Abstract
This paper presents a design and performance evaluation of three different overvoltage suppression circuits employed in a solid-state circuit breaker for medium- to high-power and low- to medium-voltage DC grids. The evaluated criteria are the requirements for passive components, as well as the breaker performance in terms of peak switch overvoltage, peak short-circuit current, fault clearance time and rate of voltage rise during the fault clearing process. Additionally, the impact of the stray inductance in the solid-state breaker design on the anticipated overvoltage is also investigated. Design and operating limitations of each configuration from an application perspective are also discussed. From simulations of a 1.8 kV and 500 A breaker for high-power medium-voltage DC applications it is shown that the most effective overvoltage suppression is achieved by means of using a metal-oxide varistor and a snubber capacitor connected in parallel with the main switch at a cost of high fault current. A medium-power solid-state DC breaker prototype rated at 1.5 kV and 50 A was also designed and constructed. The experimental results reveal that using only a metal-oxide varistor can be sufficient when the breaker employs high-voltage discrete semiconductors with long current falling time and is used in medium-power medium-voltage grids.
Highlights
Low-and medium-voltage DC (LVDC and MVDC) grids are attractive grid concepts for electricity distribution due to their advantageous characteristics compared to the MV alternating current (AC) counterparts [1]–[7]
The most suitable type of direct current circuit breaker (DCCB) for LVDC and MVDC grids should be chosen based on the design and operating constraints of the loads and power sources connected to the grid, as well as, the design and operating limitations arised in the grid itself
DESIGN PRINCIPLES OF CON1, CON2 AND CON3 The design of the three investigated overvoltage suppression configurations requires the following assumptions to be made for simplicity: (i) Insulated Gate Bipolar Transistors (IGBTs) have been considered for the switches in the breaker design due to their ruggedness over other high power semiconductor devices; (ii) on-state resistances of IGBTs are neglected; (iii) stray inductance of the IGBT module is low enough and it is neglected; (iv) line inductances are neglected as well; (v) a simple passive gate drive unit is considered for all configurations
Summary
Low-and medium-voltage DC (LVDC and MVDC) grids are attractive grid concepts for electricity distribution due to their advantageous characteristics compared to the MV alternating current (AC) counterparts [1]–[7]. A decisive factor for the envisaged expansion of LVDC and MVDC grids is the advancement in high-power semiconductors technology [7]. One of the main showstoppers for LVDC and MVDC grid realization is the lack of high performance short-circuit protection systems [1], [19]. The inherently low inductances occurring in these grid concepts, mostly due to the short power lines and the absence of transformers (i.e. lack of leakage inductance), lead to the rapid rise of the fault current. Traditional mechanical AC breakers cannot clear direct fault currents due to the absence of natural zero crossing for the current. The most suitable type of DCCB for LVDC and MVDC grids should be chosen based on the design and operating constraints of the loads and power sources connected to the grid, as well as, the design and operating limitations arised in the grid itself
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