Multilevel Converter Control via Resonant Transformer Isolation
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Solution Overview
Problem
Multilevel converters require extensive sensing for controlling average output DC link voltage and power factor, which is challenging due to demanding isolation requirements for medium voltage applications, leading to increased complexity and potential reductions in measurement accuracy.
Innovation Solution
A control method and converter design that utilize a resonant transformer and operate the DC/DC converter in an open loop mode, allowing the active stage to be controlled based solely on output DC voltage, input voltage, and input current, reducing the need for additional sensing and achieving a constant average output DC link voltage and sinusoidal input current with a controllable power factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If extensive sensing elements are used to measure line input voltage, line input current, DC link output voltage, and DC link voltages of all levels, then the control precision of average output DC link voltage and power factor is improved, but the device complexity and isolation requirements increase
Solution Approach 1:
The patent extracts and eliminates the need for sensing elements on the secondary sides of DC/DC converters and DC link voltage sensors on active front end units. By using a resonant DC/DC converter with galvanic isolation, the control unit only needs to sense the output DC voltage, input voltage, and input current, removing multiple sensing requirements while maintaining control precision
Solution Approach 2:
The resonant transformer acts as an intermediary that provides galvanic isolation between the primary and secondary sides. This allows the control unit to operate the DC/DC converter in open-loop mode without requiring feedback sensors on the secondary side, reducing sensing complexity while maintaining measurement accuracy for controlled variables
2Ease of operation
If multiple sensing elements are deployed for measuring currents and voltages on each level, then the control of power factor and total harmonic distortion is improved, but the isolation requirements and potential reduction in measurement accuracy worsen
Solution Approach 1:
The patent removes the requirement for multiple current sensors on secondary sides and voltage sensors on DC link capacitors by designing a control scheme that only requires sensing of output DC voltage, input voltage, and input current. This extraction of unnecessary sensors reduces isolation requirements and maintains measurement reliability
Solution Approach 2:
The control unit uses feedback from the sensed output DC voltage, input voltage, and input current to actively control the active front end stage. This feedback mechanism, combined with open-loop control of the resonant DC/DC converter, achieves effective power factor and THD control without requiring additional sensors that would compromise reliability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach simplifies the sensing requirements, enhances measurement accuracy, and optimizes efficiency by operating the DC/DC converter at a fixed operating point, achieving zero voltage switching and quasi-zero current switching, while maintaining a constant output DC link voltage and low total harmonic distortion.
Implementation Method 1
a DC/DC converter for transforming the intermediate DC voltage into an output DC voltage at a DC output. The DC/DC converter has a resonant transformer formed by a resonant circuit and a transformer
Implementation Method 2
The DC/DC converter has a resonant transformer formed by a resonant circuit and a transformer
Data Source
AI summary
A converter includes an active stage for converting an AC input voltage at an AC input into an intermediate DC voltage, and a DC/DC converter for transforming the intermediate DC voltage into an output DC voltage at a DC output. The DC/DC converter has a resonant transformer formed by a resonant circuit and a transformer. The converter also includes control unit configured to actively operate the active stage only based on an output DC voltage of the DC/DC converter, an input voltage, and an input current of the converter, and to operate the DC/DC converter in an open loop mode. A method for operating such a converter is also provided.