Journal of Operation and Automation in Power Engineering
Volume:6 Issue: 2, Summer - Autumn 2018

A dual mechanical port machine (DMPM) is used as an electrically variable transmission (EVT) in hybrid electric vehicle (HEV). In the conventional HEV, this machine is replaced by a planetary gearbox and two electric machines and makes this structure simpler. This paper presents field oriented control (FOC) for DMPM. For HEV application, drive efficiency and wide operating speed range are important. The control strategy, which uses the maximum torque per ampere (MTPA) method at low speed and flux weakening (FW) method at high speed are proposed. The model of DMPM considering the magnetic coupling between two air gaps has been developed in MATLAB/Simulink and the proposed control strategy is applied to DMPM. The simulation results have been provided with a brief discussion at the end.

Electric vehicle (EV) aggregator, as an agent between the electricity market and EV owners, participates in the future and pool market to supply EVs’ requirement. Because of the uncertain nature of pool prices and EVs’ behaviour, this paper proposed a two-stage scenario-based model to obtain optimal decision making of an EV aggregator. To deal with mentioned uncertainties, the aggregator’s risk aversion is applied using conditional value at risk (CVaR) method in the proposed model. The proposed two-stage risk-constrained decision-making problem is applied to maximize EV aggregator’s expected profit in an uncertain environment. The aggregator can participate in the future and pool market to buy the required energy of EVs and offer optimal charge/discharge prices to the EV owners. In this model, in order to assess the effects of EVs owners’ reaction to the aggregator’s offered prices on the purchases from electricity markets, a sensitivity analysis over risk factor is performed. The numerical results demonstrate that with the application of the proposed model, the aggregator can supply EVs with lower purchases from markets.

Intermittent nature of wind power faced ISO and power producers with new challenges. Wind power uncertainty has increased the required reserve capacity and deployment reserve. Consequently, large-scale wind power generation increases ISO costs and consequently reserve prices. On the other hand, since wind power producers are price taker, large-scale wind power generation decreases residual demand and consequently decreases energy and reserve prices. In this paper, impacts of large-scale wind power generation on energy and reserve markets are studied. To this end, we need to know bids of power producers. But, bids of power producers are unknown and changes if wind power penetration is varied. To overcome this problem, first equilibrium of day-ahead energy market is computed at the presence of large-scale wind power generation considering hour-ahead deployment reserve market scenarios. Then, equilibrium of hour-ahead reserve market is computed considering results of day-ahead market. Finally, impacts of large-scale wind power generation on energy and reserve markets are studied at the markets equilibria. The presented model is applied to an 18-unit power system and the results are analyzed.

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.

This paper presents a novel multi-port DC/DC converter which is suitable to be used as the interface of hybrid renewable energy systems. The converter contains three unidirectional power flow ports which two of them are input ports and are connected to two independent energy sources while the third one is the output port that feeds a standalone load. Furthermore, the proposed converter contains a bidirectional power flow port to charge/discharge an energy storage system (battery). In addition to multi-port structure, high boost value of voltage gain is the other merit of the converter. Hybrid system is composed of fuel cell (FC), photovoltaic (PV) panels and a battery pack. Different operating states are discussed, and a control system based on decoupling networks is presented. The control system is able to seek and extract maximum power of PV panel, adjust generated power of FC, and handle charging and discharging modes of battery. In order to control operating modes of the proposed converter, a power management method is also presented. By the way, small signal model is presented for the converter.The bode diagram has been plotted from the small signal model. Then the controller it was designed from the bode diagram. The results of simulation by the PI controller are presented. Also, the simulation results by P&O algorithm for the converter has been evaluated. Several Simulation and experimental tests have been carried out to evaluate the analysis and feasibility of the aforementioned system. The results verify well performance of the converter and confirm the simulations and theoretical results.

Accurate computing of the saturated inductances of Permanent Magnet Synchronous Machine (PMSM) is very important during the design process. In this paper, a new method is presented based on the B-H characteristic of the stator material and unsaturated inductances formulations. This method is used to calculate the saturated inductances of the axial flux PMSM. The synchronous inductance and all of the leakage inductances can be calculated using this method. Two motors with different slot/pole combinations are selected as the case studies. The effectiveness and accuracy of the method is confirmed by 3D Finite Element Analysis (FEA). This method can be extended to other types of electric machines comprising multi-phase winding in their armature such as induction motors and other types of synchronous motors.

This paper presents a new nonlinear backstepping controller for a direct-driven permanent magnet synchronous generator-based wind turbine, which is connected to the power system via back-to-back converters. The proposed controller deals with maximum power point tracking (MPPT) in normal condition and enhances the low-voltage ride-through (LVRT) capability in fault conditions. In this method, to improve LVRT capability, machine-side converter controls dc-link voltage and MPPT is performed by grid side converter. Hence, PMSG output power is reduced very fast and dc-link voltage variation is reduced. Due to nonlinear relationship between dc-link voltage and controller input, nonlinear backstepping controller has good performances. By applying the proposed controller, dc-link overvoltage is significantly decreased. The proposed controller has good performance in comparison with Proportional-Integral (PI) controller and Sliding Mode Controller (SMC). In asymmetrical faults, to decrease grid side active power oscillations, the nonlinear backstepping dual-current controller is designed for positive- and negative- sequence components. The simulation results confirm that the proposed controller is efficient in different conditions.

The optimal management of distributed generation (DG) enhances the efficiency of the distribution system; On the other hand, increasing the interest of customers in optimizing their consumption improves the performance of DG. This act is called demand side management. In this study, a new method based on the intelligent algorithm is proposed to optimal operate the demand side management in the presence of DG units and demand response. Firstly, the best location and capacity of different technologies of DG are selected by optimizing the technical index including the active and reactive loss and the voltage profile. Secondly, the daily performance of multi-DG and grid is optimized with and without considering the demand response. The economic and environmental indices are optimized in this step. In both steps, the non-dominated sorting firefly algorithm is utilized to multi-objective optimize the objective functions and then the fuzzy decision-making method is used to select the best result from the Pareto optimal solutions. Finally, the proposed method is implemented on the IEEE 33-bus distribution system and actual 101-bus distribution systems in Khoy-Iran. The obtained numerical results indicate the impact of the proposed method on improving the technical, economic and environmental indices of the distribution system.

In recent years, most of the loads and distributed generations are connected to the AC grid through the power electronic converters. Using the DC grid beside the AC grid can reduce the conversion stages and power losses. Protection of the DC grids is a challenging issue because of the new structures of DC grids and fast transients of the DC faults. This paper studies the protection of the low voltage DC (LVDC) system in the presence of the photovoltaic (PV) and energy storage systems (ESS). An LVDC system consisting of a DC microgrid is considered and Different operating modes are analyzed. DC faults behavior and protection challenges are discussed for each mode through simulations employing MATLAB software. Finally, some methods are presented to solve the protection challenges. The results show that changing the protection arrangement of the system and choosing suitable control logics for the ESS and the PV prevent the unwanted outage of the loads and provide the possibility of the microgrid operation in islanded mode.

The purpose of this paper is the calculation of Unbalanced Magnetic Force (UMF) in permanent magnet brushless DC (PMBLDC) machines with diametrically asymmetric winding and investigation of UMF variations in the presence of phase advance angle. This paper presents an analytical model of UMF in surface mounted PMBLDC machines that have a fractional ratio of slot number to pole number. This model is according to a 2-D analytical field model. By an appropriate choice for slot number to the pole number ratio, the magnitude of UMF is zero and this is achieved only when the stator slot and coils distribution are symmetrical about the diameter of the machine. The presented model is validated by 2-D finite element analysis and a good agreement is obtained between them. Also, UMF is calculated in the presence of different phase advance angles. UMF was calculated for 33-slot/34-pole and 36-slot/34-pole external rotor machines with analytical and finite element method. A machine with 33-slot/34-pole has significantly larger UMF than the 36-slot/34-pole machine. Also, UMF is calculated for the 33-slot/34-pole machine in the presence of phase advanced angles and results show that the magnitude of UMF changes with the amount of phase advance angle periodically. The impact of phase advance angle method on the magnitude of UMF is investigated for the first time by finite element method. Due to increasing or decreasing of the magnitude of UMF in the presence of different phase advance angles, the magnitude of UMF is an important feature in the selection of appropriate phase advance angle.

This paper presents a model for line extension scheduled to participate in responsive loads in the power system aiming the improvement of techno-economical parameters. The model is studied with the presence of photovoltaic generators that produce variable power depending on the geographical condition. The investment cost of the transmission expansion plan, demand response operation cost, generation costs and the sum of the voltage deviations are the four indices that the optimization problem is designed based on these four criteria. Objective functions are dynamic variables that change daily due to variation in generation and load. A multi-objective optimization method based on the analytic hierarchy technique is employed to solve the problem. The Pareto-optimal set is extracted with gravitational search style and the best solution is fund by AHT manner. Studies are carried out on the modified 30-bus and 24-bus IEEE test system to confirm the capability of the presented model. Two frameworks are defined to compare the suggested manner. A different amount of PV penetration is discussed in several scenarios. Also, load uncertainty is formulated and involved based on probability distribution function.