Phil Ciufo

Solar PV and Battery Storage Integration using a New Configuration of a Three-Level NPC Inverter With Advanced Control Strategy

In this paper, a novel configuration of a three-level neutral-point-clamped (NPC) inverter that can integrate solar photovoltaic (PV) with battery storage in a grid-connected system is proposed. The strength of the proposed topology lies in a novel, extended unbalance three-level vector modulation technique that can generate the correct ac voltage under unbalanced dc voltage conditions. This paper presents the design philosophy of the proposed configuration and the theoretical framework of the proposed modulation technique. A new control algorithm for the proposed system is also presented in order to control the power delivery between the solar PV, battery, and grid, which simultaneously provides maximum power point tracking (MPPT) operation for the solar PV. The effectiveness of the proposed methodology is investigated by the simulation of several scenarios, including battery charging and discharging with different levels of solar irradiation. The proposed methodology and topology is further validated using an experimental setup in the laboratory.

Rectifier Capacitor Filter Stress Analysis When Subject to Regular Voltage Fluctuations

Lamp flicker levels that arise as a result of voltage fluctuations can exceed limits set by appropriate standards. New lamp types such as compact fluorescent lights are less sensitive to voltage fluctuations as their flicker characteristics are considerably different compared to those of the traditional incandescent lamp. These differences could support the moderation of the present voltage fluctuation and flicker standards and hence the associated limits. The potential detrimental effects on electrical equipment which may be caused by relaxation of these limits should be investigated before any changes to the present standards take place. The impact of voltage fluctuations on a full-bridge rectifier with a capacitor filter is considered as a case study in this paper. Such a circuit is found at the front end of many different types of equipment that are connected to the public ac supply network. The capacitor ripple current characteristic is of particular interest. The research reported in this paper indicates that the filter capacitor will accumulate and dissipate increased amount of charge when the rectifier is subjected to ac source voltage fluctuations. The consequence is that the RMS value of the capacitor current will increase, where the magnitude of this increase is related to the modulation frequency and magnitude of the fluctuating voltage. Therefore, an ac supply with a voltage fluctuation component will cause a full-bridge rectifier with capacitor filter to sustain increased stress. This stress may accelerate the capacitor ageing process, eventually resulting in premature equipment failure. The research indicates that there is a need for indices other that the short-term and long-term flicker indices required for equipment compatibility levels.

Power Quality Concerns in Implementing Smart Distribution-Grid Applications

This paper maps the expected and possible adverse consequences for power quality of introducing several smart distribution-grid technologies and applications. The material presented in this paper is the result of discussions in an international CIGRE-CIRED joint working group. The following technologies and applications are discussed: 1) microgrids; 2) advanced voltage control; 3) feeder reconfiguration; and 4) demand-side management. Recommendations are given based on the mapping.

A Novel Modulation Technique and a New Balancing Control Strategy for a Single-Phase Five-Level ANPC Converter

This paper proposes a novel modulation technique and a new balancing control strategy for a single-phase five-level flying-capacitor (FC)-based active-neutral-point-clamped (ANPC) converter. The proposed modulator can control the FC voltage to follow the requested reference value and simultaneously generate the required ac output voltage regardless of the values of the dc capacitor voltages of the converter. By implementing this method, smaller values of the dc-link capacitor and FC can be used even in applications that could experience ripple or transient in the capacitor voltage. In a single-phase five-level ANPC converter applications, where the capacitors can experience pulsation power and dc-link balancing issues, such as grid-connected photovoltaic system, the selection of the reference voltage value for the FC can play an important role to balance the average values of the dc-link capacitor voltage. The proposed new control strategy uses a new reference voltage for the FC to be applied by the new modulator to have an average balanced dc-link voltages as well as an ac output voltage with good power quality. Simulation studies and experimental results demonstrate the effectiveness of the proposed modulation technique and control strategy even with relatively small dc capacitors to produce high-quality output voltage and current waveforms while maintaining an average balanced dc-link voltages.

Large Scale Proactive Power-Quality Monitoring: An Example From Australia

In Australia and many other countries, distribution network service providers (DNSPs) have an obligation to their customers to provide electrical power that is reliable and of high quality. Failure to do so may have significant implications ranging from financial penalties theoretically through to the loss of a license to distribute electricity. In order to ensure the reliability and quality of supply are met, DNSPs engage in monitoring and reporting practice. This paper provides an overview of a large long-running power-quality monitoring project that has involved most of Australias DNSPs at one time or another. This paper describes the challenges associated with conducting the project as well as some of the important outcomes and lessons learned. A number of novel reporting techniques that have been developed as part of the monitoring project are also presented. A discussion about large-volume data management, and issues related to reporting requirements in future distribution networks is included.

Statistical analysis of overvoltages due to the energisation of a 132 kV underground cable

Analysis by means of simulation studies is essential for providing useful information to distribution engineers and researchers regarding high frequency switching transients in cable systems. The behaviour of transients due to switching is strongly dependent on the pole closing span of the circuit breaker and also the closing angle of the power frequency voltage. This behaviour requires the study of overvoltage magnitude distributions to be carried out using a statistical approach. This paper presents an analysis of overvoltage sensitivity due to circuit breaker operations when energising an unloaded 132 kV underground cable system. Based on two approaches, the overvoltage values at the sending and receiving end tends to vary between approximately 1.8 p.u. to up to 2.1 p.u. respectively. Other related information is presented especially the useful data for consideration of protective schemes as well as the coordination of insulation systems.

Power quality in the future grid — Results from CIGRE/CIRED JWG C4.24

This paper gives a status report on activities of CIGRE/CIRED JWG C4.24. The following issues are addressed in the paper: Introduction, scope of the report and terminology; New developments in power electronics (PE); Changes in probability of interference; Microgrids and PQ; Volt-VAR control and PQ; Feeder reconfiguration and PQ; Demand side management and PQ; New measurement techniques; New mitigation.

Methods for Harmonic Analysis and Reporting in Future Grid Applications

The rollout of advanced metering infrastructure, advanced distribution automation schemes, and integration of generation into distribution networks, along with a raising of awareness of power quality (PQ), means that there is an increase in the availability of power system monitoring data. In particular, the data for harmonics, whether it is voltage or current harmonics, is now available from a large number of sites and from a diverse range of PQ instruments. The traditional analysis and reporting of power quality examines harmonic orders to the 50th. This means that the harmonic data available for analysis are significantly larger than, for example, steady-state voltage variations where only a few parameters are examined (e.g., the voltage on each phase). Higher frequency components, sometimes called high-frequency harmonics, in the 10–250 kHz range arising primarily due to power-electronic interfaced generation are also becoming significant. Given the vast amount of harmonic data that will be captured through grid instrumentation, a significant challenge lies in developing methods of analysis and reporting that reduces the data to a form that is easily understood and clearly identifies issues but does not omit important details. This paper introduces a number of novel methods of analysis and reporting which can be used to reduce vast amounts of harmonic data for individual harmonic orders down to a small number of indices or graphical representations which can be used to describe harmonic behavior at an individual site as well as at many sites across an electricity network. The methods presented can be used to rank site performance in order for mitigation strategies. The application of each method described is investigated using real-world data.

Visualising the effect of DG on voltage profile in medium voltage distribution networks

Distributed renewable generation is increasing all over the world. The effect of Distributed Generation (DG) on system voltage profile can be examined through sensitivity studies. The sensitivity matrix depicts variations in the voltage magnitude with respect to changes in active and reactive power associated with loads and local generation at different buses in the system. This sensitivity matrix represents a large amount of data which is difficult to interpret. Furthermore the vast amount of information becomes cumbersome to utilise during the design process. Visualisation can be used as an effective tool to examine the voltage magnitudes and the spheres of influence created by DG installations at different buses. To identify the system condition in a clear and insightful way, visualisation is carried out on a 33 bus distribution network using MATLAB.

Novel modulation and control strategy for five-level ANPC converter with unbalanced DC voltage applied to a single-phase grid connected PV system

This paper proposes a new control strategy and a novel modulation technique for a grid-connected photo-voltaic (PV) system using a single-phase five-level flying capacitor (FC) based active-neutral-point-clamped (ANPC) converter. The proposed modulator can control the FC voltage to follow the requested reference value and simultaneously generate the required ac output voltage regardless of the values of the dc capacitor voltages of the converter. By implementing this method, smaller values of dc-link and flying capacitors can be used even in applications that could experience ripple or transient in the capacitors voltage. In the grid-connected single-phase five-level ANPC, where the capacitors can experience pulsation power and dc-link balancing issues, the selection of the reference voltage value for the FC can play an important role to balance the average values of the dc-link capacitors voltage. The proposed new control strategy uses a new reference voltage for the FC to be applied by the new modulator to have an average balanced dc-link voltages as well as an ac output voltage with good power quality. Simulation studies demonstrate the effectiveness of the proposed modulation technique and control strategy even with using relatively small dc capacitors to produce high quality output voltage and current and maintaining an average balanced dc-link voltages.