• Proceedings of the KIEE Conference
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• 2005.11b
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• pp.87-89
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• 2005

If the three phases are not balanced, the current in neutral line is not zero. Then, the induced voltage can be generated In communication line. The KEPCO's rule about unbalanced current in single electric pole is a twenty percent of phase current. But the unbalanced current in double electric pole can't decide the rule because there are many different views. This paper develops the calculation and analysis technique of neutral current in single electric pole and double electric pole using equivalent circuit analysis, vector analysis and EMTP simulation.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.1
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• pp.84-90
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• 2012

Various methods have been proposed to identify the flux position in an interior permanent magnet synchronous motor (IPMSM) without the use of mechanical sensors. To achieve this, a method that uses both the back electromotive force (EMF) and the saliency to identify the flux position in the IPMSM without the injection of high-frequency components at low speeds has been reported. This method was then extended in order to drive the motor with no load to a light load. We propose a combination of these methods with different proportional-integral (PI) controllers for controlling $di_{dest}$/dt and $di_{qest}$/dt. We also introduce compensation values $F_L$ and $F_H$ to reduce the position error when the estimation rule is being selected.

• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.2
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• pp.127-133
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• 2019

This paper proposes a restarting method for extended electromotive force (EEMF)-based sensorless permanent magnet synchronous motor (PMSM) drive systems. The sensorless PMSM drive systems generally estimate the rotor speed and angle based on EEMF. However, if the inverter is stopped while the PMSM is rotating, the initial rotor speed and angle are required for restart. Therefore, the proposed restarting method estimates the initial rotor speed and angle using the short-circuit current generated by applying zero voltage vector from the inverter. The validity of the proposed method is verified by simulation and experimental results.

• Journal of Power Electronics
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• v.11 no.3
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• pp.360-368
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• 2011

This paper proposes an active frequency with a positive feedback in the d-q frame anti-islanding method suitable for a robust phase-locked loop (PLL) algorithm using the FFT concept. In general, PLL algorithms for grid-connected PV PCS use d-q transformation and controllers to make zero an imaginary part of the transformed voltage vector. In a real grid system, the grid voltage is not ideal. It may be unbalanced, noisy and have many harmonics. For these reasons, the d-q transformed components do not have a pure DC component. The controller tuning of a PLL algorithm is difficult. The proposed PLL algorithm using the FFT concept can use the strong noise cancelation characteristics of a FFT algorithm without a PI controller. Therefore, the proposed PLL algorithm has no gain-tuning of a PI controller, and it is hardly influenced by voltage drops, phase step changes and harmonics. Islanding prediction is a necessary feature of inverter-based photovoltaic (PV) systems in order to meet the stringent standard requirements for interconnection with an electrical grid. Both passive and active anti-islanding methods exist. Typically, active methods modify a given parameter, which also affects the shape and quality of the grid injected current. In this paper, the active anti-islanding algorithm for a grid-connected PV PCS uses positive feedback control in the d-q frame. The proposed PLL and anti-islanding algorithm are implemented for a 250kW PV PCS. This system has four DC/DC converters each with a 25kW power rating. This is only one-third of the total system power. The experimental results show that the proposed PLL, anti-islanding method and topology demonstrate good performance in a 250kW PV PCS.

• Journal of the Korean Society of Marine Environment & Safety
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• v.13 no.2 s.29
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• pp.169-172
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• 2007

This paper presents circuit models and control algorithms of distributed generation system(DGS) which consists of Z-type converter and PWM inverter. Z-type converter which employs both the L and C passive components and shoot-through zero vectors instead qf the conventional DC/DC converter in order to step up DC-link voltage. Discrete time sliding mode control with the asymptotic observer is used for current control. This system am be used for power conversion of DC renewable energy.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.8
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• pp.1261-1267
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• 2009

The Direct Torque Control[DTC] controls torque and flux by restricting the flux and torque errors within respective hysteresis bands, and motor torque and flux are controlled by the stator voltage space vector using optimum inverter switching table. And the Current Error Compensation method is on the basis of compensating current difference between the induction motor and its numerical model, in which the identical stator voltage is supplied for both the actual motor and the model so that the gaps between stator currents of the two can be forced to decay to zero as time proceeds. Consequently, the rotor speed approaches to the model speed, namely, setting value and the system can control motor speed precisely. This paper proposes a new sensorless speed control of induction motor using DTC and Current Error Compensation, which requires neither shaft encoder, speed estimator nor PI controllers. And through computer simulation, confirm effectiveness of proposed method.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.6
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• pp.653-658
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• 2013

This paper describes a new sensorless speed control method for permanent magnet synchronous motor(PMSM) using direct torque control(DTC). The direct torque control offers fast torque response, lesser hardware and processing costs as compared to vector controlled drives. In this paper the current error compensation technique is applied for sensorless speed control of synchronous motor. Through this method, the controlled stator voltage is applied to the synchronous motor so that the error between stator currents of the mathematical model and the actual motor can be forced to decay to zero as time proceeds and therefore, the motor speed approaches to the setting value. Especially, any PI controllers are not necessary in this control method. The simulation results indicate good speed and load responses from the low speed range to the high.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.9
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• pp.935-939
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• 2015

This paper describes sensorless speed control of brushless DC motors by using direct torque control. Direct torque control offers fast torque response, robust specification of parameter changes, and lower hardware and processing costs compared to vector-controlled drives. In this paper, the current error compensation method is applied to the sensorless speed control of a brushless DC motor. Through this control technique, the controlled stator voltage is applied to the brushless DC motor such that the error between the stator currents in the mathematical model and the actual motor can be forced to decay to zero as time proceeds, and therefore, the motor speed approaches the setting value. This paper discusses the composition of the controller, which can carry out robust speed control without any proportional-integral (PI) controllers. The simulation results show that the control system has good dynamic speed and load responses at wide ranges of speed.