Triangular conduction mode (TCM) is used in grid-tied inverters to achieve high efficiency by its soft switching feature. However, it suffers from a wide switching frequency variation over the whole power range, which impacts the weighted efficiency. To address this issue, this article proposes a novel trapezoidal wave control method for a single-phase grid-tied T-type inverter. By the proposed method, the inductor current is divided into three stages in a switching cycle, so it looks like trapezoidal wave rather than triangular wave. The proposed trapezoidal wave has two independent conduction times. In order to simplify the control, the proportion between the two conduction times is controlled as a variable. As a result, only one conduction time needs to be calculated, and the derived equation is easy to be calculated in digital controllers. Furthermore, this article proposes a design consideration for the value selection of the proportion between the two conduction times, which ensures proper operation of the circuit. The proposed scheme has three advantages. First, it realizes soft switching in every switching cycle. Second, it reduces the switching frequency and related losses compared to the full-bridge inverter in TCM operation and thus improves efficiency. Third, it can be applied over the whole line cycle as a uniform operation mode. Therefore, mode transitions are avoided, which improves the quality of the grid-injected current. A prototype has been built and the experimental results verify the feasibility of the proposed scheme.

中文翻译：

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单相并网T型逆变器的新型梯形波控制方法


并网逆变器采用三角导通模式（TCM），通过其软开关特性实现高效率。然而，它在整个功率范围内开关频率变化很大，这会影响加权效率。为了解决这个问题，本文提出了一种用于单相并网T型逆变器的新型梯形波控制方法。通过所提出的方法，电感电流在一个开关周期内被分为三个阶段，因此它看起来像梯形波而不是三角波。所提出的梯形波具有两个独立的传导时间。为了简化控制，将两个导通时间之间的比例作为变量进行控制。因此，只需要计算一个导通时间，并且推导的方程很容易在数字控制器中计算。此外，本文提出了两个导通时间比例值选择的设计考虑，以确保电路的正常运行。所提出的方案具有三个优点。首先，它在每个开关周期实现软开关。其次，与 TCM 运行中的全桥逆变器相比，它降低了开关频率和相关损耗，从而提高了效率。第三，可以作为统一的运行模式应用于整个生产线周期。因此，避免了模式转换，从而提高了电网注入电流的质量。搭建了样机，实验结果验证了该方案的可行性。