• Journal of Advanced Marine Engineering and Technology
• /
• v.11 no.2
• /
• pp.37-50
• /
• 1987

In an effort to conserve electric power, variable voltage variable frequency pulse width modulated (PWM) inverters are being applied increasingly to the variable speed control of the induction motors. The use of the PWM technique in motor drive applications is considered advantageous in many ways. For industrial applications, the PWM drive obtains its DC input through simple uncontrolled rectification of the commercial AC line and is favored for its good power factor, good efficiency, its relative freedom regulation problem, and mainly for its ability to operate the motor with nearly sinusoidal current waveforms. The purpose of this paper is to design a three phase natural sampled PWM inverter using microprocessor with simple control algorithm and hybrid control circuit has been built to implement this PWM scheme. In this system, the microprocessor can be used only for calculations directly related to motor control tasks by the design of hybrid circuit which sends PWM signals to the motor.

• Journal of Power Electronics
• /
• v.14 no.5
• /
• pp.890-898
• /
• 2014

Critical conduction mode boost power factor correction converters operating at the boundary of continuous conduction mode and discontinuous conduction mode have been widely used for power applications lower than 300W. This paper proposes an enhanced variable on-time control method for the critical conduction mode boost PFC converter to improve the total harmonic distortion characteristic. The inductor current, which varies according to the input voltage, is analyzed in detail and the optimal on-time is obtained to minimize the total harmonic distortion with a digital controller using a TMS320F28335. The switch on-time varies according to the input voltage based on the computed optimal on-time. The performance of the proposed control method is verified by a 100W PFC converter. It is shown that the optimized on-time reduces the total harmonic distortion about 52% (from 10.48% to 5.5%) at 220V when compared to the variable on-time control method.

• Nuclear Engineering and Technology
• /
• v.49 no.1
• /
• pp.141-147
• /
• 2017

Mechanical shim is an advanced technology for reactor power and axial offset control with control rod assemblies. To address the adverse accuracy impact on the ex-core power range neutron flux measurements-based axial offset control resulting from the variable positions of control rod assemblies, the lead-lag-compensated in-core self-powered vanadium detector signals are utilized. The prompt ${\gamma}$ current of self-powered detector is ignored normally due to its weakness compared with the delayed ${\beta}$ current, although it promptly reflects the flux change of the core. Based on the features of the prompt ${\gamma}$ current, a method for configuration of the lead-lag dynamic compensator is proposed. The simulations indicate that the method can improve dynamic response significantly with negligible adverse effects on the steady response. The robustness of the design implies that the method is of great value for engineering applications.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.27 no.5
• /
• pp.425-430
• /
• 2022

A pumped storage power station is an important means to solve the problem of peak load regulation and ensures the safety of power grid operation. The doubly fed variable-speed pumped storage (DFVSPS) system adopts a doubly fed induction machine (DFIM) to replace the synchronous machine used in traditional pumped storage. The stator of DFIM is connected to the power grid, and the three-phase excitation windings are symmetrically distributed on the rotor. Excitation current is supplied by the converter. The active and reactive power of the unit can be quickly adjusted by adjusting the amplitude, frequency, and phase of the rotor-side voltage or current through the converter. Compared with a conventional pumped storage hydropower station (C-PSH), DFVSPS power stations have various operating modes and frequent start-up and shutdown. This study introduces the structure and principle of the DFVSPS unit. Mathematical models of the unit, including a model of DFIM, a model of the pump-turbine, and a model of the converter and its control, are established. Fast power control strategies are proposed for the unit model. A 300 MW model of the DFVSPS unit is established in MATLAB/Simulink, and the response characteristics in generating mode are examined.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.57 no.4
• /
• pp.356-361
• /
• 2008

The conventional drive system of SRM has a current sensor per each phase. The torque demand signal generated by the outer control loop is translated into individual current reference signal for each phase. The torque is controlled by regulating these currents. Using the SRM in a variable-speed control, the phase currents are generally regulated to achieve a square wave. The simplest form of current regulation uses fixed frequency delta modulation of the phase voltages. The aim of this paper is to regulate 3-phases current of SRM by only single current sensor using delta modulation with digital chip. In this paper, the asymmetric bridge converter which is able to control independently phases and be excited simultaneously is used as the driver system for 6/4 poles SRM. And the current sensor is replaced 3 sensors of each phase with only one on bus line of converter so as to detect current of every phase. The proposed delta modulation technique has been implemented in a simple digital logic circuit using EPLD(Electrically Programmable Logic Device). This method is verified through simulation and experiment results.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.21 no.6
• /
• pp.473-480
• /
• 2016

This study proposes a performance improvement for parallel-connected thyristor dual converters using a circulating current with an unbalanced parallel operation compensator. The proposed control method determines a variable reference value for the voltage PI controller according to voltage error at firing angle control applied to a difference current control. This method uses circulating current control to maintain a stable voltage and excellent current response during parallel operation. The effectiveness of the proposed control is verified with a simulation and an experiment based on the comparison of the performance of the proposed control method with other conventional methods.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.21 no.2
• /
• pp.168-174
• /
• 2016

In this paper, current control using PI controller in the synchronous reference frame is analyzed through the relationship among bandwidth, resonance frequency, and sampling frequency in the grid-connected inverter with LCL filter. Stability is investigated by using bode plot in frequency domain and root locus in discrete domain. The feedback variable is the grid current, which is regulated by the PI controller in the synchronous reference frame. System delay is modeled as 1.5Ts, which contains computational and PWM modulator delay. Two resonance frequencies are given at 815 Hz and 3.16 kHz from LCL filter parameters. Sufficient phase and gain margins can be obtained to guarantee stable current control, in case that resonance frequency is above one-sixth of the sampling frequency. Unstable current control is performed when resonance frequency is below one-sixth of the sampling frequency. Analysis results of stability from frequency response and discrete response is the same regardless of resonance frequency. Finally, stability of current control based on theoretical analysis is clearly verified through simulation and experiment in grid-connected inverters with LCL filter.

• Proceedings of the KIPE Conference
• /
• 1999.07a
• /
• pp.295-298
• /
• 1999

In this paper, the diode bridge-type ZVT(Zero-Voltage Transition) inverter is proposed. It consists of one auxiliary switch, three resonant inductors and six blocking diodes. So, the advantage of the proposed topology is the reduction of the auxiliary switch. The topology of the proposed ZVT inverter is analyzed with a description of the control conditions based on the load current. Therefore, this paper two control algorithms were discussed. A variable resonant pattern control algorithm by using load current feedback and a resonant period control algorithm by using resonant inductor current feedback is proposed in order to achieve the ZVT switching condition in full control range and the reducing current spike main switches cause by reverse recovery problem.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.55 no.3
• /
• pp.133-140
• /
• 2006

This paper is proposed an efficiency optimization control algorithm for a synchronous reluctance motor(SynRM) which minimizes the copper and iron losses. Also, this paper presents a speed estimated control scheme of SynRM using artificial neural network(ANN). There exists a variety of combinations of d and q-axis current which provide a specific motor torque. The objective of the efficiency optimization controller is to seek a combination of d and q-axis current components, which provides minimum losses at a certain operating point in steady state. It is shown that the current components which directly govern the torque production have been very well regulated by the efficiency optimization control scheme. The proposed algorithm allows the electromagnetic losses in variable speed and torque drives to be reduced while keeping good torque control dynamics. The control performance of ANN is evaluated by analysis for various operating conditions. Analysis results are presented to show the validity of the proposed algorithm.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.14 no.4
• /
• pp.293-298
• /
• 2009

This paper presents a variable gain current control algorithm for the stabilized grid connection between the grid and a doubly fed induction(DFIG) as a wind power generator. The performance of a RSC current controller depends highly on accurate machine parameters, and especially requires a fast and robust response regardless of the disturbances such as voltage sag. However, parameter variations of a DFIG occur at the point of grid connection, which affects the current controller gains based on DFIG parameters after a DFIG is connected to the grid. Thus, performance degrades when actual machine parameters depart from values used in the control system. In the proposed algorithm, current controller gains of the rotor side converter(RSC) are changed after a DFIG is connected to the grid. The simulation results and experimental results for a 750kW are shown to illustrate the feasibility of the proposed algorithm.