Sharif Digital Repository

This paper is focused on improving the post-fault performance of cascaded H-bridge multilevel inverters by decreasing the common-mode voltage. First, an algorithm is proposed to determine the optimal post-fault state among all possible states, which have the same maximum available voltage. Furthermore, a modified technique is proposed to calculate the references of inverter phase voltages under faulty conditions. This technique leads to a decrease in the common-mode voltage when the required output voltage is less than its maximum value. These solutions are mutually employed in the post-fault control system. Simulation and experimental results confirm the effectiveness of the proposed... 

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... 

The leakage current originated from the fluctuations of the common-mode voltage (CMV) is an issue in a transformerless grid-connected photovoltaic (PV) system. In this paper, a modified space vector modulation based on the Fourier transform analysis is proposed to reduce the leakage current in a three-phase quasi-Z-source inverter (qZSI). The CMV harmonic content in a qZSI contains low and high-frequency harmonics which cause safety and EMI problems respectively. By implementing the proposed modulation in a three-phase qZSI, the low-frequency harmonics of the CMV are mainly reduced. The distribution of the high-frequency harmonics is also modified in a way they can be simply filtered.... 

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. ©... 

The leakage current originated from the fluctuations of the common-mode voltage (CMV) is an issue in a transformerless grid-connected photovoltaic system. In this paper, a modified space vector modulation based on the Fourier transform analysis is proposed to reduce the leakage current in a three-phase quasi-Z-source inverter (qZSI). The CMV harmonic content in a qZSI contains low-and high-frequency harmonics that cause safety and electromagnetic interference problems, respectively. By implementing the proposed modulation in a three-phase qZSI, the low-frequency harmonics of the CMV are mainly reduced. The distribution of the high-frequency harmonics is also modified in a way they can be... 

In This paper, a new post-fault control method for symmetric cascaded H-bridge multilevel inverters (CHB-MLIs) is proposed with the aim of the development of CHB-MLIs performance under faulty conditions due to decrease in common mode voltage (CMV). In other words, this technique addresses the exclusive process to select the optimal post-fault state among all available states possess the same amplitude of the output line to line voltages. As a result, this process leads to provide computed phase voltages references to apply to PWM block. Hence, this technique leads to decrease the common mode voltage and eliminate it under some desired output line-line voltages. Finally, the feasibility of... 

In a transformerless grid-connected photovoltaic system, many issues arise from the leakage current flow into the ground, as EMI problems. The leakage current is originated from the common-mode voltage fluctuations. In this paper, the common-mode voltage harmonics in a three-phase quasi-Z-source inverter are analyzed using Fourier transform and a closed-loop formulation is presented for the harmonics value. The shoot-through mode in a quasi-Z-source inverter causes extra fluctuations in the common-mode voltage comparing to a classic inverter. The proposed harmonic analysis method provides a systematic way to figure out how shoot-through mode and also other parameters affect the common-mode... 

In Z-source family inverters, shoot-through (ST) states are applied as a part of passive state in each switching cycle. The distribution of ST intervals along a switching period affects the system parameters as total harmonic distortion (THD), switching loss and common-mode voltage (CMV). In this paper, ST methods in a three-phase quasi-Z-source inverter (q-ZSI) are compared due to the CMV level. High-frequency harmonics of CMV cause leakage current flow in a transformerless grid-connected photovoltaic (PV) system. Through the comparison of the ST methods, the method with minimum CMV is identified. The experimental results are Prasented for a low voltage q-ZSI prototype. © 2018 IEEE  

A charge sharing technique for high-speed double-tail comparators is presented. This technique is applied to the pre-amplifier stage of the dynamic comparators so that the maximum differential gain is applied to the latch during the latching process reducing the input referred offset voltage. In dynamic comparators a large portion of the input referred offset voltage is coming from the latch, and the proposed technique is introduced to alleviate this issue. Monte- Carlo simulations show that the proposed technique reduces the offset voltage from 16 mV to 8 mV. Due to the charge sharing technique, the pre-amplifier draws just enough power for its operation reducing the average power by 40%... 

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  

Leakage current is originated from common-mode voltage (CMV) time variations in a grid-connected photovoltaic (PV) system and results in several deficiencies. In this paper, a new method is proposed for CMV reduction in a three-phase voltage source inverter (VSI) system. The proposed method is based on space vector modulation and it utilizes only odd and zero vectors. By using the proposed method, the number of fluctuations of the CMV waveform per switching cycle is reduced; therefore, the amount of high-frequency harmonics of CMV is decreased. In addition, because of applying both active and zero vectors by the proposed method, the total harmonic distortion becomes less than most of other... 

A novel structure of Capacitive Digital to Analog Converters (CDAC) for Successive Approximation Register Analog to Digital Converters (SAR ADC) is presented. In this CDAC, a number of pre-charged capacitors are placed in different series configurations to produce a desired voltage level. Therefore, given an input code, a series configuration of the capacitors is created to produce a voltage. Current is drawn from the supply voltage only in one step of the ADC conversion to reduce the power consumption. Therefore, the proposed CDAC consumes a fixed and small amount of power regardless of the input code. The output common mode voltage (Vcm) of the DAC remains fixed for all the digital codes.... 

A low-power technique for high-resolution comparators is introduced. In this technique, p-type metal-oxide-semiconductor field-effect transistors are employed as the input of the latch of the comparator just like the input of the preamplifier. The latch and preamplifier stages are activated in a special pattern using an inverter-based controller. Unlike the conventional comparator, the preamplification delay can be set to an optimum low value even if after the preamplification, the output voltages is less than n-channel metal-oxide semiconductor voltage threshold. As a result, the proposed comparator reduces the power consumption significantly and enhances the speed. The speed and power...