DC-AC Inverter Modulation Index Control Without Load-Side Sensing
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Solution Overview
Problem
Vehicular power systems face challenges in efficiently controlling DC-to-AC inversion due to limited space and varying load characteristics, which complicates the design and implementation of power generation systems, especially in not being able to sense voltage and current at the load, limiting the ability to control the AC output waveform effectively.
Innovation Solution
The method involves recursively updating a modulation index using measurements of input voltage and current to control a power inverter, generating pulse width modulation signals, and iteratively adjusting the modulation index to maintain a constant output voltage independent of load changes, without direct sensing of load voltage and current, by utilizing a direct-quadrature-zero transform and proportional-integral controller.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct sensing of load voltage and current is implemented, then control precision of AC output waveform is improved, but device complexity and space requirements increase
Solution Approach 1:
The patent creates a virtual model (copy) of the load side by transforming current measurements through direct-quadrature-zero transformation to obtain virtual voltage and current information. This copying approach allows the control system to achieve precise control of the AC output waveform without physically sensing the load side, thereby reducing device complexity while maintaining measurement precision through mathematical modeling
Solution Approach 2:
The patent replaces physical sensing mechanisms (voltage and current sensors on the load side) with an electrical/mathematical transformation system. By using direct-quadrature-zero transformation on measured current signals, the system substitutes mechanical/physical sensing with electrical signal processing, reducing the need for additional sensors and simplifying the overall device structure while maintaining control precision
2Adaptability or versatility
If modulation index is adjusted frequently to maintain constant output voltage, then adaptability to load changes is improved, but system stability may be compromised
Solution Approach 1:
The patent implements a feedback control mechanism where the modulation index is recursively updated based on measured input voltage and current, and calculated output power. The control system continuously monitors the actual output and adjusts the modulation index to maintain constant output voltage, creating a closed-loop feedback system that adapts to load changes while maintaining stability through proportional-integral control
Solution Approach 2:
The patent makes the modulation index dynamic by recursively updating it based on real-time measurements of input voltage, current, and calculated output power. This dynamic adjustment allows the system to adapt to varying load conditions while maintaining constant output voltage, transforming a static parameter into a dynamic control variable that responds to system conditions
3Measurement precision
If multiple sensing points are added to measure load voltage and current, then measurement accuracy is improved, but the space occupation within the vehicle increases
Solution Approach 1:
The patent creates virtual measurements through mathematical transformation of available sensor data. By applying direct-quadrature-zero transformation to measured current signals and using the relationship between input and output power, the system generates virtual voltage and current information without adding physical sensors to the load side, thereby maintaining measurement accuracy while avoiding additional space occupation
Solution Approach 2:
The patent makes the existing current sensors multi-functional by using them not only for basic current measurement but also for deriving virtual voltage information through mathematical transformation. This universal use of existing sensors eliminates the need for separate voltage sensors on the load side, reducing space requirements while maintaining comprehensive measurement capabilities
Data Source
AI summary
Techniques are disclosed for recursively determining a modulation index for controlling a DC-to-AC inverter. A modulation index can be selected initially. The input voltage to the power inverter can be measured. Based on the input voltage and the selected modulation index, an output voltage of the power inverter may be estimated. The output current of the power inverter can be measured. Using the estimated output voltage and the measured output current, a real power and a reactive power can be determined. The real power and the reactive power can be used to determine an updated modulation index. The updated modulation index factor can be used to generate pulse width modulation signals that are used to control the power inverter.