Investigation and Comparison of Separate Meter-In Separate Meter-Out Control Strategies

In the later years, there has been an increased focus on new valve types, which yield the possibility to do Separate Meter-In Separate Meter-Out (SMISMO) control. This includes both digital valves, but proportional valves with separate metering spools and build in pressure sensors are also emerging. The possibility to independently control the meter-in and meter-out side not only increase the functionality of the system, but also opens up for better performance and/or lowered energy consumption. The focus of the current paper is therefore on investigation and comparison of what may be obtained using multivariable control strategies for SMISMO control of a single axis hydraulic system with a differential cylinder, when not taking other measures to improve performance. The paper first presents an experimentally verified model of the system considered, from which a linear model is derived. Based on the model, the control strategies are discussed and several H_∞ controllers are designed, for which both simulation and experimental results are presented. The controllers are evaluated with regard to performance and robustness and compared to a simple SISO control. Based on the findings, the possibilities and limitations of the approach and the different controllers are outlined and discussed.