Energy-storage-free SVG system and networking control method thereof

Abstract

The invention relates to the technical field, in particular to an energy-storage-free SVG (static var generator) system and a network construction control method thereof, and the method comprises the steps: determining a static working point of a DC side voltage through SVG (static var generator) system matching control, and taking the static working point as an input reference value of three-phase cluster voltage balance control. And cluster voltage balance control is carried out by superposing the component which is in the same phase as the reactive voltage component, and balance signals of each phase of the three phases are generated, so that direct current side voltage balance among the three phases is realized. And superposing the balance signal and the voltage reference value to obtain a voltage modulation wave. And meanwhile, the charging and discharging priorities of the full-bridge sub-modules in the phase are sorted, and corresponding full-bridge sub-module switching signals are distributed according to a sorting result, so that voltage balance among the full-bridge sub-modules in the phase is realized, and stable control of frequency and voltage of a power grid side is realized based on inter-phase and intra-phase voltage balance control.

Description

Technical Field

[0001] The invention relates to the technical field, and in particular to a non-energy storage SVG system and a network construction control method thereof. Background Art

[0002] With the development of power electronics technology, static var generator (SVG) plays an increasingly important role in power transmission, distribution and access to new energy. Based on power electronic converters, SVG systems can adjust reactive power output in real time, respond to grid voltage fluctuations and load changes, and provide efficient reactive power compensation, especially in power systems with large grid load changes and access to renewable energy. In SVG technology, the cascaded H-Bridge (CHB) architecture is an important topology. The cascaded H-bridge SVG system consists of multiple H-bridge submodules connected in series. Each H-bridge module is powered by an independent DC power supply and can dynamically adjust its output reactive power. Compared with traditional unit-type SVG systems, the cascaded H-bridge SVG system has significant advantages in improving power quality and suppressing harmonics due to its modular structure and multi-level output, making it a key technology in power transmission and distribution systems. In the flexible direct current transmission system, most renewable energy power generation is transmitted to the grid side through power electronic equipment. However, with the decrease in the proportion of traditional synchronous units, the system frequency changes will accelerate after a large disturbance occurs on the grid side, the voltage amplitude will fluctuate more violently, and even wide-band oscillation problems will occur.

[0003] Grid-Froming Control (GFM) has been proposed as a promising solution to address these challenges. Devices using GFM control strategies can regulate the voltage and frequency of the grid by simulating the behavior of synchronous generators. They usually rely on droop control to establish the relationship between active power and frequency and reactive power and voltage amplitude. Although droop control provides a simple and effective mechanism to achieve grid-forming behavior, it also requires flexible active power output and DC-side energy storage. In view of the actual application scenarios of SVG, as a key and commonly used reactive power compensation device, real-time control of active power, reduction of operating costs, and response to rapid voltage fluctuations and frequency disturbances caused by renewable energy are necessary. Therefore, the traditional droop grid-forming control method is not suitable for SVG systems. For the grid-connected cascaded SVG system, due to the different states of the three-phase branches at startup, the average voltage between the three-phase DC side will produce voltage imbalance. The phenomenon of phase-to-phase voltage imbalance will produce overmodulation, thereby reducing the grid-forming support capacity of the SVG system and the stability of the system. Therefore, balanced control of the phase-to-phase DC side voltage is necessary for the cascaded SVG system. Similarly, since the cascaded SVG system adopts a multi-module, multi-level output mode, the charging and discharging time of each module in the phase is also different, resulting in an imbalance between the DC side voltages of each module in the phase. Phase imbalance can also lead to overmodulation, thereby reducing the SVG system's network support capability and system stability. Therefore, in order to cope with the rapid voltage fluctuations and frequency disturbances caused by renewable energy, in addition to the voltage network support capability, the stability of the SVG system's operation is also a factor that needs to be considered. So in general, there is currently a lack of a low-cost, no-additional-energy-storage cascaded SVG system network control method that can operate stably under unbalanced internal conditions (such as capacity imbalance) and unbalanced external conditions (such as line impedance imbalance, load imbalance). Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a non-energy storage SVG system and a network control method thereof in view of the deficiencies in the above-mentioned prior art, so as to solve the technical problem that the current cascade SVG system is internally unbalanced and causes unstable system operation.

[0005] The objective of the present invention is achieved by the following technical solutions: In a first aspect, the present invention provides a method for controlling a network of a SVG system without energy storage, comprising: Obtain grid-side frequency and voltage reference values; By means of matching control of the SVG system, a static operating point of the DC side voltage is obtained, and the static operating point of the DC side voltage is used as an input reference value for voltage balance control of the three-phase cluster; According to the static working point of the DC side voltage, the cluster voltage balance control is performed by superimposing the component in phase with the reactive voltage component; the balanced voltage signal of the three-phase cluster is obtained; and the DC side voltage balance among the three phases is completed; The voltage modulation wave is obtained by superimposing the balanced voltage signal and the voltage reference value; The charging and discharging priorities of the full-bridge submodules in the phase are sorted; the switch signals of the corresponding full-bridge submodules are allocated according to the sequence to achieve voltage balance among the full-bridge submodules in the phase; the switch signal is obtained according to the switch voltage modulation wave.

[0006] As a further improvement of the present invention, the static operating point of the DC side voltage is obtained through matching control of the SVG system, specifically including: Obtain the SVG system power reference value, the SVG system output power, and the average value of the three-phase cluster voltage; Equivalent modeling is performed on the three-phase output power of the SVG system; the total equivalent output power is calculated based on the three-phase equivalent power; The SVG matching control is performed according to the total equivalent output power, the power reference value and the average value of the three-phase cluster voltage to obtain the operating frequency of the SVG system and the static operating point of the DC side voltage.

[0007] As a further improvement of the present invention, SVG matching control is performed according to the total equivalent output power, the power reference value and the average value of the three-phase cluster voltage, specifically including: The operating frequency of the SVG system is:

[0008] The static operating point of the DC side voltage is:

[0009] In the formula, is the operating frequency of the SVG system; is a first proportional controller; is the power reference value of the SVG system; is the total equivalent output power; is the second proportional controller; is the average value of the three-phase cluster voltage; is the matching ratio between the DC side voltage and frequency; is the grid side frequency reference value; is the DC side voltage reference value.

[0010] As a further improvement of the present invention, cluster voltage balance control is performed according to the static operating point of the DC side voltage by superimposing a component in phase with the reactive voltage component, specifically including: The capacitor voltage of the three-phase cluster is obtained, and the average capacitor voltage of the three-phase cluster is obtained according to the capacitor voltage of the three-phase cluster; the q-axis component of the DC side current is obtained; PI control is performed according to the static operating point of the DC side voltage and the average capacitor voltage of the three-phase cluster to obtain a control current signal; After the control current signal and the q-axis component of the DC side current are controlled by the current inner loop, an inverse dq coordinate transformation is performed to obtain the balanced voltage signals of the three-phase cluster respectively.

[0011] As a further improvement of the present invention, the switching signal is obtained according to the switching voltage modulation wave, specifically including: the voltage modulation wave is modulated by a carrier stacking algorithm to obtain the switching signal.

[0012] As a further improvement of the present invention, the carrier stacking algorithm modulation includes: Each phase uses 2N phase-aligned triangular carriers, which are compared with the superimposed modulated wave to generate a 2N+1 level output, where N is the number of cascaded sub-modules per phase.

[0013] As a further improvement of the present invention, the charging and discharging priorities of the full-bridge submodules in the phase are sorted; the switch signals of the corresponding full-bridge submodules are distributed according to the sequence to achieve voltage balance between the full-bridge submodules in the phase, specifically including: Real-time acquisition of capacitor voltage of full-bridge submodules in each phase and instantaneous power of SVG system; When the instantaneous power is positive, the full-bridge submodule with the highest capacitor voltage is discharged; when the instantaneous power is negative, the full-bridge submodule with the lowest capacitor voltage is charged; The switching signal modulated by the carrier stacking algorithm is dynamically allocated according to the charging and discharging priority sorting results of the full-bridge sub-modules.

[0014] As a further improvement of the present invention, after the voltages between the full-bridge sub-modules in the phase are balanced, the operating frequency of the SVG system is adjusted through a frequency synchronization mechanism, so that the operating frequency of the SVG system tracks the grid frequency, and the static operating point of the DC side voltage is dynamically corrected according to the power deviation.

[0015] In a second aspect, the present invention provides a non-storage energy SVG system, comprising: A three-phase topology circuit, wherein the three-phase topology circuit is obtained by cascading N full-bridge sub-modules; The voltage and current detection module is used to obtain the three-phase voltage value of each full-bridge sub-module; A digital signal processor, used to implement the above-mentioned network control method of the SVG system without energy storage; A multi-channel PWM signal distributor dynamically distributes switching signals to each full-bridge sub-module according to the energy sorting results.

[0016] In a third aspect, the present invention provides a computer-readable storage medium storing one or more programs, wherein the one or more programs include instructions, which, when executed by a computing device, enable the computing device to execute the above-mentioned energy storage-free SVG system networking control method.

[0017] In a fourth aspect, the present invention provides a computing device, comprising: One or more processors, a memory and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include steps for executing the above-mentioned method for controlling the networking of the SVG system without energy storage.

[0018] The beneficial effects of the present invention are as follows: the present invention provides a method for controlling a network of an SVG system without energy storage, which has a simple control structure and proposes a SVG network control method by utilizing the matching relationship between the DC bus voltage and the AC side frequency. Through the matching control of the SVG system and the cluster voltage balance control, the voltage balance control between the three phases is realized, which effectively improves the stability of the grid voltage and avoids the influence of voltage fluctuations on the power system. The voltage balance within the phase is achieved by sorting the full-bridge sub-modules within the phase. The present invention realizes the active support construction of the AC port voltage and the DC side voltage balance without energy storage, and does not require additional overall voltage control. The method of the present invention enables the SVG cascade system to achieve a faster frequency response than the traditional network control, and has a better voltage support capability than the traditional grid-following control, especially in the case of internal parameter imbalance or external working condition imbalance, the system can achieve network control and parameter performance without difference adjustment and stable operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 It is a circuit diagram of a control strategy applicable to a cascaded H-bridge SVG system proposed by the present invention.

[0021] Figure 2 It is a control block diagram applicable to the cascaded H-bridge SVG system proposed by the present invention.

[0022] Figure 3 It is a schematic diagram of equivalent modeling of the cascaded H-bridge SVG power level proposed in the present invention.

[0023] Figure 4It is a block diagram of the phase-to-phase cluster DC side voltage balance control proposed by the present invention.

[0024] Figure 5 It is a carrier stacking modulation principle diagram and an intra-phase submodule DC side voltage balance control block diagram proposed by the present invention.

[0025] Figure 6 It is a network control block diagram of the SVG system proposed by the present invention.

[0026] Figure 7 The cascaded H-bridge SVG system proposed in the present invention is a simulated waveform diagram of external load frequency and support voltage (a), output power and average value of DC side voltage of each phase (b).

[0027] Figure 8 The cascaded H-bridge SVG system proposed in the present invention is a simulation waveform diagram of the external line impedance frequency and support voltage (a), output power and average value of DC side voltage of each phase (b).

[0028] Fig. 9 The cascaded H-bridge SVG system proposed in the present invention is a simulation waveform diagram of the frequency and support voltage (a), output power and the average value of the DC side voltage of each phase (b) when the internal capacitance value is unbalanced when the system is started.

[0029] Fig.10 It is a schematic diagram of the structure of electronic equipment integrated with the network control method of the energy storage-free SVG system proposed by the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose and technical solution of the present invention clearer and easier to understand, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, wherein the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0032] Example 1 like Figures 1 to 9 As shown, this embodiment provides a method for controlling the network construction of a SVG system without energy storage, which includes the DC side voltage balance control between the three phases and the DC side voltage balance control of each cascade submodule in the phase; wherein the interphase balance control is realized by superimposing the same-phase component as the reactive voltage component, and the internal balance control includes the energy sorting method of the submodule. The following is a specific implementation method.

[0033] The SVG system in this embodiment is as follows Figure 1As shown in the figure, a cascaded H-bridge SVG system includes a three-phase topology circuit. Each phase topology structure in the three-phase topology circuit includes N cascaded full-bridge sub-modules. The voltage of each full-bridge sub-module can be independently controlled to output multiple levels of positive and negative voltages. The SVG system finally passes through the filter inductor. and filter resistor Incorporate into the AC measurement infinite network.

[0034] First, obtain the grid-side frequency and voltage reference values; Through the matching control of the SVG system, the static operating point of the DC side voltage is obtained. And the static operating point of the DC side voltage is used as an input reference value for three-phase cluster voltage balance control.

[0035] In this embodiment, the networking characteristic is that matching control provides frequency following, reference voltage instructions and balance control instructions to complete voltage support.

[0036] Obtain the SVG system power reference value, the SVG system output power, and the average value of the three-phase cluster voltage; Equivalent modeling is performed on the three-phase output power of the SVG system; the total equivalent output power is calculated based on the three-phase equivalent power; The SVG matching control is performed according to the total equivalent output power, the power reference value and the average value of the three-phase cluster voltage to obtain the operating frequency of the SVG system and the static operating point of the DC side voltage.

[0037] The SVG matching control is performed according to the total equivalent output power, the power reference value and the average value of the three-phase cluster voltage, specifically including: The operating frequency of the SVG system is:

[0038] The static operating point of the DC side voltage is:

[0039] In the formula, is the operating frequency of the SVG system; is a first proportional controller; is the power reference value of the SVG system; is the total equivalent output power; is the second proportional controller; is the average value of the three-phase cluster voltage; is the matching ratio between the DC side voltage and frequency; is the grid side frequency reference value; is the DC side voltage reference value.

[0040] In this embodiment, the average value of the three-phase cluster voltage is :

[0041] In the formula, , , Represent the average voltage of the full-bridge sub-module of phase a, b, and c respectively.

[0042] According to the static working point of the DC side voltage, the cluster voltage balance control is performed by superimposing the component in phase with the reactive voltage component; the balanced voltage signal of the three-phase cluster is obtained; and the DC side voltage balance between the three phases is completed. Figure 4 As shown, the capacitor voltage of the three-phase cluster is obtained, and the average capacitor voltage of the three-phase cluster is obtained according to the capacitor voltage of the three-phase cluster; the q-axis component of the DC side current is obtained; PI control is performed according to the static operating point of the DC side voltage and the average capacitor voltage of the three-phase cluster to obtain a control current signal; After the control current signal and the q-axis component of the DC side current are controlled by the current inner loop, an inverse dq coordinate transformation is performed to obtain the balanced voltage signals of the three-phase cluster.

[0043] In the transient process, the capacitor voltage contains a double frequency fundamental component, so a low-pass filter needs to be added to the control loop to eliminate its influence. Taking phase a as an example, the balance control is based on the DC side voltage reference value provided by the matching control (i.e., the static operating point of the DC side voltage). , the average capacitor voltage of the phase a cluster as well as q Shaft current , generating a balanced voltage signal of the a-phase cluster , as shown below:

[0044] because and All are DC quantities, and the output of the secondary current loop needs to be multiplied by " ”, which is equivalent to performing the inverse dq Coordinate transformation. During system operation, the current of phase a q Axis Component Greater than d Axis Component Therefore, multiply the voltage control amount by Compared to multiplying by cos "(i.e. compensating the component that is in phase with the reactive current is faster than compensating the component that is in phase with the active current) can achieve faster balance convergence.

[0045] The balanced voltage signal With the command voltage reference value After superposition, a voltage modulated wave is obtained; The charging and discharging priorities of the full-bridge submodules in the phase of the SVG system are sorted; the switching signals of the corresponding full-bridge submodules are allocated according to the sequence to achieve voltage balance among the full-bridge submodules in the phase.

[0046] In this embodiment, the switching signal is obtained according to the switching voltage modulation wave. The voltage modulation wave is modulated by the carrier stacking algorithm (PD-SPWM) to obtain the switching signal. Each phase uses 2N phase-aligned triangular carriers, which are compared with the superimposed modulation wave to generate a 2N+1 level output, where N is the number of cascaded submodules per phase.

[0047] The individual voltage balance control within the phase is as follows: the capacitor voltage of the full-bridge submodule within each phase and the instantaneous power of the SVG system are obtained in real time; When the instantaneous power is positive, the full-bridge submodule with the highest capacitor voltage is discharged; when the instantaneous power is negative, the full-bridge submodule with the lowest capacitor voltage is charged; The switching signal modulated by the carrier stacking algorithm is dynamically allocated according to the charging and discharging priority sorting results of the full-bridge sub-modules.

[0048] Specifically, the initial switching signal and Obtained by carrier stacking modulation. Then, a sorting method is used to sort the capacitor voltages of the submodules in each phase. The distribution of the switching signal is determined by the sign of the instantaneous power of each phase. When the instantaneous power is positive, it indicates power output, and the submodules with relatively high capacitor voltages are discharged first. On the contrary, when the instantaneous power is negative, it indicates power absorption, and the submodules with relatively low capacitor voltages are charged first. This ensures the individual voltage balance of the submodules. Since the reference value of the overall DC side voltage is given by the synchronization loop, the system no longer requires an additional overall DC side voltage control loop. In summary, the grid-type cascaded H-bridge SVG system of the present invention realizes the support of the grid side voltage, the following of the frequency, the DC side voltage balance between phases, and the DC side voltage balance control between submodules within the phase, and can still operate stably under unbalanced conditions.

[0049] In addition, after the voltages between the full-bridge sub-modules in the phase are balanced, the operating frequency of the SVG system is adjusted through a frequency synchronization mechanism so that the operating frequency of the SVG system tracks the grid frequency and the static operating point of the DC side voltage is dynamically corrected according to the power deviation.

[0050] Under the framework of the present invention, the active power provided by SVG follows the given reference (If only reactive power output is required, =0), the stability of the grid-side voltage support depends on the frequency synchronization performance in the matching control and the bandwidth of the voltage balancing mechanism. The balanced control of the DC side voltage of the submodule helps to generate the synchronous frequency quickly and stably.

[0051] Example 2 As a further optimization of this embodiment, the specific control block diagram of equivalent circuit modeling, voltage cluster balance control, voltage balance control between sub-modules within a phase, and SVG matching control network support proposed in this embodiment is as follows: Figure 3-Figure 6 shown.

[0052] First, the output power of the three-phase cascaded H-bridge SVG system is equivalently modeled. Taking phase a as an example, when the converter loss is ignored, the following equation holds:

[0053] in is the overall output power of phase a, is the equivalent model coefficient, is the average voltage of the full-bridge submodule of phase a. Since this system adopts carrier stacking modulation, the coefficient N in this formula is actually smaller than the number of cascades (number of submodules) of each phase, and an equivalent derivation is required. Take a quarter cycle as the research object. When there are k submodules running at this time, the modulation wave amplitude satisfies:

[0054] in is the number of cascades for each phase. At this time, the running time of k submodules is:

[0055] At this time, the output power of phase a It can be expressed as:

[0056] It can be seen that the equivalent model coefficient N can be corrected by the following formula:

[0057] Similarly, the equivalent power expressions of phase b and phase c are derived. By adding the power of all three phases, the total equivalent output power expression of the SVG system under cluster voltage balance control is obtained:

[0058] in Represents the average value of the three-phase cluster voltage:

[0059] The relationship between the output power and the three-phase DC link voltage dynamics is established through the total equivalent output power expression. dq In the coordinate system, the output power can also be expressed as:

[0060] In this embodiment, the angular frequency difference between the SVG system and the grid side is The dynamic equation is:

[0061] in, Indicates the grid frequency. Figure 6 The synchronization mechanism in SVG, the working frequency It can be expressed as:

[0062] in, Indicates the matching ratio between DC side voltage and frequency, For proportional controller; proportional controller As the equivalent PI parameter of the power outer loop. This PI regulation synchronization structure is similar to the phase-locked loop in the traditional grid following control, which achieves faster frequency following. On the other hand, its output power can appropriately and quickly track the reference value (i.e. = = 0).

[0063] According to the equivalent model, the control loop needs to be connected in a cascade configuration by adding a second proportional controller The controller is used to obtain the entire DC side voltage of a single phase and limit the overcurrent, ensuring that the system can operate under extreme conditions.

[0064] In addition, the modulation strategy adopted in this embodiment is carrier stacking (PD-SPWM) modulation, and its principle is as follows: Figure 5 As shown in Figure 2. The voltage modulation wave of SVG is composed of an open-loop reference signal and a cluster voltage balance control signal. Figure 5 As shown, N cascaded submodules require 2N equal-phase, stacked triangle waves as carrier signals to independently control the positive and negative level outputs of each submodule. Each carrier independently controls the switching state of a single submodule in each phase. Therefore, by comparing 2N carrier waveforms with the modulation wave, 2N+1 voltage levels can be achieved, thereby effectively reducing harmonic distortion. For the carrier stacking modulation strategy, in order to avoid insufficient output level and ensure more stable system operation, it is necessary to perform separate voltage balance control on the full-bridge submodule in each phase. The algorithm flow chart is shown in Figure 5 The initial switching signal and Obtained by carrier stacking modulation. Then, a sorting method is used to sort the capacitor voltages of the full-bridge sub-modules in each phase. The distribution of the switching signal is determined by the sign of the instantaneous power of each phase. When the instantaneous power is positive, it indicates power output, and the full-bridge sub-module with a relatively high capacitor voltage is discharged first. On the contrary, when the instantaneous power is negative, it indicates power absorption, and the sub-module with a relatively low capacitor voltage is charged first. This ensures the individual voltage balance of the sub-modules. Since the reference value of the overall DC side voltage is given by the synchronization loop, the system no longer requires an additional overall DC side voltage control loop. In summary, the meshed cascade H-bridge SVG system of this embodiment realizes the support of the grid side voltage, the following of the frequency, the DC side voltage balance between the phases, and the DC side voltage balance control between the sub-modules within the phase, and can still operate stably under unbalanced conditions.

[0065] In addition, this embodiment also uses MATLAB / Simulink to simulate the cascaded H-bridge SVG system of the present invention. In the simulation model, the system control method proposed in this embodiment is adopted. In order to facilitate the explanation of the network support capability and the ability to cope with unbalanced working conditions, a grid-connected cascaded H-bridge SVG system with 10 cascaded sub-modules per phase is simulated and tested for its performance under three different balanced operating conditions. The grid-side frequency value is set to 0.97 (pu), and the grid voltage support reference value is The initial value is set to (pu). The SVG system started 0.5 seconds ago and has reached a stable state.

[0066] The simulation waveform under unbalanced external load condition is as follows Figure 7 In order to verify the active voltage support capability of the SVG system without energy storage under unbalanced conditions and the module voltage control and balancing performance, the unbalanced load is connected at 1 second and the grid forming voltage reference value is increased to 3.5 seconds. (pu) Figure 7 (a) shows that at 1 second, when an unbalanced external load is connected, the SVG frequency quickly tracks the grid-side frequency after a short transient process (fluctuation does not exceed 0.02pu). Similarly, at 3.5 seconds, the increase in the grid-forming voltage reference causes the frequency to follow the grid-side frequency within 0.5 seconds (fluctuation does not exceed 0.03pu). During this period, the SVG maintains an almost constant voltage to support the grid side, and quickly and actively adjusts the supporting voltage according to the grid-forming voltage reference, demonstrating its active voltage support capability under unbalanced conditions. Figure 7In (b), it can be observed that at 1 second, the cluster voltage undergoes a 2.5 second transient process after the unbalanced external load is connected, converging to the static operating point. At 3.5 seconds, the increase in the grid voltage reference value causes a temporary voltage imbalance, which is completely resolved within 2.5 seconds. This verifies the system's cluster voltage balancing capability under unbalanced conditions.

[0067] The simulation waveform under unbalanced line impedance conditions is as follows Figure 8 As shown, at 1 second, an unbalanced line impedance is introduced. Figure 8 (a) shows that at 1 second, with the connection of the unbalanced external line impedance, the SVG frequency quickly tracks the grid-side frequency after a short transient process (fluctuation does not exceed 0.005pu). During this period, the SVG exhibits a temporary voltage imbalance when supporting the grid side, which recovers to the given value within 1 second (fluctuation does not exceed 0.02pu), demonstrating its voltage support capability under such unbalanced conditions. Figure 8 In (b), it can be observed that at 1 second, with the connection of the unbalanced external load, the three-phase cluster voltage undergoes a transient process of 2.5 seconds and converges to the static operating point, verifying the cluster voltage balancing capability of the system under such unbalanced conditions.

[0068] The simulation waveform under the condition of unbalanced capacitance of internal submodules is as follows Fig. 9 During startup, balance control was intentionally disabled before steady state was reached (0.5 seconds) and then enabled at 1 second. Fig. 9 In (a), it can be observed that the SVG support voltage remains at a given value even in the presence of an internal impedance imbalance during startup. At 1 second, when the balance control is activated, the SVG frequency quickly tracks the grid-side frequency (fluctuation does not exceed 0.002 pu) after a short transient process. Similarly, when the grid voltage reference value increases at 4 seconds, the frequency follows the grid-side frequency within 0.5 seconds (fluctuation does not exceed 0.02 pu). During this process, the SVG support voltage to the grid remains almost unchanged and quickly follows the given reference value, demonstrating the active voltage support capability under such unbalanced conditions.

[0069] Example 3 This embodiment provides a non-storage SVG system, including: a three-phase topology circuit, a voltage and current detection module, a digital signal processor, and a multi-channel PWM signal distributor. Each module specifically includes: Three-phase topology circuit, the three-phase topology circuit is obtained by cascading N full-bridge sub-modules; The voltage and current detection module is used to obtain the three-phase voltage value of each full-bridge sub-module; A digital signal processor, used to implement the network control method of the SVG system without energy storage in Example 1 or Example 2; A multi-channel PWM signal distributor dynamically distributes switching signals to each full-bridge sub-module according to the energy sorting results.

[0070] Example 4 In one embodiment of the present invention, a computer-readable storage medium is provided, which belongs to a memory device of a terminal device and is mainly used to store programs and data. Computer-readable storage media include both storage media built into the terminal and extended storage media supported by the terminal. Specifically, any tangible medium that can store programs and be used by an instruction execution system, device or device falls into this category. The storage medium provides storage space for storing a terminal operating system and instructions (including one or more computer programs and their codes) that can be loaded and executed by a processor. Examples include electrical connections, portable disks, hard disks, RAM, ROM, EPROM / flash memory, optical fibers, CD-ROMs, optical storage devices, magnetic storage devices, etc., and combinations thereof.

[0071] In addition, computer-readable storage media also refers to data signals propagated in baseband or as carrier waves, which carry readable program codes and can be in the form of electromagnetic signals, optical signals, etc. Readable storage media are not limited to the above types, but also include other media that can send, propagate or transmit programs for use by instruction execution systems, devices or devices. Program codes can be transmitted by wireless, wired, optical cable, RF, etc.

[0072] Program code can be written in a variety of programming languages, such as object-oriented languages ​​(Python, Java, C++, etc.) and procedural languages ​​(C, etc.). The code can be executed completely or partially on the user's device, as a stand-alone software package, or partially / completely on a remote device. The remote device is connected to the user's device via a LAN, WAN, or Internet service provider.

[0073] The processor may load and execute one or more instructions stored in a computer-readable storage medium to implement the corresponding steps of the method for controlling the networking of the SVG system without energy storage in the above embodiment; the processor may load and execute the following steps of one or more instructions in the computer-readable storage medium: Obtain grid-side frequency and voltage reference values; By means of matching control of the SVG system, a static operating point of the DC side voltage is obtained, and the static operating point of the DC side voltage is used as an input reference value for voltage balance control of the three-phase cluster; According to the static working point of the DC side voltage, the cluster voltage balance control is performed by superimposing the component in phase with the reactive voltage component; the balanced voltage signal of the three-phase cluster is obtained; and the DC side voltage balance among the three phases is completed; The voltage modulation wave is obtained by superimposing the balanced voltage signal and the voltage reference value; The charging and discharging priorities of the full-bridge submodules in the phase of the SVG system are sorted; the switching signals of the corresponding full-bridge submodules are allocated according to the sequence to achieve voltage balance among the full-bridge submodules in the phase.

[0074] Example 5 Fig.10 The present invention is a block diagram of an electronic device provided according to an embodiment.

[0075] See also Fig.10 The terminal device 600 is an electronic device, and the electronic device is in the form of a general computing device. The components of the electronic device may include but are not limited to: at least one processing unit 610, at least one storage unit 620, a bus 630 connecting different platform components (including the storage unit 620 and the processing unit 610), a display unit 640, etc.

[0076] The storage unit stores program codes, which can be executed by the processing unit 610, so that the processing unit 610 performs the steps according to various exemplary embodiments of the present invention described in the above method section of this specification. For example, the processing unit 610 can perform the following steps: Figure 1 Follow the steps shown in .

[0077] The storage unit 620 may include a readable medium in the form of a volatile storage unit, such as a random access storage unit (RAM) 6201 and / or a cache storage unit 6202 , and may further include a read-only storage unit (ROM) 6203 .

[0078] The storage unit 620 may also include a program / utility 6204 having a set (at least one) of program modules 6205, such program modules 6205 including but not limited to: an operating system, one or more application programs, other program modules, and program data, each of which or some combination may include an implementation of a network environment.

[0079] Bus 630 may represent one or more of several types of bus structures, including a memory unit bus or memory unit controller, a peripheral bus, an accelerated graphics port, a processing unit, or a local bus using any of a variety of bus architectures.

[0080] The electronic device 600 may also communicate with one or more external devices 700 (e.g., keyboards, pointing devices, Bluetooth devices, etc.), may also communicate with one or more devices that enable a user to interact with the electronic device 600, and / or communicate with any device that enables the electronic device 600 to communicate with one or more other computing devices (e.g., routers, modems, etc.). Such communication may be performed via an input / output (I / O) interface 650. Furthermore, the electronic device 600 may also communicate with one or more networks (e.g., a local area network (LAN), a wide area network (WAN), and / or a public network, such as the Internet) via a network adapter 660. The network adapter 660 may communicate with other modules of the electronic device 600 via a bus 630. It should be understood that, although not shown in the figure, other hardware and / or software modules may be used in conjunction with the electronic device 600, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage platforms, etc.

Claims

1. A network control method for a SVG system without energy storage, characterized in that: include: Obtain grid-side frequency and voltage reference values; By means of matching control of the SVG system, a static operating point of the DC side voltage is obtained, and the static operating point of the DC side voltage is used as an input reference value for voltage balance control of the three-phase cluster; According to the static working point of the DC side voltage, the cluster voltage balance control is performed by superimposing the component in phase with the reactive voltage component; the balanced voltage signal of the three-phase cluster is obtained; and the DC side voltage balance among the three phases is completed; The voltage modulation wave is obtained by superimposing the balanced voltage signal and the voltage reference value; The charging and discharging priorities of the full-bridge submodules in the phase of the SVG system are sorted; the switch signals of the corresponding full-bridge submodules are allocated according to the sequence to achieve voltage balance between the full-bridge submodules in the phase; the switch signal is obtained according to the switch voltage modulation wave.

2. The method for controlling a network of a SVG system without energy storage according to claim 1, characterized in that: Through the matching control of the SVG system, the static operating point of the DC side voltage is obtained, including: Obtain the SVG system power reference value, the SVG system output power, and the average value of the three-phase cluster voltage; Equivalent modeling is performed on the three-phase output power of the SVG system; the total equivalent output power is calculated based on the three-phase equivalent power; The SVG matching control is performed according to the total equivalent output power, the power reference value and the average value of the three-phase cluster voltage to obtain the operating frequency of the SVG system and the static operating point of the DC side voltage.

3. The method for controlling the network construction of a SVG system without energy storage according to claim 2, characterized in that: SVG matching control is performed based on the total equivalent output power, power reference value and the average value of the three-phase cluster voltage, including: The operating frequency of the SVG system is: The static operating point of the DC side voltage is: In the formula, is the operating frequency of the SVG system; is a first proportional controller; is the power reference value of the SVG system; is the total equivalent output power; is the second proportional controller; is the average value of the three-phase cluster voltage; is the matching ratio between the DC side voltage and frequency; is the grid side frequency reference value; is the DC side voltage reference value.

4. The method for controlling a network of a SVG system without energy storage according to claim 1, characterized in that: According to the static working point of the DC side voltage, cluster voltage balance control is performed by superimposing a component in phase with the reactive voltage component, specifically including: The capacitor voltage of the three-phase cluster is obtained, and the average capacitor voltage of the three-phase cluster is obtained according to the capacitor voltage of the three-phase cluster; the q-axis component of the DC side current is obtained; PI control is performed according to the static operating point of the DC side voltage and the average capacitor voltage of the three-phase cluster to obtain a control current signal; After the control current signal and the q-axis component of the DC side current are controlled by the current inner loop, an inverse dq coordinate transformation is performed to obtain the balanced voltage signals of the three-phase cluster respectively.

5. The method for controlling a network of a SVG system without energy storage according to claim 1, characterized in that: The switching signal is obtained according to the switching voltage modulation wave, specifically including: the voltage modulation wave is modulated by a carrier stacking algorithm to obtain the switching signal.

6. The method for controlling the network construction of a SVG system without energy storage according to claim 5, characterized in that: The carrier stacking algorithm modulation includes: Each phase uses 2N phase-aligned triangular carriers, which are compared with the superimposed modulated wave to generate a 2N+1 level output, where N is the number of cascaded sub-modules per phase.

7. The method for controlling the network construction of a SVG system without energy storage according to claim 6, characterized in that: Sort the charging and discharging priorities of each full-bridge submodule in the phase; distribute the switch signals of the corresponding full-bridge submodules according to the sequence to achieve voltage balance between the full-bridge submodules in the phase, specifically including: Real-time acquisition of capacitor voltage of full-bridge submodules in each phase and instantaneous power of SVG system; When the instantaneous power is positive, the full-bridge submodule with the highest capacitor voltage is discharged; when the instantaneous power is negative, the full-bridge submodule with the lowest capacitor voltage is charged; The switching signal modulated by the carrier stacking algorithm is dynamically allocated according to the charging and discharging priority sorting results of the full-bridge sub-modules.

8. The method for controlling a network of a SVG system without energy storage according to claim 1, characterized in that: After the voltages between the full-bridge sub-modules in the phase are balanced, the operating frequency of the SVG system is adjusted through a frequency synchronization mechanism so that the operating frequency of the SVG system tracks the grid frequency and the static operating point of the DC side voltage is dynamically corrected according to the power deviation.

9. A SVG system without energy storage, characterized in that: include: A three-phase topology circuit, wherein the three-phase topology circuit is obtained by cascading N full-bridge sub-modules; The voltage and current detection module is used to obtain the three-phase voltage value of each full-bridge sub-module; A digital signal processor, used to implement the network control method of the SVG system without energy storage as described in claims 1-7; A multi-channel PWM signal distributor dynamically distributes switching signals to each full-bridge sub-module according to the energy sorting results.

10. A computer-readable storage medium storing one or more programs, characterized in that: The one or more programs include instructions, and when the instructions are executed by a computing device, the computing device executes the method for controlling the networking of an SVG system without energy storage as claimed in any one of claims 1 to 7.

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