How does a low-voltage static var generator (SVG) avoid resonance risks and improve system stability without the need for capacitor banks?
Publish Time: 2026-01-29
In modern industrial and commercial power distribution systems, the widespread use of nonlinear loads (such as frequency converters, LED lighting, and switching power supplies) has led to increasingly serious harmonic pollution of the power grid. Traditional reactive power compensation devices mostly rely on capacitor bank switching, which, although low in cost, is prone to forming an LC resonant circuit with the system inductance. This can cause resonance amplification at specific frequencies, resulting in equipment overheating, protection malfunctions, or even system collapse. However, a low-voltage static var generator (SVG), with its fully controlled power electronic architecture, completely eliminates the need for fixed capacitor banks, fundamentally avoiding resonance risks. It also significantly improves the stability and power quality of the power distribution system with its fast, continuous, and precise dynamic compensation capabilities.1. Root Cause of Resonance: Inherent Defects of Traditional Capacitor CompensationThe capacitive reactance of the capacitor bank and the inductive reactance of the power grid or transformer may meet the resonance condition at a certain frequency. When this frequency approaches a harmonic, the system impedance drops sharply, causing the harmonic current to be amplified significantly. This "passive" compensation not only fails to suppress harmonics but may also exacerbate distortion, threatening the safety of sensitive equipment. Especially in scenarios with frequent load fluctuations, fixed-capacity capacitors struggle to match real-time reactive power demands, further increasing operational risks.2. SVG's Active Compensation Mechanism: From "Passive Absorption" to "Active Injection"Low-voltage SVG employs an IGBT-based self-commutating three-phase bridge inverter circuit, directly connected to the grid via a reactor. Its core principle is: a high-speed DSP controller monitors system voltage and current in real time, calculates the required reactive power component, and actively injects a compensation current with controllable amplitude and phase into the grid. This process does not rely on energy storage components but maintains voltage stability through a small-capacity DC-side support capacitor; energy exchange is entirely achieved by power electronic switches. Therefore, SVG is essentially a controlled current source, with output characteristics independent of system impedance, completely cutting off the LC resonant path.3. Wideband Response and Harmonic Compatibility: Dual Protection for System SafetySVG's control bandwidth reaches 2–10kHz, with a response time of less than 10ms. It can not only dynamically track fundamental reactive power changes but also synchronously compensate for 2–50th harmonic currents. In harmonic environments, SVG does not "attract" harmonics like capacitors; instead, it actively cancels some harmonic components, reducing the total harmonic distortion rate. More importantly, its output impedance is highly inductive, exhibiting high impedance characteristics to each harmonic, effectively suppressing harmonic current inflow and eliminating the physical conditions for resonance at its source.4. Continuous Smooth Regulation: Avoiding Step Impacts and Improving Voltage StabilityTraditional capacitor switching is discrete and stepped, easily causing voltage flicker and reactive power over-compensation/under-compensation. SVG, however, can achieve continuous stepless regulation from -100% to +100% of rated capacity, with reactive power output changing in real time with the load, maintaining a power factor constant above 0.95. This smooth control significantly reduces voltage fluctuations, making it particularly suitable for impact loads such as welding machines and stamping equipment, significantly improving power supply stability and equipment reliability. 5. System-Level Collaboration: Building a New Flexible Power Distribution EcosystemModern low-voltage static var generators (SVG) generally support communication protocols such as Modbus and IEC 61850, enabling them to connect to energy management systems and participate in global reactive power optimization and scheduling. Multiple SVGs can also operate in parallel, achieving capacity expansion and N+1 redundancy, further enhancing system robustness. In renewable energy integration or microgrid scenarios, SVGs can also provide voltage support and inertia simulation, enhancing the stability of weak power grids.Low-voltage static var generators (SVGs), by eliminating capacitor banks and adopting fully controlled power electronics technology, not only completely avoid the fatal flaw of traditional LC resonance compensation methods, but also, with millisecond-level response, continuous adjustment, and harmonic compatibility, construct an intelligent, flexible, and safe reactive power support barrier for modern power distribution systems. In today's increasingly stringent power quality requirements, SVGs have transformed from an "optional" to a "must-have" for ensuring continuous industrial production and reliable operation of critical facilities.
