The noninverting synchronous buck-boost converter is preferable to operate in buck and boost operating modes to obtain a high operating efficiency. However, the dead zone, which degrades the performance of the converter, will occur when the converter shifts from buck operating mode to boost operating mode or vice versa. Therefore, the origin of the dead zone is derived in this paper by analyzing the relationship between the voltage conversion ratio and the duty cycles of the switches. Based on this, a series of three-mode and four-mode modulation schemes are systematically derived to completely eliminate the dead zone. The ripple and average value of the inductor current under different modulation schemes are investigated to evaluate the performance of these modulation schemes. To demonstrate the effectiveness of the proposed modulation schemes, two implementations of a four-mode modulation scheme are presented and experimentally tested as the examples for all modulation schemes. Experimental results correspond well with the theoretical analysis in both implementations over the entire input voltage range.