Rotor Angle Determination Using Phase-Shifted PWM Signals
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Solution Overview
Problem
Existing methods for determining the rotor angle of synchronous machines, especially at low speeds, are inefficient and unreliable, often requiring additional voltage or current pulses and relying on encoders, which can disrupt smooth operation and increase costs in series-produced vehicles.
Innovation Solution
Modifying pulse-width-modulated (PWM) drive signals by applying phase shifts to generate multiple switching patterns, allowing for rotor angle determination without encoders, thereby extending the duration of active voltage phasors at the neutral point and improving measurement accuracy and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional voltage or current pulses are applied to determine rotor angle, then measurement accuracy improves, but operation smoothness deteriorates and energy consumption increases
Solution Approach 1:
The system uses the existing PWM drive signals to determine rotor angle without requiring additional separate measurement excitations. The neutral point potentials are derived from the normal operating voltage vectors already applied to the synchronous machine phases, making the measurement system self-sufficient and eliminating harmful additional excitations.
Solution Approach 2:
The PWM drive signals serve dual purposes: both driving the synchronous machine and enabling rotor angle determination. The same voltage vectors used for motor control also create measurable neutral point potentials that contain rotor angle information, eliminating the need for separate measurement excitations.
2Measurement precision
If encoders are used to determine rotor angle, then measurement accuracy improves, but device complexity and cost increase
Solution Approach 1:
The mechanical encoder system is replaced with an electrical measurement method that uses neutral point potentials. Instead of mechanical sensors and encoders, the system electronically determines rotor angle by analyzing the potentials at the neutral point during normal PWM operation, significantly reducing device complexity.
Solution Approach 2:
The neutral point potentials serve as an intermediary that contains information about rotor angle without requiring direct mechanical measurement. By measuring these electrical potentials and processing them through the control device, the system indirectly determines rotor angle with reduced complexity.
3Reliability
If PWM drive signals are phase-shifted to extend active voltage phasor duration, then rotor angle determination reliability improves, but switching pattern complexity increases
Solution Approach 1:
The system applies periodic phase shifts to PWM drive signals in a cyclic manner. Multiple switching patterns are generated by systematically shifting phase angles, and these patterns are applied in sequence to ensure reliable rotor angle determination while maintaining manageable complexity through regular, repeating cycles.
Solution Approach 2:
The switching patterns are made dynamic through variable phase shifts. The control device adjusts the phase angles of PWM signals to extend the duration of active voltage phasors, creating adaptable switching patterns that optimize measurement conditions while managing complexity through controlled variability.
Data Source
AI summary
Determining the rotor angle of a synchronous machine. In one aspect, the invention provides a method that includes generating a multiplicity of pulse-width-modulated drive signals for the phases of an inverter feeding the synchronous machine depending on a voltage to be fed into the synchronous machine, and applying a first phase shift to one or more of the multiplicity of pulse-width-modulated drive signals, so that the duration of the switching states of the inverter is extended in order to generate a first switching pattern for the phases of the inverter. The method also includes applying a second phase shift to one or more of the multiplicity of pulse-width-modulated drive signals for generating a second switching pattern, selecting one or more of the first and second switching patterns, determining one or more of neutral point potentials at the neutral point of the synchronous machine, and calculating the rotor angle of the synchronous machine.