Zhao Xu

Zhao Xu
The Hong Kong Polytechnic University | PolyU · Department of Electrical Engineering

PhD

About

286
Publications
47,303
Reads
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8,863
Citations
Additional affiliations
July 2017 - present
The Hong Kong Polytechnic University
Position
  • Professor
February 2010 - July 2017
The Hong Kong Polytechnic University
Position
  • Professor (Associate)
May 2006 - February 2010
Technical University of Denmark
Position
  • Professor

Publications

Publications (286)
Article
Full-text available
Abstract Variable renewable generation and load fluctuations induce significant balancing cost in power system operation. To overcome this issue, this paper proposes a control architecture that leverages inherent regulation capabilities of wind turbines to minimize the system‐wide balancing costs. Instead of handling wind power fluctuations via pow...
Article
To increase the energy utilization efficiency, it becomes fairly promising to convert the surplus electricity from renewable generation to other forms of energy for multi-dimensional consumption. In this paper, we propose a hybrid energy scheduling model for a multi-energy microgrid with the integration of the hydrogen energy storage system (HESS)...
Article
The single-phase microinverter (SMI) is becoming one of the most cost-efficient interfaces for bridging photovoltaics (PV) and power systems. However, in the maximum power point tracking operation, the SMI injects an intermittent active power to the grid, which leads to voltage variations at the point of common coupling (PCC). This certainly dampen...
Article
Decentralized peer-to-peer energy sharing techniques are highly promising to become the next-generation regime for smart building energy management, which can impulse the realization of nearly net-zero energy buildings. In this context, this paper proposes a comprehensive energy sharing framework for smart buildings in considering multiple dynamic...
Article
Full-text available
This paper proposed two strategies for permanent magnet synchronous generator-based wind turbine (PMSG-based WT) with independent grid-forming ability considering the coordination of two-end converters of WT and the demand response in stand-alone operation mode (SAOM). In Strategy I, the grid side converter (GSC) of WT is controlled as an ideal vol...
Article
Since the connection of small-scale wind farms to distribution networks, power grid voltage stability has been reduced with increasing wind penetration in recent years, owing to the variable reactive power consumption of wind generators. In this study, a two-stage reactive power optimization method based on the alternating direction method of multi...
Preprint
Energy management of buildings is of vital importance for the urban low-carbon transition. This paper proposes a sustainable energy cooperation framework for the building community by communication-efficient peer-to-peer transaction. Firstly, the energy cooperation of buildings is formulated as a social welfare maximization problem, in which buildi...
Article
Full-text available
The requirement of fast fault isolation poses a great challenge to the safe operation of multi-terminal direct current (MTDC) systems. In order to make a better tradeoff between the speed and reliability of the protection scheme, it is imperative to mine more valuable information from fault transient signals. This paper puts forward a data-driven f...
Article
Full-text available
Traditional permanent magnet synchronous generator (PMSG)‐based wind turbine (WT) normally utilises phase lock loop (PLL) for obtaining accurate phase angle of AC grid to make sure of maximum power point tracking (MPPT). However, a weak AC system with a low short circuit ratio (SCR) and high control bandwidth of PLL might have impaired effects on t...
Article
Full-text available
As the local energy sources are mostly uncertain and fluctuating in nature, the ‘energy risk’ due to discrepancies between committed energy transactions and metered measurements is prominent in peer to peer (P2P) markets. We propose a P2P market settlement mechanism which lowers this risk and maximizes the welfare of buyers and sellers. The risk in...
Article
Full-text available
With growing concerns on environmental pollution and energy crisis together with the low-carbon transition requirements, renewable energy techniques have been regarded as a crucial solution for ensuring energy clean and sustainable development. This Special Issue is organized to introduce the latest research in the field of high-penetration renewab...
Article
Full-text available
The increasing penetration of photovoltaic (PV) energy in power grids will impose system instability issues, especially in the occurrence of faults. However, very limited research has been conducted on the low‐voltage ride‐through (LVRT) control of PV systems in the low‐voltage distribution networks (LVDNs) with predominantly resistive line impedan...
Article
Full-text available
Accurate power system state estimation (SE) is essential for power system control, optimisation, and security analyses. In this work, a model‐free and fully data‐driven approach was proposed for power system static SE based on a conditional generative adversarial network (GAN). Comparing with the conventional SE approach, i.e. weighted least square...
Article
Full-text available
In this study, a novel data-driven based dynamic pricing framework is proposed for sharing rooftop photovoltaic (PV) energy in a single apartment building. In this framework, the input includes the load data, electricity price data, and PV power data and the output includes the pricing strategy for local PV generations. Specifically, the building e...
Article
Full-text available
This paper focuses on optimal voltage regulators (VRs) planning to maximize the photovoltaic (PV) energy integration in distribution grids. To describe the amount of dynamic PV energy that can be integrated into the power system, the concept of PV accommodation capability (PVAC) is introduced and modeled with optimization. Our proposed planning mod...
Article
Full-text available
In this paper, a novel machine learning based data-driven pricing method is proposed for sharing rooftop photovoltaic (PV) generation and energy storage (ES) in an electrically interconnected residential building cluster (RBC). In the studied problem, the energy sharing process is modeled by the leader-followers Stackelberg game where the owner of...
Article
Deployment of PV generation has been recognized as one of the promising measures taken for mitigating the environmental issues worldwide. To seamlessly integrate PV and other renewables, accurate prediction is imperative to ensure the reliability and economy of the power system. Distinguished from most existing methods, this work presents a novel r...
Article
High renewables embedded microgrid is an emerging paradigm of distributed power systems, which can locally digest intermittent generation and load demand. Due to less aggregation effect, the uncertainty issues associated with renewables and load become much more evident in small-scale microgrids, which make the energy scheduling issue even more cha...
Article
The unbalanced nature of the distribution networks (DNs) and communication asynchrony pose considerable challenges to the distributed voltage regulation. In this paper, two distributed voltage control algorithms are proposed to overcome these challenges in multiphase unbalanced DNs. The proposed algorithms can be leveraged in online implementations...
Article
Full-text available
Traditional way to enable frequency support provided by MTDC system for the connected weak AC systems is to modify the power reference of each converter under standard power‐sharing droop control based on the weak grid's frequency deviations. However, this scheme artificially couples all asynchronous AC systems to tackle with the frequency disturba...
Preprint
As the local energy sources are mostly uncertain and fluctuating in nature, the ‘energy risk’ due to discrepancies between committed energy transactions and metered measurements is prominent in peer to peer (P2P) markets. We propose a P2P market settlement mechanism which lowers this risk and maximizes the welfare of buyers and sellers. The risk in...
Preprint
Full-text available
As the local energy sources are mostly uncertain and fluctuating in nature, the ‘energy risk’ due to discrepancies between committed energy transactions and metered measurements is prominent in peer to peer (P2P) markets. We propose a P2P market settlement mechanism which lowers this risk and maximizes the welfare of buyers and sellers. The risk in...
Article
The identification of the distribution system topology is the key concern in distribution system state estimation and the precondition for its energy management. However, lacking sufficient measurement devices, full-scale identification of entire distribution grid can hardly be achievable in practice. The frequent topology changes in distribution s...
Article
This paper proposes a hierarchically coordinated control scheme for DC MG clusters under uncertainty. In each MG, the tertiary level controller optimizes the operating cost in the MG considering the real-time uncertainties of renewable generations and loads deviated from the forecasting data; and the primary controller responds to the real-time pow...
Article
Full-text available
This paper proposes a novel two-stage game-theoretic residential photovoltaic (PV) panels planning framework for distribution grids with potential PV prosumers. One innovative contribution is that a residential PV panels location-allocation model is integrated with the energy sharing mechanism to increase economic benefits to PV prosumers and meanw...
Article
Full-text available
This paper proposes a novel framework for home energy management (HEM) based on reinforcement learning in achieving efficient home-based demand response (DR). The concerned hour-ahead energy consumption scheduling problem is duly formulated as a finite Markov decision process (FMDP) with discrete time steps. To tackle this problem, a data-driven me...
Article
The hybrid fuel cell/supercapacitor (FC/SC) system is a promising on-board power supply system for more electric aircraft (MEA), where system stability is a critical issue due to the high penetration of constant power loads in MEA. This paper proposes a composite finite-time controller for decentralized power sharing and stabilization of the hybrid...
Article
This paper presents a new real-time optimal mileage based dispatch (OMD) algorithm for a generating company (GenCo) responding to the automatic generation control (AGC) dispatch signals in real time in context of a performance-based frequency regulation market. Distinguished from traditional methods, the proposed method innovatively incorporates th...
Chapter
Accurate prediction of solar power is important to the grid operator for ensuring energy management from multiple sources without jeopardizing stability and to the PV plant owner for scheduling plant maintenance periods and avoiding power imbalance costs. It is evident that meteorological data like solar irradiance is more readily available than th...
Article
For the conventional configuration of the single-phase electric springs, the electrolytic capacitor (E-cap) is required for buffering the double-line-frequency DC-link power. This demands large capacitance and constant average DC-link voltage for achieving sufficiently low voltage ripples of the E-cap, which renders low efficiency and poor reliabil...
Article
Hybrid AC/DC microgrids (MGs) provide efficient integration of renewable sources into grids and the interconnec-tion of multiple MGs can improve system reliability, efficiency and economy by energy sharing. In this paper, a distributed and robust energy management system is proposed for networked hybrid AC/DC MGs. For each individual MG, an adjusta...
Article
Full-text available
The wind-photovoltaic (PV) hybrid renewable energy system (HRES), which consists of permanent magnet synchronous generators (PMSG) and PV arrays, is becoming a cost-effective electric source for powering islanded areas. However, high penetration of renewables makes the power system vulnerable to transient voltage faults, which undermines the stabil...
Article
Full-text available
Existing converter models for DC fault analysis are normally reduced as simplified electrical components, whereas it overlooks the impacts of fast converter current control loops dynamics. Therefore, the DC fault current calculation with the traditional simplified converter models becomes invalid when the simulation time is longer. To overcome this...
Conference Paper
Full-text available
The application of artificial neural network to load forecasting can overcome the problem of dynamic load change, and its ability to adapt to nonlinear relationships makes the prediction result satisfactory. This paper firstly reviews and introduces the concepts and basic principles of load prediction, discusses various methods for load forecasting...
Article
Full-text available
As an emerging paradigm in distributed power systems, microgrids provide promising solutions to local renewable energy generation and load demand satisfaction. However, the intermittency of renewables and temporal uncertainty in electrical load create great challenges to energy scheduling, especially for small-scale microgrids. Instead of deploying...
Article
In this paper, we study the optimal sizing planning of renewable distributed generation (RDG) in distribution networks to minimize the long-term cost, including the investment cost, maintenance cost, and operating cost. In particular, the operating cost itself is optimized by solving an optimal power flow (OPF) problem at each time t based on uncer...
Article
Series dc electric springs (series ESs) can tackle the intermittency of the renewable generations (RGs) with reduced storage capacity in dc microgrids (MGs). They can actively manipulate the power profiles of the serially connected noncritical loads (NCLs) to follow the fluctuating RG. In the process of regulating the dc bus voltages, the power rat...
Preprint
Economic dispatch (ED) plays an important role in economic operation of the microgrid (MG). However, the communication links among distributed generators (DGs) may practically be corrupted by additive noise, resulting in erroneous deviations from ED commands. To deal with such issues, this paper proposes a distributed noise-resilient ED strategy fo...
Article
This article presents a coordinated control scheme enabling the voltage source converter-based high-voltage direct current (VSC-HVDC) transmission system connected offshore wind farm to provide frequency response. Once the onshore system frequency deviates, the proposed control strategy will be activated so that both the wind farm and the VSC-HVDC...
Article
Conventional wind power smoothing control adopts hard-coded filtering algorithms to produce smoothed power output without considering the actual system need. This paper proposes a novel smoothing control paradigm in context of performance-based regulation service, in which the actual balancing need is considered and formulated as AGC regulation mil...
Conference Paper
Full-text available
In this paper, thermostatically controlled loads (TCLs) to the provision of fastancillary services are investigated. In a residential community, a population of TCLs in smart buildings is able to respond to fast regulation signals in a distributed way via sparse communication infrastructure. A two-layer distributed consensus protocol (TLDCP) is pro...
Article
Full-text available
Inertia effect and damping capacity, which are the basic characteristics of traditional power systems, are critical to grid frequency stability. However, the inertia and damping characteristics of grid-tied photovoltaic generation systems (GPVGS), which may affect the frequency stability of the grid with high proportional GPVGS, are not yet clear....
Article
Full-text available
Economic dispatch (ED) plays an important role in safeguarding secure and economic operation of the microgrid (MG). However, the communication links among distributed generators (DGs) may practically be corrupted by additive noise, resulting in erroneous deviations from ED commands or even blackouts. To deal with such issues, this paper proposes a...
Article
Full-text available
It is of great significance for voltage source converter (VSC) based multi-terminal DC (MTDC) grid to isolate the DC fault lines within several milliseconds after DC fault. Existing protection schemes and fault analysis methods are mainly based on the numerical simulations, which are lack of the theoretical analysis. In this paper, a high-frequency...
Article
To counterbalance the significant challenges imposed by renewable distributed generations penetration, this paper discusses the need of distributed energy storage system investment in distribution networks and proposes a robust optimization based storage investment model. The operational constraints of distribution network (e.g., voltage profile an...
Article
In this paper, we propose a distributed online voltage control algorithm for distribution networks with multiple photovoltaic (PV) systems based on dual ascent method. Conventional distributed algorithms implement voltage control only when the algorithms converge. However, our proposed algorithm is able to carry out voltage control immediately. In...
Article
The growing integration of renewable energy sources, especially the residential photovoltaic (PV) systems, in the distribution networks (DNs) aggravates the ramp-events in transmission system. To address this issue, we propose a novel look ahead dispatch model for the ramp minimization in DNs using distributed energy storage systems (ESSs). The dis...
Article
Due to the increasing penetration of wind power into the distribution network, preserving system security and reliability becomes a significant challenge for the system operator. In the smart grid environment, the demand side is required to take more responsibilities to accommodate the uncertainty of wind power generations, known as demand response...
Article
Given the ever-increased penetration of wind power generation in today's power systems, wind farms tend to operate in a dispatchable way to a certain extent by actively fulfilling dispatch orders from system operators. This paper is focused on the challenging issue of coordinating the interactive wind turbines in a wind farm, which are influenced b...
Article
Full-text available
Bypassing the faulty power unit(s) of the regenerative cascaded multilevel inverter (CMI) directly results in a series of adverse influences. The existing solutions are not easy to implement and only effective for the Y-connected devices composed of regenerative CMIs. To bypass the faulty power units seamlessly, the corresponding control strategies...
Article
To ensure the proper operation of power system, some independent system operators have specified that wind power plants should be able to manipulate power output for frequency control. This article presents a combined control scheme which exploits the self-capability of permanent magnet synchronous generator-based wind turbine to provide primary fr...
Article
Full-text available
With development of two‐way communication technology, residential users are able to reshape their energy consumption patterns based on demand response signals. This study proposes an optimal residential energy resource scheduling model to minimise the home electricity cost while fully considering the user's life convenience, the user's thermal comf...