Fault detection in a three-phase dab converter
A system and method of fault detection based on a detailed waveform analysis is presented for transient and steady-state fault operation of 3-Φ DAB converter. Main symptoms of the converter during normal and fault conditions have been identified and a unique pattern in DC bias of phase currents under fault mode is noted. The logic-based fault diagnosis scheme is used to detect the fault and identify the faulty transistor.
1. A method of detecting an open-circuit fault in a three-phase dual active bridge converter comprising:
detecting that a fault has occurred by sensing a phase current for each phase on a primary side of the dual active bridge converter and identifying whether a DC bias is present in the phase current for each phase;
identifying whether the fault occurred on a primary side or a secondary side of the dual active bridge converter based on an identification the DC bias of the phase current for each phase;
identifying exactly which transistor has failed using a DC bias pattern; and
continuing operation of the three-phase dual active bridge converter without power derating when the fault is identified in the secondary side.
2. The method of claim 1 , further comprising:
passing the sensed phase current through a low-pass filter.
3. The method of claim 1 , further comprising:
calculating the moving average of the sensed current for each phase over a switching period.
4. The method of claim 1 , further comprising:
identifying the DC bias as positive or negative.
5. The method of claim 1 , wherein identifying whether the fault occurred on a primary side or a secondary side of the dual active bridge converter comprises:
identifying the fault on the primary side if all phase currents show DC bias; and
identifying the fault on the secondary side if some but not all phase currents show DC bias.
6. The method of claim 1 , wherein identifying exactly which transistor has failed comprises:
identifying a faulty transistor based on a table of known DC biases for a fault.
7. The method of claim 1 , further comprising:
stopping operation of the three-phase dual active bridge converter when the fault is identified in the primary side.
8. The method of claim 7 , wherein operation is stopped prior to an excessive rise in a magnetizing current of an isolation transformer of the three-phase dual active bridge converter.
9. The method of claim 1 , wherein detecting that a fault has occurred comprises:
identifying a threshold on the input DC current.
10. The method of claim 9 , wherein the threshold is 15% to identify a fault on the primary side.
11. The method of claim 9 , wherein the threshold is 7% to identify a fault on the secondary side.
12. A system for detecting a fault in a three-phase dual active bridge converter, the system comprising:
a dual active bridge converter comprising a primary side converter, a secondary side converter, and a transformer;
an interface for measuring a current at an output terminal of the primary side converter, the interface coupled to an input of a low-pass filter;
the low-pass filter configured to isolate a DC signal component derived from the measured current at the output terminal of the primary side converter;
a controller adapted to perform the followings steps:
detect polarity states of a DC signal component in each phase of the output terminal of the primary side converter during one or more successive sampling intervals;
compare the polarity states to a bias pattern;
matching the polarity states to a corresponding fault of the bias pattern during one or more sampling intervals to identify the fault on the primary side converter or the secondary side converter; and
continuing operation of the three-phase dual active bridge converter without power derating when the fault is identified in the secondary side converter.
13. The system according to claim 12 , wherein detecting the polarity states of the DC signal further comprises comparing the input to a second input coupled to a DC reference voltage.