Shiqi Ji

Series-Connected HV-IGBTs Using Active Voltage Balancing Control With Status Feedback Circuit

Transient voltage unbalance is the major problem that limits the application of series-connected IGBTs in high-voltage and high-power converters. Asynchronous gate delay causes series-connected IGBTs not to turn-on and turn-off at the same time resulting in severely unbalanced voltage sharing. An active voltage balancing control technique is proposed in this paper to solve the asynchronous gate delay problem. By sampling the feedback signal caused by unbalanced voltage sharing, the microcontroller generates a time delay for the gate driver to compensate the asynchronous gate delay. The most vital part of active voltage balancing control, the status feedback circuit, is also discussed in detail in this paper. The function of the status feedback circuit and the effect of active voltage balancing control are verified in a two series-connected HV-IGBTs platform in rated operation (5 kV bus voltage and 600 A load current).

HVIGBT Physical Model Analysis During Transient

The insulated gate bipolar transistor (IGBT) physical models are studied in details. The difference between low-voltage IGBT (LVIGBT) and high-voltage IGBT (HVIGBT) is analyzed and the shortage of the LVIGBT model used for HVIGBT is discussed. The physical model considering the effect of carrier concentrate on excess carrier lifetime is established for HVIGBT. The HVIGBT transient model is presented with different excess carrier lifetime in the base. The new description of steady-state U-I characteristics is also obtained with numerical method. The test experiment was performed in a Buck converter using 6500 V HVIGBT with different bus voltage and load current. The accuracy of the transient model of HVIGBT is verified by experiment and simulation results. The verification of some key parameters to describe the external characteristics is also given in the paper.

Parameter design of voltage balancing circuit for series connected HV-IGBTs

Applying power semiconductor devices in series connection is a direct and effective scheme to improve the voltage rating and power rating of power electronic converter. The key issue of device series connection is voltage balancing in static switching state and dynamic switching state. Active clamping circuit samples overvoltage on insulated gate bipolar transistor (IGBT), injects current into the gate and thus could increase the gate voltage and suppress the overvoltage effectively. In this paper, a voltage balancing circuit for high voltage IGBT (HV-IGBT) series connection is presented. The voltage balancing circuit is composed of static state voltage balancing sub-circuit across collector and emitter, dynamic state voltage balancing sub-circuit across collector and emitter and active clamping sub-circuit across collector and gate. The functions and principles of the three sub-circuits are then described. Besides the topology, the parameters of the voltage balancing circuit influence the voltage balance of series connected HV-IGBTs seriously. Based on quantitatively analyzing the relationships among the parameters of HV-IGBTs, the parameters of voltage balancing circuit and the voltage balancing indexes of the series connected devices, a parameter design method for the presented voltage balancing circuit is proposed. This parameter design method comprehensively considers the switching loss of HV-IGBT, the loss of voltage balancing circuit, the electrical stress on HV-IGBT and the switching frequency in order to guarantee the efficiency, reliability and performance of the system. The proposed parameter design method is applied to the development process of a series connection circuit with Infineon 6500V/600A HV-IGBTs. Experimental results verify the validity and feasibility of the proposed method.

Physical Model Analysis During Transient for Series-Connected HVIGBTs

Obvious differences are observed between simulation and experimental results for series-connected insulated-gate bipolar transistors (IGBTs) using current IGBT models. Here, the cause of these errors is analyzed in detail. A physical model based on more effective assumptions for a 2-D structure is proposed in this paper. The relationship between carrier concentration and lifetime is considered in the model in order to achieve an accurate description for excess carrier distribution. Testing was performed in a buck converter using series-connected non-punch-through (NPT) planar-gate 6500 V/600 A high-voltage IGBTs (HVIGBTs) at various bus voltages using an asynchronous control signal. The accuracy of HVIGBT transient model is verified by comparing experimental and simulation results in buck converters using two and three series-connected IGBTs. The function of the RC snubber circuit is also evaluated using the proposed model.

Research on HVIGBT transient mixture model and parameter extraction method

This paper presents a kind of HVIGBT transient mixture model and corresponding parameter extraction method. The HVIGBT model can divide into MOSFET and BJT two parts. The two models are formed respectively according to HVIGBT work principle, in addition, the carrier transport equations have been simplified for avoiding Kirk effect in BJT model. The transient model is realized in PSIM software in the paper. Extraction methods, which include estimation by empirical values, calculation by testing waveforms and comparison with same type models, are adopted in extracting model parameters. Through comparing testing and simulation waveforms, the models simulation accuracy is proved.

Laminated busbar design and stray parameter analysis of three-level converter based on HVIGBT series connection

Multilevel technology and power semiconductor devices in series connection can both effectively improve the converter system power capacity. But both of them will enlarge the system size and lead to complex busbar structure which may cause large stray parameters, especially the stray inductances. Large stray inductance has a critical effect during the device transient process and may cause device damage and failure. Therefore, the laminated busbar structure is widely used in high power converters to decrease the wiring stray inductances. In this paper, based on the current commutation loop (CCL) analysis of a 3-level high-voltage insulated gate bipolar transistor (HVIGBT) series bridge, the structure design method of the 3-level HVIGBT series connection test platform is described. The influence of the laminated busbar to the adjacent busbar is analyzed and the improved stray parameter calculation method is proposed. The experimental results verify the validity of the structure design method and the veracity of the stray parameter calculation method.

Active voltage balancing control for 10kV three-level converter using series-connected HV-IGBTs

The integration of series connection of insulated gate bipolar transistors (IGBTs) and multi-level can achieve high voltage converters with low total harmonics distortion (THD). However, due to the transient voltage unbalance, the series connection technology has not been widely applied. Asynchronous gate drive signals, which cause series-connected IGBTs not to turn-on and turn-off at the same time, result in serious unbalanced voltage sharing. This paper presents an active voltage balancing control with its electromagnetic compatibility (EMC) design to solve the asynchronous gate signal problem. The effectiveness of the active voltage balancing control has been experimentally validated in a 10kV dc-link voltage three-level bridge using two 4.5kV HV-IGBTs in series-connection.

Parameter Design of a Three-Level Converter Based on Series-Connected HV-IGBTs

Although the maximum collector-emitter voltage of a high-voltage insulated-gate bipolar transistor (HV-IGBT) reaches 3300 V or higher, it still cannot satisfy the requirements of some high-voltage high-power converters. Applying power semiconductor devices in series connection can effectively improve the voltage rating and power rating of a power electronic converter. The key issue of device series connection is voltage balancing in static switching state and dynamic switching state. In this paper, a three-level converter based on series-connected HV-IGBTs is presented, its voltage-balancing subcircuits are analyzed, and the parameter design method for the converter is proposed. During the design process, key performance indexes of the series connection circuit, such as the voltage-balancing effect, loss of the voltage-balancing circuit, switching loss, and switching time, are comprehensively considered. Moreover, component parameters of the three-level converter are calculated considering the influence of the voltage-balancing circuit. The proposed parameter design method is applied in the development of a three-level HV-IGBT (4500 V/600 A) series connection test platform with 10 000-V rated dc-link voltage. Experimental results verify the validity of the proposed method.

Structure design and analysis of high voltage IGBTs series connection experimental platform

Insulated Gate Bipolar Transistor (IGBT) has the advantages of high rated voltage, high rated current, high switching speed and easy to drive. But a single IGBT still cannot meet the needs of the high-voltage converters at present. IGBT series and parallel connection can greatly extend the application of IGBT because it can effectively improve the system voltage and current capacity. Generally, the volume of high voltage IGBTs series connection converter is large because of the insulation and thermal performance requirements. It means that the bus bar structure is complex, and the stray parameters of the commutating loops, especially the stray inductance, will significantly influence the switching processes. It becomes one of the key points for the safe operation of the converter. In this paper, the design principles for complex physical bus bar are presented. Based on the finite element analyses, the bus bar structure of a high voltage IGBTs series connection experimental platform is designed and improved. The performance of the improved bus bar structure is verified by simulations and experiments.

Behavior model for series connected high voltage IGBTs

The tail current of insulation gate bipolar transistor (IGBT), which is difficult to describe accurately, influences the series connection characteristics of IGBTs remarkably. In this paper, the series connection characteristics of 6500V/600A high voltage IGBTs (HV-IGBTs) are analyzed, and a behavior model for series connected HV-IGBTs is proposed. The model is implemented in PSIM with switches, capacitances and control blocks. The currents of HV-IGBTs are described piecewise in this model. In order to reflect the series connection characteristics accurately, the tail current is compensated and the model parameters are extracted based on test results of series connected HV-IGBTs. The proposed model is applied to simulate the series connection characteristics of two HV-IGBTs with active clamping circuits. The comparison between simulation results and experiment results verify the validity and precision of the proposed model.