A microstructural model considering self-accommodated groups of martensite as independent formations has been developed. Equations describing the growth and shrinkage of the groups of martensite and martensite reorientation have been deduced from the hypotheses of the equilibrium of generalized thermodynamic forces, including the driving force, the force due to mixing of the phases and the friction force. This approach allows modelling of common deformation effects in shape memory alloys such as pseudoelasticity, ferroplasticity, transformation plasticity and strain recovery, and it also explains the less-known phenomenon of the oriented transformation deformation consisting in the spontaneous strain accumulation on cooling after the stress, which was applied at the beginning of the direct transformation, is removed.