Impulse Width Modulation for Brushless DC Motor Current Control
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Solution Overview
Problem
Existing methods for controlling current in brushless DC motor windings, such as pulse width modulation, suffer from ripple currents and heating issues, while two-quadrant controllers are limited in their ability to manage current direction, and hysteric choppers are nonlinear and unpredictable.
Innovation Solution
The implementation of impulse width modulation (IWM) with an H-bridge switching configuration, which provides four-quadrant control by determining the appropriate switch timing for each duty cycle to deliver current impulses in desired directions, reducing switch operations and eliminating ripple currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If pulse width modulation is used to control current in brushless DC motor windings, then the motor can operate continuously, but ripple currents are generated causing heating issues
Solution Approach 1:
The patent applies periodic action by using impulse width modulation that delivers current to the motor windings in periodic impulse bursts rather than continuous flow. The controller switches H-bridge components to provide current impulses at specific intervals, allowing the windings to coast between impulses. This periodic delivery eliminates continuous ripple currents while maintaining motor operation, directly resolving the heating issue caused by conventional PWM's continuous current delivery.
2Device complexity
If hysteric choppers are used for current control, then switching can be simplified, but the control becomes nonlinear and unpredictable
Solution Approach 1:
The patent employs feedback by using Hall effect sensors to continuously monitor the actual current in the motor windings and rotor position. The controller processes this feedback information to determine when and in which direction to deliver current impulses. This feedback mechanism ensures predictable and reliable control by allowing the controller to make informed switching decisions based on real-time motor state, eliminating the nonlinearity and unpredictability of hysteric chopper methods while maintaining simplified switching through the H-bridge configuration.
Data Source
AI summary
A method and apparatus for controlling a brushless direct current motor. An H-bridge is configured to couple a direct current power source to windings of the brushless direct current motor. The H-bridge comprises a plurality of switches. A motor controller is configured to close one of the plurality of switches to put the H-bridge in a coast configuration, wherein the windings of the motor are short circuited. A desired direction for a current impulse to the windings is identified. The one of the plurality of switches is opened in response to identifying a first desired direction for the current impulse to provide the current impulse in the first desired direction to the windings. Another of the plurality of switches is closed in response to identifying a second desired direction for the current impulse to provide the current impulse in the second desired direction to the windings.