In recent years, surprisingly, the small household appliance market is exceptionally hot, many small household appliance enterprises orders full, small household appliance and related enterprises performance has also risen sharply. As the core component of electric small household appliances, the AC series excitation motor market is also developing rapidly. Compared with DC or induction motors, series excitation motors have the advantages of simple structure, mature technology, high power density, cost-effective and so on, and are widely used in small household appliances. However, due to the shortcomings of soft torque characteristics, large variation of motor speed with load, and poor speed regulation performance, series-excited motors are subject to many limitations in practical application. Especially in some multi-functional food processor, chef machine, multi-functional wall-breaking cooking machine and other products, only by simple voltage reduction, tap speed control can not reach the use of requirements. For this reason, the series motor must be equipped with a powerful electronic speed control device to meet the performance requirements of the end product.

At present, the series excitation motor speed control mainly has the following ways:

In the motor rotor installed a multi-pole magnetic ring, corresponding to the motor bracket installed a Hall sensor, the Hall sensor will detect the rotating magnetic field signal is converted into a speed signal and sent to the power controller.

A circular grating is installed on the motor rotor, corresponding to a grating sensor is installed on the motor bracket, and the sensor converts the light signal, which changes with the rotational speed at high frequency, into a rotational speed signal and sends it to the power controller.

Power controller according to the speed signal according to the principle of negative feedback regulation to control the output voltage in order to stabilise the motor speed within a certain accuracy. The power controller is divided into two types: silicon controlled speed control and PWM inverter control.

Series excitation motor configured with the above negative feedback speed control device, the performance can be greatly improved, the speed range can be from dozens of revolutions to tens of thousands of revolutions, the speed change is smooth, to achieve the real stepless speed change. At the same time, the negative feedback control can limit the high speed at no load, greatly reduce the noise of the product, reduce the motor spark. And the negative feedback function can make the motor in low speed according to the load automatically adjust the current, motor torque characteristic hardness greatly improved, solve the series excitation motor speed fluctuation, low gear torque reduction shortcomings.

With the rapid development of today's power electronics technology, a variety of control semiconductor devices SCR, MOSFET, BJT, IGBT, GTO, etc. and the development of PWM control technology is becoming more and more perfect, negative feedback control power inverter has been widely used, mature technology. Compared with brushless DC motors, negative feedback series-excited motor in the performance of a certain gap, but the cost is low, cost-effective, so it has been widely used, such as drum washing machines, wall-breakers, kitchen robots, and other products most of the use of the series-excited motor with negative feedback.