Solid State Transformer Fault-Tolerant Phase Branch Reconfiguration
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Solution Overview
Problem
Solid state transformers (SSTs) face significant operational disruptions and economic losses due to open circuit or short circuit faults in cells of phase branches, requiring immediate shutdown and restart, which affects power supply and increases switching losses.
Innovation Solution
Implementing a method to operate the SST in a fault tolerance control mode by switching off the faulty phase branch and controlling the remaining branches as a single phase branch, using discontinuous pulse width modulation (DPWM) to minimize switching losses and maintain DC capacitor voltage balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the SST is stopped and restarted after a cell fault to replace the faulty cell, then the faulty cell can be replaced, but the normal power supply to the load is affected and economic losses occur
Solution Approach 1:
The control method is prepared in advance to handle faults. When a fault occurs in one phase branch, the system has pre-configured control strategies to redistribute power through remaining healthy phase branches, allowing continuous operation without shutdown for cell replacement
Solution Approach 2:
The control mode changes from normal three-phase independent control to fault-tolerance mode where two healthy phase branches are reconfigured. The controller adjusts switching patterns and power distribution parameters to maintain operation with reduced capacity, avoiding complete shutdown
2Reliability
If the SST is stopped immediately upon detecting a cell fault, then the faulty cell can be replaced safely, but switching losses increase and operation is disrupted
Solution Approach 1:
The system maintains continuous power conversion operation by redistributing load to healthy phase branches. The useful action of power conversion continues without interruption, minimizing switching losses that would occur during complete shutdown and restart cycles
Solution Approach 2:
The fault in one phase branch is converted into a reconfiguration opportunity. The control system utilizes the remaining healthy phase branches to continue power conversion, transforming the harmful fault condition into a manageable operational state that reduces overall energy loss compared to complete shutdown
3Productivity
If all three phase branches are individually controlled in normal operation, then each phase can be optimized independently, but the system complexity increases and fault tolerance decreases
Solution Approach 1:
The control system dynamically adapts between normal mode (independent three-phase control for optimal efficiency) and fault-tolerance mode (reconfigured two-phase control). This dynamic switching allows the system to maintain high operational efficiency during normal conditions while automatically providing enhanced fault tolerance when needed
Solution Approach 2:
The control method serves multiple functions: it provides optimized independent control for normal operation and automatically transitions to a universal fault-tolerance mode that can handle various fault conditions. The same control architecture handles both efficiency optimization and fault protection, reducing overall system complexity
Data Source
AI summary
A solid state transformer (SST) is provided, and is concerned with improving the fault tolerance of the SST. A method of operating the SST and an SST device including the SST are also provided. The SST has three parallel phase branches each having multiple cells, and each phase branch is connectable via a switch to a power grid. The method comprises operating the SST in a first control mode, in which each of the three phase branches is individually controlled. Further, when an open-circuit or short-circuit fault occurs in a cell of a particular phase branch, the method further comprises opening the switch connecting the particular phase branch to the power grid, and operating the SST in a second control mode, in which the two phase branches other than the particular phase branch are jointly controlled as a single phase branch.