Photometric investigation and orbital period analyses of the WUMa binaries FP Lyn, FV CVn and V354 UMa

New light curves and photometric solutions of FP Lyn, FV CVn and V354 UMa are presented. We found that these three systems are W-subtype shallow contact binaries. In addition, it is obvious that the light curves of FP Lyn and V354 UMa are asymmetric. Therefore, a hot spot was added on the primary star of FP Lyn and a dark spot was added on the secondary star of V354 UMa. At the same time, we added a third light to the photometric solution of FP Lyn for the final result. The obtained mass ratios and fill-out factors are q = 1.153 and f = 13.4% for FP Lyn, q = 1.075 and f = 4.6% for FV CVn, and q = 3.623 and f = 10.7% for V354 UMa respectively. The investigations of orbital period for these three systems indicate that the periods are variable. FP Lyn and V354 UMa were discovered to have secularly increasing components with rates of dp/dt = 4.19 × 10−7 d yr−1 and dp/dt = 7.70 × 10−7 d yr−1 respectively, which are feasibly caused by conservative mass transfer from the less massive component to the more massive component. In addition, some variable components were discovered for FV CVn, including a rate of dp/dt = −1.13 × 10−6 d yr−1 accompanied by a cyclic oscillation with amplitude and period of 0.0069 d and 10.65 yr respectively. The most likely explanation for the long-term decrease is angular momentum loss. The existence of an additional star is the most plausible explanation for the periodic variation.