Controlled Voltage Source Inverter Research Articles

Optimized sliding surface predictive control of a voltage source inverter with improved steady-state performance

In this paper, an optimized sliding surface predictive control of a three-phase voltage source inverter is introduced. In power electronics, the model predictive control method (MPC) is broadly used and applied to a wide range of energy conversion systems. However, analyzing the stability of the MPC is not a straightforward task, and Lyapunov-based approaches are used to examine the stability characteristics in most cases. MPC is a nonlinear control technique, and the traditional frequency-domain stability tools cannot be used to examine the closed-loop stability. Therefore, a poor design of the MPC without considering the stability may worsen the system performance. Even the norm choice of the objective function leads to closed-loop instability, for example, ℓ1 norm is not a sufficient choice to guarantee the global asymptotical stability. Even though ℓ1 norm offers a low computational burden during the online optimization process, the system may suffer from closed-loop instability. For all these reasons, a stability-guaranteed objective function design procedure is proposed in this paper. The proposed objective function selection process is based on the sliding-mode control theory. The objective function is reformulated as a sliding surface function, and the switching combination that satisfies the sliding mode control stability criteria is selected as an optimum input. The mathematical concepts are experimentally validated, and the results demonstrate the potency of the proposed strategy.

Advanced single-loop discrete-time control for T-type voltage source inverter with minimum capacitor voltage ripple modulation

This research focuses on improving the performance of the voltage source inverter (VSI), which has been widely used in practical applications such as uninterruptible power supply (UPS), photovoltaic (PV) systems in standalone mode. To reduce the total harmonic distortion (THD) of the output voltage without increasing the switching frequency, the T-type three levels inverter with enhanced modulation strategy, which minimizes the voltage ripple of the two input capacitors, is employed. In addition, a new single-loop fully digital control strategy in which various advanced control techniques such as proportional-integral observer, one-step ahead minimum prediction error, and model-based current command generator is also proposed to fulfill the strict requirements of the output voltage. The proposed control strategy is capable of achieving excellent output voltage regulation and high robustness against the parameters variation with low computational cost. Real-time simulations based on hardware in the loop (HIL) platform are conducted to confirm the validity of the method.

Sensorless predictive control of voltage source inverters for renewable energies integration under unbalanced and distorted grid conditions

Sensorless predictive control of voltage source inverters for renewable energies integration under unbalanced and distorted grid conditions

A Comparison of Instantaneous and Extension p-q Methods for Current Controlled Voltage Source Inverter in Microgrid

ABSTRACT With the advancement in technology and population growth, the motivation of integrating utility grid with the microgrid through power electronic converters increases. This paper presents the control of power electronic converter connected at the grid side. This converter regulates the power flow between renewable energy system (RES), load and grid in addition to the compensation of harmonic and reactive power. The reference currents are generated to decide the power flow from RES to the load and to suppress the harmonic and reactive power in the grid making grid current sinusoidal. In this paper, the reference current generation techniques like instantaneous p-q method and extension p-q method are implemented and compared. Linear Quadratic Regulator (LQR) is used to track the reference current. The control law of LQR is designed in a simple way using simplified equivalent circuit of a three-phase grid integrated renewable energy system. The system is tested experimentally under balanced and unbalanced conditions in two different modes such as insufficient renewable power and excess renewable power. The supremacy of extension p-q method over instantaneous p-q method is proved by getting low total harmonic distortion and better power factor under balanced and unbalanced conditions experimentally.

A Novel H∞ Robust Control Strategy for Voltage Source Inverter in Microgrid

The voltage control performance of the voltage source inverter (VSI) in a microgrid may change under different load conditions. However, in the case of traditional control strategies, the robustness of VSI is insufficient. In response to the above problems, a novel robust control scheme for VSI in the microgrid based on H∞ hybrid sensitivity is proposed in this study. The grid-side interference during the VSI operation is taken as the variable, and the sensitivity function is designed to build a H∞ robust voltage controller for VSI. In addition, an adaptive virtual impedance group is designed to further improve the voltage control robustness under a variety of operation conditions. Finally, comparative simulation experiments are carried out to verify the anti-interference ability of the proposed control strategy under different working conditions.

Reactive power correction using virtual synchronous generator technique for droop controlled voltage source inverters in islanded microgrid

Reactive power correction using virtual synchronous generator technique for droop controlled voltage source inverters in islanded microgrid

Analysis of virtual inductances on the stability of the voltage control loops for LC‐filtered voltage‐controlled voltage‐source inverters in microgrids

Voltage-controlled voltage-source inverters (VVSIs) have been widely used in microgrids. Typically, LC filters are adopted by the VVSIs to improve the quality of the output voltage. Resonances of the LC filters that may cause oscillations to the VVSIs can be damped by well-designed voltage controllers. However, the virtual inductance (VI) that is widely applied to improve power sharing between VVSIs will reduce the stability margin of the voltage control loop and introduce new oscillations on the LC filters even if the well-designed voltage controllers have been used, which has not been reported in the literature. Furthermore, since the VI will introduce a cross-coupling into the system, the conventional methods for analyzing the resonances of the LC-filtered VVSIs cannot be used for analyzing the oscillations caused by the VI. Therefore, the stability of the LC-filtered VVSI with the VI is investigated based on a new model proposed in this paper. Besides, to enhance the stability of the VVSI, the application of a low-pass filter or a band-pass filter in the VI is studied. Moreover, when connecting the VVSIs, the effects of the line impedance on the stability of the VVSIs while using the VI are investigated. Finally, simulation and experimental results have been provided, which verifies the correctness of the analysis in this paper.

Robust model predictive control for three-level voltage source inverters

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

Hardware-in-the-Loop Testing of Seamless Interactions of Multi-Purpose Grid-Tied PV Inverter Based on SFT-PLL Control Strategy

This paper introduces a multifunction interactive PV system that has the ability to feed a nonlinear local load in either grid-tied topology (GTT) or off-grid topology (OGT) and transits between the two topologies are seamless. The interactive PV system utilizes a sliding Fourier transform-based phase-locked loop (SFT-PLL) as an adaptive and robust control technique for extracting the fundamental load current. Further, the SFT-PLL is also used to synchronize the inverter output voltage with the grid during the GTT. The proposed synchronization technique has a superior immunity to the weak grid problems. The SFT-PLL based control technique has a very good ability to mitigate the nonlinear load harmonics and to deliver active current to the grid with a unity power factor. Moreover, the proposed control technique is able to keep a balanced grid current when the connected load is unbalanced whether the PV source is available or not. The DC-link voltage is controlled by the controller of the voltage source inverter (VSI) during GTT. During the OGT, the AC load voltage is regulated by the VSI controller while the DC-link voltage is regulated by the boost converter controller to satisfy the power requirements of the connected load. The simulation and experimental results show the effectiveness of the proposed control technique in feeding a balanced current with THD adheres to the IEEE-519 standard at different operating conditions. The performance of the proposed method is compared with recently published adaptive filtering techniques to show its effectiveness especially when the load current has a DC-offset.

A Sliding Mode Controller Based on Robust Model Reference Adaptive Proportional-integral Control for Stand-alone Three-phase Inverter

This paper proposes a sliding mode controller based on robust model reference adaptive proportional-integral (RMRA-PI) control for a stand-alone voltage source inverter (SA-VSI). The proposed controller has two control loops where the coefficients of PI controller are regulated by the adaptive sliding law. This method is used to regulate the output voltage of the inverter under different load conditions and uncertainty, and adapts the output to the reference model to reduce the total harmonic distortion (THD). In this paper, the stability of the proposed controller is proven by using Lyapunov's theory and Barbalet's lemma. The proposed controller performs well in voltage regulation such as low THD under sudden load change and uncertainty. Also, the results of the proposed controller are compared with PI controller to show the effectiveness of the presented control system.

Machine Learning Based Intentional Islanding Algorithm for DERs in Disaster Management

Currently, research work is primarily dependent on the collection of large sets of data from systems and making predictions based on the knowledge obtained from the data, which is generally termed as `data mining'. These data mining algorithms are of great importance in improving the performance of different applications. In this regard, Machine Learning (ML) algorithms have been demonstrated to be excellent tools to cope with difficult problems. In this paper, a classification learner based supervised ML algorithm is proposed for intentional islanding of DERs based on the live data collected from supervisory control and data acquisition (SCADA) system in post disaster situations. Literature presents various islanding detection techniques and also intentional islanding algorithms to address different problems in AC networks. These algorithms majorly work based on the control of current source or voltage source inverters. On the other hand, a low voltage DC distribution system allowing the removal of inverter is proposed, which is supposed to be more advantageous by reducing losses and is also economical when working with DERs. In this paper, ML based intentional islanding algorithm for DERs based low voltage DC distribution system is proposed by considering the effects of natural disasters. The learner models trained are fine tree, linear SVM, quadratic SVM and Gaussian SVM. The training of fine tree model is achieved with higher accuracy of 99.8%. The main objective of this work is to achieve a faster and accurate decision making. The performance of the ML based intentional islanding algorithm is compared with the earlier proposed artificial intelligence (AI) based intentional islanding algorithms. The AI algorithms proposed earlier are fuzzy inference systems (FIS), artificial neural networks (ANN) and adaptive network based fuzzy inference system (ANFIS). The comparison shows that, the decision making with ML based intentional islanding algorithm is faster and accurate than all other algorithms.

Combined use of the nearest vector selecting technique and low-frequency quarter-wave symmetric space vector PWM in control of three-phase multilevel voltage source inverter

The paper offers the problem’s solution of the three-phase multilevel voltage source inverter (MLVSI) control with low dynamic losses in power semiconductor switches. The proposed technique is based on a single approach that operates with values of the integer and fractional parts of the relative values of the reference delta voltages, and it allows combining the use of the space-vector control, choosing the nearest vector (SVC), with the low-frequency space-vector pulse-width modulation with the quarter-wave symmetry of the output voltages (QWS-SVPWM). Depending on the impedance kind of a generalized load, the integrated voltage harmonics factor (weighted THD) of the appropriate order is being minimized by applying one of the two mentioned modulation methods (SVC or QWS-SVPWM) for a current range of voltage amplitude modulation index. Like its components, the combined algorithm is suitable for MLVSI of any circuit configuration and any number of equal output voltage levels.

An Efficient Hybrid Technique for Power Flow Management in Smart Grid with Renewable Energy Resources

ABSTRACT In this paper, an optimal power flow management of a hybrid renewable energy source (HRES) with a hybrid approach is proposed. Here, the proposed method is the consolidation of Improved Bear Smell Search (IBSS) and Sparrow Search Algorithm (SSA); hence, it is named as IB4SA technique. Here, the IBSS generates the voltage source inverter control signals based on the power exchange variety between the source side and load side. In the proposed work, the Bear Smell Search (BSS) is incorporated by crossover and mutation function, therefore it is named as IBSS. The multi-objective function is designed by the grid needed active with reactive power varieties generated based on the available source power. SSA process guarantees the detection of online control signals using a parallel implementation against active with reactive power varieties. The control method based on the proposed approach improves the control parameters of the power controller under power flow variations. The power flow management of the smart-grid system is controlled using the proposed technique based on variations in the parameters of the source and load side. The proposed technique is responsible for controlling energy sources using both renewable energy sources and energy storage devices, in order to generate the power requirement by the grid. The proposed approach is executed in MATLAB/Simulink work site and the performance is analyzed with the existing approaches. The statistical analysis for Case 1, 2, and 3 using proposed as well as existing approaches are analyzed. In Case 1, using the proposed technique the parameter of with mean represents 0.528, median represents 0.512 and standard deviation represents 0.033. In Case 2, using the proposed technique the parameter of with mean implies 0.671, median implies 0.656, and standard deviation implies 0.026.

Accurate and Fast Amplitude Estimation of Signal Distorted by Noise and Harmonics for Control of VSI

Arriving at an accurate and fast amplitude estimation of the sine-wave distorted by harmonics and noise is important for the control of voltage source inverters in grid-connected photovoltaic system. In this article, the three-point interpolation discrete Fourier transform method based on the maximum sidelobe decay windows is proposed for accurate amplitude estimation. The proposed amplitude estimator is speeded-up by using the guaranteed stable recursive method. The influence of noise on the proposed amplitude estimator is investigated, and the amplitude estimation error caused by the spectral interference is also analyzed. The accuracy and effectiveness of the proposed method are verified through simulation and experiments, where the state-of-art amplitude estimation methods and the boundaries specified in the Standard IEEE C37.118.1-2011 are considered.

An Improved Lyapunov Function Based Control Strategy for Multitasking Distributed PV Inverter

The ELF (Extended Lyapunov Function) based control approach for single phase two-stage multitasking PV (photovoltaic) inverter is demonstrated in this paper. The introduced PV inverter can operate under the uncertainty of non-linear loads and PV characteristic beyond giving the closed feedback system stability analysis. The two stage PV inverter is introduced, in initial step a boost circuit is used to harnessing of crest power at PV panel side. Here time ratio of the boost circuit is planed with adaptive INC (Incremental Conductance Method). In the secondary step, the control of grid connected VSI (Voltage Source Inverter) is managed by ELF (Extended Lyapunov Function) strategy. To get best dynamic response, difference of PV feed forward to the loss component of DC bus capacitor. Other side, control of VSI and maintain stability of PV inverter, the ELF technique is reduces error in-between input and output, with there is no disturbance of equilibrium point in PV inverter. The PV inverter performance observed at changing of insolation and load variations using MATLAB /simulation. Various simulation results are presented to validate the harmonics compensation strategy.

Model-Free Predictive Current Control for Multilevel Voltage Source Inverters

This article proposes a generalization of the model-free predictive current controller (MFPCC) for multilevel voltage source inverters (VSIs). MFPCC is an alternative to mitigate the parameter sensitivity faced by model-based PCC (MPCC), but it requires a constant update of the stored current variations (CVs) associated with each VSI state to provide a prediction, which results in a satisfactory closed-loop response. When a multilevel VSI is considered the number of states increases, which results in a decrease of the CV update rate, since only one state can be updated at each sample. To solve this issue, the extended adjacent state scheme is used to reduce the possible number of solution candidates and then a controlled CV is used to compensate the updated CV. Simulation and experimental results obtained with a sampling rate of 5 kHz show that the proposed MFPCC exhibits performance similar to the one of MPCC for nominal parameters. However, a better current response is obtained in the case of the load parameter mismatch, especially at steady state.

HIL-Assessed Fast and Accurate Single-Phase Power Calculation Algorithm for Voltage Source Inverters Supplying to High Total Demand Distortion Nonlinear Loads

The dynamic performance of the local control of single-phase voltage source inverters (VSIs) can be degraded when supplying to nonlinear loads (NLLs) in microgrids. When this control is based on the droop principles, a proper calculation of the active and reactive averaged powers (P–Q) is essential for a proficient dynamic response against abrupt NLL changes. In this work, a VSI supplying to an NLL was studied, focusing the attention on the P–Q calculation stage. This stage first generated the direct and in-quadrature signals from the measured load current through a second-order generalized integrator (SOGI). Then, the instantaneous power quantities were obtained by multiplying each filtered current by the output voltage, and filtered later by utilizing a SOGI to acquire the averaged P–Q parameters. The proposed algorithm was compared with previous proposals, while keeping the active power steady-state ripple constant, which resulted in a faster calculation of the averaged active power. In this case, the steady-state averaged reactive power presented less ripple than the best proposal to which it was compared. When reducing the velocity of the proposed algorithm for the active power, it also showed a reduction in its steady-state ripple. Simulations, hardware-in-the-loop, and experimental tests were carried out to verify the effectiveness of the proposal.

Updated PSO optimised fuzzy‐PI controlled buck type multi‐phase inverter‐based PMSM drive with an over‐current protection scheme

This study confers a novel approach towards fuzzy-PI (proportional–integral) controlled pulse width modulation (PWM) controlled permanent magnet synchronous motor (PMSM) drive operated through a conventional voltage source inverter (VSI) supplemented with buck-converter fed current source inverter (CSI). It is observed that in a PWM controlled VSI, output voltage and current obtained contains certain harmonic distortion. A buck-converter fed CSI is capable of minimising the voltage and current ripples prominently even with the application of PWM. Thereby, in this study, an economic, as well as robust design procedure for the buck converter, fed CSI is proposed. Moreover, a particle swarm optimisation (PSO) mechanism is introduced to optimise the performance of the proposed fuzzy logic controller. Additionally, an over-current protection scheme of the PMSM motor is proposed. The performance of a PMSM drive is analysed in MATLAB/SIMULINK platform. Furthermore, the proposed concept is tested and verified in a real-time test-bench developed in the laboratory. Finally, from the performed test conditions, it can be confirmed that the proposed current control strategy of the drive system shows excellent performance in various operating conditions and can be employed in light-weight electric vehicles.

Modeling of single phase off-grid inverter for small standalone system applications

This paper presents the detail circuitry modeling of single phase off-grid inverter for small standalone system applications. The entire model is developed in MATLAB/Simulink platform using circuitry model. This off grid inverter consists of a high frequency DC-DC step up converter cascaded with a full bridge PI control voltage source inverter using SPWM modulation with LC filter to produce sine wave output. This is a common design used in many small commercial off-grid inverter. This off-grid inverter model is capable to produce AC sinewave output voltage at 230 V 50 Hz up to 1 kW power from a 48 V DC lead acid battery source. The AC sine wave output waveform achieved a voltage Total Harmonic Distortion (THD) of less than 1 % which is almost a pure sine wave. The conversion efficiency performance of the off-grid inverter achieved more than 94 %. The performance of the model is validated by real commercial off-grid inverter. The performance validation experiment shows that the off-grid inverter Simulink model conversion efficiency and THD performance are comparable to the commercial off-grid inverter. This model contributes to assist small to medium standalone system load and battery sizing design with greater accuracy.

Hybrid Modulation for Modular Voltage Source Inverters with Coupled Reactors

This paper proposes and discusses a concept of a hybrid modulation for the control of modular voltage source inverters with coupled reactors. The use of coupled reactors as the integrating elements leads to significant reduction in the size and weight of the circuit. The proposed modulation combines novel coarsely quantized pulse amplitude modulation (CQ-PAM) and innovative space-vector pulse width modulation (SVPWM). The former enjoys very low transistor switching frequency and low harmonic elimination, while the latter ensures high resolution of amplitude control. The SVPWM is based on the use of barycentric coordinates. The feasibility of the proposed solution is verified by simulations and laboratory tests of a 12-pulse modular voltage source inverters with two-level and three-level component inverters.