A frugal approach to hydrostatic transmission design for off-grid electricity generation from low water heads

Hydrostatic transmissions (HSTs) are widely used in industrial and mobile applications, such as aerospace systems, construction and agricultural machinery, and off-road vehicles. HSTs have emerged as power transmission and velocity governors for renewable power plants, such as wind turbines, wave power plants, and hydropower plants. This paper presents a mathematical model and results of a frugal HST operating as a velocity governor and power transmitter for a micro-hydroelectric power plant with an output power not higher than 17 kW. The HST was simulated to analyze pressure, flow rate, angular velocity, and solenoid valve activation. Unlike systems designed for larger turbines, this paper deals with a frugal design that minimizes complexity by employing a single accumulator and eliminating auxiliary charging circuits, such as small pumps and motors used for system charging and leakage compensation. This approach simplifies components and lowers costs, making it ideal for affordable, compact energy systems. Additionally, the achieved design has a versatile four-pump configuration in which the pumps can either share the same shaft or operate independently. When operating independently, each pump can connect to distinct energy sources (e.g., waves, wind, or biomass), enabling the development of hybrid systems for electric power generation. The results show that the obtained HST is capable of maintaining a suitable angular velocity range, with a low number of valve activations and deactivations for changes in the input angular velocity of the hydraulic pumps. The findings suggest that the development of frugal mechatronic products demands enhanced knowledge of system modeling and a comprehensive understanding of the components and constraints inherent to the targeted problem.