ICBT Converter Pulse Control for EMI Reduction
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Solution Overview
Problem
The Quasi-Two Level (Q2L) converter, also known as the integrated capacitor-blocked transistor (ICBT) converter, faces challenges in controlling the rapid transitions between voltage levels, leading to high electromagnetic interference (EMI) and insulation stress, with a high demand for advanced control due to lower capacitance requirements and faster charging/discharging times compared to Modular Multilevel Converters (MMC).
Innovation Solution
A voltage source converter with a control unit that generates trapezoidal-shaped pulses by synchronizing the initiation of transitions between two voltage levels without delay, using control signals that start and end at specific times relative to other cells, and can be adjusted based on dwell time, number of cells, pulse number, and AC frequency, allowing for phase-shifted carriers or references to optimize the transition process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the ICBT converter uses fast transition between voltage levels, then the capacitance per cell can be reduced, but the control complexity and demand increase significantly
Solution Approach 1:
The patent segments the single pulse train generation into multiple independent pulse trains, one for each cell. Each pulse train is generated independently based on local carrier-wave comparisons, eliminating the need for complex centralized control while enabling fast transitions with reduced capacitance requirements.
Solution Approach 2:
The patent implements preliminary action by pre-positioning multiple carrier waves at different phase angles before the transition is needed. When a voltage level transition is required, the appropriate pulse train is already prepared and can be immediately activated, enabling fast transitions without complex real-time control decisions.
2Speed
If the transition between voltage levels is made rapidly, then the dwell time is reduced, but electromagnetic interference and insulation stress increase
Solution Approach 1:
The patent uses periodic carrier waves with specific frequencies and phase angles to generate pulse trains. By carefully selecting the carrier frequency and phase relationships, the transitions occur at optimal moments that reduce electromagnetic interference and insulation stress while maintaining fast transition speeds.
Solution Approach 2:
The patent changes multiple parameters simultaneously: carrier wave frequency, phase angle, amplitude, and pulse width. By adjusting these parameters in combination, the system achieves fast transitions while controlling the rate of change of voltage (dv/dt) to minimize electromagnetic interference and insulation stress on connected reactors.
3Device complexity
If multiple pulse trains are generated independently for each cell, then the control scheme is simplified, but the synchronization between cells becomes more challenging
Solution Approach 1:
The patent creates equipotentiality in the control scheme by using identical carrier wave frequencies and symmetric phase angle relationships for all cells. This symmetry ensures that all pulse trains are naturally synchronized to the same reference frame, eliminating synchronization errors while maintaining independent generation for each cell.
Solution Approach 2:
The patent implements feedback by continuously monitoring the actual voltage levels and comparing them with the reference waveform. This feedback mechanism allows each cell to independently adjust its pulse train timing and width to maintain precise synchronization with the overall converter operation, ensuring reliability without complex centralized coordination.
Data Source
AI summary
A voltage source converter as well as a method and computer program product for controlling the converter. The converter includes at least one phase leg connected between a first DC terminal having a first voltage and a second DC terminal having a second voltage, the phase leg including an upper arm and a lower arm with cells, where a junction between the arms is connected to a corresponding AC terminal. The converter also includes a control unit configured to control the cells to output a train of pulses of trapezoidal shape where the generation of a first control signal for a first cell used to initiate a transition between two levels of a pulse coincides with the decision that a transition is to be made.