Inverter Control Circuit LC Filter Resonance Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Inverter circuits using ΔΣ modulators face issues with outputting a sinusoidal voltage when an LC filter is connected, as the LC resonant frequency amplifies quantization noise, resulting in a waveform with high peaks at specific frequencies, deviating from a pure sine wave.
Innovation Solution
Incorporating an LC filter within the control loop of the ΔΣ modulator and utilizing a two-input filter with specific transfer characteristics to generate a switching signal that compensates for the resonant frequency, ensuring the output voltage matches the target sinusoidal waveform by adjusting the filter's gain and phase characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an LC filter is connected to smooth the AC voltage output from the main circuit, then the waveform quality is improved, but the LC resonant frequency amplifies quantization noise, causing high peaks at specific frequencies and deviating from a pure sine wave
Solution Approach 1:
The patent applies feedback by incorporating the LC filter within the control loop of the ΔΣ modulator. The output voltage from the LC filter is fed back to the modulator, allowing the system to sense and compensate for resonance effects. This feedback mechanism enables the modulator to adjust its switching signals dynamically, preventing the amplification of quantization noise at the LC resonant frequency while maintaining waveform quality.
Solution Approach 2:
The patent introduces a two-input filter as an intermediary element with specific transfer characteristics. This filter receives both the quantization noise signal and the output voltage signal, and generates a compensation signal that counteracts the resonant frequency amplification. The two-input filter acts as a mediator that processes multiple signals and produces a corrected switching signal, eliminating the harmful resonance peaks while preserving the desired sinusoidal waveform.
2Object-affected harmful factors
If a ΔΣ modulator is used to convert instruction values to switching signals, then EMI is reduced due to uniform spectrum distribution, but the output voltage cannot be sinusoidal when an LC filter is connected due to resonant frequency amplification
Solution Approach 1:
The patent merges the LC filter within the control loop of the ΔΣ modulator, creating an integrated system where the filter and modulator work together. This merging allows the benefits of ΔΣ modulation (low EMI) to be preserved while the LC filter's waveform smoothing capability is enhanced through the feedback connection, eliminating the resonant frequency amplification issue that would otherwise prevent sinusoidal output.
Solution Approach 2:
The patent changes the system parameters by introducing a two-input filter with specific transfer characteristics that are designed to counteract the LC resonant frequency. By adjusting the filter's parameters (cut-off frequency, gain, phase characteristics) to match and oppose the LC resonance, the system transforms the harmful resonant amplification into a compensated response, enabling accurate sinusoidal output while maintaining the EMI reduction benefits of ΔΣ modulation.
Data Source
AI summary
An inverter control circuit has a quantizer configured to generate a switching signal which changes over switches of a main circuit converting a DC voltage into an AC voltage, and a filter circuit configured to generate a signal having specific transfer characteristic by using a signal correlated with an output voltage of an LC filter which smooths the AC voltage and an instruction signal corresponding to a target value of an output voltage of the main circuit, wherein the quantizer generates the switching signal by quantizing an output signal of the filter circuit.