Chunguang Ren

Power flow algorithms compare based on voltage instability and reliability analysis

The “nose point” of P-V curve is a key point in the system static security-stability analysis. It is always considered as the system voltage collapse point. How to get the precise system or bus load power and bus voltage of the nose point is a practical and important issue. Taken the system contingencies and reliability assessment into consideration, the requirements for accuracy and calculating time of the algorithms have become more rigorous than before. In this paper, the Improved Bisection Searching Technique (IBSST) algorithm is proposed and compared with the traditional Continuation Power Flow algorithm (CPF) through the analysis on a practical 220kV Taiyuan power system in Shanxi Province of China. The results show that the IBSST is superior to CPF in aspects of accuracy, calculating time and stability of algorithm.

High-Performance Three-Phase PWM Converter With a Reduced DC-Link Capacitor Under Unbalanced AC Voltage Conditions

A high-performance three-phase pulse width modulation (PWM) converter with reduced dc-link capacitor under unbalanced ac voltage conditions is proposed in this paper. The unique feature of the converter lies in that sinusoidal symmetrical ac currents and ripple free dc voltage can be achieved simultaneously without using a bulky capacitor, which was thought to be a dilemma in the past. The control scheme is implemented in an α–β frame, so the complex rotate transformations are avoided, and it does not require the extraction of positive and negative sequence currents, which simplifies the control algorithm. A two-quadrant operation active power compensator together with its controller is developed to suppress the voltage ripple in the dc-link. Compared with the passive compensation method, the compensator is equipped with a smaller capacitor to reduce the system size, weight, and cost. Moreover, the compensator could be integrated with the conventional three-phase three-leg PWM converter seamlessly. The effectiveness of the proposed control schemes is verified by the experiment results.

Design of secondary voltage regulation system of DC microgrid based on vanadium redox battery storages

In a DC microgrid (MG) with droop control system only, there exists an inherent deviation between DC bus voltage and its rated value during the steady-state operations. In order to eliminate the inherent deviation, a secondary voltage regulation system (SVRS) based on vanadium redox battery (VRB) storages is proposed in this paper. It adopts double closed loop control strategy coordinating with the bus voltage regulation system with droop control (VRSDC) to realize the zero steady-state error regulation of bus voltage. Four cases are studied, and their simulation results verify its effectiveness.

The control method of bidirectional AC/DC converter with unbalanced voltage in hybrid micro-grid

Three phase AC/DC converter based on the traditional double loop control may act as a link bridge in hybrid micro-grid due to its bidirectional power flow with unit power factor on AC side. When the AC/DC converter works on the condition of unbalanced voltage on the AC side, a second order ripple voltage will be generated in the DC-link and some amount of third harmonic current will exist in the AC side, which could deteriorate the operation of the micro-grid. By analyzing of the power flow under unbalanced voltage conditions, a three-phase AC/DC converter system, based on super capacitor compensation, is presented. The system can guarantee the AC current sinusoidal and symmetrical, and can keep DC-link voltage fluctuating lightly around rating during the super capacitor working. As an energy buffer, the super capacitor mitigates the active power ripple. Simulation and experimental results are provided to verify the feasibility of the control system.