F. Aalizadeh; M. Hosseinpour; A. Dejamkhooy; H. Shayeghi
Abstract
Grid-connected inverter-based photovoltaic (PV) systems play an important role in Distributed Power Generation (DPG). For this application, quasi impedance source inverter is very suitable due to its ability to increase or decrease the output voltage of the inverter in a single-stage and high reliable ...
Read More
Grid-connected inverter-based photovoltaic (PV) systems play an important role in Distributed Power Generation (DPG). For this application, quasi impedance source inverter is very suitable due to its ability to increase or decrease the output voltage of the inverter in a single-stage and high reliable condition. Conventionally, to remove the harmonics, which are yielded by switching the grid-connected inverter, LCL filters are utilized at the inverter output. These filters can cause some problems at the Point of Common Coupling (PCC). The aim of this paper is to improve the quality of the injected power of the photovoltaic array, which is connected to the low voltage grid by quasi-Z-source inverter (QZSI). For this purpose, a two-stage control procedure containing DC and AC stages is performed. In the DC stage, the dynamic characteristics of the quasi-Z-source network are investigated by small-signal analysis. Using the transfer functions obtained from the dynamic model, the capacitor voltage of the quasi-Z-source network is suitably controlled to generate the appropriate voltage to the grid interface inverter. In the AC stage, in order to inject high-quality current into the grid as well as eliminating the resonance peak caused by the LCL filter, a systematic procedure is used to design the PR controller parameters and active damping coefficient. Simulation of the overall system includes solar panels, maximum power point tracking algorithm, quasi-Z-source inverter, and LCL filter to model the grid-tied PV system with the possible details. Simulations are carried out in MATLAB/Simulink environment, and results depict suitable performance of the studied power conditioning system with designed parameters.
M. Hosseinpour; R. Akbari; A. Dejamkhooy; F. Sedaghati
Abstract
Hybrid 2/3 level inverter is a combination of three-level diode clamped inverter and conventional two-level inverter. This structure has the advantages of both two-level and three-level structures. Also, the number of switches is less than three level diode clamped inverter. In this paper, a modified ...
Read More
Hybrid 2/3 level inverter is a combination of three-level diode clamped inverter and conventional two-level inverter. This structure has the advantages of both two-level and three-level structures. Also, the number of switches is less than three level diode clamped inverter. In this paper, a modified structure for a hybrid 2/3 level inverter, which is based on quasi-Z-source network, is investigated. This structure improves the performance of the 2/3 level inverter and develops the voltage boost capability of the structure. Increasing the output voltage can be achieved by selecting the appropriate short-circuit interval in quasi-Z-source network. In addition, short-circuit intervals in quasi-Z-source networks allow the inverter to operate without any dead time, which results in higher quality for output AC voltage. A modified switching method is presented for the proposed inverter and the related calculations are performed. Also, a simple control scheme is proposed to balance the neutral-point of the structure and to compensate the voltage imbalance of the Quasi network’s capacitors. The proposed structure can be used to connect different distributed generation sources to an islanded load or to a low voltage grid. Simulations are carried out in MATLAB/Simulink environment and results depict suitable performance of proposed inverter.
M. Hosseinpour; S. Mansoori; H. Shayeghi
Abstract
A new optimization method is proposed in this paper for finding the firing angles in multi-level voltage source inverters to eliminate low-order selective harmonics and reduce total harmonic distortion (THD) value of the output voltage. For thid end, Fourier series is used for calculating objective function ...
Read More
A new optimization method is proposed in this paper for finding the firing angles in multi-level voltage source inverters to eliminate low-order selective harmonics and reduce total harmonic distortion (THD) value of the output voltage. For thid end, Fourier series is used for calculating objective function and selecting specific harmonics. Regarding the nature and complexity of the employed non-algebraic equations in the optimization problem for achieving the optimal angle in the multi-level inverter, a recent developed meta-heuristic method known as Salp Swarm Algorithm (SSA) is presented. In the proposed method, the optimal angles for a given multi-level inverter are obtained based on the objective function such that the magnitudes of the selective harmonics and the THD value of the output voltage are reduced. The method is applied on a cascaded H-bridge type five-level inverter. The simulation results illustrate that the magnitudes of the selective harmonics and the THD percentage of the output voltage have been reduced through selecting the optimal switching angle by the proposed optimization algorithm. The result of this method are compared with those of SPWM method. Moreover, the performance of SSA algorithm with respect to PSO algorithm is compared which shows its rapid convergence speed and less THD value.
Power Electronic
M. M. Rahimian; M. Hoseinpour; A. Dejamkhooy
Abstract
Recently, hybrid modular multi-level converters, which are configured as full and half bridge sub-modules, are developed and utilized in the wide area of applications. Compared to its non-hybrid counterpart, these converters have several advantages such as the ability to nullify the DC side fault current ...
Read More
Recently, hybrid modular multi-level converters, which are configured as full and half bridge sub-modules, are developed and utilized in the wide area of applications. Compared to its non-hybrid counterpart, these converters have several advantages such as the ability to nullify the DC side fault current and controlling AC side reactive power during the faults. This paper proposes a modified phase shifted PWM method (PS-PWM) which uses a combination of an improved PS-PWM with cancelled mismatch pulses and a third harmonic injection method. The proposed method not only reduces output voltage harmonic content and uneven loss distribution between sub-modules but also extends the linear operating range of the inverter, which improves the DC bus utilization. The mathematical analysis is derived for the proposed method and in order to study the efficiency of the system using the proposed method, the loss calculation has been done and compared with traditional PS-PWM method. Simulation results in Matlab/Simulink show the suitable performance of the presented scheme.
