**Author details**

losses are 20.7%. Electrical machine losses are composed of the following elements: stator and rotor resistive losses, iron losses, additional losses and mechanical losses. Mechanical losses include friction in the motor bearings. Bearing losses depend on the shaft speed, bearing type, properties of the lubricants and the load. The converter losses take place mostly in the semiconductor switches and in the auxiliary power systems. In this study, the losses of the

**Figure 14.** Measured Sankey diagram of the DDH with a motor speed of 400 rpm and a payload of 150 kg (the efficien‐

It was challenging to create the DDH test setup due to the asymmetrical double-acting cylinder used and the difficulty of finding matching displacements of the pump/motors in order to fulfill *R*Q = *R*A. Moreover, another challenge was the location of the hydraulic accumulators and external leakage pump/motor lines. The Sankey diagrams showed that electrical machine losses are in second place after the dominant hydro-mechanical losses. Taking pressure balancing into consideration, the hydro-mechanical losses in the system will be reduced in the

This paper described a DDH setup and its potential for applicability to NRMMs. It investigates the compensation of pump/motor displacement for an asymmetrical double-acting cylinder and the location of hydraulic accumulators and external leakage pump/motor lines. The review was carried out for four different alternative cases. The mathematical model used in the review suggested Case IV as the least sensitive case. Further investigations were performed in Matlab Simulink. According to the simulations, Cases II, III and IV did not fulfill the requirements of a leakage line where the maximum allowed constant pressure was 0.3 MPa and, in the short term, it was 1 MPa. Therefore, only Case I can be used for the realization of the DDH setup, in

which both external leakage lines are connected to line A (accumulator A).

frequency converter are not included.

cy of the frequency converter is not included) [19].

162 New Applications of Electric Drives

second DDH prototype.

**7. Conclusion**

Tatiana A. Minav1\*, Jani E. Heikkinen2 and Matti Pietola1

\*Address all correspondence to: tatiana.minav@aalto.fi

1 Department of Engineering Design and Production, School of Engineering, Aalto University, Finland

2 Independent researcher, http://orcid.org/0000-0002-5991-7580, Helsinki, Finland
