Abstract : This paper proposes a control method for multilevel frequency converters based on grid voltage compensation. Starting from the main circuit topology and using the regular sampling method for low-voltage frequency converters as the basic theory, the theoretical analysis and algorithm derivation process suitable for multilevel frequency converter control are described in detail. The sampling principle and sampling timing suitable for digital signal processing are also presented. By directly adjusting the output voltage in real time according to the changes in grid voltage, ideal mechanical characteristics and operating effects comparable to closed-loop systems can be obtained. This method not only has the advantages of simple calculation steps, good output SPWM symmetry, high accuracy, and convenient control, but is also applicable to any number of levels and topology. Experimental results show that it has better performance and high application value compared with other multilevel control methods. Keywords: grid voltage compensation; multilevel inverter; sampling; SPWM 1 Introduction In recent years, multilevel inverters have been increasingly widely used in high-voltage, high-power inverter devices. The basic topology is divided into three forms: diode clamping, flying capacitor, and multilevel series. In comparison, the multilevel series type has the following advantages: (1) It adopts the power unit series connection instead of the power device series connection scheme, which saves a lot of clamping diodes and voltage balancing capacitors in the circuit; each power unit adopts a modular structure, which can be interchanged and is easy to maintain. (2) The inverter structure is based on the traditional two-level inverter unit form. The main circuit topology is very simple. (3) Each inverter bridge is powered by an independent DC voltage source, and there is no problem of neutral point voltage imbalance. Most of these inverters adopt an open-loop control scheme. The fluctuation of the grid voltage directly affects the output voltage, which in turn affects the output power of the motor. If the output voltage can be adjusted in real time according to the change of grid voltage without affecting the system structure, the ideal mechanical characteristics and operating effect comparable to the closed-loop system can be obtained directly. [b]2. Principle of High-Power Inverter with Multiple Units in Series 2.1 Main Circuit Topology[/b] Multiple units in series means using several low-voltage output power units connected in series to directly obtain a high-voltage output, thereby synthesizing the power output of the entire inverter. Figure 1 shows the main circuit topology of a high-power inverter with six power units connected in series. [b][align=center]For more details, please click: Research on Control Method of Multi-Level Inverter Based on Grid Voltage Compensation[/align][/b]