## JMAG-Express CLUB E

### Secrets of JMAG-Express

Many users have inquired about the difference between the calculation methods used in JMAG-Express and JMAG.
Therefore, We are revealing the secrets behind the calculation methods to our users only.

Secret content Posted Date
1. Calculation Method used in Express 2009-09-25
2. Accuracy of Express 2009-09-25

### 1. Calculation Method used in Express

Many people have asked if JMAG-Express uses the magnetic circuit method because of the vast speed the calculations are performed, when in fact, JMAG-Express uses the finite element method (FEM). However, the purpose of the calculation performed in JMAG-Express and JMAG differ. JMAG-Express focuses on evaluating the approximate motor characteristics by obtaining the flux linkage, motor inductance, and iron losses for a current value with the finite element method, and then uses these results to obtain the torque, losses, and efficiency. In the previous version of JMAG-Express, a fixed current of 1 A is applied which causes the results to become more inaccurate as the difference in the current driving the motor increases. However, in JMAG-Express ver. 1.00901, the accuracy of the calculation has been enhanced by applying currents appropriate for the model.

### 2. Accuracy of Express

To provide proof rather than conjecture, we have compared the results obtained using JMAG-Express Ver. 1.00801 and the results obtained using JMAG-Studio for an analysis of the IPM motor indicated in Fig. 1. Using JMAG-Studio, the torque and losses are calculated from each current value that is iteratively obtained for a specified voltage at each rotation speed. Using JMAG-Express Ver. 1.00801, the maximum current is set to a standard value of 5 A.
The comparison of these results is indicated in Fig. 2. Although the results do not match exactly, the results obtained using JMAG-Express Ver. 1.00801follow the results obtained in JMAG-Studio closely.

Fig. 1 IPM motor

The results obtained for a maximum current that is exaggerated to 50 A are also compared to show the current dependency. The comparison of these results is indicated in Fig. 3. The difference in the results that are obtained by JMAG-Express Ver. 1.00801 and JMAG-Studio are obvious. The difference in the results is especially large when the current is substantial at low rotation speeds. However, as described above, JMAG-Express ver. 1.00901 has been enhanced to address these issues and exceed our users’ expectations.

Fig. 2-a Comparison of the torque

Fig. 3-a Comparison of the torque

Fig. 2-b Comparison of the copper losses

Fig. 3-b Comparison of the copper losses

Fig. 2-c Comparison of the iron losses

Fig. 3-c Comparison of the iron losses