New grid-tied cascaded multilevel inverter topology with reduced number of switches

Performance of multilevel inverters (MLI) are distinguished because of their low harmonic waveform generation, low filtering requirements on AC side and high voltage application. Among different (MLI) topologies, cascaded multi-level inverters (CMLI) are easier to implement and are much more cost effective. The main drawback of multilevel inverters is requirement of more than one isolated DC source and a lot of switches which makes them bulky and expensive to implement. To address this issue, researchers have investigated new topologies with reduced number of switches compared to conventional multilevel converters. In this paper, a new grid-tied cascaded multi-level topology with reduced number of switches is proposed. Compared to a standard 11-level MLI, the number of switches are reduced. The objective of the design is to reduce the number of DC sources and switches in order to reach the same level of the output voltage. Finally, performance of the proposed topology with a range of modulation and load power factor, operation regarding connection to the grid with closed loop control and comparative study with the other topologies is presented

Development of a Smart Energy Community by Coupling Neighbouring Community Microgrids for Enhanced Power Sharing Using Customised Droop Control

This article aims to develop a smart isolated energy community (EC) by coupling the neighbouring rural community microgrids (CMGs) with enhanced droop control for efficient power sharing. This recommended solution employs a power management (PM) based droop-control to enable independent neighbouring CMGs to share power on an available basis by not constraining CMG inverters to equal power sharing. During the grid-connected mode, the droop control may have different power setpoints of each CMG. However, during the standalone mode of operation, the power setpoint should be defined according to their power rating and availability to maintain the system stability. In this article, a PM strategy is developed to maintain the power setpoints of the autonomous CMGs. An improper selection of power setpoints in autonomous CMG can raise the DC link voltage to an unmanageable value and can cause an inadvertent shutdown of CMG. The suggested PM-based droop control enables the CMG inverter not to restrict the inverter to equal power share but to distribute its active power as available in an asymmetric way, if required. The dynamic performance of the proposed coupled system incorporated with two remote isolated CMGs is investigated in a MATLAB environment. Further, a laboratory prototype of the proposed system has been developed using a LabVIEW-based sbRIO controller to verify the efficacy of the proposed approach

Fault Identification of LCC HVDC Using Signal Processing Techniques

Line commutated HVDC (LCC HVDC) technology has been in operation with a high level reliability and little maintenance requirements for more than 30 years. This technology plays an important role in particular in the wind energy industry. The current-source based or classical LCC-HVDC systems are being considered for buried cable transmission as well as overhead transmission. The fault analysis and protection of LCC-HVDC system is a very important aspect in terms of power system stability. This paper presents a comparative study of abc to dq0 transformation, and wavelet transform-based analysis for the identification of faults in an LCC HVDC system

Probabilistic Risk Assessment of Power Quality Variations and Events under Temporal and Spatial Characteristic of Increased PV Integration in Low-Voltage Distribution Networks

The aim of this paper is to perform a probabilistic risk assessment of power quality variations and events that may arise due to high photovoltaic distributed generation (PVDG) integration in a low-voltage distribution network (LVDN). Due to the spatial and temporal behavior of PV generation and load demand, such an assessment is vital before integrating PVDG at the existing load buses. Two power quality (PQ) variations such as voltage magnitude variation and phase unbalance together with one PQ abnormal event are considered as the PQ impact metrics. These PQ impact metrics are assessed in terms of two PQ indices, namely site and system indices. A Monte Carlo based simulation is applied for the probabilistic risk assessment. From the results, site overvoltage shows a likely impact to observe as the PVDG integration increases. The probability of 20% of customers violating 1.1 p.u. at 100% penetration level is 0.5. Integration of PVDG reduces the voltage unbalance as compared with no or low PVDG penetration. There is a higher probability of observing deep sag at the site as PVDG integration increases. This probabilistic approach can be used as a tool to assess the likely impacts due to PVDG integration against the worst-case scenarios

Community Microgrid Based on Micro-Wind Generation System

Penetration of renewable energy sources (such as solar/wind) are being explored mostly as micro power generation (μGen) or mega power plant system. In recent years, emphasis has been given on Microgrid (μGrid) systems because of their few advantages over μGen systems in terms of power quality, stability, reliability, economics etc. But the commercial installation of the μGrid system is not yet progressing significantly. This paper presents the techno-economic aspects of μGen and μGrid systems towards the development of grid connected community based μGrid (C-μGrid) system. Emphasis has been given to identify the benefits of the μGrid over the μGen system. As a case study, wind energy μGen based C-μGrid system has been considered. Ireland has been chosen as a geographical location where wind power based μGen system is not yet very popular with present REFIT (Renewable Energy Feed-in-Tariff) policy. To discuss the issues, techno-economic analysis has been performed for both the systems. It shows that if the same REFIT policy is applied for C-μGrid system, the system could show better performance over the μGen system in terms of stability and cost of energy (COE)

Power Loss Comparison of DC Side and AC Side Cascaded Modular Multilevel Inverters

High-voltage DC (HVDC) transmission systems based on voltage source converter technology are increasingly being used for interconnecting power networks and for transporting energy from remote renewable energy sources. Modular multilevel converters (MMCs) are emerging as the technology of choice for future HVDC transmission systems. Several MMC topologies have been introduced for high power applications and among them the AC side and the DC side cascaded topologies have received most interest because of their high efficiency, low switching losses and good modularity. In high power applications, the efficiency of the converter is an important consideration. Hence it is essential converter power loss analysis is addressed at design stage. Due to the high number of switches the various MMC topologies, the power loss calculations is particularly complex. This paper presents the analysis of the power losses in both DC side and AC side cascaded converters and compares their overall efficiency for a 500 MW power rating. The nominal values of efficiency quoted for an existing HVDC interconnector between Ireland and Wales are used to verify the methodology used for power loss calculations presented in this paper

Probabilistics Risk Assessment of Power Quality Variations and Events Under Temporal and Spatial Characteristic of Increased PV Integration in Low Voltage Distribution Networks

Integration of PVDG reduces the voltage unbalance as compared with no or low PVDG penetration. There is a higher probability of observing deep sag at the site as PVDG integration increases. This probabilistic approach can be used as a tool to assess the likely impacts due to PVDG integration against the worst-case scenarios

A Study on the Power Quality of DG Integrated Building Energy System in Virtual Environment

In this paper, the electrical energy demand of a typical residential building has been extracted from a Virtual Environment (VE) simulation. The extracted energy demand is generated by input load demand and hourly operating information. Based on the electrical energy demand for a typical day, a building integrated photovoltaic (PV) system is then simulated in MATLAB to extract the current/voltage disturbance information into the network. Outcome of this simulation shows the voltage/current waveform along with the disturbances at different locations in the building. The city of Dublin, Ireland has been chosen as a geographical location and VE-Pro software has been used to develop the virtual environment simulation for the building energy system. The simulation based on VE-Pro and MATLAB indicates the scope for possible placement of Custom Power Devices (CPDs) to improve the power quality of the DG integrated building energy system

Sustainability of Grid-tie Micro-generation System

Both the outcomes of technical and economical feasibility analysis of a renewable based power system should be positive to achieve sustainability. Energy production or Renewable Energy Feed-in-Tariff (REFIT) cost should be lower or higher respectively than the existing grid electricity cost. As the renewable energy sources are variable and where REFIT is also applicable for the system connected to the grid, the detailed hourly time series analysis is very important. Based on this issue, in this paper, a techno-economic feasibility analysis has been performed for a PV based micro-generation system to find out the possible ways to make the micro-generation (μGen) system sustainable in low irradiation region. As a case study, the city of Dublin, Ireland has been chosen for the detailed analysis. Analysis shows how the technological improvement can help to popularize the μGen system in Ireland. The procedure can be followed by other countries as well

Harmonic Power Compensation Capacity of Shunt APF and its Relationship to Design Parameters

VSI-based three-phase; power exchange mechanism; switching dynamics; three-phase systems; active losses; single-phase systems; power tetrahedron phasor diagram; shunt active power filter; harmonic power compensation capacity; four-wire systems; hysteresis band current contro