Neutral Point Clamped Inverter Research Articles

DC-Link Capacitors’ Voltage Balance in an HB-NPC Five-Level Grid-Tied Inverter via the Common-Mode Control Component

This paper presents a control method to balance, in average, the DC-link capacitor voltages while injecting power to the grid using an h-bridge neutral-point clamped five-level inverter grid-tied through an LCL filter. The method exploits the structure of a particular model representation of the system comprising a differential-mode part and a common-mode part, which turn out to be decoupled from one another. These decoupled representation enormously facilitates the control design as it can be performed as two independent processes as well. The first design process involves the differential-mode model part and focuses on the grid current injection, while the second design process focuses on the balance of the DC-link capacitors voltages, and is based on the common-mode model part. Out of this, two control components are derived, namely differential-mode and common-mode control components, which are later recombined to form the two control signals, one per inverter branch, required as references in a conventional modulation algorithm to generate the switching sequence. Numerical and experimental results are performed to evaluate the performance of the proposed controller for the h-bridge neutral-point clamped inverter subject to those interconnections.

Disturbance Observer Based Sensorless Predictive Control for High Performance PMBLDCM Drive Considering Iron Loss

The control of motor drive without considering iron loss affects the phase back electromotive force and the torque performance. This article investigates the performance of permanent magnet brushless direct current motor (PMBLDCM) modeling taking impact of iron loss into account. A disturbance observer based sensorless scheme is proposed for PMBLDCM model with precise estimation of the rotor angular position. The effect of unmodeled nonlinear parameters on iron loss of PMBLDCM are regarded as disturbances for the proposed sensorless approach. A linear feedback control law with optimal current vector formulation is introduced to minimize the current ripple and torque ripple resulting in reduced copper loss. In order to select optimum switching vector considering the effect of iron loss, a model predictive control technique is proposed for the three-phase three-level neutral point clamped voltage source inverter driven PMBLDCM. The proposed sensorless predictive control (SPC) algorithm is verified both by simulation and experiments. The SPC approach demonstrates improved performance compared to the conventional approach in which the effect of iron loss is not taken into account.

Cascaded control for LCL filter based grid‐tied system with reduced sensors

This work implements a cascaded control for the LCL filter-based grid-connected neutral point clamped (NPC) inverter with the reduced sensor. The conventional three-loop control requires two current sensors for the inverter side, two voltage sensors for the voltage side, and two current sensors for the grid side in total for sensing. This work proposes a novel cascaded control scheme that allows a considerable reduction of grid-side current sensors and capacitor-side voltage sensors. Only two inverter-side current sensors are required for the same. The sensing point is implemented by the proposed estimation algorithm. As an outcome, the hardware complexity, weight, size, and implementation cost of the system are downsized. A comparative assessment is performed between the conventional technique and the proposed methodology. The system is analysed for grid inductance and LCL filter parametric variations in order to assure the robustness and stability of the system. In addition, the system is also investigated for the influence of digital control delay. The implemented system offers enhanced system stability and improved dynamic performance. In order to meet grid regulation, it offers an economical solution. The proposed system is justified by simulated results on the MATLAB/Simulink platform and verified by the experimental results.

Performance Enhancement of a Three Phase Boost-Cascaded Fifteen Level Inverter Using the PI Controller

Photovoltaic power generation is a potential alternative energy source that offers several benefits over other alternative energy sources such as wind, sun, ocean, biomass, geothermal, and so on. Multilevel inverters are essential for power conversion in solar power generation. These multilevel inverters employ three distinct topologies: diode-clamped (neutral-point clamped) inverter, capacitor-clamped (flying capacitor) inverter, and cascaded H-bridge multilevel inverter. The cascaded H-bridge multilevel inverter is more appropriate for photovoltaic applications than the other two topologies. The proposed system asymmetrical cascaded multilevel inverter (ACMLI) is energized using a photovoltaic system (PV). A three-phase cascaded H-bridge fifteen-level inverter for grid-connected solar systems is given in this study utilizing a proportional integral controller. The harmonic distortion was removed using a multicarrier pulse width modulation method. The MATLAB/Simulink is used to simulate the performance of a three-phase cascaded H-bridge fifteen-level inverter in terms of harmonic content and number of switches. To test the performance of the designed system, a hardware prototype was created. From the obtained results, the proposed method reduces the switch count, harmonic distortion, and rejects the external disturbances of input and output variables.

Robust adaptive direct speed control of PMSG-based airborne wind energy system using FCS-MPC method

Electricity generation using airborne wind energy system (AWES) tends to be more efficient than that of conventional wind turbines due to their ability at extracting higher speeds from wind at higher altitudes by the tethered kite generator system (TKGS). The speed regulation of a permanent synchronous machine (PMSM) attached to a kite to maximize harvested power from wind is the topic of the present research. To track the optimal speed produced by TKGS, a finite-control-set model predictive control (FCS-MPC) with a new cost function is directly employed to generate appropriate gate signals for a 3-level neutral point clamped (3-L NPC) inverter that drives a PMSM. A novel adaptive algorithm is also provided for adjusting the weight coefficients of the cost function to improve the system’s performance across a wider range of change in the operating conditions. Moreover, a terminal sliding mode disturbance observer (TSMDO) is designed to estimate the load torque. A terminal sliding mode speed controller (TSMSC) is also used to produce the current reference for the optimizing algorithm in FCS-MPC. The proposed control scheme eliminates the need for a cascade structure while significantly reduces current deformation and torque oscillations. Additionally, the controller operates as fast as a traditional direct speed controller without the use of a cascade structure and is more robust against parameter uncertainties. To illustrate the success of the suggested controller, the results of simulations are presented in MATLAB/SIMULINK® software. The performance of the proposed technique is evaluated in three situations which simulates a grid-connected PMSM fed by a back to back 3-L NPC. In the first scenario, it is demonstrated that the suggested technique performs well when the system’s operational conditions vary. The performance of the adaptive tuning mechanism of the cost function weight factors is investigated in the second scenario, which takes into account model parameter uncertainty. The impacts of the disturbance observer (DO) on the system performance are explored in the final scenario, and it is discovered that the disturbance observer may increase the speed response and DC link voltage tracking performance. All of the simulation results show that the new technique outperformed the traditional FSC-MPC.

Comparative evaluation of different DC-AC converter topologies for cryogenic applications utilizing superconducting materials

Modern transportation applications including electric vehicles (EVs), more electric aircraft (MEA) and electric comprise of different power conversion systems. Reduced weight and improved semiconductor efficiency are the major challenges towards their improved overall performance. To overcome them, cryogenic operation of power electronics converters (CPEC), electric motors, cables, and energy storage components has been under research and evaluation. CPEC are being investigated to drive superconducting machines (SCM) because of their lightweight structure and improved efficiency. CPEC can offer improved switching performance, reduced conduction losses and therefore increased efficiency; because of reduced on-resistance and increased carrier mobility of active devices. This article will discuss how can the benefits of lower operating temperature (< 93 K) be utilized in determining the most suitable DC-AC converter configuration. The paper compares three basic converter topologies: (a) two level voltage source inverter (2L-VSI), (b) three level t-type neutral point clamped inverter (3L-TNPC) and (c) two-level current source inverter (2L-CSI). Analysis is provided based on volume of passive components, electromagnetic interference (EMI) spectra and number of active devices, where all components considered are compatible with low temperatures. It can be observed that utilization of cryogenic temperature affects the volume of passive components, and therefore the overall selection of converter.

Model Predictive Control of PMSM Motor Drive for Electric Vehicle Applications with Space Vector Modulation

The Multi-Level Inverters (MLI) are most predominantly used in industrial applications as they reduce dv/dt ratio, switching stress of the power semiconductor switches, etc. The industries are slowly shifting from three phase inverters to five phase inverters as they produce lower current per phase, less switching losses, low Common Mode Voltage (CMV), etc. The Space Vector Modulation (SVM) is one of the controlling techniques for driving the inverters which reduces the Total Harmonic Distortion (THD) and improves the dc link balancing. The switching vectors available for five phase Three Level (3L) Neutral Point Clamped (NPC) Inverter is 243 vectors, out of which 51 vectors are selected that produce zero CMV. The controlling of the inverter is done by Model Predictive Control (MPC) Technique in which the error is reduced. The performance of the inverter is evaluated through MATLAB Simulink.

New control strategy for multifunctional grid-connected photovoltaic systems

The main aim of this work consists of proposing a new control strategy for multifunctional grid-connected photovoltaic systems (GCPVSs) to enhance the power quality at the point of common coupling (PCC) while considering the inverter-rated capacity. In addition, an Adaptive neuro-fuzzy inference system (ANFIS) based maximum power point tracking (MPPT) controller for a two-phase interleaved boost converter is proposed to improve the dc-link voltage oscillation of the GCPVS. The control strategy takes into account the inverter's rated capacity in terms of power, which is defined by its maximal current modulus. It limits the inverter current to prevent overrating operations, and it also manages the GCPVS's functions: active power injection, reactive power compensation, and current harmonic filtering. The Active power injection into the grid takes precedence over power quality enhancement. Then, The reactive power compensation takes priority over the filtering of nonlinear load current harmonics. The proposed strategy is applied to a grid-connected PV system through an interleaved boost converter and a three-level neutral point clamped (NPC) inverter. Various scenarios with different solar irradiation levels are investigated using MATLAB/Simulink environment. Compared with another existing control strategy in terms of grid current total harmonic distortion (THD) enhancement, the simulations results indicate the superiority of the proposed method. Furthermore, the simulation results also show that the multifunctional GCPVS can perfectly perform all its functions simultaneously with up to 16.95% reduction in grid current THD.

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%.

A Pulse-Width Modulation Control Approach for the High-Voltage Gain Operation of a Z-Source Neutral-Point Clamped Inverters

This paper deals with a developed pulse-width modulation technique for a Z-source three-level NPC inverter. This technique overcomes the limitation of the boost capability of the Z-source NPC inverter; hence, it may suit applications that involve a high-voltage boosting gain. The proposed modulation strategy is based on the discontinuous pulse-width modulation strategy of the neutral-point clamped inverter. It guarantees an improved current and voltage profile at the output and ensures a high-voltage gain by decoupling control for the shoot-through duty ratio and the modulation index. The effectiveness of the proposed modulation strategy is tested through an intensive simulation. Experimental tests, carried out on the digital development board, demonstrate the feasibility of the proposed control.

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.

Combined Vector and Direct Controls Based on Five-Level Inverter for High Performance of IM Drive

The goal of this study was to figure out how to regulate an induction motor in a hybrid electric vehicle. Conventional combined vector and direct control induction motors take advantage of the advantages of vector control and direct torque control. It is also a method that avoids some of the difficulties in implementing both of the two control methods. However, for this method of control, the statoric current has a great wealth of harmonic components which, unfortunately, results in a strong undulation of the torque regardless of the region speed. To solve this problem, a five-level neutral point clamped inverter was used. Through multilevel inverter operation, the voltage is closer to the sine wave. The speed and torque are then successfully controlled with a lower level of ripple in the torque response which improves system performance. The analysis of this study was verified with simulation in the MATLAB/Simulink interface. The simulation results demonstrate the high performance of this control strategy.

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.

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.

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.

High-Gain Observer-Based Fault Detection Scheme for Short-Circuit Switch Faults in Grid-Connected PV Systems by using Optimizers

This paper proposes a model-based fault diagnosis scheme for grid-connected photovoltaic systems with distributed maximum power point tracking (MPPT) strategy. Specifically, short-circuit switch faults in optimizers (boost dc/dc converters in series connection for MPPT purposes) are considered in this study. Depending on the application, SCFs can be more or less detrimental to the stability and integrity of systems. In systems with high penetration, disturbances in voltage or frequency can be generated that can, in the worst case, cause instabilities in the system. Hence, a fast fault detection strategy is mandatory. It is worth noting that, unlike other works reported to date, the control action of the optimizers presents singularities under this fault scenario, making the fault diagnosis task difficult. For this, a decoupled subsystem from i) dc/ac converter dynamics and ii) irradiance changes are obtained for fault and disturbance isolation purposes. Then, a dedicated high-gain observers bank is proposed for a residual generation. In this way, fault time detection is achieved in 8 switching periods. Finally, a numerical evaluation has been carried out to validate the ideas proposed in this paper. For this, three series-connected optimizers interconnected to a three-phase 220V 60 Hz grid through a neutral point clamped (NPC) inverter with a first-order L filter were considered in the simulation.

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.

Improving Power Density of a Three-Level ANPC Structure Using the Electro-Thermal Model of Inverter and a Modified SPWM Technique

Multilevel inverter structures have become an interesting substitute for the well-known two-level inverters in a variety of applications due to their exceptional characteristics when compared to conventional inverters. One major issue regarding multilevel structures is the unequal junction temperature of the switches which deteriorates the power density and increase the cost of the inverter by reducing the maximum achievable output power with a given thermal model and cooling system. Hence, on account of the aggressive goals of power density and cost in a majority of power electronic applications, this article proposes a new technique for reducing the maximum junction temperature of switches in a three-level active neutral-point clamped (ANPC) inverter based on a junction temperature estimation method and a modified SPWM control scheme. This technique can ensure up to a 12% rise in the power density value when compared to basic SPWM techniques with no loss distribution algorithm. Moreover, the suggested approach can be used as a protection stage in the inverter which protects the inverter in transient loads, while allowing for reaching the maximum power capability of the inverter. Finally, the simulations of the proposed technique are validated with experimental results of a 400 V, 20 kW three-level ANPC inverter, controlled by the conventional and proposed techniques.