Standalone micro grid power quality improvement using inertia and power reserves of the wind generation systems

Abstract

Keywords:Standalone MG MG frequency regulation Inertia and frequency droop DFIG inertia Pitch angle power reserve DFIG reactive power capability a b s t r a c t This paper proposes two controllers for employing part of variable speed wind generation systems kinetic energy in supporting the standalone MG frequency. The first controller acts similar to the frequency droop control, while the second controller emulates both the inertia response and the frequency droop control simultaneously. The MG frequency dropped only to 49.9 Hz with employing the proposed controllers compared with 49.68 Hz without employing the proposed controllers. Also, the injected active power from the storage device dropped from 20 kW to only 3 kW after employing the proposed controllers. In addition, the reactive power capability of the Double Fed Induction Generator (DFIG) wind generation system has been employed to maintain the standalone MG bus voltage at acceptable level. If there are fixed speed wind generation systems in the standalone MG, this paper proposed using the pitch angle controller to employ a suitable wind turbine power reserve in MG frequency supporting during the standalone mode. Results proved the effectiveness of the proposed controllers in improvement the MG overall performance during and subsequent the islanding occurrence.

Participation in primary frequency regulation of wind turbines using hybrid control method

“…The structure of DFIG‐based wind generator model is shown as Figure . The model contains 5 parts: wind speed model, aerodynamic model, pitch angle control model, mechanical drive model, and DFIG model with its control system . The rotor that supplies AC excitation current is connected to power grid via the converter, and the stator is connected directly to the power system.…”

“…The DFIG can adjust rotor speed to the change following wind speed so as to keep the C P , of the DFIG in maximum value, thus produce the maximum wind power. The control mode is called the maximum wind energy utilization mode (MPPT mode) . In the MPPT model, rotor speed keeps in ω opt that makes P at maximum value.…”

“…The model contains 5 parts: wind speed model, aerodynamic model, pitch angle control model, mechanical drive model, and DFIG model with its control system. 18 The rotor that supplies AC excitation current is connected to power grid via the converter, and the stator is connected directly to the power system. Though DFIG and power grid are tightly coupled in topology structure, from the view of control strategy, they are electromechanical decoupling on the condition of MPPT operation mode.…”

“…The control mode is called the maximum wind energy utilization mode (MPPT mode). 18,20 In the MPPT model, rotor speed keeps in ω opt that makes P at maximum value. When the wind turbine works at the optimum speed tracking area, rotor speed of wind turbine has not reached maximum value.…”

“…15,16 However, since the active power regulation capability of wind turbines is affected by the degree of the system frequency fluctuation, the conventional inertia control is severely influenced by the disturbance type and the operation condition of wind generators. 17,18 The frequency regulation result of conventional virtual inertia control is weakened, because this method cannot adjust its control strategy to meet the different types of frequency disturbances. The rotor speed will change when the wind turbine starts to participate in system frequency regulation.…”