Thyristor Inverter Research Articles

Features of operation of ship electrical power systems with electrical propulsion systems

THE PURPOSE. Consider the issue of the presence of distortions in the form of sinusoidal voltage and current in autonomous electrical power systems with electrical propulsion systems, built on the principle of the unified electric power system. Compare the results of the study of voltage distortion for electrical power systems with electrical propulsion systems of various structures and give recommendations for their application.METHODS. For research, unified electric power systems with DC electrical propulsion systems on the Yeysk ferry and alternating current on the asymmetric icebreaker Baltika are considered. The possibilities of programming with frequency control of modern drives of rudder propellers with AC motors are analyzed.RESULTS. Oscillograms of voltages and currents of generators were obtained using thyristor converters and inverters to control electrical propulsion systems in various modes. Significant ripples and distortions of the sinusoidal voltage and generator currents were noted when thyristor converters are used to power DC propulsion electric motors. Also, small deviations from the sinusoidal form of the ship's network voltage were recorded when inverters were used to control AC propulsion motors as part of rudder propellers.CONCLUSION. The issue of ensuring the quality of electricity produced in autonomous electrical power systems of sea vessels is of great relevance and importance. To ensure the best results, it is advisable to use azimuthing podded drive with AC electric motors, the rotation speed of which is implemented by inverter frequency converters with a DC link.

Experimental Studies on Dynamic Performances of Wind Power Plants Composed of Series-Connected Wind Generators and Synchronous-Compensator-Commutated Thyristor Inverter

Dynamic performances of wind power plants composed of series-connected wind generators and synchronous-compensator-commutated thyristor inverter were studied experimentally and by simulation. A series of experiments were carried out with an experimental setup composed of series-connected two sets of thyristor rectifiers with permanent magnet synchronous generators (PMSGs) as wind turbine generators and current-source thyristor inverter having synchronous compensator. The individual PMSG is driven by a vector-controlled induction motor that can simulate the characteristics of a wind turbine. A startup method for the wind power plant is explained, and the usefulness of this method is shown. Also, experimental studies were carried out on the effects of the moment of inertia of the wind turbine/generator on the dynamic responses, such as the tip speed ratio of the wind turbine. Furthermore, the dynamic simulations are performed under the same conditions as the experiments, and the similar results are obtained. It is shown that the dynamic performances can be discussed through both the experimental setup as well as the computer simulation.

A Combined Frequency Converter for Soft Acceleration of Induction Electric Drives with Heavy Starting Conditions

The usability of a thyristor frequency converter with a supplementary controlled series compensator for soft starting of induction motors with high torque of inertia of actuating mechanisms is considered as an alternative to transistor converters. It is shown that the supplemental device, in the form of a transistor–capacitor convertor, can be considered as an adjustable capacitor, the equivalent capacitance of which can be varied from very large values (to a maximum of infinitely large) to some fixed minimum value. The voltage of an adjustable series capacitor provides the desired switching conditions of thyristor inverter, and the capacitive reactance ensures the compensation of reactive power consumed by the induction motor and thyristor inverter, reducing the current load of the motor and converter. The addition of a thyristor current converter with a controlled series compensator of reactive power in the form of a transistor–capacitor unit makes it possible to carry out a soft start of induction motors similar to the starting modes of synchronous machines. Simulation results confirming the achievement of the desired effect are presented. It is shown that the supplemental device in the form of transistor–capacitor converter is a robust system well adaptable to various conditions of electric-drive operation. The functional equivalence of a transistor frequency converter and thyristor frequency converter with a supplemental transistor–capacitor unit with a substantially lower cost of the latter makes possible a new mechanism for soft starting of powerful electric drives with induction motors under conditions of high torques of inertia of actuating mechanisms.

Comparative Study of Frequency Converters for Doubly Fed Induction Machines

The efficient utilization of energy sources seems to be one of the most challenging problems for designers and scientists alike. This challenge particularly applies to power electronics, where the increasing value of energy density leads to demands for optimization processes and better exploitation (and distribution) of available power sources. As a result, the implementation of frequency-controlled systems is more often in the spotlight. The systems with doubly fed induction machines and a frequency converter in the rotor circuit are typical representatives of these demands. In a wide spectrum of power electronic systems, frequency converters are often used that have a constant current, a diode rectifier, and a thyristor inverter. This article provides a novel approach to modeling methodology, and presents a unique comparison of four different frequency converter schemes that are connected to a doubly fed induction machine. This article presents the modeling methodology itself, as well as the results based on an asynchronous generator motor fed by different frequency converters, a spectral analysis of the output voltage of the used frequency converters, and a comparison of the different technologies. Based on the above, this paper recommends the use of a multistage-multilevel frequency converter scheme.

Design and Implementation of a Hybrid System for the Mitigation of PQ Problems of Medium-Frequency Induction Steel-Melting Furnaces

This paper describes a hybrid system for the mitigation of power quality (PQ) problems of medium-frequency coreless induction steel-melting furnaces. The hybrid system is composed of passive shunt-detuned filters and a hybrid active power filter (HAPF). Since the single-phase load-resonant thyristor inverter of the work coil operates at variable frequency and supplied from a multipulse thyristor rectifier, interharmonic current components, due to cross-modulation phenomenon across ac–dc–ac link, appear in supply lines. The frequencies of these interharmonics are migrating in time over a wide range, and they interact with passive shunt LC filters and other power-system components resulting in harmful effects on the overall system. Reactive power compensation of medium-frequency coreless induction steel-melting furnace is achieved by passive shunt-detuned filter banks, thus avoiding the amplification risk of interharmonic current components. Interharmonics are satisfactorily suppressed by a HAPF with K control strategy. The performance of controller is improved by modifying the conventional K control strategy and adding feedforward control loops for dominant characteristic harmonics. The resulting hybrid system is operating in a steel-melt shop successfully since March 2013.

A method for improving the energy efficiency of an alternating current electric locomotive in the regenerative braking mode

A method for improving the power factor of an ac locomotive with the commutator motor operating in the regenerative braking mode is proposed. The method improves the control system algorithm of the power converter. The new switching method of inverter thyristors regulates the curve of the instantaneous power during the main switching. It allows reducing the period in which the energy flow passes to the locomotive, leading an increase in the average value of the instantaneous power. A “traction substation–electric traction network–locomotive in the regenerative braking mode” mathematical model is presented to verify efficiency of the method. The model consists of several interacting electric power substations, a section of electric traction grid, a locomotive power transformer, a four-zone inverter, a control system of reversible converter, and a dc circuit. The model is realized in the OrCAD software.

Performance Optimization of a Three Phase Inverter Thyristor

Performance Optimization of a Three Phase Inverter Thyristor

Studies on a Hybrid Wind Turbine Generating System Using a Current‐Source Thyristor Inverter

SUMMARYA practical‐scale hybrid wind turbine generating system is developed for generating a constant output power even when the wind velocity fluctuates. The system consists of a wind turbine synchronous generator (SG), a rectifier, a current‐source thyristor inverter, an SG driven by a prime mover, and a duplex reactor. A high‐quality output voltage waveform is always obtained from the system, which has a very simple configuration. Experimental results show the feasibility of the system. A model of the system is also developed to predict the dynamic performance when the system conditions such as the wind velocity and load are changed, and good agreement between the simulated and experimental performance is observed, confirming the validity of the dynamic model.

Studies on a Wind Turbine Generating System that Employs a Thyristor Inverter

SummaryA new wind turbine generating system that employs a current‐source thyristor inverter is proposed, and the steady‐state and dynamic performances for a practical system are discussed. The proposed system is essentially based on the shaft generator system that is widely used in large ships, and it has many features such as high reliability and generation of output power of high quality. It is shown that electric power with constant frequency and voltage with low distortion can be obtained by using this novel system despite the changes in the velocity of natural wind. A dynamic model of the system is also developed, and a good agreement between simulated and experimental performances is obtained, thereby confirming the validity of the model.

A study of a single-phase thyristor inverter

The results of studying the switching processes in a single-phase thyristor inverter operating at a low-voltage controlled thyristor rectifier with constant output current are given. Depending on the angle of rectifier voltage regulating, three switching modes are identified and considered. The maximum values of currents and voltages are defined for each of the modes. The waveforms of currents and voltages are given. It is shown that the nature and duration of the inverter switching processes depend strongly on the angle of rectifier regulating, which is especially to be considered when the inverter operates at higher frequencies.

Comparing the Quality of Power Generated from DFIG with Different Types of Rotor Converters

In this paper the quality of power generated from wind energy conversion system employing a double fed induction generator (DFIG) is investigated. The DFIG performance is tested with 3 types of converters interfacing the rotor with the grid. These are: the six-step thyristor inverter with diode rectifier, six-step IGBT inverter with diode rectifier, and 3-level IGBT-PWM inverter with diode rectifier. The harmonics in current and voltage, power factor value, and the transient behavior in each system are investigated and compared. Comparison is done at sub-and super-synchronous DFIG operational speed. In the system with lowest power quality passive filters or LC filter are added and improvement in system performance is recorded. From this study the optimum system from point of view of cost and control complexity is concluded.

Effects of System Parameters on the Performance Characteristics of a Wind Turbine Generating System Using a Current-Source Thyristor Inverter

The effects of various system parameters on the performance characteristics of a wind turbine generating system using a current-source thyristor inverter are investigated. The configuration of the system and a simulation model for predicting the dynamic performances of the system are first explained. Then, the effects of various parameters of the system, such as the short-circuit ratio of the synchronous compensator, on the steady-state characteristics and the dynamic performances of the system are discussed.

Studies on a Wind Turbine Generating System that Employs a Thyristor Inverter

A new wind turbine generating system that employs a current-source thyristor inverter is proposed, and the steady-state and dynamic performances for a practical system are discussed. The proposed system is essentially based on the shaft generator system that is widely used in large ships, and it has many features such as high reliability and generation of output power of high quality. It is shown that electric power with constant frequency and voltage with low distortion can be obtained by using this novel system despite the changes in the velocity of natural wind. A dynamic model of the system is also developed, and a good agreement between simulated and experimental performances is obtained, thereby confirming the validity of the model.

Development of a dc 1 MV power supply technology for NB injectors

Major issues of neutral beam (NB) injector power supplies are high-speed switching, regulation and transmission of dc ultra-high voltage (UHV) and suppression of surge energy input to the beam source at high voltage breakdown. A gate turn-off thyristor inverter type power supply where the control is performed on the low voltage ac side was designed for the ITER NB. Based on the remarkable progress of a high power IEGT (injection enhanced gate transistor), the design of the inverter has been modified to increase efficiency and compactness using such new elements. The power loss in the inverter is reduced to 0.5 MW from 1.6 MW by adopting the IEGT inverter system at the same frequency of 150 Hz. Further, power supply performance has been studied for higher frequency operation of the inverter at 300 Hz. It was confirmed that the voltage regulation was stable even when the filter capacitor was reduced to 1/5 of the original value by circuit simulation. For the transmission line of the dc UHV with intermediate voltages, a disc shape multi-conductor bushing with a transmission line test chamber has been developed. The dimensions of the bushing are 1.8 m (diameter) and 140 mm (thickness) at the edge. Electric fields at the conductor surface and insulator surface were designed to be lower than 5 kV mm−1 and 7 kV mm−1, respectively. An electric field at the bottom of the ground potential outer conductor was designed to be lower than 1.2 kV mm−1 to prevent particle levitation which triggers breakdown. The prototype transmission line has passed the lightning impulse test up to 1300 kV. A dc UHV up to 1175 kV was successfully sustained for 300 s. To prevent electric damage of the beam source at high voltage breakdown, core snubbers using Fe-based nanocrystalline soft magnetic materials have been adopted to dissipate the surge energy.

Low-cost current-fed PMSM drive system with sinusoidal input currents

Standard low- and medium-power drives are based on the voltage-source converter topology. There has been less research work on dual topology drives, based on a current-fed inverter structure. Although energy storage is more efficient in capacitors than in inductors, due to some inherent advantages of current-source converter topology, and at the first place, the absence of a dc-link electrolytic capacitor, a current-source drive system made with a considerably reduced dc link inductor could be better low-cost solution with improved reliability, lifetime, and transient response than conventional drive. This paper is about a new current-fed drive topology with sinusoidal input currents, which is applied to a permanent-magnet synchronous machine in low-cost applications. A three-switch front-end pulsewidth modulator buck rectifier with an appropriate control technique, a simple thyristor inverter at the output, together with a small dc choke (which can be embedded in the machine), virtually offers an inductorless integrated drive system solution and could challenge standard industry solutions. System description, analysis, design guidelines, simulated results, and measured experimental results will be presented.

Control of a Hybrid Asymmetric Multilevel Inverter for Competitive Medium-Voltage Industrial Drives

In symmetric multilevel inverters, there is a tradeoff between the output quality and the reliability and efficiency of the converter. New asymmetric and hybrid solutions, using different voltages and devices in various parts of the inverter, promise significant improvements for medium-voltage industrial drives. This paper investigates such a hybrid asymmetric nine-level inverter. It consists of a three-phase three-level integrated gate-commutated thyristor inverter (main inverter), with a two-level insulated-gate bipolar transistor H-bridge (subinverter) in series with each phase. To keep the power part simple and the efficiency high, the subinverters have no feeding from the net and can only supply reactive power. This is a very interesting solution in terms of power quality, efficiency, reliability, and cost. But the nonsupplied intermediate-circuit capacitors form an unstable system. This paper proposes a control method to stabilize their voltages. Power balancing is guaranteed by varying the common-mode voltage, using an online nonlinear model-predictive controller. The controller predicts the system evolution as a function of the control inputs. A cost function of system and control quantities is iteratively minimized in real time, to find the optimal control to apply to the system. Simulations and measurements demonstrate stable behavior in steady state and during transients. Precharging of the nonsupplied capacitors is also an issue to consider. This paper proposes a startup method that charges them in parallel with the supplied ones, without any additional equipment. Measurements show its successful application in the proposed drive system.

A Simple Energy Recovery Circuit for High-Power Inverters With Complete Turn-On and Turn-Off Snubbers

This paper presents and analyzes an active energy recovery circuit for the inductive turn-on snubber and capacitive turn-off snubber used on high-power gate-turn-off thyristor inverters. The circuit performs as a simple switched-mode power supply and recovers the inductive and capacitive snubbers energy induced in power inverters back into the dc rail with the aid of an extra switch. The features and operation of the proposed circuit are given and supported by PSpice simulations and experimental results.

Current source thyristor inverter and its active compensation system

A grid-commutated thyristor inverter based power electronic interface for a direct-drive modular permanent magnet generator in a variable-speed wind energy conversion system is described. The AC/DC/AC power electronic interface consists mainly of a diode rectifier and a thyristor inverter. The inverter ignition angle can be adjusted continuously to control turbine speed so that the optimal energy capture is achieved. The reactive power and harmonic characteristics of the thyristor converter system have to be compensated to meet the standards for grid connection. An active compensation system is discussed to minimise the harmonic distortion and to provide reactive power control. A simple method of deriving the reference current for the active compensator is proposed on the basis of optimal operation conditions. Several compensation schemes are considered. Experimental results from a laboratory model are presented along with computer simulation results, which are in good agreement.

Transient Performance Analysis of Shaft Generator Systems

A shaft generator system, which consists of a shaft generator, a rectifier, an externally commutated thyristor inverter, an ac reactor, and a synchronous compensator, is widely used in a ship to feed sufficient power to the electric apparatus by using a part of the power produced by the main engine. We have already analyzed the steady-state performances of this type of generating system in some detail. However, transient characteristics of the shaft generator system have been investigated little.In this paper, transient performances of the shaft generator system are analyzed in detail. A set of transient equations is derived first for the systems with ordinary ac reactor or duplex reactor to achieve output voltage without distortion, and a block diagram representation of the equations is then obtained. Transient responses of the system when the load was changed are calculated through the diagram and compared with experimental results. Also, the block diagram is modified to take the effects of the magnetic-saturation phenomenon of synchronous compensator into account to obtain an accurate simulated result. Moreover, the effects of the duplex reactor and inertia constant of synchronous compensator on the transient responses are clarified for the cases when various system variables are changed.

Soft-switched current-source inverter for single-phase utility interfaces

A novel soft-switched current-source inverter for single-phase utility interfaces is presented. To provide the soft-switching capability under the pulsewidth modulation for a single-phase line-commutated thyristor inverter, an auxiliary resonant switch to bypass the current on the DC side is connected across the DC input of a thyristor inverter.