AC system are mainly used in photovoltaic systems in our country, which can collect the electric energy that solar panels transmitted ,and charge storable batteries, it mainly includes solar panel,solar controller,storage battery,solar inverters sometimes.
For example, solar energy lighting system which be mainly used in our northwest district ,and the power supplying system of microwave station are all AC system. These systems have simple configuration and low cost feature but for the reason of variety in load AC voltage aspects (For instance,12V,24V,48V.. and so on). It is very difficult to accomplish standardization and compatibility of systems, especially in electric power for civil use, and our loads are mostly AC loads, so the photovoltaic electrical source that afforded by DC is difficult to access to markets as goods. In addition, photovoltaic generator will achieve on-grid function, finally. We must adopt matured market model, photovoltaic generator system will assuredly become the mainstream of . photovoltaic generator.
The photovoltaic generator systems: the photovoltaic generator systems that adopt AC electrical power output, which consisting four parts of solar array , charging and discharging controller ,storable battery ,and inverter(,storable battery will be removed in on-grid generation.). However ,for the highly requirement of photovoltaic generator systems on inverter ,inverter is the key component.
1.Requirement of highly efficiency. For the reason of the high price of solar panels ,the efficiency of inverter must be promoted in order to maximize the benefits of solar panels and increase the efficiency of photovoltaic generator systems.
2.Requirement of highly reliability: At present, photovoltaic generator systems are mostly used in backcountry district ,and most power stations have not clerks on duty and maintenance .For this case, inverter must has a reasonable circuit structure ,strictly component sieve ,and has various protection function. For example, reversed polarity connection protection in DC input , short circuit protection in AC output, overheat protection, overload protection….and so on.
3. DC input voltage is required to adapt to a wide range of voltage as solar batteries vary with the load and intensity of sunshine. The battery is very important to solar battery’s voltage , but the battery’s voltage fluctuates with its remaining capacity and the change of internal resistance , especially when the aging battery’s terminal voltage changes in a wider scope, For example, the 12V battery’s terminal voltage can vary between 10V and 16V, so it requires the inverter to operate nomally in a wide range of DC input voltage and to ensure the stability of AC output voltage.
4. In the medium and large-capacity photovoltaic system, the inverter should output sine waves with low distortion, because if the power is supplied with square wave, the output will contain more harmonic waves which will produce the additional losses. Many photovoltaic systems are loaded on communication equipment or instrumentation which have a higher requirement on power supply quality. As a result, when the medium and large-capacity photovoltaic systems work together, the output is required to be sine wave current to avoid the contamination. Inverters convert direct current to alternating current, if the DC voltage is a bit low, the AC A-C transformaer will increase the voltage , enables it to standard AC voltage and frequency.
For large-capacity inverter, its DC bus voltage is high ,so the AC output can reach 220V without the help of step-up transformer. While for the medium and small-capacity inverter, because of its low DC voltage such as 12V, 24V, step-up circuit must be designed. Generally, the medium and small-capacity inverter have three types: push-pull inverter circuit, full-bridge inverter circuit and the high-frequency boost inverter circuit . In the push-pull circuit, the neutral plug of the step-up transformer is connected to positive supply, and two power tube work by turns,and then the output is AC power. The power transistor is to take sides and it is simple to drive and control circuits, besides, due to the inverter’s leakage inductance, short-circuit current is restricted so as to improve the reliability of the circuit.Its shortcoming lies in that the transformer ,with a low utilization rate, is not good at driving inductive load.
