A no-energy-storage SVG system and a network construction control method thereof

Abstract

The application relates to the technical field, in particular to a SVG (static var generator) system without energy storage and a network construction control method thereof. The method comprises the following steps: determining a static working point of a DC side voltage through SVG system matching control, and taking the static working point as an input reference value of three-phase cluster voltage balance control. A component in phase with a reactive voltage component is used for cluster voltage balance control to generate a balance signal of each phase of the three phases, so that the DC side voltage balance among the three phases is realized. The balance signal and a voltage reference value are superposed to obtain a voltage modulation wave. Meanwhile, the priority of charging and discharging of each full-bridge sub-module in the phase is sorted, and corresponding full-bridge sub-module switch signals are distributed according to the sorting result, so that the voltage balance among the full-bridge sub-modules in the phase is realized. Based on the inter-phase and intra-phase voltage balance control, the stable control of the grid side frequency and voltage is realized.

Description

Technical Field

[0001] This invention relates to the technical field, specifically to an energy storage-free SVG system and its network control method. Background Technology

[0002] With the development of power electronics technology, Static Var Generators (SVGs) are playing an increasingly important role in power transmission, distribution, and renewable energy integration. Based on power electronic converters, SVG systems can adjust reactive power output in real time, responding to grid voltage fluctuations and load changes, providing efficient reactive power compensation. They exhibit significant advantages, especially in power systems with large grid load variations and renewable energy integration. In SVG technology, the Cascaded H-Bridge (CHB) architecture is an important topology. A 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 to traditional modular SVG systems, the Cascaded H-Bridge SVG system, with its modular structure and multi-level output, has significant advantages in improving power quality and suppressing harmonics, making it a key technology in power transmission and distribution systems. In flexible DC transmission systems, most new energy power generation is transmitted to the grid side through power electronic equipment. However, as the proportion of traditional synchronous units decreases, the system frequency changes faster and the voltage amplitude fluctuates more violently after a large disturbance occurs on the grid side, and even broadband oscillations may occur.

[0003] Grid-Froming Control (GFM) has emerged as a promising solution to address these challenges. Devices employing GFM control strategies can regulate grid voltage and frequency by simulating the behavior of synchronous generators. They typically rely on droop control to establish relationships between active power and frequency, and reactive power and voltage amplitude. While droop control provides a simple and effective mechanism for achieving grid-froming behavior, it also requires flexible active power output and DC-side energy storage. Given the practical application scenarios of SVG (Static Var Generator), as a critical and commonly used reactive power compensation device, real-time control of active power, reduction of operating costs, and handling of rapid voltage fluctuations and frequency disturbances caused by renewable energy are essential. Therefore, traditional droop grid-froming control methods are not suitable for SVG systems. For grid-connected cascaded SVG systems, voltage imbalance occurs due to the different states of the three-phase branches during startup, resulting in an average DC-side voltage imbalance between the three phases. This phase-to-phase voltage imbalance leads to overmodulation, reducing the grid support capability and stability of the SVG system. Therefore, balanced DC-side voltage control between phases is necessary for cascaded SVG systems. Similarly, because cascaded SVG systems employ a multi-module, multi-level output mode, the charging and discharging times of each module within a phase differ, leading to an imbalance in the DC-side voltages of the modules within that phase. This phase imbalance can also cause overmodulation, thereby reducing the grid support capability and stability of the SVG system. Therefore, to cope with rapid voltage fluctuations and frequency disturbances caused by renewable energy sources, in addition to voltage grid support capability, the operational stability of the SVG system is also a factor to consider. In general, there is currently a lack of a low-cost, grid-based control method for cascaded SVG systems that requires no additional energy storage and can operate stably under unbalanced internal conditions (such as capacity imbalance) and external conditions (such as line impedance imbalance and load imbalance). Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an energy storage-free SVG system and its network control method to address the shortcomings of the prior art, thereby solving the technical problem of unstable system operation caused by internal imbalance in the current cascaded SVG system.

[0005] The objective of this invention is achieved through the following technical solutions:

[0006] In a first aspect, the present invention provides a grid control method for an energy storage-free SVG system, comprising:

[0007] Obtain reference values ​​for grid-side frequency and voltage;

[0008] The static operating point of the DC-side voltage is obtained through the matching control of the SVG system, and the static operating point of the DC-side voltage is used as the input reference value for the three-phase cluster voltage balance control.

[0009] Based on the static operating point of the DC-side voltage, cluster voltage balance control is performed by superimposing components that are in phase with the reactive voltage component; the balance voltage signal of the three-phase cluster is obtained; and the DC-side voltage balance between the three phases is completed.

[0010] The balanced voltage signal is superimposed with the voltage reference value to obtain a voltage modulation wave;

[0011] The charging and discharging priorities of each full-bridge submodule within a phase are sorted; the switching signals of the corresponding full-bridge submodules are allocated according to the order to achieve voltage balance among the full-bridge submodules within a phase; the switching signals are obtained based on the switching voltage modulation wave.

[0012] As a further improvement of the present invention, the static operating point of the DC-side voltage is obtained through the matching control of the SVG system, specifically including:

[0013] Obtain the SVG system power reference value, the SVG system output power, and the average value of the three-phase cluster voltage;

[0014] The three-phase output power of the SVG system is modeled equivalently; the total equivalent output power is calculated based on the obtained three-phase equivalent power.

[0015] Based on the total equivalent output power, power reference value, and average value of the three-phase cluster voltage, SVG matching control is performed to obtain the operating frequency and static operating point of the DC side voltage of the SVG system.

[0016] As a further improvement of the present invention, SVG matching control is performed based on the total equivalent output power, the power reference value, and the average value of the three-phase cluster voltage, specifically including:

[0017] The operating frequency of the SVG system is:

[0018]

[0019] The quiescent operating point of the DC side voltage is:

[0020]

[0021] In the formula, This refers to the operating frequency of the SVG system. It is the first proportional controller; This is the power reference value for the SVG system; This represents the total equivalent output power. It is the second proportional controller; This represents the average value of the three-phase cluster voltage; This refers to the matching ratio between the DC-side voltage and the frequency. This is the reference value for the grid-side frequency. This is the reference value for the DC side voltage.

[0022] As a further improvement of the present invention, based on the static operating point of the DC-side voltage, cluster voltage balance control is performed using components superimposed with those in phase with the reactive voltage component, specifically including:

[0023] Obtain the capacitor voltage of the three-phase cluster, and obtain the average capacitor voltage of the three-phase cluster based on the capacitor voltage of the three-phase cluster; obtain the q-axis component of the DC side current;

[0024] Based on the static operating point of the DC side voltage and the average capacitor voltage of the three-phase cluster, PI control is performed to obtain the control current signal;

[0025] The control current signal and the q-axis component of the DC side current are subjected to inverse dq coordinate transformation after being controlled by the inner current loop, and the balanced voltage signals of the three-phase cluster are obtained respectively.

[0026] As a further improvement of the present invention, the switching signal is obtained from the switching voltage modulation wave, specifically including: the voltage modulation wave is modulated by a carrier stacking algorithm to obtain the switching signal.

[0027] As a further improvement of the present invention, the carrier stacking algorithm modulation includes:

[0028] Each phase uses 2N phase-aligned triangular carrier waves, 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.

[0029] As a further improvement of the present invention, the charging and discharging priorities of each full-bridge submodule within a phase are sorted; the switching signals of the corresponding full-bridge submodules are allocated according to the order to achieve voltage balance among the full-bridge submodules within a phase, specifically including:

[0030] Real-time acquisition of capacitor voltages in each phase's full-bridge submodules and instantaneous power of the SVG system;

[0031] When the instantaneous power is positive, the full-bridge submodule with the highest relative capacitor voltage is discharged; when the instantaneous power is negative, the full-bridge submodule with the lowest relative capacitor voltage is charged.

[0032] The switching signals modulated by the carrier stacking algorithm are dynamically allocated based on the charging and discharging priority ranking results of the full-bridge submodules.

[0033] As a further improvement of the present invention, after the voltage balance between each full-bridge submodule within the phase, 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.

[0034] In a second aspect, the present invention provides an energy storage-free SVG system, comprising:

[0035] Three-phase topology circuit, wherein each three-phase topology circuit is obtained by cascading N full-bridge sub-modules;

[0036] The voltage and current detection module is used to obtain the three-phase voltage values ​​of each full-bridge sub-module;

[0037] A digital signal processor is used to implement the above-mentioned network control method for energy storage-free SVG systems;

[0038] A multi-channel PWM signal distributor dynamically distributes switching signals to each full-bridge submodule based on energy sorting results.

[0039] Thirdly, the present invention provides a computer-readable storage medium for storing one or more programs, the one or more programs including instructions that, when executed by a computing device, cause the computing device to perform the above-described energy storage-free SVG system network control method.

[0040] Fourthly, the present invention provides a computing device, comprising:

[0041] 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 performing the above-described energy storage-free SVG system grid control method.

[0042] The beneficial effects of this invention are as follows: This invention provides a grid-based control method for SVG systems without energy storage. The control structure is simple, and an SVG grid-based control method is proposed by utilizing the matching relationship between DC bus voltage and AC side frequency. Through the matching control and cluster voltage balance control of the SVG system, voltage balance control between the three phases is achieved, effectively improving the stability of the grid voltage and avoiding the impact of voltage fluctuations on the power system. Voltage balance within a phase is achieved by sequencing the full-bridge submodules within each phase. This invention achieves active support construction of AC port voltage and DC side voltage balance without energy storage, and requires no additional overall voltage control. The method of this invention enables SVG cascaded systems to achieve faster frequency response than traditional grid-based control and has better voltage support capability than traditional grid-based control, especially under conditions of internal parameter imbalance or external operating condition imbalance, the system can achieve grid-based control, error-free adjustment of parameter performance, and stable operation. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a circuit diagram of the control strategy for cascaded H-bridge SVG systems proposed in this invention.

[0045] Figure 2 This is a control block diagram for a cascaded H-bridge SVG system proposed in this invention.

[0046] Figure 3 This is a schematic diagram of the equivalent modeling of the cascaded H-bridge SVG power level proposed in this invention.

[0047] Figure 4 This is the block diagram of the DC-side voltage balance control for interphase clusters proposed in this invention.

[0048] Figure 5 This invention presents a schematic diagram of carrier stacking modulation and a block diagram of DC-side voltage balance control for in-phase sub-modules.

[0049] Figure 6 This is the control block diagram of the SVG system network proposed in this invention.

[0050] Figure 7 The simulation waveforms of the cascaded H-bridge SVG system proposed in this invention are shown in the external load frequency and support voltage (a), output power and average DC side voltage of each phase (b).

[0051] Figure 8 The simulation waveforms of the cascaded H-bridge SVG system proposed in this invention are shown in the external line impedance frequency and support voltage (a), output power and average DC side voltage of each phase (b).

[0052] Figure 9 The simulation waveforms of the frequency and supporting voltage (a), output power and average DC-side voltage of each phase of the cascaded H-bridge SVG system proposed in this invention under the condition of unbalanced internal capacitance value are shown in the figure.

[0053] Figure 10 This is a schematic diagram of the electronic device structure integrated with the grid control method for the energy storage-free SVG system proposed in this invention. Detailed Implementation

[0054] To make the objectives and technical solutions of this invention clearer and easier to understand, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0055] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. The described embodiments are only some embodiments of the present invention, and not all embodiments.

[0056] Example 1

[0057] like Figures 1 to 9 As shown, this embodiment provides a grid control method for an energy storage-free SVG system. This method includes DC-side voltage balance control between each phase of the three-phase system and DC-side voltage balance control of each level of interconnected submodules within a phase. The phase-to-phase balance control is achieved by superimposing components in phase with the reactive voltage components, and the internal balance control includes an energy sequencing method for the submodules. The specific implementation is as follows.

[0058] The SVG system in this embodiment is as follows: Figure 1 The diagram shows a cascaded H-bridge SVG system, comprising a three-phase topology. Each phase of the three-phase topology consists of N cascaded full-bridge submodules. The voltage of each full-bridge submodule can be independently controlled, resulting in multiple levels of positive and negative output. The SVG system finally passes through a filter inductor. and filter resistor It is incorporated into the AC measurement infinite network.

[0059] First, obtain reference values ​​for the grid-side frequency and voltage;

[0060] The static operating point of the DC-side voltage is obtained through the matching control of the SVG system. The static operating point of the DC side voltage is used as the input reference value for the three-phase cluster voltage balance control.

[0061] In this embodiment, the network characteristics are achieved by providing frequency following, reference voltage commands, and balance control commands through matching control to support voltage.

[0062] Obtain the SVG system power reference value, the SVG system output power, and the average value of the three-phase cluster voltage;

[0063] The three-phase output power of the SVG system is modeled equivalently; the total equivalent output power is calculated based on the obtained three-phase equivalent power.

[0064] Based on the total equivalent output power, power reference value, and average value of the three-phase cluster voltage, SVG matching control is performed to obtain the operating frequency and static operating point of the DC side voltage of the SVG system.

[0065] Specifically, SVG matching control is performed based on the total equivalent output power, power reference value, and average value of the three-phase cluster voltage, including:

[0066] The operating frequency of the SVG system is:

[0067]

[0068] The quiescent operating point of the DC side voltage is:

[0069]

[0070] In the formula, This refers to the operating frequency of the SVG system. It is the first proportional controller; This is the power reference value for the SVG system; This represents the total equivalent output power. It is the second proportional controller; This represents the average value of the three-phase cluster voltage; This refers to the matching ratio between the DC-side voltage and the frequency. This is the reference value for the grid-side frequency. This is the reference value for the DC side voltage.

[0071] In this embodiment, the average value of the three-phase cluster voltage :

[0072]

[0073] In the formula, , , These represent the average voltages of the a, b, and c phase full-bridge submodules, respectively.

[0074] Based on the static operating point of the DC-side voltage, cluster voltage balance control is performed using components superimposed with those 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. For example... 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 based on the capacitor voltage of the three-phase cluster; the q-axis component of the DC-side current is obtained.

[0075] Based on the static operating point of the DC side voltage and the average capacitor voltage of the three-phase cluster, PI control is performed to obtain the control current signal;

[0076] After the control current signal and the q-axis component of the DC side current are controlled by the inner current loop, they undergo inverse dq coordinate transformation to obtain the balanced voltage signal of the three-phase cluster.

[0077] During transient processes, the capacitor voltage contains a second harmonic fundamental frequency component, therefore a low-pass filter needs to be added to the control loop to eliminate its influence. Taking phase a as an example, this balancing control is based on the DC-side voltage reference value (i.e., the static operating point of the DC-side voltage) provided by the matching control. Average capacitor voltage of phase a cluster as well as q shaft current Generate the balanced voltage signal of phase a cluster. As shown below:

[0078]

[0079] because and Both are DC currents; the output of the secondary current loop needs to be multiplied by "". This is equivalent to executing the reverse. dq Coordinate transformation. During system operation, the phase a current... q Axial components Greater than d Axial components Therefore, multiply the voltage control quantity by " "Compared to multiplying by" cos (That is, compensating for the component in phase with the reactive current can achieve faster balance convergence than compensating for the component in phase with the active current.)

[0080] Balance voltage signal Compared with the command voltage reference value After superposition, a voltage-modulated wave is obtained;

[0081] The charging and discharging priorities of each full-bridge submodule within a phase in the SVG system are sorted; the switching signals of the corresponding full-bridge submodules are allocated according to the order to achieve voltage balance among the full-bridge submodules within a phase.

[0082] In this embodiment, the switching signal is obtained from the switching voltage modulation wave. The voltage modulation wave is modulated using a 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 sub-modules per phase.

[0083] Individual voltage balance control within a phase involves real-time acquisition of the capacitor voltage of the full-bridge submodules and the instantaneous power of the SVG system within each phase.

[0084] When the instantaneous power is positive, the full-bridge submodule with the highest relative capacitor voltage is discharged; when the instantaneous power is negative, the full-bridge submodule with the lowest relative capacitor voltage is charged.

[0085] The switching signals modulated by the carrier stacking algorithm are dynamically allocated based on the charging and discharging priority ranking results of the full-bridge submodules.

[0086] Specifically, the initial switching signal and The voltage is obtained through carrier stacking modulation. Then, a sorting method is used to sort the capacitor voltages of the submodules in each phase. The allocation of switching signals is determined by the sign of the instantaneous power of each phase. When the instantaneous power is positive, it indicates power output, and submodules with relatively higher capacitor voltages are discharged first. Conversely, when the instantaneous power is negative, it indicates power absorption, and submodules with relatively lower capacitor voltages are charged first. This ensures individual voltage balance for each submodule. Since the reference value for the overall DC-side voltage is provided 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 this invention achieves grid-side voltage support, frequency tracking, inter-phase DC-side voltage balance, and intra-phase submodule DC-side voltage balance control, and can still operate stably under unbalanced conditions.

[0087] In addition, after balancing the voltage between each full-bridge submodule within the phase, 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.

[0088] Under the architecture of this invention, the active power provided by the SVG follows a given reference. (If only reactive power output is required, then let) =0), the stability of the grid-side voltage support depends on the frequency synchronization performance and the bandwidth of the voltage balancing mechanism in the matching control. The balancing control of the DC-side voltage of the submodule helps to generate a synchronization frequency quickly and stably.

[0089] Example 2

[0090] As a further preferred embodiment, the specific control block diagram for equivalent circuit modeling, voltage cluster balance control, inter-phase submodule voltage balance control, and SVG matching control network support proposed in this embodiment for network-type SVG cascaded H-bridge systems is as follows: Figures 3-6 As shown.

[0091] First, the output power of the three-phase cascaded H-bridge SVG system is modeled equivalently. Taking phase a as an example, when converter losses are ignored, the following equation holds:

[0092]

[0093] in This represents the overall output power of phase a. These are the coefficients of the equivalent model. Let N be the average voltage of the full-bridge submodule in phase a. Since this system uses carrier-layered modulation, the coefficient N in this equation is actually smaller than the number of cascaded phases (number of submodules), requiring equivalent derivation. Taking a quarter-cycle as the research object, when k submodules are running at this time, the modulation amplitude satisfies:

[0094]

[0095] in Let be the number of cascaded phases. The runtime of the k submodules is then:

[0096]

[0097] At this time, the output power of phase a It can be represented as:

[0098]

[0099] Therefore, the equivalent model coefficient N can be corrected using the following formula:

[0100]

[0101] Similarly, the equivalent power expressions for phases b and c are derived. By summing the power of all three phases, the total equivalent output power expression of the SVG system under cluster voltage balance control is obtained:

[0102]

[0103] in This represents the average value of the three-phase cluster voltage:

[0104]

[0105] The relationship between output power and the dynamics of the three-phase DC link voltage was established through the expression for total equivalent output power. dq In the coordinate system, the output power can also be expressed by the equation:

[0106]

[0107] In this embodiment, the angular frequency difference between the SVG system and the power grid side... The dynamic equation is given by:

[0108]

[0109] in, Indicates the power grid frequency. According to... Figure 6 The synchronization mechanism in SVG, the operating frequency of SVG It can be represented as:

[0110]

[0111] in, This indicates the matching ratio between the DC-side voltage and the frequency. For proportional controller; proportional controller As the equivalent PI parameter of the power outer loop, this PI-regulated synchronization structure is similar to the phase-locked loop in traditional grid following control, achieving faster frequency following. Furthermore, its output power can appropriately and quickly track the reference value (i.e., ...) according to the actual application. = = 0).

[0112] According to the equivalent model, the control loop needs to be configured by adding a second proportional controller in the cascade configuration. The controller is adjusted to acquire the full DC-side voltage of a single phase and limit overcurrent, ensuring the system can operate under extreme conditions.

[0113] Furthermore, the modulation strategy used in this embodiment is carrier stacking (PD-SPWM) modulation, the principle of which is as follows: Figure 5 As shown. The voltage modulation wave of the SVG is composed of an open-loop reference signal and a cluster voltage balance control signal. For example... Figure 5 As shown, N cascaded submodules require 2N triangular waves of equal phase, stacked vertically, as carrier signals to independently control the positive and negative output levels of each submodule. Each carrier independently controls the switching state of a single submodule in each phase. Therefore, by comparing the 2N carrier waveforms with the modulation wave, 2N+1 voltage levels can be achieved, effectively reducing harmonic distortion. For the carrier stacking modulation strategy, to avoid insufficient output levels and ensure more stable system operation, individual voltage balancing control is required for each full-bridge submodule in each phase. The algorithm flowchart is as follows. Figure 5 As shown. Initial switching signal. and The voltage is obtained through carrier-layer modulation. Then, a sorting method is used to sort the capacitor voltages of the full-bridge submodules in each phase. The allocation of switching signals 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 submodules with relatively higher capacitor voltages are discharged first. Conversely, when the instantaneous power is negative, it indicates power absorption, and the submodules with relatively lower capacitor voltages are charged first. This ensures individual voltage balance for each submodule. Since the reference value for the overall DC-side voltage is provided by the synchronization loop, the system no longer requires an additional overall DC-side voltage control loop. In summary, this embodiment of the grid-type cascaded H-bridge SVG system achieves grid-side voltage support, frequency tracking, inter-phase DC-side voltage balance, and intra-phase submodule DC-side voltage balance control, and can still operate stably under unbalanced conditions.

[0114] Furthermore, 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. To facilitate the explanation of the grid support capability and the ability to cope with unbalanced operating conditions, the performance of a grid-connected cascaded H-bridge SVG system with 10 cascaded sub-modules per phase was simulated and tested under three different balanced operating conditions. The grid-side frequency was set to 0.97 (pu), and the grid voltage support reference value was... The initial value is set to (pu). The SVG system started up 0.5 seconds ago and has reached a stable state.

[0115] The simulation waveform under unbalanced external load conditions is as follows: Figure 7 As shown, to verify the active voltage support capability of the SVG system under unbalanced conditions without energy storage, as well as the module voltage control and balancing performance, the unbalanced load was connected after 1 second, and the grid voltage reference value was increased to [value missing] after 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 brief transient process (fluctuation not exceeding 0.02 pu). Similarly, at 3.5 seconds, the increase in the grid voltage reference value causes the frequency to follow the grid-side frequency within 0.5 seconds (fluctuation not exceeding 0.03 pu). During this period, the SVG maintains a nearly constant voltage to support the grid side and actively adjusts the support voltage rapidly according to the grid voltage reference value, 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 transient process of 2.5 seconds after connecting the unbalanced external load, converging to the quiescent 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 ability to balance the cluster voltage under unbalanced conditions.

[0116] The simulated waveform under unbalanced line impedance conditions is as follows: Figure 8 As shown, an unbalanced line impedance is introduced at 1 second. Figure 8 (a) shows that at 1 second, with the connection of an unbalanced external line impedance, the SVG frequency rapidly tracks the grid-side frequency after a brief transient process (fluctuation not exceeding 0.005 pu). During this period, the SVG exhibits a temporary voltage imbalance while supporting the grid side, which recovers to a given value within 1 second (fluctuation not exceeding 0.02 pu), demonstrating its voltage support capability under such imbalance 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 experienced a transient process of 2.5 seconds and converged to the static operating point, verifying the system's ability to balance the cluster voltage under such unbalanced conditions.

[0117] The simulation waveform under the condition of capacitor imbalance in the internal submodule is as follows: Figure 9 As shown. During startup, balance control is intentionally disabled before reaching steady state (0.5 seconds), and then enabled at 1 second. Figure 9 In (a), it can be observed that even with internal impedance imbalance during startup, the SVG support voltage remains at a given value. At 1 second, after the balancing control is activated, the SVG frequency rapidly tracks the grid-side frequency (fluctuation not exceeding 0.002 pu) after a brief 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 not exceeding 0.02 pu). Throughout this process, the SVG's support voltage to the grid remains almost constant and rapidly follows the given reference value, demonstrating its active voltage support capability under such imbalance conditions.

[0118] Example 3

[0119] This embodiment provides an energy storage-free 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:

[0120] Three-phase topology circuit, each of the three-phase topology circuits is obtained by cascading N full-bridge sub-modules;

[0121] The voltage and current detection module is used to obtain the three-phase voltage values ​​of each full-bridge sub-module;

[0122] A digital signal processor is used to implement the network control method for the energy storage-free SVG system in Embodiment 1 or Embodiment 2;

[0123] A multi-channel PWM signal distributor dynamically distributes switching signals to each full-bridge submodule based on energy sorting results.

[0124] Example 4

[0125] In one embodiment of the present invention, a computer-readable storage medium is provided, which belongs to the memory device of a terminal device and is mainly used for storing programs and data. The computer-readable storage medium includes both storage media built into the terminal and extended storage media supported by the terminal. Specifically, any tangible medium capable of storing programs and used by an instruction execution system, apparatus, or device falls within this category. The storage medium provides storage space for storing the terminal operating system and instructions (including one or more computer programs and their code) 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, and combinations thereof.

[0126] Furthermore, computer-readable storage media also include data signals propagated in baseband or as carrier waves, carrying readable program code, which may be in the form of electromagnetic signals, optical signals, etc. Readable storage media are not limited to the types mentioned above, but also include other media capable of sending, propagating, or transmitting programs for use by instruction execution systems, devices, or apparatuses. Program code can be transmitted wirelessly, wired, optically, RF, etc.

[0127] The program code can be written in various programming languages, such as object-oriented languages ​​(Python, Java, C++, etc.) and procedural languages ​​(C, etc.). The code can be executed fully or partially on the user's device, or as a standalone software package, or partially / fully on a remote device. The remote device is connected to the user's device via a LAN, WAN, or Internet service provider.

[0128] One or more instructions stored in a computer-readable storage medium can be loaded and executed by a processor to implement the corresponding steps of the grid control method for the energy storage-free SVG system in the above embodiments; one or more instructions in the computer-readable storage medium are loaded and executed by the processor to perform the following steps:

[0129] Obtain reference values ​​for grid-side frequency and voltage;

[0130] The static operating point of the DC-side voltage is obtained through the matching control of the SVG system, and the static operating point of the DC-side voltage is used as the input reference value for the three-phase cluster voltage balance control.

[0131] Based on the static operating point of the DC-side voltage, cluster voltage balance control is performed by superimposing components that are in phase with the reactive voltage component; the balance voltage signal of the three-phase cluster is obtained; and the DC-side voltage balance between the three phases is completed.

[0132] The balanced voltage signal is superimposed with the voltage reference value to obtain a voltage modulation wave;

[0133] The charging and discharging priorities of each full-bridge submodule within a phase in the SVG system are sorted; the switching signals of the corresponding full-bridge submodules are allocated according to the order to achieve voltage balance among the full-bridge submodules within a phase.

[0134] Example 5

[0135] Figure 10 This is a block diagram of an electronic device according to an embodiment of the present invention.

[0136] Please see Figure 10 The terminal device 600 is an electronic device, which takes the form of a general-purpose 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 storage unit 620 and processing unit 610), a display unit 640, etc.

[0137] The storage unit stores program code, which can be executed by the processing unit 610 to perform the steps described in the method section of this specification according to various exemplary embodiments of the present invention. For example, the processing unit 610 can perform actions such as... Figure 1 The steps are shown in the figure.

[0138] Storage unit 620 may include a readable medium in the form of a volatile storage unit, such as random access memory (RAM) 6201 and / or cache memory 6202, and may further include a read-only memory (ROM) 6203.

[0139] Storage unit 620 may also include a program / utility 6204 having a set (at least one) program module 6205, such program module 6205 including but not limited to: operating system, one or more application programs, other program modules and program data, each or some combination of these examples may include an implementation of a network environment.

[0140] Bus 630 can represent one or more of several types of bus structures, including a memory cell bus or memory cell controller, a peripheral bus, a graphics acceleration port, a processing unit, or a local bus using any of the multiple bus structures.

[0141] Electronic device 600 can also communicate with one or more external devices 700 (e.g., keyboard, pointing device, Bluetooth device, etc.), and with one or more devices that enable a user to interact with electronic device 600, and / or with any device that enables electronic device 600 to communicate with one or more other computing devices (e.g., router, modem, etc.). This communication can be performed via input / output (I / O) interface 650. Furthermore, electronic device 600 can also communicate with one or more networks (e.g., local area network (LAN), wide area network (WAN), and / or public networks, such as the Internet) via network adapter 660. Network adapter 660 can communicate with other modules of electronic device 600 via bus 630. It should be understood that, although not shown in the figures, other hardware and / or software modules can be used in conjunction with 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.

Claims

1. A grid-based control method for an energy storage-free SVG system, characterized in that, include: Obtain reference values ​​for grid-side frequency and voltage; The static operating point of the DC-side voltage is obtained through the matching control of the SVG system, and the static operating point of the DC-side voltage is used as the input reference value for the three-phase cluster voltage balance control. Based on the static operating point of the DC side voltage, the cluster voltage balance control is performed by superimposing the component in phase with the reactive voltage component to obtain the balance voltage signal of the three-phase cluster, thus completing the DC side voltage balance between the three phases. The balanced voltage signal is superimposed with the voltage reference value to obtain a voltage modulation wave; The charging and discharging priorities of each full-bridge submodule within a phase in the SVG system are sorted, and the switching signals of the corresponding full-bridge submodules are allocated according to the order to achieve voltage balance among the full-bridge submodules within a phase; the switching signals are obtained based on the switching voltage modulation wave. Based on the static operating point of the DC-side voltage, cluster voltage balance control is performed using components that are in phase with the reactive voltage component, specifically including: Obtain the capacitor voltage of the three-phase cluster, obtain the average capacitor voltage of the three-phase cluster based on the capacitor voltage of the three-phase cluster, and obtain the q-axis component of the DC side current. Based on the static operating point of the DC side voltage and the average capacitor voltage of the three-phase cluster, PI control is performed to obtain the control current signal; The control current signal and the q-axis component of the DC side current are subjected to inverse dq coordinate transformation after being controlled by the inner current loop, and the balanced voltage signals of the three-phase cluster are obtained respectively.

2. The grid control method for an energy storage-free SVG system according to claim 1, characterized in that, The static operating point of the DC-side voltage is obtained through the 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; The three-phase output power of the SVG system is modeled equivalently; the total equivalent output power is calculated based on the obtained three-phase equivalent power. Based on the total equivalent output power, power reference value, and average value of the three-phase cluster voltage, SVG matching control is performed to obtain the operating frequency and static operating point of the DC side voltage of the SVG system.

3. The grid control method for an energy storage-free SVG system according to claim 2, characterized in that, SVG matching control is performed based on the total equivalent output power, power reference value, and average value of three-phase cluster voltage, specifically including: The operating frequency of the SVG system is: The quiescent operating point of the DC side voltage is: In the formula, This refers to the operating frequency of the SVG system. It is the first proportional controller; This is the power reference value for the SVG system; This represents the total equivalent output power. It is a second proportional controller; This represents the average value of the three-phase cluster voltage; This refers to the matching ratio between the DC-side voltage and the frequency. This is the reference value for the grid-side frequency. This is the reference value for the DC side voltage.

4. The grid control method for an energy storage-free SVG system according to claim 1, characterized in that, The switching signal is obtained from the switching voltage modulation wave, specifically including: the voltage modulation wave is modulated by a carrier stacking algorithm to obtain the switching signal.

5. The grid control method for an energy storage-free SVG system according to claim 4, characterized in that, The carrier stacking algorithm modulation includes: Each phase uses 2N phase-aligned triangular carrier waves, 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.

6. The grid control method for an energy storage-free SVG system according to claim 5, characterized in that, The charging and discharging priorities of each full-bridge submodule within a phase are sorted; the switching signals of the corresponding full-bridge submodules are allocated according to the order to achieve voltage balance among the full-bridge submodules within a phase, specifically including: Real-time acquisition of capacitor voltages in each phase's full-bridge submodules and instantaneous power of the SVG system; When the instantaneous power is positive, the full-bridge submodule with the highest relative capacitor voltage is discharged; when the instantaneous power is negative, the full-bridge submodule with the lowest relative capacitor voltage is charged. The switching signals modulated by the carrier stacking algorithm are dynamically allocated based on the charging and discharging priority ranking results of the full-bridge submodules.

7. The grid control method for an energy storage-free SVG system according to claim 1, characterized in that, After balancing the voltages among the full-bridge submodules within a phase, the system also adjusts the operating frequency of the SVG system through a frequency synchronization mechanism, enabling the SVG system to track the grid frequency and dynamically correct the static operating point of the DC-side voltage based on the power deviation.

8. A non-energy storage SVG system, characterized in that, include: Three-phase topology circuit, wherein each 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 values ​​of each full-bridge sub-module; A digital signal processor for implementing the network control method for an energy storage-free SVG system according to any one of claims 1-7; A multi-channel PWM signal distributor dynamically distributes switching signals to each full-bridge submodule based on energy sorting results.

9. A computer-readable storage medium for storing one or more programs, characterized in that, The one or more programs include instructions that, when executed by a computing device, cause the computing device to perform the grid control method for an energy storage-free SVG system according to any one of claims 1 to 7.

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