Talking about photovoltaic inverters Part 3: How to solve the problem of low power factor of photovoltaic power generation on industrial and commercial roofs

Preface

Power factor assessment and power adjustment charges are effective means to ensure the safe and efficient operation of the power grid, and are institutional guarantees to encourage users to adjust the power factor independently. The pilot and promotion of photovoltaic power generation is an important part of the national energy strategy and the only way for the development of the State Grid. Unexpected power adjustment fines caused by photovoltaic access will not only hinder the promotion of photovoltaic power generation, but also reduce users' trust in power supply companies.

The practical significance of power factor

Improving the power factor is not only a measure to meet the assessment of the State Grid, but also has great benefits for enterprises. First, it can save electricity, reduce production costs, and reduce the electricity expenses of enterprises. For example, when cosØ=0.5, the loss is 4 times that when cosØ=1. Second, it can reduce the power loss of the line and improve the transmission efficiency of the power grid.

Why did the power factor of the factory become lower after adding photovoltaics?

If the factory uses electricity directly, the load directly draws energy from the grid, as shown below:

After connecting to the photovoltaic system, the inverter is usually set with a power factor of 1, without any reactive power. When the photovoltaic energy is insufficient, the load absorbs energy from both the solar photovoltaic and the grid.

If the local load remains unchanged, the power factor value displayed on the smart meter will decrease and become lower as photovoltaic power generation increases.

Solution 1: There is an automatic compensation device locally

According to the "Power Factor Adjustment Electricity Fee Method" (Document No. 215 of Water Resources and Electric Power Finance) issued by the Ministry of Water Resources and Electric Power and the State Price Bureau, all power users with a capacity of 100kV˙A and above must undergo power factor assessment. If the assessment standard is not met, a power factor adjustment fee (i.e., power adjustment fee) will be charged, and those who exceed the assessment standard will be rewarded in proportion to the excess. The user power factor assessment standard is 0.85 or 0.90. If the power factor is far below the standard, it will not only cause a burden on the operation of the power grid, but also the amount of fines for power adjustment will be very large. Since the user load and the nature of the load may not be consistent at different times of the day, users generally install reactive power compensation (mostly capacitive equipment) devices with automatic switching functions to automatically adjust the compensation intensity.

The capacitor compensation cabinet continuously calculates and switches the number of capacitors to ensure that the output power factor is close to 1.

Solution 2: Use the inverter's PF regulation function to form a closed-loop regulation

Using the power reactive power control function of the inverter, an intelligent controller is installed. The intelligent controller continuously collects the power factor value on the smart meter, continuously calculates the reactive power that needs to be configured for the entire system, and then sends the command to each inverter through RS485. The advantage of this method is that it does not require a capacitor compensation cabinet and is low in cost. However, when the photovoltaic power is high, there may be load limitation caused by reactive power (the machine's apparent load power is certain), and the maximum active power output cannot be achieved, affecting customer benefits.

Summarize:

By giving examples of two common solutions, the author explains why the power factor becomes lower after installing a photovoltaic power generation system under the same power factor load. In general, the local automatic compensation device method ensures the power factor of the power grid without affecting photovoltaic power generation, and the effect is good and it is more commonly used. The method of using the PF adjustment function of the inverter to form a closed-loop adjustment will affect the maximum power of solar power generation, and the powerless capacity of general inverters is limited, so this method is generally not commonly used.