• The Transactions of the Korean Institute of Power Electronics
• /
• v.21 no.6
• /
• pp.538-541
• /
• 2016

This paper proposes an LCL-filter design for space vector pulse width modulation (SVM) in grid-connected three-phase inverter systems. Although there are a several studies in progress, the existing methods are erroneous because they do not focus on the other switching methods. This paper presents the design methodology for an LCL-filter that is optimized for SVM switching operations. The design procedure for the LCL-filter is presented step-by-step. The inverter-side inductor was determined by an analysis of the ripple components, mathematically. Based on the reactive power absorption ratio, the filter capacitor was determined. The grid-side inductor was determined by the ripple attenuation factor of the output current. Experimental results verify the validity of the design method for the LCL-filter.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.1 no.2
• /
• pp.70-73
• /
• 1987

This paper itltroduces a simple stair-case PWM using the pseudo-sinusoidal method. In a configuration of controller, the value of sine as a fundamental factor divided into stair-case level and the three-phase PWM inverter is composed by digital compound for each value of stair-case level. The three-phase output pulse at a fixed carrier frequency and a variable reference frequency is obtained under the effect of reduced harmonics. In this experiment, using the power FET as the switching device, 0.5 H.P. induction motor operation is performed when the switching frequency is 20KHz.

• Proceedings of the KIPE Conference
• /
• 2013.07a
• /
• pp.489-490
• /
• 2013

계통 연계형 발전시스템은 스위칭 주파수를 기본으로 하는 배수 고조파들이 발생한다. 이 때 인버터의 출력 전류 고조파는 계통의 전력품질에 영향을 주므로 저역통과 필터를 이용하여 제거해 주어야 한다. 일반적으로 사용하는 L, LC필터는 구성이 간단하고 제어가 용이한 장점이 있지만 동적특성이 좋지 않고 필터의 성능향상을 위해서는 인덕턴스를 증가시켜야 하기 때문에 필터의 부피가 커지는 단점을 가지고 있다. 이에 반해 LCL필터는 LC필터에 비해 더 낮은 용량으로 높은 고조파 감쇄 효과를 구현 할 수 있다는 장점이 있다. 그리고 2레벨 인버터에 비해 3레벨 인버터는 높은 효율과 낮은 THD발생으로 계통 연계 시스템에 많이 적용되고 있다. 본 눈문에서는 계통연계형 3레벨 인버터의 LCL필터 설계를 하여 이를 컴퓨터 시뮬레이션과 실험을 통하여 타당성을 검증한다.

• Journal of IKEEE
• /
• v.21 no.2
• /
• pp.105-114
• /
• 2017

This paper proposes a design method of an LCL-filter for grid-tied three-level inverter systems. The demand for three-phase PWM inverters in applications such as wind or solar power generation systems has been increase in recent years. To reduce harmonic components caused by switching operation, such inverters are connected to the grid via an LCL filter. Although there are research results for designing LCL-filter, the modulation method should be fully considered to make the filter perform desired cancellation ability with minimized size. This paper presents the design methodology for an LCL-filter that is optimized for SVM switching operations. The simulation and experimental results verify the validity of the LCL-filter designed with proposed method in this paper.

• Journal of Power Electronics
• /
• v.17 no.2
• /
• pp.368-379
• /
• 2017

In this paper, a direct torque control algorithm with novel duty cycle-based modulation is proposed for permanent magnet synchronous motor drives fed by neutral-point clamped three-level inverters. Compared with the standard DTC, the proposed algorithm can suppress steady-state torque ripples as well as ensure neutral-point potential balance and smooth vector switching. A unified torque/flux evaluation table with multiple voltage vectors and precise control levels is established and used in this method. This table can be used to evaluate the effects of duty-cycle vectors on torque and flux directly, and the elements of the table are independent of the motor parameters. Consequently, a high number of appropriate voltage vectors and their corresponding duty cycles can be selected as candidate vectors to reduce torque ripples by looking up the table. Furthermore, small vectors are incorporated into the table to ensure the neutral-point potential balance with the numerous candidate vectors. The feasibility and effectiveness of the proposed algorithm are verified by both simulations and experiments.

• Journal of Power Electronics
• /
• v.18 no.2
• /
• pp.445-455
• /
• 2018

A novel algorithm is proposed to regulate the neutral point potential in neutral point clamped three-level inverters. Oscillations of the neutral point potential and an unbalanced dc-link voltage cause distortions of the output voltage. Large capacitors, which make the application costly and bulky, are needed to eliminate oscillations. Thus, the algorithm proposed in this paper utilizes the finite-control-set model predictive control and the multistage medium vector to solve these issues. The proposed strategy consists of a two-step prediction and a cost function to evaluate the selected multistage medium vector. Unlike the virtual vector method, the multistage medium vector is a mixture of the virtual vector and the original vector. In addition, its amplitude is variable. The neutral point current generated by it can be used to adjust the neutral point potential. When compared with the virtual vector method, the multistage medium vector contributes to decreasing the regulation time when the modulation index is high. The vectors are rearranged to cope with the variable switching frequency of the model predictive control. Simulation and experimental results verify the validity of the proposed strategy.

• Journal of Power Electronics
• /
• v.12 no.2
• /
• pp.344-356
• /
• 2012

In recent years, multilevel technology has become an effective and practical solution in the field of moderate and high voltage applications. This paper discusses an APF with a three-level NPC inverter. Obviously, the application of such converter to APFs is hindered by the problem of the voltage unbalance of DC capacitors, which leads to system instability. This paper comprehensively analyzes the theoretical limitations of the neutral-point voltage balancing problem for tracking different harmonic currents utilizing current switching functions from the space vector PWM (SVPWM) point of view. The fluctuation of the neutral point caused by the load currents of certain order harmonic frequency is reported and quantified. Furthermore, this paper presents a close-loop digital control algorithm of the DC voltage for this APF. A PI controller regulates the DC voltage in the outer-loop controller. In the current-loop controller, this paper proposes a simple neutral-point voltage control method. The neutral-point voltage imbalance is restrained by selecting small vectors that will move the neutral-point voltage in the direction opposite the direction of the unbalance. The experiment results illustrate that the performance of the proposed approach is satisfactory.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.20 no.3
• /
• pp.273-279
• /
• 2015

A zero vector selection method to reduce switching losses for model predictive control (MPC) of voltage source inverter is proposed. A conventional MPC of voltage source inverter has not been proposed, and a method to select the redundancy of the zero vector is required for this study. In this paper, the redundancy of the zero vectors is selected with generating a zero sequence voltage to reduce switching losses. The zero vector of 2-level inverter is determined by determining sign of the zero sequence voltage. In the proposed method, the quality of the current is retained and switching loss can be reduced compared with the conventional method. This result was verified by P-sim simulation and experiments.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.21 no.1
• /
• pp.131-141
• /
• 2007

This paper proposes analysis on new equipment for power quality in electric railway. The proposed equipment consists of series inverter and parallel inverter. Each inverter is connected by capacitor as dc link. This structure can be compensated for active and reactive power in catenary through transformer. We verified the proposed equipment using the PSCAD/EMTDC and the calculation results from the proposed approach are widely described in the paper.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.22 no.12
• /
• pp.64-70
• /
• 2008

In case that conventional PRC(Pseudo-Randomized Frequency Carrier) modulation scheme is applied to a three-phase HBML(H-Bridge Multi-Level Inverter), the dominant harmonics spectra appear at twice switching frequency. In this paper, the dominant harmonics spectra spreading effect of the conventional PRC scheme was improved by using three stage MUXs(Multiplexers) and two triangular carriers with fixed frequency which has mutual relation of the twice frequency. To confirm the validity of the improved PRC scheme, the experiment were performed on a 1.5[kw] three-phase HBML based induction motor drives. And, the harmonics spectra of the conventional and improved PRC schemes are compared and discussed.