• Journal of IKEEE
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• v.24 no.1
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• pp.170-177
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• 2020

This paper presents an open-fault tolerance control method for active neutral point clamped (ANPC) inverter with high frequency/low frequency (HF/LF) modulation. By applying the ANPC inverter with SiC MOSFETs and Si IGBTs, the system efficiency and performance can be improved compared to a Si-based inverter. HF/LF modulation is used for a megawatt-scale inverter to minimize the commutation loop. The open-switch failure in megawatt-scale inverter causes severe damage to load and huge expenses when the inverter has been shut-down. The proposed tolerance control of open-switch failure provides continuous operation and improved reliability to the ANPC inverter. The effectiveness of the proposed fault tolerance control is verified by simulation results.

• Journal of Power Electronics
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• v.19 no.4
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• pp.989-999
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• 2019

This paper proposes a fault-tolerant control strategy with finite control set model predictive control (FCS-MPC) based on hierarchical optimization for five-level H-bridge neutral-point-clamped (5L-HNPC) inverter-fed induction motor drives. Fault-tolerant operation is analyzed, and the fault-tolerant control algorithm is improved. Adopting FCS-MPC based on hierarchical optimization, where the voltage is used as the controlled objective, called model predictive voltage control (MPVC), the postfault controller is simplified as a two layer control. The first layer is the voltage jump limit, and the second layer is the voltage following control, which adopts the optimal control strategy to ensure the current following performance and uniqueness of the optimal solution. Finally, simulation and experimental results verify that 5L-HNPC inverter-fed induction motor drives have strong fault tolerant capability and that the FCS-MPVC based on hierarchical optimization is feasible.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.489-490
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• 2016

본 논문에서는 인버터 시스템의 가격을 줄이기 위해 3-레벨 NPC 인버터의 중성단에 하나의 션트 저항을 삽입함으로써 AC 전동기의 3상 전류를 획득하는 방법을 제안한다. 션트 저항으로부터 정확한 상 전류를 획득하기 위해서는 최소한의 시간이 필요하며 때문에 측정불가영역이 존재하게 된다. 기존의 측정불가영역으로 부터 상 전류를 복원하는 방법은 스위칭 패턴을 이동시키거나 공간 벡터 전압 변조 기법(SVPWM) 이외의 변조 기법을 이용하였는데 이러한 방법은 전류에 고조파를 증가시켜 효율을 떨어뜨리고 소음을 발생시킨다. 본 논문에서는 동기 좌표계 d-q축 비례적분제어기와 전동기 시스템의 전달함수를 이용하여 지령 전류로부터 실제 전류와 같은 전류를 얻는 방법을 통해 기존의 문제점들을 개선하는 방법을 제안한다. 제안된 방법은 시뮬레이션을 통해 증명하였다.

• Journal of Electrical Engineering and Technology
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• v.12 no.5
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• pp.1872-1882
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• 2017

Medium voltage drive systems driven by high-power multi-level inverters operating at low switching frequency can reduce the switching losses of the power device and increase the output power. Employing subsection synchronous current harmonic minimum pulse width modulation (CHMPWM) technique can maintain the total harmonic distortion of current at a very low level. It can also reduce the losses of the system, improve the system control performance and increase the efficiency of DC-link voltage accordingly. This paper proposes a subsection synchronous CHMPWM approach of active neutral point clamped five-level (ANPC-5L) inverter under low switching frequency operation. The subsection synchronous scheme is obtained by theoretical calculation based on the allowed maximum switching frequency. The genetic algorithm (GA) is adopted to get the high-precision initial values. So the expected switching angles can be achieved with the help of sequential quadratic programming (SQP) algorithm. The selection principle of multiple sets of the switching angles is also presented. Finally, the validity of the theoretical analysis and the superiority of the CHMPWM are verified through both the simulation results and experimental results.

• Journal of Power Electronics
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• v.16 no.6
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• pp.2109-2118
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• 2016

Based on the space vector pulse width modulation (SVPWM) theory, this paper realizes an easier SVPWM strategy, which is equivalently implemented by CBSPWM with zero-sequence voltage injection. The traditional SVPWM strategy has no effect on controlling the neutral-point voltage balance. In order to solve the neutral-point voltage unbalance problem for neutral-point-clamped (NPC) three-level inverters, this paper proposes a neutral-point voltage balance controller. The proposed controller realizes controlling the neutral-point voltage balance by dynamically calculating the offset superimposed to the three-phase modulation waves of an equivalent SVPWM strategy. Compared with the traditional SVPWM strategy, the proposed neutral-point voltage balance controller has a strong ability to balance the neutral-point voltage, has good steady-state performance, improves the output waveforms quality and is easy for digital implementation. An experiment has been carried out on a NPC three-level inverter prototype based on a digital signal processor-complex programmable logic device (DSP-CPLD). The obtained experimental results verify the effectiveness of the proposed neutral-point voltage balance controller.

• Proceedings of the KIPE Conference
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• 1998.07a
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• pp.63-69
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• 1998

A new current controlled PWM technique with NPC structure is proposed in this paper. A current controlled PWM technique with neutral-point-clamped pulse-width modulation inverter composed of main switching devices which operates as switch for PWM and auxiliary switching devices to clamp the output terminal potential to the neutral point potential is described. The proposed current controller has a first and second current band. The switching pattern will be made by the first current band. According to the second current band, the output state of the switching pattern is changed into positive and negative state. This inverter output contains less harmonic content and lower switching frequency than that of conventional current controlled PWM technique at the same current limit. Two inverters are compared analytically and the performance is investigated by the computer simulation.

• Journal of IKEEE
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• v.24 no.3
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• pp.867-876
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• 2020

This paper proposes a neutral-point voltage ripple reduction of high frequency injection sensorless control of IPMSM fed by a three-level inverter. The high frequency voltage injection method has been successfully applied to sensorless control for IPMSM at low speed region. In the process of high frequency voltage injection sensorless control for IPMSM, the neutral-point voltage ripple is increased. It should be reduced because it distorts the output current and decreases a life time of DC-link capacitor. The proposed method in this paper reduces the neutral-point voltage ripple by compensating the reference voltage, and the compensation value is calculated simply with reference voltages and currents. The effectiveness of the proposed method is verified by simulation results.

• Journal of Power Electronics
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• v.19 no.3
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• pp.702-713
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• 2019

Multilevel Inverters (MLIs) are widely used in medium voltage applications due to their various advantages. In addition, there are numerous types of MLIs for such applications. However, the diode-less 3-level (3L) T-type Neutral Point Clamped (NPC) MLI is the most advantageous due to its low conduction losses and high potential efficiency. The power circuit of a 3L T-type NPC is derived by the conventional two level inverter by a slight modification. In order to explore the MLI performance for various Pulse Width Modulation (PWM) schemes, this paper examines the operation of a 3L (five level line to line) T-type NPC MLI for various types of Multi-Carriers Pulse Width Modulation (MCPWM) schemes. These PWM schemes are compared in terms of their voltage profile, total harmonic distortion (THD) and conduction losses. In addition, a 3L T-type NPC MLI is also compared with the conventional NPC in terms of number of switches, clamping diodes, main diodes and capacitors. Moreover, the capacitor-balancing problem is also investigated using the Neutral Point Fluctuation (NPF) method with all of the MCPWM schemes. A 1kW 3L T-type NPC MLI is simulated in MATLAB/Simulink and implemented experimentally and its performance is tested with a 1HP induction motor. The results indicate that the 3L T-type NPC MLI has better performance than conventional NPC MLIs.

• Journal of Power Electronics
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• v.14 no.5
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• pp.926-936
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• 2014

A simplified and effective space vector pulse-width modulation (SVPWM) algorithm with two and three levels for three-phase voltage-source converters is proposed in this study. The proposed SVPWM algorithm only uses several linear calculations on three-phase modulated voltages without any complicated trigonometric calculations adopted by conventional SVPWM. This simplified SVPWM also avoids choosing the vector sector required by conventional SVPWM. A two-level overmodulation scheme is integrated into the proposed two-level SVPMW to generate the output voltage that increases from a linear region to a six-step state with a smoothly linear transition characteristic and a simple overmodulation process without a lookup table and complicated nonlinear functions. The three-level SVPWM with a proportional-integral controller effectively balances the neutral point potential of the neutral point clamped converter. Results from the simulation in MATLAB/Simulink and the experiment based on a digital signal processor are provided to clearly demonstrate the validity and effectiveness of the proposed strategies.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.4
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• pp.369-372
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• 2017

This paper presents a control scheme for three-level NPC inverters using small DC-link capacitors. To reduce the inverter system volume, the film capacitor with small capacitance is a promising candidate for the DC-link. When small capacitors are applied in a three level inverter, however, the AC ripple component increases in the DC-link NPV (neutral point voltage). In addition, the three-phase input grid currents are distorted when the DC-link capacitors are fed by diode rectifier. In this paper, the additional circuit is applied to compensate for small capacitor systems defect, and the offset voltage injection method is presented for the stabilization in NPV. These two proposed processes evidently ensure the quality improvement of the input grid currents and output load currents. The feasibility of the proposed method is verified by experimental results.