What is the power factor rating of an inverter?

What is the power factor of an PV or wind power inverter?

Sunplus Product Page

Overview

Inverters are generally designed to generate power at unity power factor, particularly at full power. The actual requirements vary, but one example is:

The power factor must be greater than 0.90 for generated power greater than or equal to 50% of full power.

Unfortunately, older inverter designs have poor power factors when operating at low power levels. Filter capacitors on the inverter output, which are used to filter the high-frequency switching noise, can cause low power factors. When the generated power is high, the capacitive load becomes a small fraction of the total and has little effect on the power factor, but at low power levels, this capacitive load can result in power factors as low as 0.5.

The power factor of newer designs is typically adjustable from &#;0.80 to 0.85 or higher.

Measuring or Estimating Power Factor

Want more information on High power factor grid connected inverter? Feel free to contact us.

You can use our WattNode meters (those that report power factor) to directly measure the inverter power factor. Alternatively, you can estimate the power factor of an inverter. This estimate may not work for all inverters, depending on their control logic and output filter circuitry. The following equations disregard the real power consumption of an inverter when it is idle, which may range from a fraction of a watt to a few watts for larger inverters. Generally, the reactive power due to the filter capacitors ranges from tens to hundreds of VARs, so the small idle power is negligible by comparison when estimating the power factor.

General Equations

Inverter Power Factor Equations

In real life, the power factor will generally be higher than 0.9 unless the generated power is low, probably less than 20% of full-scale. So you could simplify and assume near unity power factor when generating and near zero power factor the rest of the time. But if you have an oversized inverter running in the 10-20% of full-scale range, you may measure power factor values far lower than 0.9, perhaps 0.5.

See Also

There are two things relating to PF rating on inverters.

One is output kVA load minimum tolerable power factor for output loads. HF inverters are usually limited on their output power factor loading due to their two-stage design with HV DC filter capacitor. Too much inductive loading can creating a problem with peak over-voltage on HV DC voltage point that can damage its filter cap or high voltage IGBT's. Common limit is no worse than a load power factor of 0.8.

Second is power factor presented on input AC when battery charging from AC input grid or generator. Some HF inverter/chargers just use regular rectifiers from AC input to HV DC point which results in poor power factor during charging from AC input. This is of more concern when charging through inverter/charger from a generator.

Low frequency inverters are much better at handling poor power factor loads and provide good AC input power factor during AC input battery charging.

In practice there are two types of poor power factor. One is due to high short peaks of output current loading on inverter caused by simple rectifier-filter AC to DC power supply appliances, like you might find on an VFD drive three phase inverter air conditioner. This just causes high peak currents resulting in more inverter efficiency loss and therefore less real output power capability.

Other type of poor power factor is due to inductive AC motors, like pumps and conventional air conditioner compressors. Because of the inductive component of load, the AC sinewave voltage peak occurs before the AC sinewave load current peak. There can actually be a short period of load current reversal during a portion of AC cycle. A HF inverter can have an issue with this short reverse current push.

In both power factor cases, the inverter efficiency will degrade causing greater inverter losses and internal heating at high loads.

Inverter, generators, and transformers are really rated for VA loading (called apparent power) not actually watts (real power) of load. When load power factor is 1.0, VA equals watts.

If you are looking for more details, kindly visit Lithium Ion Battery for Solar Panel for Germany.