DC Hybrid Power System Research Articles

An Experimental Investigation into the Feasibility of a DC Hybrid Power Plant for a Northern Sea Route Ship

Increasingly, the melting of Arctic ice due to global warming has provided opportunities for commercial shipping between Asia and Europe. Given the vulnerability of the Arctic environment, especially due to emissions of short-lived pollutants from shipping activities, a more effective propulsion system with a comprehensive control strategy is required to reduce fuel consumption, thus potentially mitigating the impacts of shipping activities on the northern sea route (NSR). In this paper, a shipboard DC hybrid system powered by a combination of diesel generator sets and batteries is proposed and analysed in terms of its application on a ship in the NSR. The specific fuel consumption and various losses in the power sources were analysed to develop an efficiency-optimisation control strategy for the proposed DC hybrid power system. To evaluate the performance of the hybrid power system with the proposed optimisation control strategy, lab-scale experiments have been conducted in the Shanghai Marine Diesel Engine Research Institute to compare the proposed system with a conventional hybrid system. The experimental results indicate that the proposed DC hybrid power plant with the energy optimisation control contributes a 5.35% fuel saving compared with the DC fixed-speed diesel electric configuration during a scaled-down NSR scenario.

Model-based efficiency and emissions evaluation of a marine hybrid power system with load profile

In this paper, an efficiency and emissions evaluation framework for marine DC hybrid power systems is developed based on the physics- and data-based models of the power components. The proposed framework is tested under the operational profile of a real-case semi-submersible drill rig with all-electric propulsion and a suggetsed DC hybrid power system with batteries. The applied load profile, including propulsion, drilling, auxiliary, and hotel loads, shows high fluctuations, indicating the need for battery hybridization. In addition to the operational profile, the impact of the onboard power system configuration, sectionalized and common bus, on the emissions and efficiency has been studied. The results include the total energy efficiency of the ship powertrain from fuel to propulsion load and total CO2 emissions. For the considered vessel power system and operational profile, it is observed that the sectionalized bus configuration performs slightly better in terms of energy efficiency, and consequently fuel consumption and CO2 emissions.

Data-Driven Efficiency Modeling and Analysis of All-Electric Ship Powertrain: A Comparison of Power System Architectures

In this article, a data-driven dynamic efficiency model is developed for efficiency evaluation and comparison of ship electric powertrain with various system configurations. Based on the proposed method, the entire powertrain efficiency is assessed from the fuel consumption to the propulsion unit and the rest of the onboard load. The efficiency model is repeated for the conventional diesel electric and the hybrid power system with batteries. In the latter case, the efficiency of the battery system is also included in the model. Then, the analysis is extended for different power system architectures such as AC and DC onboard power systems. As a case study, system efficiency in a cruise ship is investigated using a real operational profile. A comprehensive analysis is performed to demonstrate the loss distribution in each subsystem of a hybrid AC and DC power system. For a fair comparison between AC and DC, the battery charge level is equalized based on fuel compensation. The case study shows that hybridizing the ship power system increases system efficiency and enhances operational flexibility for the studied use case vessel. Furthermore, the DC hybrid power system can improve the efficiency of the whole ship powertrain due to the variable-speed operation of engines.

Dynamic Modeling, Stability Analysis, and Power Management of Shipboard DC Hybrid Power Systems

This article proposes a framework for the stability analysis and control testing of marine hybrid power systems with dc power architecture. The dynamics of such active systems are increasingly influenced by interactive modes, such as the highly dynamic loads and varying load sharing scenarios, electromechanical modes, and integration of energy storage systems (ESS). Hence, a dynamic model of the entire system is developed, including the power electronics and ESS, electromechanical systems, different controllers, low level and high level, and propulsion loads. The proposed analytical model is used to establish not only the small-signal stability analysis but also time-domain simulations. Then, a set of dynamic analyses and tests has been performed to identify the stability challenges that a vessel may be exposed to during a real operation. The suggestions for improving the system performance are given as the control modification at different levels. To emulate the real operation, a ship operational profile is used for the tests. Finally, the proposed dynamic model is verified with the experimental results conducted in a full-scale hybrid power systems laboratory. The results show that the system dynamics can be affected significantly by the interaction of the high- and low-level controls of the converters, which is usually neglected in conventional models.

Dynamic Modeling and Simulation of a Stand-alone DC Hybrid Microgrid for a Base Transceiver Station in Nigeria

This work considers the dynamic modeling and simulation of a DC hybrid power system for a rural base transceiver station in Nigeria currently being powered by an AC diesel generator (DG). The transient behaviour of the system is studied under varying solar irradiation to ascertain the stability of the power supplied to the sensitive telecommunication equipment. Each component of the system is designed and simulated in a MATLAB/Simulink environment and connected to form the whole system. A permanent Magnet DC diesel generator is used as back-up power for the system. A detailed presentation of the solar array, buck converter, battery storage system, battery controller, diesel generator and the load are presented in this paper. The result shows a stable power output to the load at rated voltage of 48 V.

Dynamic Modeling, Simulation, and Testing of a Marine DC Hybrid Power System

The hybridization of power systems offers the low-emission and energy-efficient marine vessels. However, it increases the complexity of the power system. Design, analysis, control, and optimization of such a sophisticated system require reliable and efficient modeling tools to cover a wide range of applications. In this work, a typical dc hybrid power system model is developed using a bond graph modeling approach. Necessary component models of varying degrees of fidelity are developed and integrated to build a system model with reasonable accuracy. The developed system model, along with the rule-based energy management system, is used to simulate the entire system and to investigate the load-sharing strategies, as well as the system stability in various operating scenarios. Moreover, the simulation results are validated with experimental results conducted on a full-scale laboratory setup of the dc hybrid power system and with a ship load profile. The results show that the system model is capable of capturing the fundamental dynamics of the real system. The hybrid power system model is further used to analyze the bus voltage deviation from its nominal value. The computational efficiency presented by the system is fairly good as it can simulate faster than real-time. The developed system model can be used to build up a comprehensive simulation platform for different system analysis and control designs.

Control Strategy to Generate PWM Signals with Stability Analysis for Dual Input Power Converter System

The prime role of a renewable resource based DC hybrid power system is, to maintain the output voltage constant with higher efficiency. In order to achieve this the duty cycles of the converter switches are dynamically controlled. Multiple input single output (MISO) converter uses separate controller for adjusting the duty cycle, this complicates the design and implementation of the system. Hence, to overcome this limitation a centralized controller is used. The control strategy depends on the pattern of gating signals given to the converter switches. When independent controller is employed, then gating signals of any pattern can be used to drive the switches. However, if a single controller is used, and then a definite pattern is very much essential otherwise, the output voltage and efficiency gets affected. In this paper, an attempt is made to validate and evaluate the performance parameters of MISO converter with two pattern of gating signals; they are synchronized and unsynchronized pulses at their rising edge. The control strategy focusses on the generation of these gating pulses. PID controller is tuned appropriately to determine the gains to achieve the stability of the proposed converter. The dual input power converter validated to show how the PWM pattern affects the efficiency, ripple and regulation of the converter. Using MATLAB SIMULINK platform the simulation of the proposed concept with dual input converter in closed loop is validated. Simulation results proves that synchronized pulses gives DC efficiency of 87% at designed output of 12V output. Converter with unsynchronized PWM pulses operates at lesser efficiency of 75% and the output voltage is of 10V.

Control Strategy to Generate PWM Signals with Stability Analysis for Dual Input Power Converter System

The prime role of a renewable resource based DC hybrid power system is, to maintain the output voltage constant with higher efficiency. In order to achieve this the duty cycles of the converter switches are dynamically controlled. Multiple input single output (MISO) converter uses separate controller for adjusting the duty cycle, this complicates the design and implementation of the system. Hence, to overcome this limitation a centralized controller is used. The control strategy depends on the pattern of gating signals given to the converter switches. When independent controller is employed, then gating signals of any pattern can be used to drive the switches. However, if a single controller is used, and then a definite pattern is very much essential otherwise, the output voltage and efficiency gets affected. In this paper, an attempt is made to validate and evaluate the performance parameters of MISO converter with two pattern of gating signals; they are synchronized and unsynchronized pulses at their rising edge. The control strategy focusses on the generation of these gating pulses. PID controller is tuned appropriately to determine the gains to achieve the stability of the proposed converter. The dual input power converter validated to show how the PWM pattern affects the efficiency, ripple and regulation of the converter. Using MATLAB SIMULINK platform the simulation of the proposed concept with dual input converter in closed loop is validated. Simulation results proves that synchronized pulses gives DC efficiency of 87% at designed output of 12V output. Converter with unsynchronized PWM pulses operates at lesser efficiency of 75% and the output voltage is of 10V.

Research on AC & DC hybrid power supply system with high‐proportion renewable energy of data centre

In the background of the energy Internet, the number of data centres is increasing, aiming at the shortcomings of power supply and reliability in power supply system of traditional data centre and the development trend of green data centres. This article proposes an AC & DC hybrid power supply system with high-proportion renewable energy. The system includes photovoltaic generation, wind power generation, photothermal power generation, thermal utilisation system, power storage system, and different types of loads. Therein, a multi-port power electronic transformer is used to realise AC & DC multi-level mixing system with high proportion of variety of distributed renewable energy. Thereafter, the power supply, power grid, and the load can efficiently complement each other by using the integrated energy storage system such as electricity storage and heat storage. In detail, the rationality and functionality of the AC & DC hybrid power system are analysed through the system simulation and power supply reliability calculation. Moreover, the results show that the proposed hybrid power supply can effectively improve the impact of high-proportion renewable energy access to the grid and provide a new design scheme for the green data centre.

Design and Application Research of an Power Grid Safety Supervision and Management Business Integrated Platform Based On SoTower3.0

Power grid is a kind of important public infrastructure which plays an essential role in guaranteeing the normal operation of economy and society. With several decades of technological development application, State Grid Corporation of China (SGCC) has made remarkable achievements such as the Ultrahigh voltage(UHV) AC and DC hybrid power system, the widespread use of new technology and equipments and the continuing large quantities of projects construction. New problems occur due to the abovementioned new situation, especially in the power grid information technology aspect. The integrated platform for safety supervision and management of power grid enterprises can improve the informatization level of the power grid safety supervision and management and provide a solid guarantee for the reliable operation of the power grid. This paper introduces SoTower3.0 power grid safety supervision and management integrated platform software, which has8 types of functions, including safety accident analysis, potential safety hazard management, comprehensive business management, safety supervision management, safety evaluation, safety training examination, basic security construction and system management, providing informatization support for the efficiency improvement of the power grid safety supervision and management. In addition, the paper analyzes the advantages of the developed SoTower platform application, introduces the system framework design and the specific contents of the above-mentioned 8 functions. Nowadays, the platform has already been applied in power grid enterprises in China, so the network structure and the effectiveness of the applied platform have also been given in this paper.

Analysis and Verification of Differential Protect Operation of AC / DC Hybrid Power

In this paper, the characteristics of AC / DC hybrid faults are analyzed, and the influence of AC / DC hybrid power system on AC current differential protection is analyzed and discussed. When the DC commutation fails, the power frequency current injected into the AC power grid is ahead of its voltage. At this time, the phase angle between the power frequency current and the voltage will change, which will cause the action of the AC line fault. If the current decreases, the brake current will increase, as a result, differential protection refused to action. The PSCAD is used as the platform to simulate the differential protection operation. And the parameter identification based transmission line protection with shunt reactors is proposed. Simulation results show the correctness of the theoretical analysis.

Piecewise Normalized Normal Constraint Method Applied to Minimization of Voltage Deviation and Active Power Loss in an AC–DC Hybrid Power System

In this paper, we establish a mathematical model of the multi-objective reactive power optimization (MORPO) problem in an ac–dc hybrid power system. To get an evenly distributed set of Pareto solutions of this MORPO problem throughout a whole day, we propose a piecewise normalized normal constraint (PNNC) method. Based on this method, the Pareto frontier is divided into four arcs so that the fluctuation of angle between the tangent line at each Pareto point and its sub-Utopia line is reduced. By doing so, the original MORPO problem is transformed into four sets of single objective optimization problems, which can be solved efficiently by a nonlinear primal-dual interior-point method. Performance of the PNNC method is tested on a real ac–dc interconnection system. The results demonstrate that it has the capability to generate a more evenly distributed set of Pareto solutions when compared with the normalized normal constraint (NNC) and weighted sum (WS) methods. In addition, a fuzzy-based membership value assignment method is employed to derive 96 optimal compromise solutions corresponding to 96 time periods in a whole day; the numerical outcomes show that a saving in active power loss and an improvement in the voltage profile can be gained simultaneously.

Optimized efficiency of all-electric ships by dc hybrid power systems

Hybrid power systems with dc distribution are being considered for commercial marine vessels to comply with new stringent environmental regulations, and to achieve higher fuel economy. In this paper, detailed efficiency analysis of a shipboard dc hybrid power system is carried out. An optimization algorithm is proposed to minimize fuel consumption under various loading conditions. The studied system includes diesel engines, synchronous generator–rectifier units, a full-bridge bidirectional converter, and a Li-Ion battery bank as energy storage. In order to evaluate potential fuel saving provided by such a system, an online optimization strategy for fuel consumption is implemented. An Offshore Support Vessel (OSV) is simulated over different operating modes using the online control strategy. The resulted consumed fuel in the simulation is compared to that of a conventional ac power system, and also a dc power system without energy storage. The results show that while the dc system without energy storage provides noticeable fuel saving compared to the conventional ac system, optimal utilization of the energy storage in the dc system results in twice as much fuel saving.

Modeling and Simulation of All-Electric Ships With Low-Voltage DC Hybrid Power Systems

DC hybrid power systems are of interest for future low emission, fuel-efficient vessels. In spite of the advantages they offer onboard a ship, they result in a complex, interconnected system, which requires effective analysis tools to enable a full realization of the advantages. Modeling and simulation are essential tools to facilitate design, analysis, and optimization of the system. This paper reviews modeling of hybrid electric ship components including mechanical and electrical elements. Power electronic converters are modeled by nonlinear averaging methods to suit system-level studies. A unified model for bidirectional converters is proposed to avoid transitions between two separate models. A simulation platform using the derived models is developed for the system-level analysis of hybrid electric ships. Simulation results of power sharing among two diesel generators, a fuel cell module, and an energy storage system are presented for three modes of operation.

Monte Carlo simulation and bootstrap method based assessment of available transfer capability in AC–DC hybrid systems

In practical power markets, available transfer capability (ATC) can provide important information for all parts of power market participants and the assessment of ATC should be carried out instantly. As high voltage direct current (HVDC) systems have been extensively used in modern power systems, less work has been done on evaluation of ATC in AC–DC hybrid power systems. This paper is dealing with the evaluation of ATC for the integration of HVDC link with an AC power system. The mathematical model of ATC for AC–DC hybrid power system is formulated. Considering the time-varying and uncertainties of the power system, several statistical indices are presented to evaluate ATC. A novel approach combined Monte Carlo simulation with bootstrap method is proposed to calculate these statistics. Sequential solution method is employed to deal with the AC–DC power flow and golden section search method is used to accelerate convergence of load flow. The algorithm is developed in the environment of MATLAB R2008a with MATPOWER. Case studies with a modified IEEE RTS-79 24-bus AC–DC hybrid power system and IEEE 3-area RTS-96 system are used to demonstrate the presented approach. The results show that the proposed method is effective and practical. Some new problems are suggested at the end of paper.