Electric Machine PWM Phase Offset for Current Detection
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Solution Overview
Problem
Current electrical machines with multiple sub-machines face interference in current detection due to differing PWM pulse patterns and timing, which disrupts the measurement of stator coil currents, especially when the pulse patterns are not synchronized.
Innovation Solution
Implementing a control unit that generates PWM signals with time-delayed edges and centers for sub-machines, allowing for a phase offset between control patterns, and using current sensors to detect currents during pulse centers, while adjusting pulse duty factors to avoid interference and optimize current detection intervals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If PWM pulses are generated for sub-machines with different timing patterns, then the intermediate circuit capacitor is overloaded and power losses increase, but if PWM pulses are synchronized, then current detection is disrupted by electromagnetic interference
Solution Approach 1:
The control unit generates PWM pulses with periodic timing patterns where pulses for different sub-machines are alternately shifted. During one PWM period, pulses for the first sub-machine are shifted to allow current detection, while during the next PWM period, pulses for the second sub-machine are shifted. This periodic alternation reduces intermediate circuit capacitor loading and power losses while maintaining current detection accuracy through electromagnetic field management.
2Measurement precision
If PWM pulse edges coincide with current detection timing, then current detection is disrupted by electromagnetic fields from switching, but if PWM edges are delayed, then current detection can proceed undisturbed
Solution Approach 1:
The control unit preliminarily shifts the PWM pulse timing so that pulse edges occur before the current detection time window. By advancing the PWM switching action, the electromagnetic field transients from switching settle before current detection begins, ensuring accurate measurement. The shifted timing is calculated in advance to provide sufficient settling time while maintaining efficient operation.
3Loss of energy
If PWM pulses for sub-machines are generated with phase offset, then intermediate circuit capacitor is relieved and power losses reduce, but then current detection may be disrupted by overlapping electromagnetic fields
Solution Approach 1:
The control unit implements periodic alternation of phase offset patterns. During one PWM period, a phase offset is applied to reduce capacitor loading, while during the next PWM period, the offset is adjusted or removed to enable accurate current detection. This periodic switching between different phase offset states allows the system to benefit from reduced power losses while periodically eliminating electromagnetic interference for accurate measurement.
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 solution effectively relieves the intermediate circuit capacitor, reduces power losses, and ensures undisturbed current detection by aligning pulse edges with current detection intervals, maintaining voltage control within safe limits and minimizing disruptions.
Implementation Method 1
The sub-machines each have part of the stator coils of the stator and are each designed to generate a rotating magnetic field independently of one another for rotating the rotor
Implementation Method 2
The control unit is designed to detect the phase current of at least one phase of the sub-machine during a pulse center of a PWM pulse
Data Source
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AI summary
The invention relates to an electric machine, in particular an electric motor and/or generator. The electric machine has a stator and a rotor which is designed to be permanently magnetic or to be energized in particular. The machine has at least two sub-machines. Each of the sub-machines has the same number of phases. According to the invention, the machine has a power output stage for each sub-machine, and the machine also has at least one control unit which is connected to the power output stages. The control unit is designed to generate a pulse width-modulated signal for actuating the power output stages. The control unit is also designed to generate the PWM signal for the sub-machines such that an ascending or descending side of a PWM pulse for one sub-machine, said side representing a switching time in each case, and a pulse center of a PWM pulse for another sub-machine of the sub-machines are delayed relative to each other.