Unbalanced Load Conditions Research Articles

Robustness of unified power quality conditioner by neural network based on admittance estimation

This paper attempts to improve the dynamic performance of unified power quality conditioner (UPQC) by using of neural network based on admittance estimation strategy (NN-ADES). For improve the efficiency, tracking capability and robustness of UPQC, a control strategy is used for estimation of fundamental admittance components (conductance and susceptance) of distorted source voltage. In this method, the admittance components weight values of estimated admittance components input conductance clustered value which is very near to weight values of actual admittance components. The NN-ADES strategy is suitable for where load periodicity not constant. The neural network admittance estimation strategy for UPQC is implemented using MATLAB and FPGA board for mitigating balanced or unbalanced load conditions, voltage sag or voltage swell and harmonics of source voltage. Test results of proposed UPQC have produced acceptable results under balanced/unbalanced load conditions.

A modified energy management scheme to support phase balancing in grid interfaced photovoltaic/fuel cell system

This paper presents improved energy management for grid-inverter of a hybrid photovoltaic (PV)/fuel cell (FC) energy system with unbalanced sensitive loads. In the system, unbalanced loads draw unbalanced currents at each phase and consume power from energy units at different levels. This condition makes the grid unbalanced, which cannot be compensated by a conventional energy management controller used in grid inverters. For this, a phase balancing control method is proposed in order to improve the grid quality under unbalanced loading conditions. The proposed method calculates power differentiation values based on multiple-frame αβ/dq transform instead of abc/dq transform in the conventional method. Thus, it eliminates negative & zero sequence components in addition to power flow control. Under unbalanced loading conditions, the proposed method removes the deficiency of the conventional energy management method which generates the symmetrical current references to trigger the switching elements of the inverter. In performance results, the system with unbalanced loads is tested for different case studies, which supply different power from energy units to grids. The results show that the proposed method provides power balancing at the grid-side and eliminates negative & zero sequence components at grid-side currents.

Zero-Sequence Voltage Injection Method for DC Capacitor Voltage Balancing of Wye-Connected CHB Converter under Unbalanced Grid and Load Conditions

Leg capacitor energy balancing control is one of the crucial issues for stable operation of a cascaded H-bridge (CHB) converter. Because this topology inherently consists of numerous submodule cells with DC capacitors, the cell voltages and leg capacitor energy instantaneously fluctuate depending on operation sequence of the CHB converter. In general, a wye-connected CHB-converter-based static synchronous compensator (STATCOM) utilizes a zero-sequence voltage component for leg capacitor energy balancing. In this paper, to improve the dynamics of leg energy balancing control, a feedforward calculation method of the zero-sequence voltage injection is proposed. The feedforward term can be instantaneously calculated by using the information from the measured leg voltages and leg currents, and the method ensures successful regulation of the leg energy balance even under unbalanced grid and load conditions. Moreover, the verification of the proposed method is supported by the mathematical vector theorems. A 50MVA full-scale wye-connected CHB–STATCOM system simulation was performed to verify the proposed feedforward calculation method considering unbalanced grid as well as unbalanced load conditions.

Power Quality Enhancement in Grid-Connected PV/Wind/Battery Using UPQC: Atom Search Optimization

Nowadays, the integration of hybrid renewable energy system (HRES) in grid connected load system are encouraged to increase reliability and reduce losses. The HRES system is connected to the grid system to meet required load demand and the integrated design creates the power quality (PQ) issues in the system due to non-linear load, critical load and unbalanced load conditions. Hence, in this paper, atom search optimization (ASO) with unified power quality conditioner (UPQC) is designed to solve the PQ issues in HRES system. The main objective of the work is the mitigation of PQ issues and compensate load demand in HRES system. The PQ issue problems are solved with the help of UPQC device in the system. The UPQC performance is increased by introducing fractional order proportional integral derivative (FOPID) with ASO based controller in series and shunt active power filter to mitigate PQ issues of current and voltage. Initially, HRES is designed with photovoltaic (PV) system, wind turbine (WT) and battery energy storage system (BESS) which connected with the load system. To analysis the presentation of the proposed controller structure, the non-linear load is connected with the system to create PQ issues in the system. The PQ issues are mitigated and load demand is reimbursed with the assistance of HRES system. The proposed method is employed in the MATLAB/Simulink platform and performances were analysed. Three different cases are used to validate the performance of the proposed method such as Sag, Swell, and disturbances. Additionally, total harmonic distortion (THD) is analysed. The proposed method is compared with existing methods of proportional integral (PI) controller, gravitational search algorithm (GSA), biogeography based optimisation (BBO), grey wolf optimization (GWO), extended search algorithm (ESA), random forest algorithm (RFA) and genetic algorithm (GA).

Reliability and Economic Efficiency Analysis of 4-Leg Inverter Compared with 3-Leg Inverters

The 4-leg inverter can adjust the load current or output voltage even under unbalanced load conditions, but it is known that the additional switch arm to the 3-leg inverter can increase the overall cost and the failure rate. This paper aims to analyze the failure rate and mean time between failures (MTBF) of 3-leg inverters and 4-leg inverters using part count failure analysis (PCA) and fault-tree analysis (FTA), and to compare the price of the inverters. The FTA can analyze the failure rate, including the type, number and connection status of the circuit components, and moreover the redundancy effect of the 4-leg inverter. For more accurate failure-rate prediction, the failure rate and MTBF of the 4-leg inverter according to the lifecycle of the controller are analyzed. Finally, by comparing the price of 3-leg inverters and 4-leg inverters using the cost model of major parts, the degree of reliability improvement against price increase is quantitatively analyzed.

A Duality Based Quasi-Steady-State Model of Three-Phase Five-Limb Sen Transformer

A three-phase five-limb transformer is a potential application form of the Sen Transformer (ST), especially for the scenarios with significantly unbalanced load conditions. This paper proposes a quasi-steady-state model of three-phase five-limb ST (TPFLST) based on duality. Firstly, an equivalent circuit model that takes into account the eddy current effect and the coupling effect involving the magnetic circuit can be derived according to the equivalent magnetic circuit of the TPFLST. The iron-core of the TPFLST may be represented by the parallel combination of the resistances reflecting the power loss of the iron-core and the saturable inductances considering the ferromagnetic hysteresis in virtue of the principle of duality. Subsequently, an electric circuit model of the voltage and current of each winding for the TPFLST is able to be accomplished on the basis of the electrical connection between the TPFLST and the external systems in accordance with Kirchhoff’s voltage and current law. Consequently, a quasi-steady-state model of the TPFLST which considers the coupling relationship involving the magnetic and electric circuits can be formed by combining the equivalent circuit model and the electric circuit model. With the help of MATLAB, the effectiveness of the proposed model may be verified by comparing the results about power flow control including power, voltage, and current with the ones from the existing literature. Furthermore, the TPFLST is found to be better-suited for the unbalanced load condition according to a comparison among the unbalanced degrees of output currents for the STs with different core structures under unbalanced load conditions.

Grid Integration of Renewable Energy Sources using GA Technique for Improving Power Quality

Hybrid Renewable energy sources (HRES) are rapidly increasingly compared to the traditional system since they are less effective to the environment and meet the huge demand required by the utilities. In the proposed paper the modelling, control and design analysis is implemented with PV, wind and battery as an energy storing device. The grid-interfacing inverter is regulated with a single-stage, three-phase RES-based distributed generation (DG) system. A genetic algorithm (GA) based shunt active power filter (SHAPF) is used to mitigate the power quality issues under nonlinear and unbalanced load conditions. The DG is grid-connected through a current-controlled –voltage source inverter (CC-VSI) via a DC link capacitor. Here the VSI is utilized to transfer the power from DG to the point of common coupling (PCC), SAPF to compensate for load current harmonics, under distorted supply voltage conditions, reactive power demand and load current imbalance. Both of these functions are important either individually or concurrently. As a result, the proposed controller regulates the power flow, controls it and acts as a SHAPF or does both at the same time. The proposed method is employed in the MATLAB/Simulink platform and performances were analysed.

Stress analysis of different cross-section for passenger truck chassis with a material of ASTM A148 Gr 80–50

This research aims to optimize on an optimal condition to increase the capacity of passenger truck chassis and focus analysis of stress for the different cross-section in different loading conditions with the consideration of stress concentration factor. Chassis is a significant component in the vehicle, and different types of failures occur due to static loading conditions. Unbalanced loading conditions in the construction of lorry and passenger trucks; the actual unloading carrying capacity for passenger bus is less than the lorry one in the local area. Maximum stress and maximum deflection are the main criteria for designing the passenger truck chassis. The present study determined the maximum stress and maximum deflection to recognize critical regions under loading. Stress was analyzed using different cross-sections under different loading conditions. As a result, I cross-section is important to increase the chassis capacity, and the effects of stress concentration factor are necessary to choose the essential profile. And that used to fix chassis characteristics of the static condition. Finite element analysis enables to predict the region that tends to fail due to loading implemented. This study definitively answers the question regarding chassis stress analysis in different cross-sections and loading conditions. I cross-section is the best, which has less stress and deflection.

DC Voltage Balancing Strategy of a Bipolar-Output Active Rectifier for More Electric Aircraft Based on Zero Vector Redistribution

The ±270 V bipolar dc distribution has become an attractive power supply scheme in more electric aircraft (MEA). In this paper, a dc voltage balancing strategy based on zero vector redistribution (ZVR) is proposed for a three-phase coupled inductor-based bipolar-output active rectifier (TCIBAR) to achieve balanced ±270 V power supply for MEAs. First, the mathematical model of the TCIBAR is developed in the rotating reference frame and the zero-sequence equivalent circuit of the three-phase coupled inductor (TCI) branch is derived. On this basis, the effect mechanism of the zero-sequence voltage is analyzed in balancing the output dc voltages of the TCIBAR. Second, a voltage balancing control scheme is designed to control the zero-sequence voltage and maintain the dc voltage balance of the TCIBAR under unbalanced load condition. Finally, a ZVR - space vector pulse width modulation (ZVR-SVPWM) method is proposed. With the ZVR-SVPWM method, the duration time of zero vectors can be redistributed to modulate the desired zero-sequence voltage for the TCIBAR. The proposed dc voltage balancing strategy for the TCIBAR is implemented on an experimental platform, and the experimental results verify the feasibility and effectiveness of the proposed control scheme and ZVR-SVPWM method.

Mathematical Morphology-Based Artificial Technique for Renewable Power Application

This paper suggests a combined novel control strategy for DFIG based wind power systems (WPS) under both nonlinear and unbalanced load conditions. The combined control approach is designed by coordinating the machine side converter (MSC) and the load side converter (LSC) control approaches. The proposed MSC control approach is designed by using a model predictive control (MPC) approach to generate appropriate real and reactive power. The MSC controller selects an appropriate rotor voltage vector by using a minimized optimization cost function for the converter operation. It shows its superiority by eliminating the requirement of transformation, switching table, and the PWM techniques. The proposed MSC reduces the cost, complexity, and computational burden of the WPS. On the other hand, the LSC control approach is designed by using a mathematical morphological technique (MMT) for appropriate DC component extraction. Due to the appropriate DC-component extraction, the WPS can compensate the harmonics during both steady and dynamic states. Further, the LSC controller also provides active power filter operation even under the shutdown of WPS condition. To verify the applicability of coordinated control operation, the WPS-based microgrid system is tested under various test conditions. The proposed WPS is designed by using a MATLAB/Simulink software.

Analysis of Fractional Order Sliding Mode Control in a D-STATCOM Integrated Power Distribution System

At present, the disturbances like the voltage fluctuations, resulting from the grid’s complexities and unbalanced load conditions, create severe power quality concerns like total harmonic distortion (THD) and voltage unbalance factor (VUF) of the grid voltage. Though the custom power devices such as distribution-static compensators (D-STATCOMs) improve these power quality concerns, however, the accompanying controller plays the substantial role. Therefore, this paper proposes a fractional-order sliding mode control (FOSMC) for a D-STATCOM to compensate the low power distribution system by injecting/absorbing a specific extent of the reactive power under disturbances. FOSMC is a non-linear robust control in which the sliding surface is designed by using the Riemann-Liouville ( RL ) function and the chattering phenomenon is minimized by using the exponential reaching law. The stability of FOSMC is evidenced by employing the Lyapunov stability criteria. Moreover, the performance of the proposed FOSMC is further accessed while doing its parametric variations. The complete system is demonstrated with a model of 400V, 180kVA radial distributor along with D-STATCOM under two test scenarios in MATLAB/Simulink environment. The results of the proposed controller are compared with the fixed frequency sliding mode control (FFSMC) and conventional proportional-integral (PI) control. The results validate the superiority of the proposed controller in terms of rapid tracking, fast convergence, and overall damping with very low THD and VUF.

Study on the influence of bank slope soil deformation on wharf structure

After a large-scale construction period, there are a large number of old high piled wharfs in China’s ports. The pile cap piles and beam members of some wharfs close to the earth retaining structure appear obvious dislocation, and some of them are increasing year by year. In this paper, the typical section of Tianjin Port 16 ∼ 18 wharf is taken as the research object, and a three-dimensional mathematical model is established to simulate the deformation trend of wharf structure with bank slope soil under unbalanced load condition. The results show that the pile cap plays a positive role in the stability of the wharf slope. Partial load can cause the deformation of soil along the bank. The horizontal earth pressure acting on several rows of piles behind the pile cap is large, which leads to large deformation and internal force of the pile body. When the force between the pile top and the beam exceeds the lap strength between them, the pile top and beam will be staggered. The fundamental method to avoid or improve the seaward movement of high piled wharf and bank slope is to block or reduce the horizontal earth pressure from the rear storage area to the front. The scheme of sheet pile wall or bored pile can be selected according to the actual situation.

Analysis of 0–9 kHz Current Harmonics in a Three-Phase Power Converter Under Unbalanced-Load Conditions

Analysis of 0–9 kHz Current Harmonics in a Three-Phase Power Converter Under Unbalanced-Load Conditions

Modified Q–f Droop Curve Method for Islanding Detection With Zero Non-Detection Zone

In this paper, a modified Q-f droop curve method for inverter-based distributed generator is proposed. The proposed method has merits such as detecting islanding with zero non-detection zone, negligible effects on power quality and simple implementation. A new parameter is embedded in the reactive power reference to accelerate the frequency deviation at the point of common coupling, until the islanding is detected. Therefore, a passive under/over frequency relay will be simply sufficient to detect islanding within the permissible limit. The proposed method is modelled with computer-aided design SIMULINK/MATLAB environment. The proposed method is analysed for operation with unity and non-unity power factors. The performance is validated for various loading quality factors with a negligible change in detection time. In addition, it is confirmed that the proposed system is stable under unbalanced loading and switching conditions. The proper operation of proposed islanding detection method under multi distributed generators connection is validated. The results of the hardware experimentations are presented to confirm the proposed method analysis and simulations.

A coordinated control strategy for battery/supercapacitor hybrid energy storage system to eliminate unbalanced voltage in a standalone AC microgrid

PurposeA standalone microgrid (MG) is able to use local renewable resources and reduce the loss in long distance transmission. But the single-phase device in a standalone MG can cause the voltage unbalance condition and additional power loss that reduces the cycle life of battery. This paper proposes an energy management strategy for the battery/supercapacitor (SC) hybrid energy storage system (HESS) to improve the transient performance of bus voltage under unbalanced load condition in a standalone AC microgrid (MG).Design/methodology/approachThe SC has high power density and much more cycling times than battery and thus to be controlled to absorb the transient and unbalanced active power as well as the reactive power under unbalanced condition. Under the proposed energy management design, the battery only needs to generate balanced power to balance the steady state power demand. The energy management strategy for battery/SC HESS in a standalone AC MG is validated in simulation study using PSCAD/EMTDC.FindingsThe results show that the energy management strategy of HESS maintains the bus voltage and eliminates the unbalance condition under single-phase load. In addition, with the SC to absorb the reactive power and unbalanced active power, the unnecessary power loss in battery is reduced with shown less accumulate depth of discharge and higher average efficiency.Originality/valueWith this technology, the service life of the HESS can be extended and the total cost can be reduced.

Proficient operation of grid interfaced solar PV system for power quality improvement during adverse grid conditions

The penetration of solar energy into the distribution network is affected by the seasonal and day-to-day variability of the solar power generation. In underdeveloped and developing countries, the power quality (PQ) deterioration issues are primarily observed due to the presence of the weak utility grid. Therefore, smart grid operability is achieved through power exchange along with the improvement in PQ indices by the application of the biquad filter, thereby exhibiting multifunctional control capability. The biquad filter is less affected by quantization errors and involves no additional usage of sensors or control loops, which are the significant advantages observed in its implementation. The biquad filter utilization in this work, includes the estimation of fundamental load current along with mitigation of harmonics, improving PQ, reactive power compensation, and satisfactory performance during voltage unbalance, sag, distortion, swell, and unbalanced loading conditions, which are observed during weak grid conditions. The stochastic inputs of the solar PV array interfaced utility grid system are agitated due to the erratic availability of solar power, and are overcome through an adaptive perturb and observe technique, which uses a variable perturbation step size. Test cases considered here, validate the performance in accordance to the IEEE-519 standard.

Implementation of three-phase four-leg inverter using SiC MOSFET for UPS applications

This study implemented a 30 kW, 750 Vdc, silicon-carbide (SiC)-based uninterruptible power supply(UPS) applied it on a three-phase four-leg inverter. For component selection, LC filter and DC-link capacitor were designed based on the PSIM simulation. SiC MOSFET was used to achieve higher efficiency and better reliability than the conventional Si IGBT-based UPS applications. Furthermore, desaturation (DeSat) protection method was applied to protect the overcurrent during the short-circuit condition of SiC MOSFET. Thus, the DeSat protection method was applied to SiC MOSFET, thereby enabling a 1 μs protection by complementally switching and zener diode voltage optimization. Accordingly, the transient time of the DeSat protection can be disregarded, thereby enabling fast protection. Meanwhile, several topologies have been studied for unbalanced loads compensation. The current research used a three-phase four-leg inverter topology for compactness and neutral current control. In addition, voltage compensation became possible even in unbalanced load condition by introducing a dual-loop controller for the three-phase four-leg inverter. A dual-loop controller comprises PR and PI controllers to the stationary αβo and synchronous dqo reference frames, respectively. Thermal and efficiency tests were also performed in the rated power test. Under a 30 kW load condition, the surface epoxy molding compound temperature of SiC MOSFET was approximately 72 °C, and the highest efficiency was approximately 99.1% under 10 kW load condition. Finally, the effectiveness of the implementation was demonstrated through the experiment results.

A Second-Order Sliding Mode Controller of Quad-Rotor UAV Based on PID Sliding Mode Surface with Unbalanced Load

Quad-rotor unmanned aerial vehicle (UAV) is a typical multiple-input-multiple-output underactuated system with couplings and nonlinearity. Usually, the flying environment is very complex, so that it is impossible for the UAV to avoid effects derived from disturbances and uncertainties. In order to improve the reliability of flight control, we established the dynamic model of quad-rotor UAV by Newton-Euler equation in unbalanced load conditions. Considering external disturbances in the attitude, a second-order sliding mode controller was designed with PID sliding mode surface and Extended State Observer (ESO). The simulation experiments have got good control performance, illustrating the effectiveness of our controller. Meanwhile, the controller was implemented in a quad-rotor UAV, which carried a pan-tilt camera for aerial photography. The actual flight experiments proved that this paper dealt with the high stabilization flight control problem for the quad-rotor UAV, which laid a good foundation for autonomous flight of the UAV.

MMLSTOGI based control for suppression of current harmonics in PV‐tied grid

In a photovoltaic array (PVA) tied grid system, PVA and the grid are connected at AC bus (ACB) to feed the power to the grid and the load connected locally at the ACB. The photovoltaic energy conversion system (PVECS) requires an improved dynamic controller to control the grid voltage harmonics under variable solar power and nonlinear unbalanced load conditions. The conventional filtering controllers are unable to remove the sub-harmonics and DC-offset in the input signal. Moreover, their attenuation for the dominant lower order harmonics is unsatisfactory for unbalanced loading conditions and highly nonlinear loads. A MMLSTOGI (mixed multi-level second and third order generalized integrator) based control is used in this work. It effectively mitigates the dominant lower-order harmonics and the DC-offset of load currents and extracts their in-phase and quadrature-phase fundamental components (FCs). The PVA is connected at ACB through interfacing voltage source converter (VSC). The DC-link voltage is ascertained by generating its reference value using an incremental conductance (InC) based maximum power point tracking. The PVA power is feed-forwarded in the control to enhance the dynamics of the system. The control is validated on a developed model in MATLAB SIMULINK background, and using a developed prototype.

DSOGI-PLL With In-Loop Filter Based Solar Grid Interfaced System for Alleviating Power Quality Problems

This article deals with a dual second-order generalized integrator phase-locked loop (DSOGI-PLL) with in-loop filter-based control approach for a single-stage, three-phase three-wire solar-grid-interfaced system under abnormal grid voltage conditions, unbalanced load conditions, and varying solar insolation levels. The DSOGI with in-loop filter algorithm with enhanced filtering capability, employed for both voltages and currents, helps to attenuate the harmonics, eliminates dc offset, and estimates the sequence components. This algorithm elicits the fundamental component of highly nonlinear load current required for calculating the reference magnitude of the grid currents. Even during unbalanced load conditions, these fundamental components of currents are free from the dc offset and dominant harmonics of double frequency. In order to maintain the sinusoidal and balanced grid currents, the positive sequence voltages are estimated to get the accurate unit templates during the unbalanced and abnormal grid voltages conditions. Moreover, these positive sequence voltages are used by PLL to compute the phase required for the magnitude and the angle calculation of the currents and voltages. The dc-link voltage is maintained at maximum power point by an incremental conductance based technique. This system is simulated in MATLAB/Simulink environment. Test results on a developed laboratory prototype are observed in accordance with the standard of the IEEE-519.