Three-level Voltage Research Articles

Performance Analysis of Three-Phase Inverter Using Different Techniques for the Grid- Connected Pv System

The model of a three-phase voltage source inverter is examined based on space vector theory. SVPWM offers an improved outcome with the inverter as compared to the conservative SPWM technique for the inverter. There is a 15.5% upsurge in the line voltage of the inverter. SVPWM better exploits the available DC-link power with the SVPWM inverter. It has been revealed that the SVPWM method utilizes DC bus voltage extra competently and produces a smaller amount of harmonic distortion and easier digital realization in a three-phase voltage-source inverter. For converter‘s gating signals generation, the space-vector pulse width modulation (SVPWM) strategy lessens the switching losses by restricting the switching to two-thirds of the pulse duty cycle. A hypothetical study regarding the use of the SVPWM the three-level voltage inverter and simulation results are offered to prove the usefulness of the SVPWM in the involvement in the switching power losses lessening, output voltages with fewer harmonics. Nevertheless, despite all the above-cited benefits that SVPWM enjoys over SPWM, the SVPWM technique used in three-level inverters is more difficult on account of a large number of inverter switching states. The attained simulation outcomes were satisfactory. As prospects, future experimental works will authenticate the simulation results. A software simulation model is developed in Matlab/Simulink.

Converter-Free Power Delivery Using Voltage Stacking for Near/Subthreshold Operation

Integrated circuits operating in the near/subthreshold region offer low energy consumption. However, due to the constrained voltage scalability of SRAMs, efficient power delivery is difficult to achieve. A traditional implementation would require at least two distinct voltage supplies generated by possibly two power converters. In this article, a new implementation for near/subthreshold operation is presented. The proposed implementation consists of a new “converter-free” design based on a three-level voltage stack operating at 1.8 V ± 5%. Here, the leakage current from the SRAMs in the top stack is recycled to sustain the near/subthreshold operation of the logic circuits in the two lower stacks. A test chip with the proposed voltage-stacking technique was implemented in a 28-nm low- Vth (LVT) fully depleted silicon on insulator (FDSOI) technology. The test chip is an ultralow-power advanced system-on-chip (SoC) consisting of an RISC-V core, a coarse-grained reconfigurable accelerator, and peripherals. The SoC uses a current sink and an adaptive body-bias controller for voltage regulation of the intermediate voltage rails between the stacks. The proposed system achieves up to 95% power delivery efficiency with negligible area overhead (~ 1%). The silicon measurement shows that the system energy efficiency is improved by 1.6× on average, and the energy consumption is reduced by 37% on average compared to the flat implementation.

Robust model predictive control for three-level voltage source inverters

To solve the problem of parameter mismatch in model predictive control (MPC), this paper presents a robust model predictive control method based on a fixed window optimization (FWO) algorithm for a three-level voltage source inverter that only needs to sample the current value. When compared with the traditional observer-based model predictive control (such as the Luenberger observer, sliding mode observer (SMO) and Kalman filter (KMF)), the proposed method does not require an observer with a complicated design, and its algorithm is simple and easy to understand. Meanwhile, high current sampling accuracy is not needed in the proposed method. However, it is necessary in some types of model-free predictive control. In addition, low switching frequency operation and delay compensation are also considered in this paper. In general, the proposed method is simple to implement and does not have high requirements in terms of the accuracy of its current sensor. Experimental results show that the proposed method can accurately estimate parameter values and improve the parameter robustness of MPC.

Topology and Voltage-Balance Control of a Single-Phase Active Neutral Point Clamped Seven-Level Inverter

This article proposed a single-phase active neutral point clamped seven-level (SANPC-7L) inverter topology with only eight power switches and three dc-link capacitors. Compared with the existing single-phase seven-level inverters, the quantity of power switches and voltage stresses across them are both reduced. Modulation logic expression of every switch is derived based on the Karnaugh map technique. Like the existing counterparts with three series-connected dc-link capacitors, there is a severe capacitor voltage imbalance issue. This issue is hard to address as there are no redundant switching states that can be selected to balance the dc-link capacitor voltages. This article gives a comprehensive analysis on the capacitor voltage imbalance issue. It indicates that the over charge or discharge of the middle capacitor voltage is the root cause of this issue, while the upper and lower capacitor voltages can be automatically balanced. To overcome this issue, a variable-reference voltage-balance control method is used to enable a three-level voltage waveform to appear in every switching period, and thus the middle capacitor voltage can be controlled at 1/3 of the dc-link voltage. Both the simulation and experimental results have been presented to verify the proposed topology with the variable-reference voltage-balance control strategy.

Three-level quadratic boost DC-DC converter associated to a SRM drive for water pumping photovoltaic powered systems

This paper presents a water pumping system powered by solar photovoltaic (PV) panels employing a switched reluctance motor (SRM) drive and a three-level quadratic Boost (3LQB) DC-DC converter for a dual output. The DC-DC topology is characterized by quadratic voltage static gain, capability to ensure voltage balance in the output capacitors and reduced voltage stress across power switches and diodes. The three-level voltage of the DC-DC converter allows to connect an asymmetrical half-bridge (AHB) converter integrated into the SRM drive. The DC-DC converter also operates in continuous conduction mode (CCM) which, combined with a proposed maximum power point tracking (MPPT) algorithm, helps to optimize the power supplied by the PV panels. A laboratory prototype was also developed and installed in a workbench to verify its practical implementation considering all devices involved. The tests were performed considering different loads and solar irradiations to verify the system performance under different situations. The PV panels were simulated using a remotely controlled DC power source to impose the typical characteristic I-V curves of the PV panels according to solar irradiation and the water pump behavior was emulated in the laboratory using a controlled torque load coupled to the SRM drive. The experimental results indicate that the proposed solution allows to fully exploit the solar energy to provide as much as possible a continuous water flow in isolated pumping solutions. The operating limits of this solution should be determined by the minimum water flow rate required, necessary head (elevation) and net positive suction head (NPSH).

Voltage profile and power quality improvement in photovoltaic farms integrated medium voltage grid using dynamic voltage restorer

<p class="Abstract">In this paper, we have presented a simulation study to analyze the power quality of three phases medium voltage grid connected with distribution generation (DG) such as photovoltaic (PV) farms and its control schemes. The system uses two-stage energy conversion topology composed of a DC to DC boost converter for the extraction of maximum power available from the solar PV system based on incremental inductance technique and a three-level voltage source inverter (VSI) to connect PV farm to the power grid. To maintain the grid voltage and frequency within tolerance following disturbances such as voltage swells and sags, a fuzzy logic-based Dynamic Voltage Restorer is proposed. The role of the DVR is to protect critical loads from disturbances coming from the network. Different fault conditions scenarios are tested and the results such as voltage stability, real and reactive powers, current and power factor at the point of common coupling (PCC) are compared with and without the DVR system.</p>

FFS modulated VSC with different phase‐shifted 12‐pulse configured transformers for grid integrated large‐scale solar PV plant

The requirement for high capacity power conditioning unit (PCU) has increased for application in large-scale solar photovoltaic (PV) plant for optimisation of the balance of system cost. For high power applications, one of the most important criteria for designing of PCU is to have lower switching losses to minimise the heat generated in the power switching devices. Conventionally, PCU utilises traditional two-level or three-level voltage source converter (VSC) topology with high-frequency switching techniques and due to this, they have lower conversion efficiency and higher device switching losses. In this study, fundamental frequency switching (FFS) modulated three-level neutral point clamp (3L-NPC) VSC is used for MW scale PCU, as they have lower switching losses, higher conversion efficiency and higher AC/DC voltage ratio. The 3L-NPC VSC generates lower order current harmonics, which are mitigated by using different phase-shifted 12-pulse PCU transformers located at different pooling location inside solar PV plant. The PV plant configuration for a 40 MW (AC) plant capacity is developed in the Matlab/Simulink environment and implemented in real-time simulator OPAL-RT to validate the proposed concept. Harmonics, steady-state and dynamic performances are demonstrated at constant and changing solar irradiance levels.

Multi-terminal dc grid overall control with modular multilevel converters

This paper presents a control philosophy for multiterminal DC grids, which are embedded in the main AC grid. DC transmission lines maintain higher power flow at longer distances compared with AC lines. The voltage losses are also much lower. DC power transmission is good option for Russian north. Arctic seashore regions of Russia don't have well developed electrical infrastructure therefore power line lengths are significant there. Considering above it is possible to use DC grids for supply mining enterprises in Arctic regions (offshore drilling platforms for example). Three different control layers are presented in an hierarchical way: local, primary and secondary. This whole control strategy is verified in a scaled three-nodes DC grid. In one of these nodes, a modular multilevel converter (MMC) is implemented (five sub-modules per arm). A novel model-based optimization method to control AC and circulating currents is discussed. In the remaining nodes, three-level voltage source converters (VSC) are installed. For their local controllers, a new variant for classical PI controllers are used, which allow to adapt the values of the PI parameters with respect to the measured variables. Concerning the primary control, droop control technique has been chosen. Regarding secondary level, a new power flow technique is suggested. Unbalance conditions are also verified in order to show the robustness of the whole control strategy.

High performance of sensorless sliding mode control of doubly fed induction motor associated with two multilevel inverters fed by VFDPC_SVM rectifier

A robust sensorless control based on the sliding-mode observer applied to a doubly fed induction motor associated with two three-level NPC-type voltage inverters fed by PWM rectifier with constant switching frequency and without line voltage sensors, is presented in this paper. Also, we present an improved direct power control with virtual flux (VFDPC_SVM) for the control of three phase rectifier. Simulation results of this proposed system were analyzed using MATLAB environment.

A Hybrid Multilevel Inverter Scheme for Nine-Phase PPMIM Drive by Using Three-Phase Five-Leg Inverters

In pole-phase modulation, the phase order is coming down by pole ratio times in high pole mode, which results in the higher magnitude of spatial harmonics as well as higher torque ripple. In this article, the available three identical voltage-fed windings per effective phase in three-phase 12-pole (3PH-12PO) mode are used to develop the simple multilevel inverter (MLI) configuration for minimizing torque ripple. The proposed MLI scheme is realized with three five-leg inverter modules. Each five-leg inverter module will generate three-level voltage across the phase, thereby resultant voltage seen by each phase winding is five-level voltage in 3PH-12PO mode. This multilevel voltage will improve the torque ripple profile of the motor drive. In addition, the proposed MLI scheme along with phase grouping will enrich the linear modulation range of the pole-phase-modulated induction motor (PPMIM) drive in nine-phase four-pole (9PH-4PO) mode. The switches used to generate a multilevel voltage in 3PH-12PO mode are effectively utilized for blocking the flow of circulating currents. As compared with other conventional nine-phase five-level inverters the proposed five-level inverter requires only 30 switches and it does not require extra clamping diodes/capacitors and extra bidirectional switches for isolating neutrals in 9PH-4PO operation. The validation of proposed MLI scheme is done on a 5-hp nine-phase IM with Ansys Maxwell as well as laboratory prototype for entire modulation range using V/f = constant control.

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.

Sensorless DTSMC of a three‐level VSI fed PMSM drive

This study proposes a novel sliding mode control (SMC) structure for a three-level voltage source inverter (VSI). The proposed controller is implemented in discrete time and is applied for the closed-loop speed control of permanent magnet synchronous motor (PMSM) drive powered from a three-level cascaded H-bridge VSI. The proposed discrete time SMC (DTSMC) has the distinct advantages of control over maximum switching frequency and relatively lower total harmonic distortion compared to that of a conventional hysteresis modulation (HM) control. Unlike HM, the proposed DTSMC relates the maximum switching frequency to sampling time, resulting in better utilisation of the bandwidth of the VSI. Additionally, a procedure to combine the DTSMC with a sliding mode observer to achieve sensor-less operation of the PMSM drive is presented. Verification of the proposed DTSMC is conducted using simulation and experimental tests. The simulation and experimental results are presented.

PWM control techniques for three phase three level inverter drives

In this paper two very efficient pulse width modulation techniques were discussed named Sin pulse width modulation and space vector pulse width modulation. The basic structure of the three-level inverter neutral-point clamped is introduced and the basic idea about space vector pulse width modulation for three-level voltage source inverter has been discussed in detail. Nearest three vectors space vector pulse width modulation control algorithm is adopted as the control strategy for the three phase three level NPC inverter in order to compensate the neutral-point shifting. Mathematical formulation for calculating switching sequence has determined. Comparative analysis proving superiority of the space vector pulse width modulation technique over the conventional pulse width modulation, and the results of the simulations of inverter confirm the feasibility and advantage of the space vector pulse width modulation strategy over sin pulse width modulation in terms of good utilization of dc-bus voltage, low current ripple and reduced switching frequency. Space vector pulse width modulation provides advantages better fundamental output voltage and useful in improving harmonic performance and reducing total harmonic distortion.

A Highly-Efficient Fuzzy-Based Controller With High Reduction Inputs and Membership Functions for a Grid-Connected Photovoltaic System

Most conventional Fuzzy Logic Controller (FLC) rules are based on the knowledge and experience of expert operators: given a specific input, FLCs produce the same output. However, FLCs do not perform very well when dealing with complex problems that comprise several input variables. Hence, an optimization tool is highly desirable to reduce the number of inputs and consequently maximize the controller performance, leading to easier maintenance and implementation. This paper, presents an enhanced fuzzy logic controller applied to a photovoltaic system. Specifically, both inputs and membership functions are reduced, resulting in a Highly Reduced Fuzzy Logic Controller (HRFLC), to model a 100kW gridconnected Photovoltaic Panel (PV) as part of a Maximum Power Point Tracking (MPPT) scheme. A DC to DC boost converter is included to transfer the total energy to the grid over a three-level Voltage Source Converter (VSC), which is controlled by varying its duty cycle. FLC generates control parameters to simulate different weather conditions. In this study, only one input representing the current variation (ΔI) of the FLC is used to provide an effective and accurate solution. This reduction in simulation inputs results in a novel HRFLC which simplifies the solar electric system design with output Membership Functions (MFs). Both are achieved by grouping two rules instead of using an existing state-of-the-art method with twenty-five MFs. To the best of our knowledge, this is the first FLC able to provide such rules compression. Finally, a comparison with different techniques such as Perturb and Observe (PandO) shows that HRFLC can improve the dynamic and the steady state performance of the PV system. Notably, experimental results report a steady state error of 0.119%, a transient time of 0.28s and an MPPT tracking accuracy of 0.009s.

Bidirectional Three-Level Stacked Neutral-Point-Clamped Converter for Electric Vehicle Charging Stations

Electric vehicles (EVs) powered by batteries and other energy storage devices (ESDs), e.g., ultracapacitors, are expected to play an important role in the development of a more sustainable future. In this context, charging stations (CSs) are supposed to become the main sources of energy for charging the batteries, being strongly dependent on power electronic converters. This paper analyzes a bidirectional single-phase, three-level stacked neutral-point-clamped (3L-SNPC) converter for CS applications, which may behave as a rectifier or an inverter depending on the power flow direction. Besides, the derived analysis can be easily extended to the development of a three-phase version. Considering that the CS is capable of integrating the utility grid and renewable energy sources, it is possible to absorb or inject energy into the ac grid with high power factor and reduced harmonic content of the current. The main advantages of the bidirectional topology are the existence of a three-level voltage waveform across each leg and the neutral point, while filtering requirements are reduced when compared with typical two-level structures used in EV CSs; the voltage stresses on all semiconductors are equal to half of the total dc-link voltage; power factor is nearly unity in any operation mode; and the voltages across the dc-link capacitors are balanced. The thorough design of the power and control stages is presented, as well as experimental results from a laboratory prototype are discussed in detail.

Interval Type 2 Fuzzy-Logic-Based Solar Power MPPT Algorithm Connected to AC Grid

In this article, an interval type-2 fuzzy logic controller (IT2FLC) is used as a Maximum Power Point Tracker (MPPT) to supply a large scale interconnected grid. The IT2FLC has the advantage of being able to regulate the MPP in case of severe variations of the weather conditions. A photovoltaic array is connected to AC grid via a DC-DC boost converter and a three-phase three-level Voltage Source Converter (VSC). The duty cycle of the boost converter is switched by the IT2FLC. A three phase VSC converts the VDC link voltage to AC and keeps unity power factor. The VSC control system uses two control loops: an external control loop which regulates DC link voltage to alternative current and an internal control loop which regulates the active and the reactive grid currents. Vd and Vq voltage outputs of the current controller are converted to three modulating signals used by the PWM Generator.

Direct torque control of doubly fed induction motor using three-level NPC inverter

This article presents the direct torque control (DTC) strategy for the doubly fed induction motor (DFIM) connected to two three-level voltage source inverters (3LVSIs) with neutral point clamped (NPC) structure. This control method allows to reduce the torque and flux ripples as well as to optimize the total harmonic distortion (THD) of motor currents. The use of 3LVSI increases the number of generated voltage, which allows improving the quality of its waveform and thus improves the DTC strategy. The system modeling and control are implemented in Matlab/Simulink environment. The analysis of simulation results shows the better performances of this control, especially in terms of torque and flux behavior, compared to conventional DTC.

Enhancing the performance of cascaded three-level VSC STATCOM by ANN controller with SVPWM integegration

This article presents a cascaded three-level voltage source converter (VSC) based STATCOM employing an artificial neuron network (ANN) controller with a new simple circuit of space vector pulse width modulation (SVPWM) technique. The main aim of utilizing ANN controller and SVPWM technique is to minimize response time (RT) of STATCOM and improve its performance regard to PF amplitude, and total harmonic distortion (THD) of VSC output current during the period of lagging/leading PF loads (inductive/capacitive loads). The performance of STATCOM is tested using MATLAB/SIMULINK in IEEE 3-bus system. The simulation results clearly proved that the STATCOM with intelligent controller is more efficient compared to a conventional controller (PI controller), where ANN enables the voltage and current to be in the same phase rapidly (during 1.5 cycles) with THD less than 5%.

Wide Load Range ZVS Three-level DC-DC Converter: Modular Structure, Redundancy Ability, and Reduced Filters Size

In future dc distributed power systems, high performance high voltage dc-dc converters with redundancy ability are welcome. However, most existing high voltage dc-dc converters do not have redundancy ability. To solve this problem, a wide load range zero-voltage switching (ZVS) three-level (TL) dc-dc converter is proposed, which has some definitely good features. The primary switches have reduced voltage stress, which is only Vin/2. Moreover, no extra clamping component is needed, which results simple primary structure. Redundancy ability can be obtained by both primary and secondary sides, which means high system reliability. With proper designing of magnetizing inductance, all primary switches can obtain ZVS down to 0 output current, and in addition, the added conduction loss can be neglected. TL voltage waveform before the output inductor is obtained, which leads small volume of the output filter. Four secondary MOSFETs can be switched in zero-current switching (ZCS) condition over wide load range. Finally, both the primary and secondary power stages are modular architecture, which permits realizing any given system specifications by low voltage, standardized power modules. The operation principle, soft switching characteristics are presented in this paper, and the experimental results from a 1 kW prototype are also provided to validate the proposed converter.

A Network Analysis Modeling Method of the Power Electronic Converter for Hardware-in-the-Loop Application

The application of field-programmable gate array (FPGA) in the hardware-in-the-loop simulation (HiLs) has enabled the time step reaching the range of hundreds of nanoseconds. However, the time performance of FPGA-based real-time simulation remains to be improved. In this article, a network analysis modeling method for FPGA-based real-time simulation of the power electronic converter is proposed. An ideal switching network unit, without requiring a large amount of memory, is used to determine the topology of the circuit and solve interface voltages/currents from the torn circuit. A parallel integration method is then implemented to obtain the status of the circuit element. At last, a diode-clamped three-level voltage source converter is used as a case study to demonstrate the effectiveness of the method. A 40-ns simulation step is finally achieved on the National Instruments (NI) FlexRIO PXIe-7975 platform. The accuracy of the proposed method is also verified against the results from MATLAB/Simulink.