Search

Fault current controller (FCC) technology, also frequently referred to as fault current limiter (FCL) technology,has been identified as a potentially viable solution for expanding the capacity of the transmission system and its service life to meet the growing demand for electricity, by addressing the impacts of the resulting higher fault currents. This document reports on the program supported by the California Institute for Energy and Environment under the California Energy Commission in the development of distribution class FCC technology. The project focused on test plan development, prototyping, laboratory test, and field demonstration, with a view toward potential further technical development and application of the technology in transmission-level systems. The University of California Irvineled the project with overall responsibility for project management, administration, coordination, and technical guidance, with the support of the California Institute for Energy & Environment (CIEE) at the University of California, Berkeley. Southern California Edison Co. (SCE) was the host utility for the field demonstration, providing on-site engineering personnel, expertise and support. Zenergy Power and the EPRI/Silicon Power team were engaged to prototype a passive type FCC and an active FCC, respectively, for laboratory testing and field demonstration.A full-size three-phase distribution level high temperature superconductor (HTS) FCC prototype was designed, built, and field tested by Zenergy Power, plc. The prototype FCC went through several iterations of extensive testing at Powertech Labs Inc., Surrey, BC, Canada and at the High Voltage Laboratory of SCE’s Westminster facility prior to field installation. It was then installed at SCE’s Avanti “Circuit of the Future” for field demonstration from March 2009 through October 2010. The EPRI/Silicon Power team has completed an initial design for asolid-state based FCC. Due to design changesthat were necessary to improve the thermal management of the prototype but were beyond the scope of this project, this design did not advance to the laboratory and field test stages during the project period.This report provides a technology survey of FCC technology, including both the saturable core and solid-state types represented by this project, followed by detailed design considerations, laboratory test procedures and results, field test installation and metering, and field demonstration outcomes. The report concludes with a summary of the lessons learned and recommendations for future research efforts

The challenges associated with incorporating a large amount of distributed generation (DG), including fuel cells, into a radial distribution feeder are examined using a dynamic MATLAB/SIMULINK™ model. Two generic distribution feeder models are used to investigate possible scenarios where voltage problems may occur. Modern inverter topologies make ancillary services, such as on-demand reactive power generation/consumption economical to include, which expands the design space across which DG can function in the distribution system. The simulation platform enables testing of the following local control goals: DG connected with unity power factor, DG and load connected with unity power factor, DG connected with local voltage regulation (LVR), and DG connected with real power curtailment. Both the LVR and curtailment strategies can regulate the voltage of the simple circuit case, but the circuit utilizing a substation with load drop compensation has no universal solution. Even DG with a penetration level around 10% of rated circuit power can cause overvoltage problems with load drop compensation. The real power curtailment control strategy creates the best overall circuit efficiency, while all other control strategies result in low light load efficiency at high DG penetrations. The lack of a universal solution implies that some degree of communication will be needed to reliably install a large amount of DG on a distribution circuit. © 2010 American Society of Mechanical Engineers.

While the integration of base-load fuel cells into the built environment is expected to provide numerous benefits to the user, the steady-state and dynamic behavior of these stationary fuel cell systems can produce an undesirable impact on the grid distribution circuit at the point of connection. In the present paper, a load-following active power filter (LFAPF) is proposed to mitigate the grid impact of such systems and instead improve overall local power quality. To evaluate the strategy, the LFAPF is integrated into a SOFC system inverter with one-cycle control (OCC) to provide the fundamental benefits of a traditional active power filter (APF) while also damping out short-term line current transients. The LFAPF benefit is illustrated through simulation of an SOFC interconnected with the utility electric distribution system and a building electricity demand that is modeled as a dynamic non-linear load. Three installation cases are examined: (1) a load-following SOFC, (2) a base-loaded SOFC, and (3) an offline SOFC. Without LFAPF, the load-following SOFC causes load transients due to the finite SOFC response time, and the base-loaded SOFC case has transients that appear more severe because they represent a larger overall percentage of the grid-provided load. The integration of an LFAPF improves the steady-state behavior over the base case and mitigates voltage sags and step changes. Thus integrating an LFAPF can, by providing useful services to both the utility and the end-user, facilitate the integration of an SOFC into the distribution system. © 2009 Elsevier B.V. All rights reserved.

Proper converter design can allow solid oxide fuel cells operated as distributed generators to mutually benefit both the load and the electric utility during steady-state conditions, but dynamic load variations still present challenges. Unlike standard synchronous generators, fuel cells lack rotating inertia and their output power ramp rate is limited by design. Two strategies are herein investigated to mitigate the impact of a large load perturbation on the electric utility grid: 1) external use of ultracapacitor electrical storage connected through a dc-dc converter and 2) internal reduction of steady-state fuel utilization in the fuel cell to enable faster response to output power perturbations. Both strategies successfully eliminate the impact of a load perturbation on the utility grid. The external ultracapacitor strategy requires more capital investment while the internal fuel utilization strategy requires higher fuel use. This success implies that there is substantial flexibility for designing load-following fuel cell systems that are model citizens. © 2009 IEEE.

Adding distributed generation (DG) is a desirable strategy for providing highly efficient and environmentally benign services for electric power, heating, and cooling. The interface between a solid oxide fuel cell (SOFC), typical loads, and the electrical grid is simulated in Matlab/Simulink and analyzed to assess the interactions between DG and the electrical grid. A commercial building load profile is measured during both steady-state and transient conditions. The load data are combined with the following models that are designed to account for physical features: a One-Cycle Control grid-connected inverter, a One-Cycle Control active power filter, an SOFC, and capacitor storage. High penetration of DG without any power filter increases the percentage of undesirable harmonics provided by the grid, but combined use of an inverter and active power filter allows the DG system interconnection to improve the grid tie-line flow by lowering total harmonic distortion and increasing the power factor to unity. © 2008 Elsevier B.V. All rights reserved.

Solar energy is desirable due to its renewable and pollution-free properties. In order to utilize the present utility grid infrastructure for power transmission and distribution, grid connected dc-to-ac inverters are needed for solar power generation. However, previously proposed voltage source inverters with a two-power-stage structure or a cascaded structure increase the circuit complexity, power losses, and system cost In addition, conventional maximum power point tracking (MPPT) methods usually need power calculation and complex logic judgment, so expensive multipliers and/or microprocessors are needed. This leads to high inverter capital cost, which becomes a major barrier for the wide use of solar power generation. A cost-effective MPPT method integrated within the One-Cycle Control (OCC) core is proposed in this paper. When integrated with a three-phase boost type inverter, the proposed method tracks MPP with good precision, and solar power is converted into three-phase ac power with a single power stage. There is no power calculation in the controller, which yields a simple and cost-effective solution. Experiments have been carried out with a photovoltaic source to verify good performance. © 2006 IEEE.

This paper proposes a new maximum power point tracking (MPPT) method in combination with One-cycle control for photovoltaic power generation. This control scheme is based on the automatic current-adjusting feature of One-cycle control. The output current of the Inverter can be adjusted according to the voltage of the photovoltaic (PV) array so as to extract the maximum power from it. In the mean time, One-cycle control guarantees that the output current is in the same shape of and in phase with the grid voltage. All these are accomplished in one power stage and a simple control circuit. No detection and calculation of power are needed. Compared with previously proposed approaches, this method Is much more efficient and more cost-effective and yet exhibits excellent performance. The principle is explained qualitatively and extensive experiments have been carried out to verify and validate the proposed method.

This paper introduces a new controller for three-phase four-wire inverters, with the control goal of generating high-quality three-phase output voltages for all sorts of linear/nonlinear and balanced/unbalanced loads. The proposed controller employs a circuit-level decoupling method, and it is implemented by logic circuitry in combination with a control core and a feedback signal processor. Almost all dc--dc control methods can be adapted as the control core, while the feedback signal processor can be implemented by either voltage compensator and/or current compensator. The implementation of the controller is simple and flexible with only logic and analog circuitry needed. Yet, it demonstrated experimentally excellent load handling and source voltage noise l rejection ability. The prototype is tested under balanced and unbalanced resistive and nonlinear loads, as well as under extreme load transients. It is also tested with power from a noisy dc input source. In all cases, the prototype demonstrated high-quality output voltages. Index Terms--Analog control, inverter, three-phase, uninterruptible power supply.

Recently, a new multilevel inverter--Hexagram inverter has been reported for medium-voltage (MV) variable-speed drives (VSDs). This paper will propose a Hexagram rectifier as the active front end for the Hexagram-based MV VSD systems. The control of the Hexagram rectifier is based on one-cycle control--an excellent control scheme for switching power converters. With the proposed control scheme, unity power factor at the source side can be achieved, the six modules will equally share the output power, and the voltage stress of the converter will be reduced six times. A 1-MW simulation model and a 1.2-kW experimental prototype have been built to demonstrate the proposed Hexagram rectifier and its control scheme. Index Terms--Multilevel systems, pulsewidth-modulated (PWM) power converters, rectifiers, variable-speed drives (VSDs).

Alternative energy sources, such as solar energy and fuel cells, are desirable due to their pollution-free property. In order to utilize the present infrastructure of the utility grid for power transmission and distribution, grid-connected dc-to-ac inverters are required for alternative energy source power generation. For many of these applications, the input dc voltage is usually below peak voltage of the output and may vary in a wide range. Thus single-stage buck-type inverters may not be adequate, since they have very limited input voltage range and require the input dc voltage to be higher than the peak of the output voltage. For this reason, two-power-stage topologies, cascaded topologies and multilevel topologies are reported for applications where the input voltage is lower than the peak of the output voltage. Typically, one dc--dc power stage is required to boost the dc voltage in addition to an inverter for dc--ac conversion, which yields increased circuitry complexity. One-stage inverters for low dc voltage to high ac voltage conversion have been reported for non-grid-connected inverters based on the topology of a current source inverter. In this paper, the one-cycle control (OCC) method and the pulse width modulation (PWM) method have been proposed for a three-phase boost-type grid-connected inverter. The inverter features a single power stage that converts dc power to grid-connected ac power by injecting three in phase sinusoidal currents into grids, which may reduce power losses and circuit complexity. The input dc voltage is lower than the peak grid voltage and can vary in a wide range, which greatly suits the power conversion from photovoltaic or fuel cells to grid lines. The dc inductance may be kept low because the average dc current is maintained constant in a switching cycle. With the OCC method, the inverter preserves the advantages of simple circuitry, good stability and fast dynamic response and maximum power point tracking (MPPT) function can be conveniently integrated into the control core. Experiments have been performed with a 1.5-kW laboratory prototype that demonstrated the good performance of the inverter and MPPT function. Index Terms--Boost type, grid connected, maximum power point tracking (MPPT), one cycle control (OCC), photovoltaic (PV), three-phase inverter.

This paper introduces a new controller for a three-phase inverter, with a control goal of generating desired three-phase output voltages. The proposed controller employs a circuit-level decoupling method, and it is implemented by logic circuitry in combination with a control core and a feedback signal processor. Almost all dc--dc controllers can be adapted as the control core, whereas the feedback signal processor can be implemented by either voltage compensator and/or current compensator. The controller's implementation is simple and flexible with logic and analog circuitry. Yet, it demonstrates experimentally excellent load handling, source voltage noise rejection, and reference tracking ability. The prototype is tested under resistive load, highly nonlinear load, and extreme load transients; aside from that, it is also tested under noisy source voltage and sudden reference change. In all cases, the prototype demonstrated high-quality output voltages. Index Terms--Analog control, inverter, three-phase, uninterruptible power supply (UPS).

A new multilevel inverter-Hexagram inverter is proposed for medium-voltage (MV) variable-speed-drive (VSD) applications, which is composed of six standard two-level voltage source inverter (VSI) modules interconnected through the inductors. With six ac terminals, it can be used for both three- and six-phase drives. This paper studies its six-phase applications. Compared to a same output power and voltage VSI, the proposed inverter has the current stress reduced to half and voltage stress reduced to one-third; whereas compared to a same output power and current VSI, the voltage stress is reduced to one-sixth. The other advantages of the new inverter include a modular structure resulting in easy construction and maintenance, no voltage unbalance problem, easy control with well-developed VSI control techniques, automatic and equal current and power sharing among the modules, and fewer components and lower dc energy storage requirements compared to the cascaded H-bridge (CHB) inverter. These eminent features make it a strong candidate for MV VSD applications. Index Terms--AC motor drives, inverters, multilevel systems, power conversion.

This paper synthesized a family of multilevel converters that is constructed by using multiple well-developed single- and/or three-phase converter building blocks. The resulting advantages include a modular structure that leads to convenient construction and maintenance as well as easy extension to higher voltage levels. One successful example from this family is the cascaded H-bridge converter, which is now widely used for volt-amperes reactive (VAR) compensation and motor drive applications due to its many advantages. Another emerging member is the Hexagram converter, composed of six interconnected three-phase converter modules, which has many eminent features such as lowered component count and lowered dc energy storage requirement compared to the cascaded H-bridge converter, and thus, is a promising candidate for high-power applications. Index Terms--Circuit topology, multilevel systems, power conversion, power electronics.

A forward converter of interleaved series input and parallel output (ISIPO) structure is proposed in this paper. Theoretical analysis indicates that by using two auxiliary diodes and the unique architecture, the proposed ISIPO forward converter can realize natural magnetizing reset, the leakage and magnetizing energy in the transformers can be recycled, and the voltage stress on each switch is clamped at Vin. In addition, by parallel connection of the transformers, the output rectifier and filters can distribute power losses and thermal stresses of the transformers and semiconductors, and the interleaved operation can reduce the current ripple in output capacitors. All these features make the proposed forward converter suitable for dc-dc converters with high input voltage, high output current, and high power density. The theoretical analysis is verified by a 1000 W experimental prototype. Index Terms--Current Sharing, demagnetizing, forward converter, interleaved, interleaved series input and parallel output (ISIPO).

Grid-connected inverters are necessary for converting the dc power generated by photovoltaic or fuel cells to the ac power of the utility grid. Parallel operation of these inverters extends the power range to a much higher level and allows modular design. This paper studies current sharing and circulating current among paralleled inverter modules and proposes a new parallel operation method based on one-cycle control (OCC) with combined vector operation and bipolar operation. With some minor additions to the original OCC circuit and a simple add-on communication path among the individual modules, the current is properly shared among all the inverters and the circulating current is limited to an acceptable range, while OCC advantages such as constant switching frequency, no multipliers, and simple circuitry are preserved. Two OCC inverters of 1.5 kW each were built and tied together using the proposed parallel operation. Experiments were conducted to demonstrate the simplicity and effectiveness of this method. Index Terms--Circulating current, current sharing, grid-connected inverter, one-cycle control (OCC), parallel operation, three-phase inverter, vector operation.

Parallel operation of three-phase power-factor-corrected (PFC) rectifiers is a critical issue for high-power applications, since it extends the power range to a much higher level and allows modular design. The technical challenges are current sharing and circulating current control among the modules. This paper studies these phenomena within two paralleled rectifiers and proposes a new current-sharing method based on One-Cycle Control (OCC) with vector operation and bipolar operation. With some minor additions to the original OCC circuit and a simple add-on communication path among the individual modules, the input current is shared and the circulating current is limited, while the OCC advantages, such as constant switching frequency, no multipliers, and simple circuitry, are preserved. Two OCC PFC rectifiers of 2.5 kW each were built and tied together using the proposed parallel operation method. Experiments have demonstrated the simplicity and the effectiveness of this method. Index Terms--Circulating current, current sharing, one-cycle control (OCC), parallel rectifier, power factor correction (PFC), vector operation.

The paper presents a resonant converter topology capable of providing zero ripple conditions at either its input or output current. The basic properties of the proposed topology are discussed in detail. The remarkable symmetry and the proportional voltages of the circuit allow it to maintain ripple-less current independent of the load or switching frequency. Theoretical predictions are well supported by simulation and experimental results. Index Terms--Coupled inductor, dc-dc converter, dc-dc transformer, isolated converter, resonant power conversion, zero ripple conditions (ZRC).

Power factor corrected (PFC) rectifiers, active power filters (APFs), static VAR compensators (STATCOM), and grid-connected inverters (GCI) are indispensable elements in distributed generation power systems. PFC rectifiers are essential for load side harmonic and reactive power correction, APFs can suppress the harmonics generated by nonlinear loads or sources, STATCOMs can control the power flow in the grid, while GCIs are the key elements bridging the renewable energy sources and the power grid. Previous theory and experiments have demonstrated that one-cycle control is capable of controlling all above mentioned three-phase converters, featuring excellent performance, simple circuitry, and low cost. This paper further unifies the control key equations for the previously mentioned converters, which results in a universal solution that realizes all these functions with a same controller. The concept has been verified by a I-kVA prototype and supported by a series of experimental results. Index Terms--Active power filter (APF), grid-connected inverter (GCI), one-cycle control (OCC), power factor corrected (PFC) rectifier, static VAR compensators (STATCOM), three-phase converters, vector control, voltage source inverter.

The power quality of the ac electric system has become a great concern due to the rapidly increasing numbers of electronic equipment being connected to the grid. In order to reduce harmonic contamination in power lines and to improve its transmission efficiency, the research on active power filters (APF) has become a hot topic. Many control methods for APF were proposed in recent years. Among them, one-cycle control (OCC) has shown great promise featuring excellent harmonic suppression, simple circuitry, robust performance, and low cost for the control of three-phase APFs. Theory and experiments in previous papers have demonstrated the validity of OCC-controlled APFs working with balanced line voltages and balanced nonlinear loads. However, in reality, neither three-phase grid voltages nor three-phase nonlinear loads are balanced at all times; therefore, it is vital for an APF to be able to handle unbalanced sources and/or loads. In this paper, the OCC-controlled three-phase APF working with unbalanced three-phase line voltages and unbalanced loads are studied, respectively. Theoretical analyses and experimental results indicate that with OCC control, sinusoidal input currents can be realized, whether the input voltages and/or the nonlinear loads are balanced or unbalanced. Index Terms--Active power filter (APF), asymmetric power systems, harmonic current suppression, one-cycle control (OCC), power quality, unbalanced load, unbalanced power systems.

One-cycle control power-factor correction (OCC-PFC) with vector operation is a promising rectification method that eliminates harmonics and improves the power factor. It features great simplicity, high performance, and excellent stability. This paper performs analysis and design of OCC-PFC in both the steady-state and dynamic transients. The sufficient stability condition for three-phase OCC-PFC is derived. Some typical large-signal perturbations in practice are then used to verify the theoretical predictions. The paper also provides some guidelines for the selection of the circuit parameters in practical application. All analysis results were verified by simulation or experiments based on a three-phase 1-kW pre-industrial OCC-PFC prototype. Index Terms--One-cycle control (OCC), power-factor correction (PFC), power quality control, rectifier.

Renewable energy, such as solar energy, is desirable for power generation due to their unlimited existence and environmental friendly nature. However, the high initial investment impedes its wide commercialization. This paper proposes a cost-effective single-stage inverter with maximum power point tracking (MPPT) in combination with one-cycle control (OCC) for photovoltaic power generation. This control scheme is based on the output current-adjusting feature of OCC. The output current of the inverter can be adjusted according to the voltage of the photovoltaic (PV) array so as to extract the maximum power from it. In the mean time, OCC guarantees that the output current is proportional and in phase with the grid voltage. All these are accomplished in one power stage and a simple control circuit. No detection and calculation of power are needed. Compared with previously proposed approaches, this method is much more efficient and cost-effective and yet exhibits excellent performance. The principle is explained qualitatively and extensive experiments have been carried out to verify the proposed method. Index Terms--Grid connected inverters, maximum power point tracking, MPPT, one-cycle control (OCC), photovoltaic, PV, solar energy.

In this paper, analysis and design for a single-phase active power filter (APF) with one-cycle control is presented. The proposed control method eliminates the need of sensing the load current, a nontrivial task of calculating the harmonics and reactive current components, as well as the use of multipliers, as reported by many previously reported approaches. In addition, the switching loss is reduced by employing unipolar operation, where only two out of four switches are operated at switching frequency while the other two are stationary on or off during an entire half-line cycle. The design methodology taking electromagnetic interference filter into account is also discussed in detail. The theoretical analysis is verified by experiments. Index Terms--Active power filter (APF), harmonic elimination, one-cycle control, power quality, rectifier.

Active power filters (APFs) provides an effective measure to eliminate the power line harmonic/reactive currents generated by nonlinear loads or by distributed energy sources that are connected to the grid. Active power filters are typically connected in parallel to the harmonic/reactive current sources and cancel the harmonic/reactive components in the line current so that the current flow into and from the grid is sinusoidal and in phase with the grid voltage. Since the APFs process only the harmonic/reactive power, their power-handling capability can be much higher than that of the cascade power-factor-correction methods. In this paper, the one-cycle control method is extended to control three-phase APFs. The proposed control approach employs one integrator with reset along with several logic and linear components to control a voltage-source coverter to achieve three-phase unity power factor for the current to and from the power grid. No multipliers or sensors for the load current and the APF inductor current are required. Furthermore, there is no need to calculate the reference for controlling APF inductor current so that complicated digital computation is eliminated. The operation switching frequency is constant that is desirable for industrial applications. The proposed control approach features great simplicity, excellent harmonic/reactive current cancellation, and solid stability. It is a cost-effective solution for power quality control for electronic equipment, build. rags, industrial facilities, ships, airplanes, distributed power generation stations, etc. All findings are supported by experimental results. Index Terms--Active power filter (APF), one-cycle control, power-factor correction (PFC), power quality control.

A unified constant-frequency integration (UCI) controller for a three-phase star-connected switch three-level rectifier (VIENNA) with unity-power-factor-correction is proposed. One of advantages of this rectifier is that the switch voltage stress is one half of the total output voltage. The proposed control approach is based on one-cycle control and features great simplicity and reliability: all three phases will be power factor corrected using one or two integrators with reset along with several flips-flops, comparators and logic and linear components. It does not require multipliers to scale the current reference according to the output power level as used in many other control approaches. In addition, the input voltage sensor is eliminated. It employs constant switching frequency modulation that is desirable for industrial applications. The proposed controller can operate by sensing either the inductor currents or the switching currents. If the switching currents are sensed, the cost is further reduced because switching currents are easier to sense comparing with inductor currents. The proposed approach is supported by experimental results. Index Terms--One cycle control, power factor correction.

In this paper, a three-phase six-switch standard boost rectifier with unity-power-factor correction is investigated. A general equation is derived that relates the input phase voltages, output dc voltage, and duty ratios of the switches in continuous conduction mode. Based on one of the solutions and using one-cycle control, a unified constant-frequency integration controller for PFC is proposed. For the standard bridge boost rectifier, a unity power factor and low total harmonic distortion can be realized in all three phases with a simple circuit that is composed of one integrator with reset along with several flips-flops, comparators, and some logic and linear components. It does not require multipliers and three-phase voltage sensors, which are required in many other control approaches. In addition, it employs constant-switching-frequency modulation that is desirable for industrial applications. The proposed control approach is simple and reliable. All findings are supported by experiments. Index Terms--One-cycle control, power-factor correction (PFC), power quality control, three-phase rectifier.