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The flying capacitor multicell inverter (FCMI) possesses natural balancing property. With the phase-shifted carrier-based scheme, natural balancing can be achieved in a straightforward manner. However, to achieve natural balancing with the harmonically optimal phase-disposition (PD) carrier-based scheme, the conventional approaches require (n − 1) × (n − 1) trapezoidal carrier signals for an n-level inverter, which is ( n − 1) × (n − 2) times more than that in the standard PD scheme. This paper proposes two improved natural balancing strategies for FCMI under PD scheme, which use the same (n − 1) carrier signals as used in the standard PD scheme. In the first scheme, the on-line detections are performed of (i) the band in which the modulation signal is located, (ii) corresponding period number of the carrier, and (iii) rising or falling half cycle of the carrier waveform to generate the switching signals based on certain rules. In the second strategy, the output voltage level selection is first processed and the switching signals are then generated according to a rule based on preferential cell selection algorithm. These methods are easy to use and can be simply implemented as compared to the other available methods. Simulation and experimental results are presented for a five-level inverter to verify these proposed schemes. [ABSTRACT FROM AUTHOR]

This paper proposes a flying-capacitor-based chopper circuit for dc capacitor voltage equalization in diode-clamped multilevel inverters. Its important features are reduced voltage stress across the chopper switches, possible reduction in the chopper switching frequency, improved reliability, and ride-through capability enhancement. This topology is analyzed using three-and four-level flying-capacitor-based chopper circuit configurations. These configurations are different in capacitor and semiconductor device count and correspondingly reduce the device voltage stresses by half and one-third, respectively. The detailed working principles and control schemes for these circuits are presented. It is shown that, by preferentially selecting the available chopper switch states, the dc-link capacitor voltages can be efficiently equalized in addition to having tightly regulated flying-capacitor voltages around their references. The various operating modes of the chopper are described along with their preferential selection logic to achieve the desired performances. The performance of the proposed chopper and corresponding control schemes are confirmed through both simulation and experimental investigations. [ABSTRACT FROM AUTHOR]

This paper examines the application of a diodeclamped multilevel inverter (DCMLI).based distribution static compensator (DSTATCOM) connected to a three-phase, four-wire (3p4w) distribution system. The DCMLI has an inherent unbalancing problem among its dc capacitor voltages. Additionally, when the load contains a dc part, the neutral point of the compensator also becomes unbalanced. In this paper, the effects of different loading conditions on the dc capacitor voltages of the inverter are studied. Two new control circuits are proposed for equalizing the capacitor voltages. Different control techniques are presented for the equalizing circuits. Equations of the proposed equalizing controllers are developed corresponding to the control of the switching devices. Comparative studies of different control techniques and the performances of the two controllers are performed. Simulation studies are performed using PSCADIEMTDC to validate the efficacy of the proposed equalizing controller circuits. [ABSTRACT FROM AUTHOR]

This paper focuses on the development of multilevel hysteresis current regulation strategies. Two such strategies have been discussed and some modifications in their control tasks have been proposed to achieve more reliable and improved performance. In general, the multiband concept has been used while making the proposals. The hysteresis band size considerations have also been presented by taking into account the desired and existing system conditions. The proposed modulation schemes have been applied to a five-level flying-capacitor inverter, whose operation under hysteresis current control mode is much less established. A new method of flying-capacitor voltage balancing is proposed which ensures balanced flying-capacitor voltages and, at the same time, maintains the desired current profile. It uses a time-based approach for controlling the capacitor voltages and achieves appreciable voltage spectrum under wide range of load power factor conditions. The performance of the proposed strategies is confirmed through both simulation and experimental investigations. [ABSTRACT FROM AUTHOR]

In this paper, load compensation using multilevel inverter-based distribution static compensator (DSTATCOM) is presented. The DSTATCOM is connected to a three-phase four-wire (3p4w) distribution system. Two different multilevel inverter topologies are used to realize the DSTATCOM. They are diode-clamped multilevel inverter (DCMLI) and flying capacitor multilevel inverter (FCMLI). A compensating technique has been derived, which uses the state feedback control to the multilevel inverters-based DSTATCOMs. A switching strategy for the multi-level inverters that ensures utilization of all output voltage states of the inverter for efficient tracking of references has been proposed. The schemes of dc-link capacitor volthge control for DCMLI and flying capacitor voltage control for FCMLI have been discussed. Comparative studies of performances of the two DSTATCOM topologies are performed. The simulation studies are performed using PSCAD/EMTDC to validate the efficacy of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Abstract: This paper discusses the effects of thyristor controlled series compensator (TCSC), a series FACTS controller, on the transient stability of a power system. Trajectory sensitivity analysis (TSA) has been used to measure the transient stability condition of the system. The TCSC is modeled by a variable capacitor, the value of which changes with the firing angle. It is shown that TSA can be used in the design of the controller. The optimal locations of the TCSC-controller for different fault conditions can also be identified with the help of TSA. The paper depicts the advantage of the use of TCSC with a suitable controller over fixed capacitor operation. [Copyright &y& Elsevier]

Flying capacitor multilevel inverter (FCMLI) is a multiple voltage level inverter topology intended for high voltage and power operations with low distortion. It uses capacitors, called flying capacitors for clamping the voltage across the power semiconductor devices. In this paper, the implementation of a distribution static compensator (DSTATCOM) using an FCMLI is presented. A hysteresis current control technique for controlling the injected current by the FCMLI-based DSTATCOM is discussed. A new method for controlling the flying capacitor voltages is proposed which ensures that their voltages remain constant and at the same time maintain the desired current profile under the hysteresis current control operation. Simulation studies are performed using PSCAD/EMTDC to validate the efficacy of the control scheme and the FCMLI-based DSTATCOM. [ABSTRACT FROM AUTHOR]

The flying capacitor multilevel inverter (FCMLI) is a multiple voltage level inverter topology intended for high-power and high-voltage operations at low distortion. It uses capacitors, called flying capacitors, to clamp the voltage across the power semiconductor devices. A method for controlling the FCMLI is proposed which ensures that the flying capacitor voltages remain nearly constant using the preferential charging and discharging of these capacitors. A static synchronous compensator (STATCOM) and a static synchronous series compensator (SSSC) based on five-level flying capacitor inverters are proposed. Control schemes for both the FACTS controllers are developed and verified in terms of voltage control, power flow control, and power oscillation damping when installed in a single-machine infinite bus (SMIB) system. Simulation studies are performed using PSCAD/EMTDC to validate the efficacy of the control scheme and the FCMLI-based flexible alternating current transmission system (FACTS) controllers. [ABSTRACT FROM AUTHOR]

A new comprehensive planning methodology is proposed for implementing distribution network reinforcement. The load growth, voltage profile, distribution line loss, and reliability are considered in this procedure. A time-segmentation technique is employed to reduce the computational load. Options considered range from supporting the load growth using the traditional approach of upgrading the conventional equipment in the distribution network, through to the use of dispatchable distributed generators (DDG). The objective function is composed of the construction cost, loss cost and reliability cost. As constraints, the bus voltages and the feeder currents should be maintained within the standard level. The DDG output power should not be less than a ratio of its rated power because of efficiency. A hybrid optimization method, called modified discrete particle swarm optimization, is employed to solve this nonlinear and discrete optimization problem. A comparison is performed between the optimized solution based on planning of capacitors along with tap-changing transformer and line upgrading and when DDGs are included in the optimization. [ABSTRACT FROM PUBLISHER]

Abstract: An iterative based strategy is proposed for finding the optimal rating and location of fixed and switched capacitors in distribution networks. The substation Load Tap Changer tap is also set during this procedure. A Modified Discrete Particle Swarm Optimization is employed in the proposed strategy. The objective function is composed of the distribution line loss cost and the capacitors investment cost. The line loss is calculated using estimation of the load duration curve to multiple levels. The constraints are the bus voltage and the feeder current which should be maintained within their standard range. For validation of the proposed method, two case studies are tested. The first case study is the semi-urban 37-bus distribution system which is connected at bus 2 of the Roy Billinton Test System which is located in the secondary side of a 33/11kV distribution substation. The second case is a 33kV distribution network based on the modification of the 18-bus IEEE distribution system. The results are compared with prior publications to illustrate the accuracy of the proposed strategy. [Copyright &y& Elsevier]

A novel H-bridge multilevel pulsewidth modulation converter topology based on a series connection of a high-voltage diode-clamped inverter and a low-voltage conventional inverter is proposed in this paper. A dc link voltage arrangement for the new hybrid and asymmetric solution is presented to have a maximum number of output voltage levels by preserving the adjacent switching vectors between voltage levels. Hence, a 15-level hybrid converter can be attained with a minimum number of power components. A comparative study has been carried out to present high performance of the proposed configuration to approach a very low total harmonic distortion of voltage and current, which leads to the possible elimination of the output filter. Regarding the proposed configuration, a new cascade inverter is verified by cascading an asymmetrical diode-clamped inverter, in which 19 levels can be synthesized in output voltage with the same number of components. To balance the dc link capacitor voltages for the maximum output voltage resolution as well as synthesize asymmetrical dc link combination, a new multi-output boost converter is utilized at the dc link voltage of a seven-level H-bridge diode-clamped inverter. Simulation and hardware results based on different modulations are presented to confirm the validity of the proposed approach to achieve a high-quality output voltage. [ABSTRACT FROM PUBLISHER]

Voltage imbalance in capacitors is a well-known problem in compensator topologies which use two or more capacitors. This imbalance may exist even if the load does not contain any dc component, due to practical factors. However, when the load contains a dc part, the voltage imbalance problem becomes critical. In this paper, a two-quadrant chopper has been used to regulate the capacitor voltages in a two-capacitor compensator structure. Two different control strategies for the two-quadrant chopper to equalize the voltage of the capacitors have been proposed. The strategies are validated through detailed simulation studies. Experiments have also been carried out to validate the hysteresis control of chopper. [ABSTRACT FROM AUTHOR]

This paper presents a high-voltage pulsed-power system based on low-voltage switch–capacitor units that are connected to a current source for several applications such as plasma systems. A modified positive buck–boost converter topology is used to utilize the current source concept, and a series of low-voltage switch–capacitor units is connected to the current source in order to provide a high voltage with a high voltage stress (dv/dt) as demanded by the loads. This pulsed-power converter is flexible in terms of energy control because the stored energy in the current source can be adjusted by changing the current magnitude to significantly improve the efficiency of various systems with different requirements. The output-voltage magnitude and stress (dv/dt) can be controlled by a proper selection of components and control algorithm to turn on and off the switching devices. [ABSTRACT FROM PUBLISHER]

The output voltage quality of some of the single-phase multilevel inverters can be improved when their dc-link voltages are regulated asymmetrically. Symmetrical and asymmetrical multilevel diode-clamped inverters have the problem of dc-link capacitor voltage balancing, especially when power factor of the load is close to unity. In this paper, a new single-inductor multi-output dc/dc converter is proposed that can control the dc-link voltages of a single-phase diode-clamped inverter asymmetrically to achieve voltage quality enhancement. The circuit of the presented converter is explained and the main equations are developed. A control strategy is proposed and explained in details. To validate the versatility of the proposed combination of the suggested dc–dc converter and the asymmetrical four-level diode-clamped inverter (ADCI), simulations and experiments have been directed. It is concluded that the proposed combination of introduced multioutput dc–dc converter and single-phase ADCI is a good candidate for power conversion in residential photovoltaic (PV) utilization. [ABSTRACT FROM PUBLISHER]

This paper presents a novel topology for the generation of high voltage pulses that uses both slow and fast solid-state power switches. This topology includes diode-capacitor units in parallel with commutation circuits connected to a positive buck-boost converter. This enables the generation of a range of high output voltages with a given number of capacitors. The advantages of this topology are the use of slow switches and a reduced number of diodes in comparison with conventional Marx generator. Simulations performed for single and repetitive pulse generation and experimental tests of a prototype hardware verify the proposed topology. [ABSTRACT FROM AUTHOR]

Improving efficiency and flexibility in pulsed power supply technologies is the most substantial concern of pulsed power systems specifically with regard to plasma generation. Recently, the improvement of pulsed power supply has become of greater concern due to the extension of pulsed power applications to environmental and industrial areas. With this respect, a current source based topology is proposed in this paper as a pulsed power supply which gives the possibility of power flow control during load supplying mode. The main contribution in this configuration is utilization of lowmedium voltage semiconductor switches for high voltage generation. A number of switch-diode-capacitor units are designated at the output of topology to exchange the current source energy into voltage form and generate a pulsed power with sufficient voltage magnitude and stress. Simulations carried out in Matlab/SIMULINK platform as well as experimental tests on a prototype setup have verified the capability of this topology in performing desired duties. Being efficient and flexible are the main advantages of this topology. [ABSTRACT FROM AUTHOR]