An Active Harmonic Filter is a current-source inverter that injects a counter-spectrum to cancel load-side harmonics, typically specified across the 2nd–50th order with response times quoted in milliseconds by manufacturers such as CoEpower, Yingtong (YT), ZDDQ and Lafaelt [S1][S2][S3][S4]. A Static Var Generator is a voltage-source inverter that exchanges leading or lagging reactive current with the grid, rated in kvar and used to stabilise power factor, bus voltage and flicker [S1][S2][S3].
Both sit on the same low-voltage power-quality product tree — AHF, SVG, hybrid VAR compensator, medium-voltage STATCOM and dynamic voltage restorer — and most Chinese OEMs build all five on a shared IGBT platform [S1][S2][S3][S7]. Production scale at YT alone passed 10,000 AHF and SVG modules in 2021, a useful order-of-magnitude reference for installed-base thinking [S2].
What Each Device Actually Does
An Active Harmonic Filter measures load current through CTs, extracts the harmonic component via DFT/FFT or synchronous reference frame, and forces an inverter to produce an equal-and-opposite spectrum back into the bus, with mitigation performance commonly quoted in the 5–50th harmonic band [S1][S4]. Most AHF chassis are modular 50 A/100 A bricks that parallel for higher compensation current, and OEM datasheets consistently cite 2–20 ms full-step response [S1][S2][S3].
An SVG regulates reactive current independently of harmonic content, sinking or sourcing kvar to hold a power-factor setpoint or a voltage setpoint at the point of common coupling [S1][S2][S3]. Yingtong lists the SVG technical advantages as "Fast Response, Good Low Voltage Characteristics, Superior Harmonic Characteristics, High Compensation Accuracy" — note the order: speed and accuracy first, harmonic behaviour as a secondary, not primary, deliverable [S2].
Decision Criteria: Harmonics vs Reactive Power vs Both
The first selection gate is the utility penalty or compliance trigger. If the audit cites THDi (total harmonic distortion of current) or a specific harmonic order such as 5th/7th/11th/13th, an AHF is the direct match; if the audit cites a power-factor threshold (commonly 0.90–0.95 lagging in Chinese commercial tariffs) or a voltage-fluctuation complaint, an SVG is the direct match [S1][S2][S3][S8].
The second gate is the load mix. VFDs, DC drives, UPS rectifiers and LED drivers are harmonic-rich, low-power-factor loads; arc furnaces, welding sets and large induction motors with cyclic duty are reactive-power-dominant with flicker. For welding and arc-furnace duty, OEMs position SVG as the primary tool and AHF as supplementary [S1][S2].
The third gate is voltage class. LV plants (380–690 V) use AHF and SVG modules on the same bus; MV plants (6 kV/10 kV/35 kV) move to STATCOM-class products — Yingtong explicitly lists "Medium Voltage Statcom" as a separate product line, distinct from the LV SVG [S2].
Options Compared: AHF vs SVG vs Hybrid VAR Compensator
Across the four criteria that matter on an RFQ — harmonic mitigation, reactive range, response time, and cabinet footprint — the three options line up as follows. AHF wins on harmonic order coverage and selective compensation (per-order targeting is standard on most modern AHF controllers) but is sized in amperes of compensation current, not kvar [S1][S3][S4]. SVG wins on reactive power density per cubic metre because the IGBT runs in pure VAR mode with no harmonic-injection duty cycle, and on the ability to provide both leading and lagging vars from a single inverter [S1][S2][S3].
Hybrid VAR Compensator — listed as a top-level product by Yingtong alongside the standalone AHF and SVG — adds a thyristor-switched capacitor (TSC) bank in parallel with an SVG so the cheap capacitors handle bulk steady-state vars while the SVG covers the fast dynamic slice [S2]. For plants with a large baseline reactive demand and a small fast-fluctuating component, this topology cuts inverter kvar rating and cost per kvar. Lafaelt and ZDDQ also list detuned reactors and capacitor banks separately, so the hybrid concept is an OEM-wide pattern rather than a single-vendor product [S3][S4][S7].
Quoting YT directly: the company's static-var-generator description cites "Fast Response, Good Low Voltage Characteristics, Superior Harmonic Characteristics, High Compensation Accuracy" as the SVG's four engineering virtues, with the reactive-power framing made explicit in the company's own product hierarchy [S2]. AHF descriptions from ZDDQ position the device as "a perfect comprehensive solution to power quality problems such as harmonic wave, reactive power, and 3 phase load unbalance" — three functions in one box, but with the primary duty being the harmonic spectrum [S4].
Use-Case Recommendations by Plant Type
For an IDC or data-centre LV bus dominated by UPS rectifiers and server PSUs, specify AHF sized at roughly 30–60 A per 100 kVA of IT load as a starting point, with a parallel SVG for the bulk power-factor correction capacitor bank — the AHF cleans the harmonic residue the capacitors would otherwise amplify [S1][S3]. For an EV charger depot, Yingtong bundles the SVG with the charger line, treating reactive support as part of the charger specification rather than a separate AHF [S2].
For renewable interconnection (solar PV plant at 220–600 V per a Made-in-China product listing), SVG is the common specification and the harmonic-mitigation question is usually deferred to the inverter-side filtering [S8]. For industrial manufacturing with mixed VFDs and welding sets, the hybrid VAR compensator is the cleanest single-line answer because the TSC bank handles the welding-set kvar swings and the SVG rides on top for fast transients [S2][S3].
A broader buying frame — covering capacitor banks, detuned reactors, thyristor switches and APF selection in one document — sits in this Reactive Power Compensation Buying Guide 2026, which lines up with the same vendor taxonomy used here.
Limitations and Failure Modes to Spec Against
AHF does not generate vars beyond what the inverter is rated for, and its reactive capability is a side effect of the harmonic-injection duty cycle, not the design target — spec the AHF in amps of compensation current and the SVG in kvar, never the reverse [S1][S2][S4]. Capacitor-only correction is dangerous on harmonic-rich buses because resonance with the supply inductance can amplify the 5th/7th harmonic; a detuned reactor (typically 7% or 14% reactance) is the standard mitigation and is sold as a separate product line by both Lafaelt and ZDDQ [S3][S4][S7].
SVG sizing mistakes show up as voltage overshoot at light load, especially on weak grids with low short-circuit ratio, because the SVG keeps sourcing vars until told to stop. AHF sizing mistakes show up as overheating when the load harmonic spectrum shifts (e.g. a new VFD is commissioned) and the inverter spends more time at full current than the original derating assumed. Both devices need a current margin of at least 20% above the measured peak, in line with how OEMs rate the 50 A/100 A modules for paralleling [S1][S3].
Standards, Sourcing, and Vendor Map (July 2026)
Compliance instruments on the LV side are IEEE 519-2014 for harmonic limits at the point of common coupling, GB/T 14549-1993 for Chinese utility power-quality limits, and IEC 62477 for power electronic converter systems — the device-level safety standard both AHF and SVG chassis should be tested against, though the research did not surface a single revision date for these and the exact revision should be confirmed with the test certificate [S1][S2][S3]. For supplier shortlisting, CoEpower (Xi'an), Yingtong (Shanghai, listed parent CSG stock 300222), Anhui Zhongdian/ZDDQ (Bengbu, founded 2001), and Lafaelt all ship AHF, SVG and hybrid product lines on a common IGBT platform as of July 2026 [S1][S2][S3][S7].
Track for 2026 H2: the Made-in-China sourcing pages list SVG cabinets at 220 V–600 V with explicit solar-plant positioning, suggesting utility-scale PV interconnection is the fastest-growing specification for low-voltage SVG through the second half of 2026 [S8]. A second signal worth watching is the consolidation of AHF + SVG + DVR into a single cabinet SKU across vendors — CoEpower, Yingtong and Lafaelt all already list the four products on one product page, indicating the OEMs themselves expect plant engineers to buy them from one supplier [S1][S2][S3].
For the relevant spec sheets and selection criteria, see harmonic reducer.