Sensorless BLDC Overmodulation PWM for Higher Output
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Solution Overview
Problem
In sensorless sinusoidal drive of three-phase direct-current brushless motors, the use of dead time for positional detection limits the duty ratio to less than 100%, resulting in reduced motor output, increased switching frequency leading to heat generation, and decreased maximum rotation speed.
Innovation Solution
A motor driving method employing overmodulation PWM control with a modulation degree exceeding 100% to improve motor output, reduce noise and vibration, and decrease switching frequency, while maintaining positional detection precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dead time is used for positional detection in sensorless sinusoidal drive, then positional detection precision is maintained, but motor output is reduced and maximum rotation speed decreases
Solution Approach 1:
The patent applies overmodulation PWM control by changing the modulation degree parameter from the conventional limit of 100% to a range of 100-130%. This parameter change allows the motor to operate in an overmodulation state where the modulation signal amplitude exceeds the carrier amplitude, enabling duty ratios greater than 100% and thereby increasing motor output and maximum rotation speed while maintaining positional detection precision through preserved dead time functionality
2Reliability
If duty ratio is limited to less than 100% for positional detection, then positional detection is secured, but motor maximum output cannot be high
Solution Approach 1:
The patent changes the modulation degree parameter to enable overmodulation control with values between 100-130%, allowing duty ratios to exceed 100%. This parameter change resolves the contradiction by enabling the motor to operate at higher power output levels while maintaining the dead time necessary for positional detection, thus achieving both high motor maximum output and reliable positional detection
3Productivity
If conventional PWM control is used with modulation degree at 100%, then switching frequency is high, but heat generation in switching devices increases
Solution Approach 1:
The patent changes the modulation degree parameter to the overmodulation range of 100-130%, which alters the PWM control characteristics. This parameter change reduces the switching frequency of the switching devices while maintaining effective motor control, thereby reducing heat generation and energy loss in the switching devices without sacrificing productivity
Data Source
AI summary
The control circuit is configured to, upon reception of an input of a given minimum value as a modulation signal, output a pulse signal at a duty ratio of 0% to an inverter circuit, upon reception of an input of a given maximum value as the modulation signal, output a pulse signal at a duty ratio of 100% to the inverter circuit, and in an overmodulation state, output a pulse signal at a duty ratio of 100% to the inverter circuit. The overmodulation state is a state in which an overmodulation signal having a maximum modulation degree of more than 100% is input as the modulation signal and an instantaneous value of the modulation signal is more than the given maximum value. The maximum modulation degree is a ratio of a maximum value of the modulation signal to the given maximum value.