Topology and Control Strategy of PV MVDC Grid-Connected Converter with LVRT Capability

This paper proposes an isolated buck-boost topology and control strategy for the photovoltaic (PV) medium-voltage DC (MVDC) converter with low-voltage ride through (LVRT) capability. The proposed isolated buck-boost topology operates on either boost or buck mode by only controlling the active semiconductors on the low-voltage side. Based on this topology, medium-voltage (MV) dc–dc module is able to be developed to reduce the number of modules and increase the power density in the converter, which corresponds to the first contribution. As another contribution, a LVRT method based on an LC filter for MVDC converter is proposed without additional circuit and a feedback capacitor current control method for the isolated buck-boost converter is proposed to solve the instability problem caused by the resonance spike of the LC filter. Five kV/50 kW SiC-based dc–dc modules and ±10 kV/200 kW PV MVDC converters were developed. Experiments of the converter for MVDC system in the normal and LVRT conditions are presented. The experimental results verify the effectiveness of the proposed topology and control strategy.

Noise Analysis of Trans-impedance Amplifier (TIA) in Variety Op Amp for use in Visible Light Communication (VLC) System

VLC is a complex system with lots of challenges in its implementation. One of its problems is noise that originated from internal and external sources (sunlight, artificial light, etc). Internal noise is originated from active components of analog front-end (AFE) circuit, which will be discussed in this paper, especially on the trans-impedance amplifier (TIA) domain. The noise characteristics of AFE circuit in VLC system has been analyzed using the variety of available commercial Op Amp and different types of the photodiode (Si, Si-PIN, Si APD). The approach of this research is based on analytical calculus and simulation using MATLAB®. The results of this research show that the main factor that affecting the noise is en, the feedback resistor (Rf), and junction capacitor in the photodiode (Cj). Besides that, the design concept of multi channel TIA (8 channel) using IC Op Amp, with consideration of pin number of each Op Amp, supply needs, the initial value of Rf, converter to 8-DIP and feedback capacitor (Cf) channel, also discussed in this paper.

A 100-MS/s CMOS Sample-and-Hold Circuit with Input Common Mode Feedback

A high performance sample-and-hold (S/H) circuit with input common mode feedback (ICMFB) is presented. The ICMFB is used to ensure that the input common mode voltage for the sample-and-hold amplifier (SHA) is maintained at a known value during the hold phase of operation in order to reduce the differential output error when the sample capacitor and feedback capacitor has mismatch. Meanwhile, bootstrapped switches are used to lower the switch on-resistance and reduce the effect of switch non-idealities. Then a low power two stage high gain wideband SHA is designed to guarantee the holding accuracy. Hspice simulated results based on SMIC 0.13μm 1P5M CMOS process under 1.2V supply voltage shows a 108.4 dB spurious free dynamic range (SFDR) at Nyquist input @Fs=100MS/s. The designed S/H circuit has been used in the front end of 14-bit 100MS/s Pipelined ADC adapted for single-ended applications.

On the oscillation limits of HBT cross-coupled oscillators

In evaluating the potential of a given integrated-circuit technology, the negative conductance approach is used to estimate a maximum frequency limit for the ability of Heterojunction Bipolar Transistor (HBT) cross-coupled architecture to function as an oscillator at high frequencies. In this paper, the simple low-frequency estimation of the negative conductance, commonly used in the literature, is extended by deriving a new expression that takes into account the HBT parasitics. An expression for the frequency at which the negative conductance of the circuit crosses zero is given, which gives maximum frequency of oscillation for an ideal tank (no tank losses). In addition, the effect of the feedback capacitor, which is commonly added for direct current (DC) decoupling and boosting the negative conductance, is analyzed and new insight on the choice of the value of this capacitance is introduced. The results were proven by simulations using SiGe HBT transistors with an ft of 190 GHz.