Method and system for improving electric energy quality of limited capacity system containing pulse load

Abstract

The invention relates to the field of electric energy quality treatment of an electric power system, and discloses a method for improving the electric energy quality of a limited-capacity system containing a pulse load, and the method comprises the following steps: S1, Clark conversion; s2, positive and negative sequence separation and Park transformation; s3, direct current component extraction; s4, performing inverse transformation and instruction synthesis, and synthesizing required compensation instruction current; s5, on the basis of a timing hysteresis comparison method, a fixed-frequency timer is used for replacing a traditional hysteresis comparator, current tracking of a fixed switching frequency is achieved, and the electric energy quality of a limited-capacity system containing a pulse load is improved, and the system is characterized by comprising a limited-capacity power source, the pulse load and an SVG device connected to an alternating-current bus in parallel; according to the scheme, through an improved SVG detection and control strategy, the electric energy quality problem of a limited capacity system containing a pulse load is effectively solved, and the power supply reliability and stability of the system are improved.

Description

Technical Field

[0001] This invention relates to the field of power quality management in power systems, specifically to a method and system for improving the power quality of finite-capacity systems with pulsed loads. Background Technology

[0002] With the increasing level of industrial automation, high-power pulse loads such as large welding machines, rolling mills, cranes, and electric vehicle charging stations are being used more and more widely. These loads are characterized by high instantaneous power, frequent start-stop, and rapid power changes, posing a severe challenge to power supply systems (especially finite-capacity systems, such as independent power stations, diesel generator sets, or weakly connected microgrids). Typical characteristics of finite-capacity systems include system capacity being comparable to the peak load power, low system inertia, and low short-circuit capacity, resulting in weak disturbance immunity.

[0003] When a pulse load is connected to such a system, the following power quality problems are likely to occur: (1) voltage and frequency fluctuate violently, affecting the stable operation of other precision equipment on the same bus; (2) harmonic pollution causes voltage waveform distortion and increases system losses; (3) power factor decreases, reducing energy transmission efficiency.

[0004] The common improvement measures currently include two categories: (1) enhancing system inertia, such as increasing the rotational inertia of the generator set, but this method has problems such as large equipment size, high cost and slow response; (2) using compensation devices, such as passive filters that are prone to system resonance, and traditional static var compensators (SVCs) have a slow response speed, making it difficult to meet the millisecond-level fast compensation requirements.

[0005] While active power compensation devices (such as static var generators, SVG) possess relatively fast response capabilities, their traditional detection and control strategies are typically designed based on ideal grid conditions (symmetrical voltage, sinusoidal voltage, and stable frequency). In finite-capacity systems with voltage distortion and frequency fluctuations, the following challenges arise: Decreased detection accuracy: Under voltage distortion and three-phase unbalanced conditions, the accuracy of traditional reactive current detection methods (such as the traditional dq0 method) is significantly reduced; Degraded control performance: Pulsed loads require control strategies with extremely high dynamic response speeds. However, traditional hysteresis control and other methods are difficult to maintain optimal performance when the system frequency fluctuates. Inconsistent switching frequencies may lead to increased device stress and decreased tracking performance.

[0006] In summary, existing technologies lack a comprehensive solution that can adapt to the harsh operating conditions (voltage distortion, frequency fluctuation) of finite capacity systems and can quickly and accurately compensate for instantaneous reactive power and harmonics caused by pulse loads. Therefore, we propose a method and system for improving the power quality of finite capacity systems with pulse loads. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method and system for improving the power quality of finite-capacity systems with pulsed loads, thereby improving issues such as system voltage fluctuations, frequency fluctuations, harmonic pollution, and power factor.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: a method for improving the power quality of a finite-capacity system with pulsed loads, comprising the following steps: S1: Clark transform; S2: Separation of positive and negative order and Park transformation; S3: DC component extraction; S4: Inverse transformation and command synthesis, synthesizing the required compensation command current; S5: Based on the timed hysteresis comparator method, a fixed-frequency timer is used to replace the traditional hysteresis comparator to achieve current tracking at a fixed switching frequency.

[0009] Preferably, S1 includes the following: real-time acquisition of three-phase bus voltage and load current, and transformation of them from a three-phase stationary coordinate system (a, b, c) to a two-phase stationary coordinate system (α, β) using Clark transformation (abc / αβ transformation).

[0010] Preferably, S2 includes the following: performing positive-order Park transform (rotational angular frequency + ω) and negative-order Park transform (rotational angular frequency - ω) on the αβ components respectively, to achieve decoupling of the positive-order and negative-order components.

[0011] Preferably, step S3 includes the following: After transformation, the fundamental positive-sequence and negative-sequence components are represented as DC components in their respective rotating coordinate systems. A low-pass filter (LPF) is used to filter out AC harmonics, extracting the positive-sequence DC component (i_d). + ,i_q + ) and negative order components (i_d) - , i_q - ).

[0012] Preferably, S4 includes the following: performing inverse Park transform and inverse Clark transform on the filtered DC component to reconstruct the three-phase fundamental positive sequence current (including reactive and active components), negative sequence current and zero sequence current.

[0013] Preferably, S5 includes the following: C1: Error Calculation: Compare the compensation command current i_ref generated by the reactive current detection module with the actual compensation current i_actual output by the SVG to obtain the current error signal Δi = i_ref – i_actual; C2: Timed sampling and decision: The timer samples the error signal Δi at a fixed frequency (e.g., 5kHz) and determines its sign; C3: PWM signal generation: At the end of each timing cycle, a PWM signal is generated based on the sign of Δi. If Δi > 0, the control switch is turned on to increase the output current; if Δi < 0, it is turned off to decrease the current.

[0014] Preferably, the AC side inductance is 2 mH.

[0015] Preferably, the DC side voltage is set to 600 V.

[0016] Preferably, the DC-side capacitor has a value of 4 mF.

[0017] A system for improving the power quality of a finite-capacity system with a pulsed load includes a finite-capacity power supply, a pulsed load, and an SVG device connected in parallel to the AC bus. The SVG device consists of the following three modules: The main circuit module, as the energy conversion unit, adopts a voltage-source three-phase full-bridge inverter structure, including a three-phase inverter bridge composed of fully controlled devices such as IGBTs, DC-side support capacitors, and AC-side connecting reactors; the DC capacitors are used to maintain voltage stability and reactive power exchange, and the AC reactors are used for filtering and energy control. The reactive current detection module, as a sensing unit, is responsible for real-time detection of reactive and harmonic currents that need to be compensated. The control strategy module, as the decision-making and execution unit, receives the compensation current command issued by the detection module, and uses an improved timing hysteresis comparison method to generate a PWM drive signal to precisely control the operation of the switching devices in the main circuit module.

[0018] Compared with the prior art, the present invention provides a method and system for improving the power quality of a finite-capacity system with pulsed loads, which has the following beneficial effects: High precision and strong adaptability: The improved dq0 detection method overcomes the effects of voltage distortion and load asymmetry, resulting in high detection accuracy.

[0019] Fast dynamic response: The timed hysteresis control strategy enables fast current tracking at a fixed switching frequency, with a response speed in the millisecond range.

[0020] The comprehensive treatment has significant effects: it can simultaneously and effectively suppress voltage / frequency fluctuations, reduce harmonic distortion rate, and improve power factor.

[0021] The system exhibits good robustness: it maintains stable and excellent compensation performance under various pulse loads and complex operating conditions.

[0022] Compact structure and easy integration: The device has high power density and is particularly suitable for space-constrained stand-alone power plants or microgrid scenarios. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a finite-capacity system containing SVG. Figure 2 This is the equivalent structure diagram of the SVG main circuit; Figure 3 The principle block diagram of the improved dq0 reactive current detection method; Figure 4 Block diagram of the improved timing hysteresis comparison control strategy; Figure 5 This is a diagram of the overall system simulation structure; Figure 6 This is a schematic diagram before SVG deployment; Figure 7 This is a schematic diagram showing the effect of SVG implementation. Figure 8 A schematic diagram comparing the alternating current before and after adding SVG; Figure 9 A diagram showing the frequency changes before and after adding SVG; Figure 10 A schematic diagram showing the comparison of DC voltage before and after the addition of SVG; Figure 11 This is a comparison chart of current distortion rate before and after adding SVG. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] A system for improving power quality in finite-capacity systems with pulsed loads, comprising a finite-capacity power supply, a pulsed load, and an SVG device connected in parallel to the AC bus. The SVG device consists of the following three modules: (1) Main circuit module: As an energy conversion unit, it adopts a voltage-source three-phase full-bridge inverter structure, including a three-phase inverter bridge composed of fully controlled devices such as IGBTs, DC-side support capacitors, and AC-side connecting reactors. The DC capacitors are used to maintain voltage stability and reactive power exchange, while the AC reactors are used for filtering and energy control.

[0026] (2) Reactive current detection module As a sensing unit, it is responsible for real-time detection of reactive and harmonic currents that need compensation. This invention employs an improved dq0 detection method (see below for details), which can accurately separate the fundamental positive-sequence reactive current, negative-sequence current, and harmonic components from distorted and unbalanced grid voltages.

[0027] (3) Control Strategy Module As a decision-making and execution unit, it receives compensation current commands from the detection module, generates PWM drive signals using an improved timing hysteresis comparison method, and precisely controls the operation of switching devices in the main circuit module.

[0028] The methods for improving the power quality of finite-capacity systems with pulsed loads are detailed below: Traditional dq0 methods suffer from large detection errors when the grid voltage is distorted. This invention employs a dual-synchronous rotating coordinate transformation decoupling strategy for positive and negative sequence components to achieve accurate separation of the fundamental positive, negative, and zero-sequence components. The specific steps are as follows: S1: Clark Transform: Real-time acquisition of three-phase bus voltage and load current, and transformation of them from a three-phase stationary coordinate system (a, b, c) to a two-phase stationary coordinate system (α, β) using Clark transformation (abc / αβ transformation).

[0029] S2: Separation of positive and negative order and Park transform: The αβ components are subjected to positive order Park transform (rotational angular frequency + ω) and negative order Park transform (rotational angular frequency - ω) respectively to achieve decoupling of positive and negative order components.

[0030] S3: DC Component Extraction: After transformation, the fundamental positive-sequence and negative-sequence components are represented as DC components in their respective rotating coordinate systems. A low-pass filter (LPF) is used to filter out AC harmonics, extracting the positive-sequence DC component (i_d). + , i_q + ) and negative order components (i_d) - , i_q - ).

[0031] S4: Inverse Transformation and Command Synthesis: The filtered DC component undergoes inverse Park and inverse Clark transforms to reconstruct the three-phase fundamental positive-sequence current (including reactive and active components), negative-sequence current, and zero-sequence current. Finally, the required compensation command current is synthesized.

[0032] Improved Control Strategy: To address the issue of inconsistent switching frequencies and performance degradation during frequency fluctuations in traditional hysteresis control, this invention employs an improved timing hysteresis comparator method. This method replaces the traditional hysteresis comparator with a fixed-frequency timer, achieving current tracking at a fixed switching frequency. The specific steps are as follows: C1: Error Calculation: Compare the compensation command current i_ref generated by the reactive current detection module with the actual compensation current i_actual output by the SVG to obtain the current error signal Δi = i_ref – i_actual.

[0033] C2: Timed sampling and decision: The timer samples the error signal Δi at a fixed frequency (e.g., 5kHz) and determines its positive or negative sign.

[0034] C3: PWM signal generation: At the end of each timing cycle, a PWM signal is generated based on the sign of Δi. If Δi > 0, the control switch is turned on to increase the output current; if Δi < 0, it is turned off to decrease the current.

[0035] The advantages of this method are: the switching frequency is fixed, which is conducive to heat dissipation design and device selection; the equivalent loop width adapts to change, which avoids excessively high switching frequency when the current changes suddenly while ensuring tracking accuracy, and is more adaptable to frequency fluctuation conditions.

[0036] 4. Collaborative design of key parameters: To achieve the best match between SVG performance and the characteristics of a limited-capacity system and a pulsed load, the following optimization design was performed on the key parameters of the main circuit: AC side inductance: preferably 2 mH, to achieve a balance between suppressing switching harmonics and ensuring dynamic response speed.

[0037] DC side voltage: set to 600 V, taking into account compensation capacity, current tracking capability, device withstand voltage and cost.

[0038] DC-side capacitor: The value is 4 mF, which effectively suppresses DC voltage fluctuations caused by pulse loads and balances dynamic response and voltage support requirements.

[0039] See Figure 1 : Overall connectivity: Limited capacity power sources (such as diesel generator sets): These serve as the main power source for the system, with their output connected to the AC bus.

[0040] Pulsating loads (such as large welding machines and radar): connected in parallel to the AC bus, are the root cause of power quality problems.

[0041] SVG device: As the core compensation device of this invention, it is also connected in parallel to the AC bus. Its connection "side-by-side" with the pulse load means that it draws current from the same point and injects compensation current into the same point.

[0042] Working principle: The problem arises when a pulse load starts, it instantly draws a huge amount of active and reactive current from the AC bus, like a "current black hole." Due to the small inertia and high internal resistance of power sources with limited capacity (such as diesel generators), they cannot provide such a large current instantaneously, causing the bus voltage to drop instantly and the frequency to fluctuate accordingly.

[0043] Solution: The SVG device acts as a "fast-response backup power source," but it does not provide active power; it only provides reactive power and harmonic current. When a pulsed load requires a large reactive current, the SVG instantaneously "generates" an equal and opposite reactive current through its inverter and injects it into the AC bus. In this way, the reactive current required by the pulsed load is provided by the SVG nearby, while the limited-capacity power source only needs to provide a steady active current, thereby maintaining the stability of the bus voltage and frequency.

[0044] See Figure 2 : Component Connections: This is a typical voltage-source three-phase full-bridge inverter circuit, and its specific connections are as follows: DC-side capacitor: Connected between the positive (P) and negative (N) terminals of the DC bus. Its function is to stabilize the DC-side voltage, providing a stable "voltage platform" for reactive power exchange.

[0045] A three-phase full-bridge inverter consists of six fully controlled switching devices (such as IGBTs) and anti-parallel diodes. Each pair of switching devices forms one bridge arm, for a total of three bridge arms. The input terminals of the three bridge arms are connected to the positive (P) and negative (N) terminals of the DC bus, respectively.

[0046] AC-side connection reactors (L): One end of each of the three reactors is connected to the output points (A, B, C) of the three inverter bridge arms, and the other end is connected to the system AC bus. This reactor is crucial, serving two purposes: firstly, to filter out high-frequency harmonics generated by the switches, and secondly, to control the energy exchange between the inverter AC-side voltage and the system voltage.

[0047] Working principle: The self-commutated three-phase bridge inverter circuit is the core component of SVG reactive power compensation. Connected to the finite-capacity system via reactors, it feeds back system parameters detected by current and voltage detection circuits to the control center in real time. The control center calculates the reactive power requiring compensation using a specific algorithm, controlling the output current on the AC side or the phase and amplitude of the voltage injected into the system to absorb or generate the necessary reactive power. This achieves dynamic reactive power compensation across the entire range, from inductive to capacitive reactive power. Throughout this process, the SVG exhibits fast response and high control accuracy, effectively maintaining the stability of the finite-capacity system.

[0048] See Figure 3 : Signal flow and connectivity: Input signals: Real-time acquisition of three-phase system voltage (ua, ub, uc) and three-phase load current (ia, ib, ic).

[0049] Clark transform (abc / αβ): Converts voltage and current signals in a three-phase stationary coordinate system into signals in a two-phase stationary coordinate system (α, β). This is a mathematical processing module with no physical connection, but logically it "receives" three-phase signals and "outputs" two-phase signals.

[0050] Separation of positive and negative orders and double Park transform: The αβ voltage signal is fed into two phase-locked loops (PLLs), one to lock the positive sequence phase (+ωt) and the other to lock the negative sequence phase (-ωt).

[0051] Using these two phases, the αβ current signal is subjected to positive-sequence Park transform (dq+) and negative-sequence Park transform (dq-) respectively to obtain the DC components in the positive-sequence and negative-sequence rotating coordinate systems.

[0052] Low-pass filter (LPF): Filters the four DC components mentioned above to remove the harmonic AC components and extract the pure fundamental positive-sequence and negative-sequence DC components.

[0053] Inverse Park Transform and Instruction Synthesis: The filtered DC currents are subjected to inverse Park transform to restore the fundamental positive-sequence and negative-sequence currents in the αβ coordinate system.

[0054] These components are synthesized in the αβ coordinate system, and the fundamental positive sequence current, negative sequence current and zero sequence current in the three-phase coordinate system are finally reconstructed through the inverse Clark transformation.

[0055] Command generation: Based on the compensation target (such as only compensating reactive power, or compensating reactive power and harmonics at the same time), the component that needs to be compensated is separated from the reconstructed current, and finally the compensation command current is generated and output to the control strategy module.

[0056] See Figure 4 : Signal flow and connectivity: Input signal: Command current (iref): from the detection module.

[0057] Actual feedback current (i): Acquired from the actual current output from the SVG to the power grid via a current sensor.

[0058] Error Calculator: Receives the two inputs above and calculates Δi = iref - i. This error signal represents the difference between the "desired output current" and the "actual output current".

[0059] Time hysteresis comparator: The core innovation is that a fixed-frequency timer (e.g., 5kHz) controls the entire comparison process.

[0060] Workflow: At the beginning of each timing cycle, the error signal Δi is sampled and latched. At the end of the cycle, the sign of Δi is determined.

[0061] If Δi > 0, it means that the actual output is less than the instruction and the output needs to be increased. Therefore, a PWM signal is generated to turn on the corresponding switch.

[0062] If Δi < 0, it means that the actual output is greater than the instruction, and the output needs to be reduced, so a shutdown signal is generated.

[0063] PWM drive circuit: Based on the output of the comparator, it generates specific PWM pulse signals with dead time to drive the six IGBTs in the main circuit to turn on and off.

[0064] To summarize the closed-loop workflow of the entire system: 1. Sensing: The detection module "watches" the voltage of the power grid and the current of the load in real time.

[0065] 2. Decision: Through an improved algorithm, the compensation current command required to offset the negative impact of the load is accurately "calculated".

[0066] 3. Execution: The control module compares the command with the actual output and generates a PWM drive signal through improved timing hysteresis control.

[0067] 4. Action: Driven by the PWM signal, the main circuit quickly and accurately "issues" the calculated compensation current.

[0068] Effect: The compensation current injected into the power grid cancels out the harmonics and reactive current of the load, ultimately ensuring that the power supply side only sees a stable, sinusoidal active current, thereby stabilizing the voltage and frequency and improving power quality.

[0069] A simulation example of improving a finite-capacity system with pulsed load: System setup: Establish a model of a diesel generator set with a rated power of 50kW and an output voltage of 400V / 50Hz.

[0070] A radar-type pulse load model with a peak power of 40kW, a duty cycle of 50ms, and a duty cycle of 0.4 is established.

[0071] according to Figure 1 As shown, an SVG device is connected in parallel on the AC bus between the generator set and the pulse load.

[0072] The specific simulation parameters are shown in Table 1.

[0073] SVG parameter settings: Main circuit: DC side capacitor C=4mF, DC side voltage setpoint Udc=600V, AC side inductor L=2mH.

[0074] Detection module: according to Figure 3 The structure shown illustrates an improved dq0 detection algorithm module built in Simulink. The inputs are the three-phase system voltage and load current, and the output is the compensation current command signal.

[0075] Control module: according to Figure 4 The structure shown illustrates an improved timing hysteresis comparison control module. The command signal output from the detection module is compared with the SVG output current feedback signal, and a PWM signal is generated by controlling a timer (switching frequency 5kHz).

[0076] Specific work process: The reactive current detection module continuously monitors the bus voltage and load current, and calculates accurate compensation current commands in real time using the improved dq0 algorithm.

[0077] The control strategy module receives the instruction and generates the corresponding PWM switching signal using an improved timing hysteresis comparison method.

[0078] Driven by the PWM signal, the main circuit module controls the inverter bridge to generate a compensation current that is equal in magnitude and opposite in direction to the detected harmonic and reactive currents, and injects it into the AC bus.

[0079] The compensation current counteracts the harmful current components generated by the pulse load, making the current waveform on the power supply side tend to be sinusoidal, effectively suppressing voltage and frequency fluctuations, improving the system power factor, and comprehensively improving power quality.

[0080] Simulation results and analysis: Simulation Structure: The overall simulation structure of the system is as follows Figure 5 As shown.

[0081] Simulation parameters: The specific simulation parameter settings are shown in Table 1.

[0082] Table 1: Simulation Parameter Settings for SVG System ; Start the simulation and observe the system operating indicators before and after the SVG is put into operation. Set the diesel generator set to a rated power of 50kW, power factor of 0.8, synchronous generator rated output voltage of 400V, frequency of 50Hz; pulse load peak power of 40kW, duty cycle of 50ms, duty cycle of 0.4, and filter capacitor of 4000μF.

[0083] Voltage waveform: such as Figure 6 as well as Figure 7 As shown, before the SVG was put into operation, the AC voltage was severely distorted; after the SVG was put into operation, the voltage waveform was restored to a sine wave, and the distortion rate was greatly reduced.

[0084] Current waveform: such as Figure 8 As shown, before the SVG was put into operation, the AC voltage was severely distorted; after the SVG was put into operation, the voltage waveform was restored to a sine wave, and the distortion rate was greatly reduced.

[0085] In summary, before the addition of SVG, the AC voltage and current distortion was severe, especially the significant current change when the peak power of the pulse load arrived. After the addition of SVG, the AC current of the system was quickly compensated, the system phase current stabilized rapidly, the reactive power was fully compensated, the voltage and current waveforms were improved to sinusoidal, and the distortion was significantly reduced.

[0086] Frequency fluctuations: such as Figure 9 As shown, before the SVG was implemented, the frequency fluctuated drastically; after the SVG was implemented, the frequency stability was significantly enhanced.

[0087] DC voltage waveform: as shown Figure 10 As shown, before the SVG was implemented, the frequency fluctuated drastically; after the SVG was implemented, the frequency stability was significantly enhanced.

[0088] Before the SVG was added, the DC bus voltage fluctuated significantly, and the pulse load caused instability to the system. After the SVG was added, the fluctuation amplitude of the DC bus voltage was significantly reduced. The DC side voltage reached the set value in about 0.1s, and after a slight overshoot, the DC voltage stabilized at the set value of 600 V.

[0089] Harmonic content: such as Figure 11 As shown, before the SVG was installed, the total harmonic distortion rate of the current was as high as about 30%; after the SVG was installed, the distortion rate dropped to below 5%, which meets the national standard.

[0090] It can be seen that before the SVG was added, the current distortion was quite severe, with the total harmonic distortion (THD) reaching about 30%, which seriously affected the power supply quality. After adding the SVG, the THD decreased to below 5%, the current distortion was significantly reduced, and it met national standards. This greatly improved the power supply quality.

[0091] In summary, this invention effectively solves the power quality problem of finite capacity systems with pulsed loads by improving the SVG detection and control strategy, thereby improving the power supply reliability and stability of the system.

[0092] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for improving the power quality of a finite-capacity system with pulsed loads, characterized in that, Includes the following steps: S1: Clark transform; S2: Separation of positive and negative order and Park transformation; S3: DC component extraction; S4: Inverse transformation and command synthesis, synthesizing the required compensation command current; S5: Based on the timed hysteresis comparator method, a fixed-frequency timer is used to replace the traditional hysteresis comparator to achieve current tracking at a fixed switching frequency.

2. The method and system for improving the power quality of a finite-capacity system with pulsed loads according to claim 1, characterized in that: The S1 includes the following: real-time acquisition of three-phase bus voltage and load current, and transformation of them from a three-phase stationary coordinate system (a, b, c) to a two-phase stationary coordinate system (α, β) using Clark transformation (abc / αβ transformation).

3. The method and system for improving the power quality of a finite-capacity system with pulsed loads according to claim 1, characterized in that: The S2 includes the following: performing positive-order Park transform (rotational angular frequency + ω) and negative-order Park transform (rotational angular frequency - ω) on the αβ components respectively, to achieve decoupling of the positive-order and negative-order components.

4. The method and system for improving the power quality of a finite-capacity system with pulsed loads according to claim 1, characterized in that: S3 includes the following: After transformation, the fundamental positive-sequence and negative-sequence components are represented as DC components in their respective rotating coordinate systems. A low-pass filter (LPF) is used to filter out AC harmonics, extracting the positive-sequence DC component (i_d). + , i_q + ) and negative order components (i_d) - , i_q - ).

5. The method and system for improving the power quality of a finite-capacity system with pulsed loads according to claim 1, characterized in that: The S4 includes the following: performing inverse Park transform and inverse Clark transform on the filtered DC component to reconstruct the three-phase fundamental positive sequence current (including reactive and active components), negative sequence current and zero sequence current.

6. The method and system for improving the power quality of a finite-capacity system with pulsed loads according to claim 1, characterized in that: S5 includes the following: C1: Error Calculation: Compare the compensation command current i_ref generated by the reactive current detection module with the actual compensation current i_actual output by the SVG to obtain the current error signal Δi = i_ref – i_actual; C2: Timed sampling and decision: The timer samples the error signal Δi at a fixed frequency (e.g., 5kHz) and determines its sign; C3: PWM signal generation: At the end of each timing cycle, a PWM signal is generated based on the sign of Δi. If Δi > 0, the control switch is turned on to increase the output current; if Δi < 0, it is turned off to decrease the current.

7. A system for improving the power quality of a finite-capacity system with pulsed loads, characterized in that, Including a limited-capacity power supply, a pulse load, and an SVG device connected in parallel to the AC bus, the SVG device consists of the following three modules: The main circuit module, as the energy conversion unit, adopts a voltage-source three-phase full-bridge inverter structure, including a three-phase inverter bridge composed of fully controlled devices such as IGBTs, DC-side support capacitors, and AC-side connecting reactors; the DC capacitors are used to maintain voltage stability and reactive power exchange, and the AC reactors are used for filtering and energy control. The reactive current detection module, as a sensing unit, is responsible for real-time detection of reactive and harmonic currents that need to be compensated. The control strategy module, as the decision-making and execution unit, receives the compensation current command issued by the detection module, and uses an improved timing hysteresis comparison method to generate a PWM drive signal to precisely control the operation of the switching devices in the main circuit module.

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