Weijia Yang
Uppsala University
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Featured researches published by Weijia Yang.
Electric Power Components and Systems | 2015
Wencheng Guo; Jiandong Yang; Jieping Chen; Weijia Yang; Yi Teng; Wei Zeng
Abstract Aiming at studying the regulation quality of isolated turbine regulating systems under load disturbance and different regulation modes, the complete mathematical model of a turbine regulating system under three regulation modes is established. Then, based on dominant poles and null points, the method of order reduction for a high-order system of time response of the frequency is proposed. By this method, the complete high-order systems are solved and the regulation quality for time response of the frequency is studied. The results indicate that (1) the tail wave, which is the main body of time response of the frequency and the principal factor that determines the regulation quality, is mainly determined by the dominant poles; (2) for the three regulation modes, by deleting the high-order terms, the three equivalent overall transfer functions are fourth order, third order, and third order, respectively, and can be solved; (3) the analytical fluctuation equations of time response of the frequency solved from low-order equivalent overall transfer functions accurately simulate the fluctuation characteristics of time response; and (4) based on damped vibrations decomposed from analytical fluctuation equations, the regulation qualities of three regulation modes are analyzed.
IEEE Transactions on Power Systems | 2017
Weijia Yang; Per Norrlund; Linn Saarinen; Jiandong Yang; Wei Zeng; Urban Lundin
Nowadays, the wear and tear of hydropower turbines is increasing, due to more regulation movements caused by the increasing integration of intermittent renewable energy sources. In this paper, a controller filter is proposed as a solution to the tradeoff between reducing the wear of turbines and maintaining the regulation performance and thereby the frequency quality of the power systems. The widely used dead zone is compared with a floating dead zone and a linear filter, by time-domain simulation and frequency-domain analysis. Simulink models are built and compared with onsite measurement. Then, the time-domain simulation is used to investigate the guide vane movement, the load disturbance and the power system frequency, based on a one-day grid frequency data measured in this study. In the theoretical analysis, the describing functions method and the Nyquist criterion are adopted to examine the stability of the system with different filters. The results show that the floating dead zone, especially the one after the controller, has a better performance than the dead zone on both the wear reduction and frequency quality. The linear filter has a relatively weak impact on both guide vane movements and the frequency quality. Other related conclusion and understandings are also obtained.
Electric Power Components and Systems | 2015
Weijia Yang; Jiandong Yang; Wencheng Guo; Per Norrlund
Abstract Currently, the Thoma criterion is often violated to diminish the cross-section of the surge tank; therefore, the surge fluctuation is aggravated and the frequency stability becomes more deteriorative. The focus of this article is on stabilizing the low-frequency oscillation of an isolated hydropower plant caused by surge fluctuation. From a new perspective of hydropower plant operation mode, frequency stability under power control is investigated and compared with frequency control by adopting the Hurwitz criterion and numerical simulation. In a theoretical derivation, the governor equations of frequency control and power control are introduced to the mathematical model. For numerical simulation, a governor model with a control mode switch-over function is built. The frequency oscillations under frequency control, power control, and control mode switch-over are simulated and investigated, respectively, with different governor parameters and operation cases. The result shows that the power control has a better performance on frequency stability at the expense of rapidity compared with the frequency control. Other recommendations regarding worst operation cases and choice of control modes are also developed.
IEEE Transactions on Power Systems | 2018
Linn Saarinen; Per Norrlund; Weijia Yang; Urban Lundin
Power systems are making a transition from purely technical, centrally planned systems to market based, decentralized systems. The need for balancing power and frequency control reserves are increasing, partially due to variable renewable production, which gives an opportunity for new incomes but also a challenge in terms of changed modes of operation with risk for reduced lifetime for controllable power plants. This paper investigates how the allocation of a sold volume of frequency control reserves within a large hydropower production fleet can affect the costs of providing primary and secondary reserves, in terms of its impact on wear and fatigue, production losses, and the quality of the delivered frequency control. The results show that for primary control, low static gain in the governors results in poor quality and a large amount of load cycles of the units. High static gain, on the other hand, increases the production losses. The control work of the fleet can be reduced by using a proper balance of primary and secondary control gain on each unit, although the intuitive results from linear models exaggerate this effect. Automatic secondary control improves the system frequency quality but also increases the wear.
IOP Conference Series: Earth and Environmental Science | 2016
Weijia Yang; Per Norrlund; Jiandong Yang
Since a few years, there has been a tendency that hydropower turbines experience fatigue to a greater extent, due to increasingly more regulation movements of governor actuators. The aim of this pa ...
IOP Conference Series: Earth and Environmental Science | 2018
Renbo Tang; Jiandong Yang; Weijia Yang
Nowadays the frequency regulation of pumped-storage units becomes more and more important, due to the more complex structure of the grid and greater proportion of the renewable intermittent sources. The aim of this paper is to investigate the stability of pumped-storage plants (PSPs), and the subject of study is PSPs with surge tanks, shared water conduits and a common busbar. Firstly, the equations of each component in the system are deduced and simplified, to establish a linear time-invariant model by adopting the simplified transfer function (STF). A real Chinese PSP is taken as the engineering instance of this work, and simulation results of the STF model are validated with results of on-site measurements and computations based on the method of characteristics (MOC). Then, through both theoretical analysis and simulations, operating stability of the PSP system is studied under various islanded operating cases to reveal the influence of the hydraulic coupling and the electrical coupling. The results demonstrate the significant influence of the governor control modes and the parameter settings on stability of frequency regulation of the PSP. Suggestions of control strategy are also obtained.
International Journal of Electrical Power & Energy Systems | 2015
Wencheng Guo; Jiandong Yang; Weijia Yang; Jieping Chen; Yi Teng
Energies | 2015
Weijia Yang; Jiandong Yang; Wencheng Guo; Wei Zeng; Chao Wang; Linn Saarinen; Per Norrlund
Renewable Energy | 2016
Weijia Yang; Per Norrlund; Linn Saarinen; Jiandong Yang; Wencheng Guo; Wei Zeng
Renewable Energy | 2016
Wei Zeng; Jiandong Yang; Weijia Yang