Shiyi Shao’s research while affiliated with Nanjing Nari-Relays Electric CO., LTD and other places

This study presents the performance analysis and testing of a 250 kW medium-speed brushless doubly-fed induction generator (DFIG), and its associated power electronics and control systems. The experimental tests confirm the design, and show the system's steady-state and dynamic performance and grid low-voltage ride-through capability. The medium-speed brushless DFIG in combination with a simplified two-stage gearbox promises a low-cost low-maintenance and reliable drivetrain for wind turbine applications.

Compared with the Doubly fed induction generators (DFIG), the brushless doubly fed induction generator (BDFIG) has a commercial potential for wind power generation due to its lower cost and higher reliability. In the most recent grid codes, wind generators are required to be capable of riding through low voltage faults. As a result of the negative sequence, induction generators response differently in asymmetrical voltage dips compared with the symmetrical dip. This paper gave a full behavior analysis of the BDFIG under different types of the asymmetrical fault and proposed a novel control strategy for the BDFIG to ride through asymmetrical low voltage dips without any extra hardware such as crowbars. The proposed control strategies are experimentally verified by a 250-kW BDFIG.

A coupled-circuit model for the brushless doubly fed machine (BDFM) has been developed. The transformation of the model into the d-q axis form, ultimately in a synchronous reference frame in which machine currents and voltages have constant values in the steady state, has been carried out. A model-reduction technique is presented, which gives a concise representation of the `nested-loop' rotor design using a single d-q pair. These models have been experimentally verified and give a convenient and accurate way of calculating the dynamic behaviour of a BDFM. The ability to represent the BDFM with a single d-q pair considerably simplifies the design of suitable controllers.

The brushless doubly fed induction generator (BDFIG) shows commercial promise for wind power generation due to its lower cost and higher reliability when compared with the conventional DFIG. In the most recent grid codes, wind generators are required to be able to ride through a low-voltage fault and meet the reactive current demand from the grid. A low-voltage ride-through (LVRT) capability is therefore important for wind generators which are integrated into the grid. In this paper, the authors propose a control strategy enabling the BDFIG to successfully ride through a symmetrical voltage dip. The control strategy has been implemented on a 250-kW BDFIG, and the experimental results indicate that the LVRT is possible without a crowbar.

The brushless doubly fed induction generator (DFIG) (BDFIG) shows commercial promise for wind power generation because of its lower maintenance needs compared to the widely used DFIG. From power grid codes, installed wind turbines are sometimes required to be capable of operating under unbalanced grid conditions. This paper presents a novel controller for BDFIG-based wind generators operated with asymmetrical voltage supplies. Two synchronous reference frames, the positive and the negative, are introduced for applying a vector control scheme to separately control two sequences arising from the unbalanced voltage. Different control strategies are discussed for reducing the consequent oscillations. It is demonstrated that the proposed controller shows a significant performance improvement over the conventional controller and is effective to cope with potentially unbalanced conditions.

This paper presents a generalized vector control system for a generic brushless doubly fed (induction) machine (BDFM) with nested-loop type rotor. The generic BDFM consists of p1/p2 pole-pair stator windings and a nested-loop rotor with N number of loops per nest. The vector control system is derived based on the basic BDFM equation in the synchronous mode accompanied with an appropriate synchronization approach to the grid. An analysis is performed for the vector control system using the generic BDFM vector model. The analysis proves the efficacy of the proposed approach in BDFM electromagnetic torque and rotor flux control. In fact, in the proposed vector control system, the BDFM torque can be controlled very effectively promising a high-performance BDFM shaft speed control system. A closed-loop shaft speed control system is composed based on the presented vector control system whose performance is examined both in simulations and experiments. The results confirm the high performance of the proposed approach in BDFM shaft speed control as well as a very close agreement between the simulations and experiments. Tests are performed on a 180-frame prototype BDFM.

This paper devises an electronic based emulator for tubular Direct Drive Linear Wave Energy Converter (DDLWEC). The emulator is able to output expected voltage sourced waveforms and include related impedances of a DDLWEC, which provides convenience and cost saving for testing various power conversion methods for the DDLWECs in a wide range of wave conditions. Two various ac/dc power conversion topologies have been developed to work in conjunction with a tubular DDLWEC, and their performances are tested by using the emulator. Both topologies are able to effectively handle the irregular electrical outputs from DDLWECs. The unidirectional ac/dc topology has advantage in cost saving. On the other hand, the H-Bridge topology can allow reversible energy flow and can slightly improve the power extraction from DDLWECs.

This paper discusses the dynamic behavior of the brushless doubly fed induction generator during the grid faults which lead to a decrease in the generator's terminal voltage. The variation of the fluxes, back EMFs, and currents are analyzed during and after the voltage dip. Furthermore, two alternative approaches are proposed to improve the generator ride-through capability using crowbar and series dynamic resistor circuits. Appropriate values for their resistances are calculated analytically. Finally, the coupled circuit model and the generator's speed and reactive power controllers are simulated to validate the theoretical results and the effectiveness of the proposed solutions. Moreover, experiments are performed to validate the coupled circuit model used.

The paper presents a low-cost variable-speed drive system comprising a brushless doubly-fed motor (BDFM) and a fractionally rated unidirectional frequency converter. A simple control algorithm is proposed for regulating the drive's speed and torque. A method of starting the BDFM in the cascade mode is presented and the starting performance is analyzed. The efficiency of the BDFM is discussed and the dynamic performance of the drive is verified by experimental results obtained from a 180 frame-size BDFM. Index Terms—Brushless doubly-fed motor (BDFM), dynamic performance, phase angle controller, unidirectional converter.

The Brushless Doubly-Fed Induction Generator (BDFIG) shows commercial promise for wind power generation due to its lower cost and higher reliability compared to the Doubly-Fed Induction Generator (DFIG). For the purposes of commercialisation, the BDFIG must meet grid codes at all times. Nowadays, all new wind generators have to ride through certain grid faults, and the Low-Voltage Ride Through (LVRT) capability has become one of the most important points on which to assess the performance a generator. This paper, for the first time, proposes a control scheme to enable the the BDFIG to ride through symmetrical voltage dips. Simulation results and experimental results on a prototype BDFIG show that the proposed scheme gives the capability to ride through low voltage faults.