Iman Mazhari

Design and implementation of distributed control architecture of an AC-stacked PV inverter

A control scheme for a distributed Inverter Molecule™ architecture is analyzed and implemented in this paper. An Inverter Molecule is a building block for a novel distributed inverter architecture suitable for PV/Battery applications which exceeds the performance metrics obtained by Central/String- inverters with or without DC/DC optimizers or by Micro-Inverters. The proposed transformerless architecture utilizes low-voltage semiconductor devices with much higher yields than their high-voltage counterparts. A group of Inverter Molecules operate autonomously and cooperatively to maintain the grid interconnection requirements while providing maximum power control on each molecules PV panel. This paper overviews the state-of the-art control methods implemented mostly on cascaded H-bridge derived topologies and further establishes a distributed control scheme for Inverter Molecule architecture that does not need any high bandwidth communications except a heartbeat signal at line frequency. Experimental results are presented for a lab-scaled prototype.

Locking frequency band detection method for grid-tied PV inverter islanding protection

Islanding is an undesired event in which a portion of utility system containing both load and distributed resources remains energized while it is isolated from the remainder of the utility system. In case of islanding, successful detection is required to protect the equipment, and provide safety of the maintenance service workers. This paper shows an implementation of a novel algorithm named Locking Frequency Band Detection (LFBD) method on a distributed PV inverter architecture. Fast detection, easy implementation, no impact on the power quality and zero Non Detection Zone (NDZ) are among many benefits of the proposed algorithm.

Simulation of Induction Motor Starting With SVC

This paper presents a schematic scheme to evaluate the results from different methods for starting induction motors. The simulation of an induction motor starting is done and the results are shown. Since bus voltages in power systems have unremitting variations, significance of the voltage compensation is evident. These variations are more obvious in the bus connected to the motor. There are many methods for solving this problem. In this paper, some conventional methods starting with Wye/Delta connection and soft starter are discussed and comparison between them is done. Furthermore, for understanding the starting performance clearly, the starting with Wye/Delta connection and static var compensator (SVC) in a sample power system is done and comparison between the final results is shown. Finally, some significant conclusions are obtained and advantages and disadvantages of described methods are discussed.

Design and evaluation of high current PCB embedded inductor for high frequency inverters

This paper describes the design and evaluation of high current toroidal Printed Circuit Board (PCB) embedded inductor applicable for high frequency DC/AC converters (lower than 10MHz). The equivalent circuit model of the inductor is presented and the filtering effectiveness is verified by testing three different geometries with its own characteristics and function through a GaN converter. Besides, the temperature rise analysis is provided for all the prototypes by using finite element methods, and the obtained results are also verified by experiments. The reason behind asymmetric trend of temperature rise for the toroidal PCB embedded inductor is also discussed through both simulation and experiment, and the capability of using a heat sink to lower the temperature increment for different geometries is explained.

Multi-mode operation of different PV/BESS architectures in a microgrid: Grid-tied and island mode

The performance of two different solar photovoltaic (PV)/battery energy storage system (BESS) architectures are compared on a simulated microgrid testbed. The PV system is interfaced with the BESS at the DC link to provide reserve power. These two different integrated solutions can be compared with regards to the number of power stages, efficiency, storage system flexibility, and control complexity. A single power conversion system named Reconfigurable Solar Converter (RSC) presents more flexibility, less complexity, and multi-mode capability depending on system requirement, and results in a more efficient and economical system compared with a current indirect PV/battery system with two stages of power conversion units. There are various approaches to share the load when microgrids are islanded or disconnected from the main grid. In the islanded mode, a distributed generator (DG) like a diesel generator can enhance the reliability of the power supply and regulate the frequency and voltage within the microgrid. Different operation modes for both topologies such as PV to grid, PV plus battery to the grid, battery to the grid (DC to AC) and PV to battery (DC to DC) are simulated on a microgrid testbed, verifying the applicability of the two architectures in microgrids.

Distributed PV-battery architectures with reconfigurable power conversion units

A family of single-stage converters called Reconfigurable Solar Converter (RSC) is presented for integration of energy storage with a PV system where ramp-rate control and peak-shifting is desired. An algorithm designed to reduce the variability of photovoltaic (PV) power output by using a battery demonstrates the PV power output smoothing. The purpose of the battery is to add power to the PV output (or subtract power from the PV output) to smooth out the fast variations of the PV power that occur during periods with transient cloud shadows on the PV array. The proposed solution potentially requires minimal complexity and modifications to the PV converter for PV-battery systems application, and it will provide new architectures and utilization methods for achieving more efficient and more controllable PV farms. These architectures will potentially create flexible, retrofit and expandable platforms for current and future PV power plants.

Locking frequency band exposure method for islanding detection and prevention in distributed generation

This paper presents a novel active method in islanding detection for distributed generation and microgrids. The proposed method, Locking Frequency Band Exposure (LFBE) is a software-based algorithm that utilizes the microgrid frequency. When power demand in the microgrid exceeds the power generation, frequency falls and when the power demand from the grid matches very closely to that of local generation, the frequency does not vary appreciably. In this method, by measuring the variations of command frequency which is created by adding some disturbance to the sampled frequency at the PCC, islanding can be detected. Assuming the exact power match in the microgrid, Tank or Islanding conditions are experienced. It is also possible to discriminate between these two conditions from the microgrids behavior. This proposed method of detection is shown to be robust, able to detect both islanding and tank, and simple to be implemented.

Comparing ramp rate control method for PV-energy storage systems in cascaded and parallel architectures

Energy storage systems (ESS) are broadly employed to smooth out the fluctuation in the PV output caused by cloud passing, or variability of solar irradiance with a high ramp rate. This paper compares the smoothing operation, and ramp rate control in two different architectures: cascaded and parallel topologies. Parallel architecture with reduced number of power switches, simpler controller, and as a retrofit for common three phase inverters improves the obtained efficiency, however cascaded architecture in which two PV and ESS modules are connected in series provides better flexibility, and faster response time to ramp rate variations. In this paper, detailed comparison of the architectures is explained and their performance to reduce the ramp rate is investigated.

Thermal storage capacity to enhance network flexibility in Dual Demand Side Management

The global concern for the environment and greater increase in the demand for electricity justifies integration of electrical and thermal units in the future smart grids to improve the system efficiency and reduce costs and emissions. In the distribution networks, micro-Combined Heat and Power unit equipped with a thermal storage system is an excellent candidate to meet the electrical and thermal demands. The aim of this paper is to present agent-based optimal control methodology to obtain higher flexibility for supplier to match the generations and demands. The market-based stochastic model for reducing the overall cost of generation and increasing the financial gain as long as supplying sufficient power to consumers in distribution level is described. The proposed algorithm is able to reach the optimum cost dispatching values according to different user behaviors and statistical data for switching micro-Combined Heat and Power units which are equipped with a thermal storage.

A Comprehensive Approach to Investigate Parameters Sensitivity of Three Phases Induction Motors using MATLAB/Simulink

This paper present the schematic scheme to evaluate the effects of changing basic parameters of 3 phases induction motors. The proposed approach has been applied to four motors in varied range of power. Dynamic analysis of a three-phases induction motor is studied and the machine dynamics are presented by a set of time-varying differential equations. The analysis and simulation of the mentioned method are shown and comparison of results has been done. The obtained shows that there is a significant difference between dynamic behaviour of low power and high power simulated machines.