1.Requires a high efficiency. As the current high prices of solar cells, in order to maximize the use of solar cells, to improve system efficiency, we must try to improve inverter efficiency.
2.Requires a higher reliability. Photovoltaic power generation system is currently used in remote areas, many power plants unattended and maintenance, which requires a reasonable inverter circuit structure, strict component selection, and requested inverter with various protection features such as input DC reverse polarity protection, output short circuit protection exchange, thermal, overload protection and so on.
3.DC input voltage required to adapt to a wide range of terminal voltage due to solar cells with the load and sunlight intensity changes, although the solar cell battery voltage plays an important role, but because of the battery voltage with the remaining battery capacity and internal resistance to change fluctuate, especially when the aging battery terminal voltage when the change of its large range, such as the 12V battery, its terminal voltage can be varied between 10V ~ 16V, which requires to be in a larger inverter DC input voltage range to ensure the normal work and to ensure that the exchange of the output voltage stability.
4.In the medium and large-capacity photovoltaic power generation system, the inverter power output should be less distortion sine wave. This is because in the middle and large-capacity systems, the use of a square wave power supply, the output will contain more harmonics, high harmonics will result in additional losses, many of photovoltaic power generation system load for the communications or instrumentation These devices have high requirements for power quality, among others, large-capacity photovoltaic power generation system and network run-time, in order to avoid contamination with the public electricity grid, also called sine-wave inverter output current.
Inverter DC into the AC, if the DC voltage is low, then the step-up transformer through the exchange, that is to be the standard AC voltage and frequency. Large capacity inverter, DC bus voltage due to higher output generally does not require the exchange of step-up transformer that is able to reach 220V, in the medium and small capacity inverter, due to low DC voltage such as 12V, 24V, must be designed on the boost circuit.
Medium and small-capacity inverters generally have a push-pull inverter circuits, full-bridge inverter circuits, and three kinds of high-frequency boost inverter circuit, push-pull circuit, the step-up transformer is connected to the neutral plug power supply, 2 alternating power tube to work out an exchange of power, as power transistors were to side access, drive and control circuit is simple, while the transformer has a certain amount of leakage inductance, limit short-circuit current, thereby enhancing the reliability of the circuit. The disadvantage is the transformer utilization is low, less able to drive inductive loads.
Full-bridge inverter circuit to overcome the shortcomings of the push-pull circuit, power transistor adjusts the output pulse width, the output AC voltage of the RMS that is changed. Since the circuit has a freewheeling circuit, even for the inductive load, the output voltage waveform distortion will not. The disadvantage of the circuit on the bridge arm of the power transistor is not common ground, it must use special driver circuit or using isolated power supplies. In addition, in order to prevent the upper and lower co-arm conduction occurs, must be designed to first bring up the rear turn-off circuit, that is, you must set the dead-time, its circuit structure is more complicated.
没有评论:
发表评论