| Most of the existing tidal power generation equipments have gearboxes with fixed rotational speed increase ratios,while a few newer equipments have a direct-drive transmission structure.Under both transmission schemes,the impeller rotational speed varies with the fluctuation of the flow speed,which makes the entering rotational speed to the generator change constantly,which causes the exporting power very unsteady and difficult to use.In addition,the existing tidal power generation equipments have the trouble of low energy transformation efficiency,and the maximum power tracking through certain technical means can largely improve the power generation efficiency.Aiming at the problems of unsteady energy output and low energy conversion efficiency caused by the fluctuation of flow velocity of horizontal axis tidal power generation device,a transmission scheme based on planetary gear mechanism is designed from the transmission mechanism of hydraulic turbine to generator and aims at achieving variable speed ratio transmission between them.In this paper,a systematic study of the working characteristics of the planetary gear mechanism and the theory of optimal blade tip speed ratio is conducted in the first place,which builds the basis for the subsequent illustration of the structure scheme and working principle of the adjustable speed ratio tidal power generator.Then the overall diagram of the adjustable ratio tidal power generator is established using Solidworks modeling software.As the energy source,the impeller axle is linked to the planetary carrier through several pairs of speed increasing gear pairs as needed,the outer gear ring is connected to the generator,and finally another permanent magnet synchronous motor(PMSM)is linked to the solar wheel through several pairs of speed reducing gear pairs as needed.Then the target speed of the speed control motor in real time can be calculated by taking the optimal leaf tip speed ratio theory,the flow rate measured in real time and the ideal speed that the generator wishes to maintain as reference values,and finally the convenient characteristics of the PMSM speed control and the characteristics of the planetary gear mechanism can be used to achieve continuous infinitely variable speed control from the impeller shaft to the generator shaft,so that the generator can be maintained at a stable This theoretically improves the stability of the power output and achieves the maximum power tracking of the tidal power generator.As the rotational speed control of the PMSM fundamentally determines the function and efficiency of this device,the major content of this paper revolves around it.The mathematical model of a PMSM in the stationary coordinate system is studied and the conversion equations between the various coordinate systems are derived,offering the theoretical foundation for the later development of the rotational speed control model.The rotational speed control principle of the motor is then systematically studied.Finally,three different rotational speed control schemes for permanent magnet synchronous motors are established as comparative studies in combination with advanced control strategies,they are:(1)a rotational speed control scheme of rotational speed loop and current loop controlled by PI;(2)a rotational speed control scheme of rotational speed loop and current loop controlled by linear active disturbance rejection control;(3)a rotational speed control scheme of rotational speed loop controlled by linear active disturbance rejection control theory and current loop controlled by PI.In order to compare and analyse the dynamic regulation ability and anti-interference ability of the three rotational speed regulation schemes,three rotational speed regulation models are established in MATLAB/SIMULINK software according to the characteristics of each of the three rotational speed regulation schemes.Four types of fluctuating signals are established to simulate these conditions according to the possible flow speed fluctuations and load torque variations in reality,they are:(1)the target rotational speed signal is in the form of gradual sine and the torque signal is a constant value;(2)the target rotational speed signal is in the form of abrupt square wave and the torque signal is a constant value;(3)the target rotational speed signal is in the form of gradual sine and the torque signal is the form of abrupt square wave;(4)the target rotational speed signal and the torque signal are in the form of an abrupt square wave.By repeatedly regulating the parameters of the controller in the model,the best performance of the different rotational speed control schemes under the same operating conditions is compared separately and the best combination of parameters is given,with the relevant characteristics of rotational speed tracking,electromagnetic torque and three-phase current being selected as the indicators of measurement.After analysing the reasons for the performance gap between the three rotational speed control schemes,it is concluded that the third rotational speed control scheme with a linear active disturbance rejection control rotational speed loop and a PI control current loop has the best overall performance,with strong dynamic regulation and interference immunity,and can theoretically meet the rotational speed control requirements of adjustable speed ratio tidal power generators.This paper offers a theoretical foundation for further research and prototype verification on improving the energy conversion efficiency and output stability of tidal power generation devices through the design and speed regulation simulation of the variable ratio drive mechanism of tidal power generation devices,and also provides a reference value for others to study the variable ratio drive chain on tidal power generation devices.The new speed control scheme proposed for PMSM is also applicable to other speed control environments with high interference and high requirements for dynamic regulation and control accuracy,which has a certain reference value in the field of motor speed control. |
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