High-voltage switches required in present power electronics applications are realized by connecting existing devices in series. Unequal sharing of voltage across series-connected devices can be minimized by using active gate control techniques, snubber circuits, and active clamping circuits. The primary objectives of this paper are to discuss existing voltage-balancing techniques, to present a novel hybrid voltage-balancing technique, and to optimize the number of insulated gate bipolar transistors (IGBTs) in a series string in terms of power losses. The novel voltage-balancing technique can achieve good voltage balancing with a minimum number of components and minimum total losses (i.e., IGBT losses and balancing circuit losses). This technique was validated by both simulation and experimental work. The power loss of a high-voltage switch depends on the voltage-balancing circuit and the number of IGBTs in series and switching frequency. For a given application, the optimum number of IGBTs, in terms of power losses, depends on device characteristics and switching frequency.

Series connection of insulated gate bipolar transistors (IGBTs)

Series connection of individual semiconductors is an effective way to achieve higher voltage switches. However, the inherent unequal dynamic voltage sharing problem needs to be solved, even when well-matched gate drivers and semiconductors are used. A majority of the existing voltage balancing schemes are developed for slow-switching silicon (Si)-based semiconductors, and are also associated with a significant amount of additional losses in the control circuit or on the switches. In this paper, a novel method is proposed for balancing the dynamic voltages among series-connected silicon carbide (SiC) MOSFETs with high dv/dt rates. The method takes advantage of a small capacitor to provide additional current to the gate of the MOSFETs at turn- off , meaning the switching speed (and thus, the device voltage after turn- off ) is controlled. The proposed method generates negligible losses in the control circuit, and also does not significantly increase the switching losses of the semiconductors. Experimental results are provided to prove the effectiveness of the proposed voltage balancing scheme on two SiC MOSFETs inside a module connected in series. In order to do so, an active gate driver is designed embedding the active dv/dt control scheme as well as other essential functionalities needed for operation of SiC MOSFETs.

Active Gate-Driver With dv/dt Controller for Dynamic Voltage Balancing in Series-Connected SiC MOSFETs

Driving solutions for power semiconductor devices are experiencing new challenges since the emerging wide bandgap power devices, such as silicon carbide (SiC), with superior performance become commercially available. Generally, high switching speed is desired due to the lower switching loss, yet high $dv/dt$ and $di/dt$ can result in elevated electromagnetic interference (EMI) emission, false-triggering, and other detrimental effects during switching transients. Active gate drivers (AGDs) have been proposed to balance the switching losses and the switching speed of each switching transient. The review of the in-existence AGD methodologies for SiC devices has not been reported yet. This review starts with the essence of the slew rate control and its significance. Then, a comprehensive review categorizing the state-of-the-art AGD methodologies is presented. It is followed by a summary of the AGDs control and timing strategies. In this work, using AGD to reduce the EMI noise of a 10-kV SiC MOSFET system is reported. This work also highlights other capabilities of AGDs, including reliability enhancement of power devices and rebalancing the mismatched electrical parameters of parallel- and series-connected devices. These application scenarios of AGDs are validated via simulation and experimental results.

A Review of Switching Slew Rate Control for Silicon Carbide Devices Using Active Gate Drivers

In this paper, a new series connection topology is introduced for silicon carbide (SiC) MOSFETs. In the topology, with a single external gate drive, three series-connected SiC MOSFETs are synchronously driven. The operating principle of the proposed topology is analyzed and presented. In order to improve the current capability of the module, parallel connection of two SiC devices are also demonstrated. A 3600 V/80 A series-parallel-connected configuration with three rows in a series and two branches in parallel is constructed with six 1200 V/40 A discrete SiC MOSFETs. Switching behavior of the configuration is completed at 2300 V/78 A. Experimental results verify the validity and feasibility of the proposed topology. Analysis based on experimental results for the circuit switching speed and switching losses is given. Finally, such a series-parallel-connected circuit is integrated in a SiC MOSFETs module, capable of 3600 V/80 A. The switching characteristics of the module are compared to the discrete configuration.

A 3600 V/80 A Series--Parallel-Connected Silicon Carbide MOSFETs Module With a Single External Gate Driver

Among the various solutions for the series association of high power IGBTs, the active clamping circuit insures both protection and voltage balancing, within good reliability and compactness. Therefore, this structure has been chosen to be integrated closed to the IGBTs. The design of this circuit leads to the resolution of a compromise between a good balancing and limited additional losses. The aim of this paper is to optimise this circuit, in order to reduce the losses, in the IGBTs as well as in the active clamping circuit. This design has been validated in a 3 kV 400 A test bench, using three 1.7 kV components in series.

Optimisation and integration of an active clamping circuit for IGBT series association

In this paper experimental and simulation techniques are used to investigate the series connection of high voltage IGBT modules. An experimental setup with a power rating of 6.6 kV and 1200 A is established and used to analyze the circuit behavior in detail. An improved gate driver circuit in combination with an active overvoltage control enables safe operation of the circuit under all conditions. Additionally, the circuit is simulated with the simulation tool SABER using physics-based electro-thermal models for the description of the power semiconductor devices in the circuit. Experimental and simulated data agree very well.

M. Bruckmann

Papers

Series connection of high voltage IGBT modules