Voltage Balancing in Voltage Source Converter Director Switches
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Solution Overview
Problem
Voltage imbalance across the switch elements of the director switch and associated clamp capacitors in voltage source converters, particularly in configurations with a floating power supply, leads to instability and inefficiency in high-voltage power distribution systems.
Innovation Solution
The timing of switching the director switch elements is controlled based on the voltage level of the associated clamp capacitors and the degree of voltage imbalance, with elements associated with lower voltage clamp capacitors being turned off or on earlier or later than those with higher voltage levels to achieve voltage balancing, and the chain-link voltage is modulated to manage the transition from conducting to non-conducting states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the director switch elements are switched simultaneously regardless of clamp capacitor voltage levels, then the switching control is simple, but voltage imbalance occurs across the director switch units leading to instability
Solution Approach 1:
The patent changes the switching parameter (timing) of director switch elements based on the voltage parameter of associated clamp capacitors. By monitoring clamp capacitor voltage levels and adjusting switching timing accordingly, the system achieves voltage balancing across director switch units, preventing instability while maintaining manageable control complexity through parameter-based adaptation.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the voltage levels of clamp capacitors associated with each director switch element. This feedback information is used to dynamically adjust the switching timing of individual elements, ensuring voltage balance is maintained across all units. The feedback mechanism prevents voltage imbalance-induced instability without requiring overly complex predetermined switching schedules.
2Manufacturing precision
If the switching timing is adjusted based on clamp capacitor voltage levels to achieve voltage balancing, then voltage imbalance is reduced, but the switching control becomes more complex
Solution Approach 1:
The patent achieves precise voltage balancing by dynamically changing the switching timing parameter of director switch elements based on real-time clamp capacitor voltage measurements. This parameter adaptation allows the system to compensate for voltage imbalances with high precision, ensuring equal voltage distribution across director switch units while using straightforward voltage-based control logic.
Solution Approach 2:
The patent applies preliminary action by adjusting the switching timing of director switch elements before significant voltage imbalance can develop. By proactively monitoring clamp capacitor voltages and preemptively modifying switching sequences, the system maintains voltage balance with high precision, preventing the need for more complex corrective control measures.
3Reliability
If voltage balancing control is implemented, then system stability is maintained under circuit mismatches, but the control apparatus requires additional functionality
Solution Approach 1:
The patent implements feedback control that continuously monitors clamp capacitor voltage levels and automatically adjusts switching timing to maintain voltage balance. This feedback mechanism ensures system stability under various circuit mismatch conditions without requiring manual intervention or overly complex control apparatus, as the system self-corrects based on real-time voltage measurements.
Solution Approach 2:
The patent maintains system stability under circuit mismatches by dynamically changing switching parameters based on clamp capacitor voltage levels. The control apparatus achieves this by implementing voltage-based timing adjustment logic, which adapts to different mismatch conditions without requiring fundamentally complex control structures, thereby maintaining reliability while keeping apparatus complexity manageable.
Data Source
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AI summary
This application relates to methods and apparatus for voltage balancing of voltage source converters (VSCs) and especially for voltage balancing of clamp capacitors of a director switch of a VSC. Typically a director switch (104) of a VSC (100) comprises a plurality of series connected director switch units (200; 200-1 - 200-n) each comprising a semiconductor switching element (110). In some VSC designs each director switch units also has an associated clamp capacitor (202). The method of controls involves switching the semiconductor switching elements of the director switch units to transition the director switch between conducting and non-conducting states where the timing of switching of a semiconductor switching element is based on the voltage level (Vc1 - Vcn)of the associated clamp capacitor and also the degree of any voltage imbalance between the clamp capacitors of the director switch units. A control apparatus (901) may determine suitable switching control signals (CNT1 - CNTn). The technique is particularly applicable where a floating power supply (205) draws power from the clamp capacitor.