Wlodzimierz Koczara

DFIG-Based Power Generation System With UPS Function for Variable-Speed Applications

The power generation system with a doubly fed induction generator (DFIG), which can be used as an autonomous power system after the loss of mains in a distributed generation network, is described. After the mains outage, a fixed frequency and an amplitude of the output voltage are obtained, despite the variable rotor speed. For this reason, it can be successfully applied in the variable-speed wind turbines, adjustable speed water plants, or diesel engines. Moreover, the stand-alone operation of DFIG is useful in a flywheel-based high-energy rotary uninterruptible power supply system. An output voltage is controlled directly by the synchronization of an actual voltage vector with the reference vector represented in a synchronously rotating polar frame. The rotor current angular speed is obtained as a result of vectorial phase-locked loop operation. Any sensors or estimators of the rotor speed or position are unnecessary. Both amplitude and angle control loops are linear. The use of stand-alone operation in grid-connected systems requires mains outage detection. Also, the grid voltage recovery requires a method of synchronization and soft connection of a generator to the grid. The proposed methods of output voltage control, synchronization, and detection of mains loss were tested in a laboratory system.

Sensorless Direct Voltage Control of the Stand-Alone Slip-Ring Induction Generator

In this letter, a stand-alone power system with doubly fed induction generator is described. Direct voltage control based on the stator voltage vector, represented in rotating polar frame, does not need any feedback from the rotor speed or position. Using positive- and negative-sequence components, an unbalanced load can be supplied

Unity power factor three phase rectifiers

Boost and multilevel boost three phase rectifiers are described, and the states of operation are discussed. Hysteresis current control is addressed, and the results of simulations and laboratory tests are presented.<<ETX>>

Sensorless direct voltage control method for stand-alone slip-ring induction generator

A control method for stand alone mode operation of doubly fed induction generator is presented. The method bases on the stator voltage vector control represented in the synchronously rotated polar coordinates. The generated stator voltage is controlled by rotor currents. Amplitude of stator voltage and its frequency are controlled independently. The output signals from the voltage and the frequency regulators are the reference signals for the rotor current amplitude and frequency. This way, in spite of the variable generator speed, the fixed stator voltage amplitude and frequency, and controlled voltage phase are achieved. Developed direct voltage control method permits the DFIG the stand alone and the grid connected operation. After the mains outage the DFIG instantly supplies loads. Methods of supply grid voltage faults detection are developed. One method bases on the generated voltage vector amplitude, whereas a second bases on the voltage frequency. Both methods allows soft transients of generator disconnection from the grid. The controlled voltage phase permits for soft synchronization and grid connection after the mains reappearing. This way the load is protected from voltage phase rapid change. Applied methods allows the load to be uninterruptible supplied. Topology of power system, controller operation and results from laboratory tests of the DFIG are presented in the paper

Novel hybrid load-adaptive variable-speed generating system

Light loading of generator sets has long been the cause of accelerated aging and premature engine failure. This problem is exacerbated by impact and nonlinear loads because generator sets are oversized to cope with this condition whilst maintaining the voltage within the specified limits. A new hybrid engine-friendly load-adaptive variable speed generating system has been developed which decouples the engine from the load by means of a decoupling converter. The engine load torque can be precisely controlled independently of the load so that optimal engine operation is achieved for a wide range of load power demands. Test results show outstanding performance under the worst load conditions, superior to that of comparable systems.

Sensorless stand alone variable speed system for distributed generation

The following paper presents a variable speed stand alone power generating system. The system consists of a double fed induction machine and power electronic converter connected to the rotor. A topology and a control system allow for stand alone operation. An external power source was used for preliminary excitation. After that, the system can operate autonomously and take excitation power from the stator. The control system is based on stator voltage space vector referred to rotating frame. The speed of the rotating frame responds to stator frequency. The system is controlled by rotor current which amplitude is adjusted by controller of the stator voltage component related to x axes, whereas the rotor current frequency is controlled by stator voltage component related to y axes. In this way the stator output voltage frequency is speed independent and the control system operates without any mechanical sensor. For design a simulation program PSIM with DLL files is applied. The results of controllers calculation in a wide speed range are presented. A laboratory system was built and tested. As a controller a DSP SHARC/sup /spl trade// system with support ALTERA/sup /spl trade/// FPGA is used. The results of the laboratory tests present the generating system in transients when a step load is applied.

An application of PSIM simulation software for rapid prototyping of DSP based power electronics control systems

The paper presents power electronics research opportunities provided by PSIM simulation software and high performance floating point DSP controller. Advantages of PSIMs C/C++ modeling capabilities are shown by modeling of DSP controller runtime environment (RTE). Thanks to this feature source code of control algorithm targeted for the DSP can be embedded in power electronics circuit simulation. Therefore, more detailed system description can be built As a proof of this idea, simulation as well as experimental results of sensorless active rectifier control are provided.

Multilevel boost rectifiers as a unity power factor supply for power electronics drive and for battery charger

Single and three phase boost rectifiers operate with unity power factor and low switching frequency when a multilevel controller is used. A novel structure for multilevel control is proposed. Single phase systems operate mainly as a force commutated rectifier however line commutation is very useful especially for zero crossing supply voltage because, during overlapping, current rate is high and harmonics are reduced. In a three phase system the multilevel control is achieved by using 9 active switches. A method based on a comparison reference and available current rates or comparison voltage drops on supply side inductances is proposed to evaluate the rectifier controllability. Results of simulation and laboratory tests confirm a unity power factor.<<ETX>>

Application of a permanent magnet machine in the novel Hygen adjustable-speed load-adaptive electricity generating system

Hygen is an adjustable-speed load-adaptive electricity generating system comprising one or more energy sources, e.g. an engine-generator unit, an energy storage means and a power electronic converter system with microprocessor control. A medium frequency permanent magnet alternator is integrated into a diesel engine to form a compact generator unit. A variable-ratio boost rectifier converts the variable voltage/frequency of the generator unit and regulates the output as required by the converter system. This combination provides a compact and efficient energy delivery sub-system with many benefits.

Theory of the adjustable speed generation systems

Purpose – The purpose of this paper is to provide a new theory of adjustable speed decoupled generation which has the potential to challenge existing coupled generation based on a classical synchronous generator operating with fixed speed.Design/methodology/approach – The papers approach is a theoretical consideration of the drawbacks of conventional fixed speed generation based on a synchronous generator and proposal of problem solutions by the introduction of a decoupled generation system with additional degree of freedom. Computer calculations are used as design and for preliminary verification. Tests in a real laboratory system equipped with modern components such as electrical machines and power electronic converters proved the theory.Findings – Decoupled generation is realized in a very original way using new blocks, integration method and control. The developed system has been awarded more than six world patents. The system has additional degrees of freedom in speed and grid connection operation.O...