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Please follow the links to view the publication.Grid code interrelation, wind generation evolution and reactive compensation, special topics inside a grid code
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0788
By all appearances, the evolution of wind generation has been orientated to satisfy the requirements, every time inside narrower limits, imposed by the grid codes, standing out among all the determining ones, the administration of the reactive power. In the age of induction generator's fixed speed, the requirements to access to the network were lax, considering the lack, for any practical, end of the capability's curves. The advent of the DFIG's and the electronic switch (IGBT's) evolution, have allowed that a wind farm, in the first instance, can handle the reactive power by means of the availability of a capability curve and comply, this way, with the most restricted codes. The update has been given in very recent date, with a wind farm's activation of an integrated by DFIG's and full converter generators, whose capability's curve are similar to that of a conventional plant. Seeing to the future, probably let's be able attend the elimination of the gear's box. Nowadays the wind generators operate better with high speeds and, therefore, they need gear's box to reduce it. Considering all gear train's issues: cost, vibrations, noise, fatigue, lubrication and maintenance, eliminating the box would have big advantages. The recent versions of the grid code, authorizes the operator to treat the wind farm just like a conventional plant, using the capacity of reactive power inside the extended range of the capability curve. This is not just for reducing the limits inside which one must move the tension and the power factor; now the wind farms must satisfy polygon's critical points of operation, impossible to satisfy with the first generation machines. Under this new operation criterion, the good administration of reactive power is the result from a combination of machines contributions, switched capacitor banks and the reactive dynamic compensation get it using switch electronic devices. The grid code tacitly, yields the owner of the wind farm, the responsibility of solving extraordinary problems or out of the normal catalogue, like a subsynchronous resonance or torsional effects. Give an idea of the entail of all these factors is the purpose of this paper. (4 pages)Evaluation of reactive power control concepts for PV inverters in low-voltage grids
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0892
The proportion of renewable energies in power generation has increased significantly in recent years according to the political aims. In low-voltage grids, these are mostly distributed intermittent generation systems such as photovoltaic systems that are connected through inverters to the grid. Thus, the distribution networks have to meet hitherto unfamiliar technical challenges. A temporary reversal of the power flow can cause overvoltage problems. Traditional voltage regulation strategies cannot solve this problem. Consequently, regenerative sources need to be turned off temporarily or on the long term the grid infrastructure has to be extended by the network operator. Therefore, the distributed generation has to take part in the voltage regulation. With the help of reactive power, which is generated by the solar inverters, power capability and voltage quality of the networks can be increased. Thus, grid extension can be delayed or even avoided in many times. This paper presents a new approach to the evaluation of reactive power control strategies. Different reactive power control concepts are simulated and evaluated concerning their efficiency, effectiveness and stability. (4 pages)Single-phase transformer-less buck-boost residential fuel cell based DG
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0817
The aim of this paper is to evaluate the technical feasibility and aspects related to use, a Fuel Cell based Distributed Generation (FC-DG) in the residential single-phase applications with premium voltage quality. The paper presents a new topology of buck-boost inverter, where this single stage transformer-less inverter is employed to energize the residential load. With this new topology, the proposed DG can maintain the desired ac output voltage with high efficiency, low harmonics, fast response and good steady-state performance. It can operate as an Uninterruptable Power Supply (UPS), too. The proposed configuration is simulated using PSCAD/EMTDC software and simulation results and analytical analysis are presented to validate its effectiveness. (4 pages)Possibilities of integrating renewable generation to the distribution grid by fault current limiters
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0768
Over the last decade an evolution towards higher power requirements on distribution networks has to be stated. Due to additional connection of decentralized power generation in terms of renewables, the referred short circuit current (ISC) values for some network segments were steadily increasing. The actual network structure is based on a unidirectional power flow, assuming a centralized power generation. The electricity is transmitted via point-to-point or simple ring structures at the high voltage transmission grid and radial or point-to-point structures in the Medium Voltage Distribution Grid. Medium and low voltage distribution grids are not intended to handle a bi-directional power flow, created by the integration of renewable electricity generation. Tu guarantee a stable operation of the grid, the grid voltage must kept stable the balance between power supply and consumption has to been managed. In consequence the increased short circuit level might push installed equipment to its physical limits. Therefore new technologies like fault current limiters might be one of the solutions. (4 pages)Microgrid test site for protection systems
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0877
In this work, there are some requirements about the introduction of distribution generation in the power grids, and what they will demand in regards to protection systems and devices. From medium voltage to low voltage, there are some challenges in protecting such power grids, and due to such new necessities, it is introduced a test site, that can contribute conducting some test to get more insight into the situation. Some of the relevant challenges for such protection systems are; the change from radial grid configuration into a mesh network, and the presence of inverter interfaced distribution generation resources. Being able to facilitate the test in such environment is the goal of this work. (4 pages)Voltage control challenges and potential solutions for largescale integration of PV resources in LV networks
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0819
In this paper we illustrate PV single inverter response to voltage rise in LV networks and simulate multiple PV cascading that may result from inverter's response. We then address potential solutions to mitigate the drawbacks of simplistic control approaches, such as reinforcing the network, shifting supply phases, and implementing enhanced control processes. We elaborate on the framework of such control processes and identify main implementation challenges to make them effective. (4 pages)Improving power quality in distribution feeders with high PV penetration through inverter controls
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0749
Voltage fluctuations caused cloud transients in distribution systems with a high level of distributed photovolaic systems is of concern to electric utility companies since this can lead to power quality issues. This article proposes a scheme that can minimize this problem by allowing grid-tie inverters to generate controllable amounts of reactive current in a way to neutralize the change in active current. Inverter oversizing is not required by the implementation of this method. The performance of this technique is verified through computer simulations using PSCAD software. (4 pages)Directional undervoltage pilot scheme for distribution generation networks protection
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0816
The trends of the actual distribution networks are moving toward a high penetration of distributed generation and power electronics converters. These technologies modify contribution-to-fault current magnitude and raise concern about new protection systems to accurately detect faults on distribution networks. This paper proposes a directional under-voltage pilot scheme to detect faulted branches in distribution networks. The aim of the proposed scheme is to provide an efficient algorithm with functions for fault detection, fault localization and fault isolation. The fault detection is based on the voltage measurements at each node of the distribution network when a fault occurs, which are compared with the prefault values. Then, once the fault is detected, the proposed scheme locates the fault comparing the current direction at each node. As the direction of the current when a fault occurs is known, the scheme uses this information to locate the faulted branch. After that, a trip signal is sent to the corresponding breakers in order to isolate the branch under fault. Besides, the proposed scheme enables back up protection using communication between adjacents nodes. A distribution network has been modeled in PSCAD/EMTDC software to verify the proposed algorithm, taking into account distributed generation provided by both wind turbines (doubly fed induction generator and permanent magnet generator with full converter) and solar photovoltaic installations. The behavior of the under-voltage measurements and the current direction has been studied for both generation and loads nodes. This algorithm has been tested varying fault location and resistance along the modeled distribution network. (4 pages)Prevention and protection of single-phase-to-ground fault in power distribution system with neutral non-effectively grounded
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0142
The paper presents a novel idea to detect transient single-phase-to-ground fault based on current travelling waves in power distribution system with neutral non-effectively grounded, and an implemented scheme of protective relays based on current travelling waves and power-frequency voltages, which can identify not only permanent single-phase-to-ground faulted feeder but transient faulted feeder, which helps to prevent the transient insulation flashover from evolving to the permanent fault and phase-to-phase fault. The paper uses the amplitude and polarity characteristics of zero-sequence current travelling waves measured in all feeders to identify disturbance source and determines whether the disturbance is transient single-phase-to-ground fault based on the same disturbance source frequency. And the paper uses zero-sequence and three-phase voltages to detect permanent single-phase-to-ground fault and current travelling waves to identify the faulted device. When transient or permanent single-phase-to-ground fault is determined with the faulted source, a smart processing scheme is presented, which closes the tie switch at first and opens the faulted feeder at last, to meet the requirements of smart grid providing uninterruptible power supply to the load. (5 pages)High efficiency standalone photovoltaic system using adaptive switching of an interleaved boost converter
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0329
Photovoltaic generation is gaining increased importance as a power source in many applications. However, energy conversion efficiency is an important factor for the long term feasibility of these systems. Significant work has been carried out into improving the effectiveness of solar arrays in the last 20 years. In addition, there has been substantial research into novel power converter topologies for maximum energy efficiency. However, in photovoltaic applications, even the most promising power converter topologies do not necessarily guarantee optimum performance under all operating conditions. For example, the efficiency of the power conversion stage may be excellent during periods of high irradiance, but significantly lower in poorer light conditions. This work attempts to address this problem, by seeking to achieve higher energy conversion efficiency under sub- optimal conditions. In this paper, stand-alone photovoltaic systems using dc-dc converters are considered. A novel adaptive control scheme is proposed to maximise system efficiency over a wider range of real-time operating conditions. (7 pages)Network Rail and IEC 61850, A user's perspective of the Standard
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0016
IEC 61850 is a standard that is now gaining pace within the Electrical Supply Industry and one that is under scrutiny by Network Rail. One of the key advantages offered by IEC 61850 is interoperability based on the fact a standard communications interface is implemented between substation devices. This allows the manufacturer to diversify specific functionality whilst allowing communication with other devices. (5 pages)Application of pulse dropping in industrial drive control
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0243
The practical limits on the maximum modulation depth are considered for two level converters with space vector PWM. Maximum modulation depth is analysed as a function of minimum pulse width and deadtime compensation. A method is presented whereby the deadtime compensation algorithm naturally leads into pulse dropping for the non-current-carrying device. The proposed method is analysed and test results from a 3MW industrial drive are presented. (6 pages)Study and implementation of a four-phase interleaved 10-kw boost DC-to-DC converter for fuel cell applications
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0224
In this thesis, this choice of architecture is the current-fed full-bridge converter and use of voltage-double in the secondary circuit, the turns ratio can be reduced by half, thereby reducing losses, improving overall efficiency and practicality. And use interleaved PWM control mode to parallel with four modules, in order to reduce the current ripple on primary side for fuel cells. To ensure that the battery life and reliability in working condition, so design a feedback of constant voltage (CV) / constant current (CC) feedback circuit in terminal. Finally, implement a four modules in parallel 10kW DC-DC boost converter, and has a soft start time of 30 seconds to protect the fuel cells to a steady state. In the high-voltage input full load output, the maximum efficiency can reach 91%. (6 pages)Hardware in the loop based synchronous generator emulation test rig for more electric aircraft power systems
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0248
As more electric aircraft power systems grow in complexity and power rating, testing a piece of equipment under realistic operating conditions requires a significant effort in terms of costs and complexity of the experimental test rig. The Power Hardware in-the-Loop (HIL) concept can provide significant advantages in terms of decreased costs and complexity for testing as the performances of a device under test are evaluated in an environment that emulates in real time the behaviour of the remaining components of a complete system. This paper describes the application of the Power HIL concept to the emulation of a wound field synchronous generator of the type used in aircraft power systems. An FPGA based solution is used for real time emulation of the dynamics of the synchronous generator, whereas a bespoke three phase MOSFET based inverter with appropriate output filters, is used as a variable voltage source. (6 pages)A simple capacitor voltage balancing scheme for the cascaded five-level inverter fed AC machine drive
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0234
This paper proposes a simple scheme for balancing the series capacitor voltages at the three-phase cascaded five-level inverter fed an induction motor by using the logic circuits. Using switching patterns based on the multi-carrier technique, two series-capacitor voltages can be only balanced during one cycle. However, they have a ripple voltage, which may cause the induction motor drive to be unstable. The proposed scheme for balancing capacitor voltages can be implemented by simple logic circuits. It can be verified that the series capacitor voltages are maintained constant at wide frequency range through experimental results with 32-bit DSP and Cyclone-III FPGA. (5 pages)Comparison of DC-DC converter topologies for offshore wind-farm application
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0196
This paper compares six DC/DC converter topologies for offshore wind HVDC applications. The topologies include five conventional transformer based topologies and one novel transformerless topology. Detailed models of the DC/DC converters are simulated using PLECS, and the component stress, component count and losses are presented. The overall performance of each topology is evaluated based on the simulated results. (6 pages)Development of a novel 5kW/42V intelligent converter for automotive applications
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0313
Growing pressure on the automotive industry to produce cars with less exhaust emission, better fuel economy, and to save energy necessitated the introduction of higher voltage electrical power system to meet these requirements in short to mid-term. Already, various electric systems architectures have been proposed and investigated over the past ten years. To meet such growing demands, the automotive industry has to move to higher voltage and the 42V power-net system is the preferred option [8]. The 42V is further processed by the interleaved six-phase dc-todc buck converter system to supply power to the conventional automotive loads that are expected to remain at 14V level as well as to absorb the peak transients on the 42V bus voltage. A special DC/DC converter is therefore needed to interconnect the 14V and the 42V DC buses in the car of the future. Automotive electronics place severe demands on the performance and price of power electronic components and making the development of a suitable converter a challenging task. This paper will present the initial development of the 5kW/42V intelligent converter for automotive applications using Matlab/Simulink. (6 pages)Predictive control of a direct AC/AC matrix converter for power supply applications
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0228
The use of Model Predictive Control (MPC) is investigated for a three phase to three phase direct matrix converter with input and output LC filter for power supply applications. It allows generation of sinusoidal output voltages and input currents with low harmonic distortion. The work describes in details the design of the proposed finite states model predictive control in conjunction with a full load observer. The proposed matrix converter power supply produces unity input power factor and a perfect tracking of the sinusoidal output voltage, accurately following the imposed reference in the presence of a linear load. A simulation study is presented to validate the proposed control scheme. (6 pages)Reliability prediction sensitivity analysis - how to perform reliability prediction time efficiently
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0326
Reliability prediction according to reliability standards is often applied to estimate the reliability of electronic systems. Failure rates are typically dependent on their stress conditions (predominantly thermal and electrical stresses). However, getting the exact temperature and stress value for every single component is extremely time consuming, or sometimes impossible. Here the sensitivity of reliability prediction on the stresses is investigated in a case study of a voltage-source converter. It is found that for electrical stress designers' rules are sufficient. For thermal stress, measured temperatures where used as input. It was found that reliability prediction using averaged temperatures can provide very good agreement, compared to reliability prediction with measured component temperatures. These drastic simplifications allow to perform reliability prediction in a time efficient way. The case study was performed using IEC 62380, Telcordia SR 322 (2), and MIL-HDBK 217F(2), including the ANSI/VITA 51.1 (2008) report that updates the 15 year old MIL-HDBK 217F(2). (6 pages)A new control method of wind energy in power system
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0124
This paper addresses the new method of controlling wind turbine connected to the grid and presents the approach for implementing wind energy as a distributed generation in a power system. With the aid of a fuzzy controller that regulates the modulation index of PWM inverter in an AC-DC-AC converter, and controllable battery storage connected to DC Bus, output of voltage even during changing wind speed or unbalanced load will remain stable. The control system uses the rule-base defined on the load voltage error of the point of common coupling to determine the instantaneous value of modulation index and battery amount. This technique can give a full flexibility to the grid to provide power from wind turbines, an extra control factor for smart grids and gives this ability to have more control on a system. As a power electronics technique, it also can be used in hybrid PV/Wind energy systems. Performance of the proposed method is illustrated by simulation results. (5 pages)Inverter control of medium and high speed linear induction motors
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0361
This paper suggests a unique configuration of certain standard inverters to give better performance from medium and high speed Linear Induction Motors (LIMs). It extends the control method suggested for low speed LIMs [1] and allows a given system parameter to be optimised. (4 pages)Preservation of overcurrent relays coordination in microgrids by application of static series compensators
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0077
In this paper, the application of static series compensator as a fault current limiter is proposed to preserve the integrity of the overcurrent relays' settings in a microgrid for both modes of operations, i.e., utility-grid connected and autonomous (islanded). Static series compensator could be multiple low-power single-phase inverters that attach to the overhead conductor and dynamically control the line impedance or with the same architecture could control the impedance of the underground cables. The static series compensator would effectively increase the line impedance during faults in order to alleviate the contribution of fault current from the utility-grid, so the fault current does not change appreciably in gird-connected or autonomous modes. The static series compensators are controlled by using customary communication techniques. (5 pages)Reduction of passive filtering in aerospace starter/generator systems using a multilevel converter with predictive current control
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0250
The application of predictive current control to a multilevel converter is investigated in an aerospace starter-generator system. The use of a multilevel inverter with predictive current control enables the system to reduce the harmonic distortion in the current waveform when compared to a conventional Field Orientated Controller. It is important that the power converter is optimized to control the current harmonics as aerospace starter-generators are typically low inductance machines. Experimental results taken from a prototype inverter show a substantial reduction in THD is achieved using the proposed controller. (5 pages)Enhanced protection for inverter dominated microgrid using transient fault information
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0081
Protection of an inverter dominated microgrid is always a great challenge, as inverters are well known for their insufficient contribution to the fault current, undermining the accuracy and viability of traditional overcurrent protection schemes. Based on the wide review of solutions developed in the past, this paper proposes a novel protection strategy, with the main protection method based on the time and polarity features of initial current travelling waves using mathematical morphology (MM) technology and backup protection strategy based on the rate of change of current. Simulation tests in PSCAD/EMTDC considering different fault resistances, fault positions and fault inception angles prove this protection approach to be sensitive and reliable. (5 pages)Predictive control of a photovoltaic DC/DC converter
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0330
This paper proposes the use of a predictive controller to regulate a dc/dc converter interacting with a photovoltaic generator and a grid-connected inverter. The proposed solution rejects perturbations generated by environmental conditions and inverter transients. In addition, the predictive controller is able to recover from inverter wrong operation, i.e. drive dc-link voltage under the photovoltaic voltage. The predictive solution is contrasted with a classical PID controller to illustrate its advantages. (6 pages)Analysis and design of coupled inductor for a new single phase transformerless photovoltaic inverter topology
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0195
The demand of photovoltaic (PV) converters with high efficiency and low cost has supported the investigations in new topologies in the last years. Especially transformerless topologies are able to achieve highest efficiency values and lowest specific costs [1]. In order to support these goals as well as to obtain a high power density [2] the functional integration of magnetic components is a known technique. Integrated magnetic components will lead to reduced number of magnetic components and are able to achieve application specific functions [8]. This paper will present the design of a coupled inductor for a new transformerless buck-boost inverter topology for photovoltaic applications. The coupled inductor will serve as energy storage as well as transformer in order to transfer the power to the grid. As basis for the inductor development the inverter topology will be briefly explained. The design procedure including an analysis of the magnetic components is presented as well as simulation and experimental results. (6 pages)Discrete hardware controllers design of a single phase PFC boost converter with FPGA
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0188
A discrete control design of a single phase PFC boost converter with FPGA is presented. The average current mode control (with current reference) and Self Control (without current reference) are analyzed when implemented with discrete hardware controller. Simulation and experimental results are shown to verify the performance of both controllers. (5 pages)Power interfaces and storage selection for an ultrafast EV charging station
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0309
The paper is a summary of the research conducted so far on the ultrafast charging issues of electric vehicles with the main emphasis on the infrastructure. In order to estimate the load curve and peaks resulting from high charging rate, simulations are carried out initially to determine energy and power ratings. Energy storage options for filtering out the perspective peaks are discussed with applicable power interfaces between the grid, the vehicle and the storage buffer. Finally, an ultrafast charging architecture based on cascaded H-bridge converters is proposed. (6 pages)New design approach for higher energy efficiency with parallel converter
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0225
This paper proposes a new design approach for two non-identical converters connected in parallel to obtain higher efficiency across the load range. This is achieved by allowing one converter to be designed for efficiency, without being constrained by system requirements, such as the transient response and current ripple, which will be met by the second converter. The efficiency of the proposed parallel converter is compared to an interleaved converter, both in theory and in practice. (6 pages)Comparison of predictive control strategies for direct resonant high voltage DC power supply
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0198
This paper presents a comparison between two predictive control strategies for a HVDC power supply based on a direct resonant power converter: Input Predictive Control (IPC) and Output Predictive Control (OPC). IPC regulates the input filter capacitor voltage and OPC, the tank capacitor voltage. The resonant converter corresponds to a three phase to single phase matrix converter which feeds a resonant tank (SRPL). Both predictive strategies allow soft commutations, thus, minimizing the switching losses. Previous work has analysed the effects of the control choice on an AC voltage power supply only. The main contribution of this paper is the consideration of the effect of the control choice on the input current as well HVDC quality produced by the power supply. (6 pages)Analysis of dead-time effects in multi-phase voltage source inverters
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0170
Inverter dead-time effects have been investigated in past for three-phase voltage source inverters. Also, there have been some studies about multi-phase (more than three phase) inverters with reference to multiphase drives. Recently, a great deal of research has concentrated on PWM methods suitable for multi-phase VSIs. All PWM methods theoretically produce sinusoidal output voltages without low-order harmonics. This paper analyzes the dead-time effects on output variables of voltages source inverters if no any compensation technique is applied. In particular, an overview of three-phase inverters is considered first. Then, a generalized extension to multi- phase inverters is proposed and investigated in details. Theoretical analysis has shown that particular low-order harmonics appear as result of dead-times, and simulation results confirm the proposed analytical approach. (6 pages)Use of a 3 phase full bridge converter to drive a 6 phase switched reluctance machine
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0260
This paper explores how the use of a modified full bridge converter, coupled to a 6 phase switched reluctance motor, can produce a torque dense drive with low torque ripple, combined with standard drive electronics and a good converter VA rating. A description is provided of the new drive configuration: a prototype motor and drive are constructed and test results provided. Results are compared with those to be expected from the same switched reluctance machine driven from a conventional, asymmetric half bridge converter. (6 pages)Availability analysis of VSC-HVDC schemes for offshore windfarms
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0345
UK Round 3 offshore windfarms located more than 50km from the shore are likely to require a HVDC transmission system. The availability of these HVDC transmission schemes is a key factor in determining if these offshore windfarms are commercially and technically viable. This paper shows that a typical radial HVDC link would have an energy availability of 96.5% based on estimated reliability indices from publically available data and that the submarine cable is the component which has the greatest effect on the scheme's availability. The regional HVDC grid analysed in this paper is shown to have a higher energy availability than an equivalent radial scheme, providing additional capacity is built into the grid. Furthermore, cost-benefit analysis shows the link between a scheme's availability and profitability. (6 pages)Decoupled steady-state model of the modular multilevel converter with half-bridge cells
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0232
Modular multilevel converters, based on cascading of half-bridge converter cells, can combine low switching frequency with low harmonic interference. They can be designed for high operating voltages without direct series connection of semiconductor elements. This has led to a rapid adoption within high-power applications such as HVDC, STATCOM and railway interties. Analysing the operation of these converters in the frequency domain poses a few challenges due to the presence of significant low-order harmonic voltages in the cell capacitors. This paper presents a frequency-domain model of the MMC converter with half- bridge cells, based on a two-stage approach. First, the circuit equations are decoupled by a simple linear transformation, whereby the circuit schematic can be separated into a dc-side and an ac-side part. Second, the switching operation within the phase arms is modelled in the frequency domain by iterated convolution. The model is verified against a time- domain simulation of a converter with ratings valid for HVDC applications. It is shown that the proposed methodology, where all calculations are made in the frequency domain, can accurately reproduce the results from the simulation. (6 pages)Influence of the voltage regulation on the local stability margin of the receiving node
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0096
Application of local data at receiving node of the system to estimate and control its parameters were considered in the paper. Using Thevenin model some methods were developed, analysed and simulated allowing to estimate and control stability margin and voltage level. The results can be used to construct voltage controller on basis of power electronics. (5 pages)DC fault ride-through capability and STATCOM operation of a hybrid voltage source converter arrangement for HVDC power transmission and reactive power compensation
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0343
HVDC transmission systems are becoming increasingly popular when compared to conventional AC transmission methods. HVDC voltage source converters (VSC) can offer advantages over traditional HVDC current source converter topologies; as such, it is expected that HVDC-VSCs will be further exploited with the growth of HVDC transmission. This paper presents the DC fault ride through capability and new STATCOM modes of operation for a recently published alternating arm voltage source converter (AAC) intended for the HVDC market. Operation of the converter during a local terminal to terminal short circuit of the DC-Link is demonstrated; additionally, operation of the converter as a STATCOM during the fault is also demonstrated. (5 pages)Voltage sag mitigation using a direct matrix converter
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0229
Conventional approaches for voltage sag mitigation relies on voltage source inverters (VSIs). The bulky DC link electrolytic capacitors used in VSIs are reported to be the reason behind majority of failures of these converters. Absence of these electrolytic capacitors in Matrix Converter(MC) makes it a more reliable and compact alternative than the VSIs. This paper reports the performance of MCs as a sag mitigating device for linear loads. (6 pages)Behaviour of PMSG wind turbines with fractional controllers to a voltage decrease in the grid
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0175
The effect on permanent magnet synchronous generator (PMSG) wind turbines due to grid voltage decrease and fifth harmonic is studied in this paper by computer simulations. A multilevel power converter topology and two control strategies, namely fractional and integer-order controllers, are considered in order to evaluate that effect. A comparison between the two control strategies is presented. Finally, conclusions are duly drawn. (5 pages)Study on backup protection for traction transformer
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0134
At present, gas protection and current differential protection are generally used as the main protection for traction transformer in China high-speed railway. Overcurrent protection with busbar low-voltage start-up is used as the backup protection installed at HV side and LV side of transformer. This paper introduces the principle of overcurrent protection with busbar low-voltage start-up, and then analyses its advantages and disadvantages. According to the equivalent circuit model of the traction power supply system, this paper discusses the applicable condition of overcurrent protection with busbar low-voltage start-up, and analyses the misoperation possibility of the protection when there are remote end faults or large fault resistance. Based on the requirements of backup protection for traction power supply system, a backup protection scheme is introduced in this paper. In the scheme, a two-stage overcurrent protective relay is configured as the HV side backup protection for transformer, and a distance protective relay is used as the LV side backup protection. (4 pages)Design and development of IGBT resonant inverters for domestic induction heating applications
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0360
In this paper, resonant inverters for induction heating are developed for domestic applications. The design is based on half and full bridge single phase inverter of 1 and 4 kW rating. First, the power circuits of the two topologies are analyzed using computer aided design based on Simplorer package. Then, an experimental system was built and tested using microcontroller chip (PiccoloTMS320F28027). The performances of the topologies are highlighted and assessed. The obtained results show that two systems are able to operate satisfactory under soft switching at high frequency with high efficiency. The power control is more interesting for full bridge particularly when the angle phase control is considered. Further, the experimental results agree well with those obtained with the CAD design. This validates the design model used for the purpose. The experimental system shows high integration and flexibility to incorporate other control strategies whereby higher efficiency can be achieved. (6 pages)Evaluation of perturb and observe MPPT algorithm implementation techniques
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0156
Because of its simplicity and ease of implementation, the perturb and observe (P&O) algorithm is the most commonly applied maximum power point tracking (MPPT) control scheme in photovoltaic (PV) applications. Two techniques are usually used for implementing the P&O algorithm: reference voltage perturbation where a reference value for the PV generator output voltage is used as the control parameter and direct duty ratio perturbation where the duty ratio of the MPPT converter is used directly as the control parameter. This paper presents an experimental comparison between these two techniques when used in a photovoltaic system feeding a resistive load. The influence of the step size and the speed at which the control parameter is perturbed is investigated. The various advantages and drawbacks of each technique are identified and energy utilization efficiency is calculated for different weather conditions. Practical results obtained using a 540Wp PV experimental setup show very good agreement with numerical simulations. (6 pages)An innovative oil immersed power stack for wind power conversion using series connected GCTS
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0242
A novel 450 kW DC wind power generator has been built using Active Stator technology, with an integrated oil immersed power electronic converter. The converter utilises unpackaged series connected Reverse Blocking Gate Commutated Thyristors (RB-GCT), operating at unity gain, to achieve high power density within a sealed `i-CAN' stack enclosure. The stack is cooled with synthetic ester oil which is also utilised as a liquid dielectric to provide 3 kV isolation in a small converter footprint.. The Active Stator machine is capable of operating in four quadrants for either motoring or generating. (5 pages)Matrix converter clamp current reconstruction for fault detection
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0230
Matrix converters offer advantages over traditional AC-AC conversion technologies in high temperature environments; however in system critical applications were operation is paramount, it is desirable for the converter to continue operation under fault conditions, albeit with degraded performance. There have been several works in literature on the subject of fault tolerant matrix converters however all of these methods require a method of fault localisation for continued operation in the fault condition. It is also desirable for the fault detection and localisation scheme to use existing sensors to minimise cost. This paper describes a method of fault detection and localisation using only the existing sensors used in the operation of the converter and information know by the converters modulator. (6 pages)A novel universal control scheme for multilevel inverters
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0176
This paper presents a universal control scheme for multilevel inverters to implement popular modulation strategies for any given topology. Moreover, it can also be used for charge balance control amongst the multiple input DC sources in a given topology. The concept is mathematically modelled and the scheme is demonstrated for three different topologies. Charge balance control is also demonstrated. (6 pages)Control of an AC brushless permanent-magnet machine using long supply cables
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0265
The use of a long cable between an inverter and motor is recognised as problematic and a cause of insulation failure in motors. The cable also introduces a voltage drop and phase shift in the fundamental voltage at the motor terminals, reducing the available motor torque in open-loop control, and affecting the stability of a closed-loop controller. This paper investigates the performance of a brushless, permanent magnet motor in order to determine the maximum operating distance between the motor and its inverter. The study develops simulation models of the motor in open and closed-loop modes, with and without the inclusion of a line filter. The ability to track changes in reference speed and reject torque disturbances is shown to depend on the resistance of the damper circuits in open-loop control, but is not an issue in closed-loop control. The maximum operating distance depends on cable resistance, and a practical operating limit of 2km is given for the motor-cable combination studied. (6 pages)Efficient single-phase grid-tie inverter for small domestic photovoltaic scheme
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0328
A single-phase 1kW transformer-less grid tie inverter is presented for supplying a domestic 230V ac mains supply from a 425V dc source such as a photo-voltaic solar panel array. Permutations of super-junction MOSFETs with SiC diodes and SiC MOSFETs are investigated. A new gate driver topology with isolation and energy recovery is presented. (6 pages)Protection and control system for cophase supply traction substation
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0111
To feed electric train, the structure of traction power supply system is very different from utility grid. The single-phase traction loads result in some problems, such as negative sequence, harmonics, reactive power and crossing neutral sections. Based on the existing traction power supply system, the active power filter is used to construct cophase traction power supply system. It not only eliminates neutral sections near traction substations but also compensates harmonic current and reactive power. In a perfect operation condition, seen from the HV side, single-phase and nonlinear traction load is approximately equivalent to three-phase symmetrical resistance load. The cophase power supply testing system is introduced in this paper. And also the protection and control functions for cophase traction substation are introduced. (6 pages)Space-temporal spectral relations and energy efficiency invariance laws acting in the field of inverter-fed multiphase AC drives
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0145
The study of AC inverter drives in the case when the number of their phases is more than four allows to find out some basic laws of these systems which does not manifest themselves when the phase number is equal to three or four. Two previously unknown laws of energy efficiency invariance are established in the field of multiphase (i.e. having the number of phases more than four) AC inverter drives. These laws ignoring leads necessarily to the decrease of the multiphase drive system energy efficiency. (6 pages)Fast functional modelling for 18-pulse autotransformer rectifier units in more- electric aircraft
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0205
This paper studies the development of a functional model for an 18-pulse autotransformer rectifier unit (ATRU) in a more-electric aircraft (MEA). The developed model is a non- switching model and is in the DQ0 frame. The three-to-nine phase autotransformer is simplified to a three-to-three phase transformer and then reduced to a functional model in the DQ0 frame. The rectifier is modelled as a DC transformer with commutation losses represented by an equivalent resistor. The developed functional model is simulated and compared with an ABC benchmark model, which is built from the Dymola standard library. The DQ0 model shows significant improvement in performance under both balanced and unbalanced conditions. Particularly the DQ0 model is more than 1000 times faster than the ABC benchmark model under balanced conditions. (6 pages)Simple control method for parallel connected three-phase PWM converters
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0221
This paper presents a current-controlled parallel connected three phase converters scheme. Two voltage source inverters with a front end diode rectifier are directly paralleled without intermodule reactors. The proposed method divides the switching cycle evenly between the equally rated converters, and each converter employs just one PI regulator to get good current characteristics, both in steady states and transient states. Unlike in most previous studies, the converters utilize local feedback information to obtain equal current sharing without using any circulating current control scheme. Using MATLAB/Simulink, simulation results are given to verify the control proposed. (5 pages)