Active Neutral Point Clamped Inverter Research Articles

Neutral-point voltage balancing method for three-phase four-leg three-level ANPC inverter based on modulation waveform splitting

Abstract A neutral-point (NP) voltage balancing method based on modulation wave splitting is proposed for a three-phase four-leg (3P4L) three-level (3L) active NP clamped (ANPC) inverter. According to the principle of changing the NP current by adjusting the o-state duty cycle, the NP current injected by each carrier period is made zero by splitting the modulation waveforms of the mid-phase and N-phase. This approach eliminates low-frequency fluctuation in NP voltage under various load conditions. On this basis, according to the inverter operating state and limiting conditions, the output o-state duty cycle of the modulation wave for the intermediate phase and N-phase is adjusted to suppress the NP voltage deviation caused by various non-ideal factors. Finally, the effectiveness of the method is verified through simulation.

Simple Voltage Balancing Control of Four-Level Inverter

Multilevel inverters with improved voltage quality are widely used in applications such as motor control and electric vehicles. The four-level active neutral point clamped (4L-ANPC) inverter effectively meets the demands for high power density and low device voltage stress. However, balancing the capacitor voltage and reducing its low-frequency voltage fluctuation are critical challenges that need to be addressed. To address these challenges, this paper proposes a “variable reference + zero-sequence injection” method that requires only three reference voltage signals to determine the injected zero-sequence components. Particularly, the expression of the midpoint current, regarding the modulation index and phase current amplitude, is theoretically derived. This reveals the fundamental connection between the zero-sequence voltage signal and the midpoint current, providing a theoretical foundation for the zero-sequence injection method in four-level inverters. Subsequently, a simulation model and an experimental platform of the 4L-ANPC inverter were developed to compare and analyze the waveforms of the upper and lower capacitor voltages, phase currents, and line voltages under different modulation methods. Additionally, the upper and lower capacitor voltage waveforms were examined for various modulation indices. The results indicate that as the modulation index increases, the low-frequency voltage fluctuation in the upper and lower capacitor voltages also rises. At a modulation index of 0.95, the “variable reference + zero-sequence injection” method effectively suppresses the fluctuation in the upper and lower capacitor voltages to be no more than 1 V. These experimental findings validate the effectiveness of the proposed method.

Enhanced Four-Level Active Nested Neutral Point-Clamped Inverter

The classical four-level nested neutral point-clamped (4L NNPC) inverter-leg is a hybrid of the flying-capacitor and diode-clamped 4L-inverter-leg configurations. Though uniform reduced voltage stress (1/3 of input voltage) on constituting switches is evident in the 4L NNPC inverter-leg, trails of the drawbacks of the diode-clamping concept still exist. With the significantly rated off-the-shelf IGBT switch modules (6.5 kV, 1200 A), chances of deployment of the newly evolved Four-Level Nested T-Type inverter (4L NTTI) in certain applications is high. Compared with the classical 4L NNPC inverter, 4L NTTI involves a smaller number of power switches and low conduction losses. However, in 4L NTTI, two of the six active switches have a blocking voltage rating of 2/3 of the input voltage. Considering this limiting topological feature in 4L NTTI, a six-switch inverter-leg for the four-level active neutral point-clamped (4L ANNPC) inverter is presented in this paper. In the proposed 4L ANNPC inverter-leg, only one switch has a voltage stress of 2/3 of the input voltage. This ameliorated voltage stress translates to low-cost and -loss inverter implementation. The operational characteristics and competitiveness of the 4L ANNPC inverter are analyzed in detail and demonstrated with a prototype.

Sensorless speed controller of an induction motor with MRAS-based model predictive control

Speed sensors play critical role in induction motor (IM) control systems. However, the use of these sensors cause several drawbacks such as increasing the overall cost, decreased reliability on control and increased noise problems in data acquisition. The sensorless control methods also have been proposed in control systems of IM to increase the overall performance. On the other hand, model predictive controllers (MPCs) which is one of the most recently used controller methods require the speed measurement to perform speed and torque control of an IM. In addition to control method, the topology of voltage source inverter (VSI) affects the overall efficiency of the IM drive because of its losses and total harmonic distortion (THD) ratios delivered by the topology. The main proposal of this study is to implement an IM drive built with a three-level active neutral point clamped (3L-ANPC) voltage source inverter (VSI) and to propose an MPC that eliminates sensor requirement in speed control of IM. The proposed IM drive takes benefits of multilevel inverter topology, which reduces the torque ripple, enables low switching frequency and provides decreased harmonic distortion. The switching pulses of ANPC VSI are generated by the proposed sensorless MPC method for controlling the torque of IM. The modelling and experimental verification of the ANPC based IM drive have been carried out and the sensorless MPC controller has been validated in this study. There two types of model reference adaptive system (MRAS) have been proposed to ensure precise estimation of IM speed that should be supplied to MPC controller. These MRAS methods are titled as the rotor flux based model reference adaptive system (MRASF), and the stator current based model reference adaptive system (MRASCC) according to estimation references. The proposed MPC-based IM drive has been analyzed under variable speed and torque circumstances to detect the efficiency and reliability of MRASF and MRASCC algorithms. The efficiency indicators such as flux and torque responses, and speed control of the suggested MPC IM drive are validated with experimental analysis. The results of revealed that the IM effectively tracks the reference speed and produces the required torque depending to the precise control of proposed MPC algorithm.

Application and Verification of a Leg-Transfer Method for Three-Level Active Neutral-Point-Clamped Inverters for Railway Vehicles

In this paper, a two-leg-transfer switch structure method that can continuously supply three-phase power even when an accident occurs in a power semiconductor of a three-level active neutral-point-clamped (ANPC) inverter for railway vehicles is presented. The proposed method can minimize the ripple effect caused by power semiconductor faults by separating the faulty leg from the main circuit and connecting the load-side circuit to a neutral point. As a result of simulations, the average values of MAE and RMSE can be reduced by 1.53 [A] and 1.77 [A], respectively, when using the proposed leg-transfer switch structure compared to using the conventional structure. In the IGBT failure experiment, when the proposed method was applied to a three-level ANPC inverter, there was only a 0.21 [%] difference from the THD under normal conditions. As a result, the magnitude, phase, and total harmonic distortion of the three-phase current waveforms measured before and after the fault were identical. Thus, normal three-phase power could be effectively supplied to the load when the proposed leg-transfer switch method was applied after a power semiconductor fault occurred in the three-level ANPC inverter. If this leg-transfer switch method is applied in three-level ANPC inverterd for railway vehicles, track schedule errors can be minimized by continuously supplying three-phase power to the electric motor even when an accident occurs in a power semiconductor.

A three level NPC inverter fault detection and identification using voltage vector residual evaluation based on current path tracking method

This research describes open circuit detection and fault location for active 3-level NPC (neutral point clamped) inverter switches during normal and connected to the neutral point. This work introduces the current path tracking method to correlate the operating mode of NPC inverter and switch status in abnormal and normal conditions. Furthermore, a hierarchal diagnosis approach is introduced for open circuit faults using output Voltage Vector Residual Evaluation (VVRE). The node potential and conduction path can be derived from the model to indicate the NPC inverter circuit faults. Two steps are involved in the diagnosis. First, OC fault can be determined by analyzing the difference between the reference voltage and actual voltage vector resulting from the specified current path utilization ratio. Therefore, using a current path state reconstruction method, we can distinguish faulty transistors with similar properties. The simulated results demonstrate the robustness and efficiency of the proposed approach.

Model Predictive Control Strategy Based on Loss Equalization for Three-Level ANPC Inverters

Targeting the issue of high losses of individual switching tubes in Neutral-Point Clamped (NPC) three-level inverters, an Active Neutral-Point Clamped (ANPC) three-level inverter is used, and a model predictive control strategy using the loss equalization of the inverter is proposed. This method organizes and analyzes multiple zero-state current pathway commutation modes and adds mode three under the original two commonly used zero-state commutation modes. On this basis, the three modes are flexibly switched by model predictive control, and the output is optimized according to the value function for the space vector in each operation, while the midpoint voltage control is added to the value function. The simulation results suggest that the recommended strategy in this study may effectively realize the loss equalization control and midpoint voltage control of the ANPC inverter, which improves the operation efficiency of the electromechanical actuator.

Control Strategy of Three-level Active Neutral Point Clamped Grid Connected Inverters in Unbalanced Power Grid

Traditional phase-locked loops in three-level active neutral point-clamped inverter grid-connected systems for photovoltaic power generation exhibit a deficiency in the decoupling of positive and negative sequences under unbalanced power grid conditions. To address this issue, this study proposes the implementation of the fourth-order generalized integrator into the phase-locked loop to facilitate positive and negative sequence decoupling. Initially, a 3L-ANPC inverter grid connection system is established. However, under unbalanced grid voltage conditions, the PLL effect of the Decoupled Double Synchronous Reference Frame Phase-Locked Loop is found to be suboptimal, leading to considerable fluctuations and distortions in the output frequency signal. To address these complications, we propose an optimized phase-locked loop structure. In this improved design, the PLL first utilizes the FOGI to filter out multiple harmonics in the grid voltage prior to decoupling the positive and negative sequence voltage. This process effectively mitigates the effect on the PLL, thereby enabling rapid and precise tracking of the grid voltage. Simulation analysis is conducted by using Matlab/Simulink to substantiate the effectiveness of the proposed PLL, demonstrating its ability to reliably lock onto the frequency and phase of the fundamental voltage under conditions of unbalanced power grid voltage.

EFFECT OF VOLTAGE STRESS ON RELIABILITY OF THE 3-LEVEL ANPC MULTILEVEL INVERTER FOR WIND TURBINES

Wind power with low or no greenhouse gas emissions has been highly prevalent over the last decade. Modern renewable energy systems rely heavily on power electronic devices such as multilevel converters (MLC) to integrate renewables into the grid or provide electricity to islanding loads. These converters’ power electronic switches have a high failure rate (approximately 34 percent). As a result, the reliability evaluation of these converters is vital. Most research has focused on developing a fault-tolerant, efficient and cost-effective topology that reduces components. Still, the reliability of these topologies has received relatively little attention. This paper studies the effect of voltage stress on three-level Active Neutral Point Clamped (ANPC) multilevel inverter reliability. The series redundancy is introduced in ANPC using redundant outer switches, making ANPC a fault-tolerant topology. The reliability of this fault-tolerant topology is compared with the fault-intolerant ANPC. The voltage stress factor is calculated for fault intolerant and proposed fault-tolerant ANPC topologies. Because of the reduced stress on the switches and redundant configuration of the outer switches, the proposed fault-tolerant ANPC is more reliable. The fault-tolerant topology proposed in this paper has the lowest voltage stress factor, resulting in better reliability.

A Novel Modulation Strategy for Split-Inductor Active NPC Inverter With Loss Distribution Balancing and Thermal Stress Reduction

Neutral point clamped inverter (NPC) features low harmonics, high efficiency, and low voltage stress, et al. NPC is widely applied in renewable energy power generation systems, such as wind turbine power and photovoltaic. However, due to unbalanced power losses, NPC suffers inherent thermal unbalance among inner and outer power switches. A split-inductor active neutral point clamped inverter (SI-ANPC) was initially proposed to improve the operating reliability, providing the structural basis for balanced loss distributions. With this purpose, a novel modulation strategy with balanced loss distribution for SI-ANPC is proposed in this paper. The modulation strategy is analyzed under the unity and non-unity power factors. In specially, two redundant zero-state paths are fully used. Under the unity power factor, the power switches operate at the switching frequency or maintain the conduction state complementarily. Considering the phase angle in the non-unity power factor situation, the working patterns of power switches are rearranged to reduce the loss difference. The thermal stress is decreased on both occasions. Finally, loss calculation results, experimental waveforms, and thermal images of the inner and outer switches are presented to confirm the effectiveness of the proposed modulation strategy.

Low-complexity model predictive control of a four-level active neutral point clamped inverter without weighting factors

Abstract The four-level active neutral point clamped (ANPC) inverter has become increasingly widely used in the renewable energy industry since it offers one more voltage level without increasing the total number of active switches compared to the three-level ANPC inverter. The model predictive current control (MPCC) is a promising control method for multi-level inverters. However, the conventional MPCC suffers from high computational complexity and tedious weighting factor tuning in multi-level inverter applications. A low-complexity MPCC without weighting factors for a four-level ANPC inverter is proposed in this paper. The computational burden and voltage vector candidate set are reduced according to the relationship between voltage vector and neutral point voltage balance. The proposed MPCC shows excellent steady-state and dynamics performances while ensuring the neutral point voltage balancing. The efficacy of the proposed MPCC is verified by simulation and experimental results.

Model Predictive Torque Control-Based Induction Motor Drive with Remote Control and Monitoring Interface for Electric Vehicles

While the increased use of internal combustion engine vehicles raises carbon emissions, electric vehicles (EVs) are becoming more important for reducing air pollution. EV production costs are decreasing as technology advances since they are typically powered by alternating current induction machines (ACIM). In EV configurations that are propelled with ACIM, an inverter is required to obtain appropriate voltage levels to drive the IM. Multilevel inverters are widely preferred in the industry for DC–AC voltage conversion due to their high-power quality. In this study, the ACIM is supplied with the appropriate voltage using an active neutral point clamped (ANPC) inverter. The ANPC inverter acting as ACIM driver is controlled with model predictive torque control. The simulation of the proposed ACIM drive has been performed with torque and speed control features to determine the operational features of the experimental test bench. Furthermore, the designed ACIM drive includes remote control and monitoring functions via an Internet of Things-based module. This allows for instant monitoring of the input, output, and current values of the ANPC inverter. The graphical monitoring function is used to track the speed and torque values of ACIM while the speed can be changed remotely via the web interface.

Five-Level Unity-Gain Active Neutral-Point-Clamped Inverters Designed Using Half-Bridges

This paper proposes two novel 5-level active neutral-point-clamped (ANPC) inverters that double the voltage gain of the conventional topology from half to unity. Each phase of the proposed topologies is constituted by three half-bridges that control a flying capacitor to generate 5 symmetrical ac voltage levels. The natural voltage balancing of dc-link and flying capacitors in the proposed topologies implies that the sensors and voltage balancing controller commonly used in the conventional ANPC inverter are no longer necessary. In addition to switch count reduction, the most noteworthy merit of the proposed topology is its ease of implementation with commercial half-bridge modules, where the design of dedicated circuit is not needed. The operation of the proposed 5-level unity-gain ANPC (5L-UG-ANPC) inverters is analyzed and validated through simulation and experimental tests.

Fault analysis in the 5-level multilevel NCA DC–AC converter

The existing neutral clamped active inverter has common mode voltage with the high frequency which can reduce the severity with less voltage gain. 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. The paper presents a new 5-level active neutral point clamped DC–AC converter that can change 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 use. Compared with the traditional two-stage 5-level APC DC–AC converter, the proposed design has lower voltage stresses and greater uniformity. While improving the overall efficiency, the suggested clamped DC–AC converter saves three power switches and a capacitor. Modelling and actual tests have proven the suggested active neutral point clamped inverter’s overall operation, efficacy and achievability. The proposed circuit is finally tested with fault clearance capability.

Dual-Carrier-Based PWM Method for DC-Link Capacitor Lifetime Extension in Three-Level Hybrid ANPC Inverters

Power converters operate at varying low-, medium-, and high-voltage levels. Large electrolytic capacitors are usually used to sustain the associated dc-link current and stabilize the dc-link voltage. However, owing to different power converter applications, capacitors are affected by large ripples in the dc-link current, which increase heat exchange and reduce system reliability and lifespan. In this regard, this article proposes an innovative control technique for suppressing the ripple in the dc-link current and common-mode voltage (CMV) in hybrid active neutral point clamped inverters. The proposed control technique uses an improved dual-carrier-based pulsewidth modulation technique to create a new switching scheme by selecting the voltage vectors that contribute to the smallest ripples in the dc-link current according to each sector. Applying the proposed control technique significantly reduces the ripples in the dc-link current and CMV, which increases the reliability of the system and extends the lifetime of dc-link capacitors. The simulation and experimental results demonstrate the effectiveness of the proposed control strategy.

Single-Phase 5-Level Split-Midpoint Cross-Clamped (5L-SMCC) Inverter: An Alternative to the Two-Stage ANPC Topology

The conventional active neutral-point-clamped (ANPC) multilevel inverters are popular for single-phase applications owing to their advantage of mitigating high-frequency common-mode voltage (CMV). With the ac neutral connected to the midpoint of dc link, their voltage gain is restricted to only half. For boosting output voltage, a two-stage structure by adding a frontend dc–dc boost converter is commonly used. This article investigates the performance of the conventional two-stage 5-level ANPC inverter and proposes an improved topology by splitting the dc-link midpoint and cross clamping them to the dc-link capacitors. While using the same number of power devices and retaining the advantages of the conventional two-stage 5-level ANPC topology, such as high-frequency CMV mitigation and continuous dc source current, the proposed 5-level split-midpoint cross-clamped (5L-SMCC) inverter achieves several advantages, such as higher voltage gain, lower voltage across dc-link capacitors, lower inverter voltage stress, and natural voltage balancing for all capacitors without requiring any balancing controller or sensor. In addition, it saves one capacitor by eliminating the flying capacitor of the conventional 5-level ANPC inverter. The operation of the proposed 5L-SMCC inverter is thoroughly analyzed. For validation, simulation and experimental results are presented.

Low-Complexity Finite Set Model Predictive Control for Split-Capacitor ANPC Inverter With Different Levels Modes and Online Model Update

In this article, an improved finite-control-set model predictive control (FCS-MPC) is presented for an active neutral point clamped (ANPC) topology. The considered converter significantly reduces the required power electronics components compared with other common dc-link converters, where only seven active switches, one bidirectional switch, and two floating capacitors (FCs) are employed to produce nine levels in the phase voltage. The developed FCS-MPC handles three control objectives with only one weighting factor, namely, current control, FC balancing, and NP potential stabilization, which reduces the cumbersome effort required for weighting factors coordination. In addition, the number of iterations required to identify the optimal vector is significantly reduced, which, in turn, reduces the execution time of the algorithm. The proposed control method empowers the considered converter to operate in different modes under the faulty condition of the bidirectional switch without any structure modification, which guarantees continuous operation of the converter while ensuring the balancing of FCs and dc-link capacitors in all operating modes. The sensitivity of the proposed FCS-MPC to parameter mismatch, which is a basic issue of MPC-based techniques, is tackled by employing an extended Kalman filter (EKF) to online estimate the system parameters. The proposed FCS-MPC algorithm is experimentally validated and compared with the conventional FCS-MPC method under different operating conditions.

An intelligent technique for fault detection and localization of three-level ANPC inverter with NP connection for electric vehicles

An intelligent technique for detecting and localizing an inverter switch fault or phase fault of a Three-Level Active Neutral Point Clamped (ANPC) inverter is proposed in this research. Moreover, a 3L-ANPC inverter can gain the controllability of EV's power train and not need to be stalled even after the occurrence of the fault. Hence, an efficient fault diagnosis methodology is required to identify the type of phase fault by a Support Vector Machine (SVM), a machine learning model consisting of sets of labeled training data with regression and classification challenges. Finally, when the fault occurs, the location of the switch fault can be identified by a Deep Neural Network (DNN), which consists of layers of neurons between the input and output layers which fuses the feature extraction process with increased accuracy. Thus, the detection and localization of the open-circuit fault of the switches in the ANPC inverter help overcome all single faults, hence gaining its current controllability without stopping the vehicle. The accuracy of fault detection is improved in a precise manner. Finally, the performance of the proposed work is evaluated over other conventional models concerning varied metrics like the accuracy of identification and localization.

A new design of active NPC converter topology with higher voltage gain for solar PV applications

In the low voltage applications, the high gain multilevel inverters has seen more visibility due to the improved harmonic profile with multilevel voltage as well as boosting feature. A boost active neutral point clamped (ANPC) multilevel inverter (MLI) configuration with reduced resource count has been proposed in this paper. The proposed MLI produces 11 levels (11L) voltage with the help of 12 switches of blocking voltage ratings lesser than the peak value of output voltages. For attaining the boosting of 2.5 in output voltage, 4 capacitors are used in the proposed MLI which are inherently self-balanced. The capacitors charging as well as discharging are done by implementing the simple logic of parallel/series connection with the active power DC source. The proposed MLI is implemented and tested in the laboratory at various operating conditions, and the corresponding results and discussion are presented.

Closed-loop control of six-switch five-level active neutral point clamped inverter for photovoltaic application

Closed-loop control of six-switch five-level active neutral point clamped inverter for photovoltaic application