In general, the contribution of current harmonics from solar PV inverters does not pose a significant power quality issue. The current total harmonic distortion (ITHD) from a quality-brand inverter is typically low and negligible compared to harmonics-producing loads such as variable speed drives, where ITHD for a typical 6-pulse drive ranges between 30% – 50%.

Typically, a quality-brand inverter's datasheet will state a Current Total Harmonic Distortion of around 3%.

In Singapore, for a Grid-Tied Solar PV connection, the Licensed Electrical Worker (LEW) must submit the inverter’s power quality-related type test report to the grid operator (SP Group). One such example is the portion of the report where the inverter was tested as part of the UK Engineering Recommendation G99 requirements, showing that quality-brand inverters have harmonic current emission values well within acceptable limits.

One might wonder about the cumulative effect of multiple inverters. Measurements at several sites with cumulative rated PV outputs exceeding 1MWac provide some insight.

Here are two such sites where background harmonics were relatively low, making the inverter effects more representative (with limited 'contributions' from the local electrical network).

All measurements were performed using IEC 61000-4-30 Class A certified Power Quality instruments. The Current Harmonic Distortion (ITHD) trends were scaled to the respective aggregated inverters’ rated current, shown here as Total Demand Distortion (TDD) values. Observations indicate TDD values were less than 3%, with the sinusoidal shape of the current waveforms still visible.

Note: IEEE 519 recommends TDD values of 5% for power generation facilities.

Site #1:

• Premises Type: Warehousing / logistics
• PV Size: 1352.8 kWp
• Aggregated Inverter(s) Rated Current: 1613A @ 400V
• Measurement Point: 2500A PV-AC distribution board, directly connected to the premises' 5000A Main Switchboard (served by a 3MVA transformer) via 3000A flexible CTs (clamped on 3 sets of 500sqmm cables per phase)
• VTHD: 0.89% – 3.96% (CP95: 3.6%)

Site #2:

• Premises Type: Solar Farm (with on-site auxiliary power and lighting loads only)
• PV Size: 2652kWp (for CS1)
• Aggregated Inverter(s) Rated Current: 62A @ 22kV (for CS1)
• Measurement Point: 22kV Incomer 1 from PowerGrid (CS1) via VT and CT. The solar farm was connected to a lightly-loaded 22kV distribution network
• VTHD: 0.59% – 1.22% (CP95: 1.09%)

These measurements indicate that even with multiple inverters, the harmonic distortion remains low, and the current waveforms retain their sinusoidal shape. Therefore, while solar PV inverters do generate harmonics, their impact on power quality is generally minimal when high-quality inverters are used and the system is properly designed.

When integrating a photovoltaic (PV) system, the reactive power remains constant while the active power decreases, especially when PV generation matches consumption. This requires precise reactive power compensation to maintain a high power factor (PF).

To optimize power quality and meet grid standards, it is recommended to install an Active Harmonic Filter (AHF) that handles both harmonics and reactive power. The AHF effectively suppresses harmonics generated by the system and provides dynamic reactive power compensation, helping to stabilize the grid's power factor.

This solution enhances system stability and reliability, and also helps prevent equipment failures and energy losses caused by harmonics and reactive power issues.

YTPQC-AHF

Active Harmonic filters are highly effective in addressing and resolving the aforementioned harmonic issues. They are specifically designed to detect and counteract the negative impacts caused by harmonics, ensuring a more stable and clean power supply.

By actively filtering out the harmonic components, active power filters help to maintain the quality and integrity of the electrical system, minimizing the disturbances and potential damage that harmonics can bring. Their application is crucial in various industries and power systems to achieve optimal power performance and reliability.