Henry Chung

Development of a switched-capacitor DC/DC boost converter with continuous input current waveform

A new switched-capacitor (SC)-based dc/dc boost converter is presented. It features good regulation capability and continuous input current, giving lower conducted electromagnetic interference with the supply network than classical SC converters. The converter is realized by using two quasi-switched-capacitor boost converter cells. The dc voltage conversion ratio is controlled by the gate-source voltage of a quasi-switch in each cell, in order to adjust the charging trajectory of the capacitors. By renouncing inductive elements, the converter can be implemented in small size, light weight, high power density, and it is possible to fabricate it in an IC form. A prototype of a 20 W, 6 V/9 V dc/dc boost converter with overall efficiency of 74% and power density of 10 W/in/sup 3/ has been built. The state-space averaging technique is applied to study the static and dynamic behaviors of the converter.

Design of feedback gain vector of two-state basic PWM multifeedback regulators for large-signal stability

A method for determining boundaries on the feedback gains in a switching regulator with multiple feedback, in order to ensure stability for large changes in the load values, is developed. Using an original approach for time-domain analysis, a large-signal, nonlinear, discrete-time model of the closed-loop converter is obtained; the models equations are expressed in disturbances of the state variables due to disturbance in the load. The first step toward a global stability design is to find the constraint that ensures local stability around the operating point: the nonlinear terms (products of disturbances) are neglected in the model, the z-transform is applied to the linearized equations, and the condition that the eigenvalues are situated inside the unit circle is imposed. The nonlinear model, including the nonlinearity of the pulsewidth modulation (PWM), due to possible saturation, is then considered. A new constraint in terms of feedback gains is found in order to ensure that one and only one real equilibrium point (i.e., the quiescent operating point) exists. Putting together the constraints, boundaries on the feedback gains are found. The method is developed for converters containing two reactive elements, operating in continuous conduction mode. An example of a boost converter with inductor current and output voltage feedback is presented in detail. The large-signal stability of the design is checked by using the state-plane portrait and time-domain simulation.

Stability analysis and dynamic response of a DC-link module with a series voltage compensator

A DC-link module composed of a reduced value of DC-link capacitor and a series voltage compensator has been proposed. The voltage compensator processes the ripple voltage on the DC link and reactive power only, which can be implemented by low-voltage devices. The overall energy storage of the DC-link module is reduced, permitting the replacement of electrolytic capacitors by film capacitors in a cost-effective way. This paper focuses on the stability analysis and dynamic performance evaluation of the proposed DC-link module. Theoretical study and experimental verification are presented and the results are compared with the conventional DC-link design solution.

A new schedule-controlled strategy for charging large number of EVs with load shifting and voltage regulation

Electric vehicles (EVs) is an attractive solution to replace traditional petrol cars. The penetration of EVs posts a challenge for power systems since it would inevitably incur undesirable voltage drops. EV load shedding can be performed to regulate the grid voltage. The EV charging location is also an important factor when shifting the EV loads. This paper presents a new schedule-controlled framework with the aims of load shifting and voltage regulation to control EV charging operations for radial distribution networks. The new strategy consists of two stages, of which the initial phase performs EV scheduling in consideration of both EV constraints and power system limitations, and the second control layer checks for voltage violations with essential EV rescheduling. A voltage sensitivity analysis method is employed to alleviate the impacts of EV charging locations. The control scheme is evaluated through a modified standard IEEE 33 nodes test feeder. The results demonstrate the control scheme can effectively satisfy normal demands of EVs and achieve the voltage regulation purpose.

HLA based co-simulation framework for multiagent-based smart grid applications

Multiagent Systems (MAS) are used extensively in Smart Grid research as a mean of distributed control. The integration of power system, communication network and MAS based control system creates complex dynamics difficult to comprehend. In this paper, a co-simulation framework for the investigation of the multi-disciplinary interdependencies between the three systems will be proposed. The proposed design combines the power system simulator PSCAD/EMTDC, network simulator OPNET, and the well-recognized MAS platform JADE. In order to promote extensibility and reusability of simulation modules, as well as to enforce causality constraint, our design is in compliance with the High Level Architecture (HLA, IEEE 1516) standard.

An intelligent scatter search (ISS) algorithm for scheduling of charging a single EV

Electric vehicles (EVs) becomes popular for energy saving and environmental protection in light of sustainable development in recent years. The wide spread popularity of EVs relies on an effective strategy for charging the battery. Hence, efficient and robust algorithms are essential for implementing the charging strategies. In this paper, an intelligent scatter search (ISS) framework utilizing filter-SQP (sequential quadratic programming) and mixed-integer SQP techniques as local solvers is proposed for handling EV charging with either flexible or constant charging power under both V2G and G2V support. Simulations have been carried out to verify the effectiveness of the proposed ISS algorithm. The results demonstrated that its performance is better than other approaches including GS (global search), GA (genetic algorithm), PSO (particle swarm optimization), and SS/F (scatter search algorithm with local solver fmincon). In addition, its computational load is rather low in regulating the EV charging and thus is very suitable to minimize the operation cost for EV owners.

A new concept of high input voltage to low load voltage (1500 V – 48V) DC-DC conversion with hybrid ZVS-ZCS and asymmetrical voltage distribution

A new dc-dc converter with asymmetrical voltage distribution between two primary switch pairs is proposed. It allows an implementation with popularly used MOSFETs for the low-voltage switch pair and IGBTs for the high-voltage switch pair, giving the optimal option for a particular class of high-voltage applications. A new hybrid zero-voltage-switching (ZVS)-zero-current-switching (ZCS) technique, which is different from the ZVZCS solution, is proposed. A secondary-side snubber is used to achieve ZCS of all IGBTs in the IGBT pair; its resonant energy is fully released to the load. The energy used for achieving ZVS for the upper MOSFET in the low-voltage switch pair at the transition from the freewheeling to energy transfer stage is provided by the primary-side input capacitor and dc-blocking capacitor. All IGBTs and MOSFETs in the proposed structure are soft-switched from very light load to full load. The duty cycle of the upper switch in each pair determines the voltage distribution between the switch pairs. It is controlled by a simple PWM. A 2kW, 1500/48V experimental prototype has been built and evaluated. The experimental results confirmed the theoretical predictions.