Working Principles of Photovoltaic Inverters How to Classify How to Install How to Maintain

Issuing time:2019-12-20 16:44

The role of photovoltaic inverters

1. Active operation and shutdown functions

After sunrise in the morning, the intensity of solar radiation gradually increases, and the output of the solar cell also increases. When the output power required for the inverter task is reached, the inverter actively starts operating. After entering operation, the inverter will constantly monitor the output of the solar cell module. As long as the output power of the solar cell module is greater than the output power required for the inverter task, the inverter will continue to operate; Until sunset, the inverter can still operate even on cloudy and rainy days.

2. Maximum power tracking control function

The output of solar cell modules varies with the intensity of solar radiation and the temperature of the solar cell module itself (chip temperature). Due to the characteristic of voltage decreasing with increasing current in solar cell modules, there exists an optimal task point to obtain maximum power. The intensity of solar radiation is changing, and the optimal task point is clearly also changing.

The working principle of photovoltaic inverters

Basic working principle of photovoltaic inverters

Inversion refers to the process of converting direct current into alternating current, an inverter circuit refers to a circuit that can complete the inverter function, and an inverter refers to a device that can achieve the inverter function. Photovoltaic inverter (also known as power regulator) is a type of inverter that is commonly used in photovoltaic power generation systems, so it is called photovoltaic inverter. In addition to DC/AC conversion function, photovoltaic inverters also have automatic operation, shutdown function, and maximum power tracking control function.

The composition and structure of photovoltaic inverters

Input circuit: responsible for providing DC input voltage;

Main inverter circuit: completing the inverter program through the action of semiconductor switching devices;

Output circuit: mainly compensates and corrects the frequency, phase, voltage, and current amplitude of the AC output from the main inverter circuit to meet certain standards;

Auxiliary circuit: Replace the DC voltage of the input circuit with a DC voltage suitable for controlling the operation of the circuit, and also include a series of detection circuits;

Control circuit: providing pulse signals to the main inverter circuit, controlling the opening and closing of semiconductor devices;

Classification of photovoltaic inverters

1. Classify according to isolation methods

This includes two types: isolated and non isolated. Isolated grid connected inverters are further divided into power frequency transformer isolation and high-frequency transformer isolation. At the beginning of the development of photovoltaic grid connected inverters, power frequency transformer isolation was mostly used. However, due to its obvious shortcomings in size, weight, and cost, high-frequency transformer isolation grid connected inverters have developed rapidly in recent years. Non isolated grid connected inverters have gradually gained recognition for their high efficiency, simple control, and other advantages. Currently, they have been promoted and applied in Europe, but key issues such as reliability and common mode current need to be solved.

2. Classify according to the number of output phases

It can be divided into two categories: single-phase and three-phase grid connected inverters. In small and medium power situations, single-phase mode is generally used, while in high-power situations, three-phase grid connected inverters are often used. Classified by power level, it can be divided into low-power grid connected inverters with power levels less than 1 kVA, medium power inverters with power levels ranging from 1 kVA to 50 kVA, grid connected inverters, and high-power grid connected inverters with power levels above 50 kVA.

3. Classify according to power flow direction

It is divided into two categories: unidirectional power flow grid connected inverters and bidirectional power flow grid connected inverters. Unidirectional power flow grid connected inverters are only used for grid connected power generation, while bidirectional power flow grid connected inverters can be used not only as grid connected power generation, but also as rectifiers to improve grid voltage quality and load power factors. In recent years, bidirectional power flow grid connected inverters have begun to receive attention and are one of the future development directions.

4. Classify according to topological structure

The current topology structures used include: full bridge inverter topology, half bridge inverter topology, multi-level inverter topology, push-pull inverter topology, forward inverter topology, flyback inverter topology, etc. Among them, high-voltage and high-power photovoltaic grid connected inverters can use multi-level inverter topology, medium power photovoltaic grid connected inverters mostly use full bridge and half bridge inverter topology, and low-power photovoltaic grid connected inverters use forward and flyback inverter topology.

Differences between photovoltaic inverters and energy storage inverters

1. The self utilization rate of traditional photovoltaic inverters is only 20%, while the self utilization rate of energy storage inverters is as high as 80%.

2. When there is a power failure, the grid connected inverter becomes paralyzed, and the energy storage inverter can still work efficiently.

3. Against the backdrop of continuously decreasing subsidies for grid connected power generation, the benefits of energy storage inverters are higher than those of photovoltaic inverters.

4. Photovoltaic inverters can only generate electricity during the day, and the power generated is affected by weather, which has unpredictable problems. Energy storage inverters can perfectly solve the problems of photovoltaic inverters.

Selection of photovoltaic inverters

1. Rated output power

The rated output power represents the ability of the photovoltaic inverter to supply power to the load. A photovoltaic inverter with a high rated output power can drive more loads. When selecting a photovoltaic inverter, sufficient rated power should be considered first 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 photovoltaic inverter's output voltage. Generally, photovoltaic inverter products provide the percentage deviation of the output voltage fluctuation of the photovoltaic inverter when the DC input voltage fluctuates within the allowable range, commonly known as the voltage adjustment rate. The voltage adjustment rate of a high-performance photovoltaic inverter should be less than or equal to ± 3%, and the load adjustment rate should be less than or equal to ± 6%.

3. Overall efficiency

The overall efficiency represents the magnitude of the power loss of the photovoltaic inverter itself. Large capacity photovoltaic inverters should also provide efficiency values for full load and low load operation. Generally, the efficiency of inverters below KW level should be 80% -85%; The efficiency of 10KW level should be 85% -90%; The efficiency of higher power must be above 90% -95%.

4. Startup performance

The photovoltaic inverter should ensure reliable startup under rated load. High performance photovoltaic 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 for their own safety.

5. Type

At present, the inverters on the market are basically divided into three types: centralized inverters, series inverters, and micro inverters. Centralized inverters are mainly used in large-scale ground power plants, with a voltage level of 315v, suitable for high-voltage grid connection; Series inverters, also known as distributed inverters, are mainly used in various barren mountains, industrial and commercial areas, or on rooftops of households. The scale of power plants is generally not large, and they are integrated into the national power grid through full grid connection or residual power grid connection; Micro inverters are mainly applied by directly integrating them into battery panels, suitable for small household power plants, and are currently less commonly used in China.

How to install photovoltaic inverters

How to connect photovoltaic inverters

1. Choose a good place

The installation position of photovoltaic inverters should be as close as possible to the battery and in a dry and well ventilated place. Wall mounted photovoltaic inverters have mounting holes that can be fixed to the wall with screws. When selecting a location, please ensure that the DC terminals, sockets, switches, and fuses can still be used.

2. Connecting the battery

Connect the inverter to the battery using the included cable. The cable can be shortened, but if it is too short, a thicker and longer cable should be replaced.

3. Grounding the photovoltaic solar inverter

Grounding is very important. If the photovoltaic inverter and your equipment are not grounded, equipment failure may make the connected equipment and inverter live. If your photovoltaic inverter has a grounding point, please use a thicker wire to connect it to a suitable grounding point.

4. Insert testing equipment

Observe the maximum rated power of the photovoltaic inverter, insert the device into the AC power socket of the photovoltaic inverter, and then turn on the photovoltaic inverter. The power indicator light should light up, and you may hear the sound of the device running.

Precautions for installation of photovoltaic inverters

1. The inverter can only be powered on and operated after being approved by the debugging engineer.

2. The installation of inverters should be carried out by qualified engineers according to the steps described in this manual.

3. Inverters can only be installed on concrete bases or other non flammable installation surfaces.

4. Ensure that the grounding wire in the distribution room is well grounded, and the grounding resistance should be less than 4 Ω in a dry environment.

5. If the inverter control power is taken from the low-voltage distribution in the computer room or a heater is optional, please ensure that the computer room distribution can provide 4KW power.

How to maintain photovoltaic inverters

1. Before using photovoltaic controllers and inverters, it is necessary to read the user manual carefully.

2. Pay attention to the warning signs on the machine.

3. Before starting up, check if the input voltage is normal.

4. When operating, pay attention to whether the order of turning on and off the machine is correct, and whether the indications of each meter head and indicator light are normal.

5. During operation, pay attention to the setting of overcharging voltage and overdischarge voltage of the controller, which should meet the design requirements.

6. Once faults such as open circuit, overcurrent, overvoltage, and overheating occur, the photovoltaic controller and inverter usually automatically shut down and enter the protection state. At this time, Sunshine Hengyu New Energy suggests not to immediately start up! The cause should be identified and fixed before attempting to start.

7. There is high voltage inside the inverter cabinet. Please lock the cabinet door tightly on weekdays.

8. If the ambient temperature is greater than 30 ℃, timely heat dissipation should be carried out to prevent equipment overheating and prolong its service life.

9. Check the temperature, sound, and odor inside the machine for any abnormalities.

10. Check if the cooling fans of the modules, reactors, and transformers in the inverter can automatically start and stop according to the temperature. Is there any significant vibration or abnormal noise during the operation of the fan? If there is any abnormality, cut off the power first and then perform maintenance.

11. Check the insulation resistance between the positive pole and ground, negative pole and ground, and positive and negative poles of the DC bus, and the resistance value should be greater than 2M Ω.

12. Check for loose or corroded wiring and terminals in various parts (such as fuses, fans, power modules, input and output terminals, grounding, etc.). Once abnormalities are found, they should be repaired immediately.

13. Regularly disconnect the circuit breaker on the output side (grid side) of the AC power grid and check if the inverter can immediately stop feeding power to the grid.


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