Zhejiang University

Min Chen

Dongbo Zhang

Ning Chen

Xiaoqing Wang

Xinnan Sun

Zhaopei Liang

Bodong Li

Song Tang

Wuhua Li

Xiangning He

Chushan Li

Huan Yang

Guanlong Jia

Qinghui Huang

Xiaowei Gu

Heya Yang

Guannan Zhu

Chenghao Zhang

Lei Jing

A method for a direct current (DC) islanding detection based on positive feedback of a bus voltage at a specific frequency, essentially including three steps: extraction of a specific frequency component of the bus voltage, injection of a disturbance component of the specific frequency, and determination of DC islanding. The extraction of the specific frequency component of the bus voltage and the injection of the disturbance component of the specific frequency constitute a positive feedback mechanism in a power management unit control loop. In a grid-connected mode of a DC grid, the positive feedback mechanism fails due to a control action of a voltage management unit on a bus, and the bus voltage remains stable. In an islanding mode of the DC grid, under an action of the positive feedback mechanism, the power management unit allows the bus voltage to generate a self-excited oscillation at the specific frequency.

Method for DC islanding detection based on positive feedback of bus voltage at specific frequency

Related to is a bidirectional CLLC circuit with a coupled inductor, which is associated with a circuit topology and operation control of a bidirectional CLLC resonant converter. Provided is a structure of a bidirectional CLLC resonant circuit with a coupled inductor, including a primary side bridge, a secondary side bridge, a primary side resonant capacitor, a secondary side resonant capacitor, a coupled resonant inductor, and a transformer. Compared with a structure of a conventional bidirectional CLLC resonant circuit, two separate resonant inductors located at a primary side and a secondary side in an original resonant cavity are replaced with one coupled resonant inductor in the circuit; the coupled resonant inductor has opposite dotted terminals with the transformer, and a primary side and a secondary side of the coupled resonant inductor are respectively in serial connection with a primary side and a secondary side of the transformer.

Bidirectional CLLC resonant circuit with coupled inductor

An energy storage MMC topology is proposed to avoid the microcirculation of battery. The topology consists of six bridge arms in three stages and can be connected to DC system and AC system. Each bridge arm is composed of one bridge arm inductance and N energy storage sub-modules with the same structure in series. The energy storage sub-modules include a half-bridge power module, a battery energy storage module and a group of anti-parallel thyristors. The group of anti-parallel thyristors is connected in series over the DC cable between the battery energy storage module and a capacitor of the half-bridge power module. The switching control is performed on the battery in the energy storage MMC according to the systematic operating mode.

Energy storage MMC topology avoiding microcirculation of battery and method for controlling the same

Provided is an active power filter-based modular multilevel converter, relating to the field of power electronics. According to the converter, an active power filter circuit is provided between upper and lower arms of each phase in a modular multilevel converter. The active power filter circuit includes two switch power devices, two submodules, a capacitor, and an inductor. The upper and lower bridge-arms are connected in series by means of two submodules, the two switch power devices are connected in series and then connected in parallel to ends of intermediate submodules which are connected in series, and the capacitor and the inductor are connected in series and then connected in parallel to two ends of the switch power device connected to the lower bridge-arm. The defect of large capacitance of submodule in conventional modular multilevel topology is overcome.

Active power filter-based modular multilevel converter

Provided is a method for controlling smooth switching of an operation direction of a bidirectional resonant CLLC circuit, which applies to the bidirectional resonant CLLC circuit. The method includes the following steps: Step 1: detecting a current circuit state and controlling the bidirectional resonant CLLC circuit to operate in a forward operation state by means of a primary bridge and a secondary bridge, by a controller; Step 2: performing Step 3 when an externally transmitted reference signal received by the controller or an internal preset reference signal in the controller is an operation direction switching signal; Step 3: performing frequency conversion control, by the controller; Step 4: performing preparation of phase shift control and generating a driving signal of the secondary bridge, by the controller; Step 5: performing the phase shift control, by the controller; and Step 6: switching a circuit operation state to an inverse operation mode.

Method for controlling smooth switching of operation direction of bidirectional resonant CLLC circuit

Growing community of inventors

Zhejiang, China

Min Chen