• Journal of Power Electronics
• /
• 제16권2호
• /
• pp.704-716
• /
• 2016

Small distributed generation units are usually connected to the main electric grid through single-phase voltage source inverters. Grid operating conditions such as voltage and frequency are not constant and can fluctuate within the range values established by international standards. Furthermore, the requirements in terms of power factor correction, total harmonic distortion, and reliability are getting tighter day by day. As a result, the implementation of reliable and efficient control algorithms, which are able to adjust their control parameters in response to changeable grid operating conditions, is essential. This paper investigates the configuration topology and control algorithm of a single-phase inverter with the purpose of achieving high performance in terms of efficiency as well as total harmonic distortion of the output current. Accordingly, a Second Order Generalized Integrator with a suitable Phase Locked Loop (SOGI-PLL) is the basis of the proposed current and voltage regulation. Some practical issues related to the control algorithm are addressed, and a solution for the control architecture is proposed, based on resonant controllers that are continuously tuned on the basis of the actual grid frequency. Further, intentional islanding operation is investigated and a possible procedure for switching from grid-tied to islanding operation and vice-versa is proposed.

• Journal of Power Electronics
• /
• 제17권5호
• /
• pp.1231-1243
• /
• 2017

Grid-interactive power converters are normally synchronized with the grid using phase-locked loops (PLLs). The performance of the PLLs is affected by the non-ideal conditions in the sensed grid voltage such as harmonics, frequency deviations and the dc offsets in single-phase systems. In this paper, a single-phase PLL is presented to mitigate the effects of these non-idealities. This PLL is based on the popular second order generalized integrator (SOGI) structure. The SOGI structure is modified to eliminate the effects of input dc offsets. The resulting SOGI structure has a high-pass filtering property. Hence, this PLL is termed as a high-pass generalized integrator based PLL (HGI-PLL). It has fixed parameters which reduces the implementation complexity and aids in the implementation in low-end digital controllers. The HGI-PLL is shown to have the lowest resource utilization among the SOGI based PLLs with dc cancelling capability. Systematic design methods are evolved leading to a design that limits the unit vector THD to within 1% for given non-ideal input conditions in terms of frequency deviation and harmonic distortion. The proposed designs achieve the fastest transient response. The performance of this PLL has been verified experimentally. The results agree with the theoretical prediction.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2011년도 춘계학술대회 논문집
• /
• pp.171-176
• /
• 2011

The purposes of the research were to evaluate system performance and response of building structure under external load for full scale modal-testing-tower applied toggle bracing and lead rubber damper(LRD). The dynamic properties of the structure were measured before and after installing damper under harmonic excitation using the AMD and the results were compared. The harmonic excitation condition is to increase 0.01Hz sine sweep signal from 0.49Hz to 0.63Hz. As a result of measuring resonant frequency, before installing damper is 0.55Hz and after installing damper is 0.62Hz. The experimental results after installing damper were also distinguished from simulation results and the main cause of this results is temperature dependency property of rubber material.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제12권1호
• /
• pp.491-500
• /
• 2020

The present study proposes a time domain model for the Vortex-induced Vibration (VIV) simulation of a catenary riser under the combination of the current and oscillatory flow induced by vessel motion. In this model, the hydrodynamic force of VIV comprises excitation force, hydrodynamic damping and added mass, which are taken as functions of the non-dimensional frequency and amplitude ratio. The non-dimensional frequency is related with the response frequency, natural frequency, lock-in range and the fluid velocity. The relatively oscillatory flow induced by vessel motion is taken into account in the fluid velocity. Considering that the added mass coefficient and the non-dimensional frequency can affect each other, an iterative analysis is conducted at each time step to update the added mass coefficient and the natural frequency. This model is in detail validated against the published test models. The results show that the model can reasonably reflect the effect of the added mass coefficient on the VIV, and can well predict the riser's VIV under stationary and oscillatory flow induced by vessel motion. Based on the model, this study carries out the VIV simulation of a catenary riser with harmonic vessel motion. By analyzing the bending moment near the touchdown point, it is found that under the combination of the ocean current and oscillatory flow the vessel motion may decrease the VIV response, while increase the excited frequencies. In addition, the decreasing rate of the VIV under vessel surge is larger than that under vessel heave at small vessel motion velocity, while the situation becomes opposite at large vessel motion velocity.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2008년도 춘계학술대회논문집
• /
• pp.202-205
• /
• 2008

This paper presents an optimization of permanent magnet (PM) in a brushless dc (BLDC) motor using the response surface methodology (RSM). Size and angle of the PM are optimized to minimize the cogging torque, while reducing the magnitude of harmonic at a dominant frequency and maintaining the operating torque. A fitted RS model is constructed by verifying the high reliability of the total variation and the variation of estimated error. The optimized design is validated by carrying out the reanalysis and comparing to the initial model using the nonlinear transient finite element analysis.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2001년도 춘계학술대회논문집
• /
• pp.289-294
• /
• 2001

Three kinds of viscoelastic damper model, which has a non-linear spring as an element is studied analytically and numerically. The behavior of the damper model shows non-linear hysteresis curves which is qualitatively similar to those of real viscoelastic materials. The motion is governed by a non-linear constitutive equation and an additional equation of motion. Harmonic balance method is applied to get analytic solutions of the system. The frequency-response curves show that multiple solutions co-exist and that the jump phenomena can occur. In addition, it is shown that separate solution branch exists and that it can merge with the primary response curve. Saddle-node bifurcation sets explain the occurrences of such non-linear phenomena.

• 한국소음진동공학회논문집
• /
• 제12권1호
• /
• pp.57-64
• /
• 2002

Three kinds of viscoelastic damper model, which has a non-linear spring as an element is studied analytically and numerically The behavior of the damper model shows non-linear hysteresis curves which is qualitatively similar to those of real viscoelastic materials. The motion is governed by a non-linear constitutive equation and an additional equation of motion. Harmonic balance method is applied to get analytical solutions of the system. The frequency-response curves sallow that multiple solutions co-exist and that the jump phenomena can occur. In addition, it is shown that separate solution branch exists and that it can merge with the primary response curve. Saddle-node bifurcation sets explain the occurrences of such non-linear Phenomena.

• 전기학회논문지
• /
• 제61권5호
• /
• pp.721-725
• /
• 2012

In this paper, a novel analysis on the nonlinear response of a power amplifier (PA) with the intermodulation distortion (IMD) asymmetry is proposed based on the mutislice behavioral model. The coefficients of the odd-order and even-order polynomial of that model are represented with the PA practical circuit parameters such as intercept points, gain and amplitudes of excitation inputs. We also develop the analytic expressions to distinguish baseband frequency effect from second harmonic effect on the IMD asymmetry. We also validate the derived analytic expressions through measurements.

• 전력전자학회논문지
• /
• 제18권3호
• /
• pp.279-288
• /
• 2013

This paper proposes a improved speed control system for five-phase squirrel-cage induction motor(IM) injecting 3rd. current harmonic components with field oriented control (FOC) A five-phase IM drives present unique characteristics due to the additional degrees of freedom and also drives possess many others advantage compared with the traditional three-phase motor drive system, such as reducing a amplitude of torque pulsation at low frequency and increasing the reliability. In order to maximize the torque per ampere, the proposed motor has concentrated windings. The produced back-electromotive force is almost trapezoidal, and the motor is supplied with the combined sinusoidal plus third harmonic of currents. There is necessary to controlled 3rd harmonic current in order to high response characteristics. For presenting the superior performance of the proposed the speed control system, experimental results are presented using a 32-bit fixed point TMS320F2812 DSP with 1.5[kW] induction motor.

• Journal of Power Electronics
• /
• 제11권4호
• /
• pp.583-590
• /
• 2011

Three-level NPC inverters have been put into practical use for years especially in high voltage high power grids. This paper researches three-level active power filters (APFs). In this paper a mathematical model in the d-q coordinates is presented for 3-phase 3-wire NPC APFs. The deadbeat control scheme is obtained by using state equations. Canceling the delay of one sampling period and providing the predictive value of the harmonic current is a key problem of the deadbeat control. Based on this deadbeat control, the predictive output current value is obtained by the state observer. The delay of one sampling period is remedied in this digital control system by the state observer. The predictive harmonic command current value is obtained by the repetitive predictor synchronously. The repetitive predictor can achieve a better prediction of the harmonic current with the same sampling frequency, thus improving the overall performance of the system. The experiment results indicate that the steady-state accuracy and the dynamic response are both satisfying when the proposed control scheme is implemented.