Radiation damage in n-type high-resistivity FZ silicon wafers with a nitrogen concentration of ~1.5E15 cm^-3 exposed to 23-MeV protons has been studied by using high-resolution photoinduced transient spectroscopy (HRPITS), infrared absorption (FTIR) and photoluminescence (PL) and measurements. In order to determine the evolution of the radiation defect structure with increasing the proton fluence, the defect centers were produced by the irradiation with four proton fluences: 1E14, 5E14, 1E15, and 5E15 n(eq)/cm^2. The irradiation with each fluence resulted in the sharp increase of the material resistivity from ~2kΩcm to ~300 kΩcm. The HRPITS results show that 20 defect centers with activation energies ranging from 24 to 565 meV are formed during the irradiation and these centers can be involved in the charge compensation leading to the increase of the resistivity. The detected traps are tentatively assigned to thermal donors, interstitial carbon related complexes, small aggregates of self-interstitials, interstitial oxygen related complexes, and small aggregates of vacancies. According to the FTIR results, the introduction rate of VO complexes significantly decreases with increasing the proton fluence. For the fluences of 1E14 and 5E14 n(eq)/cm^2, the effect of the oxygen concentration in the wafer on the VO center introduction rate is also observed. With increasing the fluence from of 1E14 and 5E15 n(eq)/cm^2, the introduction rate of divacancies rises from ~0.15 to 0.3 cm-1. In the low-temperature PL spectra, the lines related to recombination of excitons bound to tri-interstitials, as well as to C(i)C(s), C(i)C(s)H and C(i)O(i) complexes are observed.