DC-link Voltage Of Inverter Research Articles

IEZ-Source Inverter Topology with Tuned PID Controller of Carrier SPWM Technique in Grid Connected System

Z-source inverters are used in controller applications, which offer higher performance than the buck-boost converter. This work presents the Improved Embedded Z (IEZ)-source inverter used for the impedance network. The Z-source inverter includes the switching topologies, so the double inductor is added to the EZ source inverter circuit. IEZ source inverter manages the Total Harmonic Distortion (THD), and the PID controller controls the inverter voltage. The Social Ski Driver (SSD) Optimization algorithm is used to tune the parameters of the PID controller. The harmonic content of the Z-source inverter is reduced by the carrier based sinusoidal Pulse Width Modulation (SPWM) technique. The Improved Embedded Z-source Inverter (IE-ZSI) is utilized to apply a grid-connected system. The inverters receive the power from the DC voltage and supply the grid-connected load with controllable voltage. The proposed work is implemented in the platform MATLAB/SIMULINK to evaluate the performance of the voltage across the capacitor, the voltage across the inductor, grid current and grid voltage. Inverter DC link voltage performance was compared to conventional Z-source inverters and embedded Z-source inverters. The proposed work achieved 1.52% THD compared with existing techniques.

A novel hybrid-fuzzy logic based UVC technique for solar-PV/grid integrated water-pumping system

The continual depletion of fossil fuels and increased green-house emissions are persuading the consumers to install micro-renewable energy sources-based water pumping system. Among numerous energy sources, the solar-PV plays a significant role in water pumping application due to its virtuous, environment friendly, noise-free and abundant nature, so on. Along with solar-PV, the grid integrated system enables the continuous operation of water pumping system during varying temperature and irradiance conditions, and also delivers available solar-PV energy to grid during non-functional of pumping system. The above operations are carried by using bidirectional inverter which is controlled by using unit-vector control (UVC) technique. It consists of proportional-integral controller, which is not suited for regulation of DC-link voltage at desired level because of improper selection of gain values. In this work, an intelligent hybrid-fuzzy logic based UVC technique evidences the intelligent knowledge base for better regulation of DC-link voltage and power-flow of bidirectional inverter. The performance and operation of proposed hybrid-fuzzy logic control UVC technique for solar-PV/Grid integrated water-pumping system is evaluated under various operating cases by using MATLAB/Simulink tool; simulated results are conferred with superlative comparisons.

Modeling and Control of Micro Grid Powered by Maximum Power PV Array and Fixed Speed Wind Energy Conversion System

In this paper, the dynamic modeling of the studied micro grid (MG) is presented for steady state and transient operation conditions. Moreover, control strategies to obtain the maximum converted power and stabilize the voltage under different operating conditions are derived. The integrated system under study has four key subsystems to supply the required electric loads. The first and second subsystems include the layout of the studied MG and the renewable generation sources from Wind turbine and PV array. The third represents the boost converter between the PV and the DC collection bus as well as the interfaced inverter to the point of common coupling (PCC) with the MG. The fourth subsystem comprises mainly the required PI controllers to regulate the modulation index of the inverter and the duty cycle of the boost converter for PV maximum in addition of regulating the boost inverter DC link voltage. The proportional and integral parameters of these controllers are tuned off-line to enhance the grid performance. The integrated system and the associated subsystems are fully validated for efficient operation under normal or fault conditions using the Matlab/Simulink/Sim Power software.

Analytical investigation of induction motor drive under DC-link voltage ripple in voltage source inverter.

Analytical analysis and mathematical model of ripple components of the DC-link voltage of three-phase voltage source inverter and its influence on an induction motor drive both in time and frequency domain are presented in this paper. The analytical expressions for the voltage and current space-vectors as a function of the DC-link voltage pulsation are derived. From the current space vectors the torque behavior is estimated again as a function of DC-link voltage pulsation. The proposed analytical method is based on the mixed p-z approach enabling presentation of the results in closed-form.

A novel MIMO SMC for comprehensive unified control of the cascaded DC‐DC and DC‐AC converters in grid connected photovoltaic systems

SummaryIt is well known that DC‐DC boost converters are cascaded with DC‐AC inverters for grid connection of the photovoltaic (PV) systems. In the traditional control approaches, the mentioned DC‐DC and DC‐AC converters are controlled separately to facilitate the controller design problem. However, from the controller design viewpoint, the overall structure of the grid connected PV generator is a multi‐input multi‐output (MIMO) system. The duty cycle of the DC‐DC converter and inverter modulation index are the control inputs and, on the other hand, generated photovoltaic DC power and exported power to the grid are control outputs. Moreover, the inverter DC link voltage should be stabilized by the closed‐loop controller as well as an internal control output. If controllers are designed separately, it means that the interaction between DC‐DC and DC‐AC controllers isn't considered accurately, and since the isolated models of DC‐DC converter and DC‐AC inverter are extracted based on some approximated assumptions, separate controller design cannot guarantee stability and robustness of the whole system in a wide range of operation. To cope with these problems, in this paper, a novel MIMO sliding mode controller (SMC) is developed for comprehensive closed‐loop control of the DC‐DC boost converter cascaded with a single‐phase DC‐AC grid connected photovoltaic inverter. In the proposed approach, the dynamic model of whole system is developed comprehensively at first, and then, a unique MIMO controller is designed to control both DC‐to‐AC and DC‐to‐DC converters together. To cope with the nonlinear characteristic of the system and uncertainty of model parameters in a wide range, a fixed‐frequency SMC is developed using the comprehensive state space model of the closed loop system. In the proposed MIMO‐SMC controller, the AC power (which is exported to the grid) and operating point of the PV source are controlled via inverter modulation index and duty cycle of the DC‐DC boost converter, respectively. Another major advantage of the proposed system is mitigating the non‐minimum phase characteristic of the boost converter through the indirect control of inverter DC link capacitor. To evaluate the performance of the designed control system, simulation results are compared with a standard linear PI controller. It is shown that the developed system has zero steady‐state error and enjoys faster dynamic response during the start‐up and step changes of AC and DC current references. Moreover, it can maintain the stability of closed‐loop systems in a wide range of operations.

Harmonic Mitigation using Hybrid Power Filter to Improve Power Quality

This paper represents a power quality improvement using harmonic mitigation method in distribution and transmission system. This include the hybrid power filter for mitigating the harmonic in the power system, the hybrid power filter is the combination active power filter ,passive power filter and voltage source inverter with the passive component like a capacitor and the inductor. The drawback of the active and the passive power filter is overcome by designing the hybrid power filter, the capability of harmonic mitigation can be increased with dc link voltage of the voltage source inverter. in this two method of implementation is adopted for harmonic mitigation in power system like hybrid mode and the passive mode , in passive mode the passive component is used in series such as capacitor and inductor and in hybrid mode the voltage source inverter is used along with the LC-filter . The power quality improvement and the reactive power control is also represented in this paper The analysis and MATLAB simulation give the proper solution to mitigate the harmonic in the distribution and the transmission system to improve the power quality and system stability . Index Terms— ,FFT Analysis hybrid power filters, passive power filters, power system harmonics, reactive power control., Total Harmonic Distortion, power quality, transmission and distribution network..

A novel Lyapunov-based robust controller design for LCL-type shunt active power filters using adaptive sliding-mode backstepping approach

In this paper, a novel hybrid two-loop nonlinear controller is designed for stabilization and robust control of the LCL-type shunt active power filter (SAPF). To cope with the instability issue of the closed-loop system and the inherent resonance of the LCL coupling, backstepping, sliding mode and adaptive controllers are combined. DC link voltage of the grid-connected inverter is regulated in an outer control loop by determining a proper reference value for an inner loop. In addition to DC link voltage control, a major objective of the proposed closed-loop system is to make the grid current in phase with the grid voltage directly. Hence, active power filtering of the grid-connected inverter can be achieved without any current feedback from the local load. To stabilize the LCL-type SAPF in a wide range of changes, all uncertain parameters of the model including the DC link capacitor and equivalent impedances of the LCL coupling network are estimated by employing a proper Lyapunov function. For practical evaluation of the developed approach, the closed-loop system is implemented by using Texas Instruments’ digital signal processor (DSP-TMS28F335). Considering the application of an adaptive-robust nonlinear controller, it is proved that the system enjoys a stable and robust performance over the whole range of utilization, and it doesn't suffer from resonance issues of the LCL-type SAPFs. Moreover, considering the experimental results, it is observed that the steady-state error of the proposed nonlinear controller is zero in a wide range of operations.

Analysis and Control of an Input-Parallel Output-Series Connected Buck-Boost DC–DC Converter for Electric Vehicle Powertrains

Many electric vehicle powertrains use a boost type dc-dc converter to step-up the battery voltage for optimization and improving vehicle performance. The converter allows variation of inverter dc-link voltage to further reduce losses. By focusing on boost operation only, previously proposed drivetrains have not fully utilized the benefits of variable dc-link. This paper describes a new non-isolated bidirectional dc-dc converter capable of voltage step-down as well as high-gain voltage step-up operation. Such wide voltage range operation can lead to improved efficiency of electric vehicle drivetrains. The proposed converter comprises two non-inverting buck-boost modules, configured to operate in various optimized modes depending on the load requirement. Compared to existing bidirectional buck-boost converters, the proposed converter offers lower switch stress, reduced converter size and better efficiency. The operation of the converter in different modes is described in detail, followed by small-signal modeling and an outline of the control scheme. Experimental results obtained in an all-SiC 5 kW prototype show stable operation while the converter emulates the behaviour of the dc-dc stage in a variable dc-link EV powertrain under the ECE 15 drive cycle. The prototype demonstrated peak efficiencies of more than 98.5% and 98% for voltage step-up and step-down operations, respectively.

DE SHM Based Harmonic Minimization for Modified PUC 15 Level Inverter

A 15-level Modified Packed U-cell (MPUC) Inverter is investigated in this study, and a Selective Harmonic Mitigation (SHM) method is used to reduce and eliminate several harmonic components on the output voltage, resulting in a lower Total Harmonic Distortion (THD) factor. The proposed MPUC-15 inverter can provide a 15-level output with only eight switches, making it the most compact inverter to date. In order to achieve the 15-level output, the inverter's dc link voltage is kept in the ratio of 1/4:3/4:1. A detailed explanation of the PMUC15 inverter's operation with various switching states is provided. The MPUC15 inverter allows for the elimination of more harmonics. However, the equation of the harmonic becomes more complex as additional switching angles emerge in the harmonic equations, which are difficult to solve using typical linear optimization methods. The SHE-PWM equations for a 15-level inverter are created and solved using Deferential Evaluation (DE) with a variable modulation index, a current optimization method. The reported output THD has been less than 5%, and angles for various modulation indexes have been compiled and provided in tabular format. The inverter prototype is built in MATLAB®/Simulink, with a Typhoon HIL SCADA setup for testing the results of the DE algorithm.

Design and Performance Analysis of PV-SMES-Based Microgrid Integrated With Power Fluctuation Suppression and Active Filtering Control

This paper proposes to integrate power fluctuation suppression and active filtering control into the centralized photovoltaic (PV) inverter based on superconducting magnetic energy storage (SMES). The superconducting coil (SC) is interfaced to the DC-link of the PV inverter through a DC/DC converter. The PV-SMES-based system performs the dual demands of transferring maximum power from PV array apart from suppressing power fluctuations and harmonics existing in microgrid. An improved sliding mode controller (SMC) was developed for the DC/DC converter to stabilize the DC-link voltage of PV inverter. The stability of the proposed controller is demonstrated using Lyapunov stability theory. The comprehensive performance of the PV-SMES-based system is verified through a series of simulation comparisons based on a lead-acid battery scheme.

Robust fractional‐order super‐twisting sliding mode control to accurately regulate lithium‐battery / super‐capacitor hybrid energy storage system

One of the main challenges in front of the inventors and researchers to compensate the power quality problems is the existence of an efficient and reliable electric energy source for dynamic voltage restorer (DVR). Recent advances in the technologies of lithium-battery (LB) and super-capacitor (SC) have made them possible to be used as hybrid energy storage system (HESS) for DC-power supply of DVR. But then, a robust and efficient controller must be essentially designed to compensate the intricate correlation between system components, unknown nonlinearities, parameter uncertainties related to the HESS. Hence, fractional-order super-twisting sliding mode control (FOSTSMC) is proposed for LB/SC-HESS to smoothly and accurately smoothly track the current reference and control the DC-link voltage of the asymmetric half-cascaded multilevel inverter of DVR during different compensation conditions. As the primary controller, FOSTSMC has compensated the unknown nonlinear parts and parameter uncertainties related to LB/SC-HESS through the real-time disturbance estimation using sliding mode state and disturbance observer (SMSDO). Both the battery current and DC-link voltage due to the physical measurability are chosen to design the control scheme based on the proposed FOSTSMC. The proposed controller has been compared with the proportional integral derivative and the sliding mode control under different probable scenarios to evaluate and validate its observability and controllability. To better present the effects of FOSTSMC, AHCMLI, and HESS-based DVR, they have been quantified as follows: Three real-time stability benchmarks that is, overshoot, undershoot and settling time are respectively attained for FOSTSMC: 0.6, 0.4, and 0.03; for sliding mode control: 1.1, 0.7 and 0.019; for proportional integral derivative: 0.9, 2, and 0.117. That is to say, FOSTSMC can smoothly and accurately track the current reference and control the DC-link voltage during different compensation conditions as compared with other controllers. Asymmetric half-cascaded multilevel inverter can provide 33 steps with consideration of 12 unidirectional switches, whereas binary, trinary, and other multilevel structures can provide less than 27 steps with consideration of 12 switches. The quasi-AC voltage synthesizer-based DVR can completely and accurately compensate the voltage sag and swell with THD of 2.12 and 2.35, respectively. The THD of mal-compensation voltage sag and swell using the conventional DVR are respectively 11.57 and 13.86.

Performance and Tracking Control of Three-Phase Induction-Motor Drive Fed from a DC-Modified Nano-grid

Nowadays, induction motor (IM) can be used in tracking systems to follow a predefined path like in robotics and servos. The modified nanogrid is a small scalable-renewable energy intermittent source that powers loads via a single-stage inverter (SSI). Higher utilization of the inverter dc-link voltage improves its output voltage and dependently, the performance of the motor tracking speed. So, this paper proposed a switched boost inverter (SBI) to feed IM from PV-source to boost its dc-link output voltage. The usage SBI utilizes minimum passive components, more active elements, introduces shot-through mode as z-source inverter and produces both ac and dc voltages simultaneously. The performance of the motor-tracking speed depends directly on the motorstator voltage. So, the proposed method depends mainly on two parameters to verify the pre-defined trajectory speed. The first proposed intention is a simple algorithm for a closed-loop dc-link boosting control based-on the reference model to compute the optimum duty ratio (D). The second one depends mainly on the modulation index (M) to produce the reference signals needed to adjust the speed of the motor through a (voltage/frequency) control of a predefined value. The modelling and validation of the proposed system was implicit with the help of Matlab/ Simulink package. The robustness of the system has been tested by selecting several speed trajectories and was able to track them. Furthermore, SBI-based system was compared with other VSI-inverter techniques such as the space-vector PWM single- and two-stage VSI inverters. Test results explored that the SBI-based system is a strong competitor to other inverter techniques especially at low-voltage intermittent supply.

Model Predictive Control of Permanent Magnet Synchronous Motors in the Overmodulation Region Including Six-Step Operation

This paper proposes a model predictive control scheme with a higher-level open-loop torque control and an underlying continuous-control-set model predictive current control (CCS-MPCC) combined with a space vector modulation and an integrated harmonic reference generator (HRG) for permanent magnet synchronous motors (PMSMs), which is able to utilize the DC-link voltage of a two-level inverter to its maximum during transient and steady-state conditions. By formulating the CCS-MPCC as a quadratic program with the voltage hexagon as inequality constraints, the MPCC's typical dynamic response can be achieved during transient operation. When the overmodulation region is reached, additional current harmonics are induced by the voltage constraints, causing a deterioration of the controller's performance. To overcome this problem a HRG is introduced, which calculates at each sampling instant a reference current that contains these harmonics by solving a boundary value problem, using an overmodulation method under the assumption of steady state.Hence, the HRG performs a model-based current reference trajectory prediction ensuring that the CCS-MPCC can enter the overmodulation region. This allows highest control dynamics even at the voltage constraint while ensuring a seamless transition from linear modulation to overmodulation and six-step operation. The method presented here is able to operate in the entire speed range including standstill. Thus, it is not necessary to switch between different controller frameworks for the constant-torque and constant-power regions. Extensive simulative and experimental investigations for a highly utilized PMSM with significant (cross-)saturation effects prove the viability of the proposed control methodology.

A Novel DC-DC Converter Based Closed Loop Control of BLDC Motor for SPV fed Water Pumping System

This Paper Presents Novel DC-DC Converter Based Closed Loop Control of BLDC Motor for SPV fed Water Pumping System Solar Photovoltaic (SPV) Array fed Water pumping System Utilizing Buck-boost DC-DC Converter in order to extract the maximum available power from Solar system. Solar energy has the greatest availability compared to other energy sources. For such solar PV systems, maximum power point tracking control is preferred for efficient operation. This concept is dealing with INC method which is one of the MPPT methods. This study deals with a buck–boost converter controlled solar photovoltaic (SPV) array fed water pumping in order to achieve the maximum efficiency of an SPV array and the soft starting of a permanent magnet brushless DC (BLDC) motor. The current sensors normally used for speed control of BLDC motor are completely eliminated. The speed of BLDC motor is controlled through the variable DC-link voltage of a voltage-source inverter (VSI). The VSI is operated by fundamental frequency switching, avoiding the losses due to high-frequency switching, in order to enhance the efficiency of the proposed system.

Discrete-Time DC-Link Voltage and Current Control of a Grid-Connected Inverter with LCL-Filter and Very Small DC-Link Capacitance

The paper presents a controller design for grid-connected inverters (GCI) with very small dc-link capacitance that are coupled to the grid via an LCL filter. The usual controller designs would fail and result in instability. The proposed controller has a cascaded structure with a current controller as inner control loop and an outer dc-link voltage controller. The controller design is performed in discrete time and it is based on a detailed stability analysis of the dc-link voltage controller to determine the controller parameters which guarantee stability for all operating points. The inner loop is a state-feedback current controller that is designed based on the discrete linear-quadratic regulator (DLQR) theory. An additional integral error feedback assures steady-state accuracy of the current control loop. The simulation and experimental results validate performance and stability of proposed controller design.

Modified Synchronous Reference Frame Control of Solar Photovoltaic-Based Microgrid for Power Quality Improvement

In this paper, solar photovoltaic (SPV)-based microgrid has been connected to grid. Modified synchronous reference frame control of PV inverter has been proposed to estimate reference current for power quality improvement. Conventionally, DC link voltage of the PV inverter is regulated using proportional integral (PI) controller, which suffers from undershoot/overshoot and long settling time during load variation. Intelligent control technique can be the better solution with more accuracy and fast dynamic response. In the present work, interval type-2 (IT-2)-based fuzzy logic controller (FLC) has been proposed to control inverter’s DC link voltage. Performance of the grid-connected SPV system is analyzed using proposed IT-2 FLC and compared with conventional PI as well as type-1 FLC. It compensates the harmonics of the nonlinear load and maintains the grid at unity power factor by supplying the reactive demand of the load. Total harmonic distortion at grid side of the system is within the limits as per IEEE-519 standard. To test the efficacy of the proposed IT-2 FLC for grid-connected SPV system MATLAB software2016(a) has been used.

Iron Loss Minimization Strategy for Predictive Torque Control of Induction Motor

Today’s modern control strategies of an induction motor (IM) drive require a power source with an adjustable output voltage frequency and amplitude. The most commonly used converter topology is a two-level voltage-source inverter (VSI). However, the utilization of a VSI introduces additional voltage and current distortion, which leads to additional power losses in the machine’s magnetic circuit. Both the transistor switching frequency and the type of the inverter control determine the total harmonic distortion (THD) of the motor’s phase currents. In this paper, the influence of the inverter DC-link voltage on the iron losses of an IM controlled by a predictive torque control (PTC) is presented. It is shown that if the IM drive operates below the rated speed, it is possible to modify the PTC algorithm to reduce the additional iron losses caused by the non-harmonic inverter output voltage. The control of the DC-link voltage is achieved by using a silicon-controlled rectifier. Experiments were conducted on a 5.5 kW IM controlled by PTC, and the results are compared against a sinusoidal voltage supply created by a synchronous generator.

Speed Control of Three Phase Induction Motor Using Universal Bridge and PID Controller

Speed control technique are generally essential in adjustable speed drive system. This system requires variable voltage and frequency supply which is obtained from a three phase voltage source inverter. This paper presents the speed control of induction motor fed by a three phase voltage source inverter using pulse width modulation method and universal bridge. To control the peak dc link voltage of voltage source inverter, a PID controller was designed. The performance analysis of open loop and closed loop speed control system is carried out in Matlab/Simulink. The simulation result shows that the speed controller has a good dynamic response and can control the induction motor successfully with a better performance.

Power factor improvement of permanent‐magnet linear vernier motor by using dual‐inverter with hybrid discontinuous PWM

A permanent-magnet linear vernier (PMLV) motor has the advantages of large force and low cost, but it suffers from a low-power factor. This study proposes an instantaneous power control algorithm by using a dual-inverter open-winding (OW) configuration to equivalently improve the PMLV motor power factor. In the proposed algorithm, the active and reactive powers for the motor operation are supplied by the main and compensation inverters, respectively. Therefore, the main inverter dc-link voltage is fully utilised to generate the active power, which is equivalent to the improvement of the motor power factor. Furthermore, a hybrid discontinuous pulse width modulation (HDPWM) scheme is proposed, which takes into consideration the power factor characteristics of the dual-inverter. Compared to the existing OW modulation ones, the proposed HDPWM technique can greatly reduce the dual-inverter loss. The experimental results are carried out to verify the proposed control strategy.

A Control Scheme without Sensors at the PV Source for Cost and Size Reduction in Two-Stage Grid Connected Inverters

In order to reduce the cost of PV facilities, the market requires low cost and highly reliable PV inverters, which must comply with several regulations. Some research has focused on decreasing the distortion of the current injected into the grid, reducing the size of the DC-link capacitors and removing sensors, while keeping a good performance of the maximum power point tracking (MPPT) algorithms. Although those objectives are different, all of them are linked to the inverter DC-link voltage control loop. Both the reduction of the DC-link capacitance and the use of sensorless MPPT algorithms require a voltage control loop faster than that of conventional implementations in order to perform properly, but the distortion of the current injected into the grid might rise as a result. This research studies a complete solution for two-stage grid-connected PV inverters, based on the features of second-order generalized integrators. The experimental tests show that the proposed implementation has a performance similar to that of the conventional control of two-stage PV inverters but at a much lower cost.