## 4 Implementation of System for Rapid Prototyping of Real-Time Control Algorithms
To evaluate the control system performance in the full operating range of the pump, we tested the closed-loop for four different loading settings. The system loading is commanded by changing the opening of the loading throttle valve (Figure 1). The level of throttle valve opening can be precisely selected using a micrometer scale between 2 to 5 mm. With the increase in the opening of the throttle valve, the loading of the system is decreased, which can be seen in the pressure output of the pump. Another specific aspect when testing the pump at different loading conditions is that the permissible range of flow rate regulation is changing due to the limitations of the mechanical and electrical components. Therefore, the reference levels used in the following figures are different depending on the selected loading. Figure 14 show the pump flow rate regulation for minima opening of the throttle valve, corresponding to the highest loading of the pump, indicated by highest output pressure. The reference signal for the flow rate is commanded between 14 and 17 L/min. It is seen that the flow rate is tracking the reference with settling time below 100 ms. The settling time is shorter when the flow rate is increased, being as small as 20 ms. The settling time is longer when the flow rate is decreased from the higher to lower level, being around 100 ms. This can be explained with dynamical asymmetry of the swashplate inside the pump for increasing or decreasing swivel angle, due to the unidirectional spring attached at the swashplate. This asymmetry is excited at higher loads when the output pressure of the pump is reflected back on the swash plate. In the experimental data, some amount of oscillating/noise artifacts are present, which is discussed in the following paragraphs. Figure 13: (**a**) Simulink implementation of the host controller. (**b**) Simulink implementation of the host controller. In Figure 15, the closed-loop response for throttle valve opening of 3 mm is presented, which is still a high loading to the system. In such loading conditions, the closed-loop shows even better performance in regards to settling time, which is in the range under 50 ms. The reference flow rate is in the range of 19 to 24 L/min. A slightly slower response can be seen when the reference flow rate is reduced, as the mean level of the flow rate signal is above the reference for a couple of noise periods. The noise oscillations around the reference are still present, but their amplitude is partially reduced. With the increase in the flow rate, the amplitude of the noise is increased. It can be judged that frequency range of the noise signal is constant and independent of the loading conditions, hence, it can be attributed to the nature of the flow rate instrument, which is an orbital volumetric hydraulic machine introducing high frequency discontinuities in the flow. Figure 14: Experimental output flow rate data—loading 2. Figure 15: Experimental output flow rate data—loading 3. The next figures are focused on experiments with lower loading of the pump, which allows it to reach its nominal (rated) parameters of a flow rate of about 26 L/min. In this mode of control, the output pressure of the pump is also reduced to about 20 to 30 bars. During the experiments, there is clear audible difference in emitted acoustic noise from the testbench when the pump works at a higher load (2 or 3 mm opening of the throttle valve) vs the situation when the pump works at lower loads (4 or 5 mm opening). This can be confirmed with the conduction of further energy analysis accounting for the power throughput of the system. With increasing the load, the heating of the pump is more pronounced, especially at the highest loading of 2 mm throttle valve opening. There are some instants when the pressure-relief valve threshold of 100 bar might be reached, therefore, the relief valve also becomes part of the system dynamic, further disturbing the open-loop mathematical model.