Research On PWM Pulse Wave Overvoltage In Wind Turbine Winding

At present,due to the soaring price of traditional energy and the aggravation of global environmental pollution,vigorous development of clean energy has become a strategic development goal of all countrise in the word.As the hosttest new energy source,wind power generation can realize the sustainable development of wind power generation only by ensuring the safe and reliable normal operation of wind trubines.Among them,the most critical part is the overvoltage protection of the interal winding of the generator.Permanent magnet synchronous generators(PMSG)typically use a PWM inverter because the pulse wave of its output is steep at its rising edge.The PWM high-frequency pulse wave transmitted through the cable will first generate over-voltage oscillation at the port of the motor,and because of the non-negligible influence of the distributed parameters in the winding,the distribution of the high-frequency pulse voltage in the stator winding is very uneven.Such a situation will cause the highest voltage to be applied to the first few turns of the winding,causing damage and premature aging of the stator winding insulation.In view of the above problems,this paper selects 1.5MW permanent magnet synchronous generator as the research model.Firstly,the equivalent circuit model of the segment winding is established under the condition of considering the distribution parameters.Derived from the lossless transmission line theory,the distribution parameter values that need to be calculated are capacitance and inductance.The electromagnetic field analysis of the permanent magnet stator winding is carried out by finite element Ansoft software,and the value of the distribution parameters of the forming winding is calculated.Secondly,by studying the cause of overvoltage generated by the PWM inverter,the distributed parameter model inside the permanent magnet fan winding is established by Matlab/Simulink software.Finally,in order to reduce the over-voltage at the wind turbine end and improve the non-uniform distribution of winding voltage,the over-voltage characteristics at the fan end,the inter-coil voltage characteristics in the stator winding and the inter-turn voltage characteristics in the stator winding are discussed respectively.By changing the rise time of PWM pulse wave,the parameters of winding distribution are simulated.Finally,it is found that effective measures such as increasing the rise time of pulse wave,reducing the equivalent capacitance of turn-to-ground and reducing the self-inductance of windings can be taken to improve the insulation characteristics and prolong the service life of wind turbines.When studying the inter-turn voltage of the fan winding,it is found that when the steep rising edge time of the PWM high-frequency pulse wave is prolonged,the over-voltage distribution is significantly suppressed.When the value of the capacitance to the ground in the winding is increased,the shunting effect to the ground is also increased,and the voltage distribution between the windings at this time is extremely uneven.The current in the winding is suppressed by the inductance.As the inductance increases,the current travels backwards more and more difficult.At this time,the first few windings in the coil are subjected to the maximum voltage.Therefore,in the manufacture of a fan,it is necessary to carefully select how to select the inductance value,relative dielectric constant and shape size of the insulating material.