Brushless Motor Drive Voltage Waveform Transition
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Solution Overview
Problem
Existing brushless motor driving techniques suffer from inefficiencies due to voltage distortion and unbalanced motor operation, leading to reduced efficiency and increased torque ripple, particularly in applications with varying temperature conditions and battery voltage levels.
Innovation Solution
The method modifies the drive voltage profile by splitting the 120-degree saturation interval into two 60-degree sub-intervals, allowing for sinusoidal or distorted waveforms with adjustable peak values by varying the control value KVAL, ensuring balanced voltage distribution between phase taps and neutral points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the drive voltage profile is amplified by increasing KVAL to achieve full supply voltage, then the maximum voltage supplied to motor windings is improved, but voltage distortion and asymmetric saturation occur leading to unbalanced motor operation
Solution Approach 1:
The patent implements dynamic switching between sinusoidal driving and square wave driving modes based on operating conditions. The control system automatically transitions from sinusoidal PWM modulation at lower speeds to three-phase square wave driving at higher speeds, optimizing performance across the entire speed range while preventing voltage distortion and saturation issues
Solution Approach 2:
The patent changes the driving parameter from sinusoidal PWM modulation to square wave driving by modifying the voltage profile shape. This parameter change allows the system to achieve full supply voltage without distortion by using a different waveform configuration that prevents asymmetric saturation in the motor windings
2Reliability
If the drive voltage profile is down-scaled by reducing KVAL to avoid saturation, then voltage distortion is reduced, but the maximum voltage supplied to motor windings is limited
Solution Approach 1:
The system dynamically adjusts the driving mode based on speed requirements. When high voltage is needed without saturation, the system switches to square wave driving mode which inherently prevents the asymmetric saturation problem while delivering full supply voltage to the motor windings
Solution Approach 2:
The patent changes the voltage profile parameter from scaled-down sinusoidal waveform to unscaled square wave waveform. This parameter change enables the system to achieve full voltage output without distortion by fundamentally altering the waveform shape rather than simply adjusting amplitude
3Ease of operation
If sinusoidal PWM modulation is used for speed control, then smooth speed variation is achieved, but spin-up time is excessive particularly in cold conditions
Solution Approach 1:
The patent employs periodic switching between driving modes. During spin-up, the system uses square wave driving which provides immediate full voltage for rapid acceleration. Once the motor reaches a certain speed, the system periodically transitions to sinusoidal PWM modulation for smooth speed control, thus reducing spin-up time while maintaining operational smoothness
Solution Approach 2:
The control system dynamically selects the driving mode based on motor speed and temperature conditions. In cold conditions or during rapid spin-up requirements, the system dynamically switches to square wave driving to reduce spin-up time, then transitions to sinusoidal modulation for normal operation, optimizing both time and smoothness characteristics
Data Source
AI summary
The method and a related device are for driving a brushless motor, according to which by acting solely on the control value, that is by reducing or increasing it, the driving mode eventually passes from a sinusoidal three-phase driving mode to a distorted square-wave three-phase driving mode for increasing or maximizing the voltage that may be supplied to each motor winding or vice versa. An effective drive voltage profile includes, cyclically, during each 60 electrical degree interval, profiles of re-constructed outphased complete drive waveforms including a first one stably in a saturated region, a second one exiting, at the beginning of the interval, a state of incipient saturation, and a third one reaching, at the end of the interval, a state of incipient saturation. In this way, by modifying the numerical control value it is possible to pass from a sinusoidal drive mode to a distorted drive mode of enhanced maximum peak value or vice versa.