Inverter Filter Non-Linearity Compensation for Voltage Distortion
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Solution Overview
Problem
Inverter-filter systems experience distortions in output voltage due to blanking time and zero current clamping, leading to reduced RMS values and increased total harmonic distortion (THD), which are difficult to compensate for effectively using existing methods.
Innovation Solution
A non-linear compensation system that compares the average output current with discontinuous current mode threshold values to introduce a compensation voltage, using a compensation waveform that includes start and finish ramps to correct distortions in the inverter output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If blanking time is introduced to protect the power stage, then reliability is improved, but manufacturing precision deteriorates due to voltage error and THD increase
Solution Approach 1:
The patent applies preliminary action by calculating and storing compensation values in advance for different current magnitudes and directions. The compensation lookup table pre-computes the necessary voltage corrections based on expected blanking time effects, allowing the system to apply precise compensation without real-time complex calculations, thus maintaining output voltage precision while preserving the protective blanking time interval.
Solution Approach 2:
The patent changes parameters by adjusting the reference voltage based on detected current characteristics. The system dynamically modifies the reference voltage magnitude and polarity according to the current direction and magnitude, compensating for the blanking time induced voltage errors. This parameter adaptation allows the system to maintain precise output voltage despite the fixed blanking time protection interval.
2Measurement precision
If conventional blanking time compensation is applied, then RMS value is improved to within +/â5% of nominal, but THD correction is insufficient and the system becomes sensitive to synchronization errors
Solution Approach 1:
The patent implements feedback by detecting the actual current direction and magnitude, then using this information to select appropriate compensation values from the lookup table. This closed-loop approach ensures that the compensation is continuously adapted to the actual operating conditions, improving both RMS accuracy and THD correction while reducing sensitivity to synchronization errors through intelligent sampling.
Solution Approach 2:
The patent replaces the mechanical synchronization approach with an intelligent sampling and lookup table method. Instead of relying on precise angular synchronization of compensation waveforms, the system uses current-based triggering and pre-computed compensation values, substituting the mechanical synchronization mechanism with a more robust digital control approach that is less sensitive to timing errors.
3Manufacturing precision
If zero current clamping compensation is added to blanking time compensation, then output voltage quality is improved, but device complexity increases
Solution Approach 1:
The patent merges blanking time compensation and zero current clamping compensation into a single unified lookup table structure. By combining both compensation functions into one table that accounts for both effects simultaneously, the system avoids the complexity of separate compensation circuits while achieving improved output voltage quality. The unified approach reduces device complexity through integration rather than multiplication of components.
Solution Approach 2:
The patent creates a universal compensation lookup table that handles multiple compensation functions (blanking time and zero current clamping) in a single structure. This multi-functional table serves both compensation purposes simultaneously, eliminating the need for separate dedicated circuits for each type of compensation and thereby reducing overall system complexity while maintaining comprehensive voltage quality improvement.
Data Source
AI summary
Inverter-filter non-linearity blanking time and zero current clamping compensation is accomplished by comparing the average output current with the discontinuous current mode threshold values to determine when the average output current is entering a discontinuous current mode and introducing a compensation voltage to the inverter drive voltage in response to the average output current entering a discontinuous current mode to compensate for discontinuous current mode distortion of the inverter output voltage.