Modern low-voltage (≤ ~1 kV) loads — VFDs, arc furnaces, welders, UPS, PV inverters — swing their reactive demand rapidly and often inject harmonics at the same time. Fixed capacitor banks cannot keep up. Active Power Factor Correction (PFC) and dynamic reactive compensation, built on voltage-source converters, close that gap.
Active PFC: Canceling Reactive Current
Active PFC measures real-time load current and voltage, computes the required compensation, and uses a PWM-controlled IGBT inverter to inject opposite-phase reactive current. The result: the source sees only the fundamental active component. Key components: IGBT-based VSI, DC-link capacitor, DSP/FPGA control. Advantages over passive PFC: Millisecond response, No over-compensation (cannot drive PF leading), Works with harmonic loads.
Dynamic Reactive Compensation: The SVG
A Static Var Generator (SVG) delivers dynamic reactive support continuously. It controls the magnitude and phase of its AC output to inject or absorb reactive current within < 1 ms — versus > 20 ms for a switched capacitor bank. It holds PF at 0.99+ (vs. the 0.8–0.95 wander of stepped banks), suppresses flicker from impact loads, and supports the bus during load swings.
Passive vs. Active — Engineering Trade
A comparison table:
| Feature | Passive (capacitor bank) | Active (SVG / AHF) |
|---|---|---|
| Response | Slow (seconds / > 20 ms) | Fast (< 1 ms) |
| Harmonic handling | Fails / can resonate | Compensates / damps |
| Over-compensation | Yes (leading PF risk) | No (adaptive) |
| Maintenance | Low (passive) | Higher (cooling, firmware) |
| Cost | Low | Higher |
For stable, predictable, low-harmonic loads a detuned capacitor bank is enough. For fast, harmonic-rich loads — VFD plants, data centers, renewable LV sidings — active correction is the engineering-correct choice.
Typical LV Application Profiles
VFD-Heavy Plants
Arc furnaces and welders cause rapid PF swings; an SVG stabilizes the bus and an AHF cleans the harmonics.
Data Centers
UPS and server farms swing PF between 0.8 and 0.9; active PFC holds PF > 0.95.
Renewable LV Sidings
PV inverters can drive PF leading at low generation; an SVG injects lagging VAr to hold the target PF.
The Converter Core: IGBT and SiC
Both AHF and SVG are bounded by their power switch. A standard IGBT is rated to ~150 °C junction temperature, switching typically below 20 kHz. A SiC MOSFET lifts that: silicon carbide is a wide-bandgap material (3.26 eV vs. silicon's 1.12 eV), tolerates ~200 °C, switches at 2–3× the IGBT frequency, and cuts switching loss by ~50% — gaining +1–3% efficiency. CHITEK low-voltage AHF/SVG platforms are built on this IGBT→SiC migration path.
Engineering Deployment Checklist
- Measure reactive demand and THDi across a full duty cycle.
- Size to the worst swing, with 10–20% headroom.
- Place at or near the LV PCC / load bus.
- Detune any retained capacitor bank to avoid LC resonance.
- Integrate with the site controller (PMS/EMS).
Conclusion
Active PFC and dynamic SVG compensation replace stepped, resonance-prone banks with millisecond, adaptive correction — essential wherever LV loads swing and distort.
Need help selecting the right active compensation solution for your low-voltage bus?
Contact CHITEK for a technical assessment and sizing recommendation.