Five-level Active-neutral-point-clamped Research Articles

Fault Analysis and Clearance in FL-APC DC–AC Converter

The traditional active neutral-point-clamped (APC) dc–ac converter maintains great common-mode voltage with high-frequency (CMV-HF) reduction capability, so it has limited voltage gain. This article presents a new five-level APC (FL-APC) dc–ac converter capable of voltage step-up in a single-stage inversion. In the suggested design, a common ground not only reduces the CMV-HF but also improves dc-link voltage usage. While comparing with traditional two-stage FL-APC dc–ac converter, the proposed design has lower voltage stresses and greater uniformity. While improving overall efficiency, the suggested clamped dc–ac converter saves three power switches and a capacitor. Modeling and actual tests have proven the suggested APC inverter’s overall operation, efficacy, and achievability. The proposed circuit is finally tested with fault clearance capability.

Matrix-Based Approach for Open-Circuit Fault-Tolerant Analysis and PWM Design of Active Neutral-Point-Clamped Converters

Active neutral-point-clamped converter adds open-circuit fault-tolerant (OCFT) capability compared with the widely used original neutral-point-clamped (NPC) topology. However, such capability is hard to utilize due to difficulties in pulse-width modulation (PWM) design and the randomness of failure points, particularly in high-level converters. Current research mainly focused on low-level topologies with a limited number of fault scenarios; moreover, the analysis and design are performed in a nonsystematic way. In this article, the OCFT operations of active NPC (ANPC) converters with multiple fault switches are investigated and the systematic PWM design process is proposed. First, different matrices are proposed for the ANPC converters to capture the complicated topology information and achieve an exhaustive analysis of the topological redundancy. Then, a step-by-step process is proposed to derive the suitable OCFT PWM patterns. The five-level ANPC converter is investigated as an example. Its experimental results validate that the proposed approach can 1) properly predict the behavior of converters systematically so that the tolerable faults and intolerable can be identified during the design procedure, and 2) the inherent fault-tolerant capability of the five-level ANPC converter can be guaranteed through the proposed method, and 3) multiswitch open-circuit faults can be easily dealt with by implementing suitable carrier-based PWM schemes.

Operation and Efficiency Analysis of a Five-Level Single-Phase Hybrid Si/SiC Active Neutral Point Clamped Converter

The ability to improve both the size and efficiency of multilevel single-phase converters is a key to uplift them as an attractive solution for industries, while the high number of switches and complex modulation techniques understandably make them unattractive. Five-level active neutral point clamped (ANPC) converter, due to its inherent advantages such as employing different switching frequencies and using different switch technologies, presents an ideal candidate for study. This article performs a comprehensive analysis of the converter to highlight the advantages of it. This analysis results in a modified hybrid modulation that effectively regulates the neutral point (NP) of the dc link. Consequently, the combination of the topology and the modified modulation make the converter ideal to utilize two different switch technologies—in this article, silicon carbide (SiC) and Si MOSFET. To evaluate the analysis and the effectiveness of modulation, a 2-kW hybrid five-level ANPC is built. The converter current behavior is analyzed to determine the power loss in the filter and switches. The efficiency measurement is performed and compared with the calculated efficiency. There is a close coherency between the measurement and the calculated results and a peak efficiency of 98.4% is achieved.

Modulation and voltage balancing control of dual five-level ANPC inverter for ship electric propulsion systems

Open-end winding motors are used extensively in ship electric propulsion systems, in which medium-voltage high-power inverters are a critical component. To increase the system voltage and power density, a dual five-level active neutral-point clamped (ANPC) inverter is proposed herein to drive medium-voltage open-end winding motors for ship electric propulsion. Each phase of this inverter comprises two five-level ANPC bridges and all the phases are powered by a common direct-current link. A hybrid modulation method is proposed to control this inverter. The series-connected switches in all the five-level ANPC bridges are operated at the fundamental frequency, and the other switches are controlled with a phase-shifted pulse-width modulation (PWM), which can achieve a natural balance between the neutral-point voltage and flying capacitor voltages in a carrier period. A closed-loop capacitor voltage balancing method based on adjusting the duty ratios of the PWM signals is proposed. The neutral-point voltage and flying capacitor voltages can be controlled independently and balanced without affecting the output phase voltage. Simulation and experimental results are presented to demonstrate the validity of this method.

Novel Five-Level ANPC Bidirectional Converter for Power Quality Enhancement during G2V/V2G Operation of Cascaded EV Charger

This paper presents a novel single-phase (SP) active-neutral point clamped (ANPC) five-level bidirectional converter (FLBC) for enhancing the power quality (PQ) during the grid-to-vehicle (G2V) and vehicle-to-grid (V2G) operation of an electric vehicle (EV) charger connected in series. This EV charger is based on a dual-active half-bridge DC-DC converter (DAHBC) with a high frequency isolation transformer. Unlike the comparable ANPC topologies found in literature, the proposed one has two more switches, i.e., ten instead of eight. However, with the addition of these components, the proposed multilevel converter not only becomes capable of properly balancing the voltage of the DC-link split capacitors under various step-changing conditions but it achieves a better efficiency, a lower stress of the switching devices and a more even distribution of the power losses. The resulting grid-tied ANPC-SPFLBC and DAHBC are accurately controlled with a cascaded control strategy and a single-phase shift (SPS) control technique, respectively. The simulation results obtained with MATLAB-SimPowerSystems as well as the experimental results obtained in laboratory validate the proposed ANPC-SPFLBC for a set of exhaustive tests in both V2G and G2V modes. A detailed power quality analysis carried out with a Fluke 43B alike demonstrates the good performance of the proposed topology.

A Novel Single-Stage Five-Level Common-Ground-Boost-Type Active Neutral-Point-Clamped (5L-CGBT-ANPC) Inverter

The conventional active neutral-point-clamped (ANPC) inverter inherits excellent high-frequency common mode voltage (CMV) mitigation ability but with a restricted voltage gain. This letter proposes a novel five-level ANPC inverter that is able to accomplish voltage-boosting within a single-stage dc–ac power conversion. A common ground in the proposed topology not only mitigates the high-frequency CMV but also enhances the dc-link voltage utilization. The proposed topology exhibits lower voltage stresses and higher compactness when compared with a conventional two-stage five-level ANPC inverter. The proposed inverter saves three power switches and one capacitor while enhancing the overall efficiency. Simulations and experimental tests have validated the overall operation, efficacy, and practicality of the proposed ANPC inverter.

Hybrid Model Predictive Control of ANPC Converters With Decoupled Low-Frequency and High-Frequency Cells

Active-neutral-point-clamped (ANPC) converters can be decomposed into a low-frequency cell (LFC) and a high-frequency cell (HFC), and fundamental-frequency operation of the LFC is becoming popular. However, balancing the dc-link voltage and three flying capacitor voltages while maintaining very fast control of the output current is always a challenging task, especially when the flying capacitor is small. This article proposes a hybrid model predictive control (MPC) to guarantee the fundamental-frequency operation of the LFC and achieve the fixed-switching frequency operation of the HFC. In the hybrid MPC, the classical MPC regulates the LFC, whereas the duty-cycle-optimized MPC regulates the HFC. The capacitor voltage balance is achieved by adjusting the duty cycles to avoid the weighting factor tuning process. The proposed MPC features a fixed switching frequency and improves the steady-state performance while guaranteeing the fundamental-frequency operation of the LFC. Simulation and experimental results on a five-level ANPC are presented to validate the advantages of the proposed hybrid MPC method over the classical MPC.

Operation and Control of a Nine-Level Modified ANPC Inverter Topology With Reduced Part Count for Grid-Connected Applications

This paper presents a nine-level active-neutral-point-clamped (ANPC) based multilevel inverter (MLI) topology for grid-connected applications requiring only ten switches. The envisaged structure comprises two parts, namely five-level ANPC unit, and a two-level converter leg whose midpoint is used as another ac terminal. An ad hoc switching state redundancy based modulation strategy is used to ensure that the voltage across the flying capacitor is tightly balanced and is implemented using a look-up table further simplifies the control complexity. The performance and effectiveness of the proposed topology with its control scheme are validated through simulations and experimental tests. Comparison with other MLIs is included to highlight the merits of the proposed topology. From the results, it will be shown that the proposed inverter requires the least part count as compared to other topologies with the same performance and output quality.

CMV reduction for five‐level ANPC converter by PS‐PWM strategy

Five-level active neutral point clamped (ANPC) converter has become one of the most attractive topologies in industry applications, especially in the field of the motor drive. A novel common-mode voltage (CMV) reduction strategy for five-level ANPC is presented, which is based on the phase-shifted pulse-width modulation (PS-PWM). A basic PS-PWM method is presented, which can realise the NP voltage and the flying capacitor (FC) voltages balance. Moreover, a general CMV reduction method is summarised. The proposed CMV reduction strategy can minimise the CMV by injecting zero-sequence voltage to the modulation wave and it does not affect the ability of NP voltage and FC voltages balance. The validity of the proposed CMV reduction method based on PS-PWM strategy is verified by simulation.

A Novel Modulation Technique and a New Balancing Control Strategy for a Single-Phase Five-Level ANPC Converter

This paper proposes a novel modulation technique and a new balancing control strategy for a single-phase five-level flying-capacitor (FC)-based active-neutral-point-clamped (ANPC) converter. The proposed modulator can control the FC voltage to follow the requested reference value and simultaneously generate the required ac output voltage regardless of the values of the dc capacitor voltages of the converter. By implementing this method, smaller values of the dc-link capacitor and FC can be used even in applications that could experience ripple or transient in the capacitor voltage. In a single-phase five-level ANPC converter applications, where the capacitors can experience pulsation power and dc-link balancing issues, such as grid-connected photovoltaic system, the selection of the reference voltage value for the FC can play an important role to balance the average values of the dc-link capacitor voltage. The proposed new control strategy uses a new reference voltage for the FC to be applied by the new modulator to have an average balanced dc-link voltages as well as an ac output voltage with good power quality. Simulation studies and experimental results demonstrate the effectiveness of the proposed modulation technique and control strategy even with relatively small dc capacitors to produce high-quality output voltage and current waveforms while maintaining an average balanced dc-link voltages.

The Common Cross-Connected Stage for the 5L ANPC Medium Voltage Multilevel Inverter

Rising interest in multilevel applications has triggered new research activities. This paper proposes a novel multilevel power electronics building block (PEBB) for the five-level active neutral point clamped (ANPC) multilevel voltage source inverter. The PEBB is composed of six switches in a crossed configuration and one capacitor. It is common to the three phases of a five-level ANPC topology, enabling a large number of levels to be generated. This PEBB is meant to be a reliable upgrade to the 5L topology, increasing output signal quality and reducing the size of the output filter in medium voltage applications. The number of levels generated by the common cross-connected stage (C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> S) PEBB and the ANPC depends on the voltage ratios chosen between the phase capacitors of the ANPC and the PEBB capacitor(s). The tradeoff stands between the ability to balance the capacitors, the rated blocking voltage of the devices, and the number of levels produced. Under a given configuration, nine levels can be produced, with the possibility to balance the capacitors up to modulation indexes in the region of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> = 0.92. The analysis of the general topology, the description of the nine-level case, and simulation results are first presented. Prototyping results are then shown, and they validate the introduced concept and topology.