The constant voltage-frequency ratio control method of permanent magnet synchronous motor is similar to the constant voltage-frequency ratio control method of AC induction motor, which controls the amplitude and frequency of the input voltage of the motor to be changed at the same time, so as to make the motor flux constant, and the constant voltage-frequency ratio control method can be adapted to the requirements of a wide range of speed regulation system.
On the premise of not feeding back physical signals such as current, voltage or position, a certain control accuracy can still be achieved, which is the biggest advantage of the constant voltage-frequency ratio control method. Constant voltage frequency ratio control method control algorithm is simple, hardware cost is low, in the field of general-purpose frequency converter has been widely used. The disadvantages of constant voltage-frequency ratio control method are also obvious, because there is no feedback speed, position or any other signals in the control process, so it is almost completely unable to obtain the motor's operating state information, and it is even more impossible to accurately control the rotational speed or electromagnetic torque, and the performance of the system is general, the dynamic response is poor, especially in the change of the given target speed or the load changes, it is easy to produce the problem of out-of-step and oscillations, etc. It is obvious that this control method can't be separately controlled. Obviously, this control method cannot control the torque and excitation current separately, and it is easy to have a large excitation current in the control process, which affects the efficiency of the motor. Therefore, this control method is often used in general-purpose inverters with lower performance requirements, such as air conditioning, conveyor drive control of assembly lines, energy-saving operation of water pumps and fans, etc.
