Neutral Point Clamped Inverter Research Articles

Reliability evaluation of carrier‐based pulse width modulated three‐level F‐type neutral point clamped inverter with power loss analysis

AbstractAn improved carrier‐based pulse‐width‐modulation (CBPWM) technique for a three‐level (3L) F‐type neutral point‐clamped (FNPC) inverter is presented in this paper. By using the proposed modulation scheme, the DC‐link capacitor voltage at the neutral point is balanced. For manufacturers, reliability is one of the major concerns for all power electronics devices and parts. This paper proposes an extensive reliability analysis of the 3L‐FNPC inverter. Considering the mean time to failure (MTTF) of each device, the reliability of the 3L‐FNPC inverter is analyzed in this present work by using two different methods, which are the approximate method and the exact method. To compute the failure rate of the equipment, only the number of components is considered in the approximate method. Alternatively, exact methods are utilized to evaluate the reliability of a system by knowing the different stress levels and various operating environments of a specific system. Because of the strong correlation between device failure and temperature stress factors, power loss analysis is used in the exact method. The MATLAB Simulink environment is used to determine the power loss of the switching devices. A solar off‐grid photovoltaic (PV) system is considered for reliability testing. Experimental mission profile data are used to estimate the lifetime of the 3L‐FNPC inverter by applying the rainflow counting algorithm, the Coffin‐Manson model, and Miner's rule. The competitiveness, effectiveness, and reliability of the 3L‐FNPC inverter with the proposed modulation technique are validated using a hardware prototype.

Grid-Connected Solar PV System with Maximum Power Point Tracking and Battery Energy Storage Integrated with Sophisticated Three-Level NPC Inverter

In this research, a solar photovoltaic system with maximum power point tracking (MPPT) and battery storage is integrated into a grid-connected system using an improved three-level neutral-point-clamped (NPC) inverter. An NPC inverter with adjustable neutral-point clamping may achieve this result. To achieve this result, a modernized NPC inverter is used. Using the three-level vector modulation approach, the correct AC voltage may be generated when DC voltage conditions are present in an unbalanced situation involving an NPC inverter. A higher degree of precision is made possible by this. In-depth information on the many possible NPC inverter designs and modulation strategies was provided. By incorporating the necessary sophisticated algorithms into the NPC inverter, the necessary solar PV-MPPT functionality is made available, allowing for the regulation of power transfer among the solar PV system, the battery, and the grid. Modified INC method is proposed which has a tracking efficiency of 99.5% for varying irradiance. The use of sufficiently sophisticated algorithms makes this a reality. Using simulation with MATLAB/Simulink, we were able to examine an NPC inverter’s performance in several setups. Several amounts of solar irradiation were used to test the battery’s charging and discharging capabilities. The probe turned out to be fruitful. Laboratory testing ensures that the proposed method works by simulating real-world conditions.

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 Reduced-Order Observer-Based Method for Simultaneous Diagnosis of Open-Switch and Current Sensor Faults of a Grid-Tied NPC Inverter

This paper presents a reduced-order observer-based simultaneous diagnosis strategy for grid-tied neutral point clamped (NPC) inverters subjected to open-switch and current sensor faults. First, the augmented descriptor system is constructed for the NPC inverter to transfer the current sensor fault into a generalized state vector. Then, the matrix transformations are applied to decouple the open-switch fault from the inverter system state and the current sensor fault. Subsequently, a reduced-order observer is developed for the transformed augmented descriptor system to achieve simultaneous precise estimation of the phase current and the current sensor fault. Finally, using the estimation results, a diagnosis algorithm with an adaptive threshold is proposed, which can not only distinguish between current sensor faults and open-switch faults, but also locate the faulty power switch and estimate different types of current sensor faults. Experimental results and comparisons are provided to verify the robustness and effectiveness of the proposed fault diagnosis algorithm.

불연속 전압 변조 방법 적용 범위에 따른 태양광 NPC 인버터의 DC-link 커패시터 신뢰성 분석

The voltage modulation method has a significant effect on the performance of 3-level neutral-point clamped (NPC) inverters such as efficiency and output quality. Discontinuous pulse width modulation (DPWM) has been proposed to improve efficiency by reducing the switching loss of power devices. In previous research, the output quality, power loss, and reliability of the power device were considered when the DPWM method was applied. However, the influence of the DPWM on the reliability of DC-link capacitors, one of the reliability-critical components, has not been investigated. In this paper, the effect of DPWM on the reliability of DC-link capacitors is studied in the NPC inverter. Considering the mission profile of the photovoltaic (PV) system, the accumulated damage of DC-link capacitors is analyzed at the component level first under different applied angles of DPWM. The reliability of DC-link capacitors is then evaluated at the system level by considering all capacitors of the NPC inverter. In addition, the current of the DC-link capacitor is analyzed through the experiment to validate the negative effect of the DPWM on the reliability of the DC-link capacitor.

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.

An Improved Finite Control-Set Model Predictive Control for Nested Neutral Point Clamped Converter

This paper presents an improved model predictive control with a finite control set (IFCS-MPC) for a four-level nested neutral point clamped (4L-NNPC) inverter. Controlling flying capacitors (FCs) voltages of 4L-NNPC, especially at low output frequency, is a challenging issue. In the proposed method, the control objectives of 4L-NNPC (current, FCs voltages, and switching losses of power devices) are formulated in terms of FCS-MPC. Furthermore, a computational burden reduction technique is introduced that reduces the search space from 216 to 96 switching states for a three-phase system. In addition to the current control, the proposed control method has the ability to control FCs voltages in the entire operating frequency range and also decreases the switching losses of the converter in comparison to the alternative methods. Also, it offers a lower computational burden than conventional FCS-MPC, which is of importance in implementation of MPC. The performance of the suggested method is verified on a 4L-NNPC in MATLAB/SIMULINK. Also, the experimental results are carried out based on a scaled-down hardware prototype validating the theoretical claims.

Duty-Cycle Correction-Based Model Predictive Current Control for PMSM Drives Fed by a Three-Level Inverter With Low Switching Frequency

In this paper, a duty-cycle correction-based model predictive current control (DC-MPCC) is proposed for permanent magnet synchronous motor (PMSM) supplied by a neutral-point clamped three-level voltage source inverter (NPC-3LVSI). Unlike the conventional MPCC, which evaluates the impact of basic voltage vectors on the concerned state variables, the proposed DC-MPCC modifies the output voltage levels with optimized duty-cycle corrections. Firstly, the last three-phase voltage levels are assumed to be kept during the next control period. Then, the current tracking error and neutral-point potential are predicted. After that, the voltage levels are modified with zero, one, or two state changes, which formulate seven candidate solutions. Subsequently, the duty-cycle corrections of the modified voltage levels are computed based on the principle of minimizing current tracking error and neutral-point voltage drift. Finally, the optimal switch sequence is generated by evaluating and sorting a cost function with a penalty on switch actions. The proposed DC-MPCC features variable switching instants, relatively lower sampling frequency, and satisfactory performance under low switching frequency. Experimental tests carried out on a NPC-3LVSI fed PMSM drive, with 100 Hz fundamental frequency and 400 Hz switching frequency, accompanied by a video demonstration, validate the effectiveness of the proposed method.

SVPWM control strategy for Novel Interleaved High Gain DC converter fed 3-level NPC Inverter for Renewable Energy Applications

The high-gain DC converter is a crucial step in the conversion process for raising the voltage from PV panels to the desired voltage level in renewable energy applications. This article proposes a three-phase grid connected PV system with a novel interleaved high gain DC converter fed 3-level Neutral-Point-Clamped (NPC) Inverter. The novel high-gain DC converter consists of an interleaved boost converter (IBC) at its input side, a switched capacitor cell, a passive clamp circuit, and a voltage multiplier unit (VMU). The interleaved arrangement eliminates the input current ripple, and the VMU is utilized to improve the overall voltage gain besides the reverse recovery problem of diodes. The proposed converter is operated at a duty cycle D = 0.6 and a high voltage conversion ratio of 17.5 which is ideal for sustainable energy applications. This paper uses the proposed converter for a grid-connected solar PV system with an NPC inverter controlled using Space Vector Pulse Width Modulation (SVPWM) technique. The SVPWM strategic approach is a prevalent modulation technique for NPC inverter due to its extensibility in choosing the ideal voltage vectors. It uses an active filter, which is more dependable, dynamically better behaved, and capable of operating accurately under distorted grid voltages under varying load conditions. The proposed grid-associated PV system with a novel interleaved converter and 3-level NPC inverter is employed in Matlab/SimPower System and experimentally verified. Power loss and efficiency calculations were performed on the DC converter side, and the efficiency was 96.07%. NPC inverters have a THD of 22.2%. Results from simulations and experiments indicate that the suggested topology can efficiently extricate the maximal amount of power from PV modules and inject energy into the grid system with excellent steady-state and dynamic performance.

Compensation-Voltage-Injection-Based Neutral-Point Voltage Fluctuation Suppression Method for NPC Converters

Three-level neutral-point clamped (NPC) inverters are widely used in the new energy power generation, motor drive, and many other occasions. However, the neutral-point voltage imbalance of an NPC inverter will affect the output of the inverter system, and the control of the neutral point voltage has become a popular research topic. In this paper, a compensation-voltage-injection-based neutral-point voltage balancing method is proposed. During the switching cycle, the average value model of the neutral-point current under different voltage vectors is applied to calculate the value of the compensation voltage that needs to be injected. The self-balance of the neutral-point voltage based on a switching cycle is realized, and the influence of modulation ratio and power factor on equalization ability is discussed. A MATLAB/Simulink simulation model and a small power prototype are established to verify the effectiveness of the method, and the simulation and experimental results show that the proposed method can effectively suppress the neutral-point voltage fluctuation in a wide range of modulation ratios and power factors.

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.

A Modified PWM Scheme to Improve the Power Quality of NPC Inverter Based Solar PV Fed Induction Motor Drive for Water Pumping

This paper proposes a modified modulating signal-based pulse width modulation (PWM) scheme for a neutral point clamped (NPC) inverter-based induction motor drive (IMD) for enhancing the efficiency of solar photovoltaic (PV) fed water-pumping systems. During the previous several decades, the use of sustainable source-based power generation systems has benefited water pumps in household life, irrigation-based activities, and industrial sectors, especially in areas where the electric grid is less available. A critical concern has long been the power quality, speed, and torque of an induction motor used in solar PV-powered water pumping. This paper focuses on the improvement of power performance by minimizing total harmonic distortions (THDs), switching losses and conduction losses, and torque ripples in the induction motor driving the PV-fed water pump by using a modified PWM scheme that generates symmetrical and balanced gate driving signals for the NPC inverter employed in the IMD. The IMD with the suggested PWM switching strategy has been tested in all feasible induction motor operating situations. To demonstrate the effectiveness of the suggested PWM scheme, a performance comparison of the proposed PWM scheme with conventional PWM schemes is performed, and also the IMD with the suggested PWM switching strategy is tested in all feasible induction motor operating situations using the MATLAB/Simulink platform.

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.

An Improved Sensorless Nonlinear Control Based on SC-MRAS Estimator of Open-End Winding Five-Phase Induction Motor Fed by Dual NPC Inverter: Hardware-in-the-Loop Implementation

This paper introduces a sensorless nonlinear control scheme based on feedback linearization control (FLC) of an open-end winding five-phase induction motor (OeW-5PIM) topology fed by a dual neutral point clamped (NPC) inverter. The suggested sensorless control is combined with the sliding mode (SM) controller to improve the dynamic performance (i.e., rising time, overshoot, etc.) of the studied motor. Furthermore, a stator-current-based model reference adaptive system (SC-MRAS) estimator is designed for the estimation of the rotor flux and the motor speed. In parallel, to enhance the robustness of the designed sensorless control against motor parameter changes, an adaptive estimation method is suggested to estimate the rotor and stator resistances during low-speed ranges. The estimation method of motor resistances is associated with the suggested sensorless control to further improve the speed estimation accuracy and minimize the speed estimation error. Finally, the effectiveness and correctness of the suggested control with the examined estimators are validated in real-time implementation using a hardware-in-the-loop (HIL) based on the dSpace 1103 board.

Simulation of 3D-space vector modulation for neutral point clamped inverters

This paper gives an idea to simulation of three-dimensional space vector modulation for neutral point clamped multilevel inverter. Three dimensional-space vector modulation (3D-SVM) algorithm is progressed method of two dimensional-space vector modulation (2D-SVM) algorithm; it leads to reduce the complexity in reference vector identification and switching time calculation, also it includes the various advantages of 2D-SVM like minimized total harmonic distortion, reduced EMI issues. A simple system for the assortment of switching state vectors to track the reference voltage vectors without using any redundant switching vectors. This proposed method tracks the reference vector by identifyinglsubcubes and prisms by using mathematicallconditions. Here the cost of the proposedltechnique is independentlof voltagellevels oflinverter. This paper realizes the accomplishment of 3D-SVM using a neutral point clamped inverter. The simulation results of the proposed method are verified using MATLAB/Simulink.

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.

Multi-objective predictive control for three-phase three-level neutral-point clamped inverter

Multi-objective predictive control for three-phase three-level neutral-point clamped inverter

Artificial neural networks controllers for three-phase neutral point clamped inverters

In this study, a new current control method consisting of proportional-resonant (PR) based artificial neural networks (ANN) has been developed for a neutral point clamped (NPC) inverter. The used NPC inverter circuit is three phase three level three leg and four wire. Current control in the inverter has been carried out primarily with PR and Hysteresis current controllers for comparison purposes. Then, a dynamic ANN structure is designed and trained using the PR current controller data from the simulation. The performance of this ANN current controller is investigated by simulation and experimental studies. The proposed ANN controller has been compared with other ANN controllers used in power electronics applications in the literature, based on the size and functions of the network structures. In addition, NPC inverters have a controller whose task is to balance the voltages of direct current (DC) bus capacitors. A separate static ANN based controller has been developed for this voltage balancing controller, which usually includes two proportional-integral (PI) controllers. The performance of these two types of ANN controllers has been experimentally verified with balanced/unbalanced, linear/non-linear loads.

Smooth Switching Method for Multi-Mode Synchronous Space Vector Modulation of NPC Three-Level Inverter

To meet the requirements of output harmonic distortion of neutral point clamped (NPC) three-level inverter under low switching frequency conditions, multi-mode synchronous space vector modulation is usually adopted. When switching between different pulse patterns, there will be oscillation in the output current. This paper proposes a smooth switching method for synchronous space vector modulation. This method compensates the phase angle of the reference voltage vector, in order to make the flux trajectories continuous before and after switching. Multi-position smooth switching can be realized in the fundamental period, and there is no delay in switching. Compared with direct switching, the total harmonic distortion rate of current during switching is reduced. The calculation of the phase angle compensation value of the reference voltage vector is not affected by the specific parameters and operating conditions of the motor, and can be carried out offline. Finally, experiments are carried out on a 7.5 kW induction motor fed by NPC three level inverter to verify the feasibility and effectiveness of the proposed method.