Dynamic Performance of Maximum Power Point Trackers in TEG Systems Under Rapidly Changing Temperature Conditions

Characterization of thermoelectric generators (TEG) is widely discussed and equipment has been built that can perform such analysis. One method is often used to perform such characterization: constant temperature with variable thermal power input. Maximum power point tracking (MPPT) methods for TEG systems are mostly tested under steady-state conditions for different constant input temperatures. However, for most TEG applications, the input temperature gradient changes, exposing the MPPT to variable tracking conditions. An example is the exhaust pipe on hybrid vehicles, for which, because of the intermittent operation of the internal combustion engine, the TEG and its MPPT controller are exposed to a cyclic temperature profile. Furthermore, there are no guidelines on how fast the MPPT must be under such dynamic conditions. In the work discussed in this paper, temperature gradients for TEG integrated in several applications were evaluated; the results showed temperature variation up to 5°C/s for TEG systems. Electrical characterization of a calcium–manganese oxide TEG was performed at steady-state for different input temperatures and a maximum temperature of 401°C. By using electrical data from characterization of the oxide module, a solar array simulator was emulated to perform as a TEG. A trapezoidal temperature profile with different gradients was used on the TEG simulator to evaluate the dynamic MPPT efficiency. It is known that the perturb and observe (P&amp;O) algorithm may have difficulty accurately tracking under rapidly changing conditions. To solve this problem, a compromise must be found between the magnitude of the increment and the sampling frequency of the control algorithm. The standard P&amp;O performance was evaluated experimentally by using different temperature gradients for different MPPT sampling frequencies, and efficiency values are provided for all cases. The results showed that a tracking speed of 2.5 Hz can be successfully implemented on a TEG system to provide ∼95% MPPT efficiency when the input temperature is changing at 5°C/s.</p

Scaled Hardware in the Loop Simulation of the Electric Motors of a CVT for Agricultural Tractors

Electrification is a very current topic for all the mobile machinery whose primary source of power is an internal combustion engine; among those the light weight passenger vehicles represent the first field of application of this trend and also the state of the art of the technology. Agriculture is a huge fuel consumer sector and for this reason the tractor industry is now working on electrification, proposing different approaches for different power sizes: the "Battery Electric Vehicle"topology is proposed for small and mid-power size tractors, while for the big ones various hybrid architectures couple the internal combustion engine to electric units. In this paper a reference tractor is considered, endowed with an input coupled hydro-mechanical Continuously Variable Transmission and an alternative compound architecture is proposed, which provides the same performances and it is more suitable for electrification. The latter is modelled in Simcenter Amesim through a lumped parameter approach, focusing on the transmission and its control. The electric motors efficiency is modelled using the maps provided by the manufacturer. The main focus of this work is the construction of an experimental setup consisting of two electric motors test benches that allows to perform scaled tests reproducing the operation of the motors inside the transmission. The experiments' target is to measure the efficiency of the electric motors and the power electronics in real conditions. A comparison between the experimental and simulated data is performed. Additionally, a methodology is investigated to perform hardware in the loop simulations of the electric subsystem of a hybrid transmission. This methodology allows for the evaluation of control strategies related to the power balance of electric motor-generators and their effect on the recoverable energy