A magnetic field vector control soft starter and its control method

Abstract

The invention relates to a magnetic field vector control soft starter and a control method thereof. At present, according to a general soft starter, a three-phase thyristor is mainly adopted to perform reduced-voltage starting, such that the space magnetic field vector of a motor rotates according to a hexagon movement trajectory. If the above method is adopted, a starting torque is small, and the rotation speed of a stator magnetic field cannot be modified, and starting rotation different is large, and as a result, reverse rotation and serious jitter in the starting of the motor will appear. According to the magnetic field vector control soft starter of the invention, a power supplying power source of the A phase, B phase and C phase of a three-phase alternating current asynchronous motor is provided with a magnetic field vector control circuit which is controlled by a microcontroller and is composed of six power thyristors; under the control of the microcontroller, the six thyristors are sequentially switched on one by one at intervals, such that a magnetic field vector control cycle can be finished after seven power frequency cycles last; constant voltage-to-frequency ratio can be maintained, namely, the main flux of the motor can be kept constant; when the motor reaches rated rotation speed, and a control mode changes into a power frequency voltage regulation soft starting mode, and starting can be realized through a voltage regulation or current limiting mode until the starting of the motor is finished.

Description

technical field [0001] The patent of the present invention relates to a magnetic field vector control soft starter and its control method. Background technique [0002] At present, ordinary soft starters mainly use three-phase thyristor step-down starting. It uses two thyristors or bidirectional thyristors connected in series and anti-parallel in each phase in the circuit structure, and realizes voltage adjustment by changing the conduction time of each phase voltage. The thyristors that are turned on are properly selected to realize the rotation of the space magnetic field vector of the motor according to the hexagonal trajectory. see image 3 , the ordinary three-phase thyristor step-down soft starter controls the triggering time of six power thyristors sequentially, and converts the three-phase power frequency AC waveform into image 3 In the middle shaded area, the mains frequency cannot be changed while changing the voltage. This method has two important disadvantages....

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The inverter structure and technology are complicated, the cost is high, and it is not easy to popularize and promote

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