• Journal of Power Electronics
• /
• v.16 no.2
• /
• pp.455-463
• /
• 2016

This paper proposes a compensation method to improve the distorted space vectors when a 3-level Neutral Point Clamped (NPC) inverter has an unbalanced neutral point voltage. Since both the neutral point voltage of the DC link and the space vector of a 3-level NPC inverter are closely related depending on the output load connecting state, a distorted space vector can occur when the neutral point voltage of a 3-level NPC inverter is unbalanced. The proposed method can improve the distorted space vectors by adjusting the injection time of the small and medium vectors and by modulating the amplitude of the carrier waveforms. In this paper, the proposed method is verified by both simulation and experimental results based on a 3-level NPC inverter.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.12 no.2
• /
• pp.115-122
• /
• 2007

In this paper, a novel fault detection method for fault tolerant control is proposed when the NPC inverter has a open failure in the switching device. The open fault of switching device is detected by checking the variation of a leg-voltage in the neutral-point-clamped inverter and the two phases control method is used for continuously balance the three phases voltage to the load. It can be achieve the fault tolerant control for improving the reliability of the NPC inverter by the fault detection and reconfiguration. This method has fast detection ability and a simple realization for fault detection, compared with a conventional method. Also, this fast detection ability improved the harmful effects such as DC-link voltage unbalance and overstress to other switching devices from a delay of fault detection. The proposed method has been verified by simulation and experiment.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.19 no.2
• /
• pp.173-183
• /
• 2014

In this paper, an analysis of power losses for the three-level T-type and neutral-point clamped (NPC) PWM inverters is presented, in which the conduction and switching losses of semiconductor devices of the inverters are taken into account. In the inverter operation, the conduction loss depends on the modulation index (MI) and power factor (PF), whereas the switching loss depends on the switching frequency. Power losses for the T-type and NPC inverters are analyzed and calculated at the different operating points of MI, PF and the switching frequency, in which the four different models of semiconductor devices are adopted. In the case of lower MI, the NPC-type is more efficient than the T-type, and vice versa. The validity of the power loss analysis has been verified by the simulation results.

• Proceedings of the KIPE Conference
• /
• 2014.07a
• /
• pp.546-547
• /
• 2014

본 논문에서는 LabVIEW와 Multisim을 이용한 Co-simultion 기능으로 얻은 시뮬레이션 결과와 그 과정을 기술한다. 3-Level NPC Inverter를 제어하였으며 동일한 조건에서 PSIM으로 시뮬레이션한 결과와 비교하여 보았다.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.13 no.1
• /
• pp.22-32
• /
• 2008

This paper proposes a linearization technique for the 3-level NPC type inverter, which increases the linear control range of Inverter up to the one-pulse inverter. The overmodulation range is divided into two modes depending on the Modulation Index, MI. In overmodulation region I, the reference angles are derived from the fourier series expansion of the reference voltage corresponding to the MI. In overmodulation region II, the holding angles are also derived in the same way. Therefore, it is possible to obtain the linear control and the maximized utilization of PWM inverter output voltage.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.27 no.6
• /
• pp.535-540
• /
• 2022

DC-link capacitors are reliability-critical components in a photovoltaic (PV) inverter. Typically, the lifetime of a DC-link capacitor is evaluated by considering the voltage and hot-spot temperature of the capacitor under the specific operating condition of the PV inverter. However, the output of the PV inverter is determined by solar irradiation and ambient temperature, which vary with the seasons; accordingly, the hot-spot temperature of the capacitor also changes. Therefore, the mission profile of the PV system should be considered to effectively evaluate the reliability of the DC-link capacitor. In this study, the reliability of the DC-link capacitor of a three-level NPC inverter is comparatively analyzed with and without considering the mission profiles of the PV system, where two mission profiles recorded in Arizona and Iza are considered. The accumulated damage of the DC-link capacitor is calculated based on the lifetime model by analyzing its thermal loading. Afterward, a reliability evaluation of the DC-link capacitor is performed at the component level and then at the system level by considering all capacitors by means of Monte Carlo analysis. Results reveal the importance of performing a mission-profile-based reliability evaluation during the design of high-reliability PV inverters to achieve the target reliability performance.

• Proceedings of the KIPE Conference
• /
• 2016.07a
• /
• pp.103-104
• /
• 2016

기존 Cascade H-bridge 인버터 토폴로지는 커패시터나 다이오드가 없이 스위치로 구성되어 있으며, 필터 없이 정현파와 유사하게 구현할 수 있다. 또한 출력전압 레벨이 높을수록 정현파와 유사하게 되어 고주파가 줄어들며, 각 셀을 직렬로 연결하면 입력전압보다 높은 출력전압 갖는다. 본 논문에서는 기존 Cascade H-bridge 인버터와 NPC(Neutral Point Clamped)가 결합한 Cascade H-bridge NPC 인버터를 제안하였다. Cascade H-bridge NPC 인버터는 기존 Cascade H-bridge 인버터 특성과 유사하며, Cascade H-bridge 인버터와 NPC 인버터의 장점을 가지고 있다. Cascade H-bridge 인버터와 Cascade H-bridge NPC 인버터를 시뮬레이션 통해 THD(Total Harmonic Distortion) 비교분석하였고 시뮬레이션은 PSIM 9.1.4을 가지고 검증하였다.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.66 no.5
• /
• pp.778-785
• /
• 2017

This paper presents a control method for reducing the distortion of the grid current at a grid-connected three-level neutral point clamped (NPC) inverter. The grid current is distorted from the 5th and 7th harmonic components in the stationary frame current also the 6th harmonic component in the synchronous frame current. In this paper, the 6th harmonic component on synchronous frame is controlled by using all-pass filters (APFs) and proportional integral (PI) controllers for distortion of the grid side. When transformed the 6th harmonic component is controlled, the 5th and 7th harmonic components are reduced. The validity of the proposed control method is verified by simulation and experiment results using a 25kW three-level NPC inverter.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.19 no.4
• /
• pp.376-382
• /
• 2014

This paper proposes the pulse width modulation (PWM) control strategy for low-speed operation in the three-level neutral-point-clamped (NPC) inverters based on the bootstrap gate drive circuit. As a purpose of the cost reduction, several papers have paid attention to the bootstrap circuit applied to the three-level NPC inverter. However, the bootstrap gate driver IC cannot generate the gate signal to the IGBT for low-speed operation, because the bootstrap capacitor voltage decreases under the threshold level. For low-speed operation, the dipolar and partial-dipolar modulations can be the effective solution. However, these modulations have drawbacks in terms of the switching loss and THD. Therefore, this paper proposes the PWM control strategy to operate the inverter at low-speed and to minimize the switching loss and harmonics. The experimental results are presented to verify the validity on the proposed method.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.54 no.5
• /
• pp.231-237
• /
• 2005

Many conventional multi-level inverters have detected switching faults by using the over voltage and current. However, fault detection of the switching elements is very difficult because the voltage and current due to each switching fault decrease more than the normal operation. Moreover, the dc-link unbalancing voltage causes a serious problem in the safety and reliability of system when the 3-level inverter faults occur Therefore, this paper proposes the simple fault diagnose method and the neutral-point-voltage control method that can protect the 3-level inverter system from the unbalancing voltage of the do-link capacitors when the faults of switching elements occur in the 3-level inverter that is very efficient in ac motor drives of the high voltage and high power applications. Through experiment results, the validity of the proposed method is demonstrated.