Szymon Piasecki

Brief view on control of grid‐interfacing AC‐DC‐AC converter and active filter under unbalanced and distorted voltage conditions

Purpose – The purpose of this paper is to consider both sides of a back‐to‐back AC‐DC‐AC interface.Design/methodology/approach – The paper presents a mathematical analysis, simulation, laboratory test in scaled model.Findings – The two main findings comprised concept of control methods for grid AC‐DC‐AC converter applied in renewable energy sources with variable speed operation under distorted grid. Active filtering functionality in case of non‐linear current of a parallel load. Second, a control algorithm dedicated for two‐level AC‐DC converter applied in industrial networks with high‐order harmonics compensation working under hard conditions – balanced and unbalanced voltage dips.Research limitations/implications – The paper shows preliminary results for AC‐DC‐AC converter and active filter (AF) during voltage dips and for harmonics compensation. Control methods and/or topology should be improved and tested in scale and after at high‐power system.Practical implications – Power quality supplied/received ...

On the Design Process of a 6-kVA Quasi-Z-inverter Employing SiC Power Devices

This paper presents the design process of a 6-kVA quasi-Z-source inverter built with SiC power devices, in particular, employing SiC MOSFETs and SiC Schottky diodes. The main design target is to find the optimal parameters and a good agreement between the efficiency and power density of the converter. The performance of the system may be influenced not only by the switching frequency but also from the specific pulsewidth modulated (PWM) method or type of SiC MOSFET, and, therefore, various design cases are analyzed. At a final step, the 6 kVA/3 × 400 VAC inverter employing the 80 mΩ SiC MOSFETs and operating at 100 kHz with the minimum switching number method is chosen for investigation and a laboratory prototype is built. From experiments, the high performance of the designed system is confirmed. More specifically, it is shown that an efficiency above 95.6% (at 400 VDC, B = 1.9) and a power density higher than 2 kW/dm3 have been reached. Last but not least, the obtained results, which can be recognized as leading in the area of impedance source converters, show the great benefits gained by employing the new power semiconductor devices.

Control of Grid Connected Converter (GCC) Under Grid Voltage Disturbances

In this chapter operation of a reliable control method of a Grid Connected Converter (GCC) under grid voltage disturbances is presented. As a GCC authors understand power electronic AC-DC converter with AC side filter and DC-link capacitor operating as an interface between the electrical grid and Active Loads (AL). At the beginning short introduction to selected grid voltage disturbances is given. Afterwards, the chosen modeling approach of a GCC is discussed and the example of passive components calculation are provided. In the next sections a brief review of a basic GCC control methods is described. A control method: Direct Power Control with Space Vector Modulation (DPC-SVM) is chosen for further development process. For the basic scheme of DPC-SVM special control modules for voltage dips and higher harmonics compensation are presented. Due to the development of new control modules and its integration with the classical DPC-SVM a new reliable (robust to selected grid voltage disturbances such as dips, higher harmonics) control method is proposed: Robust Direct Power Control with Space Vector Modulation (RDPC-SVM). The term “robust” in the name of proposed control refers to the fact that the RDPC-SVM method is expected to operate in an uncertain environment with respect to the system dynamics. This new control method can assure sinusoidal like and balanced AC current in extremely distorted grid voltage. Based on the case study from series 5–400 kVA of Voltage Source Converters (VSCs) it was verified that the control dynamic and features of the RDPC-SVM fulfill requirements of sinusoidal and balanced currents under uncertain grid voltage distortions. Moreover, the quality of current and power is significantly improved in comparison to classical methods. Hence, the negative impact of the GCC on the grid voltage (through its inner impendence) is significantly reduced i.e.: lower Total Harmonics Distortion (THD) factor of a grid current, control of active and reactive power flow assure good quality of integration with a grid even in case of increased impedance within operation limits.

SiC-based Support Converter for passive front-end AC drive applications

The paper presents a simulation study of the Support Converter (SC) for passive front-end 55 kVA AC drive, which is aimed to improve the system performance. Most of time, the converter acts as a parallel Active Power Filter (APF) taking advantage from fast SiC devices application. During the regenerative breaking the SC may feed energy back to the supply grid. The complete system, including an advanced control system based on Direct Power Control with Space Vector Modulation concept, is modeled with the use of Saber package. Moreover, an estimation of the power losses is presented on the base of simulation results and switching performance tests of SiC MOSFETs and Schottky diodes. When harmonic compensation mode is considered semiconductor power losses are expected to be on the level of 120W (0.22% of nominal drive power). The converter is also expected to restore major part of energy from regenerative braking (power limit up to 28 kW) of the drive with total efficiency around 97.5%.

Robust control of grid connected AC-DC converter for distributed generation

The paper presents control algorithm for AC-DC converter operating as an interface between the Grid and Distributed Sources. Control algorithm is intended to be applied for serially manufactured AC-DC converters. Algorithm is based on Direct Power Control Space Vector Modulated extended with harmonic and dips compensation functionalities. Simulation and selected experimental results in various operation stages for the converter are presented.

High order line filters for Grid Connected AC-DC Converter — Parameters selection and optimization

In this paper three types of the high order line filters dedicated for AC-DC Grid Connected Converter (GCC) are analyzed and compared. According to selected power quality standard and passive components minimization a design procedure is proposed for each described filter topology. Typical LCL filter is compared to LCL with Trap and LLCL line filters with use of analytical calculations and simulation study. Optimization parameters and performance indices for analyzed filters are introduced.

Grid interfacing of distributed energy sources by three-level BtB NPC converter under distorted grid voltage

This paper presents complete control algorithm for grid-connected Pulse Width Modulated (PWM) 3-level BtB (back to back) converter intended for industrial drives and renewable energy applications. The objective of control is to limit current harmonics distortion and provide ride through capability during voltage dips. Moreover, Maximum Power Point Tracking (MPPT) and Active Power Feedforward (PF) has been implemented end tested for optimizing energy flow control. Grid Side Converter (GSC) is controlled by Voltage Oriented Control (VOC) supported by synchronization loop with positive sequence extraction, resonant current controllers for higher harmonics compensation, grid voltage feedforward loop for dips compensation and DC voltage filter. At Machine Side Converter (MSC) Direct Torque Control Space Vector Modulated (DTC-SVM) has been used. Algorithm is tested in simulations and experiment from 3kVA up to 15kVA platform using three-level BtB NPC converter with LCL filter. Both controls of GSC and MSC are interacting by Power Feedforward for energy flow optimization between grid and active load.

Design of a three-phase AC/DC converter with paralleled SiC MOSFETs

This paper describes a design procedure of a three-phase AC/DC converter with special focus on semiconductors: paralleled SiC MOSFETs and SiC Schottky diodes. The converter is aimed to operate as a 14kVA Support Converter (SC) for the 55kVA AC drive system. The SC acts as active parallel filter during normal operation of the drive and is also capable to return part of the regenerative breaking energy to the supply grid. Initial calculations of power losses conducted with Matlab are verified by simulations in SABER software. Laboratory model designed on the base of calculations and simulations was tested with special attention to power losses measurements. Total efficiency of the AC/DC converter (including LC filter and gate drivers) measured during inverter operation is on the level of 98.8% at switching frequency of 40kHz.

Design of AC-DC Grid Connected Converter using Multi-Objective Optimization

Abstract Power electronic circuits, in particular AC-DC converters are complex systems, many different parameters and objectives have to be taken into account during the design process. Implementation of Multi-Objective Optimization (MOO) seems to be attractive idea, which used as designer supporting tool gives possibility for better analysis of the designed system. This paper presents a short introduction to the MOO applied in the field of power electronics. Short introduction to the subject is given in section I. Then, optimization process and its elements are briefly described in section II. Design procedure with proposed optimization parameters and performance indices for AC-DC Grid Connected Converter (GCC) interfacing distributed systems is introduced in section III. Some preliminary optimization results, achieved on the basis of analytical and simulation study, are shown at each stage of designing process. Described optimization parameters and performance indices are part of developed global optimization method dedicated for ACDC GCC introduced in section IV. Described optimization method is under development and only short introduction and basic assumptions are presented. In section V laboratory prototype of high efficient and compact 14 kVA AC-DC converter is introduced. The converter is elaborated based on performed designing and optimization procedure with the use of silicon carbide (SiC) power semiconductors. Finally, the paper is summarized and concluded in section VI. In presented work theoretical research are conducted in parallel with laboratory prototyping e.g. all theoretical ideas are verified in laboratory using modern DSP microcontrollers and prototypes of the ACDC GCC.

Coordinated control of grid-connected three-level NPC converter under distorted grid voltage

This paper presents complete control algorithm for grid-connected Pulse Width Modulated (PWM) AC/DC converter intended for industrial drives and renewable energy applications. The objective of control is to limit current harmonics distortion and provide ride through capability during voltage dips. Following improvements to Voltage Oriented Control are presented: synchronization loop with positive sequence extraction, resonant current controllers for higher harmonics compensation, grid voltage feedforward loop for dips compensation and DC voltage filter. Algorithm is tested in simulations and on experimental 15kVA platform using three-level NPC converter with LCL filter.