Inverter Control for Electric Power Steering Dead Time Compensation
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Solution Overview
Problem
Conventional power conversion systems experience distortion in current waveforms due to dead time effects, leading to torque ripple, sound, and vibration issues in electric power steering applications.
Innovation Solution
A power conversion apparatus with an inverter unit and a control unit that adjusts duty instruction values to ensure active voltage vector intervals are longer than the dead time period, preventing mismatch between voltage instruction and duty, and includes a current detecting unit to compute phase currents and voltage instruction values, thereby reducing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If zero voltage vector is generated in each half period of PWM cycle for current detection, then current detection is achieved at predetermined timings, but instruction voltage and duty do not match due to dead time influence causing current waveform distortion
Solution Approach 1:
The patent applies preliminary action by computing the active voltage vector intervals in advance for both first-half and second-half periods, ensuring they are sufficient to accommodate the dead time period. This allows the control unit to pre-adjust the duty instruction values so that the zero voltage vector intervals are properly positioned and sized before PWM generation, preventing the mismatch between instruction voltage and duty that occurs with conventional single-period methods.
2Manufacturing precision
If duty is adjusted to ensure active voltage vector interval is longer than dead time period, then mismatch between voltage instruction and duty is prevented, but control complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the PWM control into separate first-half and second-half period computations. The control unit independently computes active voltage vector intervals for each half period, allowing precise control of zero voltage vector placement in each segment. This segmentation enables the complex duty adjustment to be handled in manageable discrete steps rather than as a single complex operation.
Solution Approach 2:
The patent applies dynamics by making the duty instruction values adaptive rather than fixed. The control unit dynamically adjusts the duty instruction values based on the computed active voltage vector intervals and dead time requirements. This dynamic adjustment ensures that the zero voltage vector intervals are always properly sized and positioned regardless of operating conditions, achieving precise voltage-duty matching without static limitations.
Data Source
AI summary
A power conversion apparatus includes: an inverter unit having high and low potential-side switching elements corresponding to each phase of a winding of a rotating electrical machine; a current detecting unit; and a control unit controlling the switching elements based on a PWM reference signal and a duty instruction value. The control unit includes: a phase current computing device; and a voltage instruction value computing device. The control unit computes an active voltage vector interval in first and second half periods of one or multiple cycles of the PWM reference signal to be a predetermined period or longer, and computes first and second half duty instruction values to set first and second voltage vector intervals equal to or longer than minimum time to be in the first or second half period.