Inverter Phase Current Reconstruction via Dynamic Sampling Delay
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Solution Overview
Problem
Current methods for inverter phase current reconstruction in motor drives and power converters face inaccuracies due to limited sampling times during high modulation index operations, leading to unmeasurable regions and reduced detection capabilities.
Innovation Solution
The method involves selectively delaying low side inverter phase current sampling within a PWM cycle and adjusting pulse widths to ensure accurate current measurement, allowing for extended sampling times and improved detection capabilities across the entire voltage vector plane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current sampling is performed at fixed nominal sample times during PWM cycles, then the control method is simple and device complexity is low, but measurement precision deteriorates under high modulation index conditions due to unmeasurable regions
Solution Approach 1:
The patent implements dynamic sampling time adjustment by calculating the middle pulse width value of each PWM cycle and comparing it with a threshold. When the middle pulse width is insufficient, the sampling time is dynamically delayed to ensure accurate current measurement. This dynamic adaptation resolves the contradiction by making the sampling system flexible rather than fixed, improving measurement precision without requiring complex hardware modifications.
Solution Approach 2:
The patent changes the sampling time parameter based on PWM cycle conditions. By calculating the middle pulse width value and comparing it with a threshold, the system adjusts the sampling moment within the PWM cycle. This parameter change approach allows the system to adapt to high modulation index conditions where fixed sampling times fail, thereby improving current detection accuracy while maintaining relatively simple control logic.
2Measurement precision
If sampling is delayed when middle pulse width is insufficient, then measurement precision improves by avoiding unmeasurable regions, but loss of time increases due to extended sampling periods
Solution Approach 1:
The patent applies partial action by selectively delaying sampling only when the middle pulse width value is less than the threshold. The sampling delay is precisely calculated as (threshold - middle pulse width value), providing just enough extension to capture accurate current measurements without unnecessarily extending the PWM cycle. This partial adjustment approach improves measurement precision while minimizing time loss.
3Reliability
If middle total continuous on-time is extended for next PWM cycle, then reliability improves by ensuring sufficient sampling window, but productivity decreases due to reduced effective PWM cycles
Solution Approach 1:
The patent implements preliminary action by extending the middle total continuous on-time in advance for the next PWM cycle when the current cycle's on-time is insufficient. This proactive extension ensures that the next sampling operation will have adequate time window, improving current feedback reliability. The extension is calculated based on the threshold comparison, providing just enough advance preparation without excessively reducing the number of effective PWM cycles.
Data Source
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AI summary
Methods and apparatus are presented for sampling low side inverter phase currents, in which current sampling is selectively delayed in a given PWM cycle by a non-zero sampling delay time value from a nominal sample time if the middle pulse width value is less than a non-zero first threshold to facilitate adequate signal settling for accurate current measurement, and if a middle total continuous on-time near the end of the given PWM cycle is less than a non-zero second threshold, the middle total continuous on-time is selectively extended by adding a non-zero adjustment offset time value to a middle pulse width value for a next PWM cycle.