Journal of Circuits, Systems and Computers

Three-phase active rectifiers based on the voltage source converter topology can successfully replace traditional thyristor-based rectifiers or diode bridge plus chopper in interfacing dc-systems to the grid. However, if the application in which they are employed has a high safety issue or if there are other loads connected to the same Point of Common Coupling (PCC), and sensitive to the harmonics produced by the switching of the converter, an LCL-filter has to be used. This kind of solution has been studied in theory but its sensitivity to the value of the LCL-filter passive elements employed, to the grid side stiffness and to the parameters of the controller has never been considered in detail. In this paper the experimental results of an LCL-filter-based three-phase active rectifier are analyzed with the circuit theory approach. A "virtual circuit" is synthesized in role of the digital controller and of the feedback filters to have an homogenous model that allows a sensitivity analysis which is rigorous and straightforward for the industry.

This paper presents the modeling, analysis, and design of a thyristor-based ac–dc converter, featuring bi-directional power flow and unity power factor at the ac side in both powering and regenerating modes. By applying the y-parameter modeling technique and eliminating the effects of the high-frequency poles and zeros, small-signal models of the converter in both modes and a unified controller have been developed. The controller regulates the voltage at the dc side and operates as a feedback controller in the powering mode and a feedforward controller in the regenerating mode. Systematic procedures for determining the circuit component values of the power conversion stage and the controller are presented. The operation is illustrated with the design of a 500-W, 100-V (ac)/200-V (dc) prototype, supplying to a motor-generator set. Experimental results showing operation in the powering mode, regenerating mode, and during mode changeover are included. Circuit operations during the transient of the changeover operation are clearly identified.

Distributed power supply (DPS) systems are extensively used to supply different electronic equipment and systems such as telecom switching systems. Continuous reduction of supply voltages of digital integrated circuits from the previous industry standard of 5 V down to 1 V or even less has necessitated the use of point-of-load system architectures due to high supply currents. The input currents of the switched-mode power supplies contain typically high ripple currents necessitating the use of noise suppression (EMI) filters to meet the stringent requirements stipulated by international standards. The interactions between the load converters, EMI filters, and supply side converters may adversely affect the stability and performance of the system. The system analysis is typically made based on the behavior of the ratio between the output impedance of the supply side and the input impedance of the load side known as minor-loop gain. Certain forbidden regions in the complex plane have been developed out of which the minor-loop gain should stay in order to guarantee stability. Even if the restrictions for the behavior of the minor-loop gain are well-defined, the accurate prediction of the associated impedances is difficult or even impossible. We propose, in this paper, a method based on input invariance to cancel the load-side interactions in the small-signal sense. The only concern left is then the stability of EMI filters, which may be considered based on the input power of the associated converters.

The two prevalent s-domain models for current-mode control, the continuous-time model and the unified model, exhibit noticeable differences in their small-signal predictions and therefore have become the subject of comparisons and clarifications. The current letter presents an alternative way of deriving the unified model, thereby providing an additional guide for assessing the validity of the unified model. This letter also presents experimental data that support the accuracy of the unified model.

The theory of synergetic control was introduced in a power electronics context in a previous paper. In this paper we review the theory, then we focus on a comparison with the sliding mode approach. Common elements and main differences are underlined and illustrated through a comparative simulation example. The main advantages of synergetic control are that it is well-suited for digital implementation, it gives constant switching frequency operation, and it gives better control of the off-manifold dynamics. Finally, simulation and experimental results under transient conditions are compared. Advanced control laws with adaptation are presented and discussed to show how to better exploit the features of the synergetic control. The example used throughout the paper is the control of a boost converter operating in continuous conduction mode.

Several recommendations and standards have increased the interest in power factor correction circuits. There are multiple solutions in which line current is sinusoidal and boost rectifier is one of them. In this paper an experimental analysis of the randomized pulse width modulation (RPWM) algorithm in the boost rectifier is performed. The influence of randomization is followed: first, introduction of the RPWM switching is reflected in smaller increase of the total harmonic distortion (THD) factor in the input current. Nevertheless, decrease of the power factor is negligibly small. Second, power spectrum density (PSD) of the input current is estimated and measured to evaluate the influence of the randomization in the high frequency range. Based on this approach, lower conductive electromagnetic interference (EMI) is expected and also experimentally verified.

The active power in nonlinear single-phase circuit is measured by a new specially-developed experimental model. The experiments are carried out for sinusoidal and nonsinusoidal voltage and current waveforms. The results of the experiments show that the total active power is a sum of the active powers produced by the voltage and current harmonics with the same serial number.

Two case examples of high-speed CMOS microelectronic implementations of high-performance controllers for switching power converters are presented. The design and implementation of a current-programmed controller and a general-purpose feedforward one-cycle controller are described. The integrated circuit controllers attain high-performance by means of using current-mode analog signal processing, hence allowing high switching frequencies that extend the operation margin compared to previous designs. Global layout-extracted transistor-level simulation results for 0.8 μm and 0.35 μm standard CMOS technologies confirm both the correct operation of the circuits in terms of bandwidth as well as their functionality for the control of switching power converters. The circuits may be used either as standalone IC controllers or as controller circuits that are technology-compatible with on-chip switching power converters and on-chip loads for future powered systems-on-chip.

This paper explores the possibility of using neural network to identify faults that may occur in a HVDC converter system. Based on the ability of these networks to distinguish reliably between different types of faults, the feature can be suitably integrated with ANN based controller to improve the dynamic response of AC–DC power system. In this paper, different neural network architectures to distinguish different faults in HVDC converter are proposed, and comparison between them is made under different system perturbations and faults. The method is independent of the operating mode of the converter.

Modulation strategy for a matrix structured ac to dc converter is developed. This modulation strategy enables the input displacement factor correction without current sensing. Mathematical proof that ac to dc converter can operate with unity input displacement factor is provided by analysis based on the switching matrix approach. Theoretical analysis demonstrates the algorithm requirements. Computer simulation and experimental results supporting this ability are reported.

This paper presents a fast and simple space vector modulation algorithm for voltage source multilevel converters for calculating the switching times and the space vectors using simple geometrical considerations. This method provides the nearest switching vectors sequence to the reference vector and calculates the on-state durations of the respective switching state vectors without involving trigonometric functions, look-up tables or coordinate system transformations which increase the computational load corresponding to the modulation of a multilevel converter. The low computational cost of the proposed method is always the same and it is independent of the number of levels of the converter. In addition, a new switching sequence control technique is presented for reducing the ripple of the DC-link voltage approximately in 66%.

A DC to three-phase converter based on using a two-phase to three-phase transformation has been developed. To provide a better understanding of the operation principle, the transformer, which is the main element of the system, has been supplied by two single-phase inverters. According to this, the theoretical analysis of the proposed system is shown. This analysis is based on two-phase to three-phase transformation. The theoretical analysis and the experimental verification of the proposed principle are presented. In this paper the component minimized inverter topology is also proposed.

The main function of the on-load tap changing (OLTC) regulators consists of maintaining a constant voltage in order to feed critical loads despite the load changes or voltage changes in the ac mains. The traditional regulators are still used nowadays, but they present several disadvantages, like a slow response, which reaches from 100 ms to several seconds. These drawbacks can be overcome if the OLTC regulators would have shorter response time, commuting several times every cycle of the mains. There are two basic topologies for fast OLTC regulators. The first one consists of several taps and uses hard switching. The second one consists of two main switches commuting at high frequency, using soft-switching in order to reduce the power losses. The present topology is of the second type. This paper presents a mathematical model of the power stage of the proposed regulator. The model includes the parasitic resistances and the leakage inductances in order to obtain a better comprehension of the regulator operation. A parametric analysis has been done in order to observe the influence of the parasitic elements in the performance of the main parameters of the topology. The model is verified by experimental results obtained using a 500-W prototype.

By proper control algorithms, the energy flow between the static series compensator (SSC) and the distribution system can be fully controlled. This paper proposes and describes two control techniques to exchange electric energy between the energy storage capacitor (ESC) of the SSC and the utility. The first is based on using a shunt diode rectifier, which is placed either on the load side or the grid side (both configurations are studied). The other exploits the voltage source converter of the SSC to charge its the ESC. A design guide for the dc-capacitor is given. The proposed techniques are validated by PSCAD/EMTDC simulation.

Traditionally, magnetic component design has been based on power frequency transformers with sinusoidal excitation. However, the movement towards higher density integrated circuits means that reductions in the size of magnetic components must be achieved by operating at higher frequencies, mainly through nonsinusoidal switching circuits. As this trend continues, computing tools are required to carry out designs of magnetic components that also allow evaluation of the high frequency losses in these components. A computer design package is described here that implements a robust transformer design methodology allowing customizable transformer geometries. The concept of a critical frequency is a vital part of this methodology. In addition, the winding choice at high frequencies is optimized to give the most accurate results for the best possible speed. This paper includes a description of the software design processes used and describes the main aspects that were incorporated into the system.

A new topology for soft starting and speed regulation of wound rotor asynchronous machines is proposed. The feedback regulation is controlled by a microprocessor. A description of the microprocessor and its operation is presented. A theoretical analysis of the topology operation is carried out and verified by PSpice simulations. Experiments with 1.5 kW asynchronous machine are executed. Results of theoretical calculations, PSpice simulations and experiments are in good matching. The experimental investigations show that the proposed algorithm of soft starting is effective.

A new feeding concept for electrical transportation systems is presented, based on supercapacitive energy storage. Supercapacitors are new and powerful components for energy storage. Compared with batteries, the amount of energy supercapacitors can store is low and does not allow large vehicle autonomy. Because supercapacitors have the property to be re-loadable in a few seconds, a sequential supply system has been developed, considering repetitive feeding at the stops. To solve the problem of the high power amount needed to reach short refill times, a solution is proposed, which consists of using an intermediary supercapacitive tank placed at fixed stations, which is refilled between the bus arrivals with a much lower power. In addition to the description of the needed power electronic converters, theoretical and experimental results are presented, defining the controlled profile of the instantaneous power level, in order to achieve a fast energy transfer between two supercapacitive tanks.