Rotating Field Machine Current Control via Optimized Pulse Patterns
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Solution Overview
Problem
Existing current control methods for rotating field machines in motor vehicles suffer from current distortions and harmonics, particularly at high modulation degrees and low switching frequencies, where space vector modulation is unsuitable, leading to inaccurate feedback and compensation issues.
Innovation Solution
A control device and method that optimize both the pulse pattern and sampling times for minimum current harmonic content, allowing for reliable current control by determining fundamental components of output voltage and sampling currents at specific times with minimal deviation from the fundamental, thus reducing distortions and eliminating the need for complex parameterization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If space vector modulation is used to control the rotating field machine, then the control method is simple and suitable for variable rotational speed operation, but current distortions and harmonics occur at high modulation degrees and low switching frequencies
Solution Approach 1:
The patent changes the modulation parameters by switching from space vector modulation to optimized pulse patterns at high modulation degrees. The pulse patterns are specifically designed with optimized switching times and duty cycles to minimize current harmonics while maintaining the desired fundamental voltage component, thus resolving the contradiction between control simplicity and harmonic reduction.
Solution Approach 2:
The patent implements a dynamic modulation strategy that adapts the modulation method based on operating conditions. At low to medium modulation degrees, space vector modulation is used for simplicity, while at high modulation degrees with low switching frequencies, optimized pulse patterns are applied to eliminate current distortions, making the system dynamically adaptable to different operating points.
2Device complexity
If output current is sampled at arbitrary times and fed back to the current controller, then the feedback process is simple, but the current controller attempts to compensate deviations caused by current harmonics which cannot be influenced
Solution Approach 1:
The patent applies preliminary action by pre-optimizing the pulse patterns offline to minimize current harmonics before the actual control process. Additionally, sampling times are pre-determined and synchronized with the pulse pattern phases, ensuring that current sampling occurs at optimal moments when harmonic content is minimized, thus improving feedback accuracy without adding complex real-time processing.
Solution Approach 2:
The patent implements improved feedback by synchronizing current sampling with the optimized pulse pattern. The current sensor samples the output current at specific times determined by the pulse pattern phase, and this synchronized feedback is fed to the current controller. This ensures that the feedback signal accurately represents the fundamental current component without significant harmonic distortion, improving control reliability.
3Productivity
If sampling times are not optimized with regard to the pulse pattern, then the sampling process is simple, but inaccurate results are obtained due to current ripple components
Solution Approach 1:
The patent performs preliminary optimization of sampling times offline in synchronization with the pulse pattern. The sampling instants are pre-calculated based on the pulse pattern characteristics to coincide with moments when current ripple and harmonic content are minimal. This preliminary preparation ensures that online sampling achieves high precision without requiring complex real-time calculations, maintaining both efficiency and accuracy.
Data Source
AI summary
A control device for controlling the current of a rotating field machine of a motor vehicle, includes a current controller for determining a fundamental of an output voltage for a respective operating point, a controller for modulating the output voltage by driving a rectifier of the control device based on a pulse pattern optimized offline for the respective operating point, and a current sensor for sampling a harmonics-impacted output current, resulting from the pulse pattern that is used, of the rectifier and for returning the sampled output current to the current controller. Sampling times for sampling the output current are optimized offline in a manner specific to the pulse pattern and are predetermined as those times at which a deviation between the harmonics-impacted output current and a fundamental of the output current is less than a predetermined threshold value.