A Comprehensive VSG-Based Onshore FRT Control Strategy for OWFs with VSC-MT-HVDC Transmission

This paper proposes a communication-free control strategy at the offshore wind farm (OWF) level to enhance onshore fault ride-through (FRT) grid code compliance of the voltage source converter (VSC)-based multi-terminal high voltage direct current (MT-HVDC) grid. In this proposal, the emerging virtual synchronous generator (VSG) concept is employed to equip the Type 4 wind turbine generator (WTG)s with inherent grid forming ability. Accordingly, it is proposed to switch the offshore HVDC converters control mode from grid forming to grid feeding during onshore FRT period to realize direct wind power in-feed reduction as a function of the severity of MT-HVDC grid's overvoltage. The related dynamics are mainly characterized by the high-speed current control loop, so improved OWF response is achieved during onshore FRT period as conventional voltage/frequency modulation strategies are not employed. New analysis/amendments are also proposed to study and improve the transient active power reduction sharing between the WTGs in first few power cycles under wind wake effect. Finally, with the objective of a smooth transfer of HVDC converters and WTGs in several proposed operation states, a set of state machines are proposed considering whole WTG's dynamics. Comprehensive time-domain simulations are performed with averaged electromagnetic transient models to demonstrate the improved onshore FRT behavior in terms of minimizing the electrical stress at both MT-HVDC grid and OWF levels

Efficient low-voltage ride-through nonlinear backstepping control strategy for PMSG-based wind turbine during the grid faults

This paper presents a new nonlinear backstepping controller for a direct-driven permanent magnet synchronous generator-based wind turbine, which is connected to the power system via back-to-back converters. The proposed controller deals with maximum power point tracking (MPPT) in normal condition and enhances the low-voltage ride-through (LVRT) capability in fault conditions. In this method, to improve LVRT capability, machine-side converter controls dc-link voltage and MPPT is performed by grid side converter. Hence, PMSG output power is reduced very fast and dc-link voltage variation is reduced.  Due to nonlinear relationship between dc-link voltage and controller input, nonlinear backstepping controller has good performances. By applying the proposed controller, dc-link overvoltage is significantly decreased. The proposed controller has good performance in comparison with Proportional-Integral (PI) controller and Sliding Mode Controller (SMC). In asymmetrical faults, to decrease grid side active power oscillations, the nonlinear backstepping dual-current controller is designed for positive- and negative- sequence components. The simulation results confirm that the proposed controller is efficient in different conditions

Inertial Support by a Synchronous Power Controlled Type 4 Wind Turbine: A Restructured Control Approach

© 2018 IEEE. This paper addresses a key concern about insufficient inertia in future power systems characterized by high penetration of renewable energy sources. In this regard, effective provision of inertial support from a Synchronous Power Controlled (SPC) Type 4 Wind Turbine (WT) is investigated by emulating electrochemical and electrical characteristics of a typical synchronous generator. The kinetic energy possessed by WTs rotary masses is excavated to supply the inertial power offered by SPC solution as the main contribution and hence eliminate the need for installing extra energy storage device. In this regard, a restructured control framework is proposed that the role of dc-link voltage control and maximum power point tracking are assigned to machine and SPC based grid side power converters respectively. Based on Real-Time Digital Simulator results (frequency sweep test), the feasibility of the proposed control framework along with the influence of key control parameters on the dynamic frequency support characteristics are evaluated

Incorporation of Synchronous Power Controlled Energy Storage System in Wind Farms to Provide Inertial and Primary Frequency Support

© 2018 IEEE. Modern power systems are characterized by high renewables penetration. Therefore, dynamic frequency support from wind farms is decisive. However, existing wind farms are not designed to meet the emerging grid code requirements. In this regard, this research proposes an Energy Storage System (ESS) solution to get integrated into the present wind farms. This alternative effectively provides the desired dynamic frequency support without spilling the wind power. A Synchronous Power Controller (SPC) is well tailored to emulate electrochemical and electrical characteristics of a synchronous generator during grid support by excavating the chemical energy stored in the ESS. Also, a new State Of Charge (SOC) controller is implemented in the neighboring conventional power plant governor to maintain the ESS state of the charge in the optimum setpoint and mitigate the need for a high capacity ESS. Simulation results on a representative power network in MATLAB/SIMULINK platform demonstrate the feasibility of the proposed hybrid system and SOC controller to provide dynamic frequency support and maintaining the SOC

Performance Improvement of Direct Torque Controlled Interior Permanent Magnet Synchronous Motor Drives Using Artificial Intelligence

The main theme of this paper is to present novel controller, which is a genetic based fuzzy Logic controller, for interior permanent magnet synchronous motor drives with direct torque control. A radial basis function network has been used for online tuning of the genetic based fuzzy logic controller. Initially different operating conditions are obtained based on motor dynamics incorporating uncertainties. At each operating condition, a genetic algorithm is used to optimize fuzzy logic parameters in closed-loop direct torque control scheme. In other words, the genetic algorithm finds optimum input and output scaling factors and optimum number of membership functions. This optimization procedure is utilized to obtain the minimum speed deviation, minimum settling time, zero steady-state error. The control scheme has been verified by simulation tests with a prototype interior permanent magnet synchronous motor

Coordinated Control of Distributed Energy Resources and Conventional Power Plants for Frequency Control of Power Systems

11 Halama

Power injection model of IDC-PFC for NR-based and technical constrained MT-HVDC grids power flow studies

© 2020 Elsevier B.V. Insufficient control flexibility in multi-terminal HVDC (MT-HVDC) grids is an important motivation to install suitable power electronic-based DC power flow controller (PFC)s to ensure grid controllability, security, and reliability. This article proposes a new static power injection model (PIM) for those (interline) DC-PFCs to enable DC power flow (PF) studies and ease integration of the PFCs in the power system analysis softwares within the well-accepted Newton–Raphson (NR) solver-based framework. HVDC lines shunt conductances are also taken in to account in this newly developed paradigm. For this purpose, the IDC-PFC, as well as other MT-HVDC grid physical/control state variables are modified in cooperation to attain predefined control objective(s). Furthermore, a novel general routine (solution procedure) is proposed to handle several system physical/control limitations during the NR-based DC PF problem solution. Static/dynamic simulations are executed on an eight-bus test MT-HVDC grid to show/confirm the accuracy, effective performance, and excellent convergence property of the proposed IDC-PFC model, NR-based DC PF solver, and technical constraints handling routine. In this situation, it is proved that the original structure and symmetry of the admittance matrix can still be kept, and a few modifications are needed to be done in the Jacobin matrix

Technical Constrained Power Flow Studies for IDC-PFC Integrated into the MT-HVDC Grids

Power flow (PF) flexibility in the multi-terminal HVDC (MT-HVDC) grids is a thought-provoking issue. It leads to employing the active DC power flow controller (DC-PFC)s. Hence, this paper examines the static average model (AM) and power injection model (PIM) of an interline DC-PFC (IDC-PFC). It is to provide a suitable base for DC PF studies and easy embedding of the DC-PFCs into MT-HVDC grids' PF equations. In this regard, this paper proposes a new DC PF solver (DC-PFS) for the IDC-PFC compensated MT-HVDC grids within the well-accepted Newton-Raphson (NR) framework. It requires a few modifications in the main structure of the system's Jacobin (J) matrix compared to the uncompensated MT-HVDC grid. Also, the system's admittance matrix and its symmetry are preserved. In the proposed concept, the IDC-PFC cooperates with other MT-HVDC grid's state variables to satisfy the predetermined control objective(s). Furthermore, this paper proposes a new solution procedure (SP) to handle various system's limitations during the processes of solving the DC PF problem. Meanwhile, there is no need to modify the related J matrix. The effective and accurate performance of the IDC-PFC's models, as well as presented NR-based DC-PFS and SP, are verified by performing several simulations on the 8-bus CIGRE MT-HVDC grid

Static Modeling of the IDC-PFC to Solve DC Power Flow Equations of MT-HVDC Grids Employing the Newton-Raphson Method

© 2019 IEEE. Power transmission technology of the offshore wind farm (OWF)s is usually based on HVDC interconnection. Power flow controller (PFC)s are flexible power transmission devices which play important role in the DC power flow (PF) control especially in contingency conditions. So, these devices should be modeled to solve related MT-HVDC grid DC PF equations. In this context, an interline DC PFC (IDC-PFC) is considered as a sample PFC for modeling due to its advantages in comparison to other series and cascaded PFCs. The novelty of this work is solving the DC PF problem of the IDC-PFC compensated MT-HVDC grids by modeling of the IDC-PFC and employing the Newton-Raphson (N-R) method. An eight-bus MT-HVDC test grid is considered to authenticate the presented IDC-PFC modeling and verify the accuracy of the DC PF results obtained by employing the N-R method. The obtained static results verify the accuracy of the presented IDC-PFC modeling and the performance of the N-R method in solving flexible MT-HVDC grid PF equations. Hence, it is suitable to integrate them in the future power system analysis softwares

New Representation of Power Injection Model of IDC-PFC within NR-based MT-HVDC Grids Power Flow Studies

DC power flow controller (PFC)s are suitable equipment to provide secure/reliable operation of the multiterminal HVDC (MT-HVDC) networks. Also, they enhance the controllability of these grids. This paper proposes a new representation of the Newton-Raphson (NR) based DC power flow (PF) solver to provide suitable DC PF studies of PFC compensated/flexible MT-HVDC grids. To achieve this aim, the power injection model (PIM) (under static condition) for an interline DC PFC (IDC-PFC) is proposed and embedded within the presented DC PF solver (DC-PFS) while the symmetry and original framework of the conductance matrix of the system is yet preserved and the proposed concept imposes a few changes on the related Jacobin matrix. In the proposed model, resistive shunt admittance of HVDC lines is also taken into account. Modifying the physical and control state variables of the whole system (IDC-PFC and MT-HVDC grid) in a common collaboration, the predetermined control objective(s) are obtained. The accurate concept and effectiveness of the presented IDC-PFC models and new representation of the NR-based DC-PFS are verified by performing dynamic and static simulations on an 8-bus MT-HVDC test network