A technical and economic comparison is made between DC and AC collection systems of offshore wind farms. DC collection systems have the advantages of reduced weight and size of the DC cables and DC cables are free from reactive power compensation. The heavy 50/60Hz transformers in the offshore transmission platform of AC collection systems can be replaced with smaller size medium frequency transformers in DC collection systems. However, the need for a high power DC–DC converter with high voltage transformation ratios and DC protection methods will remain a challenge for the DC collection systems. Also, DC collection systems do not necessarily reduce the power conversion stages compared to the AC collection systems even if HVDC (High Voltage DC) transmission is used to transfer the offshore wind power from the collection systems to the onshore grids. A cost assessment study verifies that the cost reductions achieved by the reduced size of the DC cables and offshore platform are outweighed by the cost of DC protective devices and DC–DC converters. This is because the length of the DC collection cables is relatively short compared to the long distance HVDC cables. The technical comparison supported by the simulation results shows that the total losses in the DC collection systems are higher than in AC collection systems. The effect of collection bus voltages on the losses is analysed for the DC collection systems

This study presents an analysis of the energy curtailment caused by the DC series–parallel collection systems of HVDC connected offshore wind farms. Wind speed differences between the series connected wind turbines cause unequal voltages at the DC output of the wind turbines. This can lead to unacceptable over‐voltage or under‐voltage conditions. The over‐voltage and under‐voltage conditions on the turbine DC outputs can be avoided by curtailing the power outputs of the wind turbines, which will result in loss of wind power. The annual energy curtailment due to the over‐voltage limits of turbine DC–DC converters is analysed for a 200 MW DC series–parallel wind farm. The impact of wake effects on the energy curtailment losses is quantified and demonstrated with a case study.

This article presents a model-based approach to assess the battery performance of a two-wheeler EV drive train system for various user driving patterns using the selected urban drive cycles. The battery pack is one of the most expensive parts of an EV, and its life is heavily dependent on its usage pattern. The impact of the user’s driving behaviour on the performance parameters of the EV battery pack needs to be investigated. Thus, a two-wheeler EV drive train model was developed in MATLAB with a 5 kW motor, a 4.32 kWh battery, vehicle dynamics, and the power train control algorithms for in-depth analysis of battery performance. The validity of the developed model was tested against various state-of-the-art drive cycles for a duration of 3600 s. Numerous user driving behaviours, such as aggressive, moderate, and slow driving behaviours, were modelled with modified drive cycles, which were used to assess the two-wheeler battery pack performance. An optimum speed range, which ranges from 21 km/h to 34 km/h for different drive cycles, was identified, and these speed ranges minimised the battery energy consumption for the selected drive cycles with the modified drive cycle models.

This paper analyzes one of the most important power capture challenges of the DC series–parallel collection system, called the power curtailment losses. The wind speed difference between the series-connected turbines causes over- and under-voltage conditions in the output voltage of the MVDC (medium-voltage DC) converters of the wind turbine. The power curtailment losses caused by the upper-voltage tolerance levels of the MVDC converters of the wind turbines are analyzed considering a redundancy-based upper-voltage limiting condition. This analysis emphasizes the importance of choosing suitable voltage tolerance levels for the MVDC converters of wind turbines based on the wind farm configuration. The annual energy curtailment losses are quantified and evaluated by a comparative case study performed on a DC series–parallel-connected wind farm rated at 200 MW with the redundancy-based upper-voltage limiting condition.

This paper presents a harmonic compensation method for low-voltage small-scale islanded microgrids, which is implemented using a harmonic observer. The proposed system includes a harmonic observer which helps to decompose the load current harmonics of the non-linear loads. In addition to the load current harmonic decomposition approach, a feed-forward control method is also proposed to reduce the voltage distortion in the islanded microgrid. The main feature of the proposed control system is the estimation of load-induced disturbances and their compensation. Analysis and simulation results are presented to verify the performance of the proposed compensation method.