DC-Bus Voltage Range Extension in 1500 V Photovoltaic Inverters

Solar plants based on single-stage conversion photovoltaic (PV) inverters (no dc-dc boost stage) have gained popularity due to their simplicity, high efficiency, and cost effectiveness. Existing PV plants mostly operate under 1000 V and are subject to wide dc-bus voltage variations due to the effect of PV cell temperature and the voltage of the maximum power point (well below the open-circuit voltage). In particular, attractive locations, such as U.S.-Canada mountain and central regions, are subject to extreme PV surface temperatures, making the dc-bus voltage variation a challenge for single-stage solar inverters. This paper investigates 1500 V solar inverters with a focus on dc-bus voltage range extension capabilities through novel modulation and power devices utilization. A comparative analysis with the existing 1000 V solar inverters is presented to illustrate the significant advantages of the wide dc-bus range in 1500 V systems. A lower voltage limit in the dc-bus is achieved by employing a novel voltage reactive power dc-bus control strategy and modified modulation. A higher dc-bus peak voltage is obtained by maximizing the use of power switches. As a result, the 1500 V inverter dc-bus voltage is significantly extended to capture energy under extreme PV surface temperatures, greatly improving the limited range of traditional 1000 V inverters. Simulations and experimental results using a three-phase three-level neutral point-clamped inverter level are presented to validate the proposed dc-bus extension range, control strategy, and modulation scheme.