Converter Control System Research Articles

Development of a relay-vector control system for a multi-phase semiconductor converter of electric energy

A system of relay-vector control of current in the circuit of a polyphase electric machine has been developed. For this, on the basis of the analysis of electromagnetic processes in a multiphase semiconductor converter of electrical energy, its discrete mathematical model was created, which takes into account the redistribution of electromagnetic energy by individual spatial harmonic components, depending on the number of phases. Using this mathematical model, a method for relay control of spatial harmonic components of the input current of the converter in the “tube” has been developed. The formation of polyharmonic currents in each of the phases, conjugated in shape and phase with the voltage supplying the converter at each control period, is carried out by means of the optimal voltage vector of the semiconductor switch. To select the optimal control action, the objective function of the minimum deviation of the projections of the base voltage vectors of the semiconductor switch for the j-th combination of the state of the keys from the calculated control action determined by the mathematical model is used. An objective function of this type allows one to take into account different values of the amplitudes of the base voltage vectors of the semiconductor switch in the transformed orthogonal coordinate systems. In this case, there is no need to predict changes in the instantaneous values of the input current for one or two periods ahead, which is ensured by a decrease in the number of iterations to determine the optimal control action. To check the developed provisions, a simulation model of a nine-phase semiconductor converter of electrical energy with a relay vector control system was created. The results of the study of the model confirmed the adequacy of the developed technical solutions, the use of which will ensure the most complete realization of the own advantages of a multiphase electric machine in order to generally improve the weight, size and energy indicators of the autonomous power supply system.

Multi-loop current control strategy based on predictive control for multiphase pulse power supplies

For high-power quasi-continuous laser drivers, the switched pulse power supply (PPS) is a promising technique due to its higher efficiency when compared with linear drivers. However, there are some digital control challenges with high precision, fast response and zero overshoot during the flat-top current stage. To promote the use of a switched PPS, this paper proposes a digital control strategy based on predictive current control under a multiphase PPS converter circuit. The key of the proposed control strategy is that predictive inner current control is only used for the master phase circuit. Meanwhile, the current sharing control is used for balancing the phase currents, and the setting outer current controller is used for keeping the whole converter control system stable and robust. Furthermore, to obtain fast and precise current tracking, a predictive average current control independent from the load values is derived. Moreover, a reducing gain method is applied to guarantee the stability of the inner current control. When compared with the conventional multiphase control, the proposed strategy possesses a faster dynamic response and a higher accuracy. In addition, it is more flexible under digital control implementation. A 360 W dual-interleaved PPS prototype is utilized for verifying the effectiveness of the proposed control strategy.

Applying Synchronous Condenser for Damping Provision in Converter-dominated Power System

The dynamic characteristics of converter-dominated systems are governed by controlling power converters and the interactions between converter systems and conventional alternators. Frequency oscillations can appear under dynamic operation conditions caused by the phase-locked loop dynamics and interactions among the converter control systems. The oscillations may be poorly damped, which can result in reduced power generation, longer settling time, or disconnections of sensitive components. It is foreseeable that damping services will be critical for power grid stabilization in the future with high penetration of renewable generation. In this work, synchronous condensers (SCs) are evaluated and applied to provide damping services to the power grid under post-event conditions. An innovative supplementary controller for the automatic voltage regulator of SCs is proposed to improve the frequency stabilization in a converter-dominated system after disturbances. Using local and remote measurements, SCs are able to modulate the reactive power output and hence, the terminal bus voltage, which further impacts the power flow in the system; therefore, damping can be provided to the frequency oscillations. The control is implemented on an industrial-level hardware platform, and the performance is verified by the hardware-in-the-loop simulation.

Estimation of Damage Rotor Shaft of Turbogenerators with a Diode Brushless Excitation System

The damage to the rotor shafts of high-power turbo generators is estimated as a result of the resonant in-teraction between the generator and the exciter caused by the operation of the automatic excitation regulator (AER) by mathematical modeling. The analysis covers turbo generators with a capacity of 300 to 1000 MW with a diode brushless excitation system (DBES). The simulated circuit includes a turbo generator with a block transformer, a power transmission line, an exciter in the form of a reversed synchronous generator with a rotat-ing rectifier diode converter unit, a static thyristor converter, and a sub-exciter in the form of a synchronous machine with permanent magnets. When modeling the electrical part, an approach is used from the positions of its own coordinates, which ensures maximum methodological consistency of the models of the listed devices and allows directly reproducing resonant phenomena at torsional vibration frequencies with the determination of instantaneous values of currents, voltages and electromagnetic moments of the turbo generator and exciter. The mechanical system is presented taking into account the exciter and sub-exciter as a seven-mass system. AER is introduced into the mathematical model by means of transfer functions with corresponding coefficients and time constants. The control system of the thyristor converter is represented in the model by a generator of line-arly increasing signals, a body for comparing these signals with the signal from the AER and a control pulse generator. To assess the damage rate, the deformation criterion for soft and hard loads in the zone of low-cycle fatigue and the force criterion in the zone of multi-cycle fatigue were used. A comparative quantitative assess-ment of the damage in the neck of the G-E shaft line in the resonant interaction between the exciter and the generator with different automatic excitation control systems is given. The influence of attenuation of electro-magnetic transients and damping of torsional vibrations on the damage values is analyzed. The results ob-tained can be used to analyze the functioning and determine the settings of the AER.

ПРОЕКТУВАННЯ СИЛОВИХ ТРАНЗИСТОРНИХ ПЕРЕТВОРЮВАЧІВ ЕНЕРГІЇ ДЛЯ СИСТЕМ АВТОМАТИЗОВАНОГО ЕЛЕКТРОПРИВОДУ ПОСТІЙНОГО СТРУМУ

Purpose. One of the integral parts of modern mechatronic motion modules, where electric motors provide the conversion of electrical energy into useful mechanical action, are power semiconductor converters. At the current stage of industrial development, the use of energy converters as a part of a fully controlled semiconductor switches opens wide opportunities for the development and implementation of highly efficient resource- and energy-saving devices. Methodology. Two types of converters are widely used in automated DC electric drive systems: controlled thyristor rectifiers and pulse-width DC converters, the principle of operation of which is based on the key mode of operation of the regulating semiconductor, which periodically connects the source voltage to the output circuit. The paper presents a laboratory sample of a power semiconductor DC energy converter, which can ensure reliable motor operation in both motor and braking modes. Results. The presented transistor energy converter consists of two main parts: the first part performs the main role – control, and it includes a control unit, a microcontroller, and a device for displaying current information. The second part is a power module, which includes the necessary power supply modules, control drivers and power transistor switches of the converter. To obtain high quality transients of the electric drive system, the circuit is equipped with additional sensors of current, voltage and speed, which takes part in the formation of the control signal and in the protection systems against overvoltage and current jumps. Practical value. The paper substantiates the parameters of the components and proposes developed technical solutions for the construction of a microprocessor control system for a transistor DC energy converter. It is shown that in order to ensure a constant generator mode in automated electric drive systems, where the primary energy converter is an uncontrolled rectifier, it is expedient to install an energy discharge circuit in the DC link. References 18, figures 14.

Performance optimization of doubly-fed induction generator (DFIG) equipped variable-speed wind energy turbines by using three-level converter with adaptive fuzzy PI control system

The present paper aims at optimizing the performance of a Doubly Fed Induction Generator (DFIG) equipped variable-speed wind energy turbine in utility grid-connected mode. Since maximum power extraction and output power quality improvement are considered the main challenges for enormous scale variable-speed wind turbines to meet the worldwide demand for clean energy, this work has two contributions; the first concerns the use of the three-level converters to upgrade the output power quality of the wind energy turbine through reducing the total harmonic distortion (THD) of the currents delivered to the power grid, whereas the second contribution intends to design an adaptive proportional-integral (PI) control system for the rotor side converter (RSC) control. The proposed adaptive PI control system is designed by combining the intelligent and adaptive nature of fuzzy logic control (FLC) and the simpleness of the PI controller framework to effectively optimize the DFIG wind energy turbine performance. In the proposed control system, the PI controller's gains are adjusted in real-time by a supervisory system based on FLC according to the wind turbine running conditions. The adopted control scheme to controlling the RSC comprises two cascaded regulation loops for reaching the maximum power point tracking (MPPT), that intends to extract obtainable maximum power of the wind energy turbine. The internal regulation loop is applied to control the rotor current while the external regulation loop is employed to regulate the generator speed. To prove the efficiency of the three-level converter and performance of the proposed control system, simulation studies were performed utilizing MATLAB/Simulink software. The obtained results through simulation clearly show that research paper purposes are achieved and the performance optimization of the wind turbine is well done.

Design and simulation of current-fed dual-active full-bridge DC/DC converter control system applied to proton exchange membrane fuel cell

Proton exchange membrane fuel cells (PEMFC) have been increasingly applied in clean and efficient distributed power generation systems in recent years. However, the output characteristics of PEMFC are relatively soft due to the influence of multiple polarization overvoltage. With the increasement of current density, the output voltage shows to be a nonlinear downward trend. In addition, in order to ensure the lifetime of PEMFC, the output ripple current is often concerned. Considering above characteristics, in order to achieve efficient power transmission of the PEMFC system, this paper adopts the current-fed dual-active full-bridge (DAB) DC/DC converter topology, which can achieve soft switching of most switches. Furthermore, it can restrain the characteristics of the current ripple. Hence, the power transmission efficiency and current ripple requirements of PEMFC are fulfilled. Finally the current-fed DAB is designed and simulated through PSIM. The C-block is applied to simulate the PEMFC nonlinear power supply according to the actual PEMFC parameters. In order to achieve efficient constant power transmission of the nonlinear PEMFC, a novel power closed-loop control strategy is proposed.

Parametric control of efficiency of asynchronous drive by means of converter with the increased power factor

Purpose. Development of circuit solution and substantiation of parameters of control system and power part of power supply converter, provided its operation with high power factor and smooth or stepwise methods of energy efficiency control of asynchronous drive.Methodology. The provisions of the theory of electric machines, methods of circuit design of automatic systems in the Multisim component of the National Instruments electronic laboratory, mathematical modeling in the Matlab package were used for research. Findings. Digital models of pulse-phase control systems for stepwise and smooth regulation of the supply voltage of motors using the method of pulse-width modulation of the mains voltage have been developed and built, recommendations are given for the level of load sagging, at which it is necessary to reduce the supply voltage and its magnitude with relay control, and also tested a smooth control system with coordinate-phase duty cycle control to achieve rational energy efficiency of the drive. Originality. The choice of the switching limit of the relay regulator and the level of rational value of the converter output voltage is substantiated, at which rational and energy-efficient control of the drive is achieved, the algorithm for determining the RC filtering circuit parameters is proposed to ensure simultaneously the best conditions for switching the converter power switches and the implementation of continuous compensation of the engine reactive power, provided that the converter is operated with an increased power factor.Practical value. The introduction of a simplified conversion system with a high power factor will create an automatic asynchronous drive system, through which it is possible to achieve energy conservation at the engine, converter and power system, with minimal capital investment in its production.

Research on fault clearing scheme for half-bridge modular multilevel converters high voltage DC based on overhead transmission lines

Abstract When a short-circuit fault occurs on the transmission lines of high voltage DC transmission system based on modular multilevel converters, the fault cannot be cleared by adjusting the converter control system, which results in longer recovery time. Aiming at the problem above, a fault self-clearing scheme based on the fault clearing module for the half-bridge converter station is proposed. Combined with the actual operating status of the flexible DC transmission project, centralized parameter models are utilized to analyze the fault self-clearing mechanism. Besides, the impact of the discharge branch on the fault clearing effect is studied in depth to provide a design consideration for the fault clearing module and improve the comprehensive benefits of the proposed scheme. PSCAD/EMTDC simulation results show that the introduction of the fault clearing module in the half-bridge converter station can effectively suppress the fault short-circuit current and shorten the fault clearing time. In addition, circuit breakers on both sides of the line do not need to be tripped, providing a reliable guarantee for the subsequent adaptive restart process.

PCC Voltage Perturbation Path Analysis and Compensation for Grid-Connected Voltage-Source Converter Under Weak Grid

Under weak grid condition, negative influence is brought in on system stability because the grid impedance and the grid-connected converter control system are coupled to each other. The key factor affecting the stability of the system is the perturbation of the voltage fluctuation at the point of common coupling (PCC) to the phase-locked loop (PLL) and the dc-link voltage loop. In this article, the impedance model of a three-phase grid-connected converter, including the current loop, PLL, and dc-link voltage loop in the dq frame, is adopted, because it includes coupling information of the converter and reflects the transferring relationship among grid-connected system variables. Based on the transferring relationship, this article analyzes the perturbation paths of PCC voltage and proposes the corresponding compensation methods, i.e., the PLL and dc-link voltage loop compensation terms, which are inserted into the q and d axes of the current loop controller, respectively. The impedance analysis results show that the proposed method can effectively improve the system stability. In addition, the experimental results verify the correctness of the theoretical analysis and the effectiveness of the proposed method.

Stability Improvement of Cascaded Power Conversion Systems Based on Hamiltonian Energy Control Theory

It is well known that the interaction between cascaded individually designed power conversion systems can cause instability. To overcome this issue, a Hamiltonian energy control scheme is proposed, which is based on passivity control theory and port-controlled Hamiltonian framework. A complementary PI adjustment term is also included in the control algorithm to eliminate the steady-state output voltage error caused by the parameter uncertainty. The proposed control approach is applied to three different cascade structures. First, the cascade structure between dc/dc converters is considered, and the detailed controller design is given. Second, the cascade connection of a single converter and its LC filter is studied. By placing the L C filter into the Hamiltonian model of the controlled converter system, the dynamic and potential instability caused by the filter can be adjusted. Finally, the cascade structure between subsystems including filters and converters, which are common in microgrids, is studied. By using the Hamiltonian function (storage function) as the Lyapunov function candidate, the large-signal stability of each controlled converter system is proved. When the cascade structure contains multiple controlled converter systems, the stability of the entire cascaded system is guaranteed by the superposition of multiple Lyapunov functions. A 3.5 kW 220−270−350 V test bench is built in the laboratory to demonstrate the application of the proposed control approach to these three cascade structures.

Development of a vector control system of the semiconductor converter, which will provide a polyharmonic operating mode of a polyphase electric machine

A system for vector control of current in the circuit of a polyphase electric machine has been developed. For this, on the basis of the analysis of electromagnetic processes in a multiphase semiconductor converter of electrical energy, its discrete mathematical model was created, which takes into account the redistribution of electromagnetic energy by individual spatial harmonic components depending on the number of phases. Using this mathematical model and the scheme of injection of higher current harmonics, which provides a polyharmonic mode of operation of a semiconductor converter, a method for independent control of the spatial harmonic components of the input current of the converter has been developed. The formation in each of the phases of polyharmonic currents, conjugated in shape and phase with the voltage supplying the converter, is carried out by means of control actions in the form of voltage vectors of a semiconductor switch, the implementation of which is carried out by the method of multiphase space-vector modulation. To check the developed provisions, a simulation model of a nine-phase semiconductor converter of electrical energy with a vector control system was created. The results of the study of the model confirmed the adequacy of the developed technical solutions, the use of which will ensure the most complete realization of the own advantages of a multiphase electric machine in order to generally improve the weight, size and energy indicators of the autonomous power supply system.

Quantifying Cyber Attacks on Industrial MMC-HVDC Control System Using Structured Pseudospectrum

This letter assesses the impact of cyber-attacks on the control system of the modular multilevel converter (MMC)-based high-voltage dc (MMC-HVdc) transmission technology. Specifically, the small-signal model of the MMC-HVdc is characterized by a closed-loop matrix and the distance to the small-signal instability is then quantified by structured pseudospectrum. Furthermore, a vertical search method is proposed to quantify the boundary of the structured pseudospectrum. The proposed quantification model with the vertical search method can be extended to the control of other power electronics-based systems. Case studies on a two-terminal MMC-HVdc system verify the effectiveness of the qualification method.

Wind energy conversion system control robustness based on current analysis of IGBT open-circuit fault

Wind energy conversion system control robustness based on current analysis of IGBT open-circuit fault

Enhanced Frequency Control Method for Microgrid-Connected Flywheel Energy Storage System

Flywheel energy storage system (FESS) can be used for frequency regulation in microgrids. In this article, an enhanced frequency control system is presented for FESS to reduce the frequency variations of microgrid. A three-layer control system is proposed for machine-side converter of the FESS including dc-link voltage controller, speed controller, and field-oriented control system. Unlike the conventional control methods, in the proposed method, the frequency controller is implemented in the grid-side converter to increase the ramp rate of the FESS and reduce the frequency deviation against load changes. Also, the proposed three-layer control system of the machine-side converter reduces the dc-link voltage variations. Furthermore, a mode coordination system is proposed to reduce the dc-link voltage variations when the operation mode of FESS changes from flywheel speed control mode to the microgrid frequency control mode. To demonstrate the advantageous of the proposed method in comparison to the conventional method, at first, the linearized model of the FESS in microgrid is extracted, and then the small-signal analysis is carried out for optimal design of proportional integral (PI) controllers. Two control strategies are theoretically presented and experimentally compared in a prototype microgrid including a diesel generator emulator and a load emulator. The frequency control system is studied in different loading conditions. Experimental results verify the theoretical concepts proposed in this article, and show the superiority of the proposed method over the conventional method.

New Stationary Frame Transformation for Control of a Three-Phase Power Converter Under Unbalanced Grid Voltage Sags

This article deals with a new nonlinear transformation providing representation of unbalanced three-phase signals (voltage and currents) as vectors that have constant components in a new rotating d'q' frame. Using the proposed transformations, the control system of a power electronic converter operating with an unbalanced grid can be equipped with proportional-integral (PI) controllers, without the use of resonant terms, for which antiwindup structures are more complicated and nonintuitive. This article presents the derivation of new direct and inverse transformations, features, a power converter model in a new frame, simulation results showing the waveforms of signals transformed to the new non-Cartesian frame, and simulation and experimental results of the voltage-oriented control for a grid-connected power converter.

Control of Three-Phase Power Electronic Converter With Power Controllers in Stationary Frame

This article concentrates on a three-phase power converter control system that uses voltages and currents in a stationary reference frame. The advantages of such a control system include the lack of transformation between stationary and rotating reference frames and hence, there is no need for an extra algorithm such as a phase-locked loop for the grid voltage phase-angle determination, as the power components are the same in every coordinate system. The method proposed in this article uses proportional-resonant-integral controllers for tracking referenced Akagi's instantaneous power components, which contain intentional oscillations of double grid frequency. Thanks to that, the sinusoidal converter current is maintained despite the negative sequence component in grid voltage. Different targets for converter current asymmetry, from corresponding, through symmetrical, to opposite to voltage asymmetry may be achieved, depending on the operation mode and the demanded power. Moreover, the power limitation method allowing limitation of the phase-current amplitude even for unbalanced phase currents was applied.

Fully decoupled fixed-time cascade control of three-phase voltage source converters with LC output filter

This paper presents a fully decoupled fixed-time cascade control system of three-phase voltage source converters (VSCs) with LC output filter. The proposed controller has a cascade structure and it is designed in the synchronous reference frame d-q. The outer loop is for voltage control and the inner loop is for current control. A fixed-time controller is developed for voltage regulation and reference tracking before the desired pre-fixed time despite the unknown disturbances. The current controller uses PI controllers for current regulation and feedforward terms to decouple the direct and quadrature of voltage and current control loops. Unlike the conventional PI-based synchronous reference frame VSC control, the proposed approach provides better control performance with smaller and smoother control signal and enables the d-q components of voltage and current to be fully decoupled. A comparative simulation study with the conventional control system is provided to highlight the effectiveness of the proposed approach.

The Axle Box Generator Efficiency Determination Using A Scalar Frequency Controlled Induction Electric Drive

The article discusses a method for determining the axle box generator efficiency. The generator is installed in the axle box of the freight car. It is driven by a wheels pair. The axle box generator provides power supply to freight car systems: diagnostics, geolocation and telemetry. To determine the efficiency, an indirect method of determining the mechanical power transmitted to the axle box generator is considered. The electromagnetic torque is determined through the induction electric drive model parameters of the generator. The article describes an experimental unit. It consists of a test generator, an induction electric drive, and an open platform frequency converter. The converter control system was created in MexBios Development Studio software. Oscillograms of generator tests are presented.

Multirate and Mixed Solver Based Cosimulation of Combined Transient Stability, Shifted-Frequency Phasor, and Electromagnetic Models: A Practical LCC HVDC Simulation Study

The design of control and protection system of the line-commutated converter (LCC) in a meticulous way should consider both dynamics of the LCC and large-scale ac grids. Consequently, a highly accurate and efficient simulation method is desirable. In order to capture the high-frequency dynamics between ac/dc grids, the multirate and mixed solver based cosimulation by combining transient stability (TS), shifted-frequency phasor (SFP), and electromagnetic transient (EMT) models is proposed. The idea of the proposed multirate and mixed solver based cosimulations is to naturally decouple the whole system into the respective TS, EMT, and SFP subsystems. The accuracy of the proposed multirate cosimulation is guaranteed by the proposed interface models, i.e., the TS-SFP interface model (TS-SFP-IM) and the SFP-EMT interface model (SFP-EMT-IM). The efficiency is guaranteed by the natural partitioning strategy, decoupled manner based communication structure and the overall realization of time sequence. The performance of the proposed multirate cosimulation has been validated on practical ac/dc system in China.