Yunqing Pei

Auto-master-slave control technique of parallel inverters in distributed AC power systems and UPS

This work presents a new control scheme: auto-master-slave control technique of parallel connected SPWM inverters. The control scheme ensures a fast dynamic response and precise load current sharing capability. Based on auto-master-slave control technique, the control circuitry employs the real power share bus and reactive power share bus interconnecting all the paralleled inverters. With the power share buses and the power deviation controllers, the paralleled inverter with highest output power becomes the master inverter; other inverters become slave inverters. Master inverter drive the power bus, and the power deviations in slave inverter module are calculated by the power sharing controller. Hereafter, the inverters compensate for the frequency and amplitude of output voltage, and then the unbalance power was eliminated. An experiment system was built to verify this control scheme, and the results indicate the precise power balance performance for parallel operation.

Space Vector Modulator for Vienna-Type RectifiersBased on the Equivalence BetweenTwo- and Three-Level Converters:A Carrier-Based Implementation

This paper presents the equivalence between two- and three-level converters for Vienna-type rectifiers, proposing a simple and fast space vector modulator built on this principle. The use of this duality permits the simple compliance of all topological constraints of this type of nonregenerative three-level rectifier, enabling as well the extension of its operating range by the use of simpler two-level overmodulation schemes. The proposed algorithm is further simplified by deriving its carrier-based equivalent implementation, exploiting the direct correspondence existent between the zero-sequence vectors of Vienna-type rectifiers and the zero state vectors of two-level converters. As a result, the proposed algorithm is also capable of controlling the rectifier neutral point voltage. This feature makes it attractive as well for neutral-point-clamped inverters, complementing previous carrier-based space vector modulators developed for these converters. A complete experimental evaluation using a 2 kW digital signal processor-field programmable gate array controlled Vienna-type rectifier is presented for verification purposes, asserting the excellent performance attained by the proposed carrier-based space vector modulator.

Design and Implementation of a High Power Density Three-Level Parallel Resonant Converter for Capacitor Charging Pulsed-Power Supply

This paper describes the design and implementation of a prototype 30-kW (or 30-kJ/s) pulsed-power supply for capacitor charging. The system operates at 200-kHz maximum switching frequency, which is considerably higher than the conventional practice at this power level, leading to smaller passive components. A high power density of 143 W/in3 is achieved with the converter operating at a high ambient temperature of 65°C with 90°C cooling oil, by utilizing various technologies on topology, control, devices, passives, and thermal management. The experimental results demonstrate that the converter meets the performance requirements while achieving a high power density.

Improving Light and Intermediate Load Efficiencies of Buck Converters With Planar Nonlinear Inductors and Variable On Time Control

It has been addressed that light and intermediate load efficiencies of high-frequency buck converters in portable electronic devices are very important for extending lifetime of batteries. This paper proposes to utilize wide range, gradually changeable nonlinear inductors with variable on time control to improve light and intermediate load efficiencies. Integrated multipermeability magnetic cores are advanced to realize the nonlinear inductors. And based on the nonlinear inductors, variable on-time control scheme is proposed to reduce the frequency-dependent loss. The theoretical loss reduction is demonstrated by comparing loss of a converter employing conventional constant on-time control scheme and employing the proposed control scheme. A two-permeability nonlinear inductor prototype is fabricated. Its inductance could vary from 0.13 μH at full load to 0.66 μH at no load. The nonlinear inductor is employed in a 12 V input, 1.6 V output buck converter to evaluate its performance. With the purpose of comparison, other two commercial chip inductors are also tested in the converter. The results show the nonlinear inductor with variable on time control could effectively improve efficiencies of light and intermediate load conditions as theoretical analysis does.

Design of Ultrathin LTCC Coupled Inductors for Compact DC/DC Converters

It is found out that using reverse coupled inductors could effectively improve power density and dynamic performance of multiphase interleaved point of load converters. Thus, it is of great significance to conduct a research about design and fabrication of ultrathin coupled inductors for system 3-D integration. The aim of this paper is to explore the structures, modeling, and fabrication of ultrathin coupled inductors based on low-temperature cofired ceramic (LTCC) technology. Four structures classified by shapes and relative positions of windings are introduced and compared. Simple but effective analytic models are set up to calculate self-inductance, leakage inductance, and coupling coefficient for quick design, and a design guideline is summarized according to the models. We made a 1.3-mm-thick LTCC coupled inductor and two competing coil coupled inductors, and compared their characteristics and performance. They are tested in a 12-V input and 1.2-V/40-A output two-phase interleaved buck converter at three different switching frequencies. Core loss and winding loss of the inductors are quantified by simulation. Compared with conventional coil coupled inductors, the LTCC coupled inductor has higher power density and light load efficiency. Besides, it could also help to improve the transient performance of converters for its higher coupling coefficient.

A Current-Fed Multiresonant Converter with Low Circulating Energy and Zero-Current Switching for High Step-Up Power Conversion

A high-efficiency high step-up dc-dc converter is proposed for renewable energy harvesting, where the sustainable power sources, such as PV panels and fuel cells, are characterized by low-voltage high-current output. The proposed converter employs the current-fed half-bridge structure to generate a square-wave current source. Then, a multiresonant tank is used to provide high voltage gain, absorb the parasitic parameters of the transformer, and create zero-current switching (ZCS) condition for all primary switches. By applying a single capacitor instead of LC for the output filter, the maximum voltage of the resonant capacitor is clamped to the output voltage, which reduces the circulating energy within the circuit and offers ZCS to the rectifying diodes. The operation principle is introduced and the steady-state analysis is also carried out for the derivation of the dc voltage gain and the ZCS conditions of the primary switches. The performance of the proposed converter was verified by a 150-W prototype. A peak efficiency of 95.2% was achieved by running the prototype at 255 kHz with 23-V input and 350-V output.

Space Vector Modulation for Vienna-Type Rectifiers Based on the Equivalence between Two- and Three-Level Converters: A Carrier-Based Implementation

This paper presents the equivalence between two- and three-level converters for the Vienna rectifier, proposing a simple and fast space vector modulator built on this principle. The algorithm is further simplified by deriving its carrier-based equivalent implementation, which enables the midpoint voltage control by adjusting the ratio between redundant vectors, while also addressing the voltage-current polarity constraints of this non-regenerative three-level rectifier. The latter is achieved by employing a simple two-level overmodulation algorithm, which also extends the operating range of the Vienna rectifier if required. The proposed algorithm also complements previous carrier-based space vector modulators developed for the three- level neutral-point-clamped inverter, providing the midpoint balancing capability for these schemes. Experimental results obtained with a 2 kW 40 kHz 200 Vdc DSP/FPGA controlled Vienna rectifier prototype are presented for verification purposes.

Design and Implementation of High Power Density Three-Level Parallel Resonant Converter for Capacitor Charger

This paper describes the design and implementation of a prototype 30kW, 200kHz pulsed power supply. A power density greater than 100W/inch3 is achieved with the converter operating at a high ambient temperature of 65 °C, by utilizing various technologies on topology, control, devices, passives, and thermal management, which can help reduce the converter size. The experimental results demonstrate that the converter meets the performance requirements while achieving the high power density.

Ac vs. dc distribution for off-shore power delivery

This paper compares AC and DC transmission schemes for power delivery between land-based and off-shore installations. The comparison is focused on the loss, as well as on the technologies needed for each of these systems. The study shows that both AC and DC schemes can provide feasible solutions for off-shore applications. Specifically, it is shown through analysis and simulation, that DC distribution always results in lower loss for a given voltage level and a given transmission cable. In fact, depending on the voltage and cable parameters, the DC system loss could be as low as 15 to 50% of that of the corresponding AC system. The latter loss nonetheless could be reduced by the use of proper compensation at the expense of an increased complexity and cost. The study also shows that higher voltages are desirable for high power and long distance power distribution. This is advantageous for the AC scheme, which can readily use transformers at both sending and receiving ends, but represents a disadvantage for the DC case given that high-voltage DC-DC converters are a less mature technology. To this end, a modular converter topology is proposed that could be used for high voltage DC power delivery achieving a lower cost and size, better controllability, and higher reliability.

Comparative Study of Vector Control Schemes for Parallel-Connected Induction Motors

The field-oriented control is primarily used in single inverter single motor drive system, but in railway traction drive system one inverter feeds two or more motors connected in parallel. The purpose of this paper is to make comparative study between different control schemes for the parallel-connected motor drive system by simulation and experiment. First the rotor flux orientation control system for single motor is established on simulation platform and then the control system extends to the multiple motor drive systems by using the averaging model of the parallel-connected motors. The two ways of averaging, namely circuit averaging and space vector averaging, are either based on the steady state equivalent circuit of the induction motors or on the voltage space vector reference. The simulation is based on Saber simulation software and the simulation results and experimental are given to show the effectiveness of the control schemes proposed in the paper