Average Modeling and Control Design for VIENNA-Type Rectifiers Considering the DC-Link Voltage Balance

This paper presents a new average d-q model and a control approach with a carrier-based pulsewidth modulation (PWM) implementation for nonregenerative three-phase three-level boost (VIENNA-type) rectifiers. State-space analysis and an averaging technique are used to derive the relationship between the controlled duty cycle and the dc-link neutral-point voltage, based on which an optimal zero-sequence component is found for dc-link voltage balance. By utilizing this zero-sequence component, the behavior of the dc-link voltage unbalance can be modeled in d-q coordinates using averaging over a switching cycle. Therefore, the proposed model is valid for up to half of the switching frequency. With the proposed model, a new control algorithm is developed with carrier-based PWM implementation, which features great simplicity and good dc-link neutral-point regulation. Space vector representation is also utilized to analyze the voltage balancing mechanism and the region of feasible operation. Simulation and experimental results validated the proposed model and control approach.