Yogesh Patel

Analysis and design of TRAP and LCL filters for active switching converters

This paper presents two main filters widely used in industry for three phase active converters. The filters are the Trap and the LCL. These filters are primarily used to reduce switching frequency ripple and to meet IEEE 519 THD requirements. The main goal of this paper is to develop the algorithms which give optimized values of the Inductors and Capacitors of Trap and LCL filters. The algorithm also includes the effect of source inductance. Using the algorithm we will design the Trap and LCL filters for a 125kW active converter. Simulation and experimental results reveal the performance of the Trap and LCL filter. This paper also compares the Trap and LCL filter results.

Evaluation of LCL filter inductor and active front end rectifier losses under different PWM method

LCL filter and power switches are the most critical parts of high power active front end (AFE) rectifier designer. Among the LCL filter component, the main inductor located at the rectifier side is the most expensive and bulky component. This is because it is exposed to PWM voltage waveform and induce much higher core losses. This paper proposes a way to analyze the core losses of main inductor. The losses under different operation mode of AFE rectifier are compared and verified by experimental result. The losses of the IGBT/Diode in the rectifier are also studied and compared. It can be concluded that the application of the inductor and the IGBT/diode must be designed properly to allow optimal size and to avoid over heating.

DC distribution system architecture and controls for wind power applications

In this paper, Medium Voltage DC (MVDC) distribution system is proposed for wind power applications. The proposed MVDC system is favorable for off shore wind farms. The architecture of the system, control for the medium voltage three phase inverter, active and reactive power control for voltage and frequency support are discussed in the paper. The proposed topology allows for easier integration of energy storage with wind energy. The simulation results show the viability of the proposed system for active/reactive power controls for wind farms.

Mitigation of the effects of common-mode current on the operation of SCR-based rectifiers for AC drives

Common-mode current generated by the PWM AC drive at low modulation index and higher switching frequency results in overheating of the pre-charge resistor of the SCR based rectifier. In this paper, two modifications are proposed for the operation of SCR based rectifiers to significantly reduce the resistor overheating issue. The solution is cost and size effective when compared with alternative solutions. Experimental results are provided to show the reduction of common mode current flow through the pre-charge resistor and the consequent reduction in its temperature.

Hybrid damping for active front end converter

Breakthroughs in power electronics devices enabled the utilization of the IGBT as the main power switch in AFE converters and enabled the emergence of the fully controlled Active Front End, “AFE”, and low input harmonic solution. This solution employs voltage and current control loops and switching with relatively high switching frequencies of greater than 2 KHz in most applications. The AFE converter is usually connected to the grid through an LCL filter. In this paper, a hybrid technique is introduced to damp the resonance condition that may result due to the existence of the LCL filter. This technique relies on the concept of hybrid damping which combines the advantages of both active and passive damping previously introduced in literature. It will also be shown that the introduced technique overcomes previous limitations which renders this technique more practical and highly applicable to reliable industrial products.

Single phase precharge control method for active front end rectifier

Active front end rectifiers (AFE) are widely used in various industrial area applications. In these types of systems, AC pre-charge circuit, output LCL filter and power module switches are the three most critical power segments. AC pre-charge circuit design is often related to an overall high component volume and cost. Many manufacturers adopt mechanical contactors or breakers between the utility connection point and the rectifier in order to ensure a smooth pre-charge of the DC bus capacitors. Since these mechanical components are typically associated with lower reliability and increased size, the power density and lifetime of the whole system gets affected significantly. This paper proposes a simple solid state pre-charge circuit for AFE rectifiers. Solid state pre-charge circuit offers a fairly simple control while reducing the inrush current for both LCL filter and DC bus capacitors. This method also demonstrates the following advantages: 1) increased lifetime, 2) smaller foot print 3) lower cost. Basic operating theory and circuit analysis along with simulation and experimental results are presented in the paper to demonstrate the effectiveness of the proposed method.

Mitigation of the Effects of Common-Mode Current on the Operation of SCR-Based Rectifiers for AC Drives

Common-mode current generated by the pulse-width modulated (PWM) ac drive at low modulation index and higher switching frequency results in overheating of the precharge resistor of the silicon-controlled rectifier (SCR)-based rectifier. In this paper, two modifications are proposed for the operation of SCR-based rectifiers to significantly reduce the resistor overheating issue. The solution is cost and size effective when compared with alternative solutions. Experimental results are provided to show the reduction of common-mode current flow through the precharge resistor and the consequent reduction in its temperature.

Active front end rectifier design trade-off between PWM and direct power control method

Active front end rectifiers (AFE) are used widely in industrial area. For an AFE designer, LCL filter and power switches are two of the most critical components. Among the LCL filter components, the main inductor connect to rectifier power switches is the biggest and most expensive. This paper evaluates the design trade-offs of AFE rectifier and LCL filter under different PWM control method. The losses of the IGBT/Diode and the main inductor magnetics core without and without passive damping are studied. Recommendations of how to optimize an AFE rectifier are made in the end of the paper.

Medium voltage inverter to establish grid interface and provide ancillary support for a DC distributed wind farm

More utility companies now require wind power plants to participate in grid support functions including frequency, voltage and inertia support. Typical wind turbine generator configurations cannot provide grid support. In this paper, a multi-level inverter based wind turbine power conversion system is investigated. The developed inverter interfaces between the DC bus of a wind turbine power conversion system supported by energy storage elements and the grid. Two control techniques are proposed for capacitor-based and battery-based storage systems to provide grid active and reactive power support. Details of control implementation for grid interface, frequency and voltage droop support are presented. Simulation and experimental results are discussed to verify the viability of the proposed system and control techniques.