PWM Voltage Distortion Reduction in Electric Drives
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Solution Overview
Problem
Conventional Discontinuous Pulse Width Modulation (DPWM) methods for voltage source inverters face accuracy issues due to minimum and maximum pulse width limitations and dead-time constraints, leading to voltage distortion at low speed operations of electric drives.
Innovation Solution
A method and apparatus that modify the duty cycle of the voltage source inverter by producing specific signals within defined clipping values to maintain average output voltage within distortion ranges, reducing distortion effects by adjusting pulse widths to the minimum or maximum achievable values based on the duty cycle's position within these ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dead-time is inserted during each transition of switching state to prevent short-circuit, then reliability of voltage source inverter is improved, but manufacturing precision of output voltage waveform deteriorates
Solution Approach 1:
The controller proactively identifies when duty cycles would fall outside achievable ranges and preemptively adjusts them to boundary values before the distortion occurs. This preliminary correction prevents the voltage distortion that would result from unachievable duty cycles, resolving the conflict between maintaining reliability through dead-time insertion and preserving output voltage precision.
2Reliability
If minimum and maximum pulse width limitations are enforced to prevent hardware damage, then reliability of voltage source inverter is improved, but manufacturing precision of output voltage waveform deteriorates
Solution Approach 1:
The controller continuously monitors the commanded duty cycle and compares it against the achievable duty cycle range determined by minimum and maximum pulse widths. When the commanded duty cycle falls outside this range, feedback control adjusts it to the nearest achievable boundary value, preventing distortion while maintaining reliability constraints.
3Productivity
If duty cycle is reduced to very small or very large values during low speed operation, then productivity of electric drive is improved, but manufacturing precision of output voltage waveform deteriorates
Solution Approach 1:
The controller dynamically adapts the duty cycle commands based on operating conditions. During low-speed operation when voltage distortion would normally occur due to extreme duty cycle values, the system dynamically adjusts by clipping to achievable boundary values, maintaining both productivity and voltage precision across the operating range.
Data Source
AI summary
Methods and apparatus are provided for reducing voltage distortion effects at low speed operation in electric drives. The method comprises receiving a first signal having a duty cycle with a range between minimum and maximum achievable duty cycles, producing a second duty cycle based on the minimum achievable duty cycle if the duty cycle is within a distortion range and less than a first clipping value, producing a second duty cycle based on the closer of minimum and maximum pulse widths if the duty cycle is within the distortion range and between the first and a second clipping value, producing a second duty cycle based on the maximum achievable duty cycle if the duty cycle is within the distortion range and greater than the second clipping value, and transmitting a second signal to the voltage source inverter having the second duty cycle.