Regardless of whether it's a synchronous or asynchronous motor , the adoption of advanced control technology and new control methods has significantly improved system performance, potentially allowing it to replace DC motors as the dominant force in electrical control. Currently, typical high-performance AC motor control systems that are already in use or under research include synchronous motor control systems, asynchronous motor control systems, and high-precision AC motor motion control systems.
● A commutatorless motor control system uses an AC-DC-AC current-type inverter to power a conventional synchronous motor. Both the rectifier and inverter sections are composed of thyristors. Utilizing the characteristic that the synchronous motor current can lead the voltage, the inverter's thyristors operate in a natural commutation state. Simultaneously, the position of the rotor magnetic poles is detected to select the inverter's thyristors, enabling the motor to operate in a self-synchronizing state; hence, it is also called a self-controlled synchronous motor control system. Its advantages include directly using a conventional synchronous motor and conventional thyristors to construct the system, allowing for large capacity and high motor speeds. For example, the French Mediterranean high-speed train uses this scheme, and the technology is relatively mature. Its disadvantage is that because the current is supplied using a square wave while the motor windings are sinusoidal, the resulting low-speed torque ripple is relatively large.
● The inverter in the AC-AC frequency converter synchronous motor control system uses an AC-AC cyclic converter circuit composed of ordinary thyristors to provide three-phase sinusoidal current to the ordinary synchronous motor. Vector control allows for transient compensation of the excitation current, resulting in excellent system dynamic performance. It is widely used in rolling mill main drive control systems. Its advantage is a large capacity, but the speed range is limited, only adjustable from 1/2 synchronous speed downwards.
● Sinusoidal permanent magnet synchronous motor control system: The motor rotor uses permanent magnet materials, and the stator windings remain sinusoidally distributed. When three-phase sinusoidal alternating current is applied, a relatively ideal rotating magnetic field can be obtained, generating stable electromagnetic torque. Vector control technology is used to eliminate the shaft current component, allowing direct torque control via shaft current, achieving a very high level of system control performance. The disadvantage is the need for an expensive absolute position encoder. While achieving the above requirements using a common incremental code disk has some limitations, it is still possible with certain measures. Current research focuses on how to eliminate torque ripple caused by tooth harmonics and PWM control.
● The square-wave permanent magnet synchronous motor control system, also known as a brushless DC motor control system, uses permanent magnet materials for the rotor and full-pitch concentrated windings for the stator to generate a trapezoidal wave magnetic field and induced electromotive force. When a three-phase square-wave alternating current is applied, and the current and induced electromotive force are in phase, a stable electromagnetic torque can theoretically be generated. Its main advantages are that pole position detection is very simple, similar to commutatorless motors, and gating and system control are easy to implement. Its disadvantages are that due to the stator inductance, the actual current does not reach the ideal square wave, and the superposition of currents at commutation time causes torque pulsation, which has a certain impact on the system's low-speed performance.
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