Characters of Feigin-Stoyanovsky's principal subspaces of affine integrable highest weight modules are related with the sum sides of Rogers-Ramanujan-type identities. In this talk I will discuss the construction of combinatorial bases of standard modules, which relies on the the construction of quasi-particle bases of principal subspaces. From quasi-particle bases we obtain characters of certain standard modules of affine Lie algebra of type $B_l^{(1)}$. This talk is based on joint works with Slaven Ko\v zi\' c and Mirko Primc.