Current-Feedback PWM Dead Time Adjustment for Inverter Distortion
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Solution Overview
Problem
Existing pulse width modulators in voltage source inverters face challenges with dead time insertion, which can lead to waveform distortion and voltage gain or loss, and often require conservative settings that increase circuit size and cost.
Innovation Solution
A pulse width modulator circuit with adaptive dead time adjustment, using a controller to adjust dead time periods based on feedback from a current sensor, allowing for programmable dead time and improved timing precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dead time is inserted to prevent shoot-through, then switch safety is improved, but waveform distortion and voltage gain loss increase
Solution Approach 1:
The patent implements dynamic dead time adjustment where the dead time period is not fixed but varies based on operating conditions. The controller adjusts the dead time duration in real-time according to feedback from current sensors, allowing the system to maintain switch safety while minimizing waveform distortion under different load and switching conditions.
Solution Approach 2:
The patent changes the parameter of dead time duration from a conservative fixed value to a variable parameter that is optimized based on actual circuit conditions. By monitoring current waveforms and adjusting the dead time parameter dynamically, the system achieves better performance than fixed dead time approaches.
2Reliability
If conservatively long dead time is used to ensure safety, then shoot-through prevention is improved, but voltage gain loss and waveform distortion increase
Solution Approach 1:
The patent employs feedback mechanisms where current sensors monitor the actual current waveforms during switching transitions. This feedback information is used by the controller to optimize the dead time duration, ensuring it is long enough to prevent shoot-through but not excessively long to cause voltage gain loss. The system continuously adjusts based on real-time measurements.
Solution Approach 2:
The dead time is implemented as a dynamic parameter that adapts to changing operating conditions rather than a static conservative value. This allows the system to use minimal necessary dead time under light loads while maintaining adequate protection under heavy loads, optimizing the trade-off between safety and performance.
3Measurement precision
If additional external sensors are added to evaluate and adjust dead time, then dead time accuracy is improved, but circuit size and cost increase
Solution Approach 1:
The patent makes existing current sensors serve multiple functions: their primary function for current control is enhanced by also using them for dead time evaluation and adjustment. This multi-functionality eliminates the need for separate dedicated sensors for dead time measurement, reducing overall circuit complexity while maintaining measurement precision.
Solution Approach 2:
The patent merges the dead time evaluation function with the existing current sensing infrastructure. By combining these functions into a single integrated approach using the same sensor hardware and control logic, the system achieves accurate dead time adjustment without adding separate external sensors, thereby reducing circuit size and cost.
Data Source
AI summary
A pulse width modulator circuit with circuitry for providing a first and second pulse width modulation signal with dead time periods between the first and second pulse width modulation signals, an input for receiving a signal representative of a current in a load adapted to be driven in response to the first and second pulse width modulation signals, and circuitry coupled to the input for adjusting the dead time periods in response to the signal representative of a current.