Brushless Motor Phase Control for Switching Loss Reduction
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Solution Overview
Problem
Existing brushless rotating electrical machines face challenges in reducing switching losses and optimizing the load on current and voltage sources, leading to inefficiencies and increased electromagnetic compatibility issues.
Innovation Solution
A method where a selected phase winding is temporarily connected to a constant electrical potential, with other phase windings receiving pulse width modulated signals that are phase-shifted relative to each other based on current directions, reducing overall switching losses and AC voltage components in the power source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pulse-width modulated signals are applied to all phase windings simultaneously, then current control precision is improved, but switching losses increase
Solution Approach 1:
The patent applies periodic pulse-width modulated signals to the phase windings in a sequential manner rather than simultaneously. By periodically switching between different phase windings and utilizing the natural inductance of the motor windings to maintain current flow during transitions, the system achieves precise current control while significantly reducing the frequency of switching operations and associated switching losses in the power semiconductor devices.
Solution Approach 2:
The patent ensures continuous current supply to the motor phases by utilizing the inductance of the windings to maintain current flow during switching transitions. When one phase winding is disconnected, the current continues to flow through the freewheeling diode or body diode of the power transistor, ensuring uninterrupted magnetic field generation and eliminating gaps in the useful electromagnetic action.
2Speed
If switching frequency is increased to improve current control, then control responsiveness is improved, but electromagnetic compatibility deteriorates
Solution Approach 1:
By implementing periodic PWM signaling with optimized duty cycles and switching sequences, the patent achieves responsive current control while spreading the electromagnetic interference spectrum. The periodic nature of the switching allows for predictable EMI patterns that can be filtered, and the reduced overall switching frequency decreases the high-frequency noise generation compared to continuous high-frequency switching of all phases.
Solution Approach 2:
The patent utilizes the inductance of the motor windings to carry current through the switching transitions, effectively skipping the need for simultaneous switching of all phases. This rushing through of current during transition periods using stored magnetic energy minimizes the duration of high-dv/dt and high-di/dt events that generate electromagnetic interference, thereby improving EMC while maintaining control responsiveness.
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 approach minimizes switching losses, reduces the load on the current and voltage source, and improves electromagnetic compatibility by optimizing the phase shifts of pulse width modulated signals, leading to more efficient operation and easier current measurement.
Implementation Method 1
the current generated in a phase winding being determined, for example, by the duty cycle of the associated pulse-width modulated signal
Data Source
Figure 1~3
Figure 4~5
Figure 6
AI summary
The invention relates to a method for operating a brushless rotating electric machine with at least three phase windings (U,V,W), each having a first (9,12,30) and a second phase winding connection, wherein the phase windings are connected to each other, in particular the respective second phase winding connections are connected to a common star point (1), wherein individual phase windings (U,V,W) are each separately supplied with pulse width modulated voltage signals, and wherein at least temporarily at least one selected phase winding (U,V,W) is connected to a constant electrical potential (5,6).To minimize switching operations and reduce the alternating current component of the power source, the pulses of the pulse-width modulated signals applied to the other phase windings (U,V,W) are phase-shifted at least temporarily during the time when the selected phase winding (U,V,W) is connected to a constant electrical potential.