Sharif Digital Repository

Control of three phase inverters is of paramount importance in the realm of control applications. In this regard, this paper proposes active disturbance rejection control (ADRC) scheme as a new method for voltage control of three phase inverters in UPS applications. The main advantage of ADRC refers to the fact that it is model independent. In this paper, the controller is composed of a double loop structure including an inner current loop and outer voltage loop. This structure is used in a three phase inverter in order for implementation of voltage control. To draw a comparison between ADRC and PI as the common control method, a case study has been simulated in SIMULINK. Simulation results... 

In this paper; control and parallel operation of multi-modular 3-phase inverters are investigated. Active current sharing approach is selected as the fundamental control technique for parallel operation of inverters due to its high reliability. Among different methods for active current sharing; average load sharing is employed due to its acceptable stability. For this purpose; optimal control strategy and Linear Quadratic Regulator (LQR) method is proposed to parallel 3-phase 4-leg inverters. The system is modeled to be compatible and solvable with LQR equations. Using dq technique; 3-phase inverters are paralleled and controlled. The proposed method obtains both current sharing and voltage... 

In trasformerless grid-connected photovoltaic (PV) systems, common-mode voltage (CMV) fluctuations cause leakage current flow through the stray capacitance of the PV panels. Shoot-through states in a quasi-Z-source inverter (q-ZSI) increase the amplitude of high-order harmonics of CMV. In this paper, by using the modulation technique based on odd pulse width modulation and minor change in the Z network of the three-phase q-ZSI, the leakage current is blocked. No extra semiconductor element is added. By the proposed technique, CMV is kept nearly constant during switching cycles. The experimental results for CMV analysis in a 1kW prototype are presented to verify the theoretical analysis. ©... 

In trasformerless grid-connected photovoltaic (PV) systems, common-mode voltage (CMV) fluctuations cause leakage current flow through the stray capacitance of the PV panels. Shoot-through (SH) states in a quasi-Z-source inverter (q-ZSI), increase the amplitude of high order harmonics of CMV. In this paper, by using the modulation technique based on odd PWM (OPWM) and minor change in the Z network of the three-phase q-ZSI, the leakage current is blocked. No extra semiconductor element is added. By the proposed technique, CMV is kept nearly constant during switching cycles. The experimental results for CMV analysis in a 1kW prototype are presented to verify the theoretical analysis. IEEE  

This paper presents a single-phase Cascaded H-Bridge (CHB) inverter for photovoltaic applications. The proposed control strategy permits the optimum control of each string of PV panels in different insolation conditions. Based on the presented mathematical analysis, an analytic constraint is derived to check the stable operation of the inverter. A modified MPPT control strategy is also proposed based on this new condition. This strategy enhances the stability margins of the system by changing the operating point of some PV arrays. In this approach, the extracted power from high power cell is reduced to prevent instability issue and to avoid injection of highly distorted current into the... 

This paper presents an effective hybrid optimal modulation technique for a cascaded H-bridge (CHB) multilevel inverter. The introduced method is generalized optimal pulsewidth modulation, which can be extended to any m-level CHB multilevel inverter operating at any switching frequency. The presented hybrid optimal modulation strategy includes the pattern exchange and optimal modulation techniques. In the optimal modulation technique, the hybrid interior-point algorithm, which is more flexible and efficient than conventional optimization techniques, is applied. The proposed hybrid optimal modulation strategy yields balanced units' output fundamental voltages, and low total harmonic distortion... 

In this paper, the short-circuit fault in three-phase quasi-Z-source inverter (q-ZSI) is analyzed and a linear model is proposed for the short-circuit analysis. The proposed model is based on the state space equations of the system. By using this model, the most critical situation during short-circuit fault is recognized; the maximum reaction time for the protection system could be estimated and elements that are prone to failure are identified as well. The analysis is categorized into two groups, leg fault and switch fault. The linear model is confirmed by simulation of 1kw three-phase q-ZSI. © 2017 IEEE  

In this paper, the whale optimization algorithm is proposed for harmonics elimination in a cascaded multilevel inverter. In selective harmonic elimination pulse width modulation, the selected low-order harmonics are eliminated by solving nonlinear equations, while the fundamental of output waveform is adjusted to a desired value. In this paper, whale optimization algorithm is applied to a 7-level cascaded H-bridge inverter to solve the equations. Also, it was validated by experimental results, since this algorithm has an ability to search in entire solution space, the probability of catching a global best solution is very high. This method has higher accuracy and probability of convergence... 

In this paper, the whale optimization algorithm is proposed for harmonics elimination in a cascaded multilevel inverter. In selective harmonic elimination pulse width modulation, the selected low-order harmonics are eliminated by solving nonlinear equations, while the fundamental of output waveform is adjusted to a desired value. In this paper, whale optimization algorithm is applied to a 7-level cascaded H-bridge inverter to solve the equations. Also, it was validated by experimental results, since this algorithm has an ability to search in entire solution space, the probability of catching a global best solution is very high. This method has higher accuracy and probability of convergence... 

This study addresses the robust stability analysis for an islanded microgrid with droop-controlled inverter-based distributed generators (DGs). Owing to large load changes, microgrid structure reconfiguration, and higher-power demands, the low-frequency (LF) dominant modes of a microgrid stir toward unstable zone and make the system more oscillatory or even unstable. In this study, a robust two-degree-of-freedom (2DOF) decentralised droop controller, which is the combination of the conventional droop with a robust transient droop function, is utilised for each inverter-based DG unit. Unlike conventional tuning of 2DOF droop controllers, a new design procedure is proposed to robustly... 

Non-linear loads such as rectifiers are growing in industry. Three phase inverter with non-linear load can lead to highly distorted output voltage. This paper proposes a method for reducing voltage THD in three phase inverters with non-linear load. The proposed method considers the load current as a disturbance and provide a control strategy to reject it using the disturbance observer method. This method doesn't need any additional sensors or hardware and is implemented digitally in controller. Simulation results show that the presented method will reduce the total harmonic distortion of the output voltage. © 2017 IEEE  

Z-source family has been widespread in photovoltaic (PV) applications. In trasformerless grid-connected PV systems, the common mode voltage (CMV) time variations, cause the leakage current flow. This current flows through the stray capacitance of the PV panels. For a Z-Source Inverter (ZSI), the CMV would have higher high-frequency harmonics, due to the shoot through states within the switching cycles. In this paper, the CMV of a ZSI is analyzed and a simple method is proposed for the harmonic reduction of the CMV in the ZSI. The CMV reduction method is based on changing the switching states. The CMV in reduced method is compared to the CMV in the traditional ZSI in frequency domain by using... 

Fast and accurate fault detection is the primary step and one of the most important tasks in fault tolerant converters. In this paper, a fast and simple method is proposed to detect and diagnosis the faulty cell in a cascaded H-bridge multilevel inverter under a short circuit fault. In this method, the reference voltage is calculated using switching control pulses and DC-Link voltages. The comparison result of the output voltage and the reference voltage is used in conjunction with active cell pulses to detect the faulty cell. To achieve this goal, the cell which is active when the Fault signal turns to “0” is detected as the faulty cell. Furthermore, consideration of generating the active... 

In this paper, a new post-fault vector control of an induction motor, fed by a faulty Cascaded H-Bridge (CHB) inverter, is presented. Among fault tolerant control methods, waveform based methods are suitable for closed-loop control and provide higher output voltage. In order to control the speed of the motor, a rotor field oriented control (RFOC) is used. During the fault, the FOC is modified to decrease the fault impact on the motor as low as possible. The proposed method is validated by means of simulation results for different loads and faults. The results show an improvement in both the final operating point and the transient response of the motor  

This paper presents a new method for tuning various linear controllers such as Proportional-Integral (PI), Proportional-Integral-Derivative (PID) and Proportional-Resonant (PR) structures which are frequently used in power electronics and power system applications. The linear controllers maintain a general structure defined by the Internal Model Principle (IMP) of control theory. The proposed method in this paper is twofold. The first perspective uses the well-known concept of the Linear Quadratic Regulator (LQR) to address the problem as a regulation problem. The Q matrix of the LQR design is then finely adjusted in order to assure the desired transient response for the system. The second... 

Modern commercial operations consist of critical equipments that are more susceptible to voltage sag events. The consistent and smooth running of these operations is often disrupted by voltage sags. Diverse range of solutions exist which can enhance the ride through capability of sensitive devices. This paper presents various voltage dip mitigation solutions and a methodology for analyzing the effectiveness and practical viability of these solutions. The proposed approach is based on event tree method which gives an indication about the extent of process interruption in the event of voltage sags. A case study is conducted in the paper with different combinations of practical mitigation... 

Modern commercial operations consist of critical equipments that are more susceptible to voltage sag events. The consistent and smooth running of these operations is often disrupted by voltage sags. Diverse range of solutions exist which can enhance the ride through capability of sensitive devices. This paper presents various voltage dip mitigation solutions and a methodology for analyzing the effectiveness and practical viability of these solutions. The proposed approach is based on event tree method which gives an indication about the extent of process interruption in the event of voltage sags. A case study is conducted in the paper with different combinations of practical mitigation... 

This study presents a powerful application of genetic algorithm (GA) for the minimization of the total harmonic current distortion (THCD) in high-power induction motors fed by voltage source inverters, based on an approximate harmonic model. That is, optimal pulse patterns (switching angles) are determined to have the THCD minimized and the fundamental output voltage regulated concurrently. As the minimization of THCD corresponds to the minimization of harmonic copper losses of the motor windings, GA optimization technique has been utilized, in comparison with conventional optimization methods due to its capabilities of searching the entire solution space with more probability of finding the... 

This paper presents an optimal multi-loop control structure for uninterruptible power supply (UPS) applications which use voltage source inverter (VSI) coupled with LC filter. A resonant controller ensures tracking of sinusoidal voltage reference and rejection of sinusoidal current disturbance with no steady-state error if the loop remains stable. The challenges are reduction of output total harmonic distortion (THD), improving damping of the LC resonance frequency and preventing generation of fast closed-loop modes which go beyond the frequency range of inverter with limited switching frequency. An extension of the classic linear quadratic regulator (LQR) is proposed which addresses the... 

Inverter driven electrical machines need resolver for position estimation and efficient electronic commutations. In this paper, the resolver signals are also used for the purpose of mechanical fault diagnosis. Therefore, a comprehensive procedure based on winding function (WF) method is presented to propose a noninvasive index to identify the mechanical fault's type (static/dynamic eccentricity) and even its percentage. In this regard, once the resolver signals are measured and saved in health condition. Then, during the operation of the motor, calculating the proposed index using the healthy and faulty signals leads to predict the fault type and its percentage. The success of the proposed...