Inverter Output Voltage Research Articles

Optimization of the Voltage Total Harmonic Distortion in Multilevel Inverters by Using the Taguchi Method

A critical reduction in the total harmonic distortion in the output voltage of multilevel inverters can be obtained with an appropriate selection of the angles to switch the power semiconductors at low frequency. Among the methods used to obtain the required sequence of angles, it is possible to recognize both standard and optimized methods, like the Newton–Raphson method or the genetic algorithm, to mention a few. However, implementing the genetic algorithm implies using several configuration parameters, so it is difficult to know if the best option was chosen. This paper implements the Taguchi design of experiments, the Taguchi method, to obtain the appropriate switching angles for an multilevel inverter producing an output voltage of five and seven levels. Experimental results obtained from a laboratory prototype using the computed angles in the MATLAB GA solver demonstrate the superiority of the proposed method.

Intelligent Approach for Control Techniques Based on Complex Converter Structures

Hybrid frequency control strategies are used to eliminate the problem of current inversion in multilevel cascaded asymmetrical H-bridge inverters. Unfortunately, this technique results in unbalanced power at the inverter output. The improved hybrid PWM modulation strategy helps to regulate power balances within a reasonable range at high and low voltages, by adjusting the conduction angle of the cells in high frequencies. However, as the conduction angle of a high-voltage cell increases, the fundamental amplitude of the inverter output voltage decreases, since waveforms with absolute values greater than 2 E cannot be perfectly modulated. Based on mathematical models of the conduction time for each level synthesis method, a new modulation strategy is proposed to solve the problems associated with the two strategies mentioned above. This new high-frequency modulation strategy adopts a combination of pulse-width modulation (PWM) and step modulation to combine control of the high-voltage and low-voltage units. At given intervals, the control voltage signals of the low-voltage unit are exchanged. Finally, the power of each unit is balanced and the basic amplitude of the inverter output voltage is not affected. Finally, the MATLAB/Simulink simulation model and experimental platform verify the feasibility of this strategy.

Simulation design and analysis 9-level H-bridge single phase stepdown cyclo inverter

This DC-to-AC voltage converter is designed for output frequency controlled by a 9-level cascade H-bridge cyclo inverter with pulse width adjustment. The aim of the study was to determine the pattern and format of the voltage, output frequency, and Total Harmonic Distortion index of a 9-level IGBT cyclo inverter. The method used is to build a unidirectional power converter design modeling into 9 alternating levels with cyclo converter-controlled frequency settings using the Simulink MATLAB tool. The cyclo converter section is constructed with two P and N converters in a parallel arrangement. The frequency and trigger pulse width of both converters control the output voltage and frequency format of the cyclo inverter. The test results show a series of ladder waves with an output frequency, of (1/2f, 1/3f, 1/4f, 1/5f, 1/6f, 1/7f, 1/8f, 1/9f, and 1/10f). The simulation results show that the nth input frequency divider waveform is characterized by the emergence of a number of step pulses of n positive half cycles and negative half cycles. The Total Harmonic Distortion Index gets bigger when the system circuit is designed at a low frequency. This modeling can be implemented into a prototype that is used for variable-speed DC motor drivers.

A new generalized predictive current control algorithm with integration of fractional part function based modulation technique: Single phase self‐balanced type multilevel inverter topologies

SummaryIt is generally impossible to control the inverter output current (IOC) based on operator needs if only pulse width modulation (PWM) techniques are used. Conventionally, authors have reported the finite control set‐based predictive current control algorithm (FCS‐PCCA) to control the IOC with a fast dynamic response. However, this type of algorithm without a PWM stage generates a variable switching frequency (VSF) of operation, and it leads to filter design problems, inequitable thermal stress, and more current distortions that have been presented. To alleviate all these issues, a new generalized PCCA with the integration of a fractional part function‐based single carrier modulation technique (G‐PCCA‐FPF‐SCMT) has been proposed, and it provides constant switching frequency (CSF) of operation. In this technique, the normalized optimum inverter output voltage (N‐O‐IOV) has been fed with FPF‐SCMT. The particular modulation stage implementation is straightforward since even inverter level number increases, the number of references and triangular carrier signals is always only one. The complete control implementation process of the proposed technique is extremely low compared with all traditional CSF‐based PCCAs. To verify the proposed technique experimentally in both steady and transient state operations, one of the conventional five‐level switched capacitor‐based inverter topologies has been considered and elucidated vividly in both open‐loop and closed‐loop operations.

Investigation of improved Differential Y-source inverter

Y-typed networking with three winding-coupled inverter is a brand-new DC-DC and DC-AC inverter. The inverter has a simple topology structure. However, it owns powerful functions. The inverter, with two Y-shaped structures, has not adopted two independent circuits, which are replaced by some new topology parts, such as the switches, adding up to control the current. Obviously, it has now become a single-stage inverter. The improved inverter has also been called DYSI, the Differential Y-source Inverter, for it combines the Differential Boost Inverter with the Y-source Inverter. The improved inverter would produce high AC output voltage, solving the problems caused by the low output voltage in photovoltaic inverters while increasing voltages to connect with the national grid. The modulation of the improved inverter is the half-sine wave, which drives one coupled and two switches in the branch to conduct at high times. The improved inverter also has some defects. The inverter would produce abrupt energy leakage because of the incomplete coupling of inductances. Similar to other inverters, the process during which the switches turn on and turn off would inevitably generate power loss, leading to a much lower output than the ideal design. In contrast, the deficiency could be decreased by adding two diodes without loss to the circuit topology.

Vibration Analysis of Traction Drive System Components Based on the Field Test for High-Speed Train

The traction drive system of a high-speed train is the key subsystem of a high-speed train, which controls the driving and braking of the train through electromechanical coupling, and determines the running speed, power quality, and comfort of the train. The traction drive system is subjected to many internal and external excitation sources and frequency bandwidth, and the dynamic response and dynamic characteristics of the system are extremely complex. The results of the traction motor field vibration test showed that 100 Hz vibration frequency occurred during traction and braking of high-speed trains when the inverter output voltage frequency was close to 100 Hz, and its vibration amplitude was higher than other frequency bands. When traction power was cut-off, the 100 Hz frequency was not significant. Through simulation analysis of fatigue damage, it was found that 100 Hz DC-link voltage pulsation would aggravate the fatigue damage of the motor hanger. The line vibration test and bench test of the gearbox showed that there was a natural frequency of the gearbox at about 2500 Hz, when the meshing frequency was close to it. Thus, the resonance characteristic became significant.

Carrier Phase Shift Method of SPWM for Concurrent Wired and Wireless Power Transfer Systems

This paper presents an approach for concurrent power transfer to wired and wireless systems using just a single inverter. The approach utilizes a novel carrier phase-shift (CPS) method that independently controls the inverter output voltages at the fundamental and switching frequencies. This proposed method can be a cost-effective solution to wireless power transfer (WPT) systems used in contactless slip rings (CSR), which transfer power to auxiliary loads such as sensors, radars, and IoT devices. There are two separate converters in conventional CSR systems: one is for the motor drive, and the other is for the WPT system. It is proposed that the switching harmonics of the motor drive can also be utilized to excite the WPT system while the low-frequency component can still be used to drive the motor. In order to control these independently, the CPS method is introduced. The proposed method is investigated analytically for sinusoidal-PWM (SPWM). Then, an experimental setup consisting of a 3-phase 3-wire GaN-based inverter and a 3-phase motor is built. Experimental results show that the WPT and motor systems are operated concurrently, and their powers are controlled independently by the proposed method.

Optimization-Based Duty Cycle Allocation for a Five-Leg Inverter to Drive Two Electric Motors

Driving two electric motors with a five-leg voltage source inverter (FL-VSI) by connecting one phase of each motor to a common leg possesses the advantage of reducing the number of power switches. This article proposes a duty cycle allocation method to make FL-VSI use the DC bus voltage more efficiently. In this method, the motor with a smaller common leg duty cycle requirement is set as the first priority. An additional period of duty cycle is added simultaneously to the first-priority motor's three phases to compensate for the difference of the common leg duty cycle requirement between the two motors. Thereby, the duty cycles of the three legs connecting to the first-priority motor, including the common leg, are confirmed. Then, the duty cycles of the remaining two legs connecting to the second-priority motor are allocated by solving a nonlinear optimization problem. The objective of the optimization is to make the inverter output voltage close to the voltage requirement of the second-priority motor. Experiments have been implemented, and the results verify the improvement of the proposed method.

Model predictive current control for maximum power point tracking of voltage source inverter based grid connected photovoltaic system

<p>Due to the high demand of grid connected photovoltaic systems, there is a need to track the maximum power point of the PV system. As the output of PV system is dc, there should be a converter, acting as medium between PV system and dc bus capacitor to track maximum power at all the loads. Usually boost converter is acting as medium between PV system and dc link capacitor as the duty cycle of the insulated-gate bipolar transistor in boost converter is in between 0 to 1 for maximum loads during maximum power point tracking (MPPT). To make PV system stable, the balance point is dc bus. If the dc bus voltage is constant, the system will be stable. Then the transfer power will just depend on current. For this purpose, the active current reference signal is to be generated by setting up the reference voltage across dc bus. Here to generate active reference current, PI controller is used and the reference voltage is taken according to the peak voltage of the inverter output voltage. The proposed control strategy was evaluated on a three-phase inverter linked to the grid and supplied by the PV system, which is working under varying irradiation conditions.</p>

Harmonic Spectra Analysis of Digital SPWM in VSI With DC Bus Ripple and Dead-Time Effects

This paper presents a closed-form analytical solution to the harmonic spectrum of output voltage of a single-phase H-bridge inverter, and gives the precise harmonic spectrum considering the effects of dead-time and DC bus voltage ripple in a digitally controlled system. Since H-bridge is the basic block in converters, this solution and spectrum can be extended and applied to a variety of pulse width modulation (PWM)-based topologies. The interaction between modulation waveform and triangular during modulation process is fully analyzed from a mathematical perspective, so that the combined effects of digital sampling, dead-time and DC bus voltage ripple on the output voltage are summarized in time and frequency domains. Furthermore, the presented harmonic spectra do not need to judge the current polarity in calculation, which means that the exact amplitude and phase of each output harmonic can be obtained accurately, providing the important theoretical basis for system parameter design and specific harmonic compensation or elimination. The presented analysis results are verified by simulations and experiments.

Sequence-Admittance Measurement Method of Grid-Connected Inverter With Its Control System Disturbance

The impedance or admittance characteristics of the grid-connected inverter play an important role in its stability analysis. The traditional sequence-admittance measurement methods of the grid-connected inverter mostly rely on special admittance measurement equipment or adjacent grid-connected inverters for disturbance injection. Because of high hardware cost or inconvenience, the above methods are not suitable for price-conscious testers to some extent. To address the above issues, this paper proposes a sequence-admittance measurement method of the grid-connected inverter with its control system disturbance. Firstly, the sequence-admittance model of the measured grid-connected inverter when small-disturbance signal is superimposed on its modulation signal is deduced and the system equivalent circuit model is built. Then, the flow chart of the proposed sequence-admittance measurement method is designed. According to the injected small-disturbance signal, the output voltage and inductor current of the grid-connected inverter, the sequence-admittance characteristics in sub/super-synchronous frequency area can be obtained. The measurement process does not need the cooperation of external disturbance source, which saves costs and improves the measurement convenience. Finally, experiments verify the effectiveness of the proposed sequence-admittance measurement method.

Simple Discrete Control of a Single-Phase Voltage Source Inverter in a UPS System for Low Switching Frequency

Previous research has shown that the inverter output voltage distortions are higher for low switching frequencies, and it is impossible to increase the controller gains because it will cause oscillations of the output voltage. The main reason is the real frequency domain characteristic of the PWM modulator and measuring traces, which can be modelled as switching periods delays. The thesis of this paper is that by using the control system that takes care of these delays, it is possible to decrease output voltage distortions for the standard loads for relatively low switching frequencies (e.g., 12,800 Hz). The Luenberger observer was implemented in the multi-input-multi-output passivity-based control of the system with the delay, in order to predict the state variables of the inverter. It is shown that state variable prediction is unnecessary for high switching frequencies (e.g., 51,200 Hz). The theory, simulations and breadboard verification, using the inverter model controlled with the real-time interface MicroLabBox, are presented.

VSG Control for Cascaded Three-Phase Bridge Based Battery Inverter

With the increasing number of new energy sources connected to the grid, the unbalanced output of three-phase grid-connected inverters and the lack of no inertia and damping characteristics in the traditional microgrid control system will seriously affect the stability of voltage, frequency, and power angle for microgrids. This paper proposes a novel cascaded three-phase bridge inverter topology for the battery system used for the electric vehicle. Compared with traditional cascaded H-bridge inverters, the proposed multilevel inverter can achieve self-adaptive balance for three phases. The mathematical model of a cascaded three-phase bridge inverter is established in this paper. Based on the voltage and current equations of a multilevel inverter, a new modulation strategy named carrier phase-shifted-distributed pulse width modulation (CPSD-PWM) was developed, which is more suitable for cascaded three-phase bridge inverters. The harmonic analytic equations of carrier phase-shifted pulse width modulation (CPS-PWM) and CPSD-PWM are constructed by the double Fourier analysis method. Compared with the traditional PWM modulation strategy, the CPSD-PWM can reduce the output harmonics and improve the balance of the three-phase output, which can realize the three-phase adaptive balance in the cascaded three-phase bridge inverter. This paper develops a cascaded three-phase bridge multilevel power converter system based on the virtual synchronous generator (VSG) control strategy. The voltage and frequency of inverter output can be accurately controlled in both island mode and grid-connected mode through active power-frequency regulation and reactive power–voltage regulation, and the stability of primary frequency regulation for the multilevel microgrid inverter can be improved by collaborative optimization of virtual inertia and virtual damping. The CPSD-PWM modulation strategy and VSG control strategy are verified by the simulation results and experimental data for the cascaded three-phase bridge inverter.

Comparative Study of Passivity, Model Predictive, and Passivity-Based Model Predictive Controllers in Uninterruptible Power Supply Applications

Voltage source converters are widely used in distributed generation (DG) and uninterruptible power supply (UPS) applications. This paper aims to find the controller that performs best when model changes occur in the system, showing insensitivity to parameter variations. A comparison of the finite control set model predictive controller (FCS-MPC), interconnection and damping assignment passivity-based controller (IDA-PBC), and passivity-based model predictive control (PB-MPC) reveals that the PB-MPC provides high resistance to these unexpected LC filter changes in the converter. The second aim of the paper is to reduce the total harmonic distortion (THD) of the output voltage of the three-phase voltage source inverter (VSI). A high total harmonic distortion (THD) value exists in the voltage waveform of the three-phase voltage source inverter (VSI), feeding a non-linear load. A MATLAB simulation was performed using three control techniques for a three-phase VSI feeding: linear load, unbalanced load, and non-linear load. The PB-MPC performs better than the FCS-MPC and IDA-PBC in terms of having a low THD value in the output voltage of the converter under all types of applied loads, improving the THD by up to 30%, and having low variation in THD with mismatched filter parameters, as shown in the bar charts in the results section. Overall, the PB-MPC controller improves the robustness under parameter mismatch and reduces the computational burden. PB-MPC reduces the THD value because it integrates power shaping and the injection of damping resistances into the VSI.

A Novel Narendra‐based adaptive anti‐disturbance control strategy for the microgrid inverters: A novel MG VSI adaptive anti‐disturbance control strategy based on Narendra theory

AbstractThe control performance of the voltage source inverter will be reduced when it operates under complex microgrid (MG) conditions. Traditionally, problems such as high controller order and complex design may occur when robust control and secondary regulation are adopted for the inverters. Meanwhile, when the conventional adaptive control is adopted, the adaptive gain may be too high, resulting in increased sensitivity of the system to external disturbances. To address the above problems, a novel Narendra‐based adaptive anti‐disturbance control strategy for microgrid voltage source inverter is proposed in this paper. Firstly, a Narendra adaptive‐based controller is constructed, which enables the controller to adaptively adjust the system parameters to change the inverter output voltage quality. Secondly, the extended state observer (ESO) is introduced to observe and suppress the total disturbance of the system, which can make the system less sensitive and ensure the stability of the system operation. Thirdly, according to the Lyapunov stability theory, the Lyapunov function is chosen to prove the global asymptotic stability of the system, and an adaptive law is designed. Finally, the comparative experiment shows that the proposed control strategy based on Narendra adaptive anti‐disturbance can maintain excellent voltage control performance in complex working conditions, and then ensure that the inverter's output voltage always meets power quality standard in complex working conditions.

POWER SPECTRAL DENSITY OF DUAL RANDOMIZED DISCONTINUOUS PULSE WIDTH MODULATION

This paper addresses the spectral characteristics of a carrier-based dual randomized discontinuous pulse width modulation (DRDPWM) technique for reducing conducted EMI and switching losses in three-phase voltage source inverters. It combines two simple random schemes, random carrier frequency modulation (RCF-DPWM) and random pulse position modulation (RPP-DPWM). First, the modulating principle of the DRDPWM is presented. Then, the analytical expressions of power spectral density (PSD) that characterize the output voltage of the three-phase inverter are derived. Analytical and simulation results show the effectiveness of PSD spreading of the DRDPWM. Finally, experimental results verify the analytical and simulation results and prove the effectiveness of the DRDPWM scheme in spreading the spectrum compared to simple schemes (RPP-DPWM and RCF-DPWM) and conventional scheme DPWM.

Novel SVPWM Method Based on Zero-Voltage Notch of Resonant DC-Link Inverter

In order to decrease the switching loss of the auxiliary circuit of the resonant DC link (RDCL) inverter and improve the voltage utilization and system efficiency, this paper presents a new space vector pulse width modulation (SVPWM) method based on the zero-voltage notch of the resonant DC link inverter. This resonant DC link inverter reduces the current stress in the main circuit by paralleling auxiliary switch. And this method makes the operation of the auxiliary resonant circuit (ARC) less frequent, thus reducing the losses of the ARC and therefore improving the system efficiency. At the same time, this method analyzes and compensates for the missing voltage vectors based on the ideal output voltage, so that the inverter output voltage vector under this modulation is the same as the ideal SVPWM output voltage vector. Compared with the original modulation of RDCL inverter, this method does not change the switching sequence, the switching times, and the action time of the vector, while reducing the switching ripple. The effectiveness and feasibility of the modulation strategy is verified in the paper through theoretical analysis as well as experiments.

Bulanık Anahtarlama Algoritması ile DTC Kontrollü Asenkron Makine için İyileştirilmiş Tork ve Hız Performansları

Direct Torque Control (DTC) is a vector control method based on the control of the stator flux vector in the desired direction. The control of the stator flux vector is achieved by direct selection of the optimum inverter output voltage vectors. The limit values of the trajectory determined in the rotation of the stator flux vector are determined using hysteresis controllers. In this study, performance analysis of two different control methods for reducing speed and torque oscillations of a three-phase asynchronous motor controlled by direct torque control are presented. In Matlab/Simulink based simulation studies, performance analyses were made for different speed and torque references of the motor, and both the transient and steady state speed and torque changes were presented comparatively. When the obtained results are examined, it is seen that the performance of the new fuzzy-based controller, which is offered instead of the Proportional Integral Derivative (PID) controller used in traditional control, significantly decreases in the specific conditions of motor speed and torque oscillations. However, considering the control structure of the direct torque controller, the simple and plain control structure has been preserved. According to the results obtained, it has been shown that the Fuzzy Logic (FL) controller gives a better result than the PID controller at t=4.5 seconds.

Design and analysis of trans Z-source inverter for electric vehicle applications using neural network-clustering

The presented paper analyzes the detailed design of a trans Z-source inverter (ZSI) with an input from solar photovoltaic (SPV) system. Increase in SPV uses requires highly efficient SPV enabled inverters under varying weather parameters are in high demand in modern smart grid applications. The SPV-trans ZSI has high conversion efficiency because of the single-stage voltage boost conversion capability. In contradiction, the conventional voltage source inverter (VSI) requires an additional step-up transformer to boost the output voltage of inverter. This reduces the efficiency by increasing the volume of set up and also increase the cost of the system. In the proposed SPV system it provides a better output against VSI. The increase in inverter output voltage is because of shoot through time period present in ZSI. It also reduces the voltage stress and harmonics content as compared to VSI. The proposed model has been validated through MATLAB simulation.

Reduction of common mode voltage for grid-connected multilevel inverters using fuzzy logic controller

Cascaded multilevel three-phase inverters are increasing in industries of electric drives and renewable energy because of their large capacity and suffering from high voltage shock. However, the high magnitude of common mode voltage is one of the drawbacks. Thus, the techniques of modulation and control in these multilevel inverters significantly affect the power quality of the output voltage of inverters. This paper presents a technique using fuzzy logic technique for grid-connected cascaded multilevel 3-phase inverters. This technique has completely removed the current controllers and the conventional modulation using carriers. It also helps reduce the magnitude of common mode voltage and increase the dynamic response. Moreover, the ability to reduce harmonics and switching count also helps decrease the switching loss of inverter. The simulation results on a grid-connected cascaded 5-level 3-phase inverter have validated the effectiveness of the presented technique compared with that of the conventional method using phase opposition disposition (POD) and PI current controllers.