Inverter Current Beat Suppression via PLL Estimation
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Solution Overview
Problem
Existing motor drive devices struggle to effectively suppress current beats caused by voltage ripples, especially during over-modulation, due to limitations in existing control methods that require additional components like high-pass filters or voltage detection circuits, leading to instability and reduced compensation effectiveness.
Innovation Solution
The use of a Phase Locked Loop (PLL) to estimate the frequency, phase, and amplitude of current beat components in the output current of the inverter, allowing for correction of voltage commands to reduce current beats without the need for additional structures like high-pass filters or voltage detection circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a high-pass filter or low-pass filter is used to extract current beat components, then the current beat can be suppressed, but the control system becomes unstable when detection signals include noises and distortion
Solution Approach 1:
The patent replaces the mechanical filter system (high-pass or low-pass filters) with an observer-based estimation system. The observer estimates the current beat components by comparing actual motor current with commanded current, and the controller uses this estimation to generate compensating voltage commands, eliminating the need for physical filters that cause instability with noisy signals.
Solution Approach 2:
The patent introduces an intermediary estimation mechanism (observer) that mediates between the noisy current detection signals and the control system. The observer filters and estimates the beat components mathematically without directly processing the noisy signals through physical filters, thus stabilizing the control system while still suppressing current beats.
2Object-generated harmful factors
If additional structures like high-pass filters or voltage detection circuits are added to suppress current beats, then current beat suppression is improved, but device complexity and cost increase
Solution Approach 1:
The patent makes the existing observer and controller perform the additional function of current beat suppression. The observer, which already estimates motor state for control purposes, now also estimates current beat components. The controller, which already generates voltage commands for motor control, now also generates beat compensation voltage commands. This eliminates the need for separate dedicated beat suppression hardware.
Solution Approach 2:
The patent merges the current beat suppression function with the existing motor control functions. The observer and controller that already exist for motor control are enhanced to simultaneously perform beat suppression, combining multiple functions into existing structures rather than adding separate dedicated components.
3Object-generated harmful factors
If existing control methods are used to suppress current beats, then beat suppression works in normal operation, but compensation effectiveness is reduced during over-modulation
Solution Approach 1:
The patent makes the beat suppression control dynamic by continuously estimating current beat components through the observer and continuously updating voltage compensation commands based on real-time conditions. This dynamic adaptation allows the system to maintain compensation effectiveness during varying operating conditions including over-modulation, where fixed or static control methods fail.
Data Source
AI summary
An inverter, motor drive device and freezing device, with which it is possible to effectively suppress current beats in the event of over-modulation without requiring additional circuits. This motor driving device includes: a rectifier circuit that converts the AC voltage from an AC power supply into a DC voltage; a smoothing capacitor that smoothes the DC voltage output from the rectifier circuit; an inverter circuit that converts the DC voltage output from the smoothing capacitor into an AC voltage; and a controller that reduces the current beat component by estimating, using a phase locked loop process, the frequency, phase and amplitude of the current beat component in the output current of the inverter circuit, and corrects the voltage command to the inverter circuit on the basis of the estimated frequency, phase and amplitude.