Papers by Mohammad Farhadi-Kangarlu
2021 12th Power Electronics, Drive Systems, and Technologies Conference (PEDSTC), 2021
Multilevel inverters (MLIs) are popular because of their advantages such as improved output volta... more Multilevel inverters (MLIs) are popular because of their advantages such as improved output voltage quality, lower switching losses, low EMI, and ability to handle higher voltage and power levels. To generate the desired output voltage in the MLIs, there are different switching methods including multicarrier pulse-width modulation (PWM), selective harmonic elimination (SHE), and multilevel space-vector PWM (SVPWM) methods. The SHE method minimizes the number of switching and hence the switching losses. Also, the method eliminates or attenuates specified low-order harmonics and adjusts the fundamental output voltage to the desired value. However, problems arise in the low modulation indexes where the harmonic distortion of the output voltage increases considerably. To solve the problem, this paper proposes a method to adjust the DC voltage when the low output voltage is required. Therefore, the modulation index will increase and the output voltage quality will be improved. The proposed method is verified on a 7-level Cascaded H-Bridge (CHB) inverter using the SHE method solved by particle swarm optimization (PSO) algorithm.
Transformerless Grid-Connected Asymmetric PV Inverter with Constant CMV and Reactive Power Injection Capability
2021 12th Power Electronics, Drive Systems, and Technologies Conference (PEDSTC)
Transformerless inverters have been commonly used in grid-connected photovoltaic (PV) systems due... more Transformerless inverters have been commonly used in grid-connected photovoltaic (PV) systems due to their high power density, low weight and volume, and high efficiency. However, they also suffer from the issue of leakage current. On the other hand, the ability to inject reactive power is another challenge of transformerless grid-connected PV inverters. In order to reduce leakage current and provide reactive power injection (RPI) capability, a single-phase transformerless grid-connected asymmetric phase-legs PV inverter is presented in this paper. The proposed inverter improves the conventional hybrid phase-legs PV inverter, ensuring that the common-mode voltage (CMV) is always constant. As a result, the high-frequency CMV is avoided, and the leakage current is diminished. Also, the proposed inverter has the same performance in the grid power factor of unity and non-unity. In order to validate the operation of the proposed PV inverter, the simulation results are presented and compared with the conventional hybrid phase-legs inverter based on a 1 kW sample.
Multilevel converters have many advantageous features over the conventional two-level topologies ... more Multilevel converters have many advantageous features over the conventional two-level topologies including capability of handling high-voltage high-power, improved output voltage quality etc. In this paper, a new cascaded multilevel converter is proposed. The proposed multilevel converter is based on a 5-level regenerative converter. In the proposed multilevel converter, the number of active switching devices are reduced in both inverter and rectifier sides resulting in a cost-effective topology. Also, as the active rectifier is used rather than the passive one, the power flow direction can be reverse to make a regenerative topology. As the proposed topology similar 5-level cells, it has good modularity and can be extended to any number of voltage levels. The simulation results of a 9-level converter based on the proposed topology are presented to verify its operation and control.
Extended hybrid cross-switched multilevel inverter circuit topology
Circuit World, 2021
Purpose Multilevel inverters (MLIs) have been studied widely over the past two decades because of... more Purpose Multilevel inverters (MLIs) have been studied widely over the past two decades because of their inherent advantages and interesting features. However, most of the newly introduced structures suffer from the increased standing voltage of the switches, which is defined as the maximum off-state voltage on the switches, losing modularity and increased number of direct current (DC) voltage sources. The purpose of this study is to propose a new hybrid MLI topology to alleviate the mentioned problems. Design/methodology/approach The proposed approach in this study includes using the advantage of two different topologies and combine them in a way that the advantages of both of the topologies are achieved. Therefore, the approach is to design a hybrid topology from two existing topologies so that a new topology has resulted. Findings This paper proposes a new hybrid MLI with lower power electronic switches and lowers DC voltage sources in comparison with the classic structures. The p...
Multilevel Inverter Based Distribution STATCOM: Application of the Cross-Switched Multilevel Inverter
Multilevel inverters are widely used in various applications due to their interesting features. T... more Multilevel inverters are widely used in various applications due to their interesting features. They can be connected to the grid as a STATCOM to improve grid power quality and voltage control. In this paper, a distributed STATCOM (DSTATCOM) is provided based on cross-switched multilevel inverter which is connected to a low voltage distribution system. The multilevel topology employed in this paper, uses fewer switches for a certain number of output voltage levels than other conventional topologies and produces output voltage with high quality and lower harmonic distortion. In the proposed DSTATCOM system, a simple control method for balancing the capacitors voltage is presented. Also, the proposed DSTATCOM is compared with the conventional 3-level and 5-level CHB inverter based DSTATCOM. The simulation of the studied system is carried out in the MATLAB/Simulink software and the results are presented and discussed.
Improved Low Voltage Ride Through by A STATCOM Based on Neutral Point Piloted (NPP) Multilevel Inverter
2021 29th Iranian Conference on Electrical Engineering (ICEE)
By ever-increasing utilization of renewable energy systems, grid codes impose strict standards fo... more By ever-increasing utilization of renewable energy systems, grid codes impose strict standards for current compensation, especially for asymmetric grid faults namely low voltage ride through (LVRT) codes. On the other hand, multilevel voltage source inverters have achieved prominent attention considering their lower dv/dt and harmonic content. This paper introduces a STATCOM based on neutral point piloted inverter (NPPI) for the first time. The studied 5-level NPPI has a single dc bus which feds all phases of the inverter and each phase contains two internal flying capacitors. A control system has been developed for NPPI-STATCOM through which the voltage of dc bus capacitor is controlled at its reference and using redundant switching states, the voltages of internal capacitors are balanced as well. Thus, NPPI-STATCOM control system is capable of balancing the voltage of internal capacitors even being connected to a faulty grid while positive and negative-sequence reactive currents being injected to the grid. Several simulation results in MATLAB/SIMULINK confirm the above claims indicating the performance of NPPI-STATCOM and the developed control system.
P‐type non‐isolated boost DC‐DC converter with high voltage gain and extensibility for DC microgrid applications
International Journal of Circuit Theory and Applications
Design and implementation of a new high step-up DC-DC converter for renewable applications
International Journal of Circuit Theory and Applications
This paper investigates a multilevel inverter with a capability that produces a wide voltage rang... more This paper investigates a multilevel inverter with a capability that produces a wide voltage range with high quality. The selective harmonic elimination (SHE) method is considered for a single-phase 5-level cascaded H-bridge (CHB) inverter, in which the particle swarm optimization (PSO) algorithm solves the nonlinear equations. However, eliminating the low-order harmonics has been challenging when a low range of output voltage is required. To surmount such challenges and access to a wide range of output voltage, an adjustable dc-link is introduced that allows the inverter to increase the modulation index, resulting in a significant decrease in total harmonic distortion (THD). In this paper, to regulate the dc-link voltage amount, a 12-pulse rectifier is employed to allow the inverter to produce the output voltage requirements with less distortion. To prove such claims, the PSO algorithm is modified to calculate the optimal angles, as a result, the switching angles are applied in SIM...
International Journal on Electrical Engineering and Informatics
In this paper, a transformerless distribution static synchronous compensator (DSTATCOM) based on ... more In this paper, a transformerless distribution static synchronous compensator (DSTATCOM) based on the cross-switched (CS) multilevel inverter (CSMLI) is introduced. In comparison with the well-known cascaded h-bridge (CHB) topology, CS inverter produces higher number of voltage levels using fewer number of power components. Since CS inverter produces ac side voltage with high quality and has the ability to work at high voltage and power levels, the proposed CS-DSTATCOM is directly connected to the distribution grid without the need for a transformer. In the proposed CS-DSTATCOM, all the dc sources are replaced with dc capacitors. In this paper, an effective voltage balancing control scheme is proposed to keep the capacitors voltages balanced in the CS structure. The control scheme balances the capacitors voltages in two levels, i.e., inter-cell and within-cell level. On the other hand, the over-voltage and under-voltage phenomena are of the most common power quality (PQ) issues in di...
Dynamic voltage restorer based on multilevel inverter with adjustable dc-link voltage
IET Power Electronics, 2014
ABSTRACT Dynamic voltage restorer (DVR) is a power electronic converter-based custom power device... more ABSTRACT Dynamic voltage restorer (DVR) is a power electronic converter-based custom power device used to compensate for voltage variations. The inverter used in the DVR structure can have different topologies. Multilevel inverters are a good candidate to be used in the DVR structure especially in higher voltage level. This study proposes a new scheme for DVR based on a multilevel inverter. In the proposed DVR, a dc-dc converter is attached to the multilevel inverter. The dc-link voltage is regulated by the dc-dc converter considering the voltage sag magnitude. In this way, the output voltage of the multilevel inverter has always its maximum possible number of levels. This results in better quality of output voltage in both deep and shallow voltage sags. It is important to emphasise that the existing inverter-based DVR topologies do not have this capability. Also, in the proposed DVR, there is no need for an output filter. Moreover, the fundamental frequency control method for the multilevel inverter can be used instead of pulse width modulation-based methods. This can result in lower switching losses and lower switching stresses. The mathematical analysis of the operation range of the proposed DVR is given in detail. The simulation results using Power System Computer Aided Design/Electromagnetic Transient including DC (PSCAD/EMTDC) as well as the experimental results from a laboratory prototype verify the proposed DVR scheme.
Higher‐order sliding mode current controller for grid‐connected distributed energy resources with LCL$\mathrm{LCL}$ filters under unknown grid voltage conditions
IET Generation, Transmission & Distribution
SHE-PWM technique in a Cascaded H-Bridge Multilevel Inverter fed by High-Frequency Isolated DC-DC Converter for fuel cell application
2021 11th Smart Grid Conference (SGC)
2021 IEEE Kansas Power and Energy Conference (KPEC), 2021
This paper investigates a multilevel inverter with a capability that produces a wide voltage rang... more This paper investigates a multilevel inverter with a capability that produces a wide voltage range with high quality. The selective harmonic elimination (SHE) method is considered for a single-phase 5-level cascaded H-bridge (CHB) inverter, in which the particle swarm optimization (PSO) algorithm solves the nonlinear equations. However, eliminating the low-order harmonics has been challenging when a low range of output voltage is required. To surmount such challenges and access to a wide range of output voltage, an adjustable dc-link is introduced that allows the inverter to increase the modulation index, resulting in a significant decrease in total harmonic distortion (THD). In this paper, to regulate the dc-link voltage amount, a 12-pulse rectifier is employed to allow the inverter to produce the output voltage requirements with less distortion. To prove such claims, the PSO algorithm is modified to calculate the optimal angles, as a result, the switching angles are applied in SIM...
Nested Neutral Point Clamped Converter Based DSTATCOM with Mixed-Sequence Reactive Current Compensation Capability
2021 12th Power Electronics, Drive Systems, and Technologies Conference (PEDSTC)
This research deals with the low-voltage ride-through (LVRT) in a distribution grid STATCOM (DSTA... more This research deals with the low-voltage ride-through (LVRT) in a distribution grid STATCOM (DSTATCOM) based on nested neutral point clamped (NNPC) inverter. A NNPC-DSTATCOM with a LVRT control scheme is introduced through which positive-sequence (PS) and negative-sequence (NS) reactive currents are handled. NNPC based DSTATCOM contains two kinds of capacitors, i.e., dc-bus capacitor(s) and flying capacitors (FLCs) placed in the legs. Since in DSTATCOM, the dc-bus is not fed by a dc supply, a hierarchical balancing strategy is presented to stabilize the voltages of capacitors. In this strategy, first, the common dc-bus voltage is stabilized at the desired reference and then the voltages of FLCs are adjusted. NNPC-DSTATCOM has a single dc source and circulating current paths through the converter legs. Taking this advantage, the LVRT scheme is able to independently manage both PS and NC reactive currents when an unbalanced grid condition appears while maintaining the capacitors voltages balanced. Simulation results are extracted in MATLAB/SIMULINK environment proving the correspondent operation of the introduced system.
A new single-phase transformerless grid-connected PV inverter is presented in this paper. Investi... more A new single-phase transformerless grid-connected PV inverter is presented in this paper. Investigations in transformerless grid-connected PV inverters indicate the existence of the leakage current is directly related to the variable common-mode voltage (CMV), which is presented in detail. On the other hand, in recent years it has become mandatory for the transformerless grid-connected PV inverters to satisfy new grid-codes such as low-voltage ride-through (LVRT) capability via injecting reactive power during grid faults. Therefore, in this paper, the design of the proposed topology is based on retaining the constant CMV to suppress the leakage current and also to provide reactive power injection capability during grid faults. The control strategies for injecting reactive power in the LVRT condition are also examined. To validate the presented theoretical concepts, the performance and dynamic response of the proposed transformerless PV inverter are investigated by MATLAB/Simulink an...
A SOGI-PLL-Based Feedback-Feedforward Control System for Three-Phase Dynamic Voltage Restorer in the Distribution Grid
Background and Objectives: Due to the increased sensitive loads, improving power quality in distr... more Background and Objectives: Due to the increased sensitive loads, improving power quality in distribution grids by custom power tools is one of the important fields of electrical engineering. This paper proposes a new kind of three-phase three-wire dynamic voltage restorer (without including storage sources or DC link) and also its control method. Methods: The proposed structure includes an AC/AC converter, low-pass filters at the input and output sides, and three-phase injection transformers. The control system is based on the combination of feedback and feedforward control that its advantages are high speed, good response quality, and very simple implementation. To overcome the harmonics raised from AC/AC converter switching on the main line, a SOGI-PLL has been used. Also, SOGI-PLL operates independently on each phase so that the asymmetric voltage variations can be identified. Results: The proposed control method is capable to compensate the power quality problems such as voltage...
A non‐isolated single‐input dual‐output boost DC–DC converter
Iet Power Electronics, 2021
2021 12th Power Electronics, Drive Systems, and Technologies Conference (PEDSTC), 2021
Multilevel inverters (MLIs) are popular because of their advantages such as improved output volta... more Multilevel inverters (MLIs) are popular because of their advantages such as improved output voltage quality, lower switching losses, low EMI, and ability to handle higher voltage and power levels. To generate the desired output voltage in the MLIs, there are different switching methods including multicarrier pulse-width modulation (PWM), selective harmonic elimination (SHE), and multilevel space-vector PWM (SVPWM) methods. The SHE method minimizes the number of switching and hence the switching losses. Also, the method eliminates or attenuates specified low-order harmonics and adjusts the fundamental output voltage to the desired value. However, problems arise in the low modulation indexes where the harmonic distortion of the output voltage increases considerably. To solve the problem, this paper proposes a method to adjust the DC voltage when the low output voltage is required. Therefore, the modulation index will increase and the output voltage quality will be improved. The propos...
DC dynamic voltage restorer (DC-DYR): A new concept for voltage regulation in DC systems
Many of the sensitive and high power loads in the AC distribution power system are direct current... more Many of the sensitive and high power loads in the AC distribution power system are direct current (DC) loads, which power quality is a fundamental issue in this type of load. There are many factors that affect the issue of power quality. The voltage sag is one of them which is the main factor in reducing power quality of grid. There are many of devices to increase voltage quality in the grid. The dynamic voltage restorer (DVR) is an economical solution to eliminate voltage-related power quality problems. In this paper, a DC dynamic voltage restorer (DC-DVR) is presented to retrieve the voltage drop at sensitive DC loads in the AC power grids. The proposed DC-DVR receives energy from output of the rectifier to maintain the load voltage constant at a nominal value. The proposed DC-DVR is in fact an isolated DC-DC converter fed from the DC bus and its output is series connected to the DC bus. The performance of the proposed DC-DVR is verified via simulations in PLECS software.
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Papers by Mohammad Farhadi-Kangarlu