Second Order Generalized Integrator Research Articles

An Enhanced Power Allocation Strategy for Microgrids Considering Frequency and Voltage Restoration

In a microgrid, load power should be properly shared among multiple distributed generation (DG) units, not only for fundamental power but also for negative sequence and harmonic power. In this paper, the operation of a microgrid under imbalance and nonlinear load conditions is studied, and a consensus algorithm-based distributed control strategy is proposed for the microgrid power allocation, frequency, and voltage restoration. First of all, the output current of DG unit is decomposed by second-order generalized integrator (SOGI) modules to obtain the fundamental power and harmonic power through the power calculation formula. Then, state values of DG units, such as local power, frequency, and voltage, are transmitted on a sparse communication network. Under the action of a consensus algorithm, the real power of DG units is allocated following the equal increment principle; the reactive power, imbalance, and harmonic power are allocated according to the capacities of DG units; and the frequency of the microgrid and the voltage at the point of common coupling (PCC) are rated. In the consensus-based strategy, DG units only communicate with their neighbor units; thus, the “plug and play” function is reserved. Compared with the centralized control strategy, the proposed strategy with a distributed consensus protocol can simplify the maintenance and possible expansions of the system, making the microgrid more flexible. Moreover, as the structure of the detailed network is not required, it is easy to apply in practice. Simulation and experiment results are presented to verify the proposed method.

Improved Position Sensorless Resonant Frequency Tracking Control Method for Linear Oscillatory Machine

To improve the reliability of control system and obtain the maximum output efficiency, it is very necessary to carry out the position sensorless piston stroke control and the resonance frequency tracking control for linear oscillatory machine (LOM) at the same time. The conventional resonant frequency tracking control method based on model reference adaptive system (MRAS) has the problem of low estimation accuracy caused by inaccurate model parameters. In order to obtain more accurate resonant frequency, an improved position sensorless resonant frequency tracking control method is proposed in this article. In this method, the adjustable model is constructed based on the mechanical dynamics equation of LOM to track the system resonant frequency. A hybrid terminal sliding-mode observer (HTSMO) is designed to replace the conventional reference model, which can obtain more accurate velocity reference signal for adjustable model by introducing the current error feedback link, thereby further improving the resonant frequency tracking accuracy. Moreover, a second-order generalized integrator (SOGI) is introduced to filter the estimated velocity signal of HTSMO. The filtered velocity signal is not only used for the adjustable model to track the resonant frequency, but also used to obtain the smooth piston stroke signal for the stroke closed-loop control. Comprehensive simulation and experimental results have proved the effectiveness and the superiority of the proposed method.

Sensorless Control of Surfaced-Mounted Permanent Magnet Synchronous Motor in a Wide-Speed Range

This paper delves into a comprehensive study of a wide-speed-range sensorless control approach for surface-mounted permanent magnet synchronous motors (SPMSMs). In the low-speed range, a novel high-frequency pulse voltage injection (HFPVI) method is introduced for rotor position estimation, which does not depend on motor saliency and is well-suited for SPMSMs. This method incorporates a second-order generalized integrator (SOGI) and a new modulation signal to enhance the accuracy of rotor position estimation. For medium-to-high speeds, an improved super-twisting sliding mode observer (STSMO) utilizing a continuous hyperbolic tangent function is proposed to mitigate chattering. Additionally, a new phase-locked loop (NPLL) is introduced to accurately obtain the rotor position. Furthermore, this paper designs an exponential weighted switching function to facilitate a smooth transition of the motor from the low-speed domain to the medium- and high-speed domains. The effectiveness and superiority of the proposed methods are validated through simulations and experiments conducted on an RTU-BOX platform. The rotor position estimation errors of the proposed new HFPVI method and the improved STSMO method under various operating conditions are both approximately 0.05 rad (2.8 elc·deg), and the SPMSM can switch smoothly from the low-speed range to the medium- and high-speed ranges.

A Secure Dual-Layer Fault Protection Strategy for Distribution Network with DERs: Enhancing Security in the Face of Communication Challenges.

Earlier protection methods mainly focused on using communication channels to transmit trip signals between the protective devices (PDs), with no solutions provided in the case of communication failure. Therefore, this paper introduces a dual-layer protection system to ensure secure protection against fault events in the Distribution Systems (DSs), particularly in light of communication failures. The initial layer uses the Total Harmonic Distortion (THD), the estimates of the amplitude voltages, and the zero-sequence grid voltage components, functioning as a fault sensor, to formulate an adaptive algorithm based on a Finite State Machine (FSM) for the detection and isolation of faults within the grid. This layer primarily relies on communication protocols for effective coordination. A Second-Order Generalized Integrator (SOGI) expedites the derivation of the estimated variables, ensuring fast detection with minimal computational overhead. The second layer uses the behavior of the positive- and negative-sequence components of the grid voltages during fault events to locate and isolate these faults. In the event that the first layer exposes a communication failure, the second layer will automatically be activated to ensure secure protection as it operates, using the local information of the Protective devices (PDs), without the need for communication channels to transmit trip signals between the PDs. The proposed protection system has been assessed using simulations with MATLAB/Simulink and providing experimental results considering an IEEE 9-bus standard radial system. The obtained results confirm the capability of the system for identifying and isolating different types of faults, varying conditions, and modifications to the grid configuration. The results show good behavior of the initial THD-based layer, with fast time responses ranging from 6 to 8.5 ms in all the examined scenarios. In contrast, the sequence-based layer exhibits a protection time response of approximately 150 ms, making it a viable backup option in the event of a communication failure.

Photovoltaic-Based q-ZSI STATCOM with MDNESOGI Control Scheme for Mitigation of Harmonics

Static compensators (STATCOMs) are often used in distribution systems to enhance power quality. There is a need to enhance the performance of STATCOM to optimize its utilization and facilitate the provision of additional ancillary services. This paper employs the multilayer discrete noise-eliminating second order generalized integrator (MDNESOGI) to regulate the quasi-impedance source inverter (qZSI)-STATCOM for power exchange with the grid. Compared to conventional second-order generalized integrator (SOGI), MDNESOGI exhibits a higher capability for rejecting DC offset. In instances of abnormal grid operation or system malfunction, the inclusion of DC rejection capability enhances the robustness and reliability of the system. The suggested control algorithm only requires two integrators, three mathematical operators, and a damping factor, making it far easier to implement than transformation-based methods. The distorted load current is broken down into its active and reactive components using this control mechanism. The reference currents are then calculated by multiplying these parts by their corresponding voltage standards. The DC offset is reduced and transient oscillations in the weight component are eliminated by adjusting the damping factor. The suggested algorithm effectively handles power quality tasks like (a) reducing harmonic distortion, (b) compensating for reactive power, (c) adjusting for power factor, and (d) balancing the load under different conditions in the distribution system. The experimental study results are used to examine the stability of the proposed control scheme in both static and dynamic scenarios. In addition, a comparison to traditional methods is provided to demonstrate the new method’s superiority. Experimentation results show that the suggested controller is superior to its contemporaries in all scenarios where power quality is a factor, meeting the IEEE standard requirements.

Compensation Method for Current Measurement Errors in the Synchronous Reference Frame of a Small-Sized Surface Vehicle Propulsion Motor

This paper proposes a new method for compensating current measurement errors in shipboard permanent magnet propulsion motors. The method utilizes cascade decoupling second-order generalized integrators (SOGIs) and adaptive linear neurons (ADALINEs) as the current harmonic extractor and the compensator, respectively. It can compensate for the dq-axes offset and scaling errors simultaneously, improving phase current distortion while reducing the ripples of motor speed and torque. Compared to the traditional motor model-based compensation strategies, the proposed method is robust against the changes in motor parameters with the online adaptive capability of the ADALINE algorithm. Furthermore, due to the good real-time performance of SOGIs and ADALINEs, the proposed compensation strategy can effectively operate in both the steady state and transient state of the motor. Finally, the effectiveness of the proposed method is verified through the physical and hardware-in-the-loop (HIL) experiments. After compensating for the current measurement errors of a 1 kW test motor with the propeller-characteristics load, the torque ripple and speed ripple are reduced by more than 65% and 80%, respectively. At the same time, the DC component and the second-order and third-order harmonics in the phase currents are also significantly reduced. Similar test results can be also obtained on the HIL platform with a 100 kW permanent magnet motor.

Smart meter for the estimation of power quality indices based on second-order generalized integrator.

With the increasing integration of renewable energy sources and nonlinear loads in the grid, it is necessary to compute energy and power quality parameters for monitoring as well as analyzing the power consumption indices (PCI) and power quality indices (PQI). Smart meters (SMs) can monitor the PCI and PQI at the consumer end. SM necessitates the measurement of voltage and current, which can be further processed by an algorithm for estimating different parameters through signal processing and arithmetic operations. This paper proposes the combined dual second-order generalized integrator (SOGI) and proportionate least mean square (PLMS) algorithm-based PCI and PQI estimation for smart metering. Dual SOGIs individually process voltage and current signals to extract the respective fundamental in-phase and quadrature components. To account the variations in grid frequency, the SOGI processing the voltage also incorporates a frequency locked loop. This prevents performance degradation on account of frequency variations. The PLMS algorithm then process the output of SOGI processing the current for extracting the fundamental active and reactive components of current. Moreover, the PLMS algorithm results in further attenuation of harmonics. Also, only two separate values of learning rate are required, which is easy to tune for better dynamic performance. With only two quantities to be determined, this results in largely reduced computation. These computations facilitate in PCI and PQI computations. The proposed smart meter calculates peak value, RMS value, and phase angle for the fundamental components of voltage and current for each phase. Additionally, it assesses fundamental power factor, total harmonic distortion (THD), distortion factor, true power factor, active power, reactive power, and apparent power for each phase. The performance validation of the proposed combined dual-SOGI-PLMS algorithm-based PCI and PQI estimation for smart metering is carried out in MATLAB/SIMULINK for fifteen different operating scenarios. Further, the real-time implementation of the proposed methodology is carried out on dSPACE MicroLab Box 1202. Comparative analysis is also presented, which reveals the computational simplicity and other merits of the proposed scheme over the earlier reported scheme.

The Study of SRM Sensorless Control Strategy Based on SOGI-FLL and ADRC-PLL Hybrid Algorithm

The inductance model used in traditional sensorless control methods for switched reluctance machines (SRMs) exhibits high-order harmonics. The precision of the motor may be impacted by the buildup of rotor estimate errors caused by these harmonics. To address this issue, this paper proposes a novel method for SRMs that employs a hybrid algorithm combining an enhanced second-order generalized integrator (SOGI)-based frequency-locked loop (FLL) and an active disturbance rejection control (ADRC)-based phase-locked loop (PLL). This approach involves coordinate transformation and parameter identification to reconstruct the motor inductance model. Rotor position errors are calculated using the unsaturated inductance difference method. In order to enhance the accuracy of motor position estimation, a hybrid algorithm is employed to efficiently filter out harmonic errors and mitigate the tremor effect caused by the rotor position differential algorithm. This hybrid algorithm enables the estimate of the motor’s speed and rotor position. A sensorless control simulation model was developed using a 12/8 pole SRM to assess the motor’s performance under varying load conditions. Based on the results obtained, it is established that the application of this method can accurately estimate the rotor’s position and rotational speed and thus improve the performance of position sensorless control. Ultimately, a prototype system for a switched reluctance motor was created, and the effectiveness and feasibility of the proposed control technique were confirmed through experimental validation. This presents an innovative approach to engineering practice.

Current balancing of scalar-controlled induction motors with long imbalanced cables for artificial lift systems

Induction motor current imbalance increases losses, torque ripple and vibrations. Current imbalance is known to appear in artificial lift systems, where motors are driven over long imbalanced cables. Power hardware modifications, namely transposition of cable phases in the wellbore, adjustment of the step-up transformer taps, and addition of balancing inductors have so far been proposed to suppress the imbalance. However, these solutions compromise the system's reliability or involve costly additional equipment, which must be customized according to the cable characteristics. This paper proposes a control method for current balancing of induction motors driven by scalar-controlled variable speed drives. In the proposed method, Second-Order Generalized Integrators (SOGIs) are used to extract the negative-sequence component of the motor currents, which is then suppressed by a Synchronous Reference Frame (SRF) current controller. The frequency and angle information required by the SOGIs and the SRF controller are obtained directly from the scalar algorithm, without needing a position sensor or observer, thus offering a novel, simple, robust and computationally effective implementation, which is also independent of the cable characteristics. The paper presents MATLAB/Simulink simulation results to illustrate the method's operating principles and performance in a variety of transient conditions. Experimental results obtained using full-scale equipment are also provided to demonstrate its effectiveness.

Grid integrated multifunctional EV charging infrastructure with improved power quality

This paper presents a grid integrated multifunctional electric vehicle (EV) charging infrastructure to power the EV batteries and simultaneously improve grid power quality. The EV charger control function is designed to operate the charger in grid-to-vehicle (G2V), vehicle-to-grid (V2G), and proposed active-filtering-mode (AFM) operating modes. In AFM mode, the proposed self-tuning filter (STF) based control algorithm effectively compensates the grid current harmonic distortions arising from nonlinear charging station load. Furthermore, the charger controller uses STF to estimate the synchronizing voltage templates for reference current generation instead of conventional phase-locked-loop (PLL) and second-order generalized integrator (SOGI) to address the nonideal grid voltage conditions. The charger controller is designed to operate in AFM operating mode simultaneously with G2V and V2G operating modes. Furthermore, to achieve these multifunctional operations in a single charger, the power electronics circuitry of the charger is developed by using an AC/DC voltage source converter and a DC/DC dual active bridge (DAB) converter. The embedded isolation in the DAB converter ensures the safety of the EV batteries from the disturbance in the AC and DC side of the charger. Furthermore, a 3.6 kVA EV charger prototype is developed in the laboratory to show the effectiveness of the control techniques.

A robust THD based communication-less protection method for electrical grids with DGs

In this paper, a protection method with two cascaded algorithms is proposed to face fault events in Electrical Distribution Systems (EDSs). The first algorithm uses the Total Harmonic Distortion (THD), the estimates of the amplitude voltages, and the zero-sequence component of the grid voltages for defining an adaptive algorithm that provides a secure detection and identification process for the faults in the grid network. The second algorithm uses the behavior of the positive and negative-sequence components of the grid voltages during the fault events to locate and isolate the faults. Its main merit is that it doesn’t need to employ communication lines for transmitting trip signals between the protective devices (PDs) of the system. A Second Order Generalized Integrator (SOGI) is used for obtaining the estimated variables and sequence components, which allows fast detection with a low computational burden. The harmonic content existing prior to the fault is taken into consideration for not affecting the detection of the fault. The performance of the protection method’s is evaluated experimentally and by using simulations in MATLAB/Simulink and employing the IEEE 9-bus standard ring system. The proposed method shows the capability for detecting, identifying, and isolating different fault types with different DG penetrations and fault resistances in different locations of the proposed network and even when the grid configuration is changed. The method is robust to the possible harmonic distortion of the network.

SAPF based on ANN-Second Order Generalized Integrator for Harmonic Absorption

Abstract: The purpose of this study is to provide a photovoltaic (PV)-based generation system that is coupled with a shunt active power filter (SAPF) in order to effectively compensate for reactive power and mitigate harmonics. The Solar Active Power Filter is made up of a DC link capacitor, a voltage source inverter (VSI), and a solar production system. With the assistance of an active power filter, the current harmonics that are brought on by nonlinear loads are capable of being significantly decreased. The artificial neural network is presented as a solution for both the generation of the reference current and the regulation of SAPF. Calculating the reference source current for SAPF requires the use of the Second Order Generalized Integrator (SOGI), which is coupled with an Artificial Neural Network (ANN) controller. ANN is also notable for its high compatibility with digital implementation, control performance, and blazingly quick dynamic reaction times. The created controller is validated with the assistance of MATLAB simulations in order to demonstrate the efficacy and superior concert of the proposed methodology

Impacts of Dynamic Frequency Feedback Loop in SOGI-PLL on Low-Frequency Oscillation in an Electric Railway System

The low-frequency oscillation (LFO) issue has occurred frequently in single-phase electric train and traction network interactive systems (hereinafter train-network systems). On a single-phase electric train, the second-order generalized integrator (SOGI) based phase-locked loops (PLLs) have been widely used and also have significant impacts on the LFO. In the SOGI-PLL, the frequency signal is dynamically feedback from PLL to SOGI for adapting frequency variety, which causes complex nonlinearity and may deteriorate the small-signal stability of train-network systems. In previous works, the small-signal impedance model of train supposes that the feedback frequency is quasi-steady-state, which ignores impacts of dynamic frequency feedback loop (DFFL) on system-level stability and causes inaccurate analysis results. Therefore, this article builds an improved impedance model of train in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> frame with considering the DFFL. Compared with fixed frequency feedback loop (FFFL) based SOGI-PLL, the DFFL-based SOGI-PLL results in an additional negative resistance behavior, which is more likely to induce the LFO. Moreover, based on proposed impedance model of train, three FFFL-based SOGI-PLLs are compared among the filtering capability, phase-locked error and negative resistance range. Finally, experiment results by hardware in the loop (HIL) platform and real low-power experimental platform are employed to verity the correctness of theoretical analysis results.

Oscillation Suppression Strategy of Three-Phase Four-Wire Grid-Connected Inverter in Weak Power Grid

As the penetration of renewable energy increases year by year, the risk of high-frequency oscillation instability increases when a three-phase, four-wire split capacitor inverter (TFSCI) is connected to the grid with complementary capacitors in weak grids. Compared to the three-phase, three-wire inverter, the TFSCI has an additional zero-sequence current loop. To improve the accuracy of the modeling and stability analysis, the effect of the zero-sequence loop needs to be considered in the impedance-based stability analysis. Therefore, a correlation model considering multi-perturbation variables is first established, based on which the inverter positive, negative, and zero sequence admittance models are derived, solving the difficult problem of impedance modeling under small perturbations. Secondly, an admittance remodeling strategy based on a negative third-order differential element and a second-order generalized integrator (SOGI) damping controller is proposed, which can improve the stability of positive, negative, and zero-sequence systems simultaneously. Finally, the effectiveness of the oscillation suppression strategy is verified by simulation and experiment.

PI/PID Controller Relay Experiment Auto-Tuning with Extended Kalman Filter and Second-Order Generalized Integrator as Parameter Estimators

PI/PID Controller Relay Experiment Auto-Tuning with Extended Kalman Filter and Second-Order Generalized Integrator as Parameter Estimators

A SOGI-based adaptive controller design for second-harmonic currents suppression of variable frequency loads in DC buildings

DC buildings with integrated DC transformers (DCTs), as a typical representative of photovoltaics, energy storage, direct current, and flexibility (PEDF) building systems, are a crucial approach to reducing carbon emissions. Heating, ventilation, and air conditioning (HVAC) systems are typical loads in DC buildings that primarily aim to enhance the air quality and thermal comfort. However, the variable frequency drives (VFDs) used in HVAC systems can generate second-harmonic currents (SHC), which decrease equipment reliability and system power efficiency. To prevent SHC on the low-voltage side from flowing to the high-voltage bus, even in the grid, a second order generalized integrator (SOGI)-based adaptive controller for suppressing the SHC of variable frequency loads in DC buildings is proposed. The controller employs a phase-locked loop (PLL) to provide feedback on the VFD output frequency to the DCT control loop's notch filter, enabling adaptive suppression of the variable frequency SHC. Firstly, an accurate small-signal model of DCT based on Fourier series is established, which considers the inductor current. Then, the formula for DCT equivalent impedance is derived based on the model, and the feasibility of suppressing the SHC by increasing the equivalent impedance at variable frequency is analyzed. To enhance the stability of DC buildings, the parameters of the controller are designed to improve dynamic performance. Finally, the simulation results and experimental results verify the effectiveness and feasibility of the proposed adaptive controller compared to other suppression strategies.© 2017 Elsevier Inc. All rights reserved.

Single-phase grid-connected power control in dq synchronous reference frame with space vector modulation using FPGA

This paper presents the performance of controlling the active and reactive power of single-phase grid connected inverter by dq synchronous reference frame and space vector modulation (SVM) which is implemented by using field programmable gate array (FPGA) due to the flexibility they offer in comparison to other digital signal processors, hence it become the standard instruments for implementing various types of pulse width modulation (PWM) digital signal processors (DSPs). The SVM method has used because of its superiority in terms of harmonic distortion, switching losses and utilization of direct current (DC) bus. The synchronization is achieved by using second order generalized integrator (SOGI) due to its simple structure, certain filtering ability and frequency adaptability, in which the phase locked loop (PLL) ensures high performance for single-phase inverter. The active and reactive inverter current has been controlled and decoupled from each other and the dynamic response has been improved and became fast with proper feed-forward and decoupling grid voltage term. The system has simulated by MATLAB and the result shows robust control of injected grid current, active and reactive power control and DC link voltage control.

Model Predictive Control of Transformerless Series Custom Power Device for Voltage Quality Improvement

A single-phase series custom power device (Se-CPD), based on model predictive control (MPC), is presented in this paper to compensate for erratic supply voltage conditions such as voltage sag, swell, and harmonics. The control strategy for Se-CPD encapsulates the generation of reference voltage and optimal switching signals for the voltage source inverter (VSI) of the Se-CPD. The reference voltage extraction from the distorted point of common coupling (PCC) voltage is synthesized using a second-order generalized integrator (SOGI) without any phase delay, unlike the case that uses a low-pass filter (LPF). An MPC realizes the generation of optimal switching signals for Se-CPD with its intuitive and straightforward implementation, without any modulation stage, and considers the converter’s switching characteristics in the MPC algorithm itself. The simulation results, using MATLAB/Simulink and the real-time simulation results using the OPAL-RT OP4510 real-time simulator, are presented to validate the SOGI-MPC’s effectiveness for voltage quality improvement.

A Unified Control of Grid-Interactive Off-Board EV Battery Charger With Improved Power Quality

This article presents a self-tuning filter (STF) and sliding mode control (SMC)-based control algorithm for a grid-interactive off-board electric vehicle (EV) battery charger to power the EV batteries and simultaneously improve the grid power quality. In grid-connected operation (GCO), the charger uses the STF-based control strategy to estimate the fundamental load current and synchronize voltage templates to generate a pure sinusoidal reference current. Compared to the phase-locked loop (PLL) and the second-order generalized integrator (SOGI), the STF-based technique precisely estimates the synchronizing voltage templates during nonideal grid voltage conditions. Therefore, in GCO, the charger reference current ensures the unit power factor in the grid-to-vehicle/vehicle-to-grid (G2V/V2G) operation mode and the harmonic free grid current in the charger-for-grid (C4G) operation mode. Furthermore, the charger operates in the vehicle-to-load (V2L) operation mode during grid outages to maintain an uninterrupted supply to the residential load. The control algorithm also includes a grid synchronization technique to achieve a smooth transition between GCO and V2L. Furthermore, an SMC-based dc-link voltage controller (SMC-DLVC) is proposed to reduce dc-link voltage overshoot with finite-time convergence during external disturbances in all operation modes. The performance of the proposed control algorithm is validated in a 12.6-kVA off-board charger laboratory prototype under ideal/nonideal grid voltage conditions.

A whole control strategy for cascaded H‐bridge rectifiers under distorted grid voltage and unbalanced load

AbstractControl for single‐phase cascaded H‐bridge rectifier (CHBR) under distorted grid voltage is seldom discussed in the existing control methods; a modified direct power control (DPC) scheme is therefore proposed in this paper. A simple power control structure with proportional‐integral control method is first presented, which can discard phase‐locked loop (PLL) and coordinate transformation. Then, an improved fictitious orthogonal algorithm is proposed to provide a better anti‐disturbance ability compared with the traditional second‐order generalized integrator (SOGI). Since the orthogonal component of the grid current runs concurrently with the power reference, it offers an excellent dynamic performance in inner loop. On the other hand, a voltage balancing control (VBC) model by the relationship between the difference of dc‐side voltage square and that of power is established. On this basis, an internal model VBC (IM‐VBC) method is provided to reduce the parameter tuning complexity. With this method, the dynamic performance of voltage balancing on the dc side is improved. Finally, several test results on hardware‐in‐the‐loop (HIL) and scale‐down platform are demonstrated, which validate the effectiveness and superiority of the proposed control strategy.