• Energy Research

Most traditional Var compensation-based voltage regulation methods are developed following the single-phase Volt-Var response rule. These methods typically have competent voltage regulation performance with balanced photovoltaic (PV) integration. However, certain randomness of single-phase rooftop PV installation may lead to significant PV power imbalance across three phases, especially in low voltage (LV) distribution systems. In such unbalanced situations, unintended inter-phase Volt-Var response which is ignored in the single-phase Volt-Var response rule will become significant and greatly challenge the effectiveness of the traditional methods on voltage regulation. This can further cause inverter saturation and consequently makes distribution systems vulnerable to overvoltage problems. In this paper, the mathematical equations of unbalanced three-phase Volt-Var response are first derived and analyzed to identify the strong MVE (mutual Var compensation effect) and the weak MVE. This analysis provides the theoretical foundation for the development of the proposed inter-phase coordinated consensus algorithm, which can successfully overcome PV imbalance-induced voltage regulation challenges (e.g., inverter saturation and network overvoltage), while does not need exact system parameters. The effectiveness of this method has been validated by time-series simulations with a real LV distribution system and recorded data.

In many countries, it is common for medium voltage (MV) and low voltage (LV) to share the same pole and power line corridor, and this has been a general practice for decades. The MV line and the LV line separation distance may be short under some situations; therefore the mutual coupling may become substantial, which can have a significant impact on network voltages. In the literature, such coupling effect is generally ignored, and there is a lack of a detailed model of the coupled MV and LV lines for incorporation into load flow programs. This study develops a model for unbalanced distribution lines considering the mutual coupling between different voltage levels. Then the established model is utilised in a current injection load flow program to analyse the MV/LV coupling impacts on distribution system voltage.

Power system low frequency oscillations influence dynamic behaviour of a complex power system and threaten its security. The dynamic performance of power system can be improved by damping low frequency oscillation with the help of supplementary controllers. This paper presents the design of supplementary controller for Static Var Compensator (SVC) to damp low frequency, in particular inter-area oscillations. The controller is designed based on H ∞ loop-shaping technique in which the robust stabilization of the normalised coprime factor plant is formulated into a generalized H ∞ problem. Moreover, the selection of proper feedback signal from the available measurements of the system plays vital role in designing the controller. The residue analysis is used to select the suitable locally available signal as an input signal to the proposed controller. Two power systems with varying sizes and complexities are used to test with the design of the proposed controller. The power systems include the benchmark, two-area system for low frequency oscillation studies and a modified version of a practical system. Both eigenvalue analysis and time domain simulations are used to study the performance of the proposed H ∞ controller.

Abstract Uncertainties at end-user and aggregator levels can be highly detrimental to the practical implementation of residential load control schemes for electricity market applications. Uncertainty factors such as end-user non-compliance, comfort violations and load set-point changes associated with the demand response aggregator are unavoidable in practice. This paper proposes a novel two-stage control algorithm for robust centralised management of aggregate residential loads which guarantee precise load set-point tracking in the presence of uncertainties occurring in real-time while ensuring that end-user thermal comfort is not compromised. The approach is underpinned by optimal selection of appliances based on an emulated supply curve followed by solving a one-step-ahead optimisation problem. Using air conditioners and water heaters as the controllable loads, the paper illustrates the effectiveness of the proposed approach in load management whilst mitigating the effects of unknown uncertainties. Further, the developed control scheme is compared with an existing industry approach. The results yield that the proposed control scheme is robust to uncertainties, preserves thermal comfort and is applicable for practical implementation under existing demand response standards.

A new methodology is proposed for the analysis of generation capacity investment in a deregulated market environment. This methodology proposes to make the investment appraisal using a probabilistic framework. The probabilistic production simulation (PPC) algorithm is used to compute the expected energy generated, taking into account system load variations and plant forced outage rates, while the Monte Carlo approach has been applied to model the electricity price variability seen in a realistic network. The model is able to capture the price and hence the profitability uncertainties for generator companies. Seasonal variation in the electricity prices and the system demand are independently modeled. The method is validated on IEEE RTS system, augmented with realistic market and plant data, by using it to compare the financial viability of several generator investments applying either conventional or directly connected generator (powerformer) technologies. The significance of the results is assessed using several financial risk measures.

This paper introduces a new power flow tracing and subsequently loss allocation method based on loop analysis. The knowledge of the loop paths aids in the visualisation of presumed transfer of power throughout the transmission network. A formalised process of loop identification, based on graph theory, is introduced to ensure that each loop contains at least one active source. This way, the system losses can be readily and justifiably allocated to the active sources in the network without involving any approximations. The proposed method is applied to both a small test system and the IEEE 14-bus test system, demonstrating the features and limitations of the proposed methodology.

This paper provides an overview of load capability and collapse margin analyses carried out on a modified CIGRE 'Nordic' test system and on the large-scale Queensland Transmission system. The importance of certain key generators in the loading capability of a transmission system is highlighted. Emphasis is also placed on the impact of potential installations of PowerformerTM on the loading capability of these two real and representative systems. PowerformerTM is a unique form of generator that can be directly connected to transmission, without the need for a step-up transformer. Select system sensitivity parameters are determined for the two systems and used to aid explanation of the relative importance of the key generators and the impact of Powerformer observer.

In distribution power systems line transposition is not a common practice and phase loading levels are always changing. Therefore, perfect balance is never achieved at a distribution level. Non-transposed lines can cause unequal voltage drops between phases and this may be further exacerbated by uneven loads in each phase. Consequently, the voltage magnitude of a certain phase may suffer a severe decrease, breaching the lower voltage limit or unbalanced three-phase voltages at a remote bus may violate the percentage voltage imbalance accepted in the standards. This paper examines the mechanism of causing uneven voltage drops and investigates the impacts of unbalanced line configurations with different phase loading levels on network voltage imbalance. Methodologies are proposed to analyze voltage drops affected by line and load imbalance. Based on these methods, general guidelines are recommended to mitigate the voltage problems, which are useful for network analysis, planning and reconfiguration.