Construction of single-phase non-isolated bridge inverter topology
From the previous analysis, it is known that the suppression approach A is to increase the common-mode loop impedance and reduce the high-frequency leakage current in the case of high-frequency changes in the common-mode voltage. The suppression pathways B and C eliminate the high-frequency voltage of the common-mode loop to eliminate the leakage current. Compared with inhibition pathway A, pathways B and C can achieve better suppression effects, and theoretically even completely eliminate leakage current. Among several circuit topologies based on leakage current suppression approach A, H5 topology has the least switching devices, Heric topology is more efficient, and H5 change topology 1 is between H5 and Heric, and the efficiency is improved compared to H5. But these three topologies all use Path A to suppress the leakage current, and the suppression effect is poor. The following is based on the aforementioned systematic analysis of the leakage current suppression mechanism, and on the basis of retaining the advantages of these three topologies, they are improved, and a better leakage current suppression effect can be achieved by changing the leakage current suppression path. In addition, through the optimization of the modulation strategy, the inverter can realize non-unit power factor operation to conform to the development direction of grid-connected inverter technology.
Improved H5 topology
Figure 1 shows an improved H5 topology (oH5 topology for short). On the basis of H5, a switch tube S6 is added, and the improved unipolar SPWM strategy shown in Figure 2 is adopted. Different from the unipolar SPWM strategy adopted by the traditional H5 inverter, the low-frequency tubes S1 and S3 are complementary to the high-frequency switching of S5 during the non-working half cycle to provide a loop for the reactive current, and the circuit can work at any power factor. In the freewheeling phase, S6 is turned on, and the potential box at point H is positioned at the midpoint of the capacitor M, and vCM is maintained at a constant value (Udc/2), that is, the purpose of eliminating high-frequency leakage current is achieved through path B. Compared with H5, a switch tube S6 is added, but since the current flowing through S6 is very small, the loss has not increased significantly, but a better leakage current suppression effect can be obtained.
Improved Heric topology
Figure 3 shows an improved topology of the Heric topology (hereinafter referred to as oHeric topology). On the basis of Heric, a two-way switch composed of switch tubes S5 and S8 is added. Also make low frequency tubes S5 and S6. It is also turned on at a high frequency in the non-working half-cycle. As shown in Figure 4, the high-frequency turn-on of S5 and S6 in the non-working half-cycle provides a path for reactive current. Therefore, after using an improved modulation strategy, the circuit can operate at any power factor. The leakage current suppression mechanism of this topology is the same as that of oH5, that is, during the freewheeling phase, S7 and S8 are turned on, and the potential of point H is located at the midpoint M of the capacitor, so that vCM is maintained at a constant value (Udc/2), eliminating high-frequency leakage current. Compared with Heric, the switch tubes S7 and S8 are added. Since the current flowing through S7 and S8 is very small, the loss has not increased significantly, but the leakage current suppression effect is improved.
Improvement of H5 change topology 1
Similar to the Heric topology, a two-way switch composed of switch tubes S7 and S8 is connected in series between the H point and the M point of the circuit shown in Figure 5 to obtain a new and improved topology, as shown in Figure 6. The leakage current suppression mechanism of this topology is consistent with oH5 and oHeric, and the unipolar SPWM strategy shown in Figure 7 is adopted. In the freewheeling phase, S7 and S8 are turned on, and the common mode voltage vcM remains unchanged at Udc/2, eliminating high-frequency leakage current. Similarly, let the low frequency tubes S1 and S3 be turned on at a high frequency during the non-working half cycle, so that the circuit can run at any power factor.