Power Converter AC Braking for High Inertia Motor Control
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Solution Overview
Problem
Existing power converter technologies face challenges in effectively braking an electric motor with high inertia, leading to reduced braking force and potential reverse rotation during deceleration, as they rely on voltage generated by the motor, which decreases at low speeds, and require additional physical devices, increasing costs.
Innovation Solution
The implementation of a power converter with an AC braking mechanism that applies high-frequency AC voltage to the motor, ensuring braking force is applied only in the stopping direction, using a configuration that includes a DC conversion unit, smoothing capacitor, AC conversion unit, current detector, and control unit to manage the braking process, thereby preventing reverse rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If short-circuit braking is performed using the voltage generated by the magnet motor when the speed is low, then the braking system is simple, but the braking force becomes extremely small when the generated voltage is less than the voltage drop of the power converter elements
Solution Approach 1:
The invention changes the voltage application parameters by applying AC voltage at a frequency higher than the rotation frequency of the motor. This parameter change ensures that the braking current flows effectively even at low speeds, maintaining sufficient braking force when the motor's generated voltage is insufficient to overcome the power converter element voltage drops.
2Ease of operation
If lagging phase control is continued to stop the motor, then the control method is simple, but the magnet is dragged by the lagging phase and reverse rotation can occur immediately before the stop
Solution Approach 1:
The invention applies AC voltage periodically at a frequency higher than the motor's rotation frequency. This periodic action creates braking forces that counteract the motor's rotation without causing the magnet to be dragged by lagging phase, preventing reverse rotation before the motor stops. The high-frequency AC voltage ensures stable deceleration to a complete stop.
3Speed
If reverse rotation braking method is applied when the speed is low, then the deceleration rate is high, but the induced voltage becomes small and reverse rotation can occur by the applied voltage
Solution Approach 1:
The invention changes the voltage frequency parameter to be higher than the motor's rotation frequency. This parameter change allows the application of braking voltage without causing reverse rotation, as the high-frequency AC voltage creates effective braking current even when the induced voltage is small at low speeds, maintaining both high deceleration rate and rotation direction stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables the power converter to efficiently stop the motor without reverse rotation, even with high inertia loads, by maintaining a consistent braking force through AC voltage application, reducing the risk of reverse rotation and minimizing additional hardware requirements.
Implementation Method 1
the control unit performs AC braking so that braking is performed by allowing AC current of a condition not applying a rotation force to an AC electric motor to flow
Implementation Method 2
a smoothing capacitor 103, the AC conversion unit 104
Data Source
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AI summary
In conventional technology, one problem resulting from short-circuit braking that used voltage generated in a magnet motor during deceleration was that when the rotation speed decreased and the generated voltage fell, if the voltage generated by the magnet motor decreased more than that amount of the voltage drop in an element of the power converter, then the current contributing to the braking force would become extremely small and the braking force would decrease to an extreme extent. A problem was that if the load inertia of the motor was great, then the motor would not come to a halt. This power converter is provided with an AC conversion unit which converts DC power into prescribed AC power, a current detector which detects the current in the AC conversion unit, and a control unit which controls output of the AC conversion unit, and is characterized in that while the AC electric motor connected to the power converter is in a deceleration mode, the control unit performs AC braking which involves braking by applying an AC current that does not result in imparting a rotational force to the aforementioned AC electric motor.