Resonant　converters　are　periodic　time-varying　system,　one　of　whose　distinctive　features　is　the　sideband　effect.　To　be　specific,　when　a　small-signal　perturbation　is　injected　into　the　converter,　a　series　of　sideband　frequency　components　will　occur.　The　two　sideband　frequency　components　around　the　switching　frequency　determine　the　small-signal　response　of　the　resonant　tank　if　it　has　sufficient　band-pass　filtering.　Using　complex　Fourier　series,　the　relationship　between　different　frequency　components　can　be　described　with　a　series　of　gains.　This　article　derives　all　the　necessary　transfer　functions　between　different　frequencies　for　resonant　converters.　Combining　them　together　forms　a　general　small-signal　model　of　resonant　converters.　There　are　multiple　frequency　components,　i.e.,　the　perturbation　frequency　and　two　sideband　frequencies　in　this　model,　hence　the　name　multifrequency　model.　Two　kinds　of　inverters,　i.e.,　the　full-bridge　and　half-bridge　structure,　and　three　modulation　methods,　i.e.,　the　switching　frequency　control,　the　duty-cycle　control,　and　the　input　voltage　control　are　considered　in　this　article.　The　experimental　results　verify　the　validity　of　the　proposed　model.