What are the best control strategies for multilevel converters in grid-connected and isolated systems?

1 Modulation techniques

One of the main challenges of multilevel converters is to generate the desired output voltage waveform with minimal harmonic distortion and switching losses. Modulation techniques are the methods that determine how the switches are turned on and off to produce the output voltage. There are different types of modulation techniques, such as pulse width modulation (PWM), space vector modulation (SVM), and selective harmonic elimination (SHE). Each technique has its own advantages and disadvantages, depending on the application and the converter topology.

2 Balancing techniques

Another challenge of multilevel converters is to maintain the voltage balance of the capacitors that form the voltage levels. If the capacitors are not balanced, the output voltage will be distorted and the converter will be unstable. Balancing techniques are the methods that regulate the charging and discharging of the capacitors to keep them at the desired voltage. There are different types of balancing techniques, such as passive, active, and hybrid. Passive techniques use resistors or diodes to dissipate the excess charge, while active techniques use additional switches or circuits to redistribute the charge. Hybrid techniques combine both passive and active elements.

3 Grid-connected systems

Grid-connected systems are systems that are connected to the utility grid and can exchange power with it. Multilevel converters can be used in grid-connected systems to interface renewable energy sources, such as solar panels or wind turbines, with the grid. In this case, the control strategy of the multilevel converter must ensure that the output voltage matches the grid voltage in terms of magnitude, frequency, and phase. Moreover, the control strategy must also comply with the grid codes and regulations, such as power quality, fault ride-through, and reactive power compensation.

4 Isolated systems

Isolated systems are systems that are not connected to the utility grid and operate independently. Multilevel converters can be used in isolated systems to supply power to loads that require different voltage levels, such as electric vehicles or industrial drives. In this case, the control strategy of the multilevel converter must ensure that the output voltage meets the load requirements in terms of magnitude, frequency, and waveform. Moreover, the control strategy must also ensure the stability and robustness of the isolated system, especially in the presence of disturbances or faults.