Abstract:1. Stability of output voltageIn the photovoltaic system, the electric energy generated by the solar cell is first stored by the battery, and then con...
1. Stability of output voltage
In the photovoltaic system, the electric energy generated by the solar cell is first stored by the battery, and then converted into 220V or 380V alternating current through the inverter
. However, the battery is affected by its own charge and discharge, and its output voltage varies in a large range. For example, the nominal 12V battery has a voltage value that can vary between 10.8 and 14.4V (beyond this range may cause damage to the battery). For a qualified inverter, when the input terminal voltage changes within this range, the steady-state output voltage change should not exceed &Plusmn; 5% of the rated value, and when the load changes suddenly, the output voltage deviation should not exceed ±10% over rated value.
2. Waveform distortion of output voltage
For sine wave inverters, the maximum allowable waveform distortion (or harmonic content) should be specified. It is usually expressed by the total waveform distortion of the output voltage, and its value should not exceed 5% (10% is allowed for single-phase output). Since the high-order harmonic current output by the inverter will generate additional losses such as eddy currents on the inductive load, if the waveform distortion of the inverter 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., because the optimal frequency operating point of the motors is 50Hz, too high or too low frequencies will cause the equipment to heat up and reduce the operating efficiency and service life of the system. The output frequency should be a relatively stable value, usually a power frequency of 50Hz.
4. Load power factor
Characterize the ability of the inverter with inductive load or capacitive load. The load power factor of the sine wave inverter is 0.7~0.9, and the rated value is 0.9. In the case of a certain load power, if the power factor of the inverter is low, the capacity of the required 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. As the current increases, the loss will inevitably increase, and the system efficiency will also decrease.
5. Inverter efficiency
The efficiency of the inverter refers to the ratio of its output power to the input power under specified working conditions, expressed as a percentage. In general, the nominal efficiency of a photovoltaic inverter refers to a pure resistance load. Under the condition of 80% load s efficiency. Due to the high overall cost of photovoltaic systems, the efficiency of photovoltaic inverters should be maximized to reduce system costs and improve the cost performance of photovoltaic systems. 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 a photovoltaic system, not only should a high-efficiency inverter be selected, but also a reasonable configuration of the system should be used to make the load of the photovoltaic system work near the best efficiency point as much as possible.
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 the rated output capacity, and its unit is expressed in VA or kVA. The rated capacity of the inverter is the product of the rated output voltage and the rated output current when the output power factor is 1 (that is, purely resistive load).
7. Starting characteristics
To characterize the ability of the inverter to start with load and the performance during dynamic operation. The inverter should ensure reliable starting under rated load.
Components such as transformers, filter inductors, electromagnetic switches and fans in power electronic equipment will generate noise. When the inverter is running normally, its noise should not exceed 80dB, and the noise of a small inverter should not exceed 65dB.