Operation Of Inverter Research Articles

Reliability Improvement by Fault-Tolerant Operation of NPC Inverter for Motor Driving

The high-reliability operation of three-level inverters is crucial to prevent equipment damage, process downtime, and economic losses. This paper investigates a three-level neutral-point-clamped inverter under all possible combinations of open-circuit and short-circuit faults and proposes a new postfault operation method without adding extra hardware. This method provides comprehensive solution for operations after single and multiple-device failures, increasing the inverter reliability by 24%. This paper classified post-fault modulations and uncovered previously unknown fault scenarios that can be addressed using the proposed control method. A new postfault modulation based on space vector modulation with virtual vectors is proposed. The feasibility of the proposed control method is verified by simulation and an experiment for one fault scenario in a three-level neutral-point-clamped inverter with a 3.73 kW motor load. This paper contributes to improving the reliability of three-level inverters.

Analysis and Damping of Low-Frequency Oscillation for DC-Link Voltage-Synchronized VSCs

For grid-connected voltage-source converters (VSCs), the dc-link voltage control (DVC) can be merged with the power-based synchronization control, leading to the dc-link voltage-synchronization control. This paper analyzes the low-frequency oscillations of dc-link voltage-synchronized VSCs, which is due to the impact of constant power load/source (CPL/CPS) in the dc link. An active damping method, based on the active power-frequency feedforward (PFF) control with a notch filter, is proposed to dampen the oscillations. It is revealed that the PFF control loop exploits the phase angle dynamic to resist the frequency deviation, which can be essentially treated as an active damper against the dynamics of dc-link CPL/CPS. Further, a loop-gain shaping method is developed for designing the notch filter, which dampens the synchronous oscillations that is inherent with active power dynamics. Experimental tests are performed under different grid frequencies and strengths, considering both the rectifier and inverter operation modes. The results validate the theoretical analysis and the effectiveness of the control approach.

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.

Development and Performance Evaluation of Integrated Hybrid Power Module for Three-Phase Servo Motor Applications.

This study aims to develop a 30 kHz/12 kW silicon carbide (SiC)/Si integrated hybrid power module (iHPM) for variable frequency drive applications, particularly industrial servo motor control, and, additionally, to theoretically and experimentally assess its dynamic characteristics and efficiency during operation. This iHPM integrates a brake circuit, a three-phase Si rectifier, and a three-phase SiC inverter within a single package to achieve a minimal current path. A space-vector pulse width modulation (SVPWM) scheme is used to control the inverter power switches. In order to reduce parasitic inductance and power loss, an inductance cancellation design is implemented in the Si rectifier and SiC inverter. The switching transients and their parasitic effects during a three-phase operation are assessed through an electromagnetic-circuit co-simulation model, by which the power loss and efficiency of the iHPM are estimated. The modeled parasitic inductance of the inverter is validated through inductance measurement, and the effectiveness of the simulated results in terms of switching transients and efficiency is verified using the experimental results of the double pulse test and open-loop inverter operation, respectively. In addition, the power loss and efficiency of the SiC MOSFET inverter are experimentally compared against those of a commercial Si IGBT inverter.

Inverter Operation Mode of a PhotoVoltaic Cascaded H-Bridge Battery Charger

The paper deals with a grid-connected single-phase battery charger integrated with photovoltaic generators (PVGs). The circuit topology consists of a multilevel architecture based on a Cascaded H-Bridge (CHB) rectifier. Its main task is to charge the batteries, primarily from the PVGs, by also assuring to keep their state-of-charge (SOC) balanced. Nevertheless, when the battery SOC overcomes a predefined upper limit, beyond which the charging process could be interrupted, the available PV power can no longer be transferred to the batteries. Therefore, to avoid an undesired curtailment of PV power production, this latter can be supplied to the grid by inverting the system operation. The paper shows how to achieve this result by implementing a dedicated control action based on a multi-step procedure. Numerical investigations are carried out on a 19-level CHB converter implemented in the PLECS environment to validate the feasibility and effectiveness of the proposed control technique.

DER integrated BTB-VSI based DSTATCOM for PQ enhancement

ABSTRACT This article demonstrates the performance of back-to-back connected voltage source inverter (BTB-VSI)-based distribution static compensator (DSTATCOM). In the proposed system, a three-phase three wire electrical utility system (EUS) is integrated with distributed energy resources (DER) through BTB-VSI. It has drawn more attention due to enhanced active power filtering, simple design procedure and performs reliable operation. The objectives of the research work is to provide clean power for weak EUS with improved power quality (PQ) such as, better voltage regulation, improved power factor (P.F), reduced total harmonic distortion (THD), balanced voltage at point of common coupling (PCC) and better optimal active power flow control (OAPFC), and so on. An artificial neurocontrol technique Kernel Hebbian Least Mean Square (KHLMS) is chosen to determine the accurate reference source current for operation of voltage source inverter (VSI). The BTB-VSI performance is investigated on both shunt compensation and OAPFC. The proposed system is converted to a simulation model and hardware unit using MATLAB/Simulink software and SPARTAN−6 field programmable gate arrays (FPGA) controller. Finally, the Simulation and experimental results illustrate that the shunt compensating ability with OAPFC of BTB-VSI performs better over VSI as per IEEE Std 1159–2019 grid code.

A Method Based on NGO-HKELM for the Autonomous Diagnosis of Semiconductor Power Switch Open-Circuit Faults in Three-Phase Grid-Connected Photovoltaic Inverters

With accelerating grid decarbonization and technological breakthroughs, grid-connected photovoltaic (PV) systems are continuously connected to distribution networks at all voltage levels. As the grid interaction interfaces between PV panels and the distribution network, PV inverters must operate flawlessly to avoid energy and financial losses. As the failure of semiconductor switches is the leading cause of abnormal operation of PV inverters and typically cannot be detected by internal protection circuits, this paper aims to develop a method for the autonomous diagnosis of semiconductor power switch open-circuit faults in three-phase grid-connected PV inverters. In this study, a ReliefF-mRMR-based multi-domain feature selection method is designed to ensure the completeness of the fault characteristics. An NGO-HKELM-based classification method is proposed to guarantee the desired balance between generalization and exploration capability. The proposed method overcomes the common problems of poor training efficiency and imbalances between generalization and exploration capabilities. The performance of the proposed method is verified with the detection of switch OC faults in a three-phase H-bridge inverter and neutral-point-clamped inverter, with diagnostic accuracy of 100% and 99.46% respectively.

Online auto-tuning of multiresonant current controller with nature-inspired optimization algorithms and disturbance in the loop approach

This paper presents a novel tuning method of a complex multiresonant current controller (MRCC). An online auto-tuning process is proposed to provide optimal coefficients suitable for the real-time operation of a grid-connected power converter. The time-consuming and inaccurate simulation stage based on the model of the plant is omitted. A novel function of constraints has been introduced into the optimization scheme to ensure the desired behavior of the control system. In this solution, the noise level of a control signal and the rise time of controlled currents are directly defined. To the author’s best knowledge, it is the first time when such a solution is proposed. Next, the most commonly used meta-heuristic optimization algorithms were applied to solve this particular optimization problem. Another original concept presented in the paper is the application of the disturbance-in-the-loop (DiL) approach. In this method, the distorted phase voltages are emulated during the tuning stage, and optimal coefficients of MRCC are selected in the off-grid operation of the power converter. The proposed solution ensures safe and efficient online tuning of the MRCC for an extremely simple performance index. As a result, the high-performance operation of the grid-connected inverter is achieved. A brief stability analysis based on Lyapunov’s stability theory is included. Experimental results obtained for grid-connected inverter indicate superior disturbance attenuation and current tracking. Advantages of the proposed approach are exhibited when compared to two analytical reference solutions.

A techno‐economic model for enhancing PV hosting capacity through capabilities of smart inverters and soft open points

AbstractThe hosting capacity of solar photovoltaics (PVs) in the distribution network can be impacted by the violation of power flow constraints such as power loss, voltage, and line loadings. In this paper, a planning structure based on optimal PV placement and optimal operation of the smart inverters and soft open point (SOP) is proposed in order to investigate the loss of power, voltage profiles, line loadings and total operation cost of the distribution system. The stochastic nature of the daily load and PV generation is considered in power flow optimization by the proposed method. Respective objective functions are optimized using a genetic algorithm (GA) according to probabilistic power flow. While the desired objective function is optimized, the optimality of the PV locations and contribution of smart inverters and SOP is ensured through GA optimization. The proposed model is investigated through numerical analyses on IEEE 33‐bus and IEEE 69‐bus distribution systems considering different cases of reactive power supports. Developed GA is able to deal with challenges of convergence that are imposed by complex nonlinear formulations. Obtained results prove the superiority of the developed program for the investigation of the PV hosting capacity in both technical and cost aspects.

Techno-economic impacts of Volt-VAR control on the high penetration of solar PV interconnection

This paper investigates the operation and control of smart inverters (SI) for solar and solar-plus-storage systems with an emphasis on Volt-VAR Control (VVC) at solar interconnections. The paper provides techno-economic recommendations for both normal-size and oversized solar inverters equipped with VVC. The objective is to minimize the voltage violations, and active power curtailment by providing reactive power support to the grid while the IEEE 1547-2018 standards are satisfied. Moreover, a collaborative VVC is tested where a battery storage system is paired with the solar facility which is becoming a popular configuration to enhance energy resilience in communities. An unbalanced distribution network is modeled based on a modified IEEE 13-bus system to which three 700 kW solar PV plants are connected through smart inverters. Solar data from the University of Louisiana’s 1.1 MW solar farm is used and grouped into 28 clusters. Those clusters represent a 2-year period with 15-min granularity. Typhoon HIL 402 real-time simulator is utilized for modeling and verifying the proposed approach. A control prototype is also developed on dSPACE MicroLabBox to further investigate the interaction between the controller and the rest of the system in a more realistic testing environment.

Nonlinear Modeling and Improved Suppression of Zero-Sequence Circulating Current for Parallel Three-Level Inverters

The parallel operation of three-level inverters can increase the current capacity and power rating of the system. However, the problem of zero-sequence circulating current (ZSCC) inevitably emerges due to the common-mode voltage difference (CMVD) between the parallel three-level inverters (PTLIs). Especially, the inverter nonlinear characteristics (INCs) will worsen the ZSCC problem and weaken the suppression effect of ZSCC. In this paper, a nonlinear equivalent model of ZSCC is established considering the INCs. Then, the simplified graphical analysis method is proposed to implement the frequency analysis of ZSCC. Furthermore, an improved ZSCC suppression strategy for the PTLIs is proposed. The INCs and original CMVD are regarded as the total disturbance and a nonlinear disturbance observer (NDOB) is designed to estimate it. Based on the NDOB, a feedback-feedforward control method is adopted to suppress ZSCC. According to the amplitude-frequency characteristics of the closed-loop control system, the controller parameters design and performance analysis are performed. The control structure is simple, the parameter design is convenient, and the suppression effect of ZSCC is evidently improved. Finally, the simulation and experimental results verify the validity of proposed strategy.

Bang-Bang Funnel Control of Three-Phase Full-Bridge Inverter Under Dual-Buck Scheme

This paper proposes a bang-bang funnel control strategy for the three-phase full-bridge inverter under dual-buck scheme. By adopting the so-called dual-buck scheme, only two switches on the different phase legs are controlled at high frequency, precluding the dead-time utilization. Furthermore, the full-bridge topology can be physically decoupled into two parallel-connected buck units, which allows the inverter to be formulated and analysed by the dynamic model of buck chopper. The bang-bang funnel controller (BBFC) works with just two control values, and it is able to restrain the tracking error between the system's output and the reference within the pre-specified funnel boundaries. The nature of BBFC makes it simpler, faster and more robust, suitable for the inverter operating in dual-buck scheme. The proposed strategy not only guarantees accurate static output performance, but also promotes the inverter's dynamic response against rapid variations of the load, the reference and the input voltage, as well as its robustness to the unexpected parameter changes of the elements. Finally, the effectiveness of the proposed strategy is validated by the simulation and experimental results.

Two-dimensional material-based complementary ambipolar field-effect transistors with ohmic-like contacts

Ambipolar field-effect transistors (FETs) possessing both electron and hole carriers enable implementation of novel reconfigurable transistors, artificial synaptic transistors, and output polarity controllable (OPC) amplifiers. Here, we fabricated a two-dimensional (2D) material-based complementary ambipolar FET and investigated its electrical characteristics. Properties of ohmic-like contacts at source/drain sides were verified from output characteristics and temperature-dependent measurements. The symmetry of electron and hole currents can be easily achieved by optimization of the MoS2 or WSe2 channels, different from the conventional ambipolar FET with fundamental issues related to Schottky barriers. In addition, we demonstrated successful operation of a complementary inverter and OPC amplifier, using the fabricated complementary ambipolar FET based on 2D materials.

Optimized 750V SiC MOSFETs for Electric Vehicle Inverter Operation

We report an AEC-Q101-qualified 750V, 15 mΩ planar SiC MOSFETs with a long short circuit withstand time (SCWT) of > 9μs at VDS=400V and VGS=15V and a low specific on-resistance (RON,SP) of 2.1 mΩ.cm2 at VGS=15V designed for xEV traction inverter applications. The RDS(on) at VGS=15V increases from 15mΩ at 25 °C to 21 mΩ at 175 °C. A low turn-on (EON) and turn-off (EOFF) switching energy loss of 95.5μJ and 67μJ at IDS=75A, VDS=400V was measured at 25 °C. The gate oxide lifetime at worst case operating fields of 5MV/cm is >> 20 years.

Stability analysis of improved combined-mode power converter and power flow control using FPGA

ABSTRACT An improved combined-mode power converter (CMPC) for a solar photovoltaic (SPV) system is presented in this paper. Ten-power electronic switches are utilised for the functioning of the converter. The proposed converter has four modes of operation: buck, boost, inverter, and mixed mode. The new CMPC topology provides a unique and complex switching sequence for implementing the mixed-mode operation. This work uses a field-programmable gate array (FPGA) for mode selection and to create PWM (MS-PWM) signals. A digital MS-PWM controller is configured to switch between improved stepped perturb and observe (ISPO) maximum-power point tracking (MPPT) and sine wave PWM (SPWM). The ISPO provides the appropriate duty cycle for buck/boost operation, while the SPWM controls the inverter operation. This work’s new digital PWM control algorithm supports mode selection, PWM generation, and reconfiguring PWM generation timings. The whole framework for constructing the MS-PWM controller employs a very high-speed integrated circuit hardware description language (VHDL). Simulation and experimental results are presented, proving that the digital MS-PWM controller uses fewer resources with improved accuracy.

The Design and Processor-In-The-Loop Implementation of a Super-Twisting Control Algorithm Based on a Luenberger Observer for a Seamless Transition between Grid-Connected and Stand-Alone Modes in Microgrids

The abrupt transfer from grid-connected (GC) to stand-alone (SA) operation modes is one of the major issues that may threaten the stability of a distributed generation (DG) system. Furthermore, if the islanding mode happens, it is vital to take into consideration the load voltages or load current waveforms as soon as feasible. This paper develops an advanced control technique based on a super-twisting sliding mode controller (ST-SMC) for a three-phase inverter operating in both the GC and SA modes. This control scheme is proposed to ensure a smooth transition from the GC to SA mode and enhance the load voltage waveforms under the islanding mode. In addition, to minimize the operational costs of the system and the complexity of the studied model, a digital Luenberger observer (DLO) with a proper design is adopted for estimating the inverter-side current. The control scheme of the whole system switches between a current control mode during the GC mode and a voltage control mode during the SA mode. The super-twisting control algorithm is applied to the outer voltage control loop involved in the cascaded voltage/current control scheme in the SA mode. Simulation tests of a three-phase inverter are performed for the purpose of assessing the suggested control performance by using the PowerSim (PSIM) software and comparing it with a classical PI controller. Furthermore, a processor-in-the-loop (PIL) implementation in a DSP board TMS32F28335 while debugging is conducted using code composer studio 6.2.0. The obtained results show efficient control properties, such as a smooth transition among the microgrid (MG) operating modes, as well as effectiveness and robustness during both the GC and SA operation modes.

Fault analysis of photovoltaic inverter

Photovoltaic power generation is one of the main forms of new energy utilization, and the reliable operation of a photovoltaic inverter, as the main component of a photovoltaic power generation system, is of great significance. Studying and mastering the faults of photovoltaic inverter and taking preventive measures is very important to ensure the stable and efficient operation of the photovoltaic power generation system. This paper expounds on the development of photovoltaic power generation and the composition of the photovoltaic power generation system, summarizes the typical faults of a photovoltaic inverter, analyzes the causes of the faults, and on this basis, puts forward the improvement measures to avoid the faults.

Comparative analysis and improved design of LLC inverters for induction heating

AbstractThis work presents a comparative analysis and design procedure of a converter based on an LLC resonant inverter used for induction heating applications depending on the transistor technology used and the selected operating frequency. A major objective of the work is to determinate the inverter design requirements leading to the optimal sizing of the components, improving its operation and minimizing power losses. Additionally, it proposes a design to obtain a great insensitivity of the inverter operation against large variations of load impedance. This article analyzes the operation of the inverter where the power regulation is carried out by phase‐shift (PS) modulation. Simple rules are formulated for the design of the resonant circuit components. The design has been verified testing a 25‐kW inverter in an industrial application of induction hardening operating at 500 kHz. Inverter efficiency is around 98.5% when using Silicon Carbide (SiC) MOSFETs.

Improved current droop control strategy of parallel inverters for microgrid based on negative feedback of current

In order to increase the current distribution accuracy of the system and restrain the system frequency fluctuation on the basis of reducing the control operation complexity, this paper proposes an improved current droop control strategy. The strategy can be described as follows: Firstly, a virtual negative inductance and a virtual resistance are introduced into the voltage and current double closed loop control to balance the output impedance of the inverter unit. Then an impedance ratio is introduced to solve the contradiction between the virtual complex impedance and potential drop. Finally, by introducing new current variables and using these current variables to form the negative feedback to the droop coefficient in the voltage equation in the droop control, the allocation of the active current and reactive current is implemented in terms of the inverter capacity, and the plug and play function of the inverter unit is realized in the low-voltage microgrid. A great number of simulation results show that by the strategy, the active and reactive currents output can be distributed in terms of the own capacities of the inverters in the system, the smooth operation of parallel inverters with the same or different capacities is ensured and the computational complexity is simplified.

Sequentially Coordinated and Cooperative Volt/Var Control of PV Inverters in Distribution Networks

Electric distribution grids are seeing an increased penetration of photovoltaic (PV) generation. High PV generation exceeding the grid load demand results in a reverse active power flow in the grid, which raises the voltage level. This paper presents a reactive power controller to overcome the overvoltage problem in the distribution system. A sequentially coordinated and cooperative volt/var control technique is presented. The proposed controller aims to use as low reactive power as possible while mitigating the voltage issues. Accordingly, it reduces the active power loss associated with reactive power flow and reduces the probability for active power curtailment of the PV system. The controller is developed for each lateral and is replicated for all laterals. The lateral controller coordinates the operation of the smart PV inverters in a sequential manner. Cooperative control is proposed between the laterals’ controllers as well and is engaged when the individual laterals’ controllers are unable to solve their overvoltage issues. The performance of the proposed controller is evaluated by comparing it to two other volt/var controllers, and it demonstrates better performance in terms of reactive power requirement. To conduct the simulation study, a modified version of the unbalanced IEEE 13-bus system is utilized, which includes an additional 44 low-voltage bus. The study involves simulating 720 operating points across daily time series. The results indicate that the proposed controller effectively addresses overvoltage problems that occur during periods of high PV generation.