Why the solar pump inverter can have such an unbelievable function, it starts from the principle of alternating current.
AC power has three elements, voltage, current and frequency, under normal circumstances, the frequency are constant 50Hz, the motor starts, 50 times per second, the power changes with the current-voltage, so we generally use the voltage and current to calculate the power. But the motor is different, its power and frequency are related, the normal rated power is the power under the frequency of 50Hz, when the frequency decreases, the power will also decrease. The rated power of the motor equals to rated torque times rated revolution, as long as the rated torque remains the same, the motor can operate, so that when the frequency and voltage drop, the rated power drops in proportion to the speed or frequency. The PV pump inverter adds the inverter function to the inverter, which can change the frequency of the AC output. When starting, the frequency is lowered to change power with speed, and after the motor starts, the frequency is raised to increase the speed. The frequency can also change with light, so that even a 1kW PV input can drive a 4kW pump to run, isn't that amazing.
Since the function of solar pump inverter is so unbelievable, can we expand their application range? The answer is no, because the output voltage, current, phase and frequency of the pump inverter are changing with the light, which can not be used in many occasions .
1. By technical restrictions, solar pump inverter can not yet be used in parallel more than one, must be an inverter with a motor, so the maximum power will be limited; there is no solar pump inverter to support energy storage, DC coupling in some low-temperature winter areas, outside the water tower will freeze, photovoltaic water lifting system will also be limited; solar pump inverter can not be connected to the grid, because the grid requires frequency and voltage synchronization.
2. Solar pump inverter can take a very limited load, at present, in addition to the pump motor, all the power stability, voltage and frequency requirements of the load can not take, such as the solar pump inverter can not directly with lights, refrigerators, computers, washing machines, even inverter air conditioning can not take, only with pure resistance load water heater.