Fault detection is very important to improve the reliability of power conversion devices. Faults of power semiconductors can be broadly divided into shorts and opens and are further classified into two types depending on whether there is an internal problem with the switch or anti-parallel diode. In this paper, fault-diagnosis methods for short-circuit and open-circuit states are proposed, respectively. A method of classifying and diagnosing faults by applying a gate signal to each switch is proposed to diagnose short-circuit conditions. This method uses only current magnitude information, which reduces the amount of required information and reduces diagnostic failures due to angle errors and current noise. A method is proposed to detect a faulty switch by applying a voltage vector and comparing the current angle with a lookup table to diagnose an open state. An iterative diagnostic algorithm is proposed to prevent diagnostic failure due to angle error and current noise. The effectiveness of the proposed diagnosis method is verified through experiments and simulations.

In this paper, a solid state circuit breaker(SSCB) for a low voltage direct current (LVDC) system is presented. The LVDC distribution system such as a household distribution, require a DC input source, DC loads, and a DC circuit breaker. The major problems in the DC distribution system are the arc problem of disconnecting power from loads and a fast acting circuit breaker for the existing power converter. Therefore, a fast acting and high-voltage-withstanding circuit breaker such as the SSCB is required. The SSCB is composed of wide-band gap power semiconductor switch, such as a SiC MOSFET. It can operate in a very short time and contain the energy-absorbing or bypass circuit to protect itself and other components in the LVDC distribution system under a short circuit fault. In this paper, an SSCB using a SiC MOSFET for LVDC applications is presented. It contains a parallel bypass circuit to reduce the fault energy. The circuit of the SSCB was simulated using PSIM and validated experimentally using a prototype.

Soft starters are used in a variety of industries to safely apply grid voltage to drive induction motors. The soft starter protect the motor from overcurrent and torque that occurs during starting of the motors by regulating the voltage applied to the motor. There are various methods to implement this soft starter, and among them, the discrete frequency control (DFC) method allows for simple operation, but research to limit the motor peak current is still insufficient. In this paper, a new method to limit the current and start the induction motor using the DFC was proposed. The proposed method calculates the feedforward component of the firing angle according to the speed command and add it to the output of additional controller to limit the current. The proposed method has the advantage of seamless transition to the phase control method when the speed command increases and can be implemented without structural change from the conventional phase control method. Using this method, it is implemented without motor parameter information, and the system efficiency is improved. The effectiveness of proposed method was verified through simulations and experiments.

In this paper, a method for estimating induction motor (IM) parameters using a soft starter has been proposed. Unlike the conventional method using a three phase inverter, the proposed method use only the soft starter to obtain IM parameters. The stator resistance, stator inductance and magnetizing inductance of the IM are estimated under the assumption of steady state because the IM connected to the grid is often used where the load torque does not change rapidly. Four quantities are defined based on currents and voltages of motor, and the angle of the rotor flux is estimated using these quantities to obtain the stator inductance and magnetizing inductance. Using the parameters obtained in this way, it is possible to estimate rotor resistance using existing methods. The effectiveness of proposed method was verified through simulations and experiments.