Chunghun Kim

Maximum Power Point Tracking of a Wind Power Plant With Predictive Gradient Ascent Method

In this paper, we present maximum power point tracking for a wind power plant (WPP) using the gradient ascent (GA) in a data-driven manner. The conventional GA method achieves fast convergent performance by considering only direct wake terms when calculating the axial induction factors. However, the conventional method might not be close to optimal even when the wind conditions are steady state. In this paper, we propose a new method using the relationships between the direct and indirect wake terms. Using the relationship between the wake terms can prevent sudden deviations after convergence to a single operating point, even when significant indirect wake terms exist in the presence of multiple wakes. Therefore, the proposed method provides not only fast convergence to an operating point, but also closer-to-optimal power production without sudden deviations compared to the conventional method. We validated the effectiveness of the proposed method using modeled WPP layouts with various wind conditions.

A model-free method for wind power plant control with variable wind

Aerodynamic interactions between wind turbines in wind power plant (WPP) have drawn attention in wind power optimization. The aerodynamic interactions can be described by a wake model which approximates the wind deficit due to upstream wind turbines. Modeling wake effect is so involved that model-free methods have been introduced for WPP control by adjusting axial induction factors of each turbine. In the previous works, model-free methods were used in data-driven manner for adjusting axial induction factor towards increasing the total power of WPP and then focused on total power optimization and time efficiency. But the analysis was done in fixed wind condition and a modification of the previous method considering variable wind condition is necessary. In this paper, we propose a variable step size according to wind condition for time efficient and improved suboptimal power production. This paper refers the consideration required for variable wind condition and some case studies are analyzed to validate the effectiveness of the proposed method.

Model predictive control in dynamic economic dispatch using Weibull distribution

This paper develops dynamic economic dispatch (DED) using model predictive control (MPC) based on Weibull probabilistic distribution function (PDF). Firstly we performed economic dispatch (ED) based onWeibull PDF.We considered the probabilistic cost about over-estimated and under-estimated cost of wind power by using Weibull PDF. Secondly we implemented DED formulated in a MPC framework using the maximum wind power capability from the ED results since ED does not consider the ramp rate constraint. By using dispatch error cost, we could consider the current status of reliable generation by using the proposed MPC method. It turns out that the DED using MPC method is very effective in coping with intermittent resource such as wind variability.

Coordinated wind power plant control for frequency support under wake effects

As the wind power penetration level increases, the inertial response of a wind power plant (WPP) is important to the grid under load and generation imbalance. In this paper, we present coordinated WPP control for frequency support under wake effects. By de-loading the power from a WPP, the inertial response can be obtained from the kinetic energy of wind turbine rotors. The coordinated WPP control considering wake effects improves the inertial response of WPP by preventing the rotor speed recovery period, which is unfavorable during a frequency drop. The proposed frequency support scheme could prevent large generation reduction right after an inertial response. In addition, more power generation is available when a WPP uses both primary and secondary control. To validate the performance, a WPP with three wind turbines was used as a case study with wake, turbine, and generator models.

Nonlinear control for PMSG wind turbine via port-controlled Hamiltonian system

This paper presents a nonlinear controller for a permanent-magnet synchronous generator (PMSG) wind turbine system in the framework of port-controlled Hamiltonian system. For the simplification, this work focuses on the nonlinear control law of the grid side converter (GSC) that is directly connected to the grid and affected during network disturbances. The proposed controller is designed through the analysis of PMSG GSC model from the passivity viewpoint in order to regulate the reference of the DC voltage and track the reference of the reactive current. In order to fulfill low voltage ride through requirements, a DC chopper is used to dissipate surplus active power in the DC-link. By using the proposed method, the exponential stability of the equilibrium point of the error dynamics at the origin is guaranteed through Lyapunov theory. Finally, the proposed method is validated through simulation by using SimPowerSystems, MATLAB/Simulink. The simulation results show that the performance has smaller overshoot and faster convergence when the proposed method is used than when the conventional method is used.

Grid voltage modulated direct power control for grid connected voltage source inverters

We propose a grid voltage modulated (GVM) direct power control (DPC) strategy for a grid-connected voltage source inverter (VSI) to control the instantaneous active and reactive powers. The GVM-DPC presents the system in d-q frame without using a phase-lock loop. In addition, the GVM method converts the system into a linear time-invariant system. The GVM-DPC is designed to obtain two separate second-order systems for not only the convergence rate of the instantaneous active and reactive powers but also the steady-state performance. In addition, the closed-loop system is exponentially stable in the whole operating range. The proposed method is verified by using MATLAB/Simulink with PLECS blockset. The simulation results show that the proposed method has not only good tracking performances in both active and reactive powers but also a lower current total harmonic distortion than that of the sliding mode control DPC method. Finally, the proposed method is validated by using a hardware-in-the-loop system with a digital signal processor. The experimental results are similar to simulation results. Moreover, the robustness to the line impedance and the grid voltage is tested and discussed.

Direct power control for three phase grid connected inverter via port-controlled Hamiltonian method

This paper presents a new direct active and reactive power control (DPC) controller scheme for a three-phase grid connected voltage source inverter (VSI) based on passivity viewpoint. The proposed method is designed in the framework of port-controlled Hamiltonian system. The proposed method is made up of two parts, one thing is a feedfoward part and the other is a feedback part. The feedforward part is calculated from the model dynamics of VSI. The feedback part is designed to compensate for system uncertainty. The proposed method is verified with simulation and experiment. The simulation uses MATLAB/Simulink and PLECS, and the experiment uses hardware in the loop (HIL) with TI TMS320F28335 DSP. The simulation and experiment results compared with those using direct power control-sliding mode control (DPC-SMC) for the grid connected VSI. The proposed method gives less total harmonic distortions, faster transient response.

Sliding mode control for LVRT of a PMSG wind turbine using stored energy in rotor inertia

This paper proposes a sliding mode controller for a permanent-magnet synchronous generator wind turbine system to satisfy low voltage ride through requirement. The generator-side converter regulates the DC link voltage instead of grid-side converter. The generator-side controller is designed using the sliding mode control considering the nonlinear relationship between the generator power and the dc-link voltage. The grid-side converter controls the grid active power to extract maximum power. The proposed control method enables regulating the DC link voltage by storing the surplus energy in the rotor inertia when a grid fault occurs. Finally, the proposed control method is validated through the numerical simulations with a topological wind turbine model. The simulation results show that the proposed method has faster conversion and smaller amplitude of oscillation than the conventional PI control.

Economic dispatch for wind farm using model predictive control method

An economic dispatch (ED) problem of committed turbines is solved minimizing each wind turbines output power variation by model predictive control (MPC) method. The proposed method could solve the ED problem on-line using prediction time horizon that could be selected flexibly considering time horizon based on wind forecasting errors. Dispatched wind turbines are classified into three groups considering variations of forecasted power generation: maximum power point tracking, balance control, and delta control. From the simulation study using 10 wind turbines we observed that the proposed method effectively provided the optimal solution to the scenario.

Coordinated control of wind turbine and energy storage system for reducing wind power fluctuation

This paper proposes a coordinated control of wind turbine and energy storage system (ESS). Because wind power (WP) is highly dependent on variable wind speed and could induce a severe stability problem to power system especially when the WP has high penetration level. To solve this problem, many power generation corporations or grid operators recently use the ESS. It has very quick response and good performance for reducing the impact of WP fluctuation but has high cost for its installation. Therefore, it is very important to design the control algorithm considering both ESS capacity and grid reliability. Thus, we propose the control algorithm to mitigate the WP fluctuation by using the coordinated control between wind turbine and ESS considering ESS state of charge (SoC) and the WP fluctuation. From deloaded control according to WP fluctuation and ESS SoC management, we can expect the ESS lifespan expansion and improved grid reliability. The effectiveness of the proposed method is validated in MATLAB/Simulink considering power system including both wind turbine generator and conventional generators which react to system frequency deviation.