**A Research on Cascaded H-Bridge Module Level Photovoltaic Inverter Based on a Switching Modulation Strategy**

#### **Wang Mao 1, Xing Zhang 1,\*, Yuhua Hu 1, Tao Zhao 1, Fusheng Wang 1, Fei Li 1 and Renxian Cao 2**

1 School of Electrical Engineering and Automation, Hefei University of Technology, Hefei 230009, China; hfut\_maow@163.com (W.M.); hfut\_hyh@163.com (Y.H.); zt\_kyyx@163.com (T.Z.); wangfusheng@hfut.edu.cn(F.W.);lifei@hfut.edu.cn(F.L.)


Received: 28 April 2019; Accepted: 13 May 2019; Published: 15 May 2019

**Abstract:** The stable operating region of a photovoltaic (PV) cascaded H-bridge (CHB) grid-tied module level inverter is extended by adopting the hybrid modulation strategy. However, the traditional single hybrid modulation method is unable to regulate the DC-side voltage of each module precisely, which may aggravate the fluctuation of modules' DC-side voltages or even cause the deviation of modules' DC-side voltages under some fault conditions and, thus, degrade the energy harvesting of PV panels. To tackle this problem, a switching modulation strategy for PV CHB inverter is proposed in this paper. When the CHB inverter is operating in normal mode, the hybrid modulation strategy containing the zero state is adopted to suppress DC-side voltage fluctuation, thereby, improving the output power of PV modules. When the CHB inverter is operating in fault mode owing to failing solar panels, the hybrid modulation strategy without the zero state is utilized to make the DC-side voltages reach the references and, thus, maintain a higher energy yield under fault conditions. Experimental results achieved by a laboratory prototype of a single-phase eleven-level CHB inverter demonstrate both the feasibility and e ffectiveness of the proposed method.

**Keywords:** cascaded H-bridge; photovoltaic inverter; module level; switching modulation strategy; energy yield
