PWM Motor Controller Fixed Delay Commutation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional PWM motor controllers for PM DC brushless motors require multiple current sensing elements and complex reassignment of PWM duty cycle delays, increasing cost and complexity, especially when operating in all four quadrants of the motor torque versus motor speed diagram.
Innovation Solution
Assigning specific half H-bridge transistor pairs to phases consistently and delaying their activation by fixed fractions of the PWM period, eliminating the need for reassignment and allowing operation with a single current sensing element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple current sensing elements are used in series with motor outputs, then motor current sensing accuracy is improved, but hardware cost and controller complexity increase
Solution Approach 1:
The patent extracts the current sensing function from the motor output lines and relocates it to the DC bus line. By placing a single current sensing element in the DC bus, the system obtains motor current information without requiring multiple sensing elements at each motor terminal, thereby reducing hardware complexity while maintaining sensing capability
Solution Approach 2:
The single current sensing element on the DC bus serves multiple functions: it senses current for PWM duty cycle control, provides feedback for motor operation monitoring, and enables operation across all four quadrants of the motor torque-speed diagram. This universal sensing approach eliminates the need for dedicated sensing elements at each motor output
2Manufacturing precision
If PWM duty cycle delay reassignment is implemented for each commutation state, then accurate motor current control is improved, but control electronics complexity and difficulty increase
Solution Approach 1:
The patent pre-establishes fixed PWM duty cycle delay relationships between transistor pairs before commutation occurs. The delay values are predetermined based on the PWM period and are applied consistently across all commutation states, eliminating the need for real-time reassignment during operation
Solution Approach 2:
Instead of dynamically adjusting PWM delays for each commutation state as in conventional approaches, the patent inverts the approach by using fixed, predetermined delay values that remain constant across all commutation states. This simplifies the control logic while maintaining effective current control
3Device complexity
If fixed PWM duty cycle delays are used for all commutation states, then control electronics complexity is reduced, but motor operation accuracy in all four quadrants may deteriorate
Solution Approach 1:
The patent adjusts the PWM duty cycle magnitude and delay duration as controllable parameters to accommodate operation in all four quadrants. By varying these parameters within the fixed-delay framework, the system maintains accurate motor control across different operating conditions without requiring complex dynamic reassignment logic
Data Source
AI summary
A method produces PWM voltage waveforms in a PWM motor controller of a three phase PM DC brushless motor, wherein the motor controller has first, second and third half H-bridge transistor pairs to generate the voltage waveforms to electronically commutate the motor. The first transistor pair is always assigned to the first phase for every commutation state requiring a voltage waveform from the first transistor pair. The second and third transistor pair are similarly assigned. The first method also includes always starting a voltage waveform generated by the first transistor pair substantially at the beginning of the PWM period when a commutation state requires a voltage waveform from the first transistor pair but delaying starting a voltage waveform generated by the second transistor pair by substantially ⅓ of the PWM period and delaying starting a voltage waveform generated by the third transistor pair by substantially ⅔ of the PWM period.