Low-Frequency Circulating Current Injection in Eight-Component Control for Modular Multilevel Matrix Converter Under Equal Frequency

The modular multilevel matrix converter (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{{\mathbf{M}}}^{3}$</tex-math></inline-formula>C) is a topology suitable for ac–ac fields, such as wind power conversion systems, large-capacity electric drives, etc. However, when the input frequency of the system is close to or equal to the output frequency, large voltage fluctuations even unbalancing will produce on the dc capacitors of the submodules, which limits the application range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{{\mathbf{M}}}^{3}$</tex-math></inline-formula>C. This article proposes a low-frequency circulating current injection method to address the issue of dc capacitor voltage fluctuations in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{{\mathbf{M}}}^{3}$</tex-math></inline-formula>C under equal frequency operating condition. The frequencies present within the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{{\mathbf{M}}}^{3}$</tex-math></inline-formula>C are used to consist of the low-frequency circulation current. Therefore, the proposed method does not require injecting common mode voltage or applying reactive power. Experimental results based on the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{{\mathbf{M}}}^{3}$</tex-math></inline-formula>C platform verify the effectiveness of the proposed method. Moreover, the dynamic performance is also good with the proposed control strategy under the conditions of output voltage or frequency change.