3.2.1. Load Step Transient Simulations

The load tip-in study was performed for two engine speeds of interest, 1600 and 1100 rpm, close to the surge limit of the compressor. The load tip-in step requested was from 2 bar BMEP to full load BMEP (19 bar). However, due to the engine speeds at which the tests were performed, the requested BMEP could not be achieved.

The study was initially performed for the model with all of the PID controllers. However, for ensuring that the results are not affected by the tuning of the controllers, the study was repeated in an open-loop environment (no PID controllers). The PID controllers in the model were removed and replaced by look-up tables for controlling the boost pressure and throttle position of the engine, as shown in Table 5. This allows a hardware capability investigation to be performed by eliminating any effects of the PID controllers. The energy provided to the compressor was divided into four sections of 0.25 seconds, and different levels of power (1, 3 and 5 kW) were provided in each section.

**Table 5.** Control of basic process parameters for the model with proportional-integral-derivative (PID) controllers and the open-loop model. BMEP, brake mean effective pressure; M/G, motor/generator.


### 3.2.2. Fixed Gear Vehicle Speed Transient Simulations

The purpose of this study was to represent the vehicle's driving conditions and test the model for a fixed gear (third) vehicle speed transient. For this reason, a driving resistance load of 30 Nm was applied to represent the rolling resistance along with the flywheel's inertia given by the following formula:

$$I\_{\rm eqg} = I\_{\rm eq,erg,g} + I\_{\rm eq,prop} + I\_{\rm eq,axle} + I\_{\rm eq,velv} \tag{3}$$

where *<sup>I</sup>*eq is the total inertia (kg·<sup>m</sup>2), *<sup>I</sup>*eq,eng is the engine's inertia, *<sup>I</sup>*eq,prop is the prop shaft inertia, *<sup>I</sup>*eq,axle is the axle inertia and *<sup>I</sup>*eq,ve<sup>h</sup> is the vehicle mass equivalent inertia, as shown in Figure 9.

**Figure 9.** Schematic of total inertia applied to the engine.

The study was performed for four different levels of targeted BMEP, as shown in Figure 10, representing the aggressiveness with which a vehicle's pedal can be pressed. The tests were repeated twice for different pre-turbine pressures, which were controlled by implementing a pre-turbine pressure/WG PID controller.

**Figure 10.** Fixed gear vehicle speed BMEP tip-ins.
