Sharif Digital Repository

Clamp mode resistor capacitor diode (CMRCD) snubbers have a simple and easy implementing structure. They have been widely adopted in the pulsed power supplies to provide a safe operating condition for the series insulated gate bipolar transistors (IGBTs). The main problem of the CMRCD snubbers is their poor performance in the voltage balancing of the series IGBTs. They are essentially overvoltage protectors and clamp the voltage of the IGBTs in a probable potentially dangerous condition. This issue diminishes the expected lifetime of the series IGBTs, where a number of them face a higher level of the voltage than that of the others. The unbalanced voltage of the series IGBTs will result in a... 

One of the major limitations of the multilevel converters is the voltage unbalance between different levels. The techniques to balance the voltage between the different levels normally involve voltage clamping or capacitor charge and discharge control. However, traditional Flying Capacitor Converter (FCC) may be quite limited by the voltage unbalance of flying-capacitors that is the most serious problem. This paper describes operating principles of a new softswitching seven-level converter topology based on FCC for self-voltage stabilization and balancing. By adding power electronic devices to the traditional FCC topology, the proposed topology regulates the DC bus voltage and balances the... 

Clamp mode snubbers are very well suited for the series structure of the insulated-gate bipolar transistors (IGBTs) in pulsed power applications. They properly meet the necessities expected from them such as the fast operating of the series IGBTs since they have no effect on the gate side. In addition, they can provide safe voltage condition for the IGBTs in short circuit faults, which are very probable in pulsed applications. The clamp mode snubber can perform its voltage balancing task whenever the power capacity of the snubber can support the injected powers due to the voltage unbalancing factors. This paper initially introduces the main factors injecting power to the snubbers. Then, it... 

This paper presents an effective hybrid optimal modulation technique for a cascaded H-bridge (CHB) multilevel inverter. The introduced method is generalized optimal pulsewidth modulation, which can be extended to any m-level CHB multilevel inverter operating at any switching frequency. The presented hybrid optimal modulation strategy includes the pattern exchange and optimal modulation techniques. In the optimal modulation technique, the hybrid interior-point algorithm, which is more flexible and efficient than conventional optimization techniques, is applied. The proposed hybrid optimal modulation strategy yields balanced units' output fundamental voltages, and low total harmonic distortion... 

Modular multilevel converter (MMC) is among the promising topologies used in high-voltage/power purposes, especially for high-voltage direct-current (HVDC) transmission systems. In this paper, a modified model predictive control (MPC) strategy for an MMC-HVDC system is presented. In the proposed MPC strategy, output current, circulating current and capacitors voltage are controlled separately. In order to reduce the computational burden of the controller, the output current is controlled directly without any optimization. For suppression of the circulating current, capacitors voltage variations are employed to settle the converter arms voltages to their reference values. In addition, the... 

This article proposes a scheme for balancing the voltage of series-connected insulated gate bipolar transistors (IGBTs), which is also very effective under short-circuit conditions. An optimized clamp-mode snubber is proposed, including an active-driver to balance the currents of the IGBTs during short-circuit, which in turn allows for a considerable reduction of the snubber capacitance. The approach is proven to be effective under short-circuit conditions by a maximum of 55 V voltage increment and a negligible difference in the current values. The effectiveness of the proposed approach is demonstrated through simulations in PSPICE software and experimental tests performed at 2 kV. ©...