Three-level Neutral Point Clamped Inverter Research Articles

Performance Investigation of Deadbeat Predictive Controllers for Three-Level Neutral Point Clamped Inverter

This article aims to improve the performance of the deadbeat (DB) predictive controller for a three-level neutral point clamped (NPC) inverter. The effect of the number of effective vectors considered for the cost function evaluation on steady-state and dynamic performance is investigated. To do that, three DB predictive controllers with different numbers of effective vectors, namely, 19 vectors-based, six vectors-based, and three vectors-based DB, are compared beside the conventional current-based model predictive control (MPC). The neutral-point (NP) voltage is balanced using the redundant vectors. Simulations and experimental tests are performed to evaluate the performance of the competing MPC algorithms in terms of four main criteria, namely: NP voltage balancing error, total harmonic distortion (THD), the computational effort required, average switching frequency, power loss, and sensitivity to parameters mismatch. Compared to conventional MPC, the experimental results show that the three vectors-based DB predictive controller has the best steady-state and dynamic performance with a reduction of computational burden up to 60% and a reduction of the current THD up to 72%.

Using vertical areas in finite set model predictive control of a three-level inverter aimed at computation reduction

In power electronics applications, finite set model predictive control (FS-MPC) has proven to be a viable strategy. However, due to the high processing power required, using this technology in multilevel converters is difficult. This strategy, which is based on predicting the behavior of the system for all conceivable states, has an issue with a numerous of possible switching states. A recent and useful strategy for dealing with the problem is the limiting of calculations based on triangle regions. Despite its success, this method has several limitations, including the computation required to locate the right triangle and the boundary modes. In this research, the vertical areas are used for the limiting of calculations. Not only determining the right zone is an easy task with this strategy, but the number of possible candidates is also reduced to two. Furthermore, the boundary mode will not occur.In the proposed method, two key advantages can be seen in the discussion of reduction of calculations: (1) new zoning, which eliminates the calculations related to the slope of the lines. (2) The number of options placed in the cost function has been reduced to 2 candidates. Simulations are used to validate the approach, which is applied to a three-level neutral point clamped (NPC) inverter.

24 Sectors DTC Control with Fuzzy Hysteresis Comparators for DFIM Fed by the Three-level NPC Inverter

This article presents 24 sectors direct torque control (DTC) with fuzzy hysteresis comparators for the doubly-fed induction motor (DFIM) using a three-level neutral point clamped (NPC) inverter. The designed DTC technique of the DFIM combines the advantages of the DTC strategy and fuzzy logic controller. The reaching conditions, stability, and robustness of the DFIM with the designed DTC technique are guaranteed. The designed DTC technique is insensitive to uncertainties, including parameter variations and external disturbances in the whole control process. Finally, the designed DTC technique with fuzzy hysteresis comparators is used to regulate the electromagnetic torque and the flux of the DFIM fed by the three-level NPC inverter and confirms the validity of the designed DTC technique. Results of simulations containing tests of robustness and tracking tests are presented.

Nonlinear control of grid-connected PV systems using active power filter with three-phase three-level NPC inverter

Grid-connected photovoltaic (PV) systems have become a significant area of interest for research scientists. Given this, this article presents a nonlinear control of grid-connected PV systems using active power filter (APF) with three-phase three-level neutral point clamped (NPC) inverter. The control objectives involve: (1) Forcing the PV output voltage to track a reference signal provided by the MPPT block in order to produce their maximum power, (2) Regulating the DC link voltage to satisfy a correct operation mode of the three-phase active power filter, and (3) Satisfying power factor correction (PFC) objective at the point of common coupling, PCC. Therefore, the suggested control strategy includes a cascade structure of two loops. The inner-loop regulator is designed using the sliding mode control technique and Lyapunov approaches to ensure the PFC objective by forcing the grid current to follow a given reference signal. The Outer-loop consists mainly of a proportional-integral (PI) regulator so that to regulate the output voltage. Further, the theory of instantaneous real power is used to calculate reference harmonics. The effectiveness of the proposed controller is demonstrated through simulation results using MATLAB/Simulink.

Fault Diagnosis Based on Attention Collaborative LSTM Networks for NPC Three-Level Inverters

To address the problem, it is difficult to extract fault features for neutral-point-clamped (NPC) three-level inverters under nonstationary conditions. This article proposes a multi-information feature fusion diagnosis method based on attention collaborative stacked long short-term memory (ASLSTM) neural networks. First, parallel structural stacked LSTM networks are constructed, which are used to automatically extract features from multisource time-series data. Then, the attention mechanism is applied to weight these features adaptively. Finally, the fault is identified by features that integrate multiple sources of information. In addition, the quantum particle swarm optimization (QPSO) algorithm is used to intelligently tune the hyperparameters of ASLSTM to improve the reasonableness of hyperparameter selection for the diagnostic model. The simulation results of the fault diagnosis of the NPC three-level inverter circuit show that the proposed method is able to extract high-discriminative features from raw data and has better diagnostic results under various conditions compared with other schemes.

Open-Circuit Fault Diagnosis of NPC Inverter Based on Improved 1-D CNN Network

With the increasing popularization of a three-level neutral point clamped (NPC) inverter, realizing an accurate and fast fault diagnosis is also required. However, most methods are either not accurate enough or require a long period of time to collect signals as input. To compensate for these drawbacks, a novel 1-D convolution neural network (CNN) with the improved stochastic gradient optimization method is proposed in this article. First, the input data are segmented to ensure that the fault diagnosis can be completed if the current of a period is collected at any time in a period. Then, the feature of the waveform is extracted by the proposed network. In the meantime, the improved Adamod (IAdamod) method is implemented to better adaptively adjust the learning rate during the training process. Specifically, the learning rate is bigger at the beginning and smaller at the end. Finally, the classifier softmax is used for classification. The experimental results demonstrate the effectiveness of the proposed method in detecting and locating the faulty devices, which has shown that it perfectly realizes the fault diagnosis with 100% accuracy and can be diagnosed online with the time of less than 0.25 ms, far less than one cycle. The proposed method is also compared the traditional methods, and shows a better performance both in speed and accuracy, the loss can be less than 0.5 in iteration 220 and achieve zero in 1000.

Real-Time Implementation of Long-Horizon Direct Model Predictive Control on an Embedded System

This paper deals with the real-time implementation of a long-horizon finite control set model predictive control (FCS-MPC) algorithm on an embedded system. The targeted application is a medium-voltage drive system which means that operation at a very low switching frequency is needed so that the switching power losses are kept relatively low. However, a small sampling interval is required to achieve a fine granularity of switching, and thus ensure superior system performance. This renders the real-time implementation of the controller challenging. To facilitate this, a high level synthesis (HLS) tool, which synthesizes C <monospace xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">++</monospace> code into VHDL, is employed to enable a higher level of abstraction and faster prototype development of the real-time solver of the long-horizon FCS-MPC problem, namely the sphere decoder. Experimental results based on a small-scale prototype, consisting of a three-level neutral point clamped (NPC) inverter and an induction machine, confirm that the algorithm can be executed in real time within the targeted control period of 25 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> s.

A Twenty Five Switch Inverter Topology for Controlling Two Independent Five-Phase Load

The inverter drives for controlling multiple loads will provide several advantages like lower power electronic components, costs, space, etc. In this paper, a new Three-Level (3L) Neutral Point Clamped (NPC) inverter topology for controlling the two independent Five-Phase Load (FPL) is proposed which is named as Twenty Five Switch Inverter (TFSI) topology. This TFSI topology has five switches and two diodes in each leg. The number of switches in the conventional two load inverter is 30 switches which is reduced to 25 switches in the proposed topology. The Space Vector Modulation (SVM) for the proposed TFSI topology has 1024 vectors which is the addition of two individual Five-Phase Three-Level (FPTL) SVM. The performance of two loads for the proposed topology is examined at different conditions like changing the fundamental frequency (f_o), switching frequency (f_sw) and modulation indices. The simulation is carried out with MATLAB/Simulink and the results are validated with hardware implementation.

Virtual Vector-Based FCS-MPC for NPC Three-Level Grid-Tied Inverter Without Weighting Factor of Neutral-Point Voltage Balancing

The neutral-point clamped (NPC) inverter is widely used in energy conversion, but the unbalance of neutral-point voltage (NPV) will lead to imprecise control and the decline of power quality. Conventional finite control set model predictive control (FCS-MPC) uses an extra NPV weighing factor to balance the NPV. But the weighting factor should tune frequently to match the best value. To cope with this problem, this paper proposes a virtual vector-based control strategy without the NPV weighting factor for NPC inverters. The paper analyses the relationship between neutral-point current and neutral-point voltage. An NPV vector is designed to inject a compensatory neutral-point current to balance the capacitor voltage. The duration time of each NPV vector is calculated from real-time unbalance of the NPV. Because each NPV balancing virtual vector contains one NPV vector, the proposed method can balance the NPV without an extra NPV weighting factor in the cost function. Besides, a cost function without the NPV weighting factor is designed for the proposed method. Finally, experiments are carried out to verify the validity of the proposed method.

A Novel Neutral-Point Potential Balance Control Method Based on Voltage Feedback for Neutral-Point Clamped Three-Level Inverter

A Novel Neutral-Point Potential Balance Control Method Based on Voltage Feedback for Neutral-Point Clamped Three-Level Inverter

A Carrier-Based Discontinuous PWM Strategy of NPC Three-Level Inverter for Common-Mode Voltage and Switching Loss Reduction

For the conventional carrier-based pulse width modulation (CBPWM) strategies of neutral point clamped (NPC) three-level inverters, the higher common-mode voltage (CMV) is a major drawback. However, with CMV suppression strategies, the switching loss is relatively high. In order to solve the above issue, a carrier-based discontinuous PWM (DPWM) strategy for NPC three-level inverter is proposed in this paper. Firstly, the reference voltage is modified by the twice injection of zero-sequence voltage. Switching states of the three-phase are clamped alternatively to reduce both the CMV and the switching loss. Secondly, the carriers are also modified by the phase opposite disposition of the upper and lower carriers. The extra switching at the border of two adjacent regions in the space vector diagram is reduced. Meanwhile, a neutral-point voltage (NPV) control method is also presented. The duty cycle of the switching state that affects the NPV is adjusted to obtain the balance control of the NPV. Still, the switching sequence in each carrier period remains the same. Finally, the feasibility and effectiveness of the proposed DPWM strategy are tested on a rapid control prototype platform based on RT-Lab.

Independent Upper- and Lower-Arm Switching Scheme Based on Reference Current Polarity for Three-Level NPC Inverters

This study presents a novel switching scheme for three-level neutral point clamped (NPC) inverters. The proposed switching method independently drives the upper- and lower-arm elements of the inverter based on the polarity information of the reference current. The proposed switching scheme does not require the inclusion of dead-time for each switching, except when the current polarity changes. Therefore, unlike the conventional inverter switching method, dead-time compensation is not needed, and the possibility of an arm-short accident is prevented. In this study, a switching procedure is detailed, and the operation mode analysis of the proposed switching scheme is presented. The effectiveness of the proposed switching method is verified experimentally by application to a grid-connected inverter that requires inverter current control.

Design and simulation of Dual Z-Source Dual-Input Hybrid 2/3 level inverter

ABSTRACT The 2/3-level hybrid inverters are a combination of three-level Neutral Point Clamped (NPC) inverter and conventional two-level inverter, which has the advantage of both two-level and three-level structures with fewer switches than the NPC inverter. In this paper, a new structure of 2/3 hybrid inverter based on dual-Z-‏source network is proposed. The proposed structure improves the performance of the 2/3-level inverter and increases its independent DC input voltages. The output voltage gain can be obtained by selecting the shoot-through interval appropriately in dual Z-source networks. In addition, shoot-through intervals in Z-source networks allow the inverter to run without dead time, thus increasing the output voltage quality. A modified switching method is presented for the proposed inverter, and the necessary calculations are performed. The proposed structure can be used to connect different distributed generation sources to the load separately from the grid or to the low-pressure network. The performed simulations show the accuracy of the proposed structure.

Torque ripple reduction of BLDC motor based on DC bus voltage automatic selection circuit and neutral point clamped three-level inverter control

The torque ripple of Brushless direct current motor (BLDCM) mainly depends on the commutation torque ripple, while the commutation torque ripple mainly depends on the current fluctuation during commutation. In this paper, the cause of current fluctuation during commutation is analyzed, and an automatic selection circuit based on DC bus voltage and a neutral-point-clamped (NPC) three-level inverter controller is proposed. The motor winding is guaranteed to bear half of the DC bus voltage, and the duty cycle is calculated so that the DC bus voltage at the moment of phase change is in a certain relationship with the back electromotive force (EMF) of the circuit, thus suppressing the current ripple during phase change and achieving the purpose of suppressing torque ripple during phase change.

Improved Neutral-Point Voltage Balancing Control With Time Delay Compensation and Antiwindup Loop for a Three-Level NPC Inverter

This article proposes an improved neutral-point voltage balancing control (NPVBC) with time delay compensation and an antiwindup loop based on a dynamic change limit for a three-level neutral-point clamped (NPC) voltage-source inverter. NPVBC is essential for a three-level NPC inverter since it has a separate dc link. In an NPVBC based on the carrier-based pulsewidth modulation (CBPWM), the neutral-point (NP) voltage is regulated by synthesizing the NP current. The conventional NP voltage balancing controller is designed as a proportional-integral controller; however, time delays due to the digital control and pulsewidth modulation, and antiwindup loop were not considered despite the fact that digital control delay disturbs the accurate synthesis of NP current and the windup phenomenon may appear on the regulator since synthesizable NP current range can be limited by operating condition. To solve these problems, this article proposes improvement methods for NPVBC with digital delay compensation and an antiwindup loop based on CBPWM. Analysis on the effect of digital delay is described, and the time delays compensation method is proposed. Furthermore, an NP voltage balancing controller with an antiwindup loop is proposed along with an analysis of the synthesizable NP current range. With the proposed method, NP voltage ripples can be reduced, and control stability of the NPVBC can be greatly improved by preventing the windup phenomenon that may occur when the inverter output is insufficient. To verify the proposed methods, simulations and experiments, including elevator tower test, were conducted, and the results verify the effectiveness of the proposed methods.

Super twisting sliding mode control of three-phase grid-tied neutral point clamped inverters

This paper presents an effective sliding mode control defined on the basis of super twisting algorithm (ST-SMC) for three-phase grid-tied three-level neutral point clamped (NPC) inverters. Unlike the existing SMC techniques devoted for grid-tied NPC inverters, the proposed ST-SMC method suppresses chattering and achieves good tracking performance while maintaining the prominent features of the sliding mode control such as robustness and simple implementation. Furthermore, the proposed ST-SMC method has the ability to operate with imbalanced and deteriorated grid voltages. The steady-state and transient performances of ST-SMC with ideal, imbalanced and deteriorated grid voltages are investigated experimentally. The experimental results expose that the presented control approach offers fast transient response and achieves the grid current control with small total harmonic distortion.

Parameter co-design of active damping loop and grid current controller for a 3-phase LCL-filtered grid-connected inverter

Under non-ideal grid conditions, especially the harmonic grid condition, the proportional resonant controller with multiple harmonic resonant controllers (HR-PR controller) is recommended to provide high quality grid currents for the 3-phase LCL-filtered grid-connected inverter. Besides, in order to solve the resonance problem, the active damping loop with the grid-side currents feedback only is preferred. However, parameters of the HR-PR controller and the active damping loop both affect the performance of LCL filter resonance suppression and stability of the inverter, which is analyzed in this paper. Moreover, the stability constraint and the resonance suppression constraint is derived to maintain the good ability of LCL filter resonance suppression and satisfy the stability requirements of the inverter. Considering the wide control bandwidth for the HR-PR controller, a co-design method of the active damping loop and HR-PR controller is proposed in this paper. By introducing the Lagrange multiplier method, the proposed co-design method obtains the optimized parameters for the active damping loop and grid currents controller in z-domain appropriately. A prototype of 3-phase LCL-filtered three-level neutral point clamped grid-connected inverter is established to validate the proposed method.

Adaptive neuro fuzzy inference system based decoupled control for neutral point clamped multi level inverter fed induction motor drive

The presence of an integrator in a reference model of a rotor flux-based model reference adaptive system (RF-MRAS) and non-linearity of the inverter in the output voltage degrade the speed response of the sensorless operation of the electric drive system in terms of DC drift, initial value issues, and inaccurate voltage acquisition. To improve the speed response, a compensating voltage component is supplemented by an amending integrator. The compensating voltage is a coalition of drift and offset voltages, and reduces DC drift and initial value issues. During low-speed operation, inaccurate voltage acquisition distorts the stator voltage critically, and it becomes considerable when the stator voltage of the machine is low. Implementing a three-level neutral point clamped inverter in speed-sensorless decoupled control of an induction motor improves the performance of the drive with superior quality of inverter output voltage. Further, the performance of the induction motor drive is improved by replacing the proportional-integral (PI) controller in the adaption mechanism of RF-MRAS with an adaptive neuro-fuzzy inference system (ANFIS) controller. A prototype model of the three-level neutral point clamped inverter (3L-NPC)-fed induction motor drive is fabricated in a laboratory, and its performance for a RF-MRAS, modified RFMRAS, and modified RFMRAS using ANFIS are compared using different benchmark tests.

Model-Free Predictive Current Control for Three-Level Inverter-Fed IPMSM With an Improved Current Difference Updating Technique

Parameter mismatches in conventional model predictive current control (MPCC) would worsen torque and THD performance. To eliminate the parameter dependence of MPCC, this letter proposes a model-free predictive current control (MFPCC) for a three-level inverter-fed interior permanent magnet synchronous motor (IPMSM). Firstly, to increase the current difference updating frequency in the diode neutral-point-clamped (NPC) three-level inverter, a synchronous updating method is proposed in a manner where the number of updated current differences during one sampling period is increased up to 6. Secondly, for the sake of computational burden alleviation, a candidate vector selection algorithm is introduced in such a way that the number of candidate vectors is reduced to only 7–9. Then, the problem of neutral-point voltage fluctuation which is inherent to the three-level NPC inverter is investigated, and a reasonable replacement method incorporating the redundancy characteristic of small vectors is developed. Finally, experimental results verify that the system robustness against mismatched parameters can be greatly enhanced by use of the proposed control scheme; meanwhile, steady-state performance and dynamic-state response of the system can be improved to some extent as well.

A Generalized Selective Harmonic Elimination PWM Formulation With Common-Mode Voltage Reduction Ability for Multilevel Converters

In this article, a generalized selective harmonic elimination pulsewidth modulation (SHE-PWM) formulation with common-mode voltage (CMV) reduction ability for multilevel converters (MLCs) is presented. The CMV is suppressed by regulating the low-order dominant zero-sequence harmonics (ZSHs) of the three-phase SHE-PWM waveforms. Two formulations are included in the proposed model to achieve the full range operation objective, i.e., with zero low-order ZSHs in low and medium modulation index (m <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> ) range and with an optimal third-harmonic injection in high m <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> range. With the proposed formulation, the amplitude of CMV can be effectively reduced for all types of MLCs over the whole m <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> range. Besides, two kinds of solving algorithms, i.e., off-line and real-time based, are introduced to provide efficient solution tools targeted at the proposed model. In this article, a case study with three-level neutral-point clamped inverters is discussed in detail to better illustrate the proposed formulation and the coupling effects between the CMV reduction and capacitor voltage balancing objectives of MLCs. Simulation and experimental results based on multiple MLC topologies are carried out to validate the effectiveness of this generalized SHE-PWM formulation with reduced CMV values.