Detailed explanation of photovoltaic grid-connected inverter parameters—power factor

The power factor of photovoltaic grid-connected inverters is a point that must be mentioned in technical parameters. In AC circuits, the cosine of the phase difference (Φ) between voltage and current is called power factor, which is represented by the symbol cosΦ. Numerically, power factor is the ratio of active power to apparent power, that is, cosΦ=P/S. Generally speaking, the power factor of resistive loads such as incandescent bulbs and resistance furnaces is 1, and the power factor of circuits with inductive loads is generally less than 1. When the power factor of the equipment is less than 0.9, a fine will be imposed.

The power factor output of the photovoltaic grid-connected inverter is required to be 1 and can be adjusted between 0.8 leading and 0.8 lagging.

Power factor is an issue that requires special attention in industrial and commercial distributed photovoltaic projects. It needs to be considered from a system perspective, not only the type and size of the load, but also the performance, test points and control methods of the reactive compensation device. It is recommended to observe the operation of the entire photovoltaic system to ensure that the system active power is normal.

What is the relationship between power factor and power consumption? If the former is small, does it mean that the power consumption is large? This question was asked by a friend on the 21st Century Power Supply Network, so I will answer it by the way:

As early as 2010, the state promulgated a new method for adjusting electricity charges based on power factor. Taking the power factor as 0.9 as an example, for every 0.01 above, the electricity charge will be reduced by 0.15%; for every 0.01 below, the electricity charge will be increased by 0.5%. Seeing this, you don’t have to worry about your family’s electricity bill being overcharged, because this decree is basically aimed at agricultural and industrial users with electricity consumption exceeding 100KW, and has no impact on ordinary people.

What kind of parameter is power factor? It can directly affect the calculation of electricity bills! Let's first look at the electricity bill calculation method for industrial users by power companies:

Total electricity fee = active electricity fee + basic electricity fee + power factor adjustment fee

(Detailed explanation of photovoltaic grid-connected inverter parameters - power factor)

The power factor is equal to the ratio of active power to apparent power. It reflects the utilization rate of power equipment. This may be too vague. Let me give you an example. Look at this picture. From this picture, it is not difficult to understand that the power factor is equivalent to the actual proportion of beer in the glass. By the same token, the power factor is the ratio of active power to apparent power.

(Detailed explanation of photovoltaic grid-connected inverter parameters - power factor)

That is to say, the power factor is closely related to active power and reactive power. Active power is easy to understand as useful work done, so how do you understand reactive power? Let's look at this picture again. When the car is moving forward, only the thrust does work, and the support force does not do work. However, without the support force, the car cannot move forward, and the thrust cannot do work. It is not difficult to understand that reactive power is an important condition for maintaining active power in certain situations.

(Detailed explanation of photovoltaic grid-connected inverter parameters - power factor)

In actual life applications, as long as there is an inductive load or a capacitive load, reactive power will be generated. Most of the power loads in the power grid, such as motors, transformers, fluorescent lamps and arc furnaces, are inductive loads. These inductive devices not only need to absorb active power from the power system during operation, but also absorb reactive power. In addition, any converter that can store and release energy can also generate reactive power. Too much reactive power will lead to a low power factor, resulting in a fine.

What should we do? At this time, we need to perform reactive power compensation. The purpose and energy-saving effect of reactive power compensation is to reduce load current, reduce line loss, improve power factor and reduce electricity costs.

(Detailed explanation of photovoltaic grid-connected inverter parameters - power factor)

Therefore, after installing parallel capacitor reactive power compensation equipment in the power grid, it will be able to provide compensation for the reactive power consumed by the inductive load, reducing the reactive power provided by the power grid power supply to the inductive load and transmitted by the line. Since the flow of reactive power in the power grid is reduced, the power loss caused by the transmission of reactive power by transformers and buses in the transmission and distribution lines can be reduced. This is the benefit of reactive power compensation.

(Detailed explanation of photovoltaic grid-connected inverter parameters - power factor)

The main purpose of reactive power compensation is to improve the power factor of the compensation system. Because the power generated by the power supply bureau is calculated in kVA or MVA, but the charges are in kW, that is, the actual useful work done. There is a difference in reactive power between the two, which is generally the reactive power in kvar.

Generally, traditional large-scale photovoltaic power stations or wind farms are equipped with SVG, reactive power compensation devices. However, online news claims that Sungrow inverters can achieve reactive voltage control in photovoltaic power stations, so that the SVG equipment originally configured in the photovoltaic power station stops running, and all reactive power instructions are required to be implemented by photovoltaic inverters with SVG functions.