Voltage Source Inverter Output Voltage Research Articles

The Influence of Switching Frequency on Control in Voltage Source Inverters

This paper aims to show how the switching frequency influences the properties of the digitally controlled voltage source inverter (VSI). The measurements of the Bode plots of the inverter are shown and discussed to present the existing signal delays and power conversion efficiency, depending on the switching/sampling frequency. Two types of controllers are presented, Single-Input–Single-Output (SISO) and Multi-Input–Single-Output (MISO), and adequate prediction units (the Smith Predictor for SISO—Coefficient Diagram Method and the full-state Luenberger Observer for MISO—Passivity Based Control) were used to compensate for the delays. It will be shown by comparing the THD of the VSI output voltage that prediction is useful with low VSI switching frequency (about 10 kHz) but is not important for the middle switching frequencies (about 25 kHz) or the high switching frequency (>50 kHz). This paper shows that increasing the switching frequency simplifies digital control without reasonably decreasing efficiency. The theoretical considerations, the Matlab/Simulink 2021b simulations, the final experimental laboratory verification are presented.

Wind turbine emulator using three-phase IM controlled through an adaptive reactive power estimator fed by soft-VSI topology

PurposeThe purpose of this paper aims to design a robust wind turbine emulator (WTE) based on a three-phase induction motor (3PIM).Design/methodology/approachThe 3PIM is driven by a soft voltage source inverter (VSI) controlled by a specific space vector modulation. By adjusting the appropriate vector sequence selection, the desired VSI output voltage allows a real wind turbine speed emulation in the laboratory, taking into account the wind profile, static and dynamic behaviors and parametric variations for theoretical and then experimental analysis. A Mexican hat profile and a sinusoidal profile are therefore used as the wind speed system input to highlight the electrical, mechanical and electromagnetic system response.FindingsThe simulation results, based on relative error data, show that the proposed reactive power control method effectively estimates the flux and the rotor time constant, thus ensuring an accurate trajectory tracking of the wind speed for the wind emulation application.Originality/valueThe proposed architecture achieves its results through the use of mathematical theory and WTE topology combine with an online adaptive estimator and Lyapunov stability adaptation control methods. These approaches are particularly relevant for low-cost or low-power alternative current (AC) motor drives in the field of renewable energy emulation. It has the advantage of eliminating the need for expensive and unreliable position transducers, thereby increasing the emulator drive life. A comparative analysis was also carried out to highlight the online adaptive estimator fast response time and accuracy.

Performance Improvement of DTC-SVM of PMSM with Compensation for the Dead Time Effect and Power Switch Loss Based on Extended Kalman Filter

Two algorithms have been extensively studied for motor control: Field Oriented Control (FOC) and Direct Torque Control (DTC). Both control algorithms use a Voltage Source Inverter (VSI) to drive a Permanent Magnet Synchronous Motor (PMSM). To prevent short-arm short-circuit accidents when driving PMSM using VSI, a dead time is used to turn off the TOP and BOTTOM switches of each arm at the same time. However, this dead-time technique causes an unexpected pole voltage to be applied to the PMSM on the VSI output voltage, causing distortion and resulting in control nonlinearity. The disturbance voltage that causes nonlinearity is difficult to measure directly with the sensor. Therefore, this paper analyzes the nonlinearity of the controller due to the distorted voltage caused by the dead time during PMSM operation using the DTC algorithm and predicts the distorted output voltage using the extended Kalman Filter (EKF) to improve control stability. As a result, The algorithm proposed in this paper has verified the improvement of torque ripple and stator flux ripple through experiments and simulations.

Grid integration of PMSG based wind energy conversion with battery storage system

In this paper, the design and implementation of a permanent magnet synchronous generator (PMSG) based wind energy conversion system and battery bank storages are connected to utility grid. It has phase locked loop (PLL) control strategy as it provides for control single-phase grid connected inverter with constant dc-link voltage. The dc-link is interfaced to a permanent magnet synchronous generator through diode bridge rectifier (DBR) with dc-dc boost converter, battery bank and single phase voltage source inverter (VSI).The dc-link voltage is maintained constant value of 48 V by controlling dc-dc converter with help of perturb and observe (P&O) algorithm based maximum power point tracker (MPPT). The VSI output voltage and frequency values are controlled based on grid parameters using PI controller and sinusoidal pulse width modulation (SPWM) technique. In this grid connected system is simulated and performances are analyzed through MATLAB software. The prototype experimental results are verified through 1 kW PMSG, 48 V battery bank with single phase grid connected system.

National Grid Connected 3-Phase Inverter based on Photovoltaic Solar System

In this paper, a national grid-connected photovoltaic (PV) system is proposed. It extracts the maximum power point (MPP) using three-incremental-steps perturb and observe (TISP&O) maximum power point tracking (MPPT) method. It improves the classic P&O by using three incremental duty ratio (ΔD) instead of a single one in the conventional P and O MPPT method. Therefore, the system's performance is improved to a higher speed and less power fluctuation around the MPP. The Boost converter controls the MPPT and then is connected to a three-phase voltage source inverter (VSI). This type of inverter needs a high and constant input voltage. A second-order low pass (LC) filter is connected to the output of VSI to reduce the total harmonic distortion (THD) of the output current. The LC filter is then connected to a step-up transformer to push up the low VSI output voltage to the high grid voltage level. The control strategy is based on the rotating reference frame (dq reference frame) and the grid phase shift angle extracted using a phase-locked loop (PLL) technique. The designed PV system supplies only active power with zero reactive power to the utility grid. The system is simulated using MATLAB / Simulink software.

Nonlinear Characteristics Compensation of Inverter for Low-Voltage Delta-Connected Induction Motor

This paper proposes a scheme that can compensate for the nonlinear characteristics of voltage source inverters (VSIs) for low-voltage delta-connected induction motors (IMs). Due to the nonlinearity introduced by the dead-time, the on/off delay, and the voltage drop across the power device, the output voltage of VSIs is seriously distorted, causing distortion in the phase current of the IM, which will lead to output torque ripple. However, the existing compensation methods for three-phase VSIs are derived from star-connected loads, or ignore the conducting properties of power devices. Moreover, the current polarity detection near the current zero is quite complex. In this paper, by taking such nonlinear characteristics into consideration, especially the conducting property of metal-oxide-semiconductor field effect transistors (MOSFETs), an output voltage model of VSIs for low-voltage delta-connected induction motors is presented. After that, in view of the difficulty in detecting the line current polarity near the current zero which might lead to the wrong compensation, an advancing current crossing zero (ACCZ) compensation is proposed. Subsequently, a compensation scheme which combines the compensation based on the VSI output voltage model and ACCZ compensation is proposed. Finally, the proposed compensation scheme is implemented based on a digital signal processor (DSP) drive system. The experimental results show that the proposed scheme has better performance than the common method in terms of suppressing the effect of the nonlinear characteristics of VSI, which demonstrates that the proposed compensation scheme is feasible and effective for the compensation of the nonlinear characteristics of VSI for low-voltage delta-connected IMs.

Time‐domain characterisation of multicarrier‐based digital SPWM of multilevel VSI

The effect of sampling frequency on digital sinusoidal pulse width modulated (SPWM) output of phase-shifted carrier-based multilevel voltage source inverter (VSI) and the characteristics of output voltage and load current has been discussed here. The generalised equation of digitally controlled phase-shifted carrier-based multilevel VSI output voltage is derived using double Fourier integral solution. The Jacobi–Anger expansion has been used to obtain the integral solution. Time-domain analysis has been used to establish the relation between sampling frequency, carrier frequency, and fundamental frequency, at different modulation indices for n-level VSI. The load current of VSI is stepped in nature due to stepped variation in the output of the digital SPWM. Therefore, the low-frequency harmonic components closer to the fundamental frequency appear in the frequency spectrum. The variation of total harmonic distortion with respect to multisampling factor (sampling to carrier frequency ratio) has been discussed at different modulation indices for multicarrier-based multilevel inverter. The analytical results are verified through simulation and laboratory experimental results.

Load-Adaptive Zero-Phase-Shift Direct Repetitive Control for Stand-Alone Four-Leg VSI

This paper deals with a dedicated load-adaptive phase compensation algorithm to be used in repetitive control (RC) based stand-alone four-leg voltage source inverter (VSI). The plant model is achieved; its inherent modifications according to the operating point are highlighted and used to properly adapt the RC structure. Modification of the RC parameters is described to obtain the desired phase compensation capabilities achieving a zero-phase-shift condition at each harmonic. This allows us to increase the gain of the repetitive controller at high-order harmonics, thus yielding a better VSI output voltage with strongly reduced total harmonic distortion and faster dynamic response. As a consequence, the VSI output voltages are almost independent from the loads to be fed, and the four-leg VSI with the proposed zero-phase-shift direct RC is an ideal candidate to supply sensitive loads in microgrid, in particular for stand-alone applications.

Sampling Effect Characterization of Digital SPWM of VSI in Time Domain

This paper characterizes the sampling effect in digital sinusoidal pulse width modulation (SPWM) of voltage source inverter (VSI). The time-domain analysis presented in this paper establishes the relation between the fundamental frequency, carrier frequency, and the sampling frequency at different modulation indices of the SPWM. The analysis investigates the effect of sampling frequency of the digital controller on the output of the VSI. It is shown that the low-frequency harmonic components appear in the frequency spectrum of the VSI output voltage due to sampling. As a result, the output current of digitally controlled VSI is stepped in nature. The double Fourier integral solution of the switched waveform for inner and outer integral limits has been used to derive the expression. The integral solution is obtained using Jacobi-Anger expansions. The generalized results developed in this paper are useful to investigate the sampling effect in high switching frequency DSPWM. The proposed sampling effect has been analyzed for SPWM of single-phase H-bridge inverter. The analytical results are verified using simulation and experimental results. The experimental results have been obtained with the use of field-programmable gate array (FPGA) as a digital controller.

Behaviour of Non-Deterministic PWM Methods and Influence of DC Link Fluctuation in Harmonic Spreading Effect of VSI Output Voltage Spectrum

The pattern of harmonic spectrum at any output voltage level of a voltage source inverter (VSI) is determined by the characteristics of the pulse width modulation (PWM) adopted. The conventional, deterministic PWM methods like sinusoidal PWM (SPWM) results mechanical vibration, acoustic noise, and limit the application scope when used in drives. This is due to the incapability of deterministic PWM in spreading the harmonic power. The random pulse width modulation (RPWM) approach creates continuous harmonic profile instead of discrete dominant harmonics and hence reduces the acoustic noises. Insufficient filtering of dc link results in the amplitude distortion of the input dc voltage to the VSI and has the most significant impact on the spectral errors (difference between theoretical and practical spectra). It is evidenced from the earlier research that deterministic PWM methods have been modified for VSIs working with fluctuating dc input. The influence of dc link fluctuation on harmonics and their spreading effect in the VSI remains invalidated. Case study is done with four different capacitor values. This paper studies the performance of both conventional SPWM and random carrier PWM (RCPWM) in both VSI working constant dc input and fluctuating dc input. MATLAB based simulation study reveals the fundamental component, total harmonic distortion (THD) and harmonic distortion factor (HSF) for various modulation indices.

A DC component in voltage-source inverters with pulse-width modulation and ways of compensating for it

The causes of the appearance of dc components in the output voltage of voltage-source inverters controlled by the method of pulse-width modulation (PWM) are shown. Two different variants to compensate for the causes of appearance of the dc component for a sinusoidal PWM and one variant for a vector PWM are suggested.

Double Integration Control for Single-Phase Unified Power Quality Conditioner Based on A Neuron Adaptive Harmonic Detection

AbstractThis paper proposes a neuron adaptive harmonic detection algorithm which can adaptively, rapidly and precisely calculate the voltage and current reference signals in presence of the system frequency variation, according to which, a Double Integration Control (DIC) strategy is applied in Unified Power Quality Conditioner (UPQC) as an interface between the hybrid power system and the load.Generally, the UPQC consists of a shunt inverter, a series inverter and a DC-link capacitor, where DIC strategy is used separately in the shunt inverter and series inverter to force the output voltage of Voltage-Source Inverter (VSI) to track the reference value with high precision. The reference value for the shunt inverter is obtained based on the Recursive Least Squares (RLS). Simulation results demonstrate the effectiveness and reliability of the proposed detection algorithm and control strategy.

An optimized SVPWM switching strategy for three-level NPC VSI and a novel switching strategy for three-level two-quadrant chopper to stabilize the voltage of capacitors

Abstract Voltage source inverter (VSI) can produce single and three-phase (3P) AC voltages from a constant or variable DC voltage. There are many ways to control the VSI output voltage. Each control way produces some harmonics at the VSI output voltage. The space vector pulse width modulation (SVPWM) may be more effective than other modulation methods, e.g. harmonic injection, phase shifting, multi career pulse width modulation, in decreasing the low order harmonics (LOH). Different switching strategies (SSs) of power electronic devices in SVPWM have some specific advantages and disadvantages with regard to one another. In this paper, a comparative study between different SVPWM SSs is carried out by considering some objective functions such as total harmonic distortion (THD), power and switching losses, the ratio of the harmonic components to the fundamental component, distortion factor (DF). It is also shown that by selecting an optimized and appropriate SS for SVPWM, the harmonic orders, which are the multiples of the frequency index (FI), are eliminated. Then, to investigate the impact of variations of the capacitors voltage and switching frequency on power quality criteria, the most appropriate and optimized SS is applied to a 3P three-level (3L) neutral-point-clamped (NPC) VSI to supply a 3P load. This paper also presents a novel and optimized SS and control approach for a 3L two-quadrant (2Q) chopper in NPC VSI superconducting magnetic energy storage (SMES). Using the proposed SS, the voltage of the VSI capacitors in SMES can be independently controlled; also, the minimum power and switching losses - as well as the proper convection - can be achieved using this same strategy. The simulation results indicate that when combined with a proportional-integral (PI) control approach the proposed SS can be easily implemented in the power networks and can balance and stabilize the multi-level VSIs’ capacitor voltage level. The voltage variation of the capacitors in the steady state condition is less than (0.062%) which is 15 times better than the IEEE standard requirement (1%). To investigate the effectiveness and reliability of the proposed approach in stabilizing capacitor voltage, SMES performance using the presented approach is compared with that of SMES when the capacitors of the 3L VSI are replaced with equal and ideal voltage sources. This comparison is carried out from the power quality point of view and it is shown that the proposed SS with a PI controller is highly reliable.

Power Quality Improving Operations of a Flux-Lock Type SFCL Integrated With Voltage or Current Controlled-Voltage Source Inverter

In this paper, the flux-lock type superconducting fault current limiter (SFCL) integrated with a voltage source inverter (VSI) controlled with its output voltage or current is proposed and its operations for power quality improvement are investigated. The suggested equipment, which consists of a flux-lock type SFCL and a VSI, can limit the fault current in case that a short-circuit happens by the operation of the flux-lock type SFCL. In addition, it can compensate the reactive power and complement the active power that the non-linear load requires by controlling VSI's output voltage or current and thus, perform the power conditioning operation, the demand side management (DSM) and the uninterruptible power supply (UPS). The specification for the suggested model was determined and its various functions such as the fault current limiting and the power quality improving operations were presented and analysed through the computer simulation. The validity of the analysis was confirmed from the analytical results based on the computer simulation and, the advantage and the limitation of the voltage control and the current control for the VSI's power quality improving operations were discussed.

Instantaneous voltage measurement technique for PWM voltage source inverters

The pulse width modulated (PWM) voltage source inverter (VSI) is almost universally used in industrial motor drives. Although measurement of the VSI output voltage is required in many applications, accurate measurement is problematic due to the high frequency inverter switching. Many commonly used inverter output voltage measurement methods, such as indirect and direct voltage measurement, produce inaccurate results under a variety of operating conditions. In this paper, the common sources of voltage measurement error are identified and an instantaneous voltage measurement technique is presented that significantly reduces inaccuracies introduced by common voltage measurement strategies. Implementation details of the proposed strategy are outlined and experimental results are used to compare the proposed technique with other methods of inverter output voltage measurement. The results demonstrate the opportunity for improvements to any inverter-driven motor control system that requires precise terminal voltage measurements to carry out the intended control objective.