Hybrid Active Neutral-point-clamped Research Articles

LCL-Filter Design Based on Modulation Index for Grid-Connected Three-Level Hybrid ANPC Inverters

This paper proposes an LCL-filter design based on the modulation index for grid-connected hybrid active neutral point clamped (ANPC) inverters. The three-level hybrid ANPC inverter consists of silicon insulated gate bipolar transistors and silicon carbide metal oxide semiconductor field effect transistors to reduce the switching losses. LCL-filter parameters for the three-level hybrid ANPC inverter are calculated using the current ripple factor. The current ripple factor is affected by phase voltage, which varies according to the modulation index, and therefore the inductance on the inverter side must be considered with the modulation index. To design inductance on the inverter side, the output phase voltage and grid voltage are used to analyze the current ripple factor. The filter capacitor and the inductance on the grid side are designed based on the reactive power absorption and current ripple attenuation. The effectiveness of the proposed LCL-filter design method is validated via simulation and experimental results.

Elimination of Abnormal Output Voltage in a Hybrid Active NPC Inverter

This article proposes a method to eliminate abnormal output voltages generated in three-level hybrid active neutral-point clamped (ANPC) inverters. The hybrid ANPC inverter is a topology in which silicon (Si) devices are replaced with silicon-carbide (SiC) devices in part from the conventional ANPC topology. The hybrid ANPC inverters have the advantages of high switching frequency and low power switching loss due to the SiC devices. In this hybrid ANPC inverter, abnormal output voltages occur when the polarity of the output pole voltage is changed from positive to negative. The cause of the abnormal voltages is the switching time difference between the Si and SiC devices, and it is various from a few nanoseconds to a few microseconds. These abnormal output voltages need to be eliminated as it leads to degraded output power quality in the hybrid ANPC inverters. The proposed switching method effectively eliminates the abnormal output voltages and reduces output current distortion. The performance of the proposed method is verified using a prototype of the new three-level hybrid ANPC inverter type through both simulations and experiments.

Capacitor Lifetime Extension in a Hybrid Active Neutral-Point-Clamped Inverter With Reduction of DC-Link Ripple Current and Common-Mode Voltage

This paper proposes a reduction method for DC-link ripple current and common-mode voltage (CMV) in a hybrid active neutral-point-clamped (ANPC) inverter. A Si and SiC hybrid ANPC inverter has been developed recently to overcome the extremely high cost of a full-SiC ANPC inverter. A hybrid ANPC requires much fewer SiC MOSFETs than a full-SiC ANPC inverter while providing a comparable power density. Voltage source inverters such as hybrid ANPC inverters utilize electrolytic capacitors, which have a large capacitance per volume, as a DC link. However, an electrolytic capacitor is one of the most vulnerable components in a power electronic converter due to its small allowable ripple current. A large ripple current flowing into the electrolytic capacitor generates a heat loss, which shortens the lifetime of the capacitor. Furthermore, the common-mode voltage (CMV) causes an undesirable leakage current and electromagnetic interference. The CMV depends on the pulse-width modulation of the voltage source inverters. The proposed method enhances the reliability of the hybrid ANPC inverter by reducing the DC-link ripple current and CMV simultaneously. The effectiveness and validity of the proposed method are verified through simulations and experimental results.

Independent switching technique to remove abnormal output voltage in hybrid active NPC inverters

This paper proposes the independent switching technique to remove abnormal output voltage in hybrid active neutral-point clamped (ANPC) inverters. The hybrid ANPC inverter is composed by mixing silicon (Si) devices and silicon carbide (SiC) devices, unlike the conventional ANPC inverter which is generally composed of Si devices only. SiC devices provide low switching losses under a high switching frequency and a high withstand ability under high temperature compared with Si devices. Therefore, the hybrid ANPC inverter using SiC devices provides low power losses, high efficiency, and high reliability compared with the conventional ANPC inverters. In this hybrid ANPC inverter, abnormal output voltages are generated when the sinusoidal output current crosses the zero point. The abnormal output voltages are momentary pulses that must not be generated, and these pulses distort the output current and degrade the power quality. These pulses have two typical causes: one is from the switching operation time difference between switches, and the other is from deadtime. This paper proposes the independent switching technique to remove the abnormal voltages caused by the two reasons and verifies the proposed technique by simulation and experiment.

Open-Circuit Fault Tolerance Method for Three-Level Hybrid Active Neutral Point Clamped Converters

Three-level converters are the most important technologies used in high power applications. Among these technologies, active neutral point clamped (ANPC) converters are mainly used for industrial applications. Meanwhile, recent developments have reduced losses and increased efficiency by using a hybrid combination of Si-IGBT and SiC-MOSFET switches to achieve hybrid ANPC (HANPC) converters. Open-circuit failure is regarded as a common and serious problem that affects the operational performance. In this paper, an effective fault-tolerant method is proposed for HANPC converters to safely re-utilize normal operation and increase the reliability of the system under fault conditions. Sequentially, regarding different topologies with reference to earlier fault tolerance methods which could not be applied to the HANPC, the proposed strategy enables continuous operation under faulty conditions effectively without using any additional devices by creating new voltage references, voltage offset, and switching sequences under the faulty conditions. Consequently, no additional costs or changes are associated with the inverter. A detailed analysis of the proposed strategy is presented highlighting the effects on the voltage, currents, and the corresponding total harmonic distortion (THD). The simulation and experimental results demonstrate the capability and effectiveness of the proposed method to maintain normal operation and eliminate the output distortion.

Switch Open-Fault Detection for a Three-Phase Hybrid Active Neutral-Point-Clamped Rectifier

This paper proposes a fault-detection method for open-switch failures in hybrid active neutral-point-clamped (HANPC) rectifiers. The basic HANPC topology comprises two SiC-based metal-oxide-semiconductor field-effect transistors (MOSFETs) and four Si insulated-gate bipolar transistors (IGBTs). A three-phase rectifier system using the HANPC topology can produce higher efficiency and lower current harmonics. An open-switch fault in a HANPC rectifier can be a MOSFET or IGBT fault. In this work, faulty cases of six different switches are analyzed based on the current distortion in the stationary reference frame. Open faults in MOSFET switches cause immediate and remarkable current distortions, whereas, open faults in IGBT switches are difficult to detect using conventional methods. To detect an IGBT fault, the proposed detection method utilizes some of the reactive power in a certain period to make an important difference, using the direct-quadrant (dq)-axis current information derived from the three-phase current. Thus, the proposed detection method is based on three-phase current measurements and does not use additional hardware. By analyzing the individual characteristics of each switch failure, the failed switch can be located exactly. The effectiveness and feasibility of the proposed fault-detection method are verified through PSIM simulations and experimental results.

Enhanced Hybrid Active-Neutral-Point-Clamped Converter With Optimized Loss Distribution-Based Modulation Scheme

The active-neutral-point-clamped (ANPC) converter is a prominent topology for medium voltage applications. To realize a high-power-density three-level ANPC converter, silicon carbide (SiC) MOSFETs may be used but they also lead to an extremely high cost. Thus, it is important to properly utilize the SiC switches in order to achieve not only a highly efficient but also a low-cost system. In this article, a three-level enhanced hybrid ANPC (E-HANPC) structure is proposed, which optimally utilizes both Si insulated gate bipolar transistors (IGBTs) and SiC MOSFETs to achieve these objectives. A dedicated modulation scheme is also proposed that enables a reduction in the conduction and switching losses and, hence, higher efficiency is achieved. The presented method optimally distributes the losses amongst the converter switches that leads to enhanced power handling capability of the E-HANPC converter. Moreover, the proposed converter also achieves short-length commutation loops for the high-frequency SiC MOSFETs, which imparts fast-switching capability with reduced overvoltage stress on these switches. To validate the efficacy of the proposed converter and modulation scheme, extensive simulation and analytical studies are performed. A prototype of the single-phase leg of the E-HANPC converter is also developed to validate its feasibility, proposed principles, and reconfirm the simulation and analytical findings.

Fault Diagnosis of Open-Switch Failure in a Grid-Connected Three-Level Si/SiC Hybrid ANPC Inverter

A diagnostic method for an open-circuit switch failure in a hybrid active neutral-point clamped (HANPC) inverter is proposed in this paper. The switching leg of the HANPC inverter consists of four silicon insulated gate bipolar transistors and two silicon carbide metal-oxide-semiconductor field-effect transistors to achieve higher efficiency and power density compared to conventional neutral-point clamped inverters. When an open-circuit failure occurs in a switching device, the output current is severely distorted, causing damage to the inverter and the connected loads. The proposed diagnostic method aims to detect the open-switch failure and protect the related devices without additional sensors or circuits. The faulty conditions of six different switches are investigated based on the current distortion in the stationary reference frame. By analyzing the individual characteristic of each switch failure, it is possible to detect the exact location of the failed switch in a short period. The effectiveness and feasibility of the proposed fault-diagnostic method are verified using simulation and experimental results.

Fault Detection Method Using a Convolution Neural Network for Hybrid Active Neutral-Point Clamped Inverters

This article presents an open-switch fault detection method for a hybrid active neutral-point clamped (HANPC) inverter based on deep learning technology. The HANPC inverter generates a three-level output voltage with four silicon switches and two silicon carbide switches per phase. The probability of open fault in switching devices increases because of the large number of switches of the entire power converter. The open-switch fault causes distortion of output currents. A convolution neural network (CNN) comprising several convolution layers and fully connected layers is used to extract features of distorted currents. A CNN network was trained using three-phase current information to determine the location of the open-switch fault. Our proposed CNN model can accurately detect approximately 99.6% of open-switch faults without requiring additional circuitry and regardless of the current level within an average time of 1.027ms. The feasibility and effectiveness of the proposed method are verified by experimental results.

Open Fault Diagnosis and Tolerance Control for Grid-Connected Hybrid Active Neutral-Point- Clamped Inverters With Optimized Carrier-Based Pulse Width Modulation

This paper proposes open fault diagnosis and tolerance control methods for grid-connected hybrid active neutral-point-clamped (ANPC) inverters with optimized carrier-based pulse width modulation. The hybrid ANPC inverter is composed of silicon carbide metal-oxide-semiconductor field effect transistors and Si-insulated gate bipolar transistors. Open faults of switch devices lead to the distortion of output currents, inverter performance degradation, and low reliability. Therefore, the open-circuit fault diagnosis and the tolerance control methods should be handled to improve the reliability of the inverter. The fault tolerance control methods for grid-connected inverters should also consider the fixed voltage modulation index as the modulation index is fixed. In this study, the proposed fault tolerance control method handles the open fault without reducing the modulation index. The implementation of the proposed method is easy and can be conducted through a simple change in the reference waveform. The effectiveness of the proposed fault detection and fault tolerance control methods was verified through the simulation and experimental results.

계통 연계형 Hybrid ANPC 인버터를 위한 LCL-필터 설계

This paper proposes an LCL-filter design procedure for three-level hybrid active neutral point clamped (ANPC) inverters in grid-connected systems. Although more active switches are used, the hybrid ANPC inverter help to balance the loss distribution. The hybrid ANPC inverter consist of silicon insulated gate bipolar transistors (Si IGBTs) and silicon carbide metal-oxide-semiconductor field effect transistors (SiC MOSFETs). The hybrid ANPC inverter can be operated at high switching frequency compared to neutral-point-clamped (NPC) inverters. Therefore, the hybrid ANPC inverter has low switching losses due to the physical characteristic of the SiC MOSFETs. The inverter-side inductance is determined by the ripple factor of the hybrid ANPC inverter. To calculate the ripple factor, the output current ripple is required. In the grid-connected inverter, the output current ripple is related to the grid voltage, output phase voltage, and inductance. Thus, the inductance is calculated by using the equation of ripple factor. The filter capacitance is designed by the reactive power absorption ratio and the grid-side inductance is determined by the ripple attenuation factor. The effectiveness of the proposed LCL-filter design method for the hybrid ANPC inverters was verified by the simulation results and experimental results.

Space Vector Modulation for SiC and Si Hybrid ANPC Converter in Medium-Voltage High-Speed Drive System

Medium-voltage high-speed drive is promising in applications, such as the centrifugal compressors and electrified transportation. However, it raises lots of design challenges for the converters, which drive the motors. A SiC and Si hybrid ANPC converter is developed to address these challenges. In this article, the essence of this hybrid structure is investigated to clearly show the derivation process of the hybrid active neutral-point-clamped (ANPC) converter and inspire future research on these hybrid topologies. A dedicated space vector modulation (SVM) scheme is proposed for the hybrid ANPC converter, which enables the three-phase hybrid ANPC converter operating with SiC mosfet s in high frequency and Si IGBTs in fundamental frequency. A neutral point (NP) voltage balancing scheme is added to the SVM scheme to balance the NP voltage imbalance under low-frequency modulation index. All these efforts make the hybrid ANPC converter become a high power density and fairly low-cost solution. A 400 Hz fundamental frequency, 3.6 kHz switching frequency, medium-voltage high-speed drive system is assumed and tested by the scaled-down experimental results. The effectiveness of the proposed SVM and NP voltage balancing method have both been verified.

A Static Ground Power Unit Based on the Improved Hybrid Active Neutral-Point-Clamped Converter

This paper proposes a new configuration for static ground power unit (GPU) based on the novel 25-level hybrid active neutral-point-clamped (HANPC) converter. The superiority of the proposed converter, as compared with conventional and other suggested multilevel converters, is significant decreasing the number of switches and minimizing the number of flying capacitors (FC) in converter. This improvement is possible by using suggested low-voltage submodule converter to the ANPC converter and proposed modulation method. This results in reduction of the size and cost of converter and makes it more feasible and reliable. Applying the active voltage balancing method for FC in the proposed HANPC converter guaranties fast charging and voltage-level regulation of FC without using balance booster circuit. Improving output voltage spectrum leads to inductance reduction of output L–C filter which enhances static GPU performance. The simulation and experimental results verify the validity and feasibility of the proposed converter.