Showing papers by "Neville R. Watson published in 2016"

Impact of solar photovoltaics on the low-voltage distribution network in New Zealand

Abstract: Residential rooftop-mounted solar photovoltaic (PV) panels are being installed at an increasing rate, both in New Zealand and globally. There have been concerns over possible issues such as overvoltage and overcurrent. These PV systems are mostly connected at low voltage (LV). This study presents a case study of simulating the entire LV network from a single utility, comprising 10,558 11 kV-415 V transformers and their associated distribution feeders. These results are also presented by network type. Various solar PV penetration levels are added to the model and the power-flow results are presented. From these results, possible maximum limits of solar PV penetration are investigated and measures to alleviate overvoltage problems are simulated. The effect of using PV inverters with voltage regulation is simulated. Results show that some minor overvoltage problems can be expected in the future, particularly in urban areas. However, in most cases the overvoltage would not be much higher than the statutory limit of 1.06 p.u.

Harmonic Instability Analysis of a Single-Phase Grid-Connected Converter Using a Harmonic State-Space Modeling Method

Abstract: The increasing number of renewable energy sources in the distribution grid is becoming a major issue for utility companies since grid-connected converters are operating at different operating points due to the probabilistic characteristics of the renewable energy. Usually, the harmonics and impedance from other renewable energy sources are not taken carefully into account in the installation and design of the systems. It can bring an unknown harmonic instability into a multiple power-sourced system and makes the analysis difficult due to the complexity of the grid network. This paper proposes a new model of a single-phase grid-connected renewable energy source by using the harmonic state-space modeling approach, which can identify such problems. The model can be extended to a multiple connected converter analysis. The modeling results show the harmonic impedance matrixes, which represent the harmonic coupling characteristic, as well as different dynamic characteristics. The theoretical modeling and analysis are verified by simulations, as well as experimental results.

Use of smart-meter data to determine distribution system topology

Abstract: Smart-meter data presents an opportunity for utilities to improve their database records, and develop a low-voltage (LV) model which may be useful for outage management and fault detection, isolation and response, phase balancing, and network planning. In addition, impact assessment studies on new technologies can be performed. This study presents several contributions in the area of determining the topology of the LV distribution system. This is in terms of identifying the transformer a particular installation control point is connected to, and the phase if that customer is single-phase. First, harmonic voltage correlation is proposed as it is more robust to noise and missing records than the prior algorithm of voltage correlation. Second, it is demonstrated that smart-meter data can be used to determine the transformer/phase to which a customer is connected and update database records in this regard. To achieve this, a new algorithm based on correlation analysis with the Fisher Z transform is developed. Third, a method to estimate LV feeder and service main impedances is presented. Further work is necessary; however, the results from trials in Auckland, New Zealand are highly promising.

Effectiveness of power electronic voltage regulators in the distribution network

Abstract: Steady-state voltage levels will be a significant problem in the future distribution network due to a high penetration of new technologies, particularly photovoltaics. A smart transformer which incorporates a fixed tap transformer with a power electronic voltage regulator has the potential to mitigate this problem by varying the line voltage automatically in response to changes in loading. This study considers various control strategies for the voltage regulator and looks at the potential impact that a smart transformer could have on reducing system voltage violations. These impact studies are performed on a computer model of an entire utility's distribution system in New Zealand.

Power-Quality Management in New Zealand

Abstract: Power quality (PQ) is a major concern in the relatively small island electrical network of New Zealand. The potential influx of new technologies, such as electric vehicles, heat-pumps, light-emitting diode lighting, etc., could potentially cause electromagnetic-compatibility problems in the future. To manage the PQ into the future, a government-funded project entitled Power Quality (PQ) in Future Electricity Networks (NZ) was instigated. This project was co-funded by the Electricity Engineers' Association of NZ (EEA) and the main deliverable was PQ guidelines that EEA members could adopt in their grid connection codes. Other objectives were to influence device standards and identify mitigation techniques. This paper gives an overview of this project and presents some key findings.

Rapid EV Chargers: Implementation of a Charger

Abstract: The uptake of electric vehicles in New Zealand is rapidly increasing and there is a desire for information about charging systems. This information is required by consumers, engineers, and businesses interested in installing charging infrastructure. This project was completed during the 2015-2016 summer break and aimed to enhance the University of Canterbury EPECentre’s knowledge of charging technologies. In addition to gaining a general understanding of charging technologies, detailed research into rapid DC chargers using the CHAdeMO protocol was conducted. The project also included the building and testing of an open source 12kW rapid DC charger using the CHAdeMO protocol. This paper combines the findings of researching the numerous charging technologies with the practical experience of building the charger. Although the charger was not tested with a compatible car due to time constraints, it was successfully built and initial testing was completed. Plans are also underway to conduct more comprehensive testing on the charger to fully characterise it.

Experimental Evaluation on the Influence of RCD Snubbers in a 3-Level Thyristor Based MLCR CSC

Abstract: Multilevel current reinjection (MLCR) concept provides self-commutation capability to thyristors, enabling thyristor based current source converters (CSC) to operate under negative firing angle. It also lowers the input current harmonic distortion. This is achieved by using an auxiliary reinjection bridge. Extensive experimental results are presented in this paper to analyse the performance of the 3-level MLCR CSC for different snubber components across the reinjection bridge. The trade-off in the choice of the snubber circuit is illustrated, with its influence on the AC side line current and DC side output voltage of the 3-level MLCR CSC.

Measurement of phase dependent impedance for 3-phase diode rectifier

Abstract: This paper presents a new method to measure the phase dependent impedance from an experimental set up. Though most of power electronics based system is gradually migrating to IGBT based voltage source converter due to their controllability, the rectifier composed of diode or thyristor components are still widely used in AC-DC applications because of their cost effectiveness and reliability. However, these topologies generate harmonic problems in their network due to their switching instant variation caused by the frequency and phase of grid voltage. Hence, a lot of solutions have been proposed to provide an optimized solution for better power quality. However, the phase dependent impedance, which is driven by both switching instant variation and frequency coupling between ac and dc network, has not been treated in the design of passive filter or harmonic compensator design for power electronics application. It is found that the phase dependent impedance shows different properties with the impedance profiles, which have been proposed in the research. This paper explains a method to measure the phase dependent impedance profile from an experimental set up. Furthermore, the results are compared with results from time-domain simulations and results from an analytical model developed in the Harmonic State-Space (HSS).

Impacts of new technologies on load profiles

Abstract: Analysis was run for the entirety of 2015 across a number of networks in New Zealand. It is shown that PV does have the ability to reduce the daily peak on a number of days across the year. The case of real interest is the annual peak, which in the case of some electricity distribution businesses would have been reduced by PV generation. The mean reduction to the daily peaks for 2015 and reduction to the single peak load of the year, for varying levels of PV, is shown in the tables below. Electric Vehicles Electric vehicles (EVs) have the potential to create huge changes in demand, not only increasing peak daily demand, but also providing enough demand to shift the daily peak temporally. EV charging load has been modelled under a variety of scenarios. If 100% of the light vehicle fleet were to be electric vehicles with a charging start time normally distributed around 6pm, with a standard deviation of two hours, the peak load on Orion’s network would be increased by 62%.

New Zealand Guideline for the Connection of PV Solar Power and Determining Hosting Capacity for PV Solar Power

Abstract: Small-scale distributed generation (DG) in New Zealand, particularly photovoltaic (PV) generation, has been growing steadily over the past few years. In the last year alone to 31 March 2016, installed PV generation of all capacities has grown by a factor of about 1.6 to reach 37 MW. Approximately 90% (33 MW) of this installed PV capacity is made up of small-scale, single phase residential grid-tied systems with ratings below 10 kW. This corresponds, on average, to approximately 300-400 new PV systems being installed each month within low voltage (LV) distribution networks. Traditionally, the flow of power in electricity distribution networks has been largely unidirectional. However, distributed generation introduces reverse power flows into the LV network when the power produced by DG systems is greater than what can be consumed locally. This introduction of reverse power flows and the dynamic behavior of DG system inverters can negatively impact the electricity network, causing issues such as over-voltage, phase imbalance, overloading of conductors and transformers, and create unique safety challenges. As such, each DG connection application received by electricity distribution businesses (EDBs) presently needs to be carefully considered for its impact on the electricity network. The resourcing demand imposed by larger numbers of connection applications, and the difficulty of technical assessment including congestion evaluation, are likely to increase substantially as DG uptake intensifies. This has prompted the Electric Power Engineering Centre (EPECentre) via its GREEN Grid programme, with the assistance of the electricity industry based Network Analysis Group (NAG), to develop a small-scale inverter based DG connection guideline for New Zealand EDBs. This has been developed on behalf of the Electricity Engineers’ Association (EEA) specifically for the connection of inverter energy systems (IES) of 10 kW or less. This paper summarizes key aspects of this guideline. This includes a streamlined connection application evaluation process that enables EDBs to efficiently categorize DG applications into three groups. These groups vary from those with minimal or moderate network impact that can be autoassessed, to those most likely to cause network congestion that require manual assessment. These categories are determined by looking at the DG hosting capacity specific to the LV network that the DG is connecting to. For two of these categories, mitigation measures for connection, are prescribed. It is also shown how DG hosting capacity can be used to simply evaluate LV network congestion in order to satisfy Electricity Industry Participation Code (EIPC) Part 6 requirements. Key technical requirements for all IES, appropriate for New Zealand conditions, are also summarized. Keywords-congestion; distributed generation; distribution network; hosting capacity; inverter; photovoltaic

The Power Quality trend in a New Zealand Distribution Company

Abstract: Power Quality is an important aspect of network operation as poor power quality causes significant economic loss and disruption. As technology develops, the characteristics of equipment utilising the electrical system is changing. The question is whether this is affecting power quality on the network. The desire for more renewable generation and the drive for energy efficiency with smart appliances and equipment are all changing the equipment being deployed. In this paper an analysis of the trends in the different power quality indices that have occurred over the years is given. This is a difficult task as it requires significant amounts of data which can only be obtained by deploying many PQ monitors and monitoring the output over many years. Fortunately Orion had the foresight to start rolling out PQ monitors in 2007. Although this is only for one electricity distribution company, the trends are expected to be similar since the same technology is deployed throughout the country. How close the trends follow Orion’s needs to be verified. The power quality indices analysed were 3, 5 & 7 harmonic voltages, voltage Total Harmonic Distortion (THD) Absolute Voltage Deviation (AVD) and Voltage Unbalance Factor (VUF). It was found that the observed network does exhibit noticeable trends, particularly in the fall and rise of the 5 and 7 voltage harmonic levels respectively. This was found to be consistent with recent technological developments and their uptake. There is a need to continue to monitor the effects of emerging technologies so as to identify possible problems before they occur and mitigate potential problems by requiring minimum standards or restricting technologies that could have an adverse effect on the network and ensure adequate power quality levels are maintained.