Multiphase Coil Driver Modulation for Lower DC-Link Ripple
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Solution Overview
Problem
Conventional three-phase voltage source inverters face limitations in flexibility when varying duty cycles to generate desired voltages, resulting in high RMS ripple current stress on the DC link storage element, which increases cost and size/weight.
Innovation Solution
The proposed coil driver utilizes a pair of half bridges and a series switch with distinct operating modes to reduce RMS ripple current stress, employing a modulation method that varies the modulator carrier angle to minimize ripple current and increase harmonic content, simplifying capacitor and EMI filter design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional PWM drive schemes are used to generate desired output voltage, then the output voltage and frequency can be regulated, but large RMS ripple current stress is imposed on the DC link storage element
Solution Approach 1:
The patent divides the conventional single PWM scheme into multiple independent PWM patterns (center aligned PWM, edge aligned PWM, and asymmetric PWM) that can be selectively applied to different phases. This segmentation allows each phase to use an optimized PWM pattern independent of others, reducing the cumulative ripple current stress on the DC link storage element while maintaining output voltage regulation capability.
2Reliability
If the DC link storage element is sized to handle worst case RMS ripple current, then reliability is ensured, but cost and size/weight increase
Solution Approach 1:
The patent changes the operational parameters of the PWM drive scheme by introducing multiple selectable PWM patterns with different duty cycle arrangements and phase relationships. By dynamically selecting and switching between these patterns, the system optimizes the ripple current characteristics, reducing the peak RMS current that the DC link storage element must handle, thereby allowing for a smaller, lighter capacitor design.
3Ease of operation
If center aligned PWM is used for all phases, then simplicity of control is maintained, but flexibility in varying duty cycles is limited
Solution Approach 1:
The patent introduces dynamic selectability among multiple PWM patterns for each phase. The system can dynamically switch between center aligned PWM, edge aligned PWM, and asymmetric PWM patterns based on operational requirements. This dynamic approach maintains the simplicity of individual PWM patterns while providing overall system flexibility in duty cycle variation and voltage generation.
Data Source
AI summary
Disclosed is a series mode modulation configuration and a parallel voltage equivalent modulation configuration. In the series mode modulation configuration a unipolar modulation is utilized. Unipolar modulation utilizes a zero vector and produces a voltage across the load with a frequency factor of 2×. In the parallel voltage equivalent mode modulation configuration there are two H bridges driving two coils with identical current. The H bridges can advantageously be operated out of phase with one another (e.g., 180 out of phase with one another to interleave the currents to further reduce ripple current stress.