Low-speed performance analysis of variable grequency hydraulic systems in parallel valve control

The variable frequency hydraulic system is characterised by high efficiency, high reliability and low cost, but has a critical disadvantage, poor low speed stability due to the limit of the minimum stable speed of pumps and low frequency of inverters. Aiming to improve the low-speed performance, a variable frequency hydraulic system in parallel valve control is proposed, in which a proportional throttle valve (PTV) works at leaking status. At low speed stages, the fixed displacement pump works above its minimum stable speed, and PTV works at leaking status to increase leakages and system damping ratios and to improve low-speed stability. In this paper, we first design the proposed system, and explain the theory basis of parallel valve control improving low-speed performance, then establish its simulation model, and make verification by simulation.