**5. Simulation results and analysis**

An important note is that simulation results were extracted through block 5 (see figure 7), where Pu is obtained directly through Te\*r, based on the drive cycle reference values. In block 3a, Pu is achieved considering Pab-plosses (note that Pab=usaisa+usbisb+uscisc, i.e. the sum of instantaneous power of motor phases a, b, c – see figure 14). Motor losses considered by LMA are based on equation (7). There are some differences in Pu values when block 5 or block 3a are considered, which seems to put in evidence the issue mentioned in 4.4.

For each drive cycle, results are presented following the same pattern: the first figure includes the main results for conventional flux regulation and LMA. The second figure

**Figure 14.** Induction motor model of figure 15 (stator d-q reference frame)

represents the load torque demanded by the drive cycle, while in the third one the motor limits and working points imposed by the drive cycle are illustrated, together with the most significant LMA´s efficiency gain zones. Finally, a table with LMA and conventional flux regulation energy performances is also presented.

From a general perspective, these results confirm the main LMA features, described in section 3.2 visible differences from conventional flux regulation occur for low load torque, particularly for relative low speeds. This agrees to the fact that in regions where Ids has a large regulation flexibility, LMA and conventional flux regulation have clearly different performances.

**5.1. ECE-R15** 

416 Induction Motors – Modelling and Control

**4.4. Induction motor model** 

includes motor iron losses.

(block 5 in figure 7).

**5. Simulation results and analysis** 

values.

� i�� i�� � � � � �

sinθ� sin (θ� <sup>−</sup> �

cosθ� cos (θ� <sup>−</sup> �

**Figure 13.** Induction motor model simulated (space vectors in stator reference frame)

losses in LMA model are higher than the ones in figure 13 model.

The "Current Control" block generates stator reference voltage (Vsdq\*) in synchronous frame (through PI´s current ids and iqs controllers), which is applied to the motor model, in phase coordinates, in order to make the real instantaneous stator currents to achieve the reference

Figure 13 presents the induction motor model considered in simulations, which also

When comparing this model to the one considered in LMA (figure 2), the major differences are in parallel (magnetizing) branch. Since core losses currents are not considered in the major circuit, it is expectable that the voltages (Vedm and Veqm) on the independent sources are larger compared to the parallel branch voltages in the equivalent model of figure 13. Since core losses are given by ((Vedm)2+(Veqm)2)/Rm, it seems plausible to admit that the core

Figure 14 shows the simulink implementation of the considered induction motor model

An important note is that simulation results were extracted through block 5 (see figure 7), where Pu is obtained directly through Te\*r, based on the drive cycle reference values. In block 3a, Pu is achieved considering Pab-plosses (note that Pab=usaisa+usbisb+uscisc, i.e. the sum of instantaneous power of motor phases a, b, c – see figure 14). Motor losses considered by LMA are based on equation (7). There are some differences in Pu values when block 5 or

For each drive cycle, results are presented following the same pattern: the first figure includes the main results for conventional flux regulation and LMA. The second figure

block 3a are considered, which seems to put in evidence the issue mentioned in 4.4.

� π) sin (θ� <sup>+</sup> �

� π) cos (θ� <sup>+</sup> �

� π)

� π)� �

i�� i�� i��

� (35)

**Figure 15.** Drive-cycle; (Id; Iq; Motor losses) – [blue:LMA; red dashed line: conventional regulation]; Pu

Evaluation of an Energy Loss-Minimization Algorithm for EVs Based on Induction Motor 419

the vehicle is immobilized (Iqs=0), LMA performance leads to very significant results (figure 15), since Ids is regulated to its minimum value, while with conventional flux regulation, Ids has its maximum value. In this case, motor iron losses are much higher when compared to

From an energy perspective, although LMA acts directly on the iron losses (since it regulates Ids), it has also an impact in motor copper losses (as mentioned in section 3.2). Although for a given torque value, Iqs with LMA is higher than with conventional flux regulation (since Ids is smaller), a better equilibrium between Ids and Iqs is achieved with LMA. Since copper losses are also dependent on Ids2 and Iqs2, the motor efficiency has a clear improvement in this drive cycle scenario, which may be seen from figure 17. Nevertheless, efficiency values are relative low, which is no surprise if one take into consideration the efficiency maps (figure 5) together with figure 17 (notice the efficiency (power) curve gains and cycle working points,

<sup>0</sup> <sup>20</sup> <sup>40</sup> <sup>60</sup> <sup>80</sup> <sup>100</sup> <sup>120</sup> <sup>140</sup> <sup>160</sup> <sup>180</sup> <sup>200</sup> <sup>0</sup>

<sup>0</sup> <sup>20</sup> <sup>40</sup> <sup>60</sup> <sup>80</sup> <sup>100</sup> <sup>120</sup> <sup>140</sup> <sup>160</sup> <sup>180</sup> <sup>200</sup> <sup>0</sup>

<sup>0</sup> <sup>20</sup> <sup>40</sup> <sup>60</sup> <sup>80</sup> <sup>100</sup> <sup>120</sup> <sup>140</sup> <sup>160</sup> <sup>180</sup> <sup>200</sup> -20

<sup>0</sup> <sup>20</sup> <sup>40</sup> <sup>60</sup> <sup>80</sup> <sup>100</sup> <sup>120</sup> <sup>140</sup> <sup>160</sup> <sup>180</sup> <sup>200</sup> <sup>0</sup>

**Figure 18.** Drive-cycle; (Id; Iq; Motor losses) – [blue:LMA; red dashed line: conventional regulation]; Pu

<sup>0</sup> <sup>20</sup> <sup>40</sup> <sup>60</sup> <sup>80</sup> <sup>100</sup> <sup>120</sup> <sup>140</sup> <sup>160</sup> <sup>180</sup> <sup>200</sup> -5000

time [s]

For about 60% of total time of the "Europe: City" cycle, the vehicle speed is also below 2000 rpm, with the motor torque between -13 Nm and 16 Nm (aprox.). The vehicle is at rest for about 25% of the drive cycle duration. Basically, it puts the motor in the same (T,) working region as ECE-R15 (see figures 17 and 20). However, since it has a short time period (195 seg.), energy level demanded is much lower – the lowest one from the chosen drive cycle set. Similar relative energy losses are achieved: 20% for LMA and 36% without LMA of Eu (table 6). In both motor and braking modes, LMA most relevant results are in low speed –

the ones with LMA.

particularly for n<2000 rpm ).

5000 n [rpm]

> 10 20 Id [A]

0 20 Iq [A]

500 Motor losses [W]

> 0 5000

Pu [W]

**5.2. Europe: City** 

low torque region.

**Figure 16.** Torques [T\_load (green); Te\*(red); Te (blue)]

**Figure 17.** ECE-R15 drive cycle points over LMA efficiency curve gain


**Table 5.** ECE-R15 energy performances (Eu: energy supplied by the induction motor for the considered drive cycle; Eab: energy absorbed by the induction motor)

In almost 50% of the ECE-R15 drive cycle duration, motor speed is between 0 and 2000 rpm, with the motor torque among -13 Nm and 16 Nm (aprox.) – see figure 16. So, LMA inclusion allows significant loss reductions (table 5): with LMA, total losses are about 20% of Eu (energy supplied by the motor); without LMA, goes up to 38% of Eu. As expected, the main Ids differences occur for n<2000 rpm, particularly for low torques (with LMA, smaller Ids values are clearly visible). In a similar way, LMA performance in braking modes brings good results, since demanded torque has always low values. It should be pointed that when the vehicle is immobilized (Iqs=0), LMA performance leads to very significant results (figure 15), since Ids is regulated to its minimum value, while with conventional flux regulation, Ids has its maximum value. In this case, motor iron losses are much higher when compared to the ones with LMA.

From an energy perspective, although LMA acts directly on the iron losses (since it regulates Ids), it has also an impact in motor copper losses (as mentioned in section 3.2). Although for a given torque value, Iqs with LMA is higher than with conventional flux regulation (since Ids is smaller), a better equilibrium between Ids and Iqs is achieved with LMA. Since copper losses are also dependent on Ids2 and Iqs2, the motor efficiency has a clear improvement in this drive cycle scenario, which may be seen from figure 17. Nevertheless, efficiency values are relative low, which is no surprise if one take into consideration the efficiency maps (figure 5) together with figure 17 (notice the efficiency (power) curve gains and cycle working points, particularly for n<2000 rpm ).

## **5.2. Europe: City**

418 Induction Motors – Modelling and Control

**Figure 16.** Torques [T\_load (green); Te\*(red); Te (blue)]

Torque [N.m]

**Figure 17.** ECE-R15 drive cycle points over LMA efficiency curve gain


0.01

T [N.m]

0 05

0 1

0.2

0 29

0 35

drive cycle; Eab: energy absorbed by the induction motor)

Without

0.01

0.1

0.05

0.1

0.29

0.35 0.01

0.05

0.2

0.29

0.35

0.2

Eu (kJ) 221,8 221,5 Eab (kJ) 305,5 266,5 Motor losses (kJ) 83,7 45,0 Energy efficiency (%) 72,6 83,1

LMA

0 1000 2000 3000 4000 5000 6000 7000

speed [rpm]

0.01

0.1

0.05

0.01

cycle points LMA eff. gains motor limits

<sup>0</sup> <sup>100</sup> <sup>200</sup> <sup>300</sup> <sup>400</sup> <sup>500</sup> <sup>600</sup> <sup>700</sup> <sup>800</sup> <sup>900</sup> -15

time [s]

LMA - CF

**Table 5.** ECE-R15 energy performances (Eu: energy supplied by the induction motor for the considered

In almost 50% of the ECE-R15 drive cycle duration, motor speed is between 0 and 2000 rpm, with the motor torque among -13 Nm and 16 Nm (aprox.) – see figure 16. So, LMA inclusion allows significant loss reductions (table 5): with LMA, total losses are about 20% of Eu (energy supplied by the motor); without LMA, goes up to 38% of Eu. As expected, the main Ids differences occur for n<2000 rpm, particularly for low torques (with LMA, smaller Ids values are clearly visible). In a similar way, LMA performance in braking modes brings good results, since demanded torque has always low values. It should be pointed that when

 With LMA

**Figure 18.** Drive-cycle; (Id; Iq; Motor losses) – [blue:LMA; red dashed line: conventional regulation]; Pu

For about 60% of total time of the "Europe: City" cycle, the vehicle speed is also below 2000 rpm, with the motor torque between -13 Nm and 16 Nm (aprox.). The vehicle is at rest for about 25% of the drive cycle duration. Basically, it puts the motor in the same (T,) working region as ECE-R15 (see figures 17 and 20). However, since it has a short time period (195 seg.), energy level demanded is much lower – the lowest one from the chosen drive cycle set. Similar relative energy losses are achieved: 20% for LMA and 36% without LMA of Eu (table 6). In both motor and braking modes, LMA most relevant results are in low speed – low torque region.

Evaluation of an Energy Loss-Minimization Algorithm for EVs Based on Induction Motor 421

values. In other words, the motor losses difference are attached to these time periods, particularly to the resting one (figure 21). On the other drive cycle periods, motor losses are very similar (notice that in some intervals, LMA losses are slightly larger. This unexpected

<sup>0</sup> <sup>20</sup> <sup>40</sup> <sup>60</sup> <sup>80</sup> <sup>100</sup> <sup>120</sup> <sup>0</sup>

<sup>0</sup> <sup>20</sup> <sup>40</sup> <sup>60</sup> <sup>80</sup> <sup>100</sup> <sup>120</sup> <sup>0</sup>

<sup>0</sup> <sup>20</sup> <sup>40</sup> <sup>60</sup> <sup>80</sup> <sup>100</sup> <sup>120</sup> -20

<sup>0</sup> <sup>20</sup> <sup>40</sup> <sup>60</sup> <sup>80</sup> <sup>100</sup> <sup>120</sup> <sup>0</sup>

<sup>0</sup> <sup>20</sup> <sup>40</sup> <sup>60</sup> <sup>80</sup> <sup>100</sup> <sup>120</sup> -1

time [s]

**Figure 21.** Drive-cycle; (Id; Iq; Motor losses) – [blue:LMA; red dashed line: conventional regulation]; Pu

LMA total losses are about 14% of Eu, while conventional regulation losses are 16% of Eu. Although curve efficiency gains in figure 23 are referred to power efficiency, cycle working points somehow agree with efficiency energy gain achieved with LMA (table 7): for n> 2000 rpm there is a significant number of points between 1% and 5 % efficiency curves gain; also

<sup>0</sup> <sup>20</sup> <sup>40</sup> <sup>60</sup> <sup>80</sup> <sup>100</sup> <sup>120</sup> <sup>140</sup> -15

time [s]

result is most probably related to the issue discussed in section 4.4).

3000 6000 n [rpm]

> 10 20 Id [A]

0 20 Iq [A]

200 400 Motor losses [W]

Pu [W]

**Figure 22.** Torques [T\_load (green); Te\*(red); Te (blue)]



0

Torque [N.m]

5

10

15

notice that some points are below 1% efficiency gain.

**Figure 19.** Torques [T\_load (green); Te\*(red); Te (blue)]

**Figure 20.** Europe: City drive cycle points over LMA efficiency curve gain


**Table 6.** Europe: City energy performances

The slightly efficiency increase for this cycle (when compared to ECE-R15) may be associated to the relative decrease of vehicle resting period (about 33% in ECE-R15).

### **5.3. 11 – Mode (Japan)**

Drive cycle period where n<2000 rpm is relative short (<33%); the motor torque lies between 13 Nm and -10 Nm and the vehicle is immobilized a little less than 25% of the cycle duration. As expected, it´s in the initial resting time period and on the final 25 sec that Ids values generated by the LMA are significantly different from the conventional flux Ids

values. In other words, the motor losses difference are attached to these time periods, particularly to the resting one (figure 21). On the other drive cycle periods, motor losses are very similar (notice that in some intervals, LMA losses are slightly larger. This unexpected result is most probably related to the issue discussed in section 4.4).

420 Induction Motors – Modelling and Control

**Figure 19.** Torques [T\_load (green); Te\*(red); Te (blue)]

Torque [N.m]

**Table 6.** Europe: City energy performances

**5.3. 11 – Mode (Japan)** 

**Figure 20.** Europe: City drive cycle points over LMA efficiency curve gain


0.01

T [N.m]

0 05

0 1

35

0.2

0 29

Without

0.01

0.1

0.05

0.1

0.29

0.35 0.35

0.01

0.05

0.2

0.29

0.2

Eu (kJ) 55,5 55,4 Eab (kJ) 75,3 66,6 Motor losses (kJ) 19,8 11,2 Energy efficiency (%) 73,6 83,2

associated to the relative decrease of vehicle resting period (about 33% in ECE-R15).

LMA

0 1000 2000 3000 4000 5000 6000 7000

speed [rpm]

0.01

0.1

0.05

0.01

cycle points LMA eff. gains motor limits

<sup>0</sup> <sup>20</sup> <sup>40</sup> <sup>60</sup> <sup>80</sup> <sup>100</sup> <sup>120</sup> <sup>140</sup> <sup>160</sup> <sup>180</sup> <sup>200</sup> -15

time [s]

LMA - CF

The slightly efficiency increase for this cycle (when compared to ECE-R15) may be

Drive cycle period where n<2000 rpm is relative short (<33%); the motor torque lies between 13 Nm and -10 Nm and the vehicle is immobilized a little less than 25% of the cycle duration. As expected, it´s in the initial resting time period and on the final 25 sec that Ids values generated by the LMA are significantly different from the conventional flux Ids

 With LMA

**Figure 21.** Drive-cycle; (Id; Iq; Motor losses) – [blue:LMA; red dashed line: conventional regulation]; Pu

**Figure 22.** Torques [T\_load (green); Te\*(red); Te (blue)]

LMA total losses are about 14% of Eu, while conventional regulation losses are 16% of Eu. Although curve efficiency gains in figure 23 are referred to power efficiency, cycle working points somehow agree with efficiency energy gain achieved with LMA (table 7): for n> 2000 rpm there is a significant number of points between 1% and 5 % efficiency curves gain; also notice that some points are below 1% efficiency gain.

Evaluation of an Energy Loss-Minimization Algorithm for EVs Based on Induction Motor 423

**Figure 24.** Drive-cycle; (Id\*-red & Id-blue); (Iq\*-red & Iq-blue); Pab and motor losses (without LMA)

<sup>0</sup> <sup>200</sup> <sup>400</sup> <sup>600</sup> <sup>800</sup> <sup>1000</sup> <sup>1200</sup> <sup>1400</sup> <sup>1600</sup> <sup>1800</sup> <sup>0</sup>

<sup>0</sup> <sup>200</sup> <sup>400</sup> <sup>600</sup> <sup>800</sup> <sup>1000</sup> <sup>1200</sup> <sup>1400</sup> <sup>1600</sup> <sup>1800</sup> <sup>0</sup>

<sup>0</sup> <sup>200</sup> <sup>400</sup> <sup>600</sup> <sup>800</sup> <sup>1000</sup> <sup>1200</sup> <sup>1400</sup> <sup>1600</sup> <sup>1800</sup> -40

<sup>0</sup> <sup>200</sup> <sup>400</sup> <sup>600</sup> <sup>800</sup> <sup>1000</sup> <sup>1200</sup> <sup>1400</sup> <sup>1600</sup> <sup>1800</sup> <sup>0</sup>

0 200 400 600 800 1000 1200 1400 1600 1800

<sup>0</sup> <sup>200</sup> <sup>400</sup> <sup>600</sup> <sup>800</sup> <sup>1000</sup> <sup>1200</sup> <sup>1400</sup> <sup>1600</sup> <sup>1800</sup> <sup>2000</sup> -30

time [s]

time [s]

5000 10000 n [rpm]

> 10 20 Id [A]

0 40 Iq [A]

500 1000 Motor losses [W]

> -1 0 1 x 10<sup>4</sup>

Pu [W]

**Figure 25.** Torques [T\_load (green); Te\*(red); Te (blue)]



0

Torque [N.m]

10

20

30

**Figure 23.** 11-Mode drive cycle points over LMA efficiency curve gain


**Table 7.** 11-Mode energy performances

## **5.4. FTP-75**

For this drive cycle, the time period for which n<2000 rpm is shorter then the previous cycles. Motor torque limit is now -20 Nm and 25 Nm (aprox), while maximum speed is 8000 rpm. Frequent accelerations, as well as its long time period (1840 sec), make this cycle the most energy demanding. At the same time, pushes the motor to its limits: figure 24 shows that motor exceeds its nominal power between [200-300] s and later in the interval [1500- 1700] sec. However, this overload (whose maximum instantaneous power is about 11 kW) occurs for a small number of intervals, each one with a very short existence. This way, it´s reasonable to assume that motor is not under electric hazardous working conditions. From a mechanical perspective, maximum speed - about 4 times motor nominal speed – is reached for relative short intervals, so one may assume that the motor (and the vehicle) will be safe in this working conditions.

Due to high speeds and relative high torque demand (figure 25), LMA shows a relative performance closer to the conventional regulation. As expected, relevant differences for Id generation occur for relative low speed (basically, when the vehicle is at rest) and low torque values, e.g. intervals [50-200; 800-950] sec. – figures 25 and 26. With LMA and without it, motor losses are, respectively, 11,4% and 13,1% of Eu (table 8). Motor efficiency map (figure 5) explains the high efficiency values associated to this cycle, while the small efficiency gain achieved is according to figures 25 and 26.

**Figure 24.** Drive-cycle; (Id\*-red & Id-blue); (Iq\*-red & Iq-blue); Pab and motor losses (without LMA)

**Figure 25.** Torques [T\_load (green); Te\*(red); Te (blue)]

**Table 7.** 11-Mode energy performances

in this working conditions.

efficiency gain achieved is according to figures 25 and 26.

**5.4. FTP-75** 

**Figure 23.** 11-Mode drive cycle points over LMA efficiency curve gain

Without

Eu (kJ) 76,7 76,7 Eab (kJ) 89,3 87,5 Motor losses (kJ) 12,5 10,8 Energy efficiency (%) 86 87,6

LMA

For this drive cycle, the time period for which n<2000 rpm is shorter then the previous cycles. Motor torque limit is now -20 Nm and 25 Nm (aprox), while maximum speed is 8000 rpm. Frequent accelerations, as well as its long time period (1840 sec), make this cycle the most energy demanding. At the same time, pushes the motor to its limits: figure 24 shows that motor exceeds its nominal power between [200-300] s and later in the interval [1500- 1700] sec. However, this overload (whose maximum instantaneous power is about 11 kW) occurs for a small number of intervals, each one with a very short existence. This way, it´s reasonable to assume that motor is not under electric hazardous working conditions. From a mechanical perspective, maximum speed - about 4 times motor nominal speed – is reached for relative short intervals, so one may assume that the motor (and the vehicle) will be safe

Due to high speeds and relative high torque demand (figure 25), LMA shows a relative performance closer to the conventional regulation. As expected, relevant differences for Id generation occur for relative low speed (basically, when the vehicle is at rest) and low torque values, e.g. intervals [50-200; 800-950] sec. – figures 25 and 26. With LMA and without it, motor losses are, respectively, 11,4% and 13,1% of Eu (table 8). Motor efficiency map (figure 5) explains the high efficiency values associated to this cycle, while the small

 With LMA

Evaluation of an Energy Loss-Minimization Algorithm for EVs Based on Induction Motor 425

Motor losses (LMA) Motor losses (without LMA)

**Europe: City 11-Mode (Japan) ECE-R15 FTP-75 <sup>0</sup>**

As a final remark, it is interesting to note that Europe:city and ECE-R15 have similar

**50**

**100**

**150**

**200**

**250**

Induction motor drives for EVs are submitted to a large set of working conditions, quite different from rated ones. Motor energy saving is fundamental for improving EVs performances. Under the loss model based approach previously discussed (LMA), a set of simulation results was presented in this book chapter, aiming to improve the induction motor energy performance. Different standard driving cycle scenarios were considered in order to evaluate the chosen LMA features: compared to conventional flux regulation, the major improvements in motor efficiency are for low load torque, particularly for relative low speeds. These are the motor working points where its efficiency is tipically lower, which is an interesting LMA feature. This is in agreement to the fact that LMA action has a more significative impact on ECE-R15 and Europe:city efficiencies, as explained through figures

Due to LMA impact on iron losses (function of Id), a possibility to be considered in future works is the impact of LMA on motors with higher power rates and/or high efficiency level

motors, where the relative weights of iron and copper losses are different.

(a) (b)

**Figure 28.** Drive-Cycles energy efficiency [%] (a) and motor losses [kJ] (b)

**Europe: City 11-Mode (Japan) ECE-R15 FTP-75 <sup>0</sup>**

**6. Conclusion** 

Motor eff (LMA) Motor eff (without LMA)

15,17 and 18, 20 analysis.

**Author details** 

*Polytechnic Institute of Porto, Portugal* 

Ricardo de Castro and Rui Esteves Araújo

*Faculty of Engineering – University of Porto, Portugal* 

Pedro Melo

efficiency levels; also the same fact can be seen for 11-Mode and FTP-75.

**Figure 26.** FTP-75 drive cycle points over LMA efficiency curve gain


**Table 8.** FTP-75 energy performances

Figures 27 and 28 present, respectively, induction motor energy consumption, efficiency and losses for each simulated drive cycle, with and without LMA.

**Figure 27.** Drive-Cycles energy consumptions [kJ]

As a final remark, it is interesting to note that Europe:city and ECE-R15 have similar efficiency levels; also the same fact can be seen for 11-Mode and FTP-75.

**Figure 28.** Drive-Cycles energy efficiency [%] (a) and motor losses [kJ] (b)
