How to choose the appropriate type of photovoltaic module for photovoltaic inverters

The core of photovoltaics: photovoltaic inverters

The function of a photovoltaic inverter is to convert the direct current generated by the solar cell into alternating current that meets the power quality requirements of the grid. It is composed of electronic components (IGBTs, capacitors, resistors, reactors, PCBs, etc.), structural components (cabinets, chassis, etc.), and auxiliary materials. According to specific functions, it can be divided into string photovoltaic inverters, centralized photovoltaic inverters, distributed photovoltaic inverters, and micro photovoltaic inverters. Photovoltaic inverters are the core of the photovoltaic power generation industry, and they are positively correlated with the development of the photovoltaic industry.

The booming photovoltaic industry has driven the growth of demand for photovoltaic inverters. However, photovoltaic inverters are a relatively large category with multiple specifications and models, and their selection is also a complex subject. Today we will introduce photovoltaic inverters and their selection techniques.

The factors that determine the selection of photovoltaic transformers include output voltage, load power factor, rated output current, rated output capacity, rated output efficiency, overload capacity, and other technical parameters. In addition, there are other requirements such as environmental conditions, electromagnetic interference and noise requirements, and safety performance requirements for protective measures. Specifically, the following points can be referred to:

1. Rated output capacity:

It represents the ability of the inverter to supply power to the load. The first consideration should be to have sufficient rated capacity to meet the electrical power requirements of the equipment under maximum load, as well as the expansion of the system and the connection of some temporary loads.

2. Adjustment performance of output voltage

The adjustment performance of the output voltage represents the stabilizing ability of the inverter's output voltage. Generally, inverters provide voltage and load adjustment rates.

Voltage adjustment rate: The deviation (%) of the output voltage of the inverter within the allowable fluctuation range of the input DC voltage should be ≤ 3%;

Load adjustment rate: A high-performance inverter should simultaneously provide a deviation (%) of the output voltage of the inverter when the load changes from 0 to 100%, which should be ≤ 6%.

Off grid photovoltaic power generation systems use batteries as energy storage devices, and the voltage variation at the battery terminals can reach about 30% of the nominal voltage. Therefore, in order to ensure stable AC voltage supply for photovoltaic power generation systems, it is necessary to require inverters to have good voltage regulation performance.

3. Overall efficiency

The overall efficiency of the inverter represents the magnitude of its own power loss. An inverter with a larger capacity also needs to provide efficiency values for full load operation and low load operation. The efficiency of inverters below the general kW level should be between 80% and 85%; The efficiency of 10kW level should be between 85% and 90%; The efficiency of higher power must be above 90% to 95%.

Special attention should be paid in the design of photovoltaic power generation system specific inverters to reduce their own power loss and improve overall efficiency. This is because the actual efficiency of a 10kW level universal inverter is only 70% to 80%, and when used in photovoltaic power generation systems, it will bring about 20% to 30% of the total power loss. So, when the household system is not using electricity, the inverter should be turned off to reduce losses when not using electricity.

4. Protection function

The inverter should have automatic protection for overvoltage, overcurrent, and short circuit, overheat protection, and protection for open circuit and phase loss.

5. Startup performance

The inverter should be reliably started at rated load. High performance inverters can achieve continuous full load startup multiple times without damaging power switching devices and other circuits. Small inverters sometimes adopt soft start or current limiting start measures or circuits for their own safety.

Form: square wave inverter, stepped wave inverter, sine wave inverter;

Operation mode: Off grid inverter, grid connected inverter;

Output AC power phase number: single-phase inverter, three-phase inverter;

Power flow direction: unidirectional inverter, bidirectional inverter.

Selection Techniques for Photovoltaic Inverters

The basic circuit composition of the inverter is shown in the figure, mainly composed of input circuit, output circuit, main inverter switch circuit (main inverter circuit), control circuit, auxiliary circuit, and protection circuit.