- Working principle of photovoltaic controller
The output characteristic curve of the solar cell is shown in Figure 1. The volt-ampere characteristic of the solar cell has a strong nonlinearity, that is, when the sunlight intensity changes, its open circuit voltage will not change much, but the maximum current generated will There is considerable variation, so its output power and maximum power point will change accordingly. However, when the sunshine intensity is constant, the current output by the solar cell is constant, which can be regarded as a constant current source. Therefore, it is necessary to research and design a solar photovoltaic power generation controller with excellent performance in order to utilize the solar energy more effectively.
1) The basic working principle of the parallel charge-discharge controller
The block diagram of the parallel charging and discharging controller is shown in Figure 2. The switching device T1 in the charging circuit of the parallel charging and discharging controller is connected in parallel with the output end of the solar cell. When the battery voltage is greater than the “full cut-off voltage”, the switching device T1 When the diode VD1 is turned on and the diode VD1 is turned off, the output current of the solar cell array is directly discharged through the T1 short circuit, and the battery is no longer charged, so as to ensure that the battery will not be overcharged and play an overcharge protection role. For more battery charging and discharging precautions, please visit tycorun.com.
VD1 is an anti-reverse charging diode. Only when the output voltage of the solar cell array is greater than the battery voltage, VDI can be turned on. On the contrary, VD1 is turned off, so as to ensure that the battery will not be reversely charged to the solar cell array at night or in rainy weather. to reverse charging protection.
The switching device T2 is a battery discharge switch. When the load current is greater than the rated current and the overload occurs or the load is short-circuited, T2 is turned off, which plays the role of output overload protection and output short-circuit protection. At the same time, when the battery voltage is lower than the “over-discharge voltage”, T2 is also turned off to perform over-discharge protection.
VD2 is an anti-reverse diode. When the polarity of the battery is reversed, VD2 is turned on to make the battery short-circuit and discharge through VD2, and a large current is generated to quickly fuse the fuse of the fuse, which plays the role of reverse battery protection.
The detection control circuit detects the battery voltage at any time. When the voltage is higher than the “full cut-off voltage”, T1 is turned on for overcharge protection; when the voltage is lower than the “overdischarge voltage”, T2 is turned off for overdischarge protection.
2) The basic working principle of the series charge-discharge controller
The block diagram of the series-type charge-discharge controller is shown in Figure 3. The series-type charge-discharge controller and the parallel-type charge-discharge controller have similar circuit structures. The only difference is the connection method of the switching device T1. The parallel-type charge-discharge controller is connected in parallel with the output end of the solar cell. , and the series T1 is connected in series in the charging circuit. When the battery voltage is higher than the “full cut-off voltage”, the TI is turned off, so that the solar cell no longer charges the battery, which plays an overcharge protection role.
- PV controller protection function
The main protection function of the photovoltaic controller is to protect the battery from charging and discharging to avoid overcharging or overdischarging the battery. The main protection functions that the photovoltaic controller should have are:
(1) High voltage (HVD) disconnection and recovery function. The controller shall have the function of input high voltage disconnection and recovery connection.
(2) Undervoltage (LVG) alarm disconnection and recovery function. When the battery voltage drops to the undervoltage setting value, an audible and visual alarm signal will be issued, and the battery will stop supplying power to the load. When the battery voltage returns to the undervoltage setting value, the battery will resume supplying power to the load.
(3) The photovoltaic controller should also have a load short-circuit protection circuit, an internal short-circuit protection circuit in the controller, a reverse discharge protection circuit for the battery through the solar cell module, and a reverse polarity protection circuit for the load, solar cell or battery, to prevent damage in areas with heavy lightning. Breakdown protection circuit due to lightning strike.
(4) Temperature compensation function. When the battery temperature is lower than 25 ℃, the battery should require a higher charging voltage in order to complete the charging process. Conversely, above this temperature the battery requires a lower charging voltage.
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