High-voltage static var generators (SVGs), as core devices in modern power electronics technology, play a crucial role in suppressing harmonics and preventing power grid pollution. Their core principle involves connecting a self-commutated bridge circuit in parallel with a reactor to the power grid, dynamically adjusting the phase and amplitude of the AC output voltage, or directly controlling the AC current to achieve real-time reactive power compensation. In this process, SVGs not only rapidly absorb or generate reactive current but also effectively suppress harmonic pollution in the power grid and improve power quality through advanced control strategies and circuit design.
The primary technical means for SVG to suppress harmonics is pulse width modulation (PWM) technology. PWM technology uses high-frequency switching to control the on/off state of power electronic devices (such as IGBTs), converting DC voltage into AC voltage with adjustable amplitude and phase. This modulation method generates a near-sinusoidal output current, reducing the generation of low-order harmonics at the source. Simultaneously, the switching frequency of PWM is much higher than the fundamental frequency of the power grid, concentrating high-order harmonic components in the high-frequency band, facilitating further attenuation by filtering devices, thereby reducing harmonic injection into the power grid.
Multiplexing and multilevel techniques in bridge converter circuits are another important means for SVG to suppress harmonics. Multiplexing technology, by connecting multiple bridge units in series and superimposing the output voltages of each unit, makes the synthesized waveform closer to a sine wave, significantly reducing harmonic content. Multilevel technology, by increasing the number of levels in the bridge circuit (e.g., three-level, five-level), reduces the voltage stress on individual components and improves the output waveform quality. The combined use of these two techniques can effectively suppress low-order harmonics and significantly reduce the amplitude of high-order harmonics, meeting the strict limits on harmonic pollution imposed by the power grid.
The harmonic suppression capability of SVG is also reflected in its closed-loop control strategy. The high-voltage static var generator (PVG) detects harmonic components in the grid current in real time. The SVG's control algorithm can quickly calculate the magnitude and phase of the harmonic current to be compensated and drive the bridge circuit to generate the opposite harmonic current for cancellation. This detection and compensation mechanism based on instantaneous reactive power theory enables the SVG to dynamically track changes in grid harmonics, achieving high-precision harmonic suppression. Furthermore, SVG control systems typically employ digital signal processors (DSPs) or field-programmable gate arrays (FPGAs) to ensure rapid response and precise execution of control commands.
In terms of hardware design, SVG further suppresses harmonic propagation by optimizing the parameters of the connecting reactors. The connecting reactors not only limit the inrush current between the SVG and the grid but also filter out potentially high-order harmonics in the current. The selection of its inductance value must comprehensively consider both harmonic suppression effectiveness and system stability, ensuring effective blocking of harmonic transmission to the grid while compensating for reactive power. In addition, the DC-side capacitor design of the SVG must also consider voltage balance and harmonic suppression to avoid additional harmonic pollution caused by capacitor voltage fluctuations.
The harmonic suppression function of SVG is also reflected in its ability to compensate for three-phase imbalance in the grid. Three-phase imbalance leads to negative-sequence and zero-sequence currents in the grid, which also pollute the grid in the form of harmonics. By independently adjusting the reactive power output of each phase, SVG can simultaneously compensate for positive-sequence, negative-sequence, and zero-sequence reactive power, thereby eliminating harmonic problems caused by three-phase imbalance. This comprehensive compensation capability enables SVG to perform exceptionally well in complex power grid environments, making it a versatile tool for improving power quality.
In practical applications, the harmonic suppression effect of SVG has been widely verified. In scenarios with severe harmonic pollution, such as renewable energy power plants, rail transit, and the metallurgical industry, SVG can not only significantly reduce grid voltage distortion rate but also improve power factor and reduce line losses. Its modular design and flexible expansion capabilities allow it to adapt to different voltage levels and compensation capacity requirements, providing customized harmonic mitigation solutions for the power grid. With the continuous advancement of power electronics technology, the harmonic suppression performance of SVG will continue to be optimized, providing strong support for building a clean and efficient modern power grid.
