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A reliable islanding detection method is one of the most important function of a well designed inverter based distributed generation (DG) system. Active islanding detection methods have negligible non-detection zone, but they bring some power quality issues to the network. In this paper an islanding detection method which addresses constant current inverter based DGs is introduced. It has both high...
This paper deals with the power flow analysis and control strategy research of unified power quality conditioner (UPQC). A UPQC is a combination of shunt and series active power filter (APF), sharing a common dc link. It can compensate almost all power quality problems such as voltage harmonics, voltage unbalance, voltage flickers, voltage sags, voltage swells, current harmonics, current unbalance,...
Voltage source converter based DSTATCOM has been accepted as the most preferred solution for reactive power management in distribution power networks which plays a vital role in improving power quality, correcting power factor and maintaining constant distribution voltages. However, the quality of DSTATCOM output voltage and current itself, such as injected harmonics and Total Harmonic Distortion...
Phase locked loop (PLL) is an important part of the current-controlled grid-connected converter. Its job is to estimate the phase angle of the grid voltage. If the PLL is not robust, the grid-voltage distortion will lead to an error in the estimated phase leading to a degradable performance of the converter. In this paper, the effect of the PLL on the operation of a current-controlled voltage-source...
A circuit that compensates the volt-seconds error across the inductor in current sensorless digital control for continuous conduction mode power factor correction (PFC) stage is presented. Low cost ad-hoc sigma-delta analog to digital converters (ΣΔ ADCs) are used to sample the PFC input and output voltage. Instead of being measured, the input current is estimated in a digital circuit to be used in...
STATCOM has been widely proposed for power quality and network stability improvement. It is easily connected in parallel to the electric network and has many advantages for electrical grids. It can improve network stability; power factor, power transfer rating and can avoid some disturbances such as sags and swells. Most of STATCOM controllers are based on voltage controllers that are based on balance...
In this paper, the effect of voltage dips on variable speed wind turbines using VSCs is treated. Three different current controllers for the VSC are described and implemented. Their performance is evaluated when the converter is subjected to different types of voltage dips, Both simulated and measured dips are used. The effect of the phase-angle jump of the dips is also taken into account.
A control strategy using sliding mode variable structure control with an integral action is used for DSTATCOM. The steady-state error of compensation current control is effectively reduced, and the response speed is increased by the integral action. The control strategy has good robustness to parameter disturbance in both transient and steady states. The strategy uses sliding mode variable structure...
This paper presents the Direct model reference adaptive internal model controller for doubly fed induction generator used in wind farms based on MIT Rule adjustment mechanism with dither injection. Direct model reference adaptive internal model controller is developed and it is tuned using MIT rule. Rotor current controller is designed using direct model reference adaptive internal model controller...
This paper addresses some major problems in steel plant power systems such as voltage fluctuations and flicker, load unbalance, current harmonics and reactive power and demonstrates the significance of reactive power management for steel plants power system. Two One-Cycle Control techniques for Hexagram Converter based STATCOM are presented. The first technique effectively achieves load balancing,...
This paper presents the digital control scheme of a single phase uninterruptible power supply (UPS). In order to obtain fast response in the current control, the authors propose the digital control scheme based on the instantaneous values. The inverter of the UPS is connected to the load in parallel to reduce the loss of the UPS. The controller is constructed by a DSP. The control schemes in all of...
In presence of grid voltage dips, Low Voltage Ride-Through (LVRT) requirements demand the wind power plant to remain connected to the grid, helping the network to keep voltage and frequency stable. Neutral-point-clamped (NPC) converters are appropriate for wind power systems, because the current trend of increasing voltage levels. Predictive current control presents as fast dynamic response and accurate...
This paper presents a new control strategy that allows the photovoltaic system operation under grid faults without overcurrent and assuring grid sinusoidal currents. The current limiter is made indirectly by using an active power limiter that is calculated dynamically based on the grid positive-sequence voltage. The paper also shows that the classic control strategies used in the PV systems cause...
Islanding of a voltage source converter (VSC) equipped DG unit is considered in this paper. Some internal controller signals are implemented in the islanding detection method in order to provide a robust operation. Particularly, the estimated frequency of the grid voltage along with a point of common coupling (PCC) voltage regulator and a dynamic reference-current limiter are proposed for islanding...
Wind energy penetration to the power market has been continuously increasing over the past decades. High penetration level requires the wind energy generation to be more reliable. For wind farms equipped with doubly fed induction generators (DFIGs), a successful low voltage ride-through scheme has been a key issue to achieve reliable and uninterrupted wind energy generation. This paper proposes a...
In this paper an implementation of improved voltage oriented control for AC-DC converter has been presented and investigated. Algorithm is based on independent control of positive and negative current sequences. It contains different blocks responsible for grid synchronization, mitigation of 100 Hz component, current control and sequence extraction. Different line voltage feedforwards have been implemented...
Voltage flicker, a phenomenon of annoying light intensity fluctuation is caused by electric arc furnace (EAF). Voltage flicker is a major power quality concern for both power companies and customers. This paper presents a model of EAF and control algorithms for distribution static synchronous compensator (DSTATCOM) for voltage flicker mitigation. The EAF was modeled as a current source controlled...
A model of the directly driven wind turbine with permanent magnet synchronous generator (D-PMSG) was described in this paper. The D-PMSG was connected to a host AC power grid by a full scale power converter system which comprised two back-to-back PWM voltage source converters (VSCs) and a common DC-link. Active and reactive power of the two VSCs were controlled independently by employing PI current...
The aim of this paper is to propose an over current limitation and voltage control strategy for a grid connected inverter with a LC output filter used in distributed generation and in case of voltage sag. This strategy relies on the control of LC output filter voltage with a resonant controller. This controller has to control current and load voltage throughout voltage sag. Generally, resonant controller...
This paper presents a new control design of an unified power quality conditioner (UPQC) for harmonics and voltage compensation in a power distribution system. The topology of the UPQC is based on a combination of two 3-phase series and parallel active power filters. The determination of voltage references for series active power filter is based on a robust three-phase digital phase locked loop (PLL)...
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