Single DC-link Current Sensor Phase Measurement
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Solution Overview
Problem
Existing methods for measuring phase currents in three-phase power devices, particularly under advanced PWM schemes, face challenges in accuracy and complexity when using a single common DC-link current sensor, especially during unfavorable duty cycle conditions and low modulation indices.
Innovation Solution
A method that computes the modulation index for each PWM signal, compares it with a threshold, and adjusts sampling windows by inverting and complementing PWM signals or inserting fixed time active vectors to ensure distinct sampling of phase currents, maintaining optimal duty cycles and improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single common DC-link current sensor is used to measure phase currents, then cost is reduced and device complexity is lowered, but measurement precision deteriorates under unfavorable duty cycle conditions and low modulation indices
Solution Approach 1:
The patent dynamically adjusts sampling timing based on real-time detection of PWM signal characteristics and modulation index. The sampling windows are adaptively positioned within PWM periods to ensure they fall within valid intervals where DC-link current corresponds to specific phase currents, even under critical duty cycle conditions. This dynamic adaptation maintains measurement precision across varying operating conditions while using a single sensor.
Solution Approach 2:
The patent changes the sampling parameters (timing, duration, and positioning of sampling windows) based on the detected modulation index and duty cycle conditions. By adjusting these parameters dynamically, the system ensures that sampling occurs during intervals where the DC-link current accurately represents the desired phase current, thereby maintaining measurement precision despite using a single common sensor.
2Measurement precision
If sampling windows are created to enable distinct phase current measurements, then measurement capability is improved, but processing complexity increases due to need for creating and managing sampling windows under various PWM conditions
Solution Approach 1:
The system automatically detects PWM signal characteristics and modulation index, then autonomously determines and positions sampling windows without external intervention. The control algorithm self-adjusts the sampling strategy based on real-time operating conditions, eliminating the need for complex external sampling window management while maintaining distinct phase current measurement capability.
Solution Approach 2:
The patent implements a feedback mechanism where the modulation index and duty cycle conditions are continuously monitored, and this information is used to adjust sampling window positioning. The system uses feedback from the PWM signal characteristics to dynamically optimize sampling timing, ensuring accurate phase current measurements while simplifying the overall control logic through rule-based adaptive behavior.
3Power
If advanced PWM schemes like SVPWM are used to enhance output voltage level, then power capability is improved, but measurement reliability deteriorates in near-boundary regions and low modulation index conditions
Solution Approach 1:
The patent dynamically adapts the sampling strategy to the specific PWM scheme being used (SPWM or SVPWM) and the current operating region. By continuously monitoring modulation index and voltage vector position, the system adjusts sampling window timing and duration to ensure reliable measurements even in challenging near-boundary regions where SVPWM operates, thereby maintaining measurement reliability while utilizing advanced PWM for enhanced power capability.
Data Source
AI summary
A method for measuring current in each phase of a three-phase inverter driven motor is based on the three-phase inverter being controlled in a PWM mode by three PWM signals including the use of a common DC-link current sensing resistor. The current on the sensing resistor is intermittently sampled. The method includes determining a modulation index for the voltage demand set by a motor controller. Based on specific mutual duty cycle conditions of the three PWM phase driving signals, sampling windows of sufficient duration are created for allowing distinct sampling of two of the phase currents.