Synchronous motor inverter drive principle and application
Before the inverter outputs the voltage to the stator of the synchronous motor, a certain excitation current is passed from the excitation device to the excitation winding of the synchronous motor, and then the inverter outputs an appropriate voltage to the armature winding of the synchronous motor to start the motor.
The angle between the armature voltage vector of the synchronous motor and the rotor pole position must be within a certain range. If it is not within this range, the synchronous motor may cause the system to lose synchronization. Before the motor starts, the angle is arbitrary, so the angle must be controlled within this range, and the motor can gradually enter the stable synchronous operation state. Through this phenomenon, we can determine that the biggest obstacle when the inverter is applied to the synchronous motor is the start-up phase.
The start-up process of the inverter-driven synchronous motor is mainly divided into the following steps.
(1) The excitation device is energized.
(2) The armature winding of the synchronous motor will be subjected to the DC voltage applied by the inverter to generate a certain stator current.
(3) The inverter slowly rotates the voltage vector applied to the armature winding according to the direction of rotation of the motor. Finally, the synchronous motor enters the synchronous running state, and the process is completed.
(4) The inverter adjusts the output voltage according to the preset acceleration and v/f curve (ie, the magnetic flux is given), and gradually accelerates to a given frequency.
Steady-state operation of the drive-driven synchronous motor and excitation adjustment during operation
Since the inverter drives the synchronous motor, there is no need to install the speed/position sensor control method, and the inverter output waveform is multi-level pwm waveform, which is the same as the waveform when controlling the asynchronous motor. The inverter is similar to the sinusoidal voltage source, no torque. Pulsating, with high reliability.
Under the working condition, manually adjust the excitation current to minimize the output current of the inverter and keep the current constant. When the excitation current condition is adjusted in real time, the inverter can measure the reactive power output to the synchronous motor, and give the excitation given signal to the excitation device and adjust the excitation current.
