Three-level Inverter Topology Research Articles

Design and Analysis of a Triple-Input Three-Level PV Inverter with Minimized Number of MPPT Controllers

Photovoltaic (PV) energy has been a preferable choice with the rise in global energy demand, as it is a sustainable, efficient, and cost-effective source of energy. Optimizing the power generation is necessary to fully utilize the PV system. Harvesting more power uses cascading of impedance source converters taking input from low-voltage PV arrays which requires multiple maximum power point tracking (MPPT) controllers. To solve this problem, a three-level inverter topology with a proposed PV arrangement, offering higher voltage boosting and a smaller size with a lower cost suitable for low-voltage panels, is designed in this article. The design criteria for parameters are discussed with the help of the small signal analysis. In this paper, three PV arrays are used to harvest maximum energy, which require only one MPPT controller and employ an extended perturb and observe (P&O) algorithm, being faster, highly efficient, and reducing the computational burden of the controller. Moreover, a three maximum power points tracker algorithm, which perturbs one parameter and observes six variables, is designed for the selected converter topology. Finally, the designed 1.1 kVA grid-connected PV system was simulated in MATLAB (R2023a) which shows that the MPPT algorithm offers better dynamics and is highly efficient with a conversion efficiency of 99.2% during uniform irradiance and 97% efficiency during variable irradiance conditions.

Performance evaluation of multilevel multiphase inverters by piece-wised linearized simulation models

The paper deals with the design issue of the computer simulation models of the traction inverter reflecting request on the rapid investigation of the efficiency performance under various operational conditions. According to this, a piece-wised linearized simulation tool PLECS is selected for model development, which considers the relevant loss behaviour of the main power circuit semiconductor components. The topologies, for which the simulation models are created, are topologies, one of which is commonly used across the automotive industry as the heart of the traction drive (VSI – Voltage Source Inverter), and its perspective alternative three-level traction inverter topology T-NPC – T-type Neutral Point Clamped. The simulation models created in the given simulation tool are thus subjected to the analysis of power parameters, which also include the calculated power losses of the entire system of semiconductor devices for both topologies of the traction inverter. Based on the obtained power parameters, the efficiency performance under various operational conditions of both topologies is evaluated. The presented methodology enables rapid investigation of operational performance enabling fast optimization methods. Any design of linearized simulation models in the PLECS simulation tool, whose core consists of semiconductor elements, can be analyzed by the proposed methodology.

Review, Comprehensive Analysis and Derivation of Analytical Power Loss Calculation Equations for Two- to Three-Level Midpoint Clamped Inverter Topologies with Hybrid Switch Configurations

Increased performance requirements in new power electronics areas of application, such as electric aircraft, make innovations on different design levels necessary. In order to quickly compare different topologies, analytical loss equations provide a fast and straightforward way to narrow down the possible solution space. The approach widely used in the literature results in long and complex terms, which can only be compared between different literature sources with great effort. Moreover, the literature lacks a detailed summarizing description of these analytical equations and their derivation, starting from the standard two-level VSI up to three-level midpoint clamped inverter topologies, such as the ANPC topology in its different modulation schemes. The application of such higher-level inverter topologies allows hybrid device configurations to become performant solutions. This work aims to give a closed-form description of the analytical loss modeling and the theoretical background and provide an implementation approach for a wide span of inverter topologies and for different modulation methods.

A Symmetric Switched-Capacitor-Based Basic Inverter Unit for Grid-Connected PV Systems

In this article, a new inverter unit is proposed. It is a compact switched-capacitor-based inverter, which is combined of four switches, two diodes, and four capacitors. Since this inverter unit is a mid-point-clamped inverter, it can mitigate the capacitive leakage current in many applications. One of the main applications of the proposed inverter is in grid-tied photovoltaic systems, where the common-mode current brings many challenges. Other than the mentioned feature, the proposed inverter includes the following advantages: 1) spontaneous balancing of the voltage across the capacitors without needing any control system or auxiliary circuits; 2) capability of full reactive power transfer; 3) low voltage stress on the capacitors compared to common three-level inverter topologies (NPC, T-type-NPC, FC, etc.); and 4) symmetric switching sequence, which causes a continuous input current. The feasibility and versatility of the proposed inverter unit is validated by experimental tests, which are conducted by using a lab-scale prototype.

Research on Control Method of Neutral Point Potential Balance of T-Type Three-level Inverter Based on PLECS

The T-type three-level inverter topology has the advantages of low electromagnetic interference, high efficiency, and low output harmonic content. This article combines constant power inverter, independent control of active and reactive power output, Analyzed and studied the neutral point potential balance control of the T-type three-level inverter topology. Through PI adjustment control on the amount of charge of the capacitor, the midpoint voltage of the capacitor is always maintained in a balanced state, and the fluctuation of the midpoint voltage is controlled within ±0.23%. This method can effectively avoid the influence of the difference of capacitance parameters on the DC side on the midpoint voltage. The PLECS software simulation verifies the reliability of the capacitor voltage equalization circuit under the condition of the voltage imbalance at the midpoint of the DC side voltage source supply capacitor voltage equalization.

Enhanced Direct Reactive Power Control-Based Multi-Level Inverter for DFIG Wind System under Variable Speeds

A novel direct reactive power control strategy based on the three-level inverter topology (DRPC-3N) is proposed for a doubly fed induction generator (DFIG)-based wind power plant system. The robustness against parametric variations and control performances of the presented methodology are analyzed under random wind speeds, taking into account the effect of the heating of the windings as well as the saturation of the magnetic circuit. The performance indices include obtaining a sinusoidal AC-generated current with low THD and less ripples in the output. Moreover, the generator can be considered as a reactive power compensator, which allows for the controlling of the active and reactive power of the stator side connected directly to the grid side using only the rotor converter. In this study, unpredictable conduct of the wind velocity that forces the DFIG to operate through all modes of operation in a continual and successive way is considered. The received wind power is utilized to extract the optimum power by using an appropriate MPPT algorithm, and the pitch angle control is activated during the overspeed to restrict the produced active power. The simulation tests are performed under Matlab/Simulink and the presented results show the robustness and effectiveness of the new DRPC strategy with the proposed topology, which means that the performances are more sophisticated.

The three-level inverter topologies analysis for application by electric centrifugal pump units

In the article, the schemes for providing AC power with frequency conversion for the induction submersible electric drive of oil production units are analyzed. The electric submersible drive is widely used and has stringent efficiency requirements, so this research is relevant. The centrifugal pump units are composed of a low-voltage power source, a frequency converter, a step-up transformer, a cable line, an electric drive and a centrifugal pump. This article discusses options for replacing the step-up transformer and two-level voltage / frequency converter with a three-level flying capacitor converter (FCC) or a three-level clamping diode converter (NPC). The expected states of the power high voltage IGBT modules are described. The waveforms of the inverter output voltage and the submersible induction motor stator voltage in different circuits are shown. A voltage levels analysis for each module is done, the electric drive starting time change is estimated, the total harmonic distortions (THD) are calculated, and a 1.1% THD reduction by applying the NPC circuit is shown. The harmonic current spectrum for each circuit is presented.

A Single Phase, Single Stage AC-DC Multilevel LLC Resonant Converter With Power Factor Correction

Single stage LLC resonant converters with inherent power factor correction are getting popularity in AC-DC converters due to its reduced size and weight. However, single stage topologies are usually less efficient in regulating the dc bus capacitor voltage pertaining to line and load transients. This paper proposes a multi-level flying capacitor based single stage AC-DC LLC topology to address the issue of voltage balancing of dc-bus capacitor and to reduce the voltage stress of the switching devices. The proposed three-level inverter topology guarantees zero voltage switching, less circulating currents, reduced switching stress and losses. The converter uses bridgeless rectification scheme for better efficiency and the power factor is made nearly unity by operating the source-side inductor in discontinuous current conduction. Variable switching frequency control is used to regulate the output voltage of the converter and pulse width modulation is used to control the dc-bus voltage. This dual control scheme is very effective to keep the dc-bus voltage nearly constant over a wide range of line and load variations. The proposed topology and control scheme have been validated by hardware results on a 250W resistive load.

Sliding mode approach applied to sensorless direct torque control of cage asynchronous motor via multi-level inverter

To improve the robustness and performance of the dynamic response of a cage asynchronous motor, a direct torque control (DTC) based on sliding mode control (SMC) is adopted to replace traditional proportional-integral (PI) and hysteresis comparators. The combination of the proposed strategy with sinusoidal pulse width modulation (SPWM) applied to a three-level neutral point clamped (NPC) inverter brings many advantages such as a reduction in harmonics, and precise and rapid tracking of the references. Simulations are performed for a three-level inverter with SM-DTC, a two-level inverter with SM-DTC and the three-level inverter with PI-DTC-SPWM. The results show that the SM-DTC method achieves better performance in terms of reference tracking, while adoption of the three-level inverter topology can effectively reduce the ripples. Applying the SM-DTC to the three-level inverter presents the best solution for achieving efficient and robust control. In addition, the use of a sliding mode speed estimator eliminates the mechanical sensor and this increases the reliability of the system.

Comparative Evaluation of Lifetime of Three-Level Inverters in Grid-Connected Photovoltaic Systems

The cost of the PV energy reduction is still required to increase the penetration level of PV systems in the energy market. The reliability of PV inverters is one of the important aspects to be enhanced in order to reduce the cost of PV energy, since it is closely related to the maintenance cost and the annual energy production. In this paper, the lifetime of NPC and T-type inverters, which are three-level inverter topologies that are widely used for PV systems, are comparatively evaluated with a 30 kW grid-connected PV system. It is performed by focusing on power devices since the power electronic components of both converters are the same except for the power devices. Therefore, this result can represent the comparison of the reliability performance of the NPC and T-type inverters. The power loss and temperature distributions of power devices are analyzed and their efficiencies are compared at different power levels with different switching frequencies. The lifetimes of the reliability-critical power devices in the NPC and T-type inverters are estimated, respectively with a one-year mission profile of the PV system, and the results are compared.

A Single DC Source-Based Three-Level Inverter Topology for a Four-Pole Open-End Winding Nine-Phase PPMIM Drives

This article proposes a three-level inverter topology for nine-phase pole phase-modulated induction motor (PPMIM) drives by using the two identical voltage profile coils (IVPC) of a four-pole stator winding. In general, the two IVPCs of each phase winding are connected in series, but in this article, these two IVPCs are separated and excited with conventional two-switch inverter legs without disturbing the flux per pole and other machine parameters. The 18 IVPCs of four-pole nine-phase induction motor (IM) are excited with 18 two-switch inverter legs and fed by the same dc source. Each two-switch inverter leg generates the two-level voltage across each IVPC winding, i.e., the resultant voltage seen by the phase winding is a three-level voltage waveform. As compared to conventional nine-phase neutral point and flying capacitor multilevel inverters (MLIs), the requirement of the dc-link magnitude for the proposed topology is reduced by 50%. The nine-phase PPMIM drive is modulated with the carrier-based three-phase space vector pulsewidth modulation in order to enhance the linear modulation range (LMR). The inverter legs associated with two IVPCs per phase in 9-phase 4-pole (9PH-4PO) mode and six IVPCs per phase in 3-phase 12-pole (3PH-12PO) mode are modulated with the same reference wave and phase-displaced triangular waves. This results in the generation of multilevel voltage with improved harmonic voltage profile, i.e., minimizes the torque pulsations of nine-phase PPMIM drive. The validation of the proposed MLI-fed 5 hp nine-phase PPMIM drive is carried out by using the Ansys Maxwell FEM tool as well as with an experimental prototype.

Comparison and optimisation of three‐level neutral point clamped dual output inverter

Multi-level inverter gives low total harmonic distortion when compared to the two-level inverter. A huge number of switches are required to enhance the performance of multi-level inverters. Conventional neutral point clamped (NPC) three-level inverter needs 12 switches to control a single three-phase load. In this research, dual input and output reduced switch count three-level inverter topology with a minimum number of switches is proposed to reduce the system cost, weight and driver circuits. The sinusoidal pulse width modulation (SPWM) control techniques are developed to control NPC dual inverters. The dual inverter with constant frequency and variable frequency mode are simulated by MATLAB Simulink software and the results are discussed in detail. The analysis plan with 15 different combinations of input parameters is developed as per the Box–Behnken method and the results are compared and discussed. Also, the results such as output voltage, VTHD, ITHD and efficiency are analysed by regression analysis and the derived regression equations can be used to predict the output parameters. The combination of input parameters and dual inverter topology, which give optimum output values are identified by composite desirability analysis. This dual inverter reduced switch count topology can be used for renewable energy applications to reduce the inverter cost and space.

Shoot-Through Control-Based Space Vector Modulation Approach for a Modified Z-Source NPC Power Inverter

Z-source Neutral Point Clamped (NPC) inverter is a converter topology that combines the benefits of both the impedance network by storing temporary energy released to the load for voltage boosting and NPC inverter by guaranteeing lower Total Harmonic Distortions (THDs) and reducing voltage stresses of switching devices. In this context, this paper deals with a modified three-level Z-source NPC inverter topology with simplified command to generate shoot-through states and reduce switching losses. For this reason, an extra power switch Insulated Gate Bipolar Transistor (IGBT) is added to insert shoot-through, thus eliminating the need for full-shoot-through on any of the three branches of the inverter. On the other hand, a modified Space Vector Modulation (SVM) strategy is proposed. This gives a number of benefits, both in terms of implementation and harmonic performance. Effectiveness of the proposed topology is verified through simulations using Matlab toolbox Simulation and laboratory experiment.

Neutral Point Potential Balancing Control for NPC Three-Level Inverter Based on Space Vector Modulation

This paper introduced the topology and space vector modulation strategy of NPC three-level inverter. A method of judging the sector where the reference vector located is proposed. The cause of neutral-point potential unbalancing is analyzed. In order to solve neutral-point voltage balancing problem, a control method fully utilizing redundant voltage vectors is proposed. Simulation results verified the correctness and effectiveness of the proposed method.

DC Decoupling-Based Three-Phase Three-Level Transformerless PV Inverter Topology for Minimization of Leakage Current

This letter presents a three-phase three-level cascaded photovoltaic (PV) inverter configuration based on the dc decoupling strategy. The given configuration requires two additional decoupling switches for the minimization of the leakage current. The leakage current is minimized by avoiding or restricting the change in terminal voltages, during the common zero state. Further, a common zero state in all the three phases is obtained using a phase opposition disposition pulsewidth modulation technique. Once the common zero state is realized, the dc decoupling switches are used to isolate the PV source and output load. Apart from the terminal voltage, the proposed configuration also reduces the transitions in the common-mode voltage. Further, this letter also presents an analysis of the terminal voltage using the switching function concept. From the given switching function analysis, an analytical expression of the terminal voltage is derived and is used to obtain the analytical waveform, which matches with the simulation results. In addition to the terminal voltage, the leakage current waveform is also given. Fast Fourier transform spectrums of both are shown. These results are further supported by the experimental waveforms which match both simulation and analytical waveforms. Further, the proposed cascaded multilevel inverter (CMLI) is also compared with the conventional CMLI.

The novel resonant DC link three-level soft-switching inverter

ABSTRACTIn the paper, the novel topology of the resonant DC link three-level soft-switching inverter is proposed to reduce switching losses and improve the efficiency of three-level inverter at high switching frequency. Symmetrical auxiliary resonant circuits are set in the DC link of three-level hard-switching inverter. Moreover, the terminal voltage of the resonant capacitors between the DC buses periodically drops to zero via the resonance of auxiliary circuits. Furthermore, under such condition, the main switches of the three-level inverter would be operated, in order to achieve zero-voltage switching. Based on the equivalent circuits in different operating modes, the paper analyses the working process of the soft-switching inverter in detail. In addition, a 3 kW laboratory prototype of resonant DC link three-phase three-level soft-switching inverter is built. The experimental results show that the main switches and auxiliary switches of the inverter are operated under soft-switching conditions, and the efficiency is significantly improved compared with the three-level hard-switching inverter. Therefore, the proposed topology can effectively reduce switching losses and prove to be more practical in engineering.

Modeling and Simulation of Five-Phase Induction Motor Fed With Pulse Width Modulated Five-Phase Multilevel Voltage Source Inverter Topologies

This paper presents modelling and simulation of five-phase induction motor fed with pulse width modulated five-phase multilevel voltage source inverter. The conventional and diode clamped multilevel five-phase inverter configurations are reviewed with pulse width modulation (PWM) techniques. A hybrid three-level inverter topology with less number of components count is proposed for five-phase induction motor drive. The dynamic analysis of five-phase voltage equations in d-q axis of the induction motor are stated and modelled using Matlab/Simulink/Simscape blocks. The simulation results based on conventional and threelevel five-phase inverters are displayed while the hybrid inverter topology showed some better performance based on the following: : at 0.0127secs maximum torque of 34.54Nm occurred, maximum stator current occurred for 0.18secs with a value of 10A, 9.99% total harmonic distortion was obtained and 15KW power rating was obtained.

A Redundant Unit to Form T-Type Three-Level Inverters Tolerant of IGBT Open-Circuit Faults in Multiple Legs

T-type multilevel (T2ML) inverters feature low total harmonic distortion and high efficiency. Reliability improvement is particularly important for T2ML inverters because they have high power device count. Methods that provide T2ML inverters with the ability to tolerate simultaneous failures of multiple switches in several legs have not been addressed in the existing literature. This paper proposes a redundant unit that can be shared across phases in a T-type three-level inverter topology to manage open-circuit faults in multiple legs. The redundant unit includes two switches and six diodes, with the extra active switches connected by diodes to each middle switch of the base inverter. Under fault conditions, a standby parallel leg consisting of middle switches and the added redundant devices can be formed in each phase of the inverter to provide an extra current path connecting the dc bus and loads. The middle switches can share the redundant unit simultaneously to replace faulted half-bridge switches. By these means, open-circuit faults in multiple legs can be tolerated simultaneously and the rated output capacity can be maintained during faulted operation. Experimental tests are given to verify the effectiveness and feasibility of this proposed fault-tolerant method.

Low‐leakage current two‐stage transformerless grid‐connected converter for residential PV application

Conventional PV-fed three-level DC-DC converter has greater leakage current due to varying common mode (CM) voltage, and thus requires galvanic isolation if interfaced with on-grid inverters. To reduce the leakage current and eliminate the requirement of galvanic isolation, a low-leakage three-level DC-DC converter is proposed for residential application. Efficacy of the converter is demonstrated by proposing a two-stage single-phase on-grid PV system by interfacing with a three-level transformerless single-phase inverter topology. The DC-DC converter has reduced leakage current, which decreases the overall leakage current in the PV inverter system. In addition, smaller filter magnetics are required for both the three-level converter and three-level inverter. The CM analysis of the proposed system is presented. The proposed system is simulated using PSCAD and a laboratory prototype is developed for experimental evaluation. The experimental results show a part-load efficiency of >96% for the overall system. Furthermore, the measured leakage current in the proposed system is <;10 mA, which is below the prescribed RMS limit, as specified in German DIN VDE 0126-1-1 standard.

Fast Finite-Switching-State Model Predictive Control Method Without Weighting Factors for T-Type Three-Level Three-Phase Inverters

Model predictive control (MPC) suffers from high computational burden and cumbersome tuning of weighting factors especially for three-level three-phase inverters. Here, a fast finite-switching-state MPC (FSS-MPC) algorithm without weighting factors is proposed. First, the deadbeat control is used to construct the voltage vector reference. Then, the T-type three-level three-phase inverter topology is selected and voltage vectors are carefully tuned in order to minimize the neutral-point (NP) voltage fluctuation. The voltage vectors that are far from the desired voltage vector reference and go against balancing the NP voltage will not participate in the cost function optimization. Thus, only 3 effective voltage vectors instead of totally 27 vectors are required in the implementation of the proposed FSS-MPC algorithm, which saves computation time up to 53.3%. Furthermore, the proposed algorithm makes the tuning of the weighting factor unnecessary, which simplifies the practical implementation and improves the portability of the algorithm. Finally, an experimental prototype was established and main results including the steady-state and dynamic performance were presented to validate the effectiveness of the proposed algorithm.