Development of a Control Method for LLC Converter Utilized for Input-Parallel-Output-Series Inverter System with Solid-State Transformers

Abstract

A multi-level power converter with series-connected solid-state transformer (SST) units for a power conditioning system for photovoltaic (PV) generation was developed. Each SST unit has an LLC converter driven by SiC-MOSFETs and a high-frequency transformer. By applying the developed converter, the system can be optimized and made lighter than a conventional system using a commercial transformer. A method for controlling the LLC converter so as to maintain its high efficiency over a wide voltage range of a PV panel is proposed. According to the results of an experimental evaluation of a prototype SST unit, the efficiency of the LLC converter is 98% or more even when the input voltage from the PV panel changes.

Novel Voltage Balance Strategy for a Cascade H-Bridge with a Wide Stable Operating Region and a Low Input Current THD

“…In the AVS method, when σp = 4, the calculation of the maximum power for a module Pmax_σp4 is the same as (8). The calculation of the minimum power for a module Pmin_σp4 is same as (9).…”

“…Considering in high power traction PET, a CHBR with 11 or more H-Bridge modules is necessary [31], which means the switching loss of CPS-PWM will be significantly higher than the AVS method. Many other studies [4,[8][9][10]12] have also shown a high sensitivity to switching losses and efficiency. Taking into account the three more important factors: SOR (voltage balance capacity), input current (stabilty and efficiency of power system) and switching loss (efficiency), the AVS method is a better one among the four methods.…”

“…Cascade H-Bridge (CHB) converters, have advantages such as modularity, multilevel output voltage, lower dv/dt [1]. CHB converters have good prospects in electrical railway traction [2][3][4], Static Synchronous Compensator [5], distribution networks, microgrids, and renewable energy generation [6][7][8][9][10]. A Cascade H-Bridge Rectifier (CHBR) has been shown in Fig.…”

Recent trends in power electronics applications as solutions in electric railways

“…The LLC converter is expected to eliminate the switching loss by the soft switching feature of the LLC converter, and the input‐series output‐parallel configuration is suitable for high power and downsized design for the isolated DC–DC converter. This circuit configuration is used in different applications with a particular control . The DC link voltage in the secondary side of the transformer is controlled to keep the DC 1.5 kV constant.…”

A Phase-Shift Control Method of Triple-Active-Bridge Converter for Reducing Power Loss Under Light Load Condition

“…However, in a system in which a DC bus including an NPC inverter with an AC voltage controller is divided by a series capacitor, since it is difficult to adjust the voltage balance of the series capacitor via an AC terminal, a balance circuit is required. In addition, as a system for interconnection with a 6.6 kV power grid system, a converter technology using an extended system in which an inverter and an insulated converter are combined as a set has been reported (1)- (3) . In these studies, to serialize one end of the unitized converter to generate a high voltage, the other end must be connected to a DC voltage source.…”