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A vibration controller based on wavelet neural network (WNN) is designed for jacket-type offshore platforms with time delay. The offshore platform is regarded as a single-degree-of-freedom (SDOF) system while wave forces are irregular disturbances, and we can rebuild them in the context of Morison equation and wave theory. To reduce the vibration, a WNN vibration controller is designed based on a...
An open-loop and closed-loop operating boost-power-stage converter with relatively low damping factor exhibit resonant behavior in transient conditions. Such an undamped transient characteristic introduces overshoot to the control-to-output-variable transfer function, which is also visible in the inductor current transient behavior. Therefore, due to the either too large duty ratio or voltage-reference...
In this paper, the performances of various active damping methods for model-based-current-control (MBCC) of single-phase grid-tied LCL-filtered voltage source inverters (VSIs) are investigated. It is shown that the proposed MBCC approach enforces the inverter current to track its reference in all circumstances provided that the inverter current reference is generated accurately. In this study, a proportional-resonant...
Grid-connected inverter is an important part of the grid-connected system. Compared with the traditional L or LC filter, LCL filter has a better high-frequency harmonic attenuation performance. However, LCL filter has resonant peak, which has a great influence on the stability of the system. This paper first analyzes the effect of passive damping method on the resonance peak; then a double closed-loop...
The voltage source inverters operating in islanded microgrid are used as sources of power similar to synchronous generators (SG) in conventional power system. Unlike synchronous generators, these inverters neither have a natural droop (P-f and Q-V) characteristics nor rotational inertia. The electrical time constant is much lesser than mechanical time constant and hence the load changes will show...
High-stiffness servo system is easy to cause mechanical resonance in elastic coupling servo system. Although on-line adaptive notch filter is effective in most cases, it will lead to a severer resonance when resonance frequency deviated from the natural torsional frequency. To explain this phenomenon, an improved discrete system model is proposed. This paper quantitatively analyzes the influence of...
The impulse-based discrete feedback control has been proposed in previous work for the second-order motion systems with damping uncertainties. The sate-dependent discrete impulse action takes place at zero crossing of one of both states, either relative position or velocity. In this paper, the proposed control method is extended to a general hybrid motion control form. We are using the paradigm of...
With the increasing penetration of distribution generations (DGs), the stability problems of the power system become more and more serious. Virtual synchronous generator (VSG) as an effective solution, can improve the converter inertia, but there is still possibility of power oscillation due to the small line impendence ratio R/X. In this paper, a small signal dynamic model is derived for the second-order...
High-speed permanent magnet motors (HSPMMs) have gained ever-increasing interests in high speed direct-drive applications due to their advantages of high-power density, small size and high efficiency. However, the low stator inductance of the HSPMM causes large current ripple in the stator current, therefore brings additional iron loss. The Modular multilevel converter (MMC) increases both voltage...
This paper presents an approach for the improvement of the accuracy of absolute magnetic encoders (AME). The encoders comprise the following two magnets: a multipolar magnet to increase the resolution and the accuracy, and a center-located bipolar magnet for the calculation of the absolute angle. The multipolar signal processing is crucial for the increasing of the encoder accuracy; however, the multipolar...
The signals of magnetic encoders (MEs) are a pair sinusoidal waves: a sine wave and a cosine wave. Due to many different causes, they contain error factors such as offsets, amplitude differences, phase shifts, and random noise. This paper proposes auto-calibration and noise-reduction methods to reduce these errors and to estimate the positions of MEs. This method includes auto-calibration and adaptive-bandwidth...
Grid-connected converters have been widely used in distributed generations. However, the resonance brought by converters in weak grid has been a great threat to system stability. Impedance-based method provides a powerful tool for stability analysis. Active damping is also widely applied to improve system stability. This paper derives the impedance model of grid-connected converter system and analyzes...
The virtual synchronous generator (VSG) is the interface between distribute generator and power grid, which has the inertia and damping characteristics of the synchronous generator. This strategy can effectively control influence of inverters on power grid. In order to reduce the circulating current and power oscillation, this paper proposed a pre-synchronization control strategy which adds the pre-synchronization...
The multiplex 3-phase winding motors suffer from the problem of the magnetic coupling between the normal winding and the fault winding. To investigate the behaviors of the dual-winding PMSMs on the short-circuited fault conditions, a fault analysis model is developed that includes a dual-winding PMSM circuit model with a short-circuited fault coil within some phase coil and an inverter model with...
Rapid growing on the power level of renewable generation units leads to that using more adaptable and flexible control techniques in this units becomes more important for grid operators. In this paper, after introducing Renewable Static Synchronous Generation Units (RSSGU) as units with flexible dynamics capability, forming of renewable Virtual Power Plants based on this RSSGUs (VPP-SSG) is suggested...
With the development of the smart meters, demand response (DR) is able to provide fast ancillary services, such as frequency control. Some recent studies demonstrated that DR can perform like thermal generators in the frequency control. However, little attention has been paid to DR's effect on the electromechanical oscillations of the power system. Fast-response DR can not only affect system frequency,...
Aiming at the difference between conventional power electronic interface converter and traditional synchronous generator in microgrid, it cannot provide inertial support and damping effect for microgrid. In this paper, a converter based on virtual synchronous generator technology is used to design the power outer loop and the electromagnetic equation, so that the power electronic converter has some...
With increased penetration of renewable energy sources in electric grid, maintaining quality voltage at the load terminal has become a challenge. Voltage disturbances like sag, swell, harmonics, etc., can propagate from one section to another section of electric grid and degrade the performance of sensitive loads. This paper explores the capability of smart transformer (ST) to improve the voltage...
The buffing process used in the repair polishing of an automotive body surface is carried out manually using skilled workers based on their own experience. However, the number of skilled workers available in the workforce is decreasing owing to the aging population. In addition, the surface quality after the buffing process has been applied is dependent on the proficiency level of the polishing worker...
Because of the low power losses and moderate cost, the magnetic powder cores are popular in producing the filtering inductors for the high efficient and cost-effective power converters. However, the soft magnetic property of the powder cores leads to the wide variation of inductance along with the changing of the inductor current in one cycle of the grid, which challenges the system stability and...
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