Research On Control Strategies Of Loss Reduction And DC-link Capacitance Reduction For IPMSM Drives

Interior permanent magnet synchronous motors(IPMSMs)are a kind of permanent magnet synchronous motor with a special rotor structure.Compared with the conventional permanent magnet synchronous motors,IPMSMs have several advantages,such as significant salient characteristic,strong flux-weakening capability,strong rotor structure,and less usage of permanent magnets.Due to these advantages,IPMSMs have broad prospects for modern power transmission applications.With the continuous increasing level of automation in China,relevant application fields have proposed higher requirements for the performance of motor drives in terms of energy-saving effect and power density.In this case,this paper will study on the control techniques of loss reduction and dc-link capacitance reduction for IPMSM drives and overcome the relevant technical difficulties,which is of great significance for the promotion of IPMSM drives in more application fields.The parameters of IPMSMs vary with operating conditions,which influences the accuracy of maximum torque per ampere(MTPA)control.To overcome this influence,this paper proposes a signal injection MTPA control method based on dc-link current harmonic.A specific signal is injected into the motor,and the MTPA indicator information extracted from the dc-link current is used to correct the deviation between the current operating point and the MTPA point automatically,thereby eliminating the influence of the sensitivity of motor parameters to the operating conditions and achieving an accurate MTPA control.In contrast to the previous signal injection methods,the proposed method avoids the coordinate transformation associated with the polar coordinate system and reduces the dependence on the system hardware.The simulation and experimental results show that the proposed method can significantly reduce the stator current magnitude of IPMSMs,thus lowering the loss of IPMSM drives.For applications where signal injection is not possible,the equation method,which employs an MTPA equation to directly calculate the MTPA current reference,is an excellent choice for realizing MTPA operation.However,the previous MTPA equations ignore the partial derivatives of the motor parameters with respect to currents,and thus,the equation method based on the conventional MTPA equations exhibits low control accuracy.Aiming at solving this problem,an MTPA control scheme based on the variable-equivalent-parameter MTPA equation is proposed.First,a novel constant-parameter MTPA equation is derived,which avoids the complicated calculations involved in the conventional constant-parameter MTPA equations;then,a variable equivalent parameter is used to comprehensively represent the values of the motor parameters and the influence of their partial derivatives with respect to currents on the MTPA current trajectory.In this case,the derived novel constant-parameter MTPA equation is extended to a variable-equivalent-parameter MTPA equation.Different from the previous MTPA equations,the variable-equivalent-parameter MTPA equation not only retains the advantages of simple calculation of the novel constant-parameter equation,but also fully takes into account the influence of the characteristc that the motor parameters vary with operating conditions on the MTPA control.Therefore,the proposed MTPA scheme can simply achieve more accurate MTPA control than the conventional equation method,and the system loss can be reduced accordingly.To suppress the dc-link capacitor ripple current of IPMSM drives with small dc-link capacitor,a dc-link capacitor current suppression method based on inverter dc-link current regulation is proposed.The reason why the dc-link capacitor ripple current is relatively large under the conventional control strategy is analyzed.It is observed that the dc-link capacitor ripple current is caused by the differences between the 6th harmonic components of the rectifier output current and the inverter dc-link current.Based on this reason,in the proposed method,the 6th harmonic component of the dc-link current is adjusted by compensating the d-and q-axis voltages in order to reduce the differences between the 6th harmonic components of the rectifier output current and the inverter dc-link current,thereby reducing the dc-link capacitor ripple current.This method does not require any motor parameter information and effectively avoids the dependence on controlled rectifiers and other auxiliary circuits.The simulation and experimental results show that the proposed method can effectively suppress the dc-link capacitor ripple current of IPMSM drives with small dc-link capacitor while ensuring the motor speed regulation performance.To improve the waveform quality of the grid current of three-phase diode rectifier-fed electrolytic capacitor-less IPMSM drives,the relationship between the rectifier output current and grid current is analyzed,and then a grid current control method based on the regulation of rectifier output current is proposed.Considering the limitation of the maximum conduction angle of the rectifier diodes,a 120? rectangular wave,which has relatively low total harmonic distortion,is selected as the ideal grid current reference,and the corresponding ideal rectifier output current reference is determined according to the relationship between the rectifier output current and the grid current.Then,the regulation of the related components of the rectifier output current indirectly makes the grid current to be outputted in accordance with the selected ideal reference.The presented method not only improves the waveform quality of the grid current of the electrolytic capacitor-less motor drive,but also achieves relatively high-performance motor speed regulation.In addition,the proposed method has the advantage of neither relying on motor parameter information nor requiring the use of additional active circuits.