Power-variable frequency operation synchronization switching method based on high voltage frequency converter motor control system

Abstract

The invention discloses a method truly realizing smooth, stable, uninterrupted and synchronization switching function between power frequency operation and variable frequency operation, and the method is based on a high voltage frequency converter motor control system; the variable-to-power frequency operation switching method comprises the following steps: allowing a main controller to use a non-code disc vector control algorithm to control a high voltage motor until the high voltage motor frequency rises to the set frequency; switching the non-code disc vector control algorithm to a constant voltage frequency ratio control algorithm, and allowing the high voltage motor frequency to continuously rise to the high voltage network voltage power frequency; sampling high voltage motor stator current and voltage so as to calculate a power factor when a high voltage frequency converter stably works, thus determining amplitude and phase object values of the high voltage frequency converter output voltage when variable frequency operation is switched to the power frequency operation; allowing the high voltage frequency converter output voltage amplitude and phase to reach object values, then gradually changing until the high voltage frequency converter output voltage amplitude and phase are consistent with the high voltage network voltage amplitude and phase, so the high voltage frequency converter output current can be gradually transferred to a power grid access contactor line, thus finishing the switching process.

Description

technical field [0001] The invention relates to a method for synchronously switching between a power frequency operation state and a variable frequency operation state based on a high-voltage frequency converter motor control system, and belongs to the technical field of high-voltage motor frequency conversion control. Background technique [0002] In some applications, such as constant pressure water supply systems, multiple water pumps are usually used in parallel cycle operation, so after using a frequency converter to start N motors, implement frequency conversion speed regulation on the N+1th motor to realize the water supply system. Constant pressure control. After the soft start of the motor is completed, it is necessary to switch from variable frequency operation to industrial frequency operation, directly connect the motor to the grid, and then the frequency converter can start other motors again or control the speed of other motors. The key to switching from varia...

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Problems solved by technology

[0004] At present, some existing soft starting methods have some defects: the thyristor soft starter has the problem of small starting torque, which cannot be applied to some industrial loads that require heavy-duty starting or constant torque starting.

In the operating state where the power grid and the inverter supply power to the motor at the same time, since the output voltage of the inverter is not a smooth sine wave, there will be some errors in the synchronous switching control algorithm, so there must be grid and inverter in this state. The circulating current between them will lead to a deviation between the output current of the inverter and the current of the motor, which may cause the failure of the vector control mode

[0005] At present, the traditional synchronous switching technology is not a real disturbance-free switching, and there are usually the following problems: 1) When switching from variable frequency operation to power frequency operation, there will be a certain degree of impact on the grid current at the moment of switching, and the magnitude of the impact current is related to The motor load is related to the size; 2) When the power frequency operation is switched to the variable frequency operation, at the moment of switching, the output current of the inverter will have a certain degree of impact, and the impact current is also related to the motor load

And so far, there is no technology that can truly achieve bumpless switching

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