Parallel Converter Current Imbalance Compensation
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Solution Overview
Problem
Power units with multiple converter modules of different types or generations experience significant current imbalances due to non-linearity characteristics, leading to thermal overload and reduced efficiency, necessitating de-rating of the converter rating.
Innovation Solution
A method involving feed-forward compensation, where compensation values are generated based on the non-linearity characteristics of each converter module, stored in a memory as functions of phase current and control values, to balance currents across modules, using either look-up tables or curve-fitted equations, allowing for precise compensation even when modules from different manufacturers or technology generations are used in parallel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If converter modules of different types or generations are used in parallel, then device versatility and flexibility are improved, but current imbalance increases due to non-linearity characteristics
Solution Approach 1:
The patent applies feed-forward compensation by pre-characterizing each converter module's non-linearity characteristics and storing compensation values in memory before operation. During parallel operation, the controller retrieves appropriate compensation values based on measured current and control signal levels, applying them proactively to counteract expected current imbalances before they affect system performance.
Solution Approach 2:
The patent changes the control parameter by introducing compensation values that modify the reference current or control signal for each converter module. These compensation values are derived from stored non-linearity characteristics and are applied dynamically based on operating conditions (current level and control signal level), effectively transforming the control parameters to achieve current balance despite hardware differences.
2Manufacturing precision
If traditional active sharing algorithms are used, then current balance is improved for identical converter modules, but system adaptability deteriorates when modules of different types are combined
Solution Approach 1:
The patent applies local quality by characterizing and compensating for the specific non-linearity characteristics of each individual converter module. Each module has its own stored compensation values in memory that are tailored to its specific hardware properties. The controller selectively applies module-specific compensation values based on the operating conditions, allowing each module to be optimized for its own characteristics while operating in parallel with other different types of modules.
3Adaptability or versatility
If converter modules operate with significant current imbalances, then device versatility is improved, but thermal overload and reliability deteriorate
Solution Approach 1:
The patent implements feedback by continuously measuring the actual current level and control signal level in each converter module, using these measurements to select appropriate compensation values from stored non-linearity characteristics. This closed-loop feedback mechanism ensures that current imbalances are actively compensated in real-time, preventing thermal overload and maintaining reliability while allowing diverse converter modules to operate together.
Data Source
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AI summary
There is described a method of controlling a power unit comprising a plurality of converter modules coupled in parallel, each converter module being configured to convert a DC voltage into AC voltages or AC voltages into a DC voltage. The method comprises (a) receiving a control value for each phase of each converter module, (b) obtaining a set of phase current values for each converter module, (c) generating a compensation value for each phase of each converter module based on the set of phase current values and a set of data stored in a memory, the set of data being representative of nonlinearity characteristics of the converter modules as functions of phase current value, (d) generating a compensated control value for each phase of each converter module based on the corresponding control value and the corresponding compensation value, and (e) supplying the compensated control values to the respective converter modules. Furthermore, a corresponding controller, power unit, wind turbine, computer program and computer program product are described.