Multisampling with Sigma-Delta ADCs for Medium-Voltage Cascaded H-Bridge Converters

The control of medium-voltage cascaded H-bridge (CHB) converters demands precise, high-bandwidth, low-latency, and isolated measurements. Traditional analog-to-digital converters (ADCs) can facilitate multisampling methods to meet these requirements but do not provide the high-voltage galvanic isolation that may be necessary in a system operating at medium voltage. Sigma-Delta ADCs (SD-ADCs) present a promising alternative due to their superior noise rejection capabilities and direct integration with the optical fiber interface. However, the inherent latency associated with SD-ADCs, stemming from their operating principles, poses challenges when integrating them with multisampling methods. This paper analyzes the integration of multisampling techniques with SD-ADCs for medium-voltage CHB converter control. First, the impact of SD-ADC-induced delays on the control system is elucidated from the passivity perspective. Second, the practical implementation of multisampling with SD-ADCs is discussed in detail. Finally, experimental results from a 2400 Vrms medium-voltage CHB converter are presented to validate the analysis and illustrate the effectiveness of the proposed implementation.