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• Numerical Comparison of PI and Neural Network-Based Controllers for the Hydrostatic Unit in Hydro-mechanical Transmissions of Self-propelled Vehicles

  Dang Ngoc Danh, Bui Viet Duc, Nguyen Thi Hue, Vu Cong Canh

  Received: May 22, 2024 / Accepted: Nov 28, 2024 / Published: Dec 20, 2024

   Abstract PDF

  The application of hydro-mechanical transmissions is recently the trend in agricultural vehicles where a continuously variable transmission ratio has advantages. Hydro-mechanical transmissions provide efficient power transfer while maneuverability is still maintained, and therefore, fuel efficiency is enhanced. Nevertheless, the main issue in their employment is a precise control of the hydrostatic unit, whose physical characteristics are highly nonlinear and affected by unknown disturbances. In order to exploit the advantages of the system, the transmission ratio of the hydrostatic unit needs to be controlled properly to maintain the optimal working point of the internal combustion engine (ICE). This article presents numerical comparison results of a proportional-integral (PI) and a neural network (NN) based controller applied to the hydrostatic unit of a hydro-mechanical transmission system, which was designed to be deployed on a self-propelled agricultural vehicle. The controls were established in a discrete-time domain aiming at a practical outcome, where the control algorithm could be implemented on an industrial computer to perform the control tasks.

• Internal Control System in Cooperatives: A Systematic Review

  Vu Thi Hai, Tran Quang Trung, Bui Thi Mai Linh

  Received: Sep 04, 2023 / Accepted: Dec 16, 2024 / Published: Dec 20, 2024

   Abstract PDF

  Internal control plays an essential role in improving the efficiency of resources and ensuring the achievement of organizational goals. This study aimed to systematically synthesize articles published in Vietnam and abroad on the topic of “internal control” and “internal control system” in cooperatives during the period of 2012-2023. The conceptual framework of internal control, research methods, and main results of publications were summarized. The findings showed that empirical studies on internal control have frequently been conducted in financial and credit organizations, however, there are limited studies in the cooperative model. The publications focused on three main contents, namely the status and structure of internal control in organizations; the roles and impacts of internal control on performance and corporative governance; and the factors affecting the effectiveness and efficiency of internal control. The COSO framework has been applied by most authors in analyzing the current situation of internal control and internal control systems. The positive impacts of internal control on efficiency (ROA and ROE) and the sustainability of cooperatives were confirmed by the authors. Limitations in human resources, scale, technology, and staff awareness of internal control were considered as barriers to implementation of internal control in organizations.