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The harmonics exacerbated by the integration of distributed energy such as wind power has been extensively studied. However, the interaction and propagation mechanism between harmonic sources in the hydro-wind complementary generation system are still not clear. To tackle this challenge, the presented study establishes the hydro-wind complementary generation system model and explores the harmonics propagation and interaction in all components. Then three operation mode of complementary system (scenario 1: stand-alone Hydroelectric Generating System, scenario 2: stand-alone Wind Farm (WF) and scenario 3: complementary generation system) are selected. The results demonstrate that the integration of HGS diminishes the harmonic at DFIG side but at the grid side. In complementary generation system, the THD

This paper proposes a novel centralized switching controller for the state of charge balancing of battery energy storage systems distributed in a DC microgrid. The main advantage of the proposed controller is that it can tolerate non-uniform and time-varying delays in the communication links between a central processor and each battery energy storage system. The central processor generates predictive estimates of the renewable energy generation/load and state of charge of each battery energy storage. The switching controller uses the predictive estimates to generate participation rates of battery energy storage systems. The proposed control strategy is integrated with the primary droop control and the secondary voltage control for the power sharing and microgrid voltage restoration. In addition, the proposed control method guarantees that the active battery energy storage systems are either charging or discharging thus eliminating circulating currents. RTDS real-time simulator is used to verify the proposed large time delay tolerant control scheme on a DC microgrid with four distributed battery energy storage systems, loads and a PV generation. Moreover, mathematically rigorous analysis of the proposed control scheme is given.

Currently, communication-based distributed cooperative control strategies are employed to control energy storage systems in an islanded DC datacentre microgrid. This paper proposes a fully decentralized, communication-less control strategy for heterogeneous energy storage devices distributed in the DC datacentre. In the proposed strategy, decentralized virtual resistance based control allocates the low frequency component of loads to batteries while the high frequency component is allocated to ultracapacitors with the virtual capacitive droop control. Furthermore, the proposed control system balances the batteries’ state of charges to a common value. During operation, the microgrid local bus voltages are regulated within 360–400 V range in accordance with the ETSI EN 300 132-3-1 standard. The proposed control approach offers advantages in terms of reliability and flexibility, as it does not require any communication infrastructure. Performance of the proposed decentralized control strategy is demonstrated on an islanded 380 VDC datacentre microgrid with variable loads, using Real-Time Digital Simulator (RTDS) with detailed switching converter models and nonlinear battery models.

There are various studies related to the advantages of implementing home energy management system (HEMS) for residential buildings to minimize the cost of energy consumption and improve user’s comfort level. However, there is still a lack of comprehensive study to evaluate benefits of utilizing HEMS technologies in various residential buildings with different insulation quality (highly or poorly insulated buildings, which can be determined by energy labels). Therefore, in this paper, a concise yet comprehensive comparative analysis is conducted to investigate the operating profits of using HEMS technologies in residential buildings with different energy labels. Moreover, this comparative analysis is performed with two different heat emission systems: radiator only system and a combination of floor–radiator system. The HEMS performance results are presented and compared for both the heating systems in terms of minimizing the cost of energy and the user’s comfort. Also, the results for each building are compared with a baseline case (without HEMS technology) for both heating systems to prove the HEMS performance effectiveness. The simulation results demonstrate that the HEMS operating profits increase as the building insulation quality rises. For example, the HEMS can minimize the cost of energy by 41% in a building with label “A” (highly insulated building), while in a building with label “G”, the energy cost minimization is 26% under the same conditions. Finally, it is proved that the HEMS is more effective with floor-radiator combination heat emission system rather than the radiator only system.

Multi-energy integrated sources are increasingly being used as the bundling-sale for electric systems. Estimating the power supply reliability and regulation performance of the fixed-speed Pumped-Storage Generation Systems (PSGSs) in suppressing power fluctuations of intermittent energy is essential to the operational safety and reliability of a system. However, the regulation process relates to the coupling fluctuations of hydraulic-mechanical-electrical factors, leading to a multiple time-scale effect to the whole hybrid power system. This makes the PSGS’s power response lagging behind the wind power fluctuation and further impacts the power supply reliability of the hybrid power system. To enable the analysis, a numerical model which describes operating states of the presented integrated system, including wind energy and PSGS, is developed in MATLAB/Simulink. Then, ten wind scenarios are selected to study complementation and regulation ability of the PSGS based on a framework of evaluation indicators. The results show that longer power response delay and larger guide vane distance opening result in weaker complementary response of PSGS to wind disturbances. It is also shown that the PSGS provides good complementary capability at lower random wind standard deviation (0.5 vs 1.5), larger wind speed mean value (15 m/s vs 13 m/s) and lower wind speed deviation (5 m/s vs 12 m/s). Furthermore, an unexpected regulation behavior is demonstrated: fast settling and peak times coincide with large variation in overshoot, undershoot and peak value of the power response. This presents a challenge in assessing performance of the integrated generation system. The proposed evaluation method and presented results are important steps to increasing the national power grid capability to accept high integration of multiple energy sources.

An explicit model predictive control (EMPC) system for a hybrid battery-ultracapacitor power source is proposed and experimentally verified in this paper. The main advantage of using the EMPC system is that the control law computation is reduced to evaluation of an explicitly defined piecewise linear function of the states. Separate EMPC systems for the total output current loop, the battery loop and the ultracapacitor loop are designed. This modular design approach allows evaluation of the performance of each individual EMPC system separately and also improves the convergence of the EMPC system design algorithm as the models used to design each loop are smaller. In order to protect the hybrid power source, the designed EMPC systems maintain operation of the hybrid power source within specified constraints, namely, battery and ultracapacitor current constraints, battery state of charge constraints and ultracapacitor voltage constraints. At the same time, the total output current EMPC system allocates high frequency current changes to the ultracapacitor and the low frequency current changes to the battery thus extending the battery lifetime. Presented experimental results verify that the hybrid power source operates within the specified constraints while allocating high and low frequency current changes to the ultracapacitor and battery respectively.

New type of electromechanical balancing device that can be used for active compensation of variable imbalance of a rotational machine is proposed. The balancing device is in a shape of ring with a number of grooves displaced around the axis of rotation. Balancing members (steel balls) are placed into the grooves, and a driving electromagnetic device is used to actively control the movement of the balancing members. The balancing members are moved between radially inner position and radially outer position of the ring. When the proposed device is attached to a rotating machine, the driving electromagnetic device is activated to generate a force on a selected balancing member, so as to displace it and to vary the balancing status. The main advantage of the proposed device is in its capability to reduce rotational imbalance in applications where the value and position of imbalance is variable. The paper presents both finite element analysis results and experimental results of prototype design.

Vibrations are one of the major factors limiting the increase of the storage density of hard disk drives. One of the sources of the vibrations is the unbalance caused by an uneven distribution of the mass on the rotational part of the hard disk drive. This technical note proposes a new method for the reduction of unbalance-induced vibrations. Vibration reduction is achieved by the so-called active balancing technique which represents a new approach as compared with traditional passive balancing methods. The proposed method is using injection of current into the existing windings of an asymmetric spindle motor in order to generate an electromagnetic force which acts against the centrifugal force caused by the unbalance. Advantages and disadvantages of this method are analyzed and discussed.