Kun Xing

Individual load impedance specification for a stable DC distributed power system

This paper continues the effort to define load impedance specification for a stable DC distributed power system. To improve the existing load impedance specification, an alternative forbidden region for Z/sub 0//Z/sub i/ is proposed, based on which individual impedance specification for each load is defined. Theoretical verification, accompanied with simulation results, shows that the proposed impedance specification is a sufficient condition for small signal system stability. Finally, conservativeness in load impedance specification is discussed.

Impedance specification and impedance improvement for DC distributed power system

In a DC distributed power system, the interaction between individually designed power modules/subsystems may cause the instability of the whole system. In the small-signal sense, these kinds of interactions can be predicted by checking impedance ratio Z/sub o//Z/sub i/ and can also be prevented by making impedance specification for power modules/subsystems. Many efforts have been made in defining impedance specification and improving I/O impedance for converters and filters. This paper summarizes work in these two areas.

Modeling and control of parallel three-phase PWM boost rectifiers in PEBB-based DC distributed power systems

Modeling and control design issues of parallel three-phase PWM boost rectifiers in DC distributed power systems are presented. Small-signal characteristics of parallel modules are investigated in comparison with those of a single module. With distributed DC bus impedance included, a master/slave control scheme is adopted to ensure load sharing. The system stability based on loop-gain analysis is discussed. The interaction possibilities are presented briefly. Simulation results with frequency domain and time domain are demonstrated.

The circulating current in paralleled three-phase boost PFC rectifiers

This paper presents modeling, simulation, and experimental results of paralleled three-phase boost PFC rectifiers. The first part of the paper describes the overall system set-up and control schemes of the PFCs. Although individual modules work as expected, a low frequency oscillation between the paralleled units was observed. Because the conventional model of the three-phase rectifier cannot predict this kind of interaction, an average model is developed for system simulation. From this model, it is shown that the interleaved discontinuous space vector modulation produces a periodic disturbance on the zero axis. Because the conventional control in a balanced three-phase system with only dq channels cannot reject this disturbance, a circulating current will flow between the paralleled modules. Based on this observation, a space vector modulation with control in the third axis is proposed for the parallel operation of the rectifiers. Simulations are done to show the feasibility of this scheme.

A 100 kW high-performance PWM rectifier with a ZCT soft-switching technique

This paper presents a 100 kW three-phase pulse-width modulated (PWM) boost rectifier that serves as the front-end power source for a DC distributed power system. A zero current transition (ZCT) soft-switching technique is applied to achieve greater performance in this high-power converter. This ZCT soft-switching technique assists the turn-on as well as the turn-off of the main and auxiliary insulated gate bipolar transistor (IGBT) switches. An issue about the implementation of the ZCT soft-switching technique in three-phase applications is discussed. A space vector modulation (SVM) scheme suitable for high power applications with high performance is identified. Experimental results demonstrate that high performance is achieved, in terms of wide control bandwidth, low total harmonic distortion (THD), unity power factor and high efficiency.

Investigation of soft-switching techniques for Power Electronics Building Blocks (PEBB)

The Power Electronics Building Blocks (PEBB) concept is very attractive for the integration of distributed power systems. However, PEBB modules have issues different from discrete power devices. For hard switching, the PEBB module usually has high switching losses, high power dissipation in capacitors and severe conductive EMI. Soft-switching may solve some of these problems. This paper investigates two representative soft-switching techniques (ZVT and ZCT) for PEBB. They are evaluated and proven by experimental results.