What Are The Main Technical Indicators Of Solar Photovoltaic Inverters?
May 09, 2024
The photovoltaic inverter is one of the important balance of systems (BOS) in the photovoltaic array system and can be used with general AC power supply equipment. Solar inverters have special features that work with photovoltaic arrays, such as maximum power point tracking and islanding effect protection. So, what are the main technical indicators of photovoltaic inverters?
1. Output voltage stability
In the photovoltaic system, the electric energy generated by the solar cells is first stored in the battery, and then inverted into 220V or 380V AC power through the inverter. However, the battery is affected by its own charge and discharge, and its output voltage has a large range of change. For example, the voltage value of a nominal 12V battery can vary between 10.8 and 14.4V (anything beyond this range may cause damage to the battery) . For a qualified inverter, when the input voltage changes within this range, the change in the steady-state output voltage should not exceed 5% of the rated value, and when the load changes suddenly, the output voltage deviation should not ±10% over rated value.
2. Output voltage waveform distortion
For sine wave inverters, the maximum allowable waveform distortion (or harmonic content) should be specified. Usually expressed as the total waveform distortion of the output voltage, its value should not exceed 5% (single-phase output allows 10%). Since the high-order harmonic current output by the inverter will generate eddy current and other additional losses on the inductive load, if the inverter waveform distortion is too large, it will cause serious heating of the load components, which is not conducive to the safety of electrical equipment and seriously affects the system. operating efficiency.
3． Rated output frequency
For loads including motors, such as washing machines, refrigerators, etc., since the optimal frequency operating point of the motor is 50Hz, if the frequency is too high or too low, it will cause the equipment to heat up and reduce the system operating efficiency and service life, so the inverter The output frequency should be a relatively stable value, usually the power frequency 50Hz, and its deviation should be within ±1% under normal working conditions.
4. Load power factor
Characterizes the inverter's ability to carry inductive or capacitive loads. The load power factor of the sine wave inverter is 0.7~0.9, and the rated value is 0.9. When the load power is constant, if the power factor of the inverter is low, the required capacity of the inverter will increase. On the one hand, the cost will increase, and at the same time, the apparent power of the AC circuit of the photovoltaic system will increase, and the circuit As the current increases, the loss will inevitably increase and the system efficiency will also decrease.
5. Inverter efficiency
The efficiency of an inverter refers to the ratio of its output power to its input power under specified working conditions, expressed as a percentage. Generally speaking, the nominal efficiency of a photovoltaic inverter refers to a pure resistive load, at 80% load. s efficiency. Since the overall cost of the photovoltaic system is high, the efficiency of the photovoltaic inverter should be maximized, the system cost should be reduced, and the cost performance of the photovoltaic system should be improved. At present, the nominal efficiency of mainstream inverters is between 80% and 95%, and the efficiency of low-power inverters is required to be no less than 85%. In the actual design process of the photovoltaic system, it is not only necessary to select a high-efficiency inverter, but also to make the photovoltaic system load work near the optimal efficiency point through reasonable system configuration.
6. Rated output current (or rated output capacity)
Indicates the rated output current of the inverter within the specified load power factor range. Some inverter products give rated output capacity, expressed in VA or kVA. The rated capacity of the inverter is when the output power factor is 1 (that is, purely resistive load), the rated output voltage is the product of the rated output current.
7. Protection measures: An inverter with excellent performance should also have complete protection functions or measures to deal with various abnormal situations that occur during actual use, so as to protect the inverter itself and other components of the system from damage. .
(1) Input undervoltage insured: When the input voltage is lower than 85% of the rated voltage, the inverter should have protection and display.
(2) Input overvoltage protection: When the input voltage is higher than 130% of the rated voltage, the inverter should have protection and display.
(3) Overcurrent protection: The overcurrent protection of the inverter should be able to ensure timely action when the load is short-circuited or the current exceeds the allowable value, so as to protect it from damage by surge current. When the operating current exceeds 150% of the rating, the inverter should be able to automatically protect.
(4) Output short-circuit protection: The inverter short-circuit protection action time should not exceed 0.5s.
(5) Input reverse connection protection: When the positive and negative input terminals are connected reversely, the inverter should have protection functions and displays.
(6) Lightning protection: The inverter should have lightning protection.
(7) Over-temperature protection, etc.
In addition, for inverters without voltage stabilization measures, the inverter should also have output over-voltage protection measures to protect the load from over-voltage damage.
8. Starting characteristics: Characterizes the inverter's ability to start with load and its performance during dynamic operation. The inverter should ensure reliable starting under rated load.
9. Noise: Transformers, filter inductors, electromagnetic switches, fans and other components in power electronic equipment all generate noise. When the inverter is operating normally, its noise should not exceed 80dB, and the noise of a small inverter should not exceed 65dB.
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