The high speed maglev is mainly characterized by propulsion using linear synchronous motor (LSM) and vehicle levitation from the guideway surface. In LSM propulsion control, the position detection sensor is used to detect running vehicle position for synchronized current generation. To maintain the stable levitating condition during vehicle running, the irregularity of guideway surface should be monitored by sensors measuring the displacement and acceleration between vehicle and guideway. In this study, the application methods of these sensors in the high speed maglev are investigated and through the experiments by using the small-scale test bed, the validity of examined methods is confirmed.
To achieve over 500 km/h speed, the high speed maglev uses the powerful linear synchronous motor (LSM) as propulsion and maintains levitation status from guideway surface minimizing the running friction. For LSM control, the precise position information of running vehicle should be detected in real-time and fed back to the controller so that the synchronized current could be provided to LSM coil installed in guideway. Here, the position error causes the mismatch of d-q transformation in inverter controller and influences the detrimental effect on the propulsion system bringing the decrease of propelling force [
For high speed maglev using electromagnetic suspension (EMS) as levitation method, the levitation gap between vehicle and guideway is maintained by only about 10 mm. Therefore, to prevent the chance of vehicle contact with the guideway surface and improve the ride comfort, the guideway irregularity should be monitored and controlled below a certain level [
In this study, regarding position detection and guideway monitoring, the sensor application methods such as data acquisition, processing and analysis are investigated first. Then, the validity of examined method is confirmed by using the small-scale test bed whose operational function is identical with the real size high speed maglev.
While in traditional wheel type train, the contact type sensors or tachometers are normally used for position detection, in high speed maglev, the non-contact type position detection is needed due to the levitated running of vehicle from the guideway surface. And since the detected data from running vehicle should be wirelessly transmitted to the controller located in several kilometers away, the problem such as signal delay and transmit cycle should be resolved.
One of the most effective methods to realize position detection in high speed maglev is to detect the tooth-slot shape of LSM stator installed in guideway by using the inductive sensor attached in vehicle bogie (
When the inductive sensor is moving along the long stator with certain gap, the magnetic flux transmitted from sensor coils mainly flows through air and stator and finally returns back into the coil. In this case, the inductance caused by magnetic flux can be expressed by Equation (1).
where N is the number of coil turns, A is the sectional area of magnetic field passage,
tooth-slot in LSM stator as shown in
Detail method to estimate the missed position due to the transmit cycle or poor resolution is explained in
The displacement and acceleration of gap between vehicle and guidewaye are used as levitation control feedback data during high speed maglev running. Simultaneously, this data could be used to measure the guideway irregularity as shown in
As this equation implies, since value
To validate the application methods which are described in previous section, a small-scale test bed which is shown in
In position detection experiment, as vehicle moves along the guideway, the sensor output corresponding to the LSM stator tooth-slot will be checked first. Then by using acquired sine wave, squares and tooth wave will be generated through data processing technique. And the effect of estimation in data missed period will be examined. In guideway irregularity monitoring experiment, as guideway irregularity, a step change is used as shown in
Result of data acquisition and processing for position detection is shown in
Hardware | Performance | ||
---|---|---|---|
Items | Value | Items | Value |
Vehicle weight | 140 kg | Max. torque | 33.2 N |
Vehicle size (L × W × H) | 1.05 × 0.7 × 0.5 m | Max. acceleration | 1 m/s2 |
Guideway size (L × W × H) | 10.3 × 0.5 × 1 m | Levitation/guidance gap | 4 mm |
Items | Value | ||
---|---|---|---|
Position Detection Sensor (ELCO Ni15-M30-LIU-Q12) | Gap Sensor (AEC 5520) | Acceleration Sensor (PCB 3711B 1110G) | |
Range | 3 - 15 mm | 0 - 8 mm | ±98.1 m/s2 pk |
Resolution | - | 1 μm | 0.012 m/s2 rms (broadband resolution) |
Bandwidth | - | 30 kHz | - |
Output | 0 - 10 VDC | ±5 VDC | ≤100 Ohm (impedance) |
Input | 15 - 30 VDC | ±11 - 17 VDC | 6 - 30 VDC |
to the slot area. The main reason of this is that LSM winding coil located in slot influences the magnetic flux emitted from sensor [
This estimation method can be also used to predict the position data in LSM stator discontinuity, the space between LSM stators as expansion joints.
Regarding the 1mm step change of guideway, the displacement and acceleration between vehicle and guideway is displayed in (a) and (b) of
aspect is similar to
In this study, the sensor application for position detection and guideway monitoring in high speed maglev was investigated and through the test bed experiment, the validity of examined method was confirmed. For position
detection method, to detect the tooth-slot shape of LSM is proposed and this method has advantage over other methods in respect to accuracy and easiness of installation. To validate this method, by using the small scale testbed, the whole procedure of position data acquisition, processing and estimation are fulfilled and the effectiveness of estimation in the presence of missed data is proved. The experiment results show that the proposed method is suitable for position detection in maglev, and especially, the estimation method is very effective to improve the accuracy of position detection. For guideway surface irregularity monitoring during maglev running, the simple method using the displacement and acceleration data between vehicle and guideway surface is proposed. Through experiment by using small scale testbed, it was confirmed that the guideway surface irregularity such as step change could be effectively estimated. Even though, there is fluctuation at the beginning and some time is needed to be settled down, this method would be effective to anticipate the long wave irregularity of guideway.
This work was supported by Core Technology Development Project of Super Speed Maglev Train funded by Ministry of Land, Infrastructure and Transport (11PRTD-B061485).