Total Cost of Ownership Optimization of Manufacturing Machines with Fast Energy Storage

Abstract

Optimization of total cost of ownership (TCO) is an important, and challenging design target for present day manufacturing machines. This paper is concerned specifically with production machines with fast reciprocating loads (> 1 Hz), e.g. weaving looms and plate punching machines. Subsequent acceleration and deceleration give rise to a reciprocating energy flow that can be handled either mechanically or electrically. The chosen solution will affect the total cost of ownership. In addition to the cost of the energy storage device itself, there are the energy bill, the size and cost of the electric drive and power supply to consider. Moreover, there are certain constraints to be met: lifetime, DC-bus voltage limits and total power factor. This paper presents a methodology that takes all these aspects into account. It applies it to a bar linkage mechanism, which is representative for the targeted applications. In the mechanical domain, springs are considered for energy storage. The structural design of the spring is included in the analysis in order to account for lifetime and inertia added by the spring. In the electric domain, three different topologies are compared: a purely passive front end, where energy is stored directly on the DC-bus, a passive front end combined with a DC/DC converter and a separate storage capacitor, and an active front end.

Energy Management Strategy for Oscillating Drivetrains Equipped with an Electric Variable Transmission

“…It is clear from this figure that the fundamental power factor is high, at 0.95. However the total power factor is a bit lower, but still reasonable at 0.7, which can be improved by adding extra line inductance to the system as it is usual in PFEbased systems, see [2]. Fundamental power factor is used to compute the energy cost, i.e.…”

“…higher the total power factor, lower the THD. Total power factor is often a parameter that needs to be taken into account in the design phase [2]. Moreover, Fig.…”

“…To reduce the subset of currents which determine the generated torque, the d − q reference frame is chosen (related to the outer rotor). The torque which is generated by the stator T s and the inner rotor T r1 can now be determined based on (1) and (2), respectively. Because the sum of the generated torque values should be zero, it is possible to obtain the torque on the outer rotor based on (3).…”

“…The fluxes which are defined in (1) and (2) are calculated based on a finite element model. As solving this model requires time and high computational effort, the calculations are done beforehand and the results are stored in look-up tables (LUTs) which are consulted during simulation.…”

“…In order to recuperate this energy, either a fully controlled Active Front End (AFE) or a Passive Front End (PFE) with an electric energy storage device, e.g. capacitor bank, can be used [2]. Another way to recover this reciprocating energy is by using a mechanical flywheel, attached to the shaft of a traditional motor, where the recovered energy can be reciprocated back during acceleration of the load.…”