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This paper introduces a novel isolated hybrid resonant converter with smooth transition between multiple operating modes. With the simple addition of a bidirectional ac switch, the highly-efficient series resonant converter operating in the discontinuous conduction mode (DCM) is combined with a phase-shifted full-bridge buck converter and a pulse width modulated (PWM) boost converter in order to provide...
An adaptive secondary-side digital control is proposed for the series resonant converter to solve the loss of ZVS under certain input and load conditions, making it a good candidate for MHz 48V voltage regulators (VRs). By means of varying AC equivalent resistance, the output voltage regulation is achieved by controlling the duty cycle of the synchronous MOSFET. An additional control variable has...
This paper proposes a digital online efficiency optimization technique for DC/DC Dual Half-Bridge Series Resonant Converters. The proposed technique implements an advanced modulation scheme which exploits the degrees of freedom inherently available in the converter modulation space in order to simultaneously regulate the output voltage and maintain the system in its maximum efficiency point. Furthermore,...
Single-phase AC/DC or DC/AC systems inherently subject to harmonic disturbance which is caused by the well-known double line frequency ripple power. This issue can be eased through the installation of bulky electrolytic capacitors in the dc-link, but such passive filtering approach may inevitably lead to low power density and limited system lifetime. An alternative approach is to use active power...
This paper introduces a novel bridgeless resonant ac-to-dc converter, capable of efficiently converting arbitrary low-amplitude input voltages into a regulated dc voltage. High-frequency resonant operation owing to LC resonance allows small footprint for passive components, thereby increasing the circuit power density without suffering from switching losses. A resonant gate drive circuit is designed...
This paper investigates the dc link voltage ripple in a modular multilevel converter (MMC). It is found that switching-frequency ripple occurs on the dc link voltage in MMC when circulating current suppressing control is implemented. The mechanism of the switching-frequency voltage ripple is investigated and explained. Circulating current suppressing control will manipulate the average values for...
The fundamental building block of cascaded static synchronous compensator used in distribution grid is H-bridge based converter module. In this paper a type of "plug and play" module was introduced to improve the device compensation performance and reliability. The module based on IGBT parallel connection was discussed about the design of electrical parameters and physical structure. In...
With voltage-balancing control, the voltage difference among sub-module (SM) capacitors in a modular multilevel converter can be reduced. However, this comes at the cost of increased device switching frequency. In this paper, the relationship between the switching frequency and SM capacitor unbalanced voltage is investigated. As the relationship depends on the voltage-balancing control schemes, a...
DC capacitor voltage imbalance is an inevitable technical concern for the multilevel diode-clamped converters with number of levels higher than two. This paper addresses the balancing of the capacitor voltages based on the capacitor current equalization considering a minimum loss space vector pulse width modulation (MLSVPWM) algorithm for five-level diode-clamped converters. In diode-clamped converter...
A new method to selectively control the amount of dc-link voltage ripple by processing the desired reactive power by a DC/DC converter in an isolated AC/DC or AC/DC/AC system is proposed. The concept can reduce the dc-link capacitors used for balancing the input and output power and thereby limiting the voltage ripple. It allows the use of a smaller dc-link capacitor and hence a longer lifetime and...
One of the main technical challenges of the Modular Multilevel Converter (MMC) for medium-voltage adjustable-speed motor drive applications is the large magnitude of the SubModule (SM) capacitor voltage ripple under low-speed operation. This paper proposes two new techniques to reduce the magnitude of SM capacitor voltage ripple of the MMC for motor drive applications. The paper presents a comprehensive...
This paper presents a study of a generalized multilevel asymmetric inverter based on a H-Bridge Cell with one Arm Series (CHB-as) and five switches. It is shown several asymmetrical arrangements of input source combinations that produce several equally spaced voltage levels with few components. Equations for determining the switching frequency employed in the low power processing cells are developed,...
In this paper is presented a shunt active power filter with a reduced number of inductors for harmonic and reactive power compensation in three-phase three-wire electrical systems. The proposed configuration is based on two single-phase shunt active power filters connected to a three-phase three-wire grid. The two single-phase cells can be achieved by a three-leg singlephase to single-phase ac-dc-ac...
This paper presents an advanced switching sequence based on boundary control for the Dual Active Bridge (DAB) DC-DC converter applied in a Solid-State Transformer (SST). The implementation of the switching sequence follows the recent advancements in curved switching surfaces for DAB converters — the Natural Switching Surface (NSS) — and contributes to higher efficiency and transient regulation. The...
This paper describes the start-up and integration of a doubly fed induction generator (DFIG)-based wind farm into the ac network through a voltage source converter-based (VSC) HVDC transmission system. A control strategy based on the closed-loop control of rotor current is proposed during DFIG cut-in process. In normal operation, an additional feedback signal is introduce to the control system of...
Many industrial applications involve loads which are very sensitive to electrical disturbances in the supply. These instances involve both various types of voltage unbalance as well as more series disturbances such as symmetrical and asymmetrical faults. This paper proposes a voltage unbalance and an unsymmetrical fault correction technique for a three phase load utilizing an industry-standard current...
As the development and installation of photovoltaic (PV) systems are still growing at an exceptionally rapid pace, relevant grid integration policies are going to change consequently in order to accept more PV systems in the grid. The next generation PV systems will play an even more active role like what the conventional power plants do today in the grid regulation participation. Requirements of...
With an imperative demand of clean and reliable electricity generation in some countries, the increasing adoption of new photovoltaic (PV) systems pushes the Distribution System Operators (DSOs) to expand the transmission/distributed lines. However, the potential cost brought by such extensions and increased maintenances introduce new obstacles. In view of this concern, the DSOs starts to reduce PV...
The new grid codes demand the wind turbine systems to ride through recurring grid faults. Many control strategies have been proposed for the Doubly Fed Induction Generator under single grid fault, but their performance under recurring grid faults have not been studied yet. In this paper, five different control strategies for DFIG to ride through single grid faults are presented, and their performance...
During grid faults, grid codes required wind turbine (WT) to provide dynamic reactive support within tens of ms as well as maintain grid connection continuously, namely low voltage ride through (LVRT). But owing to the limited DC bus voltage, the rotor side convertor in doubly fed induction generator (DFIG) cannot actually output sufficient voltage to provide reactive support until the rotor-side...
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