Donald J. Adams

Constant boost control of the Z-source inverter to minimize current ripple and voltage stress

This paper proposes two constant boost-control methods for the Z-source inverter, which can obtain maximum voltage gain at any given modulation index without producing any low-frequency ripple that is related to the output frequency and minimize the voltage stress at the same time. Thus, the Z-network requirement will be independent of the output frequency and determined only by the switching frequency. The relationship of voltage gain to modulation index is analyzed in detail and verified by simulation and experiments.

Harmonic and reactive power compensation based on the generalized instantaneous reactive power theory for three-phase four-wire systems

This paper presents harmonic and reactive power compensation based on a generalized theory of instantaneous reactive power for three-phase power systems. This new theory gives a generalized definition of instantaneous reactive power, which is valid for sinusoidal or nonsinusoidal and balanced or unbalanced three-phase power systems with or without zero-sequence currents and/or voltages. The properties and physical meanings of the newly defined instantaneous reactive power are discussed in detail. A harmonic and reactive power compensator based on the new theory for a three-phase harmonic-distorted power system with zero-sequence components in the load current and/or source voltage is then used as an example to show harmonic and reactive power measurement and compensation using the new theory. Simulation and experimental results are presented.

A power line conditioner using cascade multilevel inverters for distribution systems

A power line conditioner (PLC) using a cascade multilevel inverter is presented for voltage regulation, reactive power (VAr) compensation and harmonic filtering in this paper. The cascade M-level inverter consists of (M-1)/2 H-bridges in which each bridge has its own separate DC source. This new inverter: (1) can generate almost an sinusoidal waveform voltage with only one time switching per line cycle; (2) can eliminate transformers of multipulse inverters used in the conventional static VAr compensators; and (3) makes possible direct connection to the 13.8 kV power distribution system in parallel and series without any transformer. In other words, the power line conditioner is much more efficient and more suitable to VAr compensation and harmonic filtering of distribution systems than traditional multipulse and pulse width modulation (PWM) inverters. It has been shown that the new inverter is specially suited for VAr compensation. This paper focuses on feasibility and control schemes of the cascade inverter for voltage regulation and harmonic filtering in distribution systems. Analytical, simulated and experimental results show the superiority of the new power line conditioner.

Cascade multilevel inverters for utility applications

Cascade multilevel inverters have been developed by the authors for utility applications. A cascade M-level inverter consists of (M-1)/2 H-bridges in which each bridge has its own separate DC source. The new inverter: (1) can generate almost sinusoidal waveform voltage while only switching one time per fundamental cycle, (2) can eliminate transformers of multipulse inverters used in conventional utility interfaces and static VAr compensators, and (3) makes possible direct parallel or series connection to medium- and high-voltage power systems without any transformers. In other words, the cascade inverter is much more efficient and suitable for utility applications than traditional multipulse and pulse width modulation (PWM) inverters. The authors have experimentally demonstrated the superiority of the new inverter for reactive power (VAr) and harmonic compensation. This paper summarizes features, feasibility, and control schemes of the cascade inverter for utility applications including utility interface of renewable energy, voltage regulation, VAr compensation, and harmonic filtering in power systems. Analytical, simulated, and experimental results demonstrate the superiority of the new inverters.

Comparison of Traditional Inverters and Z-Source Inverter

In this paper, three different inverters-traditional PWM inverter, dc/dc boosted PWM inverter, and Z-source inverter were investigated and compared using fuel cell vehicle and photovoltaic domestic application as examples. Total switching device power, passive component requirement, and constant power speed ratio of each of these inverters were calculated. For purposes of comparison, an example of the total switching device power, requirement of passive components, and the constant power speed ratio of the different inverters for fuel cell vehicle powered by the same fuel cell and loaded by the same motor were conducted. The efficiencies of different systems for traction drive and photovoltaic residential application are also compared. The comparisons show that the Z-source inverter is very promising

Multilevel DC link inverter for brushless permanent magnet motors with very low inductance

Due to their long effective air gaps, permanent magnet motors tend to have low inductance. The use of ironless stator structure in present high power PM motors (several tens of kWs) reduces the inductance even further (<100 /spl mu/H). This low inductance imposes stringent current regulation demands for the inverter to obtain acceptable current ripple. An analysis of the current ripple for these low inductance brushless PM motors shows that a standard inverter with the most commonly used IGBT switching devices cannot meet the current regulation demands and will produce unacceptable current ripples due to the IGBTs limited switching frequency. This paper introduces a new multilevel DC link inverter, which can dramatically reduce the current ripple for brushless PM motor drives. The operating principle and design guidelines are included.

Harmonic and reactive power compensation based on the generalized instantaneous reactive power theory for 3-phase 4-wire systems

This paper presents harmonic and reactive power compensation based on a generalized theory of instantaneous reactive power for three-phase power systems. This new theory gives a generalized definition of instantaneous reactive power, which is valid for sinusoidal or nonsinusoidal, balanced or unbalanced, three-phase power systems with or without zero-sequence currents and/or voltages. The properties and physical meanings of the newly defined instantaneous reactive power are discussed in detail. A harmonic and reactive power compensator based on the new theory for a three-phase harmonic distorted power system with zero-sequence components in the load current and/or source voltage is then used as an example to show harmonic and reactive power measurement and compensation using the new theory. Simulation and experimental results are presented.

Integrating multiple solid oxide fuel cell modules

According to SECA program guidelines, solid oxide fuel cells (SOFC) are produced in the form of 3-10 kW modules for residential use. In addition to residential use, these modules can also be used in apartment buildings, hospitals, etc., where a higher power rating would be required. For example, a hospital might require a 250 kW power supply. To provide this power using the SOFC modules, 25 of the 10 kW modules would be required. These modules can be integrated in different configurations to yield the necessary power. This paper shows five different approaches for integrating numerous SOFC modules and will evaluate and compare each one with respect to cost, control complexity, ease of modularity, and fault tolerance.

Experimental evaluation of a soft-switching DC/DC converter for fuel cell vehicle applications

A soft-switched, isolated bi-directional DC/DC converter has been developed for fuel cell powered electric vehicles (FCPEV), in which the 12 V battery for the vehicle accessory loads is also used to start up the fuel cells and to store the energy captured during regenerative braking. The DC/DC converter interfaces the low voltage battery to the fuel cell powered higher voltage DC bus system (255 V - 425 V). Dual half-bridges interconnected through a transformer are employed to minimize the number of switching devices and their associated gate drive components. The transformer provides voltage level matching and galvanic isolation for safety requirements. Snubber capacitors and the transformer leakage inductance are utilized to achieve zero-voltage-switching (ZVS). Therefore, no extra resonant components are required for ZVS, further reducing component count. The inherent soft-switching capability and the low component count of the converter allows efficient power conversion and compact packaging. A prototype was built and successfully tested. This paper presents design considerations and testing data to evaluate the prototypes performance against the requirements for FCPEV applications.

Comparative study of power factor correction converters for single phase half-bridge inverters

A half-bridge inverter is very suitable for single-phase on-line UPS applications because it offers very desirable features. These include fewer active switches, a common neutral connection-not requiring an isolation transformer, and sinusoidal input currents if a power factor correction (PFC) converter is used at the front end. This paper presents a comparative study of PFC converters for single-phase half-bridge UPS inverters. A traditional half-bridge converter and two recently introduced AC-DC/DC-DC boost converters are comparatively investigated for active switch count, voltage stresses on the switches and capability of voltage balance control of the DC bus capacitors. Analytical and experimental results are included in this paper to illustrate performance differences among the converters in terms of input current harmonic distortion and energy efficiency.