As a universal rotation speed such as VFD motor, a full-wave rectifier circuit causes a large current peak on startup. Under heavy load, when the motor is running at maximum rotation speed, the DC voltage is high, but the AC voltage is low. This situation can be generated by a great torque motor load, but it can also be generated when a large AC current is suddenly drawn at a moment when the motor runs at very low speed. If the UPS is once unloaded by a large current when the load is off, the AC voltage can drop to 9V or less, damaging the circuit portion, through the AC filter and the rectification circuit.
The PI controller consists of two major components: an error amplifier and a proportional, integral, derivative (PID) compensator. The error amplifier is intended to keep the error signal zero, reduce any errors, and increase the gain of the PID compensator when it increases the error signal.
The error amplifier works on a classic principle: when the output is incorrect, the error amplifier will supply a signal to oppose the incorrect output. Thus, if the output is too high, the error amplifier will cause the output to be reduced. Conversely, if the output is too low the error amplifier will cause a signal to be supplied to raise the output. If the error is resulting in a negative output, the error amplifier will automatically supply a positive signal to raise the output.
The error amplifier and its feedback circuit may be expressed technically in various ways. Fundamentally, the error amplifier consists of an operational amplifier, which has a negative feedback loop, and an input of unknown value.
The error amplifier is a simple two-stage device. The input, or input voltage, is connected to the inverting input of the operational amplifier. A ¼-volt reference voltage is applied to the amplifier's non-inverting input. d2c66b5586