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In this paper, the model of turbine governor based on the physical principles is constituted to improve the accuracy of
power system dynamic simulation, making the results of simulation consistent
with the actual situation. The unit and grid coupling model
which reflects the interaction between thermal system of
power plant and power system is built using EMTDC/PSCAD. The influence of nonlinear
characteristics on the valve opening and the steam turbine mechanical power is
also analyzed in this paper. The results of simulation show that the improper
setting of parameters reflecting nonlinear characteristics of turbine governor
can lead to the cyclical oscillations of the valve
opening and the steam turbine mechanical power, and
even can lead to the power oscillation persistently.
The research achievements in this paper have a certain reference value on
exploring the causes of power oscillation from the prime mover.
As the existing coordinated control
strategies between grid and unit have limitations in isolated power system,
this paper introduces new coordinated control strategies which can improve the
stability of isolated system operation. This paper analyzes the power grid side
and unit side influence factors on the isolated power system. The dynamic models
which are suitable for islanding operation are applied to simulate and analyze
the stability and dynamic characteristics of the isolated power system under
the conditions of different load disturbances and governor parameters. With considering the differences of frequency characteristics
between the interconnected and isolated power system, the adjusting and
optimization methods of under frequency load shedding are proposed to meet the
frequency stability requirements simultaneously in the two cases. Not only
proper control strategies of the power plant but the settings of their parameters
are suggested to improve the operation stability of the isolated power system.
To confirm the correctness and effectiveness of the method mentioned above, the
isolated system operation test was conducted under the real power system
condition, and the results show that the proposed coordinated control
strategies can greatly improve stability of the isolated power system.