Rolando Burgos, Chair
Tuesday, April 11, 2017
The paper presents an alternative on-line stability monitoring method, where by performing internal perturbation, converter itself can measure source output impedance and load input admittance simultaneously. Using these measurements, and combining them with converter’s un-terminated transfer functions, equivalent system output impedance (and admittance) can be calculated out, offering a great opportunity to observe stability at both, input and output side of the converter. Additionally, using all terminal impedances, Nyquist plots for both sides can also be plotted offering better insight into system stability margins.
Impedance-based stability criterion has been proven to be a powerful tool for small-signal stability analysis and design, derived from Nyquist stability criterion and first developed in dc-dc power electronics converter systems. It requires less knowledge than state-space modeling and is design-oriented. Recently it has been extended to ac systems to address the issues and challenges coming with more and more power electronics based converters connected to the existing ac power grids, either in transmission or distribution level. With that, only terminal information is necessary to judge small-signal stability and thus online detection and tuning is feasible. A case study with multiple STATCOMs in IEEE 14-bus system is shown as an example to illustrate. It is the first time that the impedance-based method has been used to demonstrate the interactions between STATCOMs at the transmission system level.
Fred C. Lee
In this paper, a new critical-conduction-mode (CRM)-based modulation is proposed for three-phase inverters. With this modulation, soft switching is achieved and the efficiency of the inverter is improved, especially for high frequency operation with SiC MOSFET. In three-phase string PV inverter applications, by operating at switching frequency above 300 kHz, power density of the inverter is estimated to be at least three times higher than commercial products, while efficiency is estimated to be above 99%. Good performance of this proposed modulation is verified with simulation analysis. The results are also experimentally verified on a 25 kW SiC-based three-phase inverter prototype.
This paper presents a complete design procedure for an onboard motor drive system aiming at maximizing nominal power within loss (30 W) and size (8 in. x 7 in. x 1 in.) limit. Particularly, this motor drive system has EMI requirement on both input and output sides and it should be free convection cooled. Loss-size Pareto fronts of multiple three-phase topologies including two-level voltage source converter (VSC), three-level neutral point clamped (NPC) converter, T-type converter and three-phase triangular conduction mode (TCM) converter are explored in order to find the optimized design. Pareto fronts under different power level shows a maximum of 5 kVA power could be achieved by T-type converter with given limits and requirements. T-type converter is accordingly selected and constructed. A power density of 80 W/inch3 is achieved by the prototype. Finally, experimental results obtained with the free convection cooled converter prototype are presented for validating purposes, demonstrating the 99.3% efficiency (36.4 W loss) at nominal load.