In the medium and large -capacity photovoltaic system , inverter power output should be less distortion sine wave . This is due in large capacity systems, the use of a square split phase inverter wave power supply , the output will contain more harmonics , high harmonics will generate additional losses , load a lot of photovoltaic systems for communications or instrumentation, these equipment on the grid have higher quality requirements, among the large-capacity photovoltaic power generation system and network operation , in order to avoid contamination of public electricity grid, also called a sine wave inverter output current. DC inverter into alternating current, if the DC voltage is low, the AC transformer step through that get the standard AC voltage and frequency. Large -capacity inverter, due to a higher DC bus voltage, the AC output is generally not required that can achieve step-up transformer 220V, in the small -capacity inverter, due to low DC voltage, such as 12V, 24V, it must be designed to boost circuit. Medium and small -capacity inverters generally have a push-pull inverter circuit, full-bridge inverter circuit and high frequency boost inverter circuit are three push-pull circuit , the step-up transformer neutral plug connected to the positive supply , two power tubes alternatively , the output AC power is obtained , since the ground side of the power transistor connected to the drive control circuit is simple and , in addition to the transformer has a leakage inductance to limit the short circuit current, thereby increasing the reliability of the circuit . The disadvantage is that the use of low transformers, inductive load driving ability is poor . Full-bridge inverter circuit to overcome the shortcomings of the push-pull circuit , the pulse width of the power transistor to regulate the output , i.e., the output AC voltage RMS change. Since the circuit has continued flow loop , power inverter even for inductive load , the output voltage waveform is not distorted . The disadvantage of this circuit is that the upper and lower arm of the power transistor is not common ground , and therefore must be used exclusively drive circuit or the use of isolated power .
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