Inverter Side Research Articles

High‐speed main protection for multiterminal LCC‐MMC‐UHVDC based on initial wave process comparison

AbstractThe multiterminal LCC‐MMC‐UHVDC, which employs an LCC on the rectifier side and multiple FHMMCs on the inverter side, has emerged as a cutting‐edge technology. Nevertheless, distinct disparities in their protection requirements compared to those of conventional DC grids pose notable challenges in attaining the desired attributes. This paper first derives variation patterns in the time domain of initial waves under different fault conditions. By utilizing the theoretically calculated rate‐of‐change waveform for the backward current traveling wave in an external fault scenario as a reference, a main protection relay grounded in initial wave process comparison is proposed. This approach capitalizes on the disparity observed in internal faults with the theoretical waveform. To mitigate maloperations stemming from the employment of a non‐directional start‐up criterion in reverse fault scenarios, subtle noise patterns, mimicking the theoretical waveforms, are infused into the actual waveforms. This approach averts maloperations in reverse faults and obviates the need for added delays associated with directional start‐up criteria, thereby enhancing both speed and security. Case studies demonstrate that the proposed protection offers sufficient selectivity and a resistive tolerance of 600 ohms and boasts a speed of 0.2 ms, satisfying the requirements of 800 kV UHVDC systems.

A Novel Single-Stage Boost Single-Phase Inverter and Its Composite Control Strategy to Suppress Low-Frequency Input Ripples

Low-frequency pulsating ripples exist on the input side of a single-phase inverter, which bring some adverse effects and harm to the inverter and photovoltaic power generation system. In order to suppress the low-frequency pulsating ripple and reduce the filter circuit parameters, a novel single-stage boost single-phase inverter is proposed, which can suppress low-frequency ripple. And a three-closed-loop compound control strategy that can suppress input low-frequency ripples under the limitation of an energy storage inductor current and buffer capacitor voltage is proposed. The circuit topology, control strategy, key circuit parameters design, system modeling, and simulation of the inverters are deeply analyzed and studied. Simulation and experimental results show that the inverter has a good ability to suppress input low-frequency ripples.

Modeling of Grid Tied PV Inverter to Improve its Performance During Unbalanced Load and Unbalance Fault

Integrating solar through inverter brings about various challenges in the microgrids and the inverter itself. This paper aims to the study of problems in the operation of inverter during unbalance load and unbalance fault condition along with the possible control measures to mitigate those problems to ensure the safe and reliable operation of the inverter. A grid connected PV inverter is modeled using hysteresis band controller and implementing the MPPT of the PV system with the buck boost converter. During unbalance load and unbalance fault condition, the negative and zero sequence components of current exists. All the zero-sequence component of current is delivered by the grid. The negative sequence component of current also flows through the inverter resulting in high value of current and loss of stability. Also, the voltage across the dc link capacitor increases during fault. The high value of current flowing through the inverter and high voltage across dc link capacitor may damages the inverter and capacitor respectively. An inverter dual current controller is introduced replacing the hysteresis band control such that the negative sequence component of current flowing through the inverter is almost mitigated from 600A to 10A and positive sequence current is also reduced relatively to a tolerable value 150A from 550A. The total current flowing through the inverter is limited to 200A from 950A and voltage across dc link capacitor is limited to 700V from 1050V during LG fault at the inverter side thus ensuring safe operation of the inverter during voltage dip condition. A further study can be done on limiting the positive sequence component of current to a rated value and improving the performance while operating in islanded mode.

Control of Grid-Tied Inverter During Unbalanced Transient Fault

With increasing use of renewable and clean form of energy, PV systems have become popular due to its versatility and easy implementation. The overall performance of grid-connected PV systems is directly influenced by the performance of grid-tied inverter. Hence, control of grid-tied PV inverter has become a temptation. This project explores the development of grid-connected PV system and optimization of control strategies for grid-tied inverter to ensure its seamless operation and grid stability during transient faults. The transient faults occurring at the inverter side disrupts the normal operation of inverter and even lead to shut down of inverter during faults.Therefore, a control strategy is suggested and developed to control the overvoltage of DC-link capacitor and deliberately functioning and output of grid-tied inverter is improved. This is simply possible by introducing ELC so that the inverter needs not be shut down.

Harmonic Self-Compensation Control for Bidirectional Grid Tied Inverter Based on Crown Porcupine Optimization Algorithm

A self-compensating control strategy for harmonic parameters based on the crown porcupine optimization algorithm is proposed for the single-phase rectifier and two-phase inverter operation mode of the bidirectional converter. In order to improve the response speed of the inverter voltage, the instantaneous expressions of the phase angle coefficient and amplitude coefficient of the dc-side voltage doubling fluctuation are derived, and the third harmonic is calculated based on the crown porcupine optimization algorithm according to the Proportional Integral (PI) + Quasi-Proportional Resonance (QPR) double closed-loop control method and injected into the input voltage of the inverter side to offset the influence of the bus-doubling fluctuation on the output voltage of the two-phase inverters of B and C so that the total harmonic content of the two-phase output voltages of the two-phase inverters of B and C can be reduced. The total harmonic content of the B and C inverter output voltages is reduced. The effective control of the control method for single-phase rectifier two-phase inverter mode is verified through simulation. Finally, the effectiveness of the control strategy is verified by experimenting with a 15 kW LCL-type bi-directional converter prototype.

Design of a High Frequency Stability Control Algorithm for Flexible DC Systems

Abstract The suppression scheme of flexible DC high-frequency oscillation needs to be based on model construction. Related literatures have established a high-order linearization model of converter station, gradually revealing the influence of control system and its parameters on impedance characteristics. In order to ensure the full utilization of renewable energy, it is necessary to deeply study the interaction characteristics between multi-terminal VSC-HVDC (Voltage Source Converter based High Voltage Direct Current Transmission) and the receiving power grid, and design a grid-friendly control strategy. In this paper, a VSC-HVDC high-frequency stability control algorithm is established, and a double-ended VSC-HVDC bidirectional VSC stable switching controller is constructed. The switching sequence generated by the controller replaces the control sequence generated by the previous PWM (Pulse width modulation) modulation, so as to weaken the influence of the inner loop current control parameters on the stable operation of the system. The simulation results show that the reactive power fluctuation amplitude of PI control on the inverter side is 0.031 p.u, and the stabilization time is 0.43s. The reactive power fluctuation amplitude of bidirectional VSC stable switching control is less than 0.012 p.u, and the stability time is less than 0.2s. When the single-phase grounding wire is short-circuited, the bidirectional VSC regulator switch has better control performance than the PI regulator switch. Compared with the traditional PI controller, the proposed controller has better stability. The system can quickly enter a stable and non-overshoot operation state, and achieved good control effect.

Research on continuous commutation failure suppression strategy for multi-feed DC transmission system considering harmonic characteristic factors

Abstract Regarding the sustained issues of commutation failures in the hybrid double-fed DC system encompassing Line Commutated Converter High Voltage Direct Current (LCC-HVDC) and Modular Multilevel Converter High Voltage Direct Current (MMC-HVDC, from the perspective of harmonics, the harmonics in the voltage waveform of the AC bus on the inverter side are analyzed. Besides, a commutation failure suppression strategy for the hybrid doubly-fed DC transmission system based on the minimum shutdown area is designed, in which the setting value of the shutdown angle of the harmonic is considered in the minimum shutdown area. The reactive power is obtained by attaching the setting value to the reactive power control link of MMC-HVDC, and the simulation analysis in PSCAD verifies that the strategy can make the MMC-HVDC output more reactive power during the fault in the weak AC system. Increasing the shut-off margin of the manifold reduces the potential for continuous commutation failures in LCC-HVDC.

A fixed‐frequency control method for wireless power transmission battery chargers using a dual‐function compensator

AbstractHigh efficiency and unity power factor (PF) are the most important requirements of a wireless charger system simultaneous with the output voltage regulation. Achieving all above‐mentioned criteria in a wide range of the load is challenging in the system. This paper presents a novel control approach applied to series‐series wireless power transmission converter by using a dual‐function compensator to achieve unity PF and maximum efficiency during the constant power‐constant voltage (CP‐CV) charging scenarios. A semi‐active rectifier with impedance matching capability along with a switch‐controlled capacitor constitutes the dual‐function compensator on the secondary side. Meanwhile, the primary side inverter executes the CP‐CV charging scenario for the battery with various charging characteristics at a fixed‐switching frequency. Besides that, all secondary side switches experience soft switching condition throughout the battery charging. Finally, a prototype with a power of 200 W and roughly regulated efficiency of 90% is presented in order to verify the proposed control method.

Classical versus Collective Interactions in Asymmetric Trigonal Bipyramidal Alkaline Metal-Boron Halide Complexes.

Collective interactions are a novel type of chemical bond formed between metals and electron-rich substituents around an electron-poor central atom. So far only a limited number of candidates for having collective interactions are reported. In this work, we extend the newly introduced concept of collective bonding to a series of neutral boron complexes with the general formula M2BX3 (M=Li, Na, and K; X=F, Cl, and Br). Our state-of-the-art ab initio computations suggest that these complexes form trigonal bipyramidal structures with a D3h to C3v distortion along the C3 axis of symmetry. The BX3 unit in the complexes distorts from planar to pyramidal akin to a sp3 hybridized atom. Interestingly, the interaction of the metals with the pyramidal side of BX3, where the lone pair in a hypothetical [BX3]2- should be located, is weaker than the interactions of metals with the inverted side, i. e., the middle of three halogen atoms. The origin of this stronger interaction can be explained by the formation of collective interactions between metals and halogen atoms as we explored via energy decomposition within the context of the theory of interacting quantum atoms, IQA.

Solar Photo Voltaic Connected Quasi Z Source Inverter for Grid and utility Application

This paper discusses the use of quasi-Z-source inverters, in utility grid systems. These inverters enhanced dependability and one-stage buck and boost abilities make them appropriate for photovoltaic power conditioning applications. The small signal sate space method utilized for the proposed system using Quasi ZSI for utility and grid integration application. Shoot through state also implemented on dc side to enhanced the voltage gain. The Controlling of dc side and ac side also implemented in MATLAB using state space transfer function. A two-stage controlling technique implemented on two level 6 switch inverters with SPWM with P & O MPPT and PI controller. The proposed system has solar PV array rating of 5.5kW and utilized in distribution purpose. A simple boost controlling technique has been implemented to obtained the desired gain and less ripples are present in the current due to the presence of inductor in the QZSI impedance network. During light loading the surplus power injected to the grid with the help of PLL system and when load demand increases the power take from the grid smoothly without loss of synchronism. The system has better stability and fast dynamic response during transient. The THD has been observed at the inverter and load side with LC filter, THD within the permissible limit as per IEEE std 1547.

Transient overvoltage suppression of LCC‐HVDC sending‐end system based on DC current control optimisation

AbstractThe receiving‐end system AC fault of the line‐commutated‐converter‐based high voltage direct current (LCC‐HVDC) will lead to commutation failure of the inverter side. During the fault and its recovery, AC transient low voltage and transient overvoltage (TOV) will occur in the sending‐end system. The TOV has the risk of triggering the disorderly off‐grid of the nearby renewable power generations. Besides, in a serious situation, it will threaten the power system to maintain a secure and steady operation. Therefore, the authors analyse the mechanism involved in the AC transient voltage during the AC fault and the recovery period first. It reveals that the key factor causing the TOV of the sending‐end system is the setting of the DC current reference value. Then, a DC current reference value limit method based on the AC TOV sampling value is proposed, which is used to accelerate DC current recovery and suppress the TOV of the sending‐end system. Finally, the effectiveness of the designed control method has been confirmed through electromagnetic transient simulations using the CIGRE HVDC benchmark model and a ±800 kV HVDC transmission system model situated in Northwest China.

Reduction Method of Zero-Sequence Current in 6-Step Operation on One Side of Dual Inverter with a Common DC-Bus

Reduction Method of Zero-Sequence Current in 6-Step Operation on One Side of Dual Inverter with a Common DC-Bus

The Strategy of Continuous Commutation Failure Suppression by Combining Turn-off Angle Compensation and Dynamic Nonlinear VDCOL

In recent years, with the continuous growth in China’s economy, the continuous advancement of urbanization and industrialization, the contradiction between rapid economic development and the continuous reduction in traditional fossil energy reserves such as coal, oil, and natural gas, the continuous aggravation of environmental pollution has become increasingly prominent. In this era, clean energy power generation technologies such as hydropower, wind power, and solar power generation, which have the advantages of renewability, environmental protection, and economy, have developed rapidly. However, wind and photovoltaic power plants are often located in remote areas, which means significant losses in the transmission process. High-voltage direct current (HVDC) transmission technology becomes the best choice to solve this problem. The HVDC transmission system based on a grid commutator is widely used in China’s AC-DC hybrid power grid. When an AC fault occurs on the inverter side, the line-commutated converter high-voltage direct current (LCC-HVDC) system is more prone to continuous commutation failure, which brings serious harm to system operation. To better suppress the problem of continuous commutation failure on the contravariant side, this paper analyzes the mechanism of continuous commutation failure from multiple angles. The DC current command sensitivity of a voltage-dependent current order limiter (VDCOL) in the LCC-HVDC system is low, which will lead to different degrees of continuous commutation failure. In addition, the rapid rise in DC current and the drop in commutation voltage during the fault will cause the turn-off angle to drop, and the probability of continuous commutation failure of the system will increase significantly. Based on the above theoretical analysis, a new control strategy combining the dynamic compensation of the turn-off angle of a virtual inductor and the suppression of continuous commutation failure by dynamic nonlinear VDCOL is proposed. A dynamic nonlinear VDCOL control strategy is proposed for the low sensitivity of current command adjustment under conventional VDCOL control. Secondly, two concepts of virtual inductance and DC current change rate are introduced, and a control strategy based on virtual inductance is proposed to comprehensively ensure that the switching angle has sufficient commutation margin during fault recovery. Finally, based on the CIGRE standard test model in PSCAD/EMTDC, the accuracy of the correlation mechanism analysis and the effectiveness of the suppression method are verified.

Coordinated DC voltage control strategy for the receiving end hybrid LCC-VSC system

The receiving end hybrid line commutated converter (LCC) — voltage source converter (VSC) system has the obstacle that when an AC fault occurs at the sending LCC side, the DC voltage of the rectifier side will fall, resulting in the power transmission reduction of the whole system. Particularly, when the rectifier side DC voltage falls below the inverter side DC voltage, the power transmission is interrupted, posing a huge threat to the stability of the power grid at both the sending and receiving ends. To tackle these problems, a coordinated DC voltage control strategy for the receiving end is proposed. By controlling the DC voltage of the receiving VSC, the proposed method can improve the DC system power transmission capability when voltage drops at the sending side. The proposed control strategy is simple but practical, which is good for the stable and secure operation of both the sending and the receiving power system.

Enhancing Fault Detection and Classification in MMC-HVDC Systems: Integrating Harris Hawks Optimization Algorithm with Machine Learning Methods

Accurate fault detection in high-voltage direct current (HVDC) transmission lines plays a pivotal role in enhancing operational efficiency, reducing costs, and ensuring grid reliability. This research aims to develop a cost-effective and high-performance fault detection solution for HVDC systems. The primary objective is to accurately identify and localize faults within the power system. In pursuit of this goal, the paper presents a comparative analysis of current and voltage characteristics between the rectifier and inverter sides of the HVDC transmission system and their associated alternating current (AC) counterparts under various fault conditions. Voltage and current features are extracted and optimized using a metaheuristic approach, specifically Harris Hawk’s optimization method. Leveraging machine learning (ML) and artificial neural networks (ANN), this technique demonstrates its effectiveness in generating a fault locator with exceptional accuracy. With a substantial volume of data employed for learning and training, the Harris Hawks optimization method exhibits faster convergence compared to other metaheuristic methods examined in this study. The research findings are applied to simulate diverse fault types and unknown fault locations at multiple system points. Evaluating the fault detection system’s effectiveness, quantified through metrics such as specificity, accuracy, F1 score, and sensitivity, yields remarkable results, with percentages of 99.01%, 98.69%, 98.64%, and 98.67%, respectively. This research underscores the critical role of accurate fault detection in HVDC systems, offering valuable insights into optimizing grid performance and reliability.

A composite strategy for designing efficient harmonic compensators in grid connected inverters with reduced power

The harmonic controlling schemes are very important for renewable energy applications. The power efficient applications are playing significant role in grid connected inverter applications. The measures like power factor, real & reactive power, voltage at (grid, inverter and converter side), current at (grid, inverter and converter side) are need to be improve for efficient power balancing purpose. The earlier models like liner disturbance controlling LADRC, Proportional-Resonant (PR) Control with Comb Filter (PRC-CF) and PI controlling are outdated. Therefore, PR–NF–STFT-Fuzzy logic controller is proposed to cross over the above limitations. This proposed methodology can improve the PRFI-HC dynamic response, PRFI-HC of inverter current and PRFI-HC voltage. Grid-connected inverters may use the suggested approach to emit high and low frequency harmonics. In the event of many external harmonic's sources, a different analysis statement is provided to indicate the highest achievable individual grid current harmonic. At resonance frequencies, the effect of the series damping resistor on the inverter's harmonic rejection capability is examined. The suggested harmonic structure of the converter is matched by the simulations and testing findings.

Core losses analysis of the LCL filter inductor for SiC-based inverter

The ability of SiC devices to switch at high speed allows increasing significantly the power density in both converters and passive components, reducing their required size. To mitigate harmonic injection form inverters into the grid, in order to comply with power quality standards, an accurate filter design is required. Given its excellent performance, an LCL filter is the configuration most suitable in grid-connected power converters. Several parameters must be considered when designing an effective LCL filter, and the inverter-side inductor assumes a special importance because of its relevance to suppress high frequency harmonic content at the inverter side. One of the most relevant issues to be considered in the process of designing the LCL filter is the evaluation of core losses in the inverter-side inductor, which will determine the final temperature of the inductor. This paper analyses the core losses of the inverter-side inductor of an LCL filter. The proposed method is based on the computation of the current harmonics generated by the inverter and on Steinmetz’s empirical equation. As a result, core losses calculated taking into account several carrier and sideband harmonics show good agreement with the experimental values. When current harmonics are estimated by simulation, as it is done in the proposed design procedure, results are less accurate, but precise enough for a design procedure.

A Noninvasive Measurement Technique of Grid and Converter Wideband Impedance

A novel technique has been proposed to simultaneously estimate the wideband Thevenin's impedance of the grid as well as the power electronic converter from measurements sampled at the point of common coupling. The proposed algorithm is non-invasive, thus it can estimate both the impedance of the utility grid as well as the grid-tied inverter from the voltage and current measurements at the point of common coupling. It works by utilizing the harmonic information obtained from the existing voltage and current waveforms. Therefore it can circumvent the requirement of any injecting device to estimate the wideband impedance. The algorithm works on an initial <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Predictor Generation</i> phase, which is an initialization phase based on the design parameters, and a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Realtime Estimation</i> phase which runs after the inverter is commissioned. The Realtime Estimation phase uses the Singular Value Decomposition technique to efficiently utilize the existing harmonic information for the prediction. The efficacy of the technique has been tested in EMTDC/PSCAD simulations of a grid-tied inverter system. Furthermore, a Power Hardware in Loop experimental set-up has been built to validate the simulation results and thus, prove the efficacy of the proposed algorithm. The results show a mean square error of 0.05 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Omega$</tex-math></inline-formula> and 0.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Omega$</tex-math></inline-formula> for the grid and inverter side respectively.

Operation of Dual-T-Type Modular Multilevel Converter for Uninterrupted Power Supply Under Bridge Failures

Dual-T-type modular multilevel converter (DTMMC) is an alternative for existing uninterrupted power supply (UPS) due to its advantage in flexible leg reusing, multiple power ports and high operating efficiency. In this paper, a DTMMC-UPS which has series configurations on both input/output AC sides obtain high voltage grid/ load accessing interfaces is presented. In the described system, the fact that copies of T-type legs are employed makes the semiconductor failure common to happen. Moreover, both the coupling between rectifier and inverter conversions, and the confliction between inter-cell and inner-cell voltage balancing make the fault-tolerant control a tough issue. In this paper, the switch fault types are firstly clarified and diagnosed by the different impacts on the normal operating. An improved voltage vector modulation is then deduced to facilitate the planning of proper primary switching patterns, to achieve rectifier side normal operation. The secondary alternated LS-PWM is also modified to achieve inverter side normal operation. The experiment results are supplied to verify the validity of the modulation coordinated fault toleration strategy.

Development of Solar Power Plant to Support Smart Farming 4.0 at Hubbul Khoir Islamic Boarding School Indonesia

Electricity is a very crucial thing in human life today such as for communications, education, offices, household appliances, and transportation. Unfortunately, most of the electricity in Indonesia is still generated by fossil fuels such as coal. Indonesia which is on the equator has an advantage in solar power generation. Every area in Indonesia gets sunlight for a full year. In this paper, we develop a 1.62 kWp solar power plant at the Hubbul Khoir Islamic Boarding School Indonesia. Energy generated from solar panels is used to support the hydroponic farming system owned by the Islamic boarding school. Economic analysis is used to find out whether the installed generating system is profitable or not. Power quality analysis is used to determine whether the load can be supplied with good power quality. The results obtained by the monitoring system can monitor the PV output power and the power to the load with a display on the LCD screen and on the web with overall accuracy above 96%, economic analysis results show that the system will return on investment after 6.8 years with a profit in the 25th year of Rp20,871,282, and quality the power in this system has good power quality from the PLN side and the inverter side.