Active Neutral Point Clamped Research Articles

An Improved Fault-Tolerant Control Strategy for High-Power ANPC Three-Level Inverter Under Short-Circuit Fault of Power Devices

The high-power active neutral-point clamped (ANPC) three-level inverter has high-reliability requirements for the system operation, and short-circuit fault, very common, and serious problem in the operation will affect the operation stability. To solve this problem, the fault current path analyses under a single device and multi-device short-circuit fault were carried out first in this paper. Second, on the basis of the different fault condition, an improved fault-tolerant control strategy was proposed. This strategy maintains the three-level operation under a single device short-circuit fault, and under multiple device, fault operates with low withstanding voltage. Finally, the experiment was made on a 1 MW ANPC three-level platform, which proved the effectiveness of the proposed method.

Switched-Capacitor-Based Active-Neutral-Point-Clamped Seven-Level Inverter With Natural Balance and Boost Ability

This paper proposes a new active-neutral-point clamped (ANPC) seven-level inverter based on switched-capacitor technique. The proposed seven-level inverter employs only nine switches and one floating capacitor. With the input amplitude of V DC , the peak output of the proposed topology can reach 1.5V DC . Its boost ability indicates a wider range of output compared with other APNC converters. Needless for auxiliary control methods, the voltages of capacitors in dc link can naturally maintain at 0.5V DC , and the floating capacitor can get self-balance at V DC . The mechanism of natural balance for capacitors and the operation principle of the proposed topology are described in detail. The merits of the proposed topology on reduced components, lower overall voltage stress, natural balance, and boost ability are also demonstrated through the comparison against the latest similar topologies, showing its suitability for distributed generation, electric vehicle, and other applications. Definitively, the simulation and experimental prototype are implemented to verify the feasibility and performance of the proposed topology. The voltage balance of capacitors has been fully demonstrated through multiple transient experiments.

Reducing Overshoot Voltage of SiC MOSFET in Grid-Connected Hybrid Active NPC Inverters

Reducing Overshoot Voltage of SiC MOSFET in Grid-Connected Hybrid Active NPC Inverters

Multi-level model predictive controller with satisfactory optimization for multi-level converters

In this paper, a simplified Model Predictive Control (MPC) technique is proposed for a hybrid three-phase seven-level inverter based on Active Neutral Point Clamped (ANPC) converter cascaded to an H-bridge with a flying capacitor. This converter has the ability to balance switching losses, to withstand high voltages and to operate with fewer semiconductors. It is interesting for high-voltage and high-quality exigent applications. By introducing a trade-off relation between control actions reduction and the flying capacitor charge, the designed controller can maintain the capacitor voltage with less number of switching states. This reduces computations, eliminates common mode voltage, shortens optimization time, and improves output current quality. Moreover, in this work, a multilevel MPC architecture is presented, where the MPC approach is divided into two-level units. The major level unit is composed of separated sub-MPC controllers for each phase that track the three-phase current references, while the second level unit is composed of only one MPC model that balances the capacitor charge at its nominal values. An additional control design of the major level MPC is presented, where a satisfactory optimization of common mode voltage is used instead of weighting factor in the cost function, which simplifies the control approach, and solves the problem of selecting the right weighting factors. Simulation analysis shows the effectiveness of the proposed methods.

Fault Tolerant Three Level ANPC Inverter Circuit with Finite Set Model Predictive Control

An improved active neutral point clamped (ANPC) inverter circuit topology is proposed. Through the fault-tolerant leg, the fault-tolerant performance of the inverter circuit has been greatly improved. The fault-tolerant leg works as an actuating device which control the neutral point to remain stable, when there is no fault with the inverter. When some power tubes are broken the leg works as the redundant device to replace the power tubes. The finite set model predictive control method is used for this inverter circuit. This control method is quite suitable for the electronic circuit. This method is employed to lower THD and to advance its dynamic, so that the error tolerance and high power output of the aviation inverter are satisfied. The feasibility and effectiveness are proved by simulations.

Three-Level Two-Stage Decoupled Active NPC Converter With Si IGBT and SiC MOSFET

This paper presents the operation principle and benefits of a novel power converter topology named three-level two-stage decoupled active neutral point clamped (3L-TDANPC) converter, which is implemented based on a hybrid utilization of silicon (Si) insulated gate bipolar transistors (IGBTs) and silicon carbide (SiC) metal-oxide semiconductor field-effect transistors (mosfets). The 3L-TDANPC converter can achieve high efficiency with limited number of SiC mosfet modules while keeping balanced loss distribution among the switching devices, which helps increase the converter power ratings. In addition, in this 3L-TDANPC converter, the SiC mosfet has a potential to ride through short-circuit fault because of the presence of Si IGBTs. The key challenges that are associated with system resonant current are investigated and the methods to damp such resonant current are proposed and explained in detail. The simulation and experimental results based on a 1-MW 3L-TDANPC converter prototype confirm the expected benefits of this proposed converter and the effectiveness of the proposed resonant current damping methods.

An Extremely High Efficient Three-Level Active Neutral-Point-Clamped Converter Comprising SiC and Si Hybrid Power Stages

Three-level converters typically feature low switching loss and small filter size. In order to realize a high-power-density design for three-level converters, SiC MOSFETs may be selected instead of using Si insulated-gate bipolar transistors. However, all-SiC-MOSFET-based converters suffer from extremely high total cost. In this paper, a SiC MOSFET and Si device hybrid active neutral-point-clamped (ANPC) converter is proposed. It consists of four Si active switches and only two SiC MOSFETs. Thus, it has lower total cost compared to the all-SiC-MOSFET-based ANPC converter. Furthermore, a dedicated modulation scheme is proposed to completely move all the switching events from Si devices to SiC MOSFETs by using redundant switching states. As a result, the switching losses are significantly reduced and extremely high efficiency is achieved. The proposed converter has fully utilized the low-switching-loss advantage of SiC MOSFETs and the low-cost advantage of Si devices, which shows significant superiority in high-end grid-connected inverter and rectifier applications.

Tradeoff Study of Heat Sink and Output Filter Volume in a GaN HEMT Based Single-Phase Inverter

This paper presents the tradeoff study of heat sink and output filter volume of a GaN HEMT based single-phase inverter. The selected topology is three-level active neutral point clamped (ANPC) inverter, and the main aim is to explore the benefits of the GaN HEMTs at 600 V blocking class on the system level efficiency, and power density under the wide range of operating conditions. The paper starts by introducing the inverter topology, selected pulse width modulation scheme and followed by the device features, static, and dynamic characterization and continues with presenting and discussing the results of extensive experimental and analytical characterization. After this, the impact of GaN HEMTs on inverter volume is discussed in terms of heat sink and output filter volume analysis under different switching frequency and heat sink temperature conditions. The calculation of heat sink volume and single stage LC output filter volume are presented with respect to experimental results of the single phase prototype. The findings from static, dynamic characterization, and single phase prototype results clearly show that GaN HEMT has excellent switching performance under wide load current and heat sink temperature conditions. The high performance of the inverter leads to reduction of the combined total volume, including output filter and heat sink volume.

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.

Design and implementation of active neutral‐point‐clamped nine‐level reduced device count inverter: an application to grid integrated renewable energy sources

Multilevel inverters are one of the preferred choices in medium-voltage and high-power applications in the recent past. Active neutral-point-clamped (ANPC) inverter is the most popular topology, especially in the class of five-level (5L) inverters. In this study, a nine-level topology with improved output waveform quality is proposed based on ameliorating the 5L ANPC inverter with least modifications. The addition of only two switches operating at line frequency to the conventional 5L ANPC inverter while maintaining an identical precursor part count is the proposed modification. A logic form equation-based active voltage balancing scheme that is independent of load current and power factor is developed to regulate the flying capacitor voltage at the reference value. The operating principle, salient features, and the developed control scheme are comprehensively detailed. The operation of the proposed inverter considering a grid integrated case is simulated in MATLAB/Simulink, and the results corresponding to steady-state and dynamic conditions are presented. The benefits of the proposed topology are elucidated by comparing it with other classic topologies considering various prominent viewpoints. This comparison has illustrated the proposed topology's distinctive characteristics and profound advantages. The performance validation, feasibility, and practicability of the proposed inverter are established through the experimental results obtained from a laboratory-scale prototype.

Operation and Control of an Improved Hybrid Nine-Level Inverter

This paper proposes a new nine-level inverter for medium- and high-power applications. The proposed topology comprises of a three-level (3L) active neutral-point-clamped (ANPC) inverter connected in series with a floating capacitor (FC) fed H-bridge. Besides, two additional switches operating at line frequency are appended across the dc link of the 3L ANPC structure. Compared with conventional hybrid cascaded inverters, the primary advantage of this addition is doubling of the resulting root mean square output voltage. This amelioration is achieved while preserving the standard 3L ANPC and H-bridge structures with minimum topological modification. A simple logic-gate-based voltage balancing scheme is developed to regulate the FC voltage. The proposed voltage balancing method is independent of load power factor, inverter modulation index, and can balance the voltage across FC instantaneously. The step-by-step formulation of logical expressions for the generation of gating pulses is deliberated in detail and can be generalized for any $n$ -level inverter. Further, simulation results as well as the experimental measurements obtained from the laboratory prototype are presented to validate the effectiveness and practicability of the proposed configuration. Finally, the notable merits of the proposed inverter over the prior art topologies is established through a comprehensive comparative study.

Implementation of Active NPC Circuits in Transformer-Less Single-Phase Inverter With Low Leakage Current

Transformer-less grid-connected photovoltaic (PV) systems face the challenge of keeping low leakage current due to their nonisolation configurations. To better attenuate the leakage current in the single-phase systems, a few neutral-point-clamped (NPC) topologies have been proposed. This paper further proposes an active NPC method by only employing one additional switch to connect the midpoint dc link and the freewheeling circuit of traditional single-phase PV inverters. After exploring the operational principles of freewheeling circuits, the construction method and the implementation of active NPC circuits in transformer-less single-phase inverters are elaborated in detail. Since only the leakage current flows through the additional NPC switch, the presented single-phase NPC inverters could still maintain the high operational efficiency with the further attenuated leakage current. The experimental results verified the theoretical findings.

Neutral‐point potential balancing control strategy of three‐level active NPC inverter based on SHEPWM

This study proposes a novel control strategy for a three-level active neutral-point clamped (3L-ANPC) inverter using selective harmonic elimination pulse width modulation (SHEPWM). The proposed control strategy can effectively control the neutral-point potential (NP) balancing and eliminate the selective harmonics simultaneously. The three-phase SHEPWM line-to-line voltages of the inverter are considered as switching-states. Among these switching states, the six pairs of redundant switching-states generate the same line-to-line voltages and thus the same harmonic spectrums with each pair having opposite effects on NP balancing. As a result, the pair of switching-states can be swapped to control the NP while still maintaining the same inverter output. The decision to make such swap will take into account directions of output currents, polarities of NP offsets and exclusion of directly switching between P and N states. The simulation and experimental results on a Matlab/Simulink model and prototype of a three-phase 3L-ANPC inverter are used to verify the effectiveness of the proposed control strategy.

Fault-Tolerant Control of ANPC Three-Level Inverter Based on Order-Reduction Optimal Control Strategy under Multi-Device Open-Circuit Fault

The multi-device open-circuit fault is a common fault of ANPC (Active Neutral-Point Clamped) three-level inverter and effect the operation stability of the whole system. To improve the operation stability, this paper summarized the main solutions currently firstly and analyzed all the possible states of multi-device open-circuit fault. Secondly, an order-reduction optimal control strategy was proposed under multi-device open-circuit fault to realize fault-tolerant control based on the topology and control requirement of ANPC three-level inverter and operation stability. This control strategy can solve the faults with different operation states, and can works in order-reduction state under specific open-circuit faults with specific combined devices, which sacrifices the control quality to obtain the stability priority control. Finally, the simulation and experiment proved the effectiveness of the proposed strategy.

Mission Critical Analysis and Design of IGBT-Based Power Converters Applied to Mine Hoist Systems

Mine hoist systems play a vital role in gold ore transportation. They are the connection between the underground mine and the beneficiation plant. As a result, any hoist system interruption compromises the production. In this paper, it is proposed a mission critical analysis and design methodology for power converters in order to achieve proper reliability of the hoist drive system. Since the failure of power devices is responsible for a significant portion of the total downtime of power converters, a detailed study of the insulated gate bipolar transistor (IGBT) power modules lifetime is carried out. The three level neutral-point-clamped and Active Neutral Point Clamped (ANPC) IGBT-based topologies are considered for this application. The recently presented Fault-Tolerant (FT)-ANPC converter is proposed as a higher reliability solution leading to longer power modules and drive system lifetimes. All the studies are based on practical operating data from a 900-m deep shaft hoist system operating in a gold mine in southeastern Brazil.

Design and Simulation of Five Levels Active Neutralpoint Clamped Inverter

Design and Simulation of Five Levels Active Neutralpoint Clamped Inverter

A Single-Phase Transformerless Inverter With Charge Pump Circuit Concept for Grid-Tied PV Applications

This paper proposes a new single-phase transformerless photovoltaic (PV) inverter for grid-tied PV systems. The topology is derived from the concept of a charge pump circuit in order to eliminate the leakage current. It is composed of four power switches, two diodes, two capacitors, and an LCL output filter. The neutral of the grid is directly connected to the negative polarity of the PV panel that creates a constant common mode voltage and zero leakage current. The charge pump circuit generates the negative output voltage of the proposed inverter during the negative cycle. A proportional resonant control strategy is used to control the injected current. The main benefits of the proposed inverter are: 1) the neutral of the grid is directly connected to the negative terminal of the PV panel, so the leakage current is eliminated; 2) its compact size; 3) low cost; 4) the used dc voltage of the proposed inverter is the same as the full-bridge inverter (unlike neutral point clamped (NPC), active NPC, and half-bridge inverters); 5) flexible grounding configuration; 6) capability of reactive power flow; and 7) high efficiency. A complete description of the operating principle and analysis of the proposed inverter are presented. Experimental results are presented to confirm both the theoretical analysis and the concept of the proposed inverter. The obtained results clearly validate the performance of the proposed inverter and its practical application in grid-tied PV systems.

Model Predictive Controlled Active NPC Inverter for Voltage Stress Balancing Among the Semiconductor Power Switches

This paper presents a model predictive controlled three-level three-phase active neutral-point-clamped (ANPC) inverter for distributing the voltage stress among the semiconductor power switches as well as balancing the neutral-point voltage. The model predictive control (MPC) concept uses the discrete variables and effectively operates the ANPC inverter by avoiding any linear controller or modulation techniques. A 4.0 kW three-level three-phase ANPC inverter is developed in the MATLAB/Simulink environment to verify the effectiveness of the proposed MPC scheme. The results confirm that the proposed model predictive controlled ANPC inverter equally distributes the voltage across all the semiconductor power switches and provides lowest THD (0.99%) compared with the traditional NPC inverter. Moreover, the neutral-point voltage balancing is accurately maintained by the proposed MPC algorithm. Furthermore, this MPC concept shows the robustness capability against the parameter uncertainties of the system which is also analyzed by MATLAB/Simulink.

Improved Modulation Scheme for Loss Balancing of Three-Level Active NPC Converters

The three-level neutral point-clamped (NPC) converter has attracted much attention in high-power medium-voltage applications, but it is well-known that the NPC topology suffers from unequal power loss distribution among its semiconductor devices. The power loss unbalance problem becomes especially severe when the converter is operating at low fundamental frequencies. To overcome the loss unbalance problem of the NPC converter, the active NPC (ANPC) technique was introduced. However, it is demonstrated in this paper that in many cases, the conventional modulation method for the ANPC converter only marginally relieves the loss unbalance problem. This paper proposes a new modulation scheme (named the adaptive doubled frequency modulation) for the three-level ANPC converter, which significantly improves the power loss and thermal sharing among the semiconductor devices. The basic idea of the proposed scheme is adaptively adjusting the duty cycles of the switching states for every switching cycle, so as to optimize the power loss distribution. Simulation and experimental results verify this new method.