Virginia Tech Intellectual Properties Inc

Other

The University of Tennessee Research Foundation

Fred Wang

Dushan Boroyevich

Rolando Burgos

Kamiar J Karimi

Ruxi Wang

Dong Dong

Kaushik Rajashekara

Stephen Andrew Long

Paolo Mattavelli

Leon Monroe Tolbert

Gerald T Francis

Sheau-Wei Johnny Fu

Zhiyu Shen

Shuoting Zhang

Timothy N Thacker

Circuits and methods for power conversion. In some examples, a modular multi-level converter (MMC) is configured for power conversion between an alternating current (AC) bus and a direct current (DC) bus. The MMC includes submodules arranged into a phase leg for at least one phase of the AC bus. Each submodule includes an energy storage component and a switch configured for bypassing the energy storage component or connecting the energy storage component into the phase leg. The MMC includes a pre-charger circuit configured to pre-charge the energy storage components of the submodules. The pre-charger circuit is configured for providing a first DC voltage that is lower than a second DC voltage on the DC bus, and the pre-charger circuit is coupled to an end submodule of the phase leg.

Modular multi-level converter pre-chargers

A controller and infrastructure for an impedance analyzer measures responses to perturbations to respective phases of a multi-phase system at an interface between stages thereof (which may be considered as a source and load in regard to each other), such as a multi-phase electrical power system, to determine a transfer function for each phase of the multi-phase system from which the impedance of each of the source and load can be calculated, particularly for assessing the stability of the multi-phase system.

Algorithm and implementation system for measuring impedance in the D-Q domain

Approximating loci of eigenvalues or characteristic gains of a return ratio matrix of a model of a multi-phase power converter circuit by the loci of the d-d and q-q elements of said synchronous frame of reference applied to said model, allows determination and assessment of stability of the circuit or forbidden operational parameters of the combination of an AC power source and a power converter at an interface thereof by application of a standard Nyquist stability criterion.

Method of evaluating and ensuring stability of AC/DC power systems

DC link capacitance in a bi-directional AC/DC power converter using a full-bridge or H-bridge switching circuit can be greatly reduced and the power density of the power converter correspondingly increased by inclusion of a bi-directional synchronous rectifier (SR) DC/DC converter as a second stage of the power converter and controlling the second stage with a control loop having a transfer function common to both buck and boost modes of operation of the bi-directional SR DC/DC converter and a resonant transfer function to increase gain at the ripple voltage frequency (twice the AC line frequency) to control the duty cycle of the switches of the bi-directional SR DC/DC stage and controlling the duty cycle of the switches of the full-bridge or H-bridge switching circuit using a control loop including a notch filter at the ripple voltage frequency.

Two-stage single phase bi-directional PWM power converter with DC link capacitor reduction

A phase detector for a phase-locked loop includes a phase detector that is configured to become unstable, oscillate and drift rapidly in frequency in a predictable manner when a reference frequency signal is not available. When applied, for example, to a power converter connected to a power distribution grid, the predictable oscillatory and rapid frequency drift behavior when the phase detector is unstable allows very rapid and reliable detection of disconnection from the grid, referred to as islanding.

Use of PLL stability for islanding detection

An electrical power system includes an alternating current (AC) power source configured to output an AC signal, a single phase pulse-width modulated (PWM) rectifier coupled to the AC power source and to an electrical load; a DC link capacitor coupled in parallel to the load and the PWM rectifier; and an active ripple energy storage circuit. The active ripple energy storage circuit has a first terminal, a second terminal and a third terminal, the active ripple energy storage circuit being coupled in parallel to the electrical load, the PWM rectifier and the DC link capacitor via the first terminal and the second terminal, the third terminal being coupled to the second terminal, the active ripple energy storage circuit being configured to selectively absorb and discharge at least part of the ripple energy.

Electrical power system with high-density pulse width modulated (PWM) rectifier

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Knoxville, TN, United States of America

Fred Wang