Phase Shifted Carrier Balancing for Flying Capacitor Converters
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Solution Overview
Problem
Multilevel converters with flying capacitors face challenges in rapidly balancing capacitor voltages, as natural balancing mechanisms are inherently slow.
Innovation Solution
A method that generates switching signals for electrical converters by comparing a reference voltage signal with a carrier signal, determining unbalances, and phase shifting the carrier signal to accelerate voltage balancing, using a cost function optimization to minimize the route to the natural balancing region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If natural balancing mechanism is used in multilevel converters with flying capacitors, then the converter operates with simple control, but the capacitor voltage balancing is slow
Solution Approach 1:
The patent applies dynamics by making the carrier signal phase shift variable and adaptive. Instead of using a fixed natural balancing mechanism, the system dynamically adjusts the phase shift amount based on real-time capacitor voltage measurements and balancing needs. This allows the balancing speed to be optimized without requiring a completely different control architecture, resolving the contradiction between fast balancing and control simplicity.
Solution Approach 2:
The patent changes the parameter of carrier signal phase shift to accelerate balancing. By introducing a variable phase shift parameter that can be adjusted based on the degree of voltage unbalance, the system achieves faster capacitor voltage balancing. The phase shift amount is modified from the natural balancing value to an optimized value that speeds up convergence while maintaining control feasibility.
2Productivity
If phase shifting of carrier signal is applied to accelerate balancing, then the convergence rate increases, but the control complexity increases
Solution Approach 1:
The patent implements feedback by continuously monitoring capacitor voltages and using this information to adjust the carrier signal phase shift. The control system measures the actual voltage levels, compares them with reference values, and dynamically modifies the phase shift amount to achieve optimal balancing performance. This feedback mechanism enables high convergence rates while keeping the control algorithm systematic and manageable.
Solution Approach 2:
The patent applies preliminary action by pre-calculating or pre-determining optimal phase shift values based on the detected voltage unbalance state. Instead of computing complex adjustments in real-time, the system uses pre-established relationships between voltage deviations and optimal phase shifts, which simplifies the control algorithm while maintaining high balancing efficiency.
Data Source
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AI summary
An electrical converter (10) has a balancing property such that a capacitor voltage of a capacitor (16) of the electrical converter tends towards a balancing voltage. A method for controlling the electrical converter (10) comprises: generating switching signals for the electrical converter (10) based on pulse width modulation, wherein switching instants (36) are determined by comparing a reference voltage signal (38) with a carrier signal (40); determining a state of unbalance of at least one capacitor (16) of the electrical converter, the state of unbalance (vd) being based on a difference between an actual capacitor voltage and a desired reference voltage; determining, whether the state of unbalance (vd) is outside a natural balancing region (44); and, in the case, the state of unbalance (vd) is outside the natural balancing region (44), phase shifting of a regular carrier signal (40), such that the capacitor voltage of the capacitor tends more directly in the direction of the natural balancing region (44) than during pulse width modulation with the regular carrier signal (40), whereby a phase shift (48) for the phase shifting of the regular carrier signal (40) is determined by minimizing a cost function based on the state of unbalance (vd) and/or a DC link voltage ofthe electrical converter (10).