The previous discussion shows that Pinv_loss can be represented as a function of iqse and
idse. Moreover, since iqse and idse can be expressed by λdr’e* as shown in (4.10) and (4.11), Pinv_loss
and the total loss of the inverter-fed motor drive, Pdrive_loss, can be expressed as functions of λdr’e*.
These functions of λdr’e* are too complex. Thus, the numerical sweep is used to find the optimal
λdr’e*, which is implemented through MALTAB code as shown in Appendix B.
Since the Infineon BSM75GB60DL IGBT module is much over-rated for the 1.5 HP IM, a 50HP IM is used in the simulation verification here to show effective impacts of the inverter losses. The machine parameters and the basic information of the 50 HP IM and the inverter are shown in TABLE XI. The IM is tested at 1800 RPM and three load torques: 21 N·m, 42 N·m and 63 N·m, where the numerical sweep changes λdr’e* from rated value to 0.15 Wb when the
flux is too weak to support the load. The step size of the flux sweep is 0.01 Wb. Rated λdr’e* and
the optimal λdr’e* are summarized in TABLE XII. The previous Simulink model of the IFOC-
controlled IM is applied again but with three modifications: 1) The machine parameters are changed from the 1.5 HP motor to the 50 HP motor; 2) A block to calculate the inverter loss is added to the simulation; and 3) Mechanical and stray losses are removed from the simulation due to lack of experimental data, but it does not affect showing a proof of concept.
Simulation results of the torque and speed responses are shown in Fig. 55 and Fig. 56, respectively. It is seen that both rated and the optimal λdr’e* can lead to excellent tracking of
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using rated and the optimal λdr’e*. In addition, the transient here is longer than using the 1.5HP
IM, since the inertia of the 50 HP IM is much larger than that of the 1.5 HP motor, and the PI controllers also need more time to regulate the larger currents. The efficiency and the total loss of the inverter-fed motor drive are shown in Fig. 57 and Fig. 58, respectively. Again, the optimal λdr’e* leads to increased drive efficiency or decreased Pdrive_loss at different low-load conditions.
Moreover, the room for LMC shrinks as TL increases as before.
TAB LEXI.THE PAR AM ETER S AND BAS IC IN FOR M ATIO N O F THE 50HP IM
Parameter Rs (Ω) Rr’ (Ω) Lls (H) Llr’ (H) Rc (Ω) Lm (H) ωe (rad/s) P
Value 0.087 0.228 0.0008 0.0008 200 0.034696 120π 4
Parameter Vll MI Vdc_real Treal Vdc_datasheet Tdatasheet TL_rated fsw
Value 460 V 0.9 835 V 25 ◦C 300 V 125 ◦C 198 N·m 10k Hz
TAB LEXII. RATE D AN D THE OP TIM AL λd r’ e * AT TH E TESTIN G CON D IT IO N S
Condition Rated @ 1800RPM Optimal @ 1800RPM +21 N·m Optimal @ 1800RPM +42 N·m Optimal @ 1800RPM +63 N·m λdr’e* (Wb) 0.9528 0.4228 0.6028 0.7328
To show the impact of the inverter loss in changing the optimal flux point of the overall motor drive system, Pmach_loss, Pinv_loss, and Pdrive_loss of the motor drive operating at 1800 RPM
and TL=15 N·m are shown in Fig. 59 with respect to different λdr’e*. It is observed that the
individual motor or inverter will give the optimal flux at λdr3’e* or λdr4’e*, respectively. But the
optimal flux of the overall system is at λdr5’e*. Difference of drive loss using λdr3’e* and λdr5’e* is
shown in the figure. Therefore, creating a system-level power loss model is important to guarantee the optimal efficiency of the overall motor drive systems. For other operating conditions or other motors and inverters, where the magnitude of Pmach_loss and Pinv_loss are more
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comparable and Pinv_loss is more significantly changed with flux, difference of drive loss using
λdr3’e* and λdr5’e* could be much larger.
Fig. 55. The torque responses in the IFOC -controlled inverter -fed motor drive
Fig. 56. The speed responses in the IFOC -controlled inverter -fed motor drive
Fig. 57. The efficiency of using the optimal and rated λd r ’ e *
in the IFOC -controlled inverter -fed
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Fig. 58. The total loss of using the optimal and rated λd r’ e * in the IFOC -controlled inverter -fed
motor drive
Fig. 59. Pm a c h _ l o s s, Pi n v _ l o s s and Pd r i v e _ l o s s of the 50 HP motor drive at 1800RP M and 15 N ·m