As far as electrical mechanical action fast response

Power regulator from the current status quo, whether it is AC or DC, mostly analog circuitry to adjust. In this type of control circuit, the circuit quiescent operating point due to the restrictions, usually only achieve "a poor adjustment" process. Unless a person has a memory  power transformers added components, such as stepper motors. But  electric meter brings a lot of extra trouble, such as a stepping motor, not only more difficult to control, and because of Voltage stabilizer action far less electrical fast response, and affect regulation accuracy. As microprocessor judgment and memory function that makes use of microprocessor supply voltage to achieve stability control in the "no difference adjustment" possible.