Bilinear Robust   Controller to Minimize HIV Concentration in Blood Plasma Jonathan Saputra, Roberd Saragih * , Dewi Handayani Industrial and Financial Mathematics Research Group, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Indonesia. * Corresponding author. Tel.: +62222502545; email: roberd@math.itb.ac.id Manuscript submitted August 1. 2019; accepted November 3, 2019. Abstract: Human Immunodeficiency Virus (HIV) is a type of virus which attacks CD4 + T cells. Insufficient numbers of CD4 + T cells will affect the performance of immunity systems so that someone become riskier to have AIDS or other diseases. HIV phenomenon is modelled as nonlinear system with disturbance, but there is no exact method to solve problems that related with analyzing nonlinear systems with control treatment. Thus, the nonlinear system is approximated into a bilinear system by using Carleman bilinearization method. A robust   -controller is designed as a control input to accomodate the disturbances in the dynamic system. Generally, the treatment for HIV is merely to obstruct the replication process. Therefore, the robust control input is described as the chemotherapy of hypothetical drugs which aimed to clear off the HIV concentration in blood plasma. Robust   -control is designed with the coefficient matrix of the bilinear system. The simulation result is analyzed by comparing the effect of the robust control toward bilinear and nonlinear system. From numerical simulations, an individual will experience heavy symptom if the hypothetical drugs chemotherapy is not given. This finding is strengthening the urgency of robust control as a chemotherapy with a waiting time. Based on the numerical simulation with robust   -control input, bilinear system has trends that give similar interpretation with the trends of nonlinear system. Besides that, robust   -control on bilinear system has demolishing speed of HIV concentration and infected CD4 + T cells concentration which approximately equal to the demolishing speed from nonlinear system. Therefore, we can conclude that the performances of   -control on bilinear system is nearly same as the performances of nonlinear system. Key words: Human immunodeficiency virus, chemotherapy, bilinear systems, carleman bilinearization, robust   -control. 1. Introduction HIV is a virus that causes Acquired Immune Deficiency Syndrome (AIDS). HIV affects human's immune systems by infecting the CD4 + T cells in blood plasma [1]. CD4 + T cell is a type of lymphocyte which also called by helper T cells. CD4 + T cells are divided into memory T cells to remember antigen's genetic code and suppressor T cells to respond cytotoxic T cells. Someone with a weak immune system is not only susceptible for AIDS, but also susceptible for other diseases e.g. pneumonia and meningitis [2]. The concentrations of CD4 + T cells in a healthy person are in the range of 500 to 1000 cells  −3 . A person with HIV is considered whenever the concentrations of CD4 + T cells are between 200 to 500 cells  −3 [2], [3]. International Journal of Applied Physics and Mathematics 57 Volume 10, Number 2, April 2020 doi: 10.17706/ijapm.2020.10.2.57-64