A Combined High-Efficiency Region Controller to Improve Fuel Consumption of Power-Split HEVs

An improved controller for the energy management system of a power-split hybrid electric vehicle (HEV) is developed with the objectives of minimizing fuel consumption and improving drivability. Considering the specific application of vehicles plying on scheduled trips such as public transport, this paper assumes that the controller is privileged with a priori knowledge of the estimated total tractive energy requirement and the duration of the journey. In comparison to a recently introduced constant high-efficiency region (CHER)-based controller, this paper demonstrates that further reductions in fuel consumption can be achieved under certain driving cycles by limiting the internal-combustion-engine (ICE) operation to a dynamically varying high-efficiency region and adopting state-of-charge (SOC) swing control for battery energy storage. The frequency of engine on/off is therefore directly decided by the size of the energy storage, allowable swing of the SOC, and the tractive energy required. Performances of the CHER and dynamic high-efficiency region (DHER) controllers are compared through simulations against the existing controller of a commercial vehicle. The results reveal that the DHER controller outperforms the other two controllers in terms of fuel consumption in highway-style-driving scenarios. Therefore, to minimize fuel consumption while improving drivability under all driving scenarios, this paper proposes to combine the CHER controller with the DHER controller such that the best features of both controllers can be utilized

A Novel Model of Internal Combustion Engine for High Efficiency Operation of Hybrid Electric Vehicles and Power Systems

This article realizes a novel model of an internal combustion engine (ICE) based on its operating torque and speed for the purpose of designing new control strategies to optimize engine efficiency and performance in hybrid electric vehicles and power systems. The proposed model is developed such that it utilizes only a limited number of experimentally measured operating conditions of the internal combustion engine. Therefore it helps in minimizing the expensive and time consuming testing of the vehicle under a large number of operating conditions in comparison to other models. On the other hand, it is possible to utilise the model to determine a novel control strategy for fuel consumption reduction in plug-in hybrid electric vehicles (PHEV) and hybrid electric vehicles (HEV). This fuel consumption reduction is achieved through the use of the proposed model to predict the efficiency of operation of the ICE instead of the fuel utilization predicted by conventional models. In order to prove the accuracy of the proposed model, efficiency of operation of six known ICEs have been modelled and compared with three existing models utilizing larger numbers of experimental data. The errors in efficiency in comparison to known data are found to be within a reasonable range. The paper finally demonstrates the possible applications of the proposed model in high efficiency control of ICE in a model of the 2010 Toyota Prius developed using experimental data. The demonstration for the proposed model is in the form of a vehicular system however it is envisaged that this model has applications in hybrid power systems also

Steady-State Analysis and Designing Impedance Network of Z-Source Inverters

All possible steady states of a Z-source inverter are identified and analyzed with the objective of deriving design guidelines for the symmetrical impedance network. This paper shows that, in addition to the desired three dynamic states, an operating cycle can contain another three static states that do not contribute to the power conversion process. These three static states can be avoided by selecting suitably large capacitors and inductors. By using the equations derived in the steady-state analysis, this paper presents guidelines to design the impedance network accurately for the case where the inverter is operated only in active and shoot-through states. The proposed design method can also be used to predict the critical values of capacitance and inductance below which static states appear during the operating cycle. Computer simulations and laboratory experiments are used to verify the design method and to demonstrate the appearance of static states when the capacitors and inductors are sized lower than their critical values

Design of the experimental setup for a plug-in hybrid electric vehicle

This paper identifies the procedure utilized to determine the required ratings of components for the experimental setup of a 2 by 2 power-split connected plug-in hybrid electric vehicle. The test vehicle considered for this project has been selected from the available small scale conventionally driven vehicles in Western Australia. The main criteria for vehicle selection required that an existing electrical network was available, with alternator and battery and that the chassis has significant space and supportable structure for the coupling of an electric motor to the driveshaft. Following the selection of the vehicle the appropriate sizing of electrical components was undertaken considering a scaled standardized drive cycle selected to be utilized for testing. This involves the estimation and selection of the electric motor size, energy storage requirement and associated ratings of power electronics for control. The ADVISOR software package has been utilized to support the calculated sizes of electrical components for this experimental setup

Very short-term photovoltaic power forecasting with cloud modeling: A review

This paper endeavors to provide the reader with an overview of the various tools needed to forecast photovoltaic (PV) power within a very short-term horizon. The study focuses on the specific application of a large scale grid-connected PV farm. Solar resource is largely underexploited worldwide whereas it exceeds by far humans' energy needs. In the current context of global warming, PV energy could potentially play a major role to substitute fossil fuels within the main grid in the future. Indeed, the number of utility-scale PV farms is currently fast increasing globally, with planned capacities in excess of several hundred megawatts. This makes the cost of PV-generated electricity quickly plummet and reach parity with non-renewable resources. However, like many other renewable energy sources, PV power depends highly on weather conditions. This particularity makes PV energy difficult to dispatch unless a properly sized and controlled energy storage system (ESU) is used. An accurate power forecasting method is then required to ensure power continuity but also to manage the ramp rates of the overall power system. In order to perform these actions, the forecasting timeframe also called horizon must be first defined according to the grid operation that is considered. This leads to define both spatial and temporal resolutions. As a second step, an adequate source of input data must be selected. As a third step, the input data must be processed with statistical methods. Finally, the processed data are fed to a precise PV model. It is found that forecasting the irradiance and the cell temperature are the best approaches to forecast precisely swift PV power fluctuations due to the cloud cover. A combination of several sources of input data like satellite and land-based sky imaging also lead to the best results for very-short term forecasting

Design and Modeling of a Hundred Percent Renewable Energy Based Suburban Utility

This paper presents the complete system modelling, designing and controlling of an islanded minigrid power supply to the town of Carnarvon, Western Australia. Carnarvon power system is an isolated network supplying power to approximately5000 people via 205km of distribution lines. The existing power system is supplied by a number of large centralized 21MW Diesel Generators. The objective of this paper is to report the design, development and installation of a Photovoltaic (PV) diesel hybrid-power system such that the operating cost can be minimized and the load on the aging generators could be significantly reduced. The proposal includes the installation of two 25kW DC variable speed diesel generators and a suitably sized advanced battery bank at each suburban transformer to ensure hundred percent penetration of solar power by residential customers in the local area. This method of control is modelled and simulated in HOMER, PSpice and Matlab. The different modes of control used to integrate maximum solar energy, reduce diesel consumption and also the methodology imposed to store excess renewable energy for operation during the night

Stability Assessment of a Small Islanded Power Network with High Penetration of Renewable Energy

Electricity generation using renewable energy sources especially wind and solar photovoltaic is increasing rapidly and replacing fossil generation. The impact is more significant in small islanded networks which historically have relied on diesel engines for generation. Since wind and photovoltaic generation is intermittent and unpredictable, it becomes difficult to schedule and manage a small network with varying load demand. Therefore, conventional generation or some kind of energy storage is required to maintain the balance between total network generation and load demand. This paper presents a case study of a small islanded electrical network in Western Australia with various combinations of wind turbines, photovoltaic modules and diesel generators. It studies their impact on voltage and frequency stability of the network with a view to maximize the penetration of renewable energy

Droop based Demand Dispatch for Residential Loads in Smart Grid Application

Aggregated loads play a significant role in maintaining the frequency of power system when the generation is not able to follow frequency deviations. An automatic Demand Dispatch (DD) enables the power system to employ the aggregated loads for balancing demand and supply. In this paper, a Demand Side Frequency Droop (DSFD) has been proposed which provides ancillary service to the grid and maintains the frequency of the power system when the generation system is not capable of following the demand. At the time of a frequency fall/rise, Balancing Authority (BA) can detect aggregated load or group of aggregated loads that have power consumption above or below their standard maximum/minimum consumption levels. Then, the BA issues a droop-based signal to the relevant aggregator. Afterwards, the DSFD will be implemented in the aggregator or the group of aggregators to specify the required power consumption amount for bringing the frequency back to its rated level. Subsequently, this signal will be sent to the Appliance Management Unit (AMU) at each participating house. The AMU sends the signal in the form of deferral or interruptible commands to the appliances depending on the priority, availability and the specification of the appliances. It will be demonstrated that the proposed DSFD control maintains the frequency of the power system within a specified range

Proposing a New Algorithm for Defining the Shortest Distance among ZigBee-Based Communication Devices in Microgrids

To improve the controllability within Future microgrids, a communication network needs to be available to provide data transfer within the MG. Wireless technologies such as ZigBee seem to be a good alternative for data transfer within MGs mainly due to low cost, more flexibility and acceptable data transfer rate. In such networks ZigBee-based repeaters are required to strengthen the communication signals if the DG units are scattered over a vast area. This paper mainly discusses on the algorithms required for defining the shortest distance between the DG units and the MG central controller. Different methods are discussed and a new algorithm is presented. Through the numerical analyses, it is demonstrated that the proposed method leads to a high reduction in the number of repeaters than other conventional algorithms

Developing the ZigBee Based Data Payload Coding for Data Communication in Microgrids

A data coding is presented in this paper for ZigBee-based wireless data communication system for future microgrids. It is assumed that each microgrid has a central controller and each distributed generation unit in the microgrid has a local controller. The communication system is responsible for transmitting and receiving data amongst these controllers. This communication system is based on ZigBee technology, which has low cost and low power consumption. The required data to be transferred are defined and a suitable coding is also proposed. Finally, the number of transmitted symbols and the processing time delay of the proposed data coding are numerically analyzed