Showing papers presented at "European Conference on Power Electronics and Applications in 2005"

Decentralized control for parallel operation of distributed generation inverters using resistive output impedance

Abstract: In this paper, a novel wireless load-sharing controller for islanding parallel inverters in an ac distributed system is proposed. The paper explorers the resistive output impedance of the parallel-connected inverters in an island microgrid

Control of single-stage single-phase PV inverter

Abstract: In this paper the issue of control strategies for single-stage photovoltaic (PV) inverter is addressed. Two different current controllers have been implemented and an experimental comparison between them has been made. A complete control structure for the single-phase PV system is also presented. The main elements of the PV control structure are: - a maximum power point tracker (MPPT) algorithm using the incremental conductance method; - a synchronization method using the phase-locked-loop (PLL), based on delay; the input power control using the dc voltage controller and power feed-forward; - and the grid current controller implemented in two different ways, using the classical proportional integral (PI) and the novel proportional resonant (PR) controllers. The control strategy was tested experimentally on 1.5 kW PV inverter

Active-neutral-point-clamped (ANPC) multilevel converter technology

Abstract: This paper proposes a multilevel power conversion concept based on the combination of neutral-point-clamped (NPC) and floating capacitor converters In the proposed scheme, the voltage balancing across the floating capacitors is achieved by using a proper selection of redundant switching states, and the neutral-point voltage is controlled by the classical dc offset injection Experimental results are illustrated in the paper to demonstrate the system operation

Performance of diagnosis methods for IGBT open circuit faults in three phase voltage source inverters for AC variable speed drives

Abstract: Variable speed drives have become industrial standard in many applications Therefore fault diagnosis of voltage source inverters is becoming more and more important One possible fault within the inverter is an open circuit transistor fault An overview of the different strategies to detect this fault is given, including the algorithms used to localize the open transistor Previous work showed significant differences among the available methods to detect such a fault for a mains side active rectifier This paper extends the performance evaluation for the inverter connected to the machine with variable stator voltage and frequency Simulation results are presented They show the influence of the applied standard field oriented control on the currents during a fault An experimental setup in the laboratory is used to validate simulation results Typical detection results are presented including time-to-detection measurements Robust detection of open transistor faults has been found to be possible

Space vector modulation schemes for a five-phase voltage source inverter

Abstract: Application of power electronics in electric drives enables utilisation of AC machines with a phase number higher than three. Such multiphase motor drives are nowadays considered for various applications. Multiphase drives are invariably supplied from multiphase voltage source inverters (VSIs) and adequate methods for VSI pulse width modulation (PWM) are therefore required. This paper analyses different space vector PWM (SVPWM) schemes for a five-phase VSI, which can be used for five-phase motor drives. A detailed model of a five-phase VSI is presented first in terms of space vectors. Next, the existing technique of utilising only large space vectors is elaborated. It is shown that this SVPWM method leads to generation of high amounts of low-order output voltage harmonics. Finally, a novel SVPWM method is introduced, which enables operation with pure sinusoidal output voltages up to a certain reference voltage value, which is smaller than the maximum achievable with the given DC link voltage. To enable full utilisation of the DC bus voltage, this SVPWM scheme is complemented with another one, which unavoidably does lead to generation of some low order harmonics. These harmonics are however of significantly lower values than when only large vectors are used. A detailed performance evaluation of the existing and newly developed schemes is done and it is presented in terms of quality of the output voltage waveforms. Simulation results are included throughout the paper to illustrate and verify the theoretical considerations

Technologies for increased energy efficiency in railway systems

Abstract: This article gives an overview of the various possibilities of increased energy efficiency in electrical railway systems. Not only the power systems in the main traction circuit are emphasized, but also efficient solutions arising from auxiliary-optimization, reduced weight of the vehicles, aerodynamics and efficient rail automation. The main focus is on the application of energy storage in traction systems. The stationary installation in substations is described and the advantages demonstrated in a number of applications using different main strategies. A wide and varied range of benefits arise from the typical application situation

Series connection of insulated gate bipolar transistors (IGBTs)

Abstract: High-voltage switches required in present power electronics applications are realized by connecting existing devices in series. Unequal sharing of voltage across series-connected devices can be minimized by using active gate control techniques, snubber circuits, and active clamping circuits. The primary objectives of this paper are to discuss existing voltage-balancing techniques, to present a novel hybrid voltage-balancing technique, and to optimize the number of insulated gate bipolar transistors (IGBTs) in a series string in terms of power losses. The novel voltage-balancing technique can achieve good voltage balancing with a minimum number of components and minimum total losses (i.e., IGBT losses and balancing circuit losses). This technique was validated by both simulation and experimental work. The power loss of a high-voltage switch depends on the voltage-balancing circuit and the number of IGBTs in series and switching frequency. For a given application, the optimum number of IGBTs, in terms of power losses, depends on device characteristics and switching frequency.

Medium voltage converter for permanent magnet wind power generators up to 5 MW

Abstract: Wind turbines equipped with a permanent magnet excited synchronous generator have to be connected to the utility grid via a full-scale converter. Medium voltage technology tends to be more suitable for high power systems. The flexibility of full-scale converter-based systems allows easy adaptation to different grid requirements. In recent years the continuously increasing number of wind energy plants brought into operation forced the transmission system operators (TSO) to tighten their grid connection rules in order to limit the effects on network quality. These new rules demand that wind energy plants and farms support the electricity network throughout their operation

Direct model predictive control - a new direct predictive control strategy for electrical drives

Abstract: Since more than 20 years the so-called "field oriented control" is state-of-the-art for electrical drives Strategies based on this principle fulfil nearly all demands of drive technology today Due to its basic ideas, the performance of field oriented control cannot be improved without limitations Furthermore, linear controllers always produce a continuously valued output Hence, for controlling an inverter additional components, which discretise the output of the controller, have to be inserted Predictive controllers, which allow to overcome this drawback, are known in drive control for quite a long time Nevertheless all predictive control schemes proposed for controlling electrical drives until today only precalculate the system behaviour for one single future sampling cycle Powerful control strategies like model predictive control, well-known in chemical engineering, allow higher prediction horizons, but these strategies have not yet been used for drive control This paper proposes a new predictive controller for electrical drives based on model predictive control, which allows optimal control of the inverter directly, ie without using any kind of modulator In contrast to all predictive strategies published so far for drive control, the new controller optimises the control action not only for the next sampling period, but for a longer prediction horizon

Permanent magnet synchronous generators for regenerative energy conversion - a survey

Abstract: A survey on recently installed or developed permanent magnet (PM) synchronous generators for energy conversion in regenerative and alternative power supply systems is given. Its focus is for low speed machines on geared and gearless PM generator systems for wind power plants and small PM hydro generators in gearless coupling. For distributed co-generation of heat and electrical power by micro gas turbines specially designed PM generators for high speed are necessary. Design example for both low speed wind and hydro generators and high speed generators are given along with application examples

Real-time HIL simulation of a complete PMSM drive at 10 /spl mu/s time step

Abstract: This paper presents the fastest-ever-reported, real-time (RT) simulation of an AC drive on PC-cluster The RT simulator is used to simulate a complete PMSM drive circuit in a hardware-in-the-loop (HIL) application It consists of a PMSM fed by a 3-phase IGBT inverter, a DC link capacitor and a 3-phase diode bridge This drive model runs in RT and is connected to an external controller by analog and digital inputs and outputs for closed loop operation The main innovation in this work is that the real-time simulation cycle is as low as 10 mus, which constitutes to our knowledge the shortest RT simulation time step ever reported for electric drives with this level of details in modeling the drive circuit

A combined two-method MPPT control scheme for grid-connected photovoltaic systems

Abstract: In order to increase the output efficiency of a grid-connected photovoltaic (PV) system it is important to have an efficient maximum power point tracker (MPPT) In the case of low irradiation, the perturb and observe (PO) and incremental conductance (IC) methods have a poor efficiency, because of the poor resolution in the acquired signals, when a fixed point implementation is done A cost-effective two-method MPPT control scheme is proposed in this paper to track the maximum power point (MPP) at both low and high irradiation, by combining a constant voltage (CV) method and a modified PO algorithm Simulation and experimental results are presented to verify the performance of the proposed method

Energy storage on board of railway vehicles

Abstract: The proposed energy storage on board of a railway vehicle leads to a big step in the reduction of consumed energy Up to 30% energy saving are measured in a prototype light rail vehicle, at the same time reducing the peak power demand drastically Additionally, operation without catenary for several hundred meters was successfully demonstrated with the prototype light rail vehicle driving with switched off pantograph This prototype vehicle is in passenger operation since September 2003, the implemented software is optimized on energy savings About two years experience is available and the results are convincing Applying the energy storage to diesel-electrical multiple units leads to fuel savings and provides a "booster" effect on the acceleration performance The stored energy is adding additional power on top of the diesel engine power during acceleration Compared to original diesel power, this additional power can be provided with a relatively low additional weight Finally, the energy savings of up to 30% and the corresponding emission reduction will already fulfill the targets of various local and global energy saving programs set up by eg European Union and big railway operators

Converter used as a battery charger and a motor speed controller in an industrial truck

Abstract: This paper presents a bi-directional power converter used on one hand as a battery charger and on the other hand as a motor speed controller. Different possibilities are presented and a comparison of these structures is carried out. In battery charger mode, the power converter has to absorb a sinusoidal current with a unit power factor. According to the power range, two possibilities are presented: the isolated CUK converter with a 1.5 kW DC motor and a pulse width modulation (P.W.M.) inverter/rectifier to supply a 6 kW induction machine

The state-of-the-art of active filters for power conditioning

Abstract: Unlike traditional passive filters, active filters for power conditioning have multiple functions such as harmonic filtering/damping/isolation/termination, load balancing, reactive-power control for power factor correction and voltage regulation, voltage-flicker reduction, or their combinations Significant cost reductions in both power semiconductor devices and signal-processing devices have inspired many manufactures in Japan, Europe and the United States to put active filters on the market This paper deals with active filters for power conditioning, and specifically hybrid active filters for harmonic filtering of three-phase diode rectifiers

Comparison of fault ride-through strategies for wind turbines with DFIM generators

Abstract: Regenerative energy systems are confronted with increasing demands for power quality and fail-safe operation at grid voltage failures. Grid codes currently demand for fault ride-through (FRT) capability up to 15% retaining voltage and support of the grid voltage by supplying reactive current until fault clearance. The paper discusses and compares different FRT strategies, their capabilities to fulfill the codes and their impact on turbine performance

Double-sided low-temperature joining technique for power cycling capability at high temperature

Abstract: There is a demand for higher junction temperatures in power devices, but the existing packaging technology is limiting the power cycling capability if the junction temperature is increased. Limiting factors are solder interconnections and bond wires. With Replacing the chip-substrate soldering by low temperature joining technique, the power cycling capability of power modules can be increased widely. Replacing also the bond wires and using a double-sided low temperature joining technique, a further significant increase in the life-time of power devices is achieved

On DC injection to AC grids from distributed generation

Abstract: Distributed generation, DG, introduces multi-generator grids and new modes of operation. DG will likely introduce power electronic, PE, converters on a large scale at the low- and medium-voltage levels. DC injection into the AC grid is a threat from grid-connected PE converters that are badly structured. Low DC currents in AC current are difficult to measure at those low levels decided in IEEEtrade 1547 and discussed in other international working groups. Transformers and PE can be co-designed to eliminate DC injection. Modern adjustable-speed drives, ASDs, especially, those with active rectifiers, form a basis to discuss and solve issues of DC injection to AC grids from DG also named distributed energy resources, DER or even DR. DC components from power electronics, embedded in solar power, wind power, energy storage, smart houses, smart-office buildings, own generators, etc. give rise to grid-aspects like AC components give frequencies around the fundamental one. FMEA, failure mode and effects analysis, is judged to be a tool for further synthesis

Control of a doubly-fed induction wind generator under unbalanced grid voltage conditions

Abstract: Wind energy is often installed in rural, remote areas characterized by weak, unbalanced power transmission grids. In induction wind generators, unbalanced three-phase stator voltages cause a number of problems, such as overheating, over-current, and stress on the mechanical components from torque pulsations. Therefore, beyond a certain amount of unbalance, induction wind generators are switched out of the network. This can further weaken the grid. In doubly-fed induction generators, control of rotor currents allows for adjustable speed operation and reactive power control. In addition, it is possible to control the rotor currents to correct for the problems caused by unbalanced stator voltages, including torque pulsations and unbalanced stator currents. This paper presents a novel voltage mode controller design for a doubly-fed induction generator that provides variable speed, reactive power control. Also, under stator voltage unbalance conditions, the proposed control eliminates torque pulsations and draws more balanced currents from the utility

Comparison of three phase current source inverters and voltage source inverters linked with DC to DC boost converters for fuel cell generation systems

Abstract: Three phase current source inverters (CSI) and voltage source inverters linked with a DC to DC boost converter (VSI+BC) are appropriate solutions to convert electrical energy for distributed fuel cell generation systems. The performance of CSI's and VSI+BC's in this application is shown and both topologies are compared to each other concerning their power semiconductor design rating and their semiconductor power losses

Analysis of a 300 MW variable speed drive for pump-storage plant applications

Abstract: A 300 MW drive system consisting of a cyclo-converter driven doubly-fed induction machine for pump-storage stations operating in Goldisthal, Germany, is presented. The cyclo-converter supplied by ALSTOM is one of the largest in the world. Major benefits of this innovative concept are the increase of the turbine efficiency by means of speed variation and the high dynamic power control for the stabilisation of the grid. Major benefits compared to classical approaches are identified. Emphasis is placed on the behaviour of the drive at grid failures. A new modified topology is proposed to meet the grid code requirements at various grid failures

High frequency power switch - improved performance by MOSFETs and IGBTs connected in parallel

Abstract: For many high power applications semiconductors are desirable which combine the excellent switching characteristics of a MOSFET with the good conducting behaviour of an IGBT This paper presents hybrid power switches for higher frequencies with an improved performance based on the parallel connection of corresponding MOSFETs and IGBTs The objectives are to combine the advantages of both the unipolar and the bipolar power semiconductors by avoiding the drawbacks of these different semiconductor types The proposed hybrid power switches have been analyzed in a hard-switching converter under different operation conditions as well as in a ZVS inverter with resonant load For this different IGBT types have been connected in parallel to super-junction MOSFETs The performances of the resulting power switches depend strongly on the chip structure and the conductivity modulation of the bipolar devices In this paper these dependencies and their effects have been taken into account

Crowbar control algorithms for doubly fed induction generator during voltage dips

Abstract: The paper presents different control strategies of the crowbar protection when a variable speed wind turbine based on a doubly fed induction machine is generating electrical energy during a voltage dip in the grid. The proposed control strategies provide the wind generator with the capacity for don't disconnect from the grid while a voltage dip occurs, and return to the normal operation conditions. This is achieved by a protection circuit called crowbar. In addition, complementary control algorithms for flux damping and voltage recovery are proposed. Finally, the presented control strategies are validated in simulation for a 1700 KW generator

A fast power loss calculation method for long real time thermal simulation of IGBT modules for a three-phase inverter system

Abstract: A fast power losses calculation method for long real time thermal simulation of IGBT module for a three-phase inverter system is presented in this paper. The speed-up is obtained by simplifying the representation of the three-phase inverter at the system modelling stage this allows a inverter system to be simulated predicting the effective voltages and currents whilst using large time-step. An average power losses is calculated during each clock period, using a pre-defined look-up table, which stores the switching and on-state losses generated by either direct measurement or automatically based upon compact models for the semiconductor devices. This simulation methodology brings together accurate models of the electrical systems performance, state of the art-device compact models and a realistic simulation of the thermal performance in a useable period of CPU time and is suitable for a long real time thermal simulation of inverter power devices with arbitrary load. Thermal simulation results show that with the same IGBT characteristics applied, the proposed model can give the almost same thermal performance compared to the full physically based device modelling approach

Novel lumped-parameter thermal model for electrical systems

Abstract: The lumped parameter thermal model has been used for a long time for calculating the temperature rises in electrical systems (e.g electrical machines or power electronic systems). As is known, this method is used to solve thermal problems by applying thermal networks, in analogy to electrical circuits. In spite of being popular, generally this method is not applied correctly for elements with distributed heat generation. It is shown that loading the thermal model with the total power losses leads to wrong results. In this paper, a correct lumped-parameter method is developed and explained

Hybrid energy storage systems based on compressed air and supercapacitors with maximum efficiency point tracking

Abstract: Beside the high-capacity storage facilities based on hydro-power technologies, electrochemical solutions are the today's candidate for storage for renewable energy sources. However, limited life-cycles and sustainability of batteries are often inhibiting factors. This paper presents a hybrid energy storage system with high life cycle, based on compressed air energy storage (CAES). The storage and discharge are done within maximum efficiency conditions. As the maximum efficiency conditions impose the level of converted power, an intermittent time-modulated operation mode is applied to the thermodynamic converter to obtain a variable converted power. A smoothly variable output power is achieved with the help of a supercapacitive auxiliary storage device used as a filter. The paper describes the concept of the system, the power-electronic interface circuits and especially the maximum efficiency point tracking (MEPT) algorithm and the strategy used to vary the output power. In addition, the paper describes the principles of higher efficiency storage systems where the air machine is replaced by an oil hydro-pneumatic converter, used under isothermal conditions. Practical results are reported, that have been recorded from a low-power pneumatic motor coupled to a small DC generator for the purely pneumatic system, and from a first prototype of the oil-hydraulics and pneumatic system. Some economical considerations are also made, through a comparative cost evaluation of the presented hydro-pneumatic systems and a lead acid batteries system, in the context of a stand alone photovoltaic home application. This evaluation confirms the cost effectiveness of the studied hybrid storage systems

Impacts of cross-saturation on sensorless control of surface permanent magnet synchronous motors

Abstract: Cross-magnetisation complicates the sensorless control of non-salient AC machines, like surface magnet synchronous motors. The motor currents influence position estimation techniques for low speed based on "saturation induced" saliencies. This paper considers cross-saturation effects to explain the magnetic-axis shift under loaded conditions and discusses the influence of the operating point on the saliency. A finite element analysis and lab measurements validate the results

Comparison of single and two stage topologies for interface of BESS or fuel cell system using the ABB standard power electronics building blocks

Abstract: The two most popular topologies used to interface the DC voltage sources such as battery energy storage systems (BESS), fuel cells with the AC network are the single and two stage topologies. In case of the single stage topology the BESS or the fuel cell system is directly connected to the dc link of a voltage source converter and the voltage source converter is interfaced to the low voltage grid with a transformer. A two-stage solution is realized using a DC-DC conversion stage followed by a DC-AC conversion stage. The DC-DC stage boosts the DC voltage so that the DC-AC stage can be directly interfaced to the low voltage grid. Detailed comparison of these topologies is carried out using battery voltage and the installed power as variables. The commercially available ABB standard Lopak PEBB's are used for comparison of the topologies. Both solutions are offered by ABB mainly depending on the dc voltage level of the BESS

High power medium voltage drives - innovations, portfolio, trends

Abstract: The paper gives an overview over high power medium voltage drive inverters in the range between one and one hundred megawatts. First the applications and their key requirements are summarized. Then the available power semiconductors and the different inverter circuit topologies with their different properties, advantages and drawbacks are presented. The key features are compared and suitable converter types for the applications and industry branches are identified. Finally, future trends of technology, manufacturing and market are outlined