In traction application,speed range of motor is an important index for motor drives.In AC motor control,the maximum speed of the motor is limited by the output voltage capability of the traditional three-phase inverte...In traction application,speed range of motor is an important index for motor drives.In AC motor control,the maximum speed of the motor is limited by the output voltage capability of the traditional three-phase inverter with star connenction of windings.Switching the star connection to delta connection in high-speed range can extend the speed range.In order to extend the speed operation region,star-delta switch proposed by many literatures relies on mechanical relay,which needs a dead zone of tens of milliseconds and seriously affects torque output.Besides,the traditional method will cause current overshoot during the switch transient process,decreasing the device security and reliability.Aiming at the defects existing in the star-delta hard switching,this paper proposes a star-delta soft switching method.Without adding extra power electronics devices,DC-bus capacitor is used to provide the path of zero axis current in the transient process,which helps to achieve the smooth torque output and zero current switch in the transient.Experiments have been done to validate the performance of the proposed method.The switching transient from star to delta connection in the motor drive can be much more stable than hard switching method.展开更多
Transient electromagnetic method(TEM)has been widely used in the field of medium and shallow underground detection due to its high detection efficiency and large detection depth.However,due to the long turn-off time o...Transient electromagnetic method(TEM)has been widely used in the field of medium and shallow underground detection due to its high detection efficiency and large detection depth.However,due to the long turn-off time of the transmitting current caused by the inductive characteristics of the transmitting coil,the early signals will be overwhelmed by primary field.Since the early signals contain most of shallow geological signals,it is necessary to reduce the long turn-off time to get shallow layer signal.Due to lack of a reliable and effective clamping method for high-power transmission at present,we design a TEM transmitter fast turn-off circuit,combining self-resonant zero-voltage switching technology with the corresponding timing control circuit to solve this problem effectively.A transient electromagnetic transmitter based on self-resonant constant voltage clamping technology was fabricated to charge the clamping capacitor.The rated transmitting current of the transmitter is 20 A,and the turn-off time is continuously adjustable from 550-50μs.Moreover,the current drop process is approximately linear rather than exponential attenuation.Compared with the existing clamping methods,the proposed clamping method solves the problems that transient voltage suppressor(TVS)clamping cannot be used in high-power occasions and has a high failure rate.It also solves the problem of long pre-charge time in traditional capacitor clamping methods due to insufficient inductance of the small size transmitting coil.The proposed method can provide a reference for fast shutdown of large current.展开更多
By using the output inductors and body capacitances without adding any component compared with hard switching synchronous rectifier,the topology of a soft switched synchronous rectifier with phase-shifted full bridge ...By using the output inductors and body capacitances without adding any component compared with hard switching synchronous rectifier,the topology of a soft switched synchronous rectifier with phase-shifted full bridge zero voltage switching DC/DC converter is proposed. The converter efficiency is maximized due to soft switching of the full bridge MOSFETs and the synchronous MOSFETs, and also the low conduction loss of synchronous MOSFET. The operation principles of the circuit are analyzed in detail and the small-signal model is derived, also the converter dynamic characteristics are analyzed. Frequency responses of transfer functions under different values of transformer primary leakage inductance are discussed. The experimental results were obtained from a 400 V input and 100 A/12 V output DC/DC converter operating at 100 kHz. The results show that the converter efficiency is 2% higher in rated power than traditional diode rectifier.展开更多
文摘In traction application,speed range of motor is an important index for motor drives.In AC motor control,the maximum speed of the motor is limited by the output voltage capability of the traditional three-phase inverter with star connenction of windings.Switching the star connection to delta connection in high-speed range can extend the speed range.In order to extend the speed operation region,star-delta switch proposed by many literatures relies on mechanical relay,which needs a dead zone of tens of milliseconds and seriously affects torque output.Besides,the traditional method will cause current overshoot during the switch transient process,decreasing the device security and reliability.Aiming at the defects existing in the star-delta hard switching,this paper proposes a star-delta soft switching method.Without adding extra power electronics devices,DC-bus capacitor is used to provide the path of zero axis current in the transient process,which helps to achieve the smooth torque output and zero current switch in the transient.Experiments have been done to validate the performance of the proposed method.The switching transient from star to delta connection in the motor drive can be much more stable than hard switching method.
文摘Transient electromagnetic method(TEM)has been widely used in the field of medium and shallow underground detection due to its high detection efficiency and large detection depth.However,due to the long turn-off time of the transmitting current caused by the inductive characteristics of the transmitting coil,the early signals will be overwhelmed by primary field.Since the early signals contain most of shallow geological signals,it is necessary to reduce the long turn-off time to get shallow layer signal.Due to lack of a reliable and effective clamping method for high-power transmission at present,we design a TEM transmitter fast turn-off circuit,combining self-resonant zero-voltage switching technology with the corresponding timing control circuit to solve this problem effectively.A transient electromagnetic transmitter based on self-resonant constant voltage clamping technology was fabricated to charge the clamping capacitor.The rated transmitting current of the transmitter is 20 A,and the turn-off time is continuously adjustable from 550-50μs.Moreover,the current drop process is approximately linear rather than exponential attenuation.Compared with the existing clamping methods,the proposed clamping method solves the problems that transient voltage suppressor(TVS)clamping cannot be used in high-power occasions and has a high failure rate.It also solves the problem of long pre-charge time in traditional capacitor clamping methods due to insufficient inductance of the small size transmitting coil.The proposed method can provide a reference for fast shutdown of large current.
文摘By using the output inductors and body capacitances without adding any component compared with hard switching synchronous rectifier,the topology of a soft switched synchronous rectifier with phase-shifted full bridge zero voltage switching DC/DC converter is proposed. The converter efficiency is maximized due to soft switching of the full bridge MOSFETs and the synchronous MOSFETs, and also the low conduction loss of synchronous MOSFET. The operation principles of the circuit are analyzed in detail and the small-signal model is derived, also the converter dynamic characteristics are analyzed. Frequency responses of transfer functions under different values of transformer primary leakage inductance are discussed. The experimental results were obtained from a 400 V input and 100 A/12 V output DC/DC converter operating at 100 kHz. The results show that the converter efficiency is 2% higher in rated power than traditional diode rectifier.
