Research On Multipulse Rectifier Based On Harmonic Suppression At DC Side Feeding Permanent Magnet Wind Generation

The Permanent Magnet Synchronous Generator（PMSG）,due to the excellent performance,is the main development direction of the current variable speed wind turbine unit.With the further improvement of the power level of wind turbine generator system,it brings new opportunities and challenges to the full power converter of PMSG,especially the problem of machine side harmonics,higher level of the stator current and voltage,problems of harmonic and reliability more prominent.Diode-uncontrolled rectifier and voltage-type PWM rectifier are usually used for PMSG converter.Diode rectifier is low-cost,high reliability,but the stator current harmonic content is large,the power factor is low,the torque ripple is big.Although the PWM rectifier can operate at the unit power factor,a large number of power switches increase the cost of the rectifier and reduce the reliability of the system,especially high-power permanent magnet wind power generation.The capacity and price of the full-control devices are subject to constraints,simple to improve the device’s power level has been difficult to meet the requirements of the development of the converter.Multi-pulse rectifier technology has the merits of simple construction,high stability and reliability,low cost and obvious harmonic suppression,and it is the main method to solve harmonic problem in high power situation.In order to meet the requirements of the generator-side rectifier development,and further improve the harmonic suppression ability of multiple pulse rectifier and improve power factor,the multi-pulse rectifier technology and the technology of harmonic suppression at DC side are combined,trying to solve some problems,especially focus on rectification side,as the following several aspects of research.Multi-pulse rectifier can not completely eliminate the stator current low harmonics,the suppression effect for the high harmonic is not obvious,and the output voltage is not adjustable.Therefore,based on the conventional 12-pulse rectifier circuit,a parallel 18-pulse rectifier with three boost converters cascaded is studied.The harmonic suppression mechanism of active power factor correction at dc-side is analyzed under ideal state.The functional relationship between the input current of 18-pulse rectifier and the inductance current of three boost converter is deduced by using the switching function method.The inductance current waveforms of three boost converters needed are obtained,when the rectifier input currents are sinusoidal.The approximate linear input current waveforms of boost converters are given,the theoretical analysis is verified by simulation.Theoretical analysis shows that,when the boost converter input currents satisfy a particular triangle-wave that six-times of line frequency,using three boost converters can effectively suppress the rectifier input current harmonic.Compared with the traditional 18-pulse rectifier circuit and the 18-pulse rectifier with active power factor correction through simulation and comparative analysis,the results show that the control method of active power factor correction at DC side has more significant effect on harmonic suppression.Rectifier circuits for 18,24,36-pulse and other more pulse numbers,the multiple phase-shifting power supply needs to be generated by phase-shifted transformer.The phase-shifted transformer and more diode rectifier bridges increase the cost and volume of the system,which restricts the application of the multi-pulse rectifier in the permanent magnet wind power generation system and the improvement of the system power density.And multi-pulse rectifier circuit often adopts multi-group rectifier bridge parallel connection method,which need to use the balance reactor,and also not conducive to DC-bus voltage improvement.Therefore,a low harmonic and high power factor operation Six-phase Permanent Magnet Synchronous Generator（Six-PMSG）with series 12-pulse rectifier using the direct current injection method at DC side is studied.The output currents of the two sets of diode bridges satisfy the specific waveform by injecting the compensating current that produced thought parallel controllable current sources installing on the output side of the rectifier bridge.With the phase shifting of the Six-PMSG,the stator synthetic current is close to the sine wave,and the high power factor operation of Six-PMSG is realized.The simulation results demonstrate that the 11^th,13^th current harmonic in the Six-PMSG stator current basically are eliminated,with multiply 5^th,7^th harmonic content.But the total harmonic distortion of the Six-PMSG resultant current can be close to 1%due to the phase shift of the motor,and has higher power factor.The results proved the correctness of the theoretical research.And the DC side does not need the interphase reactor,the machine side does not need the power frequency transformer,which reduces the multi-pulse rectifier magnetic element volume and the cost.The better performance of the Six-PMSG meet the development of high-power permanent magnet wind power in the future.