Energy-Saving Reversible Electric Drive Based on Active Front End Rectifier and Voltage Source Inverter

Active front-end (AFE) rectifiers have become widely employed in power systems to achieve unity power factor and harmonic mitigations. The typical modeling approaches applied for AFE rectifiers in the literature mostly relied on two baselines: the detailed model and the time-average model. The former approach deals with the switching element model (SEM), which leads to significant harmonics in currents with distorted waveforms. The latter approach uses the average-value model (AVM) to overcome the currents’ harmonics as well as provide fast responses. However, even the AVM baseline has shown problems during the starting stage (lack of control signals) and over the dead-time periods, which causes serious issues in the implementation process. This paper presents an improved dynamic AVM for AFE rectifiers by precisely considering the issues mentioned above, along with the practical starting procedure and desirable initialization. The studied AFE rectifier is developed using the voltage-oriented control (VOC) technique based on the different modeling methodologies, including SEM, Conventional AVM, and the proposed AVM. The performance of all models is analyzed and compared using simulation results with MATLAB/Simulink R2023a Function blocks for all the algorithm parts and SimScape elements for the electrical circuit model. The simulation results illustrate that the performance of the proposed AVM approach can closely resemble the behavior of the SEM baseline with low harmonic distortion. To evaluate the performance of the proposed model, several case studies are investigated to verify the AFE rectifier operation, regarding mostly the total harmonic distortion (THD) wherein the THD percentages are improved to 4.78 and 2.5 from 5.14 and 2.78 for low- and high-power loads, respectively.

Reactive power compensation in grid connected AC-systems contributes to improve grid stability and reliability. Given that Active Front-End (AFE) rectifiers have the same power circuit topology of static VAR generators, they can ensure reactive power ancillary service besides their basic functions. In this context, this paper presents steady-state analysis and optimal DC-link voltage control for an AFE rectifier with reactive power ancillary service. Firstly, the minimum required level of DC-link voltage for optimal operation of the AFE rectifier with reactive power ancillary service has been investigated. Secondly, an optimal design of the DC-link voltage PI controller has been carried out to ensure the following control objectives: i) minimization of the transient DC-link voltage fluctuations in response to rough changes of the consumed active power ii) mitigation of the third harmonic component of the grid current under steady-state condition to comply with standards. A genetic algorithm based on multi-objective optimization has been proposed to determine the gains of the PI controller used in the DC-link voltage control loop. Simulation results demonstrated that the obtained control performances comply with the analytical study.

Power conversion structures for adjustable speed drives usually include a diode bridge as input stage. The current harmonics generated by the bridge rectifier contribute strongly to the degradation of the utility current quality. To avoid this problem the diode bridge could be replaced by an active front-end rectifier which provides a low total harmonic distortion, power factor correction and bidirectional power capability. However, this input stage is more expensive and has lower energy efficiency than the bridge rectifier. Furthermore, it has to be designed for the whole power of the adjustable speed drive. A well know alternative to the active front-end rectifier consists of using active filters to cancel the harmonics generated by the diode bridge. This solution has no bidirectional power capability and is often used in medium-voltage electrical drives that do not require controlled braking. This paper proposes the connection of the dc links of the diode bridge rectifier and the active filter by means of two diodes and a common-mode inductance. This new solution achieves low total harmonic distortion, unitary power factor and it also provides a robust speed drive with regenerative braking capability that can be very interesting for many applications.

This paper proposes a control strategy of an active front end (AFE) rectifier to cope with voltage deviation at the shipboard AC-power system. The voltage sags in naval ships may occur when the step load such as a large pulse power weapon is applied or when faults happen in the grid or generators themselves. In this paper, the capability of AFEs to support voltage is presented for the voltage sags. In the proposed control scheme, reactive power is utilized to achieve voltage compensation. For the verification of the effectiveness, simulation using MATLAB/Simulink and PLECS has been conducted.

This paper deals with the design and implementation of cascaded H-bridge multilevel voltage source converter-based static synchronous compensator (STATCOM) for simultaneous active and reactive power compensation, voltage stability and damping of power oscillations. The main objective is to provide active power support and maintain the voltage stability by compensating the reactive power in the power system. In this paper, the multi pulse inverter-based STATCOM has been replaced by multilevel inverter-based STATCOM to overcome the drawbacks of the former. Cascaded H-bridge (CHB) MLI for implementation of STATCOM has been used as CHB MLI is considered the best for STATCOM applications due to its modular structure and requirement of lesser number of components. MLI-based STATCOM is used to provide simultaneous reactive power and active power compensation established by using super-capacitor. The super-capacitors are connected with each DC link capacitor of CHB MLI by using the DC-DC buck boost converter. The STATCOM is also used to provide voltage stability during the power quality problems such as voltage sag and voltage swell, it is established by injecting or absorbing reactive power. The STATCOM is also used for damping the power oscillations by controlled injection of reactive power hence enhancing transient stability. Nine-level cascaded H-bridge MLI-based STATCOM is designed for simultaneous reactive power and active power compensation, voltage stability and damping the power oscillations. Exhaustive simulations have been carried out using MATLAB/Simulink and SimPowerSystems software. The simulation results are presented to prove the effectiveness of MLI-based STATCOM for simultaneous active and reactive power compensation, voltage stability and damping of power oscillation.

In this paper, the mathematical modelling and control of isolated bi-directional multi-stage, on-board charger for the electric vehicle (EV) with unity power factor operation is presented. The presented charger topology is proficient to work in grid to vehicle (G2V) mode and vehicle to grid (V2G) mode as well. The EV charger interacts with the utility grid to exchange the adequate amount of active and reactive power required in the both modes of operation. The mathematical modelling of converter is obtained in both G2V and V2G modes to obtain the state to control and output to control transfer functions through state space averaging method. These transfer functions are further used to design the controller parameters and examine the overall dynamics of the system. In this topology an active front end (AFE) rectifier is employed to maintain the adequate constant DC link voltage, which is controlled by current mode control technique. An isolated dual active bridge (DAB) converter is used to exchange the bi-directional power flow between DC link and EV battery, which is controlled by modified single phase shift modulation technique. The overall control is implemented in Simulink model to validate bi-directional power exchange between the utility grid and EV battery for a 230 V, 50 Hz, 5 kW EV charger.

Problem. The proliferation of electric vehicles has underscored the need for the development of energy-efficient charging stations and systems. These systems must deliver high efficiency, maintain a power factor close to unity, adhere to electromagnetic compatibility standards, emit low levels of higher harmonics, and enable fast charging capabilities. Current electric vehicle charging devices encounter issues such as significant power losses, high harmonic emissions to the power grid, and challenges in implementing fast charging modes. Consequently, enhancing the energy efficiency of charging stations – by reducing power losses, minimizing harmonic emissions, ensuring a high power factor, and supporting modes for regulated current and voltage sources for fast charging – is a pressing concern. Goal. The aim of this work is to perform a comparative analysis of different types of batteries for electric vehicles, exemplified by TESLA cars, presenting comparative characteristics of lithium-ion, lithium-iron-phosphate, and lithium-titanate batteries. Methodology. The study showcases an evaluation of battery units for electric vehicles and outlines a comparative assessment of lithium-ion, lithium-iron-phosphate, and lithium-titanate batteries. The research focuses on enhancing the energy efficiency of electric vehicle charging station systems through the use of active rectifiers, with modes for active power factor correction and optimal configuration. Results. An examination of the quality of converters for electric vehicle charging stations was conducted, proposing schemes for a three-phase active voltage source rectifier and an active current source rectifier. Power circuitry and space-vector switching states for power transistors are introduced. Analysis concludes that an active current rectifier may be a more promising topology. Originality. A model of a charging station based on an active current source rectifier was developed using Matlab/Simulink. Transient processes of the converter's operation and the charging of a 60 kWh battery pack were examined. It was found that the active rectifier facilitates regulation of the battery charging current, achieves a power factor close to unity, and maintains a low level of higher harmonic emissions with a harmonic distortion factor of 2.52%. Practical value. The advancement of electric vehicles necessitates the ongoing development and enhancement of the energy indicators for electric vehicle batteries and the converters of charging stations, especially those that enable fast charging. Active progress is being made in each of these areas.

Implementation of application specific soft-core architecture for switching converters

Photovoltaic solar system connected to the electric power grid operating as active power generator and reactive power compensator

The article deals with the problem of active power loss and voltage in the 220 kV electric network in the Northern part of the electric system of the Republic of Tajikistan. This problem is caused by the lack of reactive power com pentation in the nodes of the distribution network with a voltage of 10 kV and the transfer of the necessary reactive power to consumers via the electric network with a voltage of 220 kV or lower. In the nodes of the 10 kV distribution network, the maximum values of active and reactive power obtained by calculation are given. To solve the problem of reducing active power and voltage losses, it is proposed to decentralize reactive power compensation by placing reactive power compensation facilities on the 10 kV side. In order to justify the effectiveness of decentralization of reactive power compensation with the installation of reactive power compensation facilities on the 10 kV side, calculations were performed for all high-voltage substations of the Northern electric power system of the Republic of Tajikistan, as well as on the basis of the real existing 220 kV electric network for one node consisting of two transformer substations (TS Sughd - 500 and TS Hadzhent substations), using the Matlab software package, Power Systems built a computer model for optimizing the 220 kV power grid by reactive power.

Long term supporting schemes for photovoltaic (PV) system installation have led to accommodating large numbers of PV systems within load pockets in distribution grids. High penetrations of PV systems can cause new technical challenges, such as voltage rise due to reverse power flow during light load and high PV generation conditions. Therefore, new strategies are required to address the associated challenges. Moreover, due to these changes in distribution grids, a different response behavior of the distribution grid on the transmission side can be expected. Hence, a new equivalent model of distribution grids with high penetration of PV systems is needed to be addressed for future power system studies. The thesis contributions lie in three parts. The first part of the thesis copes with the PV modelling. A non-proprietary PV model of a three-phase, single stage PV system is developed in PSCAD/EMTDC and PowerFactory. Three different reactive power regulation strategies are incorporated into the models and their behavior are investigated in both simulation platforms using a distribution system with PV systems. In the second part of the thesis, the voltage rise problem is remedied by use of reactive power. On the other hand, considering large numbers of PV systems in grids, unnecessary reactive power consumption by PV systems first increases total line losses, and second it may also jeopardize the stability of the network in the case of contingencies in conventional power plants, which supply reactive power. Thus, this thesis investigates and develops the novel schemes to reduce reactive power flows while still keeping voltage within designated limits via three different approaches: 1. decentralized voltage control to the pre-defined set-points 2. developing a coordinated active power dependent (APD) voltage regulation Q(P) using local signals 3. developing a multi-objective coordinated droop-based voltage (DBV) regulation Q(V) using local signals In the third part of the thesis, furthermore, a gray-box load modeling is used to develop a new static equivalent model of a complex distribution grid with large numbers of PV systems embedded with voltage support schemes. In the proposed model, variations of voltage at the connection point simulate variations of the model’s active and reactive power. This model can simply be integrated into load-flow programs and replace the complex distribution grid, while still keeping the overall accuracy high. The thesis results, in conclusion, demonstrate: i) using rms-based simulations in PowerFactory can provide us with quite similar results using the time domain instantaneous values in PSCAD platform; ii) decentralized voltage control to specific setpoints through the PV systems in the distribution grid is fundamentally impossible due to the high level voltage control interaction and directionality among the PV systems; iii) the proposed APD method can regulate the voltage under the steady-state voltage limit and consume less total reactive power in contrast to the standard characteristic Cosf (P) proposed by German Grid Codes; iv) the proposed optimized DBV method can directly address voltage and successfully regulate it to the upper steady-state voltage limit by causing minimum reactive power consumption as well as line losses; v) it is beneficial to address PV systems as a separate entity in the equivalencing of distribution grids with high density of PV systems.

The uneven load of the electric drive of sucker-rod pumping units causes an increase in the consumption of reactive power, which requires compensation. This article discusses the issue of calculating the processes in sucker-rod pumping units in the case of individual compensation of the reactive power. Mathematical models for calculating the process of changing the capacity of cosine capacitors for reactive power compensation in the starting and steady-state modes of the electric drive of the sucker-rod pumping unit, which are characterized by the periodically varying load and moment of inertia, have been developed. The calculation is based on a mathematical model of the induction motor that takes into account the saturation of the magnetic path and the skin effect in the bars of the deep-bar rotor. The created mathematical model can be used to regulate the capacitance of the capacitors connected to the induction motor in order to reduce the reactive power consumption.

Standard pulsewidth-modulated inverter-fed induction motor drives employ a diode rectifier bridge to supply AC power from the utility to the DC link. Although a diode rectifier is the most cost-effective solution, it does not permit reversing the power flow. This prohibits operating the machine in the regenerative braking mode for active deceleration. An innovative control method substitutes conventional hardware, such as an active front-end rectifier or a chopper controlled braking resistor in the DC-link circuit, by additional software that is implemented in the standard microprocessor control. The control algorithm maximizes the power losses in the machine and in the inverter. It enables regenerative braking operation of the induction motor at high torque. The algorithm conserves the high dynamic performance of a vector-controlled drive system.

Technological developments such as Flexible AC Transmission Systems (FACTS) can improve the power quality of the power system and can respond to the ever-increasing demand for electrical energy.Superconducting magnetic energy storage (SMES) is a FACTS device that has been used for several years at utility and industrial sites throughout the United States, Japan, Europe, and South Africa to provide both transmission voltage support and power quality to customers who are vulnerable to fluctuating power quality [1]- [3].SMES systems are classified into two groups: voltage source inverter (VSI) and current source inverter (CSI) SMES.The VSI SMES has many advantages when compared with the CSI SMES; for example, in the VSI SMES, the power rating of power electronic devices that are used in the inverter is much less than that of the CSI SMES, resulting in fewer switching and power losses.Also, the VSI SMES can be used as a Static synchronous Compensator (STATCOM) when its chopper is out of service.Moreover, for the same condition, the VSI SMES can store more energy than the CSI SMES; these advantages encouraged the authors to study VSI SMES.This type of SMES is composed of a magnetic energy storage coil with various structures and power conditioning systems that are also composed of different parts, such as AC-DC filters, a multi-level chopper, a capacitor bank, and a multi-level converter (i.e. an inverter or rectifier).These power conditioning systems are also used in many different sustainable energy systems, such as bio fuels, solar power, wind power, wave power, geothermal power, and tidal power.The converter is an interface between the power network and the capacitor bank and controls the electrical energy exchange between the two.Likewise, the chopper is also an interface between the magnetic energy storage coil and the capacitor bank, and controls electrical energy exchange between them.To store the electrical energy in the capacitor bank and the magnetic energy storage coil in the range of mega joules, it is necessary to employ high power-rating converters; to overcome the limitations of the current and voltage range of the semiconductors, multi-level converters are used.The advantages of using such converters include reducing voltage on the switches, harmonic order correction, decreasing or eliminating lateral equipment, decreasing switching frequency, decreasing total harmonic distortion (THD), decreasing switching losses, and decreasing the output current ripple.

Concept design of the control method for the NBI acceleration grid power supply-conversion system of CFETR