Journal of Energy Management and Technology
Volume:3 Issue: 3, Summer 2019

Energy management system in a microgrid with uncertainties in load, renewable generation and market price is critical for stable operation of the microgrid. Scenario-based robust energy management exploiting upper and lower bounds is used to deal with the uncertainties. Taguchi’s orthogonal array method is used to reduce the large number of scenarios, considering all the possible combinations of max and min values of loads and renewable generations. In this study, uncertainty of market price is handled by robust optimization method, and worst case scenario with the maximum total cost is defined as the output result. Furthermore, demand response program is also considered for the flexible loads, which help the microgrid to operate robustly with a lower cost, in the presence of the uncertainties. In this study, two cases with typical microgrids are considered to evaluate the effectiveness of the proposed method, and GAMS tool is used for implementation of simulations. Additionally, Monte Carlo simulation is applied for verifying the effectiveness of the method.

The classical power supervisory controllers in microgrids generally have a centralized structure to determine the power reference signals of their units. However, by increasing the number and variety of energy storage or other generation units in these systems, the algorithmic complexity of centralized power management controllers increases and their reliability decreases by the addition of new units or outgoing the existing ones. Furthermore, their implementation in outer layers of a hierarchical control system, generally requires the switching between local controllers in the inner layers, with the requirement of bumpless switching to prevent the creation of transient states. To solve these problems, this paper presents a distributed power management system to control the amount of power produced by a microgrid consisting of PV arrays and battery storage system to provide the constant power requirement of the grid. Of the merits of the proposed method, are its simplicity, plug-and-play feature, modularity, more reliability, and no requirement to any switching operations in the local controllers of the PV-battery system. Moreover, in the proposed method, the operating point on the PV array power-voltage (P-V) curve can easily be shifted to the left or right-hand side of the maximum power point (MPP), creating more controllability and flexibility for the constant power generation of the entire system. The satisfactory operation of the proposed distributed control algorithm is verified through the numerical simulations of a 100 kW PV-battery system in a wide range of operating points and for critical operation modes such as fully-charged and fully-discharged batteries.

The need for electricity is playing a vital role in development nature life of communities who live in marshes which is far from any other electricity sources. For this regard, a Stand-Alone solar power system was proposed for electrification as sample Solar Photovoltaic System for home using in Haur Al-Hammar at Al-Nasiriya Governorate. The assessment of 4kW peak capacity Stand-alone Solar PV system was showed it’s satisfactory for providing electricity for all home appliances and there was an access energy that could be used for future extended in loads. This procedure can put it as a guideline design of solar power systems for electrification of many homes which close to each other. The solar photovoltaic home system could provide electricity at daylight for operation all the assumed appliances at full load and gives the user a current for appliances about (7.0A) for continuous 10 hours during night time at 50% depth of discharge. However, the performance ratio PR varies from month to month throughout the year with an average value of 50.3%.

In recent years, simultaneous optimization of two conflicted objective functions become an important topic in power system. In this paper, a multi-objective mixed-integer linear programming (MILP) based model is provided for economic-environmental scheduling of a smart apartment building. The first objective function is the operation cost of the building’s minimization. The minimization of the CO2 emission is considered as the second objective function. The proposed multi-objective problem is solved using the weighted sum approach and the ɛ-constraint method. Then, min-max fuzzy satisfying approach is carried out to select the ideal win-win strategy from the obtained efficient results. The proposed MILP-based sample model is solved using General Algebraic Modeling System (GAMS) under CPLEX solver. Also, two scenarios, weighted sum approach and ɛ-constraint method scenarios, are used to analyse the efficiency of the proposed sample model. By comparing the obtained results, it can be concluded that with considering the ɛ-constraint approach, total operation cost of the building is reduced 24.78% by optimizing the model from economical perspectives. On the other hand, solving the proposed model from environmental perspectives led to a decline of 6.96% in CO2 emission. Also, the weighted sum approach shows a reduction of 25.11% and 10.73% as a result from economic and environmental points of view, respectively.

SoC-based control unit for B4 inverters in a cheap grid-connected Photovoltaic (PV) system is proposed in this paper. Because the inverter is the main element of Photovoltaic module, we utilized the B4 one here for decrement of entire expenditure of Photovoltaic system. This paper also coupled the Photovoltaic system to the main grid via IGBT switches for removing the bulky transformers. Besides, in order to inject the real energy to the main grid, this kind inverter is able to compensate to make up the real power and mitigate the harmonics related to the non-linear loads. Instead of the conventional PV systems on which a DSP processor is used to control the B4 inverter, we applied a zynq-7020 SoC-base control unit for effective control of the B4 inverter. Several characteristics of such control units such as dedicated low power and fast 32bit×32bit multipliers, with modified algorithm, enable the application of the required control methods. The operation of the proposed control unit in a PV system is implemented on zynq-7020. Implementation of the control unit in the SoC zync-7020 is the main contribution of this paper. Comparison with the conventional DSP-based control systems, TMS320F28335 DSP processor, demonstrated the high efficiency of the proposed SoC-based control unit for B4 inverters.

Fault current limiters (FCLs) are proposed widely in literature for improving different characteristics of electric power system. Solving protection problems in smart distribution networks in presence of distributed generation (DG) is an example for the applications of FCLs discussed in recent papers. Voltage sag during faults is a power quality (PQ) concern in the power system. In this paper, it is shown that in smart distribution networks including microgrids, FCL can effectively alleviate this problem, according to the fault location. Therefore, a bidirectional non-superconducting fault current limiter (BNSFCL) is presented in this research, so that the bidirectional fault suppression has become available. Analytical analysis and simulations are provided to validate the effectiveness of the BNSFCL topology. Results show that by using proposed structure in distribution networks with microgrids, both protection and PQ status are enhanced, i.e. the BNSFCL prevents deep voltage sag and protection mis-coordination. The proposed topology can be applied in smart grid architecture _where the bidirectional current flow has made conventional protection schemes useless_ effectively and can have acceptance for implementation as one of the future power system components.

As grid-connected Photovoltaic (PV) based inverters are being used more, these systems play a more important role in the electricity generation by distributed power generators. Power injection to the grid needs to meet predefined standards. In this work, a PV based inverter consist of a Trans-Z-Source network performing as DC-DC power conversion level, is connected to the grid through a LCL filter. The connection through an LCL filter offers certain advantages, but it brings also the disadvantage of having a resonance frequency. A systematic mathematical design procedure for PR controller parameters along with active damping factor is presented and the overall control system leads to a considerably low value of grid current THD. Meanwhile the Maximum Power Point Tracking (MPPT) of the PV arrays is obtained by a modified INC method. Simulations in various conditions are carried out in MATLAB/Simulink environment and results depict suitable performance of the system with designed parameters.