Capacitor Size Research Articles

Failure in Ring Oscillators With Capacitive Load

Ring oscillators, with capacitive load intended for frequency tuning, can fail to sustain stable oscillations. Failure depends on the size of the load capacitors and their equivalent series resistance. This paper first describes the failing mechanism from an intuitive perspective. It then develops an analytical model and provides the equations for the minimum load capacitance and the range of equivalent series resistance at which the ring oscillator fails. The dependency on the number of stages of the ring oscillator as well as the trans-conductance and impedance of its gain stages are also examined. Confirmed by simulations, the model shows that the failing region reduces significantly for ring oscillators with 7 or more stages but that it can be a serious concern for 5 and especially 3-stage ring oscillators.

A 10-bit 200 MS/s pipelined ADC with parallel sampling and switched op-amp sharing technique

PurposeIn parallel sampling method, the size of the sampling capacitor is reduced to improve the bandwidth of the ADC.Design/methodology/approachVarious low-power techniques for 10-bit 200MS/s pipelined analog-to-digital converter (ADC) are presented. This work comprises two techniques including parallel sampling and switched op-amp sharing technique.FindingsThis paper aims to study the effect of parallel sampling and switched op-amp sharing techniques on power consumption in pipelined ADC. In switched op-amp sharing technique, the numbers of op-amps used in the stages are reduced. Because of the reduction in the size of capacitors in parallel sampling technique and op-amps in the switched op-amp sharing technique, the power consumption of the proposed pipelined ADC is reduced to a greater extent.Originality/valueSimulated the 10-bit 200MS/s pipelined ADC with complementary metal oxide semiconductor process and the simulation results shows a maximum differential non-linearity of +0.31/−0.31 LSB and the maximum integral non-linearity (of +0.74/−0.74 LSB with 62.9 dB SFDR, 55.90 dB SNDR and ENOB of 8.99 bits, respectively, for 18mW power consumption with the supply voltage of 1.8 V.

Stochastic Simultaneous Planning of Interruptible Loads, Renewable Generations and Capacitors in Distribution Network

Executing interruptible loads (ILs) can be significantly effective for optimal and secure operation of power systems. These ILs can aid the operators not only to increase the reliability of the power supply but also to reduce the procurement costs of the whole system. Therefore, determining the optimal location and capacity of ILs for a given incentive rate is of great interest to distribution companies. To do so, in this paper simultaneous allocation and sizing of ILs, wind turbines (WT), photovoltaic (PV) and capacitors have been done in the radial distribution network for different demand levels and subsequently the optimal value of compensation price for the ILs has been determined. Given the probabilistic nature of load, wind and solar generation as well as the price of energy at the pool, we have also proposed a stochastic model based on fuzzy decision making for modelling the technical constraints of the problem under uncertainty. The objective functions are technical constraint dissatisfaction, the total operating costs of the Distribution Company and CO2 emissions which are minimized by NSGA2. To model the uncertainties, a scenario-based method is used and then by using a scenario reduction method the number of scenarios is reduced to a certain number. The performance of the proposed method is assessed on the IEEE 33-node test feeder to verify the applicability and effectiveness of the method.

Optimal Integration of Capacitor and Distributed Generation in Distribution System Considering Load Variation Using Bat Optimization Algorithm

In this article, an efficient long-term novel scheduling technique is proposed for allocating capacitors in a combined system involving distributed generation (DG) along with radial distribution systems (RDS). We introduce a unique multi-objective function that focuses on the reduction of power loss with the maximization of voltage stability index (VSI) subjected to constraints of equality and inequality systems. Loss sensitivity factor and VSI together are involved in pre-identifying the locations of capacitors and DG. Determination of the optimal size of capacitor and DG is performed by utilizing the Bat algorithm (BA) for all the loads in RDS. The conventional approach considers the medium load of (1.0) condition generally, but the proposed method changes the feeder loads linearly, ranging from light load (0.5) to peak load (1.6) with the value of step size as 1%. BA determines the optimal size of the capacitor and DG for each step load. The curve fitting technique is used for deducing the generalized equation of capacitor size and DG for all conditions of the load with the various loading condition sized by distributed network operators (DNOs). Further, various load models such as industrial, residential, and commercial loads have been considered to show the efficiency of the present approach. Validation of results is performed in different scenarios on a 69-bus test system and on a standard IEEE 33-bus system. The results exhibit improved accuracy with less power loss value, superior bus voltage, and stability of system voltage with a higher rate of convergence.

Fast Frequency Support from Hybrid Wind Power Plants Using Supercapacitors

The concept of hybrid wind power plants (HWPPs) that consist of wind, solar and batteries has received a lot of attention, since HWPPs provide a number of advantages thanks to the complementary nature of wind and solar energy and the flexibility of batteries. Nevertheless, converter-based technologies, as interfaces of HWPPs to the utility grid, contribute to the reduction of total system inertia, making the system more volatile and creating additional threats to frequency stability. To address these operational challenges, the capability of supercapacitors (SCs) to provide fast frequency reserve (FFR) is explored in this paper to enhance the frequency response of the HWPP. Two topologies for integrating SCs into the HWPP are proposed: (1) connecting SC to the DC link of wind turbine (WT) via a DC-DC converter interface, (2) directly connecting SC to the DC link of WT without converter interface. Frequency controllers at the asset level are proposed for these two topologies accordingly. The idea of the proposed frequency controller is to provide frequency response by varying SC voltage in proportion to frequency deviation, namely droop-based FFR. A practical SC sizing method for FFR provision is also discussed. The simulation results have shown, that in the case of frequency event, the proposed frequency controllers for SCs in both topologies positively contribute to the frequency of the system by reducing the rate of change of frequency by at least 5% and improving frequency nadir by at least 10%, compared to the case where the SC has no contribution to FFR. However, the capacitor size requirement for directly connected SC is more demanding in order to achieve the same level of improvement. The performance of frequency support has been highly related to total system inertia and control parameters. Therefore, any change to the severity of frequency events or control parameters calls for the reevaluation of the capacitance.

Distribution power loss minimization via optimal sizing and placement of shunt capacitor and distributed generator with network reconfiguration

The population is speeding up and the demands for electrical energy are clearly increasing, this growth in load leads to higher power loss and Voltage drop. This paper is focused on a method to decrease the power losses and voltage profile improvement. The first suggested technique binary particle swarm optimization BPSO is utilized for solving the problem of the power loss minimization in network distribution. This work based on optimum position and sizing of the distribution generation (DG) units, shunt capacitor (SC) with network reconfiguration is applied to show the improvement of the network distribution efficiency. The MATLAB programming part and software package MATPOWER7 are used to simulate 69-bus and 33-bus test system with three different cases of loads and different number of DG and SC. The result showed a positive impact on system efficiency in comparison with other previous studies. This paper showed that increase of DG and capacitor does not usually give the best result although the increase of system cost, maintenance, and the units' distance for gas supplying.

Study of Toroidal Core Multilimb Transformer (TCMLT) for High-Power DC Application

Multimodule isolated converters incorporating excellent features of galvanic isolation, bidirectional power flow, and simple control are widely adopted in medium-voltage (MV) high-power dc-dc applications. However, the converter size and dc-link capacitor voltage balancing are significant concerns in galvanically isolated cascaded dc-dc converters. This article proposes a new design of an integrated transformer implementing toroidal cores named toroidal core multilimb transformer (TCMLT), employed in a dc-dc modular isolated bidirectional dual-active-bridge (IB-DAB) resonant converter topology. The modular design structure of the proposed transformer can be conveniently constructed and implemented for more number of participating modules conforming the compactness constraint. Moreover, an external coupling winding is implemented in the TCMLT structure to resolve the dc-link voltage balancing issue. This coupling winding method substitutes the expensive complex control circuits, which consequently results in cost reduction and reliability enhancement. Besides, the reluctance model of the proposed structure is analyzed. Based on the reluctance model, a common mode-difference mode (CM-DM) electrical circuit is realized for the proposed scheme. Furthermore, unlike the conventional approach of implementing U, UI, and EI cores for multilimb transformer (MLT) structure with separate limbs, a synthesis method of TCMLT in toroidal form is proposed. The comparative study of the proposed design with the conventional U-core MLT confirms that the proposed TCMLT offers less leakage inductance with significant size reduction. Finally, to validate the efficacy of TCMLT, a three-limb laboratory-scale prototype is employed in a 6-kW cascaded IB-DAB resonant converter topology.

Capacitor placement and sizing to minimize losses in a radial distribution network considering uncertainty using modified affine arithmetic division

In a distribution system, load and distributed generation connected to a feeder are subject to uncertainty. Conventional capacitor placement and sizing methods do not consider uncertainty in power injections, due to which the results may be erroneous. In literature, affine arithmetic (AA) is one of the tools used for incorporating uncertainty in power system analysis. However, conventional division operation in AA gives rise to extra noise terms in the resulting affine form, which are not due to the actual uncertainty sources but are due to the nonaffine operations. The present work incorporates modified AA division which does not generate any additional noises, thereby improving the accuracy. Buses in the distribution network are ranked in decreasing order of rate of change of active power loss in line with respect to the change in the effective reactive power flow in that line. The top three ranked buses are chosen as candidate buses for capacitor connection. The required affine reactive current injection at the candidate buses is calculated, and the corresponding affine capacitive kVAR required is obtained through modified AA-based backward/forward sweep (BFS) power flow analysis. The intervals for the cost incurred in losses, voltage profiles with and without capacitor are calculated, and savings for capacitor connected system is calculated. Switchable capacitors are used for reactive power injection. The proposed method is tested on 15, 33 and 118 bus radial distribution systems. The results show that the proposed modified AA method is accurate than existing interval arithmetic-based method.

Air-Cored Resonant Induction Machines: Comparison of Capacitor Tuning Criteria and Experimental Validation

The operation of air-cored resonant induction machines is very sensitive to the tuning of the capacitors. By using the equivalent circuit equations, this article explores in detail the machine performances under four different tuning criteria: (a) both stator and rotor capacitors resonating with the stator and rotor self-inductances; (b) both capacitors resonating with the leakage inductances; (c) stator capacitors tuned to compensate for the overall stator terminal reactance and no rotor capacitors; (d) stator capacitors only to cancel out the machine ideal input reactance neglecting resistances, which is the new option introduced in this article. Extensive comparisons of all tuning options in torque, efficiency, power factor, capacitor size, and feasibility are presented and their performances are compared with a pure air-cored induction machine without capacitors. Analytic expressions for the maximum efficiency and maximum torque and related slip values are also derived as functions of the machine parameters, which provides a valuable tool for design optimization. A numerical case study based on parameters of a real air-cored induction machine is discussed and the article includes the first experimental validation to be carried out on a spinning air-cored resonant induction machine prototype. Results show that using only stator capacitors to compensate for the machine equivalent terminal reactance can be a practical choice to achieve both high torque and high efficiency and avoid rotor capacitors.

A Complete Impedance Model of a PMSG-Based Wind Energy Conversion System and Its Effect On the Stability Analysis of MMC-HVDC Connected Offshore Wind Farms

Impedance modeling of a permanent magnet synchronous generator (PMSG)-based wind energy conversion system (WECS) usually ignores the machine-side dynamics, instead, the machine-side system is simplified as a constant power source, while merely keeping the detailed grid-side converter model. This simplification is mainly based upon the intuition that the dc-bus capacitor is large enough so that the machine- and grid-side dynamics can be decoupled. However, the simplification probably does not hold in practice since there is always a tendency to minimize the capacitor size to achieve a smaller package for installation. Therefore, the machine-side system should not be ignored, otherwise maybe leading to error for stability analysis. To address this issue, this paper developed a complete ac-side impedance model of the PMSG-based WECS. Then, impact factors about the coupling characteristics between machine- and grid-side systems of the PMSG-based WECS are discussed. Finally, a case study of sub/super synchronous oscillation is carried out on a practical offshore wind farm integrated with a modular multilevel converter based high-voltage dc (MMC-HVDC) transmission system in China. The results show that ignoring the machine-side system would lead to an optimistic stability judgement, which confirms the necessity of the complete model of PMSG-based WECS. Furthermore, the system can be stabilized by either changing the couplings between machine- and grid-side systems of PMSG-based WECS or implementing active damping in the wind farm side MMC.

Optimization of distributed generation units in reactive power compensated reconfigured distribution network

Capacitor Allocation (CA) and Network Reconfiguration (NR) are the traditional methods extensively applied by the researchers for power loss reduction and node voltage improvement in radial Distribution Network (DN) for the past four decades. In recent years, simultaneous optimization of CA and NR is considered to maximize the power loss reduction in a proficient manner in comparison to individual optimization of CA and NR. To solve the objective functions, this work proposes an application of Autonomous Group Particle Swarm Optimization (AGPSO) by optimal allocation and sizing of capacitors with and without NR, under four different cases, subject to satisfying operating constraints. In addition, to ascertain the impact of real power injection on further power loss reduction, this work considers placement and sizing of Distributed Generation (DG) units from single to three optimal nodes in capacitive compensated optimal DN. This proposed methodology is demonstrated using standard IEEE 33 and 69 bus test system and the results obtained by each test case have been compared with other optimization techniques. A significant amount of power loss gets minimized after optimal DG allocation in reactive power compensated optimal DN.

Optimal Capacitor Location and Sizing for Reducing the Power Loss on the Power Distribution Systems due to the Dynamic Load of the Electric Buses Charging System using the Artificial Bee Colony Algorithm

The modern power distribution system is connected to many loads, affecting the power system reliability and causing more power loss. One of the new loads is the battery charging station for electric vehicles or electric buses. The charging load will have a charge that varies with the operating time of each vehicle. Therefore, this article focuses on optimal capacitor location and sizing for reducing the power loss on the power distribution systems due to the dynamic load of the electric bus system using the artificial bee colony algorithm. The dynamic charging load of 3 types of electric bus systems was applied: Plug-in charging, Pantograph charging, and Battery swapping charging. The simulation results show that the installation of 0.3167 MVar capacitors for Plug-in electric bus systems reduced the power loss by 0.5465 MWh. In comparison, the installation of 0.2893 MVar capacitors for the Pantograph electric bus systems reduces the power loss by 0.5459 MWh. The installation of 0.2922 MVar capacitors for the Battery swapping systems reduces the power loss of 0.5517 MWh. The installation of shunt capacitors can reduce the power distribution system's power loss and the benefit of capacitors installing 1,501.27, 1,443.76, and 1,474.02 USD/year, respectively.

Power Factor Correction Using Programmable Logic Control Based Rotary Method

The power factor value of an induction motor is low. This power factor value is due to the large reactive power. Therefore, it is necessary to add capacitors to improve the power factor. The addition of this capacitor uses a capacitor bank with the rotary method. This rotary method is expected to be able to improve the low power factor. The method used is to determine the set point of the desired power factor. Then this method will add the value of the capacitor bank if it does not meet the set point. If it exceeds the set point value, this method will reduce the value of the capacitor bank. For programming this method using Programmable Logic Control. Programmable Logic Control can perform real time monitoring. The results of the test method showed that the capacitor bank worked to improve the power factor optimization. From the power factor of the drilling machine 0.54 to 0.86 in the test. Further developments can make capacitor sizes smaller and more varied in order to optimize the power factor.

Optimal Location and Sizing of Shunt Capacitors with Distributed Generation in Distribution Systems

This paper proposes a novel approach to determine an optimal location and sizing of shunt capacitors for reactive power compensation in distribution systems with distributed generation. Here, the optimal location for installing the shunt capacitors is determined using the loss sensitivity factor approach. The stochastic nature of distributed generation (i.e., wind and solar PV powers) has been considered in this paper. Optimal sizing of shunt capacitors has been determined by considering the power loss minimization as objective function and this problem is solved using the differential evolution algorithm (DEA). The results obtained with DEA are also compared with genetic algorithm (GA) and particle swarm optimization (PSO) algorithms. The effectiveness of this proposed approach has been simulated on the IEEE 15, 33, 69 and 85 bus test systems.

A modified indirect extraction method for a single-phase shunt active power filter with smaller DC-link capacitor size

Indirect extraction method is the most common method to control the single-phase active power filters (APFs) due to its simple structure. The main drawback of this extraction method is its performance dependency on the quality of the DC-link voltage. Selecting the high capacity of the DC-link capacitor leads to the high cost and size of APF, weak dynamic response and low-even-order harmonic components on the DC-link voltage. The low capacity of the DC-link capacitor decreases the cost and size of APF, decreases the sub-harmonics and inter-harmonics of the DC-link voltage, improves the dynamic response, and increases the even-order voltage harmonics. This paper proposes a new extraction method to improve the performance of the conventional indirect extraction method. The proposed method uses a small size of capacitor to achieve the aforementioned advantages. The even-order voltage harmonics are eliminated by the single-frequency-decoupled (SFD) scheme. For implementation of the SFD scheme, the proposed method uses proportional-resonant (PR) controllers, and second order generation integrator-frequency locked loop (SOGI-FLL). The effectiveness of the proposed extraction method is verified by the simulation and experiment.

A comprehensive optimization framework for EV-Renewable DG coordination

This paper develops an optimization framework for coordinating electric vehicles (EVs) and renewable energy sources (RESs) in distribution systems. A bilateral contract between EV aggregators and renewable distributed generators (DGs) is first used to maximize revenues for these market participants by optimally controlling EV charging/discharging. The developed market-based EV control model is then implemented in a distribution system and evaluated for its potential adverse effects on the system operation. An optimal capacitor sizing and placement method is proposed to resolve the negative impacts of such control model. The proposed capacitor optimization method along with the developed EV control model provides an EV-RES coordination framework that simultaneously addresses both market and operational objectives. A real distribution network is used to test the EV-RES coordination method and evaluate its performance for different loading conditions using three-phase unbalanced load flow calculations. Simulation results validate the efficiency of the proposed method in not only providing cost savings for the system operation, but also in reducing the losses and voltage deviations that would be otherwise incurred due to uncoordinated EV scheduling. The proposed EV-RES coordination framework is demonstrated to ensure economic, safe and reliable operation of distribution systems in which EVs and renewable DGs synergize.

A Hybrid Modular Multilevel Converter Family With Higher Power Density and Efficiency

Modular multilevel converter (MMC) has many advantages of scalability, reliability and easy implementation, but suffers from large number of switching devices and capacitors. To improve the power density and efficiency for medium voltage applications, this article introduces a hybrid modular multilevel converter (HMMC) family through the combination of active neutral-point-clamped converter and chain-link arm. Three topologies in HMMC family can effectively reduce chain-link voltage by half compared with traditional MMC. Single- and three-phase operation principles are presented to highlight this important features. Several critical metrics, such as component number, capacitor sizes, and semiconductor losses, are compared between the conventional MMC and HMMC topologies at three different medium voltage levels. The result indicates the best topology from the HMMC family can save around 30% devices, 50% total capacitor and 32% power losses compared with traditional MMC. A simple single-phase control method is also mentioned to balance capacitor voltage. Finally, a single-phase HMMC experimental prototype is built to verify the effectiveness of three topologies.

Optimizing location and size of capacitors for power loss reduction in radial distribution networks

Power radial distribution systems are increasingly more and more important in transmitting the electric energy from power plants to customers. However, total loss in lines are very high. This issue can be solved by allocating capacitor banks. Determining the suitable allocation and optimal sizing of capacitor banks needs an efficient approach. In this study, the diffusion and update techniques-based algorithm (DUTA) is proposed for such reason. The efficiency of DUTA is inspected on two distribution systems consisting of 15-bus and 33-bus systems with different study cases. The solutions attained by DUTA are competed with recently published methods. As a consequence, the method is more effective than the other methods in terms of the quality of solution.

Spotted hyena optimizer algorithm for capacitor allocation in radial distribution system with distributed generation and microgrid operation considering different load types

In this paper, the optimal allocation of constant and switchable capacitors is presented simultaneously in two operation modes, grid-connected and islanded, for a microgrid. Different load levels are considered by employing non-dispatchable distributed generations. The objective function includes minimising the energy losses cost, the cost of peak power losses, and the cost of the capacitor. The optimization problem is solved using the spotted hyena optimizer (SHO) algorithm to determine the optimal size and location of capacitors, considering different loading levels and the two operation modes. In this study, a three-level load and various types of loads, including constant power, constant current, and constant impedance are considered. The proposed method is implemented on a 24-bus radial distribution network. To evaluate the performance of the SHO, the results are compared with GWO and the genetic algorithm (GA). The simulation results demonstrate the superior performance of the SHO in reducing the cost of losses and improving the voltage profile during injection and non-injection of reactive power by distributed generations in two operation modes. The total cost and net saving values for DGs only with the capability of active power injection is achieved 105,780 $ and 100,560.54 $, respectively and for DGs with the capability of active and reactive power injection is obtained 89,568 $ and 76,850.46 $, respectively using the SHO. The proposed method has achieved more annual net savings due to the lower cost of losses than other optimization methods.

Hybrid Series Converter: A DC Fault-Tolerant HVDC Converter With Wide Operating Range

A compact, efficient and dc fault-tolerant hybrid series converter (HSC) topology is proposed in this article for high-voltage direct current (HVdc) applications. It contains a parallel and a series chain link (CL) per phase. The parallel CL (PCL) supports the dc-link, whereas the series CL (SCL) enables the HSC to have enhanced operating range and dc fault-tolerant capabilities. A new control technique is proposed to control the SCL submodules (SMs) capacitor voltage for its entire operating range. The performance of HSC and its control technique is evaluated using PSCAD/EMTDC for various conditions. The capability of HSC to work in the undermodulation and overmodulation index range and for HVdc system is examined. Furthermore, the response of HSC during pole-to-pole dc fault and ac faults is analyzed to substantiate its dc fault blocking and ac fault ride-through capabilities. The results obtained validate that the HSC exhibits superior performance over the existing ones. The SMs’ capacitor size design methodology in HSC and for other existing topologies is described. The loss calculation of the HSC is carried out to determine its efficiency and is compared with the prominent converter topologies. A three-phase 13-level HSC experimental setup is developed to validate its feasibility and also to reconfirm the simulation outcomes.