Mohamed Shawky El Moursi

Obtaining Performance of Type-3 Phase-Locked Loop Without Compromising the Benefits of Type-2 Control System

A phase-locked loop (PLL) is a closed-loop feedback controlxa0system that estimates the frequency as well as phase of an input signal. The most commonly deployed synchronization method in three-phase applications is a type-2 synchronous reference frame PLL. With pre/in-loop selective harmonic filtering stage, type-2 PLLs can obtain good detection speed, decent stability margins, and better disturbance rejection. However, it suffers from the finite steady-state phase error during ramp change in input signal frequency. To tackle this challenge type-3 PLLs have been developed recently, either by adding a feed-forward path to the PLL structure, or by using a second-order controller as the loop filter. However, recent analysis carried out of type-3 PLLs show that they aggravate stability problem and compromise the performance in terms of detection speed and disturbance rejection. A new concept of synchronization is proposed in this paper that obtains the performance of type-3 PLL but retains all the advantages associated with type-2 PLL. Extensive experimental results are provided to validate the proposed work.

Coordinated Frequency Control Strategy for an Islanded Microgrid With Demand Side Management Capability

This paper presents a novel coordinated frequency control (CFC) scheme with demand side management capability for an islanded microgrid. The proposed CFC scheme is a communication-free coordination among fast responding devices: thermostatically controlled loads (TCLs), photovoltaic power systems, battery energy storage systems, and a slow responding diesel generator (DZ). The fast responding devices are deployed to achieve a swift frequency regulation in transient state. In steady state, these devices are returned to their normal operating condition by changing loading conditions of the DZ without employing interdevice communication. The proposed control strategy not only achieves frequency regulation in adherence to IEEE Standard 1547, but also maintains customers’ quality of service while manipulating TCLs for frequency regulation. A comprehensive study of the proposed CFC scheme is carried out on a modified IEEE 13-bus balanced industrial distribution network using MATLAB/Simulink. In addition, real-time performances of the CFC scheme have been validated experimentally using OPAL-RT simulator, and a well-programmed TMS320F28335 microcontroller. Both the simulation and experimental results demonstrate effective performance of the proposed CFC in achieving efficient frequency regulation.

Cooperation-Driven Distributed Control Scheme for Large-Scale Wind Farm Active Power Regulation

Being more actively involved in the electricity market and power systems, wind farms are urgently expected to have similar controllable behavior to conventional generations so that demand assigned by the system operator can be met. However, determining the method of dispatching the reference among the widely spread and low-rating wind turbines is difficult. This paper provides a cooperation-driven distributed control scheme for wind farm active power regulation. Instead of competing with neighboring controllers completely, the control strategy evaluates system-wide impacts of local control actions, and aims to achieve coordinated control effect. In addition, the kinetic energy storage potential in a wind turbine is tapped to provide a buffer for power dispatch. Case studies demonstrate that a large wind farm can be effectively controlled to accurately track the demand power through the proposed control scheme.

A Control Strategy for Voltage Unbalance Mitigation in an Islanded Microgrid Considering Demand Side Management Capability

Inverter-based distributed generators (DGs) have been customarily used for voltage unbalance (VU) mitigation in microgrids. The sole dependency on DGs for VU mitigation may not be justified, particularly in islanded microgrids. Demand side management can be a potential candidate for VU mitigation in microgrids. Therefore, this paper presents a new VU mitigation scheme for an islanded microgrid by coordinating photovoltaic (PV) grid-tied inverters, and thermostatically controlled loads (TCLs). A negative sequence compensation loop working in parallel with a positive sequence compensation loop is designed for PV inverters for VU mitigation. Also, a voltage dependent model of TCLs, unlike the conventional one, along with the control strategy for VU mitigation is presented. The proposed control of TCLs not only minimizes VU, and hence, increases the dynamic reactive power reserve of the inverter based DGs, but also effectively maintains the customers’ thermal comfort. The proposed VU mitigation scheme is studied with comprehensive simulations in PSCAD/EMTDC, and is verified using a real-time digital simulator, OPAL-RT. Simulations and real-time results of the proposed scheme demonstrated the regulation of VU factor within the permissible range defined by IEC and CIGRE Working Group 36.07.

Control Approach for the Multi-Terminal HVDC System for the Accurate Power Sharing

This paper presents a new control strategy for voltage source converter based Multi-Terminal High Voltage Direct Current (MTDC) systems. The proposed control approach ensures accurate power sharing between the droop-controlled converter stations. By communicating the power-sharing index between neighboring converters, the proposed approach achieves exact droop control operation independent of the DC system topology and line parameters. The pilot voltage droop based controller, which is an alternative communication-based approach for achieving precise power sharing, was used as a base case for comparison. Modal analysis is carried out to reveal the sensitivity of the systems eigenvalues to the changes in control parameters (e.g., power droop gain, proportional integral gains of the proposed controller) and the latencies in the communication. It is demonstrated that the proposed strategy remains in the stable operation even when excessive latencies are encountered in the communication. Nonlinear simulations are conducted in the MATLAB/Simulink environment in four- and five-terminal MTDC grids, validating the capability of the proposed controller to achieve the desirable performance under various operational conditions.

Dynamic Security-Constrained Automatic Generation Control (AGC) of Integrated AC/DC Power Networks

This paper introduces an efficient algorithm to adaptively determine the droop coefficients of generating units in hybrid ac–dc networks. These generating units include conventional synchronous generators and multiterminal high-voltage direct-current (MTDC) converters. The proposed algorithm relies mainly on trajectory sensitivity to reschedule power generation according to the new calculated droop coefficients to ensure and/or system stability margin for set of credible contingencies with different load conditions. The Newton shooting method is used to find the new steady-state values for the systems when load is changed. MTDC converters are modeled in such a way to emulate the inertia behavior of the synchronous generators. This virtual emulation is achieved by providing two additional control layers that link and control the converter powers through inertia constants similar to synchronous generators. Also, an expression for generated powers controlled by the droop coefficients is developed to be utilized in the algorithm. Finally, comprehensive simulation studies on the IEEE 68-bus benchmark system are carried out using PSCAD/EMTDC interfaced with MATLAB to validate the proposed algorithm.

Multiobjective Dynamic VAR Planning Strategy With Different Shunt Compensation Technologies

High concentrations of induction motor loads can impose stress on transmission and distribution systems, leading to voltage instability in some situations. Properly sized and coordinated reactive power sources will provide for improved operation. We present a strategy for finding an optimal mix (type, size, and location) of dynamic shunt reactive compensation devices. The planning strategy is subject to satisfying steady-state, dynamic and transient performance criteria such as fault-induced delayed voltage recovery limits, as well as criteria related to single ( N–1) contingency and load disturbance events. Shunt reactive power compensation devices considered include mechanically switched capacitor banks, static reactive power compensators and static synchronous compensators. The proposed strategy employs a large number of multitimescale time-domain simulations suitable for use with high performance computing clusters and a genetic algorithm to solve the mixed-integer nonlinear programming formulation using parallel computation capabilities. The method is applied to a New England IEEE 39-bus system with assumed high penetration of induction motors. A comprehensive study shows that performance enhancement and significant cost reduction can be achieved using an optimum combination of various shunt compensator technologies.

A Modified DPC Switching Technique Based on Optimal Transition Route for of 3L-NPC Converters

This letter presents a modified switching technique for a three-level neutral-point-clamped converters controlled by direct power control (DPC). The proposed switching technique avoids the hard state transition of each phase module as well as reduces the overall switching frequency. For any phase module, it inserts sequence of vectors to avoid the direct transition from positive to negative state and vice versa. The proposed vector sequence is called optimal transition route (OTR). The OTR technique optimizes the route between the present and the next requested vector to avoid the hard transition of any module. The proposed technique not only avoids the risk of damaging the semiconductor switches, but also minimizes the switching frequency resulted in reducing the switching losses. As a result, the reliability and the overall efficiency of the converter is increased. The obtained results confirm its applicability for medium- and high-power grid-connected converters controlled by the DPC method.

DC Voltage Regulation and Frequency Support in Pilot Voltage Droop-Controlled Multiterminal HVdc Systems

This paper presents an improved pilot voltage droop based control for the multiterminal high-voltage dc (MTDC) systems. The proposed control strategy maintains adequate power sharing and efficient voltage regulation among the converter stations. The incorporation of the average voltage sharing loop enables achieving superior dynamic performance while avoiding dc system average voltage deviation from nominal value. Furthermore, the frequency consensus algorithm is used for modifying the power reference of converters to achieve the desired frequency deviation sharing between the ac areas connected through the droop controlled voltage source converters. Finally, the incorporation of the frequency locked loop enables achieving fast grid synchronization and superior dynamic performance for the control of the converter stations. The simulations carried out in the MATLAB/Simulink environment revealed the effectiveness of the controller to provide enhanced dc voltage regulation and frequency deviation sharing during disturbances in the MTDC system.