DC Offset Corrector for Discontinuous PWM Current Reconstruction
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Solution Overview
Problem
Current methods using low pass filters for DC offset removal in discontinuous pulse width modulation (DPWM) systems result in phase lag and distorted current waveforms, limiting frequency analysis and motor performance due to discontinuity in current information.
Innovation Solution
A DC offset corrector is implemented using shunt resistors and digital signal processing to remove DC offset from current measurement signals, ensuring continuous current measurement for accurate motor control by processing DPWM sector information and adjusting the DC offset value selectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If low pass filters are used for DC offset removal, then DC offset can be removed from current measurement signals, but phase lag occurs and current waveform distortion increases at higher loads
Solution Approach 1:
The patent extracts only the necessary DC offset component from the current measurement signal using selective subtraction based on DPWM sector information, rather than filtering the entire signal. This allows precise DC offset removal without introducing phase lag to the AC components of the current waveform.
Solution Approach 2:
The patent changes the approach from frequency-based filtering to selective parameter adjustment by calculating and subtracting DC offset values based on DPWM sector information. This parameter-based method eliminates phase lag while maintaining measurement precision.
2Measurement precision
If low pass filters are used for DC offset removal, then DC offset can be removed, but the reconstructed current curve becomes distorted as load increases
Solution Approach 1:
The patent segments the PWM cycle into different DPWM sectors and applies different DC offset correction strategies for each sector. This segmentation allows accurate current reconstruction by handling discontinuous measurements appropriately in each sector while maintaining overall waveform accuracy even at high loads.
Solution Approach 2:
The patent performs preliminary DC offset calculation and correction before current reconstruction, using DPWM sector information to anticipate and correct for discontinuities. This preliminary action prevents waveform distortion from occurring in the first place.
3Productivity
If discontinuous PWM is used for motor control, then switching efficiency is improved, but current measurement discontinuity occurs limiting frequency analysis
Solution Approach 1:
The patent uses DPWM sector information as feedback to guide the DC offset correction process. By continuously monitoring which DPWM sector is active and using this information to adjust DC offset removal, the system maintains accurate current measurement even with discontinuous PWM switching.
Solution Approach 2:
The patent creates a universal current measurement approach that works for both continuous and discontinuous PWM modes. The DC offset corrector uses DPWM sector information to adaptively correct measurements, making the system universally applicable to different PWM strategies while maintaining measurement continuity.
Data Source
AI summary
Disclosed embodiments are directed to a technique to remove DC offset from current measurement signals through shunt resistors in digital signal processing for current reconstruction when using discontinuous pulse width modulation (DPWM). Such measurements regarding current are pertinent to a feedback loop used for a system including a DC-link capacitor, inverter, and motor. A method of removing DC offset comprises: determining a three-phase output current signal of an inverter, wherein the inverter is coupled to a motor and a power supply; producing a voltage signal based on the three-phase output current signal and the resistances of one or more shunt resistors disposed in the inverter; applying an analog gain circuit to the voltage signal; processing the voltage signal with an analog-to-digital converter (ADC); applying a DC offset corrector to the voltage signal; and performing current reconstruction on the voltage signal to produce a continuous current signal.