Multiphase Converter Control for Symmetrical Voltage During Subsystem Failure
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Solution Overview
Problem
Existing power converters with distributed energy stores face challenges in maintaining a symmetrical three-phase voltage system when at least one energy store fails, leading to asymmetrical output voltages and potential damage due to uncontrolled terminal voltages.
Innovation Solution
The method involves determining the number of failed subsystems, short-circuiting faulty subsystems to zero voltage, and increasing the capacitor voltages of remaining subsystems to match undisturbed levels, ensuring the output voltage is symmetrical and free of DC components, using existing hardware without expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a subsystem fails in a power converter with distributed energy stores, then the converter can continue operating with reduced capacity, but the output voltage becomes asymmetrical and may contain harmful DC components
Solution Approach 1:
The patent changes the operating parameters of the remaining healthy subsystems by adjusting their switching states and capacitor voltages. When a subsystem fails, the control device modifies the switching patterns and energy storage levels of the remaining subsystems to compensate for the failure, maintaining symmetrical output voltages without requiring hardware changes or converter shutdown.
2Object-affected harmful factors
If faulty subsystems are short-circuited to zero voltage to prevent damage, then safety is improved, but the number of available subsystems for maintaining output voltage is reduced
Solution Approach 1:
The patent changes the voltage parameters of the healthy subsystems to compensate for the short-circuited faulty subsystems. By adjusting the capacitor voltages and switching states of the remaining subsystems, the system maintains the required output voltage amplitude despite having fewer active subsystems, thus balancing safety requirements with power output needs.
3Reliability
If the number of subsystems per valve branch is increased to improve fault tolerance, then redundant operation capability is enhanced, but the device complexity and cost increase
Solution Approach 1:
The patent applies partial action by using only the minimum necessary number of subsystems required to achieve the desired fault tolerance level. Rather than over-provisioning with excessive subsystems, the control method enables the converter to maintain reliable operation with fewer subsystems by optimally managing their switching states and capacitor voltages during fault conditions.
4Ease of operation
If capacitor voltages of remaining subsystems are increased to compensate for failed subsystems, then output voltage symmetry is maintained, but the stress on remaining components increases
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor banks of healthy subsystems before a fault occurs or immediately upon detection. The control device proactively adjusts the capacitor voltages of remaining subsystems to anticipated required levels, preparing them to maintain symmetrical output voltages when subsystems fail, thereby avoiding sudden excessive stress during fault transition.
Data Source
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AI summary
The invention relates to a method for controlling a converter (102) having distributed energy stores (9) with three phase modules (100), each of which comprises an upper and a lower valve branch (T1, T3, T5; T2, T4, T6) that are each equipped with at least three bipolar subsystems (10) electrically connected in series. According to the invention, failed subsystems (10) of a disturbed valve branch (T2) and subsystems (10) of an undisturbed valve branch (T1) of a disturbed phase module (100) are short-circuited according to the number of failed subsystems (10), the capacitor voltages (Uc) of the remaining subsystems (10) of the disturbed phase module (100) are increased to such an extent that the sum thereof is the same as the sum of the capacitor voltages (Uc) of the subsystems (10) of an undisturbed phase module (100), and the subsystems (10) of the undisturbed phase modules (100) are controlled accordingly before at least one subsystem (10) fails. In this way, a symmetrical voltage system having a maximum amplitude is obtained at the outputs (L1, L2, L3) of the converter (102) that has distributed energy stores (9) during malfunction.