Comparison of results

Vehicle performances of the conventional rule based EMS and the proposed EMS for varied

sampling rates are tabulated in Table 10-1.

Table 10-1: The conventional and proposed EMS vehicle performance comparison for varied sampling rates

EMS method Conventional EMS Proposed EMS

Sampling rate, sec Not applicable 30 10 1 0.01 Final SOC 0.445 0.419 0.409 0.407 0.407 Actual FE, MPG 117.5 133.3 137.9 137.2 137.8 Corrected FE, MPG 133.1 141.3 142.1 140.2 140.8 Number of engine stop-starts 44 5 5 7 7 Simulation duration, sec 341 303 304 305 320

Vehicle performances of the conventional and proposed EMS across sampling rates are

compared and discussed in following sections.

10.3.1.1Final SOC comparison

The final SOC of the proposed EMS for all sampling rates are lower than the conventional

EMS. The final SOC of the proposed EMS across sampling rates, there were only subtle

differences as shown in Figure 10-3. The final SOC is varying from 0.419 to 0.407 for the

sampling rates of 30 to 0.01 second respectively. The increase of final SOC with reduction in

sampling was expected but the differences are small. With lower sampling, the engine

when switched ON remains so for longer duration irrespective of the delta energy

150 Figure 10-3: The proposed EMS final SOC comparison for various sampling rate

10.3.1.2Fuel economy comparison

The fuel economy of the proposed EMS is better than the conventional EMS for all

sampling rates. The proposed EMS fuel economy on average across the sampling rates is

better by 6% than conventional EMS. For various sampling rates, the proposed EMS fuel

economy is close to each other varying from 140.2 to 142.1 MPG. No increasing or

decreasing fuel economy trend was observed across sampling rates.

10.3.1.3Number of engine stop – starts

The conventional EMS number of engine stop – starts is high with 44. For the proposed

EMS across sampling it varied from 5 to 7. The number of engine stop – start is 5 with 10

and 30 second sampling rates and 7 with remaining two higher sampling rates (Table 10-1).

This is due to increase in EMS sensitivity to local variation in delta energy at higher

sampling rates. With higher sampling rates the chance of activating the engine smart

charge for small changes in delta energy is higher. This can be observed in Figure 10-2 for

sampling rate of 0.01 and 1 second.

10.3.1.4Simulation duration comparison

Conventional rule based EMS are known to be real time capable. Real time capability of the

proposed EMS is measured based on the simulation duration of the proposed and

conventional EMS. Between the conventional and proposed EMS, the simulation duration is

0.419

0.409

0.407 0.407

Sampling rate 30s Sampling rate 10s Sampling rate 1s Sampling rate 0.01s

Final SOC of the proposed EMS for various sampling rates

Real Time Capability and Sampling Rate Study of the Proposed EMS

151 the same in terms of applicability to real time operation as shown in Table 10-1.

Surprisingly the proposed EMS is marginally faster than the conventional EMS. The faster

performance of the proposed EMS may be due to system structure than the sampling rate.

Further for the considered drive cycle of 2700 second, the simulation durations of the

proposed EMS is about 320 second. Therefore the proposed EMS is about 8 times faster

than real time requirement. Overall based on the simulation duration results it is concluded

that the proposed EMS is potentially real time capable.

Further the simulation duration of the proposed EMS across sampling rates from 30 to 1

second is almost same with 303 to 305 second respectively. With sampling rate of 0.01

second the simulation duration was marginally higher with 320 second. As expected the

simulation duration decreases with the reducing sampling rate but only marginally. When

sampling rate is reduced, the computational load decreases due to fewer calculations.

10.4Conclusion

For all sampling rates trial of the proposed blended rule based EMS over the considered

real world driving data, the vehicle performances such as the fuel economy, number of

engine stop – starts and final SOC are better than the conventional rule based EMS. The

proposed EMS vehicle performance across sampling rate varied only with subtle

differences.

The simulation duration across sampling rate for the proposed EMS is almost the same. The

simulation duration of the proposed EMS and the conventional rule base EMS are also the

same. For the considered drive cycle, the simulation durations in all these cases are faster

than real time. However in this study real time capability was not demonstrated on the

vehicle hardware. Therefore the proposed EMS is concluded as potentially real time

152 Overall, considering the uncertainty of real world driving which calls for a higher sampling

rate to bridge the gap between the actual and anticipated trip demand and also to

minimise the number of engine stop-starts, the 10 second sampling rate was selected for

future studies. Whenever the engine is switched ON, 10 second sampling ensures that the

engine operation is for minimum of 10 seconds unless the instantaneous vehicle speed falls

below the threshold speed (22 m/s for extra urban and 12 m/s for urban smart charge).

This makes EMS insensitive to small and frequent variations in trip demand and system

parameters (such as delta energy).

In summary,

 Simulation duration of the proposed and conventional rule based EMS are same. The proposed EMS method is potentially real time capable.

 The proposed EMS vehicle performances such as the fuel economy, number of engine stop – starts and final battery state of charge (SOC) across sampling rates of

30 to 0.01 second are almost same.

 The proposed EMS vehicle performance across sampling rates is better than conventional rule based EMS over the considered real world vehicle speed profile.

 Considering uncertainty of real world driving and to minimise the number of engine stop-starts a 10 second sampling rate for the proposed EMS was considered for

Adaptability Study of the Proposed EMS

153