Five-level NPC Research Articles

Discontinuous Pulse Width Modulation Strategy for Single-phase Five-level T-type NPC Inverter considering Symmetric Thermal Loadings of Power Devices

Discontinuous Pulse Width Modulation Strategy for Single-phase Five-level T-type NPC Inverter considering Symmetric Thermal Loadings of Power Devices

The improvement of field-oriented control performance for double stator IPMSM based on NFC powered by dual photovoltaic solar panels

This paper presents a proposed method Neuro Fuzzy Control (NFC)-Field Oriente Control (FOC)-Space Vector Modulation (SVM) using IP controller for a five-level NPC inverter-Double Stator Interior Permanent Magnet Synchronous Motor (DSIPMSM) supplied by two photovoltaic solar panels Maximum Power Point Tracking (MPPT) Fuzzy Sliding Mode Control (FSMC). The torque generated and the magnetic flux of the DSIPMSM may be independently controlled thanks to FOC, while IP controllers are used to minimize dq axis current errors to zero. A boost converter is made up of an inductor, a capacitor, and a separate input-output connection. A MPPT approach based on the FSMC algorithm is used to extract the maximum amount of energy from the solar panel while controlling the inverter duty cycle. The NFC tool is an extremely potent instrument that bridges the gaps created by the fuzzy logic controller. The proposed method’s worth was demonstrated by the simulation results in terms of durability, decoupling between the d-q axis, and dynamic performance.

Discontinuous PWM Strategy for Reliability and Efficiency Improvements of Single-Phase Five-Level T-Type Inverter

Reliability and efficiency improvements of PV inverters have a high potential to decrease the cost of PV energy. Discontinuous PWM is an effective method to improve both the efficiency and reliability of the power devices of the single-phase five-level T-type NPC inverter. However, applying DPWM gives a negative effect on the lifetime of the DC-link capacitors and thus reduces the reliability of the inverter from the system-level reliability point of view. This paper proposes the DPWM strategy to improve the lifetime of the DC-link capacitor compared with the conventional DPWM method so that both the reliability and efficiency of the single-phase five-level T-type NPC inverter are improved. Through the proposed strategy, the lifetime of the DC-link capacitor is improved, but its negative effects on the efficiency of the inverter and the lifetime of the power devices are negligible. Therefore, the advantages of applying DPWM can be sustained. Simulation and experimental results verify the feasibility and effectiveness of the proposed DPWM strategy.

Fast-Processing Capacitor Voltage Balancing Algorithm for Single-End Five-Level NPC Converters Based on Redundant Level Modulation

Fast-Processing Capacitor Voltage Balancing Algorithm for Single-End Five-Level NPC Converters Based on Redundant Level Modulation

Three Parts Modulation and Hybrid DC Capacitor Voltage Balancing for a Single-Phase Two-Leg Five-Level NPC Inverter

Capacitor voltage unbalance in NPC multilevel inverters is an inherent challenge and has a severe effect on five and higher-level inverters. Current modulation-based voltage balancing schemes for five-level NPC inverters require a high number of switching, especially at high modulation index operations. Moreover, hardware-based voltage balancing techniques come with a high component count. This paper proposes a unique three-part modulation technique combined with a hybrid voltage balancing approach to reduce switching losses and maintain voltage balancing. The modulation is composed of different carrier-based modulations, while the hybrid balancing scheme combines modulation-based and hardware-based balancing techniques. Comparative switching loss analysis demonstrates a reduction in inverter switching associated with the modulation. While the voltage unbalance characteristics of the modulation are determined considering linear loading conditions. Furthermore, balancing capacity analysis and switching loss reevaluation are used to justify the hybrid balancing performance. The concept verification use Matlab-Simulink simulation and hardware experiments on a five-level single-phase NPC inverter setup operated at different modulation index and power factor conditions.

태양광 시스템에서 불연속 전압 변조 방법 적용에 따른 단상 5-레벨 T-type NPC 인버터의 전력 반도체 소자의 전력손실 및 열 부하 분석

The pulse width modulation method has a significant effect on the power losses and thermal loadings of power devices of a single-phase five-level T-type NPC photovoltaic (PV) inverter. In this paper, the comparative analysis of the power losses and thermal loadings of a single-phase five-level T-type NPC inverter is performed under the different pulse width modulation methods. When the unipolar pulse width modulation method is applied, the power losses and thermal loadings of the power devices are evaluated, and the reliable critical power devices with the highest thermal loadings are identified. Subsequently, the power losses and thermal loadings of the power devices are analyzed by applying the discontinuous pulse width modulation methods such as one-pole clamping pulse width modulation method and equally distributed discontinuous pulse width modulation method. Their effects on the reliability of the inverter are evaluated. Additionally, the operation of a T-type NPC inverter with three PWM methods is verified through the experiment.

Active and Reactive Power Control in Transmission Line with PSO Optimized PI controlled Five Level UPFC

Abstract: In this paper, particle swarm optimization (PSO) optimized PI controlled five level UPFC is proposed for a double circuit transmission line. To enhance UPFC performance, a different approach is considered here. It uses simplified power system models to derive the decoupled power controllers, but detailed modeling of the UPFC power converters improves their ride-through capability. This paper introduces decoupled linear UPFC power controllers to obtain the reference ac voltages and currents for the two back-to-back-connected three-phase five-level NPC converters that enforce active and reactive power control in the transmission line. This paper proposes three main contributions to increase the dc-link voltage steadiness of multilevel UPFCs under line faults: 1) decoupled active and reactive linear power controllers; 2) real-time PWM generation; and 3) balancing of dc capacitor voltages. The MATLAB/SIMULINK model for the proposed circuit with PSO-optimized PI controlled five level UPFC is shown here with the results.

Active and reactive power control in transmission line with PSO optimized PI controlled five level UPFC

In this paper, particle swarm optimization (PSO) optimized PI controlled five level UPFC is proposed for a double circuit transmission line. To enhance UPFC performance, a different approach is considered here. It uses simplified power system models to derive the decoupled power controllers, but detailed modeling of the UPFC power converters improves their ride-through capability. This paper introduces decoupled linear UPFC power controllers to obtain the reference ac voltages and currents for the two back-to-back-connected three-phase five-level NPC converters that enforce active and reactive power control in the transmission line. This paper proposes three main contributions to increase the dc-link voltage steadiness of multilevel UPFCs under line faults: 1) decoupled active and reactive linear power controllers; 2) real-time PWM generation; and 3) balancing of dc capacitor voltages. The MATLAB/SIMULINK model for the proposed circuit with PSO-optimized PI controlled five level UPFC is shown here with the results.

DPWM Applying for Five-Level NPC VSI Powered by PV-Boost Converter Based on Takagi Sugeno Fuzzy Model

Power quality is interesting issue for power conversion PV system. Further there are challenges associated with extract of maximum power and minimize the part losses in commutation. In this paper, a three-phase five-level NPC voltage source inverter (VSI) using discontinuous pulse-width modulation (DPWM) and feeding by a PV/DC-DC boost converter based on a Takagi-Sugeno T-S fuzzy controller is presented. The photovoltaic energy system is described by nonlinear equations. A T-S fuzzy model is used to transform the nonlinear equations into a fuzzy model by modeling the irradiation, temperature and output voltage parameters. The control parameters have been computed based on Linear Matrix Inequalities tools (LMI) and the stability of the system is ensured by Lyapunov approach. In the second stage for power conversion (DC/AC), a discontinuous pulse-width modulation (DPWM) is used and approved; it offers the possibility of reducing switching losses and the THD harmonic rate. The simulation was performed in the MATLAB/Simulink software using an R-L load and the obtained results are confirmed the feasibility and reliability of the proposed method for the PV conversion system.

An Optimized Hybrid PWM Strategy for Five Level NPC VSI With Unequal DC-Links in a PV System

This article presents an optimized hybrid pulsewidth modulation (PWM) strategy for five-level neutral point clamped (5L-NPC) inverter with unequal dc-link capacitor voltages fed by differential power processing (DPP)-based photovoltaic (PV) system. The generation of balanced output from the 5L-NPC inverter with the unequal dc-link capacitor voltages becomes necessary in a PV system. The unequal dc-link capacitor voltages cause low order harmonics in inverter output voltage. A hybrid PWM strategy combining the advantages of space-vector PWM (SVPWM) and the nearest level modulation (NLM) methods is proposed to address the issues associated with unequal dc-link capacitor voltages in a five-level NPC inverter. The proposed hybrid PWM is optimized to achieve balanced output voltage with less total harmonic distortion at fundamental frequency. In-depth theoretical analysis of sector identification algorithm and dwell time computation for the proposed optimized hybrid PWM method are described. Simulation and experimental results are illustrated for several combinations of unequal dc-link capacitor voltages to validate the functionality and performance of the proposed optimized hybrid PWM method.

Fault Detection and Tolerance of a Hybrid Five Level Inverter

Multilevel inverters (MLIs) have received a significant attention in literature due to advent of various topologies utilising power semiconductor switches with reduced voltage stress. However, the increased component count and susceptible nature of semiconductor components increase the chance of failure in inverter. The fault in power switches, either open circuit or short circuit, if persist for long time may result in complete system shutdown. This damage can be avoided by detecting and diagnosing the fault in less period of time to continue the healthy operation. The present paper studies an open-circuit fault detection method on conventional five-level NPC inverter topology with output voltage waveform analysis by discrete wavelet packet transform (DWPT) and classifying the fault location by artificial neural network (ANN). The strategy to tolerate both abovementioned type of failure on any location after detection is proposed by implementing a novel redundant architecture in conventional five-level inverter. This architecture has an advantage of utilising less device count to tolerate fault on single as well as multiple switch combinations. The proposed work is studied in MATLAB/Simulink and validated experimentally.

Comparative Evaluation of Efficiency and Reliability of Single-Phase Five-Level NPC Inverters for Photovoltaic Systems

It is required to reduce the cost of PV energy to be competitive as an alternative energy source. The efficiency and reliability of PV inverters are important aspects to be enhanced to reduce the cost of PV energy since they contribute to the reduction of operational and maintenance costs and to the increase of annual energy production. Therefore, more comprehensive analysis on both efficiency and reliability together including the impacts of various factors is required. In this paper, single-phase five-level NPC inverter topologies for photovoltaic systems are comparatively evaluated in terms of efficiency and reliability by simulations and experiments, in which the impacts of pulse width modulation (PWM) methods and installation locations are considered. The results are expected to give an insight to determine the proper topology and PWM method depending on its installation location considering the reliability as well as the efficiency and total harmonic distortion (THD).

Neutral-Point Voltage Balancing Method for Five-Level NPC Inverters Based on Carrier-Overlapped PWM

Neutral-point voltage imbalance is one of the main problems of five-level neutral-point clamped inverters that impedes their industrial application. In order to solve this problem, a closed-loop neutral-point voltage balancing method based on carrier-overlapped pulsewidth modulation (COPWM) is proposed in this article. The four dc-link capacitor voltages are balanced by three steps: voltage balancing between the two outer capacitors, voltage balancing between the two inner capacitors, and voltage balancing between the two inner and the two outer capacitors. The relationship between the neutral-point currents and the reference voltage is studied, and the top and the bottom dc-link capacitor voltages are balanced by zero-sequence voltage injection. The two inner capacitor voltages are balanced by adjusting the width of switching signals. Simulation and experimental results are presented to confirm the validity of this method.

DC capacitor voltage stabilization for five-level NPC inverter based STATCOM under DC offset in load

DC voltage regulation of compensator plays a significant role in tracking performance of STATCOM. It is a common practice to employ voltage source inverter with split – capacitor topology for shunt compensator in three phase four wire systems. However, drift in each capacitor voltage is observed with the presence of dc component in zero sequence current although STATCOM control unit regulates total dc voltage, which results in poor tracking of reference current by the compensator. An external voltage balancing circuit is identified to be a good solution to overcome this problem. This paper proposes an improved controller for external voltage balancing circuit to restore the dc capacitors voltage. The effectiveness of the proposed control of external voltage balancing circuit is verified by simulation results showing restoration of capacitors voltage drift and there by the restoration of tracking performance of the compensator.

Generalized Synchronous Optimal Pulse Width Modulation for Multilevel Inverters

With the growing interest of the industry in high-power medium-voltage multilevel inverters and the technological limitation in high voltage power semiconductors switches, synchronous optimal pulse width modulation techniques, originally developed for two-/three-level inverters, became again a topic of interest, now to optimize multilevel waveforms. This work proposes a novel formulation for the problem of optimizing the modulation pattern of multilevel converters, including in a single optimization problem the decision of the directions for each step transition in addition to the switching angles and, thus, completely defining the optimized multilevel waveform at a given modulation index. In addition, experimental results are presented in order to demonstrate the effectiveness of this optimized modulation technique exemplar applied to a five-level NPC H–bridge feeding a permanent magnet synchronous motor.

Backstepping Control of Induction Motor Fed by Five-Level NPC Inverter

In this paper we will present a contribution to the backstepping control for induction motor (IM) based on the principle of Field Orientated Control (FOC). This law is established step by step while ensuring the stability of the machine in the closed loop, by a suitable choice of the function Lyapunov, In addition it is executed to assure the convergence the error´s speed tracking at all initials conditions are possible. Both the speed and the rotor flux are supposed obtained by sensors. The control of the IM by five-level NPC inverter generally uses Pulse-width modulation techniques (PWM). Finally, we represent some of the simulation results by simulations in Matlab/Simulink environment.

Direct Torque Control of Reversing Voltage Topology Multi-Level Inverter Fed Induction Motor

Variable speed induction motor drives find applications in various industries. The normal Induction Motor drive has a closed loop speed control. Here, we use a Multi- Level Inverter (MLI), which has emerged as an alternative in the medium-voltage high-power control to feed the Induction Motor. The Multi-Level Inverter employs a new topology known as the reversing voltage topology (RVT). To generate output voltage with higher number of levels, this topology requires less number of components and less carrier signals for PWM implementation. The proposed induction motor drive structure offers reduced device count and a simpler power-bus structure when compared to a conventional five-level NPC and flying capacitor inverter fed induction motor drives. The Induction Motor is controlled by the scalar method of Direct Torque Control (DTC). This scheme is the direct control of the torque and stator flux of a drive by inverter voltage space selection through a look-up table to maintain speed at reference. Performance comparison for various voltage vector selections has been made. This technique has a comparable performance with that of vector controlled drives

New Control Strategy of Three-Phase Five-Level NPC Rectifier -Inverter System for Induction Machine Drive

This paper proposes a control strategy of a three –phase five-level double converter for induction motor drives. The converter consists of the five-level NPC rectifier, DC link, and the five-level NPC inverter. In this control strategy, the DC link voltages are controlled by using a closed loop with an optimized stabilization system called clamping bridge. It provides a fast and flexible control of the converter capacitor voltage. This method will redress the imbalance of DC link voltage. This control strategy is completely independent from the load control, leading to a simpler implementation. The three-phase five-level NPC rectifier-inverter system is an ideal interface between a utility and renewable energy sources such as photovoltaic or wind generator.

Comparative Study between Different Modulation Strategies for Five Levels NPC Topology Inverter

The object of this paper is the study of various modulation strategies applied to the five-level inverter neutral-point-clamped NPC topology. Firstly we presented the structure of the voltage inverter three-phase five-level NPC topology. After that we model the inverter and the inverter are controlled by different strategies and then we made a comparative study between the results given by different strategies.

Fast optimum-predictive control and capacitor voltage balancing strategy for bipolar back-to-back NPC converters in high-voltage direct current transmission systems

Multilevel power converters have been introduced as the solution for high-power high-voltage switching applications where they have well-known advantages. Recently, full back-to-back connected multilevel neutral point diode clamped converters (NPC converter) have been used in high-voltage direct current (HVDC) transmission systems. Bipolar-connected back-to-back NPC converters have advantages in long-distance HVDC transmission systems over the full back-to-back connection, but greater difficulty to balance the dc capacitor voltage divider on both sending and receiving end NPC converters. This study shows that power flow control and dc capacitor voltage balancing are feasible using fast optimum-predictive-based controllers in HVDC systems using bipolar back-to-back-connected five-level NPC multilevel converters. For both converter sides, the control strategy takes in account active and reactive power, which establishes ac grid currents in both ends, and guarantees the balancing of dc bus capacitor voltages in both NPC converters. Additionally, the semiconductor switching frequency is minimised to reduce switching losses. The performance and robustness of the new fast predictive control strategy, and its capability to solve the DC capacitor voltage balancing problem of bipolar-connected back-to-back NPC converters are evaluated.