Daniel Burmester

Single Ended Primary Inductor Converter reliance of efficiency on switching frequency for use in MPPT application

This paper discusses the dependence of efficiency on the switching frequency of a Single Ended Primary Inductor Converter (SEPIC), for use in photovoltaic (PV) maximum power point tracking (MPPT) applications. An MPPT system comprises of a DC/DC converter and tracking algorithm set to run the PV at its maximum power point. The SEPIC is a non-inverting DC/DC converter able to output a voltage greater or less than the input voltage. In this paper we analyse the theoretical losses of the SEPIC and compare them with the practical losses measured at various switching frequency. The results show that the switching frequency of the device determines its physical size, cost and efficiency. The frequencies tested in this paper were 50Khz, 200kHz and 400kHz, with a 7% drop in efficiency between each frequency. As the switching frequency increases, the units become physically smaller and so cheaper. This however is at the cost of efficiency.

Distributed generation nanogrid load control system

As the worlds population becomes more reliant on power, the stability and reliability of power systems also needs to increase. One avenue of research is distributed generation (DG) which decreases the need for long distance distribution. As the generation is close to its point of use, the system becomes better equipped to endure extreme weather events and natural disasters. However, DG is typically renewable energy, which presents its own difficulties, such as, intermittency. This paper proposes a nanogrid control system which will increase the efficient use of DG renewable energy sources. This nanogrid controller implements local source/load control, demand side management, a hierarchical load algorithm and interfaces with a national grid. Simulations show that by implementing the demand side management, the amount of power purchased from the grid can be decreased by up to 23%.

A comparison between temperature and current sensing in photovoltaic maximum power point tracking

Maximum power point tracking algorithms, for photovoltaic modules, commonly use current and voltage sensing as a means of tracking the maximum power point (MPP). This paper experimentally compares the use of a temperature sensing in place of the current sensing for MPP tracking. It does so by implementing two commonly used current sensor algorithms (perturb and observe and incremental conductance) and temperature sensing algorithm (MPPT-temp [1]) to determine which is faster and more accurate. The paper shows, the standard deviation of the two current tracking algorithms is much greater than that of a temperature based algorithm. The temperature sensor also reduces the complexity of circuitry and is a more cost effective solution to maximum power point tracking of photovoltaic modules.

Impact of large-scale integration of distributed photovoltaic with the distribution network

The recent incentivation of renewable energy sources such as photovoltaic (PV) systems and deregulation of the electricity market present a major challenge to the design and operation of the conventional power system. This article presents an impact analysis of this game-changing technology distributed on the IEEE 13-bus distribution feeder using actual local demand load profile, temperature and irradiance data. We analyse impacts on active power demand, voltage and component of power losses at various penetration levels. In addition, simulation results quantifying the components of power losses which are load, line and transformer losses are presented. These losses are pivotal considerations for effective distribution system design as it transits from a passive network to an active one. Using the Open source Distribution System Simulator (OpenDSS), results show a significant decrease in active power demand, load and line losses with improvement in voltage profile at various penetration levels.

Use of Maximum Power Point Tracking Signal for Instantaneous Management of Thermostatically Controlled loads in a DC Nanogrid

In the pursuit of incentivising photovoltaic (PV) installations at a household level, this paper presents a nanogrid control system that utilizes thermostatically controlled loads (TCLs) to increase the correlation between power consumption and PV production. The maximum power point tracking signal is used to implement instantaneous control based on PV power availability, as the TCLs are used to store thermal energy and shift consumption. A model of the nanogrid has been created and simulated under a variety of load and solar irradiance conditions. The results show the system can reduce power purchased from the grid by 44%.

Instantaneous control of a DC water heater for a PV system

Small scale photovoltaic household installations present two major obstacles that hinder their potential to deliver considerable advantages to consumers. These are the intermittent nature of the power supply and large initial financial set up cost. This paper looks to address these disadvantages by analysing the dynamics of a water heater, and utilising its thermal autonomy. A control system is designed to shift the water heaters consumption to times of high PV production. It uses the maximum power point signal to ensure the availability of local production, heating the water to a high operating temperature during this time. To ensure the safety of the users, the control system ensures a constant (safe) temperature output from the water heater, by introducing a controlled cold valve at the output. Across the simulated tests conducted, the system reduced the power purchased from an external source by an average of approximately 62%.

Lightning protection analysis of main shaft bearings in wind turbine generators

One of the major reasons for downtime of wind turbine generators is damage due to lightning strikes. As a result, main shaft bearings at the interface between the rotor and the nacelle have to be protected with a proper lightning protection system. This paper uses wind turbine simulations in PSCAD to evaluate various protection techniques for the main shaft bearings. Lightning protection of bearings by the use of spark gaps, sliding contacts, and a combination of both are quantitatively analyzed here. Finally, an efficient solution for protecting the bearings is recommended. This involves the parallel connection of spark gaps and sliding contacts by which lightning current conduction can be almost completely bypassed from the bearings. Sliding contacts carry the current until the ignition of spark gaps takes place and then current will be shared by the spark gaps to reduce the stress and damage to the sliding contacts.