This paper deals with the development of an algorithm for controlling a three-level converter with neutral point clamped (3L-NPC) using pulse-width modulation of a spatial vector. The paper begins with the introduction of PLECS, a simulation program in which the converter is modeled. The next chapter deals with energy converters, and the term inverter, or DC/AC converter, is introduced. Some simpler types of rectifiers and inverters are explained, and then the paper focuses on the three-level neutral point clamped inverter. The functionality of the inverter and its control methods are defined. So far, the paper has explained the high voltage part of the system (inverter), and in the following chapters the attention is shifted to the control part of the system. It describes what pulse-width modulation is, different methods of pulse-width modulation, and the idea of a space vector as a controlled quantity. The paper first describes the modulation of the spatial vector on the example of a two-level inverter, and then this idea is extended to the modulation of the space vector for the control of a three-level inverter. This kind of control of inverter works only in ideal conditions (e.g. in a simulation software), and is not applicable in the real world. For this reason, the following chapter explains problems that can lead to circuit damage in real systems, and also explains ways to solve the same problems. It also describes how the solutions to these problems are implemented in the algorithm. The last chapter of the paper focuses on a concise description of the entire program, i.e. the algorithm, and gradually explains what happens in which part of the program. At the end of the paper, the numerical complexity of the algorithm is stated, which is an important parameter when implementing it in a real microcontroller.