• Journal of Electrical Engineering and Technology
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• v.13 no.5
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• pp.1986-1995
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• 2018

In this paper, a novel neutral-point voltage balancing scheme for NPC three-level inverters using carrier-based sinusoidal pulse width modulation (SPWM) method is developed. The new modulation approach, based on the obtained expressions of zero sequence voltage in all six sectors, can significantly suppress the low-frequency voltage oscillation in the neutral point at high modulation index and achieve a fast voltage-balancing dynamic performance. The implementation of the proposed method is very simple. Another attractive feature is that the scheme can stably control any voltage difference between the two dc-link capacitors within a certain range without using any extra hardware. Furthermore, the presented scheme is also applicable to the single-phase NPC three-level inverter. It can maintain the neutral-point voltage balance at full modulation index and improve the voltage-balancing dynamic performance of the single-phase NPC three-level inverter. The performance of the proposed strategy and its benefits over other previous techniques are verified experimentally.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.177-178
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• 2015

This paper presents a neutral point deviation compensating control algorithm applied to a 3-level NPC converter. The neutral point deviation is analyzed with a focus on the current flowing out of or into the neutral point of the dc link. Based on the zero sequence components of the reference voltages, this paper analyzes the neutral point deviation and balancing control for 3-level NPC converter. An analytical method is proposed to calculate the injected zero sequence voltage for NP balancing based on average neutral current. This paper also proposes a control scheme compensating for the neutral point deviation under generalized unbalanced grid operating conditions. The positive and negative sequence components of the pole voltages and ac input currents are employed to accurately explain the behavior of 3-level NPC converter. Simulation and experimental results for a test set up of 30kW are shown to verify the validity of the proposed algorithm.

• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.212-213
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• 2017

In this paper is presented a pre-charging sequence for single-phase cascaded neutal-point-clamped(NPC) converters for capacitors voltage balancing. capacitor imbalance problem in pre-charge sequence is caused in cascaded NPC converter by its topology. the DC link voltage at each NPC converter module can be balanced by the proposed switching method. the design and performance of the proposed sequence are verified by simulation and experimental results using prototype.

• Journal of Power Electronics
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• v.3 no.4
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• pp.205-214
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• 2003

This paper proposes a simple control strategy based on the discontinuous PWM (DPWM) to balance the DC-link voltage of three-level neutral-point-clamped (NPC) inverter at low modulation index. It introduces new DPWM methods in multi-level inverter and one of them is used for balancing the DC-link voltage. The current flowing in the neutral point of the DC-link causes the fluctuation of the DC-link voltage of the NPC inverter. The proposed DPWM method changes the path and duration time of the neutral point current, which makes the overall fluctuation of the DC-link voltage zero during a sampling time of the reference voltage vector. Therefore, by using the proposed strategy, the voltage of the DC-link can be balanced fairly well and the voltage ripple of the DC-link is also reduced significantly. Moreover, comparing with conventional methods which have to perform the complicated calculation, the proposed strategy is very simple. The validity of the proposed DPWM method is verified by the experiment.

• Journal of Electrical Engineering and Technology
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• v.12 no.3
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• pp.1203-1210
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• 2017

Switched-inductor (SL) Z-source three-level inverter is a novel high power topology. The SL based impedance network can boost the input dc voltage to a higher value than the single LC impedance network. However, as all the neutral-point-clamped (NPC) inverters, the SL Z-source three-level inverter has to balance the neutral-point (NP) potential too. The principle of the inverter is introduced and then the effects of NP potential unbalance are analyzed. A NP balancing method is proposed. Other than the methods for conventional NPC inverter without Z-source impedance network, the upper and lower shoot-through durations are corrected by the feedforward compensation factors. With the proposed method, the NP potential is balanced and the voltage boosting ability of the Z-source network is not affected obviously. Simulations are conducted to verify the proposed method.

• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.235-236
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• 2017

본 논문에서는 저압 직류 배전 시스템에 사용되는 3-레벨 NPC DAB 컨버터의 중성점 전압 제어를 위한 향상된 스위칭 알고리즘을 제안한다. 3-레벨 NPC DAB 컨버터는 구조상 정격전압 감소를 위해 중성점을 기준으로 DC-link 단에 두 개의 캐패시터가 사용되기 때문에 중성점으로 들어오는 전류에 불균형이 발생하며 중성점 전압이 흔들리는 문제점이 나타난다. 중성점 전압이 흔들릴 경우 불균형한 전압이 변압기에 형성되며 이로 인해 전류 Offset과 실효 전류의 증가에 따른 전력 손실증가 등 전체적인 컨버터의 동작에 악영향을 준다. 따라서 본 논문에서는 3-레벨 NPC DAB 컨버터의 동작원리 및 기존 스위칭 패턴을 분석하고, 향상된 스위칭 패턴을 적용시켜 중성점 전압을 제어하는 알고리즘의 타당성을 모의시험을 통해 검증하고자 한다.

• Proceedings of the KIPE Conference
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• 2016.11a
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• pp.131-132
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• 2016

3-레벨 중성점 다이오드 클램프(NPC) 컨버터는 high-power medium voltage(MV)에서 많이 응용된다. 하지만 3-레벨 중성점 다이오드 클램프(NPC) 컨버터는 각 스위치 소자에서 손실이 불균형하게 발생하게 되어 스위치 소자 간 성능이 불균형하게 된다. 따라서 본 논문에서는 단상 3-레벨 중성점 다이오드 클램프(NPC) 컨버터의 기존 모델 예측 제어의 스위칭 패턴을 분석 및 스위칭 순환방식을 이용한 효율적인 스위칭 상태를 갖는 모델 예측 제어를 제안한다. 이를 통해 PI 제어기 기반의 펄스 폭 변조 방법과 기존 모델 예측 제어 방법의 손실 비교를 통하여 제안하는 모델 예측 제어 성능을 검증한다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.9
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• pp.71-80
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• 2015

This paper proposes a convenient thermal modeling method for loss distribution control method of 3-level Active NPC(Neutral Point Clamped) inverter. In the drawback of conventional 3-level NPC, the generated losses can occur unbalance in each switching device, as a result, thermal utilization of designed system has been decreased. In order to compensate unbalanced losses, Active NPC inverter performed loss balancing control with thermal modeling during operation of each switching device. Therefore, this paper deals with a convenient thermal modeling method based on newton's law of cooling rather than conventional thermal modeling method. Both simulation and experimental results based on 10kW 3-level Active NPC inverter confirm the validity of the analysis performed in the study.

• Journal of Power Electronics
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• v.18 no.2
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• pp.432-444
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• 2018

This paper presents a capacitor voltage balancing topology using a three-level boost converter (TLBC) for a neutral point clamped (NPC) three-level inverter fed surface permanent magnet synchronous motor drive (SPMSM). It enhanced the performance of the drive in terms of its voltage THD and torque pulsation. The main attracting feature of the proposed control is the boosting of the input voltage and at the same time the balancing of the capacitor voltages. This control also reduces the computational complexity. For the purpose of close loop vector control, a software based cost effective resolver to digital converter RDC-less estimation is implemented to calculate the speed and position. The proposed drive is simulated in the MATLAB/SIMULINK environment and an experimental investigation using dSPACE DS1104 validates the proposed drive system at different operating condition.

• 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.