MODAL VERBS, various sources:

#1) Foley & Hall [Longman], "modal verbs": unit 16 - unit 18, pp.174  - 197

#2) Ungerer [Klett], Kapitel 7 (The Auxiliaries), § 219 – §255, pp. 150 – 167

#3) English G, Grammatik [Cornelsen], Modale Hilfsverben, § 83 – § 116, pp. 50 – 65

#4) Lamprecht [Cornelsen], Grammatik der englischen Sprache, § 522 -§ 581, pp. 191 – 207

#5) Swan [OUP], see under "modal auxiliary verbs" (§ 344 – § 345) and the actual auxiliaries

[#6) Hewings [CUP], unit 17 – unit 25, pp. 34 - 51]

                                                                                                                          That should do for a start!