Three-Phase Converter Active Damping for Common-Mode Resonance
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Solution Overview
Problem
Three-phase converters experience stability issues due to common-mode current resonance caused by discontinuous pulse-width modulation (DPWM), leading to inefficiencies and system instability.
Innovation Solution
The implementation of an active damping unit within the three-phase converter, which calculates and adds a zero-sequence regulation component to the modulated waves, effectively suppressing common-mode current resonance by using independent current regulators and a zero-sequence regulation component calculator to generate corrected modulated waves for the switching network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If discontinuous pulse-width modulation (DPWM) is used to reduce switching times and improve converter efficiency, then switching loss is reduced and efficiency is improved, but common-mode current resonance is generated causing system instability
Solution Approach 1:
The patent introduces a common-mode current suppression controller as an intermediary component that receives three-phase currents, transforms them to α-β coordinates, extracts common-mode current, and generates compensation signals. This mediator processes the common-mode current separately from the main control loop, allowing DPWM to maintain its efficiency benefits while the intermediary controller actively suppresses the harmful common-mode current resonance through feedback compensation.
Solution Approach 2:
The patent implements a feedback mechanism where the common-mode current suppression controller continuously monitors three-phase currents, transforms them to extract common-mode components, and feeds back compensation signals to the PWM controller. This closed-loop feedback dynamically adjusts the modulation waves to counteract common-mode current resonance, stabilizing the system while maintaining the efficiency advantages of DPWM.
2Object-generated harmful factors
If a common-mode loop is formed by connecting capacitor midpoints to redirect common-mode current, then common-mode current is reduced, but series resonance is generated at natural resonant frequency causing sharp current fluctuation
Solution Approach 1:
Instead of using a passive common-mode loop with capacitors that creates series resonance, the patent introduces an active common-mode current suppression controller as an intermediary. This controller receives three-phase currents, transforms them to α-β coordinates, extracts common-mode components, and generates active compensation signals that suppress common-mode current without creating resonant conditions, thereby avoiding the stability issues of passive filtering approaches.
Solution Approach 2:
The patent replaces the passive mechanical/electrical filtering approach (capacitor-based common-mode loop) with an active control system. Instead of relying on passive component resonance characteristics, the system uses active signal processing and feedback control to suppress common-mode current, substituting dynamic control for static filtering and avoiding resonant frequency problems.
Data Source
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AI summary
A three-phase converter is provided, and is configured to be connected between a direct current system and an alternating current system to perform interconversion between a direct current and an alternating current, where the three-phase converter includes a switching network, a three-phase filter connected to the switching network, a sampling unit connected to the three-phase filter, a control unit connected to the three-phase sampling unit, an active damping unit connected to both the control unit and the sampling unit, and a modulation unit connected between the active damping unit and the switching network, where the sampling unit is configured to: obtain three-phase currents in the three-phase filter, and send the three-phase currents to the active damping unit; the active damping unit is configured to: obtain new three-phase modulated waves according to the three-phase currents, and transmit the new three-phase modulated waves to the modulation unit; and the modulation unit is configured to modulate the new three-phase modulated waves into drive signals of the switching network, to drive the switching network to work.