062] During each control cycle of the charging process, the operating parameters on both sides of the mesh-type SVG are continuously collected;

[0063] The operating parameters that need to be collected include at least: the voltage of the supercapacitor. and SVG output voltage v g and current i0 (used to calculate the active power output of the SVG) and reactive power Using the output voltage v g Calculate the actual phase of SVG ), grid-side three-phase voltage v s (Used for calculating angular frequency and grid phase angle in phase-locked loop control) ).

[0064] (2) Power calculation

[0065] Calculate the actual active power output of the SVG using three-phase voltage and three-phase current. and reactive power .

[0066] (3) Phase-locked loop control

[0067] Using the reference value of the q-axis component of the grid-connected voltage and the q-axis component of the grid-connected voltage, the angular frequency of the grid-connected point is calculated according to the phase-locked loop principle. This frequency is then used as the input to the phase calculation stage to obtain the phase on the SVG side. Using the reference values ​​of the q-axis components of the grid voltage and the grid connection point voltage, the angular frequency at the grid connection point is calculated based on the phase-locked loop principle. This frequency is then used as the input to the phase calculation stage to obtain the phase of the AC grid side. .

[0068] (4) Active power-frequency droop control and reactive power-voltage control (early stage)

[0069] When the supercapacitor rises from zero voltage to a predetermined value Previously, control was performed in the following manner:

[0070] (4.1) The actual active power output by the SVG and active power reference value As input, the active power-frequency droop control outputs the SVG reference frequency. The SVG reference phase is further obtained through integration calculation. .

[0071] The active power and frequency transfer functions used in this control loop are shown below:

[0072]

[0073] In the formula, Let be the transfer function for active power-frequency droop control; s is a complex variable in the transfer function; This is the droop coefficient.

[0074] The core principle of active power-frequency droop control is: by simulating the active power-frequency (Pf) droop characteristics of a synchronous generator, the actual active power output of the SVG is detected in real time through a sampling circuit. And compare it with the preset active power reference value. Perform the difference calculation. Based on the preset active power droop coefficient. This converts power into a value corresponding to frequency. In essence, active power-frequency droop control controls the active power output of the SVG by changing the phase difference between the SVG and the grid side.

[0075] (4.2) Set the SVG reference phase Phase with grid side Calculate the difference, then multiply by the phase calibration factor. Phase calibration of the output This compensates for the active power-frequency droop, making the SVG reference phase... Able to follow the phase of the grid side The phase angle of the SVG generated after synchronization Phase calibration coefficient The range of values ​​for is [0, +∞); The value determines the SVG reference phase. Phase with grid side The time required for synchronization The larger the value, the faster the synchronization. However, excessively large values ​​should be avoided, as they may cause oscillations that prevent synchronization.

[0076] (4.3) The reference value of the SVG voltage for controlling reactive power-voltage control output is zero, and its phase angle is compared with that of the SVG. The input virtual impedance voltage control loop generates a modulation wave; it is then sequentially processed through AC current inner loop control, Park transformation, phase-to-phase and phase-to-phase voltage equalization, and PWM modulation to achieve pre-synchronization of the modulation wave, but it is not used to control the switching transistors in the SVG. By adopting the above control method, the current surge caused when the control method is switched after charging is completed can be reduced.

[0077] (4.4) Predicted voltage rise of supercapacitor It should not exceed ;in, This represents the effective value of the phase voltage on the AC side.

[0078] (5) Active power-frequency droop control and reactive power-voltage control (later stage)

[0079] When the supercapacitor rises from zero voltage to a predetermined value Then, control shall be carried out in the following manner:

[0080] (5.1) Close the bypass switches S1 and S2 of the charging resistors across the supercapacitor; simultaneously switch the active power-frequency droop control and the reactive power-voltage droop control; that is, enable phase calibration. Zero, no longer for SVG reference phase Phase calibration compensation is performed; simultaneously, based on the actual reactive power output of the SVG... and reactive power reference value Calculate SVG voltage reference value Reactive power reference value The value is usually 0.

[0081] (5.2) The real-time acquired SVG reference phase Compared with SVG voltage reference value The input virtual impedance voltage control loop generates a modulated wave, which is then modulated to control the switching transistors in the grid-type SVG.

[0082] The output voltage amplitude reference value is obtained based on reactive power-voltage droop control, and after being processed by virtual impedance voltage control and AC current inner loop control, it is compared with the phase angle. These components are used together as inputs to the Park transform; after in-phase and inter-phase voltage equalization processing, the resulting modulated wave is used to regulate each switch in the SVG device. Virtual impedance voltage control, AC current inner-loop control, Park transform, and in-phase and inter-phase voltage equalization control are all described in existing literature and will not be elaborated further as they are not part of the core technical solutions of this invention.

[0083] (5.3) During the charging process in this stage, the active power reference value can be adjusted. By controlling the active power input to the power grid, the charging time can be adjusted.

[0084] (6) Switch to stable operation control mode

[0085] The voltage of the DC-side supercapacitor is monitored during each control cycle until it reaches the normal operating voltage. Then, the control mode of the network-type SVG is switched to the preset stable operation control mode.

[0086] This normal operating voltage The value should be greater than the predetermined voltage rise during the charging process. The specific value is determined by the specific project, i.e., the operating voltage of the SVG during steady-state operation.

[0087] The stable operation control mode of the network-type SVG is well documented in existing literature, such as the DC capacitor self-synchronization control scheme; however, since it is not part of the core technical solution of this invention, it will not be described in detail here.

[0088] 3. Devices, equipment, and storage media for implementing the control method

[0089] To achieve the above control method, this invention also proposes an apparatus for implementing a grid-based SVG pre-charging control method based on supercapacitors and ANPC structures, including a grid parameter monitoring module, a power calculation module, a phase-locked loop control module, an active power-frequency droop control module, a phase calibration module, a reactive power-voltage droop control module, a virtual impedance voltage control module, and a modulation wave processing and modulation module.

[0090] The power grid parameter monitoring module continuously collects operating parameters from both sides of the grid-type SVG during each control cycle; the power calculation module calculates the actual active power based on the operating parameters of the grid-type SVG. With actual reactive power The phase-locked loop (PLL) control module calculates the phase on the AC grid side based on the PLL principle. The active power-frequency droop control module outputs an SVG reference frequency based on active power and the frequency transfer function. The output is used to calculate the SVG reference phase through integration. The phase calibration module will adjust the SVG reference phase. Phase with grid side As input, perform differential calibration and output phase calibration. To compensate for active power-frequency droop control, so that the SVG reference phase Able to follow the phase of the grid side Reactive power-voltage droop control module, based on the actual reactive power output of SVG. and reactive power reference value Calculate SVG voltage reference value The virtual impedance voltage control module is used to generate the modulated wave; when the voltage of the supercapacitor rises to a predetermined value... Previously, it followed the phase of the grid side. SVG phase angle And the voltage value is zero as input; the voltage of the supercapacitor rises to a predetermined value. Subsequently, the actual outputs of the active power-frequency droop control module and the reactive power-voltage droop control module are used as inputs. The modulation wave processing and modulation module is used to achieve pre-synchronization of the modulation wave and control of the switching transistors through AC current inner-loop control, Park transformation, phase-to-phase and phase-to-phase voltage equalization processing, and PWM modulation. The computational logic diagrams of some modules are shown below. Figure 2 As shown.

[0091] Based on this, the present invention also proposes a computer device, comprising: at least one processor, and a memory communicatively connected to the at least one processor, wherein the memory stores instructions that are executed by the at least one processor, the instructions being executed by the at least one processor to cause the at least one processor to perform the aforementioned grid-type SVG pre-charge control method based on supercapacitor and ANPC structure.

[0092] Furthermore, the present invention also provides a corresponding computer-readable storage medium storing computer instructions, which, by executing the stored computer instructions, enables the implementation of the aforementioned grid-type SVG pre-charge control method based on supercapacitors and ANPC structures.

[0093] 4. A specific example and simulation results

[0094] For ease of understanding, this embodiment constructs an active neutral-point clamped three-level mesh SVG model in PLECS simulation software, and pre-charges the mesh SVG using the method proposed in this patent.

[0095] The grid voltage was set to 220V, the initial voltage of the DC-side supercapacitor was 0V, and the charging resistor was 20Ω. Set to 500V.

[0096] Simulation results are as follows Figure 4 , Figure 5 As shown. Figure 4 The graph shows the active power variation. From t=0 to 1s, the system is in the uncontrolled rectifier charging stage. At t=1s, the system switches to active power-frequency droop control for constant active power charging of 6kW. Positive values ​​represent the system's output active power. Figure 4 The value shown in the image is -6000, which means that the system input is 6000W of active power to charge the DC-side supercapacitor. Figure 5 For the supercapacitor voltage change, at t=1s, uncontrolled rectifier charging is used to charge to 500V, then switching to active power-frequency droop control, which speeds up the charging speed, avoids the problem of switching between grid-type and grid-type control, and increases the system's operational stability.

[0097] In summary, the technical solution of this invention utilizes active power-frequency droop control, a type of grid-based control, to avoid the problem of switching between grid-based and grid-connected control when charging the DC-side capacitor; it also avoids the problem of instability in grid-based control under weak grid conditions, thus enhancing the operational stability of the grid-connected SVG; and simultaneously extends capacitor life and reduces costs.

[0098] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A pre-charging control method of a network-configuration type SVG based on a super capacitor and an ANPC structure, characterized in that, The method comprises the following steps: The super capacitor is located at the DC side of the grid-connected SVG with ANPC structure, all the switch tubes are controlled to be in the blocking state during the charging process, and the super capacitor is charged from the AC grid side through uncontrolled rectification and charging resistance; the reactive power-voltage droop control and the active power-frequency droop control with phase calibration are introduced, the grid-connected SVG reference phase follows the AC grid side phase, so that the grid-connected SVG can simulate the active power-frequency (P-f) droop characteristic in the synchronous generator until the voltage of the super capacitor rises to a predetermined value; When the voltage of the super capacitor rises to the predetermined value, the bypass charging resistance is switched, the active power-frequency droop control and the reactive power-voltage droop control are switched, and the outputs of the two controls are directly introduced into the virtual impedance voltage control link to generate a modulation wave, which is used for controlling the switch tubes of the grid-connected SVG after PWM modulation.

2. The method of claim 1, wherein, Before the voltage rises to the predetermined value, the output of the active power-frequency droop control is used to calculate the grid-connected SVG reference phase, and then the phase calibration is performed to make the grid-connected SVG reference phase follow the AC grid side phase; meanwhile, the output of the reactive power-voltage droop control is zero, and the calibrated reference phase is used as the input of the virtual impedance voltage control link to generate a modulation wave which does not control the switch tubes and is only used for pre-synchronization.

3. The method of claim 1, wherein at the voltage of the supercapacitor reaches a predetermined value before: In each control cycle during the charging process, the operating parameters on both sides of the grid-connected SVG are continuously collected; According to the phase-locked loop principle, the phase of the alternating current grid side is obtained ; Actual active power output by the SVG and an active power reference value As input, the SVG reference frequency is output by active power-frequency droop control The SVG reference phase is calculated by integration ; Subtracting the SVG reference phase from the grid side phase Subtracting the SVG reference phase from the grid side phase Subtracting the SVG reference phase from the grid side phase Subtracting the SVG reference phase from the grid side phase Subtracting the SVG reference phase from the grid side phase Subtracting the SVG reference phase from the grid side phase Subtracting the SVG reference phase from the grid side phase Subtracting the SVG reference phase from the grid side phase The SVG voltage reference value of the control reactive power-voltage control output is zero, which is compared with the SVG phase angle The input virtual impedance voltage control link generates a modulation wave; through AC current inner loop control, Park transformation, phase-to-phase voltage balancing processing and PWM modulation in sequence, the modulation wave is pre-synchronized, but not used to control the switch tube in the SVG; When the voltage of the super capacitor rises to a predetermined value Back: Bypass switch closing the charging resistor across the supercapacitor; simultaneously switching active power-frequency droop control and reactive power-voltage droop control; i.e. phase alignment is zero, no phase alignment compensation is performed for the SVG reference phase ; simultaneously, the SVG voltage reference value is calculated based on the actual reactive power output by the SVG and the reactive power reference value ;​ The SVG reference phase is acquired in real time The SVG voltage reference value is acquired in real time The input virtual impedance voltage control link generates a modulation wave, which is used to control the switch tube in the network configuration type SVG after modulation.

4. The method of claim 3, wherein, The operating parameters at least comprise a voltage of the super capacitor , and an SVG output voltage v g and a grid-side three-phase voltage v s .

5. The method of claim 3, wherein, predetermined value of voltage rise of the super capacitor should not exceed ; wherein, is the effective value of the phase voltage on the AC side.

6. The method of claim 3, wherein, In the active power-frequency droop control link, the active power and frequency transfer function used is as follows: ； wherein is the transfer function for the active power-frequency droop control; s is a complex variable in the transfer function; is the droop coefficient.

7. The method of claim 3, wherein, Monitoring the DC side super capacitor voltage in each control cycle until reaching the normal working voltage Then switching the control mode of the networked SVG to the preset stable operation control mode; the value of the normal working voltage should be greater than the predetermined voltage rise value in the charging process .

8. The method of claim 1, wherein, The grid-connected SVG is based on the active neutral point clamped three-level structure, each phase of which is composed of a filter inductor, a DC side voltage dividing capacitor group, a super capacitor, a main switch tube and two neutral point clamped switch tubes; the DC side voltage dividing capacitor group is composed of two capacitors with the same capacity and parameters connected in series, the super capacitor is connected after the voltage dividing capacitor, the charging resistance is connected between the main switch tube and the voltage dividing capacitor to limit the charging current, and each switch tube is synchronously selected as an IGBT or an IGCT.

9. A device for implementing a network-configuration type SVG pre-charge control method based on supercapacitors and ANPC structure, characterized in that, The method comprises the following steps: A grid parameter monitoring module is used to continuously collect the operating parameters on both sides of the grid-connected SVG in each control cycle; a power calculation module for calculating the actual active power from the operating parameters of the network-forming SVG and the actual reactive power ; A phase-locked loop control module calculates the phase of the AC grid side according to the principle of the phase-locked loop ; An active power - frequency droop control module outputs an SVG reference frequency based on an active power and frequency transfer function The SVG reference phase is calculated by integration ; Phase alignment module, aligning the SVG reference phase with the grid side phase As input, the difference between the calibrated output phase and the SVG reference phase is aligned for compensating the active power-frequency droop control, aligning the SVG reference phase with the grid side phase ; A reactive power - voltage droop control module based on the actual reactive power output by the SVG and a reactive power reference value calculating an SVG voltage reference value ; A virtual impedance voltage control module is used to generate a modulated wave; this occurs when the voltage in the supercapacitor rises to a predetermined value. Previously, it followed the phase of the grid side. SVG phase angle And the voltage value is zero as input; the voltage of the supercapacitor rises to a predetermined value. Then, the actual outputs of the active power-frequency droop control module and the reactive power-voltage droop control module are used as inputs; A modulation wave processing and modulation module is used to realize the pre-synchronization of the modulation wave and the control of the switch tubes through AC current inner loop control, Park transformation, phase-to-phase voltage balancing processing and PWM modulation.

10. A computer device, comprising: The computer readable storage medium stores computer instructions, and the computer instructions are used to make the computer execute the grid-connected SVG pre-charging control method based on the super capacitor and the ANPC structure. The computer readable storage medium stores computer instructions, and the computer instructions are used to make the computer execute the grid-connected SVG pre-charging control method based on the super capacitor and the ANPC structure.

11. A computer readable storage medium, characterized in that, ​

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