Soft start and voltage control of grid connected induction motors using floating capacitor H-bridge converters

Abstract

A system is described whereby floating capacitor Hbridge converters are located in each phase between the utility grid and a squirrel cage induction motor. Injecting a series voltage in each phase, the power electronics can be used to control the motor voltage during starting and hence limit the motor starting current to the desired level. The motor voltage can also be used under steady-state operation either to control the grid VAR or to compensate for grid voltage sags and swells. The paper presents the theory necessary to understand how to adjust the phase and magnitude of the motor voltage relative to the utility grid. Hardware experimental results show that the proposed system can successfully soft start a standard squirrel cage induction machine under various load conditions. Moreover, a range of objectives can be achieved including: power factor correction and motor voltage control. I.978-1-4799-5776-7/14/$31.00 ©2014 IEEE

Impact of Slim DC Capacitance on Floating Capacitor H-bridge Motor Drive

“…Compared with the previously proposed control method in [19]- [21], the main difference in this paper is that drastic DC capacitance reduction will results in 2 nd order DC voltage ripple. As a result, instead of constant modulation index for the H-bridge (ma represents the constant modulation index in [19]- [21]), the equivalent modulation index of the H-bridge is boosted in this paper (ma+mb represents the equivalent modulation index). This phenomenon will be taken into account in the control loop so that more accurate motor terminal voltage control can be achieved.…”

“…Then, the magnitude of the DC capacitor ripple can be obtained (see equation 7). Finally, peak DC capacitor voltage for the proposed topology will be the average DC capacitor voltage plus one-half of DC ripple voltage magnitude as: (19) Equation 19will be used to predict IGBT voltage stress.…”

“…This is because the modulation index boost can be neglected under relatively large DC capacitance, (see equation 15). However, as the DC capacitance gets smaller, the previously proposed control scheme [19]- [21] begin to lose accuracy, while the advantage of taking the ripple effect into account in the controller becomes obvious.…”

Voltage sag compensation of point of common coupling for low voltage ride-through enhancment of inverter interfaced DG using bridge type FCL

“…The high current levels occur by either faults or starting large induction motors [20,21]. The grid faults, when happen, make significant voltage sag in the power system, which force all power generation units to feed the fault location.…”

Ripple voltage minimization in single phase floating bridge converter modules using a Transformer Coupled Asymmetrical bridge converter

“…For illustration purposes a sample system that benefits from the ripple voltage minimization network described, uses single phase H-bridge converters connected to a three-phase grid (Fig.1). By injecting a series voltage in each phase, the proposed power electronics can be used to control the motor voltage during starting and hence limit the motor starting current to the desired level [17][18].The DC capacitors in Hbridges converters reported are electrolyte capacitors (8mF per phase), which is much larger than the typical DC capacitor used in a traditional three-phase inverter (400uF). The large electrolyte capacitors create a serious issue in terms of reliability for the proposed system.…”