A PERFORMANCE COMPARISON OF TRACKED VEHICLE DYNAMOMETER SYSTEMS FOR MOBILITY LOAD EMULATION OF A COMBAT HYBRID ELECTRIC POWER SYSTEM

The United States Army Tank-Automotive Research, Development and Engineering Center (TARDEC) is actively researching methods to advance the state of hybrid-electric power system technology for use in military vehicles. Supporting this research, Science Applications International Corporation (SAIC) is the lead contractor for developing the Hybrid Electric Re-Configurable Movable Integration Test-bed (HERMIT), which is operated at TARDEC in Warren, Michigan. The HERMIT is a ground-vehicle-sized series hybrid-electric test-bed featuring a diesel engine, permanent magnet generator, high voltage bus, DC-DC converter, lithium ion battery pack, left and right traction motors, thermal management system, and left and right bi-directional dynamometers. The power system is sized for a 20-22 ton tracked vehicle. The dynamometers are responsible for emulating loads that the tracked vehicle would see while running over a military theater-type course. This paper discusses the control system design for achieving mobility load emulation and compares experimental results obtained from two different sets of dynamometers running the same virtual course and duty cycle. Load emulation is defined as the ability of the measured left and right sprocket speeds to track the left and right sprocket speeds of the tracked vehicle model. The two types of dynamometers used to obtain the experimental results are an AC dynamometer and a DC dynamometer. The DC dynamometer has an inertia that is three times larger than the AC dynamometer inertia. The experimental results are analyzed with respect to the chosen duty cycle and the dynamometers used. Finally, the effect of the duty cycle on the dynamometer choice is discussed. INTRODUCTION The US Army Tank-Automotive Research, Development, and Engineering Center (TARDEC) and Science Applications International Corporation (SAIC) are examining methods to improve the state of combat hybridelectric power system technology to benefit the future force. SAIC is the lead contractor for designing, developing, and maintaining the Power and Energy System Integration Laboratory (P&E SIL) for TARDEC. The P&E SIL contains a combat hybrid electric power system sized for a 20-22 ton tracked vehicle. The power system is a series hybrid power train, and it is packaged into a Future Combat Systems (FCS) Manned Ground Vehicle (MGV)-like hull such that thermal interactions and electro-magnetic noise become significant. This series hybrid power system is most commonly referred to as the HERMIT, or Hybrid Electric Reconfigurable Movable Integration Test-bed shown in Figure 1. The physical outputs of the HERMIT power system are the left and right sprockets, which connect directly to the left and right bi-directional dynamometers (blue items on far left and right of Figure 1). The dynamometers are the mechanisms used to achieve mobility load emulation. The dynamometers work hand-in-hand with the left and right torque sensors and the Tracked Vehicle Proceedings of the 2010 Ground Vehicle Systems Engineering and Technology Symposium (GVSETS) A Performance Comparison of Tracked Vehicle Dynamometer Systems for Mobility Load Emulation of a Combat Hybrid Electric Power System. UNCLASSIFIED: Dist A. Approved for public release Page 2 of 6 Virtual Proving Ground (TVVPG) vehicle model. More details on the preceding interactions are discussed in the Control System Layout section of the paper. In addition to discussion of the HERMIT power system and TVVPG vehicle model, this paper investigates the differences in performance between the AC dynamometer pair and the DC dynamometer pair. HERMIT SERIES HYBRID POWER SYSTEM The HERMIT series hybrid power system includes a 250 kW diesel engine, 410 kW generator, 600 V DC bus, 150 kW continuous DC-DC converter, an 18 kW-hr lithium ion battery pack, and left/right 410 kW induction motors. A schematic of the power system is shown in Figure 2. The HERMIT power system components are sized for a 20 to 22 ton skid-steered, tracked vehicle. The left and right traction motor output shafts are connected directly to the left and right dynamometers by means of a 16.6 to 1 gearing and a mechanical coupling. HERMIT DYNAMOMETERS The purpose of the HERMIT dynamometers is to apply loads to the HERMIT power system that correspond to the interaction between the vehicle dynamics model and the simulated terrain. The dynamometer specifications were determined by the maximum torque, speed and power characteristics for a 20 to 22 ton skid-steered tracked vehicle. Existing data [1] was found (see Figure 3) for a 26 ton Jaguar tracked vehicle and was used as a reference point. The performance specifications of the DC and AC dynamometers are listed in Table 1. For the purpose of comparing transient performance, the most significant parameters are inertia, torque control update rate, controller type. The parameters will be discussed in greater detail in the Results From Churchville B Runs section. Table 1: Dyno Parameters