Voltage Source Converter Control for Switching Loss Reduction
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Solution Overview
Problem
Existing Voltage Source Converters face challenges in efficiently controlling high-power transmission with high voltages, leading to high switching losses and harmonic filtering issues, particularly when a large number of switching elements are connected in series.
Innovation Solution
The method involves providing each switching element with individual saw tooth voltages and reference alternating voltages, controlled using Pulse Width Modulation, with the voltage across energy storing capacitors measured and adjusted to maintain equilibrium, allowing for robust and fast control of the converter, reducing sensitivity to harmonics and disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a high number of switching elements are connected in series to handle high voltages for high-power transmission, then the voltage handling capability is improved, but the switching losses increase and harmonic filtering problems worsen
Solution Approach 1:
The converter is divided into multiple independent switching elements connected in series, where each element handles a portion of the total voltage. This segmentation allows independent control of each switching element, enabling optimized switching strategies that reduce overall switching losses while maintaining high voltage handling capability for high-power transmission.
Solution Approach 2:
The patent implements dynamic control of switching elements where the switching states and timing are continuously adjusted based on real-time voltage and current conditions. This dynamic approach allows the system to optimize switching moments to minimize losses while adapting to changing operating conditions, thereby reducing energy loss during high-power transmission.
2Power
If a high number of switching elements are connected in series to achieve high voltages, then the voltage handling capability is improved, but the harmonic filtering requirements and costs increase
Solution Approach 1:
The control system continuously monitors the output voltage waveform and capacitor voltages, using this feedback information to adjust switching element operation in real-time. This feedback control enables active harmonic compensation by dynamically modifying switching patterns to minimize harmonic distortion, thereby reducing the complexity and cost of passive filtering equipment while maintaining high voltage handling capability.
Solution Approach 2:
The patent employs parameter modulation techniques where switching frequencies, duty cycles, and timing are dynamically changed based on operating conditions. By changing these parameters adaptively, the system can optimize the output waveform quality and reduce harmonic content, thereby lowering the requirements for filtering equipment complexity and cost.
3Stability of the object's composition
If individual control of each switching element is implemented to maintain voltage balance, then the voltage balance across capacitors is improved, but the control complexity increases
Solution Approach 1:
The control system actively maintains equal voltage levels across all capacitor terminals by implementing closed-loop voltage balance control. Each switching element's control is adjusted based on its capacitor voltage status, ensuring that all capacitors operate at equipotential conditions. This approach stabilizes the voltage composition while using systematic control algorithms that manage the complexity through structured voltage monitoring and adjustment.
4Loss of energy
If switching frequency is reduced to lower switching losses, then the energy loss is improved, but the output voltage waveform quality deteriorates
Solution Approach 1:
The patent employs periodic switching patterns where each switching element operates at optimized switching intervals. By coordinating the periodic action of multiple switching elements with different switching timings, the system achieves effective voltage synthesis at lower individual switching frequencies, thereby reducing switching losses while maintaining high-quality output voltage waveforms through constructive interference of the periodic switching actions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in a smooth alternating voltage curve with reduced switching losses and lower requirements for filtering equipment, maintaining voltage balance across capacitors and improving robustness and responsiveness to operating conditions.
Implementation Method 1
at least one energy storing capacitor, a mid point of said series connection forming a phase output being configured to be connected to an alternating voltage side of the converter
Data Source
Figure 1
Figure 2~4
Figure 5~7
AI summary
In a method for controlling a Voltage Source Converter having at least one phase leg comprising a series connection of switching elements (7), in which each said element has at least two semi- conductor devices (16, 17) of turn-off type, at least two free- wheeling diodes (18, 19) connected in parallel therewith and at least one energy storing capacitor (20), each said switching element is controlled according to a Pulse Width Modulation pattern so that each switching element is switched to change between applying a zero voltage and the voltage across its capacitor across its terminals each time a saw tooth voltage wave for that switching element crosses a reference alternating voltage belonging to that switching element.