Grid Frequency Deviation Research Articles

Mitigation of voltage sags, imbalances and harmonics in sensitive industrial loads by means of a series power line conditioner

Power quality is a very important topic nowadays. Sensitive industrial equipment should be protected against steady-state distortions and temporary transients in the distribution lines. Typical disturbances that affect the voltage waveform quality are harmonics, imbalances and sags. This paper presents a solution to protect sensitive loads against voltage disturbances that is based on a series power line conditioner. The goal of the proposed design is that the load does not suffer considerable input voltage variations. To achieve that, a Proportional-Resonant (PR) controller and a reference generator block based on a low-gain PLL are used, which avoids a sag detection block. Furthermore, a frequency adaptation loop is included in the PR controller, which provides a proper controller operation even with utility grid frequency deviations. Finally, a hardware in the loop (HIL) test rig is used to validate the system.

Pitch control system design to improve frequency response capability of fixed‐speed wind turbine systems

AbstractThis paper describes a pitch control design method to deal with grid frequency deviations. The method is based on reserving a percentage of power extracted from the wind turbine. In order to validate the control method, simulations in a full power system have been carried out. The results show that the proposed pitch control can contribute to power stabilization. Copyright © 2010 John Wiley & Sons, Ltd.

Wind Farms With HVdc Delivery in Inertial Response and Primary Frequency Control

This paper develops a coordination control strategy for wind farms with line commutated converter-based HVdc delivery for participating in inertial response and primary frequency control. The coordination philosophy is to feedback the grid frequency and its derivative and adjust the delivery power of the HVdc link according to the feedback signals. The feedback loop employing the derivative of the grid frequency aims to improve the inertial response while the feedback loop employing the grid frequency deviation introduces a droop at the rectifier control loop. When the grid frequency is too high or too low, active power flow through the HVdc link will be ramped down or up. In turn, the wind generation will increase or decrease the blade angles to reduce or increase the captured wind power through pitch control. A case study demonstrates the effectiveness of the inertial enhancement and frequency droop in HVdc control. Simulation results in transient security assessment tool are given.

Harmonic Identification Algorithms Based on DCT for Power Quality Applications

The increasing demand for non-sinusoidal currents affects the quality of distribution networks. Harmonic detection is a crucial step in the cancellation of those components by active power filters. In this paper, the discrete cosine transform (DCT) is compared with different implementations based on Fourier transforms, demonstrating their equivalences and the advantages provided by the former. We demonstrate that the phase error in the presence of grid frequency deviations and the transient length are reduced by half in comparison to the discrete Fourier transform. A novel algorithm is developed to provide frequency adaptation to the DCT, taking advantage of its good features. The window width is adjusted in real time according to the actual value of the grid fundamental frequency by means of a phase-locked loop. A technique based on dithering is employed to overcome the limitation caused by the truncation of the window number of samples, so the frequency resolution is enhanced. The theoretical approach is verified by simulated and experimental results.

Frequency Deviation of Thermal Power Plants Due to Wind Farms

This paper presents the results of a study on the frequency deviation of the utility grid due to wind power fluctuations. The deviation is estimated by a deterministic method based on the transfer functions of system components. As the grid frequency is regulated, the deviation can limit high wind power penetration. The research identifies speed governors as one key component in enabling high wind penetration and there is need to factor their increased wear and tear into the ancillary services cost. It also raises the question as to whether the existing standards set for frequency deviation, which have to be complied at the points of connection of wind energy providers, are adequate to promote high wind penetration.

A NEW DSP-METHOD FOR FREQUENCY AVERAGE ESTIMATION IN POWER SYSTEMS

ABSTRACT The paper represents a new DSP method for estimating the average deviation of the power grid frequency and its rate of change. This estimation is important for monitoring and control in power system. The frequency is an important parameter for control of generating units, especially during dynamic transients caused by sudden imbalances between load and generation. The method is based on the iterative algorithm (known as Ostrogradsky's second algorithm), in which only 4-5 periods of the line signal are sufficient to achieve 0·01% estimation accuracy. A short description of this method, the computational procedure and its implementation, including its simulation on a PC are given. Further improvements of this method, including its combination with other DSP-methods, are also discussed and illustrated by experimental data.