This year’s session includes 3 final year APE project students, whose presentations are listed below.

Nikitha Rajendran

"Simulation of Power Sharing and Voltage Stability in a DC Nanogrid for Rural Electrification"

The ideology of becoming self-sufficient and shifting from utilising conventional/traditional backup resources to renewable energy resources is a vital process to reach a sustainable future. Interconnected national grids offer the integration of both high output capacity conventional sources & abundantly available distributed energy sources such as Solar (Photovoltaics, PV) & Wind. These national grids, microgrids or traditional minigrids generate adequate energy to satisfy metropolitan cities with unpredictable demands yet, they are built with high project capital investments, inflexible outdated expensive infrastructure (over/under sized), mainly operating through DC/AC conversions that produce large transmission losses & issuing overly priced tariffs for per unit energy access from the main utility. However, traditional national grids or large mini-grids are not economically viable to reach secluded or remote communities/villages in developing countries. For that matter, Off-grid generation or Rural electrification using Distributed Generation (DG) is the most feasible and practical solution for developing rural communities who have a restriction on upfront expenses. This off-grid installation is the result of building an Evolving Grid, i.e., the vision of Establishing Mutually Beneficial Local Energy Markets (EMBLEM). This pilot program developed by Scene Community focusses on providing easy energy access & power availability for communities in Kigali, Rwanda, Africa. Each household is presented with Solar panels, Batteries & a Grid Controller to supply its local DC loads creating a Solar Home System (SHS) only operating through DC/DC conversions. As a single SHS isn’t enough, all SHS’s are interconnected to a common DC bus to form an autonomous grid or a DC Nanogrid (Evolving Grid) resulting in a modular network configuration with bidirectional power flows thus establishing import & export power capabilities between households. This enables consumers to become prosumers thus creating new incomes, employment opportunities & subsidized incentive energy trading. This enables other neighbouring communities to be interdependent with each other. As it’s a modular grid interface, existing DG components can be easily incorporated or additional features may be introduced based on consumer affordability. This method improves electrical capacity, grid efficiency & majorly community lifestyle.

This report focusses on designing, analysing, testing & verifying this DC Nanogrid on MATLAB/Simulink for a sample size interconnection of 3 households/SHS. The network modelling, experimentation & observations highlight and explain PV construction & control, battery system, development of DC load consumption profiles, DC/DC conversion circuitry & mainly provide a control algorithm for the DC/DC Converter or Grid Controller that maintains bidirectional power flow with appropriate interaction between the PV & battery as well as across the households & the common DC bus/grid interface. This results in grid stability, accurate load sharing, grid voltage regulation and power balance at critical conditions.

Yushu Hong

"Design & Model Predictive Control of a High-Bandwidth Silicon Carbide MOSFET 90 kVA Grid Emulator"

In this report, a three-phase four-leg inverter is designed as the grid emulator that is able to generate arbitrary types of voltages to test the (un)balanced/(non)linear grid-connected devices in terms of power quality and grid security. The system is developed based on the current control converter built previously, with updated filter for the best trade-off between voltage distortion and dynamic response, and updated controller incorporating the current limiter to protect the semiconductors from overheat. Besides, modelling of power loss is established to evaluate the power loss of semiconductors and temperature rise of system. A switching frequency reduction method is studied to balance the voltage control and thermal performance. Subsequently, the grid emulation performance is validated through a series of testing with a current control inverter, and modular multilevel converter where the hardware in loop configuration is considered. In addition, the behaviours of grid emulator with multi-step MPC are investigated. Finally, the impact and exploitation of project is discussed.

Wenhao Ma

"A Delta-Connected STATCOM with MBSM and Energy storage"

In this paper, a novel STATCOMs is proposed which combine the multi-busbar sub-modules and partially energy storage elements. The new pattern STATCOM is composed of MBSM topology with partially energy storage components and connect parallelly to the gird in delta. According the phase-shift carrier modulation, a portion of sub-modules in each phase are by-passed if the demand voltage does not meet the maximum rating voltage, the rest multi-busbar sub modules which topology are in parallel enable to deliver the energy to the current load to realize the conduction loss reducing. Meanwhile, MBSM with partially battery energy storage (BEES) have the ability to support dynamic active power and mitigate the flexibility problem in power flow transmission. Injecting different type of circulating current in the STATCOM have varying degrees ability with diverse value of energy storage. Result of simulation indicate that injecting a circulating current greater than three times the energy storage can effectively promote the voltage balance between the MBSMs in each phase. Comparing with the traditional STATCOM, the new one is able to offer more than reactive power but short-term active support to grid.