INSULATED GATE BIPOLAR TRANSISTOR FAILURE MODE DETECTION AND PROTECTION SYSTEM AND METHOD

BACKGROUND OF THE INVENTION

An insulated gate bipolar transistor (IGBT) is a switching transistor used to permit power flow in when it is on and to stop power flow when it is off. It is a solid-state device and has no physical moving parts. Instead of opening and closing a physical connection, the IGBT is operated by applying voltage to a semiconductor component, which changes its properties to create or block an electrical path. IGBTs are commonly used as switches, e.g. in chopper and frequency converter applications, to control and convert electrical power by switching electrical devices on and off at predetermined instances. An IGBT may either be used singly or connected in series. Generally, series operation of IGBTs is considered as a straightforward method to be used in high voltage power conversion. Failure of any one IGBT located in the series string of the IGBTs may result in the abnormal operation of the overall series-connected IGBTs, and even worse the overall IGBT phase legs may be damaged. For example, failure of any one IGBT in the series string may cause voltage unbalance issues and thus affect the robustness and reliability of the overall series-connected IGBTs. Therefore, it is desirable to achieve fast and accurate fault detection, including the fault type as well as the location for the failed IGBT among series-connected IGBTs.

BRIEF DESCRIPTION OF THE INVENTIONS accordance with an embodiment disclosed herein, an assembly including an insulated gate bipolar transistor (IGBT) is provided. The IGBT is coupled with a gate driver for receiving a gating signal to drive the IGBT and providing a feedback signal of the IGBT which indicates a change of a collector-emitter voltage of the IGBT. The assembly further includes a failure mode detection unit for determining whether the IGBT is faulted and for differentiating fault types including a gate driver fault, a failed turn-on fault, a short-circuit fault, a turn-on over-voltage fault and a turn- off over-voltage fault based on a timing sequence of the gating signal and the feedback signal.

In accordance with another embodiment disclosed herein, an IGBT failure mode detection method is provided. In the method, a gating signal is sent to drive one or more series connected IGBTs, and a feedback signal of each IGBT, which indicates a change of a collector-emitter voltage of the IGBT is provided. A timing sequence of the gating signal and feedback signal of each IGBT is compared with a reference timing sequence to determine whether the IGBT is faulted and, if the IGBT is faulted, to differentiate fault types including a gate driver fault, a failed turn-on fault, a short-circuit fault, a turn-on over-voltage fault and a turn-off over-voltage fault.

BRIEF DESCRIPTION OF DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 is a block diagram of an exemplary assembly including one or more series connected IGBTs, each of which is coupled with a failure mode detection unit, according to one embodiment of the present invention.

FIG. 2 shows a timing sequence of a gating signal sent to an IGBT and a feedback signal of the IGBT in response to a rising edge of the gating signal, when the IGBT is in a normal mode.

FIG. 3 shows a timing sequence of a gating signal sent to an IGBT and a feedback signal of the IGBT in response to a rising edge of the gating signal, during a gate driver fault.

FIG. 4 shows a timing sequence of a gating signal sent to an IGBT and a feedback signal of the IGBT in response to a rising edge of the gating signal, during a failed turn-on fault.

FIG. 5 shows a timing sequence of a gating signal sent to an IGBT and a feedback signal of the IGBT in response to a rising edge of the gating signal, during a short circuit fault.

FIG. 6 shows a timing sequence of a gating signal sent to an IGBT and a feedback signal of the IGBT in response to a rising edge of the gating signal, during a turn-on over-voltage fault.

FIG. 7 shows a timing sequence of a gating signal sent to an IGBT and a feedback signal of the IGBT in response to a falling edge of the gating signal, when the IGBT is in a normal mode.

FIG. 8 shows a timing sequence of a gating signal sent to an IGBT and a feedback signal of the IGBT in response to a falling edge of the gating signal, during a turn-off over-voltage fault.

FIG. 9 is a flowchart illustrating an IGBT failure mode detection method according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Failure mode monitoring and protection are important for guaranteeing the mean time between failures (MTBF) of medium voltage drive systems, which usually use one or more insulated gate bipolar transistors (IGBT). Thus it is important to provide IGBT failure mode detection and protection units/methods for detecting any fault of the one or more IGBTs quickly and accurately.

Embodiments of the invention provide an assembly including one or more series connected IGBTs. Each IGBT is coupled with a gate driver for receiving a gating signal to drive the IGBT and providing a feedback signal of the IGBT, and is further provided with a failure mode detection unit. The failure mode detection unit is programmed to determine whether the IGBT is faulted and identify which type of fault it is based on a timing sequence of the gating signal and feedback signal. The failure mode detection unit is capable of differentiating the common types of faults that might occur to the one or more series-connected IGBTs, including a gate driver fault, a failed turn-on fault, a short-circuit fault, a turn-on over-voltage fault and a turn-off over-voltage fault.

Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this invention belongs. The terms "first", "second", and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms "a" and "an" do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. Moreover, the terms "coupled" and "connected" are not intended to distinguish between a direct or indirect coupling/connection between two components. Rather, such components may be directly or indirectly coupled/connected unless otherwise indicated.

FIG. 1 shows a block diagram of an assembly comprising N (N is a natural number and N>I) series-connected IGBTs, each of which is provided with a failure mode detection unit for detecting an IGBT failure and the failure mode. As shown in FIG. 1, each of the IGBTs has a gate terminal (G), an emitter terminal (E) and a collector terminal (C), wherein the gate terminal is coupled to a gate driver 102. A failure mode detection unit 104 either combined with or coupled to the gate driver of each IGBT. The one or more failure mode detection unit(s) 104 may be integrated in and/or communicate with a central controller 106 used to control the whole assembly. Examples of control systems suitable to be used as the central controller herein include but are not limited to complex programmable logic devices (CPID), field-programmable gate arrays (FPGA), or single chip microcomputers (SCM).

A gating signal (Gl, G2,..., or Gn) is sent to each gate driver 102, which converts the gating signal to drive power to make the IGBT turn on or off quickly. A feedback signal (FBI, FB2, ..., or FBn), which indicates the change of the collector-emitter voltage of the IGBT in response to the gating signal, is provided to the corresponding failure mode detection unit 104. The failure mode detection unit 104 is programmed to determine whether the corresponding IGBT is faulted and identify which type of fault it is if the corresponding IGBT is faulted, based on a timing sequence of the gating signal and feedback signal. Once the fault type and location is recognized, the central controller 106 may send a fault clearance signal (FC1, FC2,..., or FCn) to the gate driver 102 to deal with the fault.

The failure mode detection unit 104 may be programmed to process the gating signal and the feed-back signal of the corresponding IGBT to determine if the corresponding IGBT is faulted and further determine the fault type if the corresponding IGBT is faulted, which will be described in details hereafter below.

Referring to FIGs. 2-8, as to an IGBT in a normal mode, a pulse with certain duration (e.g., 900ns) for its feedback signal will be generated after every rising or falling edge of the gating signal, which indicates the turn-on/turn-off transience of the IGBT. However, once a fault occurs to the IGBT or its gate driver, its feedback signal may be different from that of the IGBT in the normal mode. For example, when the IGBT is in a normal turn-on mode, as shown in FIG. 2, a pulse with certain duration for the feedback signal will appear within certain time in response to a rising edge of the gating signal. Once a fault occurs to the gate driver of the IGBT, as shown in FIG. 3, a pulse for the feedback signal in response to the rising edge of the gating signal may be delayed or may even fail to appear. Once a failed turn-on fault occurs to the IGBT, as shown in FIG. 4, the duration of the pulse may last longer in comparison with the normal mode. Once a short circuit fault or a turn-on over-voltage fault occurs, as shown in FIGs. 5 and 6, a second abnormal pulse may be generated after the first normal pulse for the feedback signal in response to the rising edge of the gating signal. When the IGBT is in a normal turn-off mode, as shown in FIG. 7, a pulse with certain duration for the feedback signal will appear within certain time in response to a falling edge of the gating signal. Once a turn-off over-voltage fault occurs, as shown in FIG. 8, a pulse for the feedback signal in response to the falling edge of the gating signal may delay and the duration of the pulse may last longer in comparison with the normal mode.

In some embodiments, the failure mode detection unit is programmed to compare a timing sequence of the gating signal and feedback signal of the corresponding IGBT (actual timing sequence) with a standard timing sequence of the gating signal and feedback signal of an IGBT in a normal mode (reference timing sequence), and thereby determine whether the corresponding IGBT is faulted. Moreover, based on the actual timing sequence, it also can be identified which kind of the fault occurs.

Referring to FIGs. 2-8, in some specific embodiments, the failure mode detection unit is programmed to compare:

(a) an interval ti between a rising edge of the gating signal and a rising edge of a first feedback signal pulse that immediately follows the rising edge of the gating signal, with a maximum turn-on ack-wait time Ti;

(b) a duration t2 of the first feedback signal pulse, with a maximum turn-on ack time T2;

(c) an interval t3 between a falling edge of the first feedback signal pulse and a rising edge of a second feedback signal pulse that immediately follows the first feedback signal pulse, with a short-circuit blanking time T3.1 and an over-voltage blanking time T3.2;

(d) a duration t» of the second feedback signal pulse, with a maximum over-voltage time T4;

(e) an interval ts between a falling edge of the gating signal and a rising edge of a third feedback signal pulse that immediately follows the falling edge of the gating signal pulse, with a maximum turn-off ack-wait time T5; and

(f) a duration t6 of the third feedback signal pulse, with a maximum turn-off ack time T6, and thereby determine whether the corresponding IGBT is faulted and differentiate fault types including the gate driver fault, failed turn-on fault, short-circuit fault, turn-on over-voltage fault and turn-off over-voltage fault.

In a specific embodiment, the maximum turn-on ack-wait time Ti is approximately 160ns, the maximum turn-on ack time T2 is approximately 800ns, the short-circuit blanking time T3.] is approximately 6us (6000ns), the over-voltage blanking time T3.2 is approximately 500ns, the maximum over-voltage time T4 is approximately 800ns, the maximum turn-off ack-wait time T5 is approximately 550ns and the maximum turn-off ack time T6 is approximately lus (1000ns).

In some embodiments, the failure mode detection unit 104 is programmed to diagnose that: a gate driver fault occurs if ti>Ti; a failed turn-on fault occurs to the IGBT if tiT2; a short-circuit fault occurs to the IGBT if tiT4; a turn-off over-voltage fault occurs to the IGBT if ts>Ts and tT6.

Once any one or more IGBTs are detected by its/their corresponding failure mode detection unit(s) as with any type of fault as described above, a fault signal will be fed back to the central controller 106 to report not only the location of the faulted IGBT but also the fault type. The central controller 106 may send out a fault clearance signal (FC1, FC2, ..., or FCn) in response to the fault signal, to deal with the faulted IGBT according to the recognized fault type. The fault clearance signal may be an instruction to shut down the gating signal sent to the one or more IGBTs, or an instruction to isolate the faulted IGBT from its gate driver and thereby from the other parts of the assembly, or even an instruction to ignore the fault. The central controller 106 may respond differently to different types of faults, and send out different fault clearance signals in response to different types of faults.

In some embodiments, by series-connecting M (M is a natural number and 1Ti; a failed turn-on fault occurs to the IGBT if tiT2; a short-circuit fault occurs to the IGBT if tiT4; a turn-off over-voltage fault occurs to the IGBT if t5>T5 and t6>T6.

7. The assembly as claimed in claim 6, wherein T], T2, T3.1, T3.2, T4, T5, and T6 are 160ns, 800ns, 6us, 500ns, 800ns, 550ns and l^s, respectively.

8. An insulated gate bipolar transistor (IGBT) failure mode detection method, comprising: obtaining a gating signal to drive one or more series connected IGBTs; obtaining a feedback signal of each IGBT, which indicates a change of a collector-emitter voltage of the IGBT; and comparing a timing sequence of the gating signal and feedback signal of each IGBT with a reference timing sequence to determine whether the IGBT is faulted and, if the IGBT is faulted, to differentiate fault types including a gate driver fault, a failed turn-on fault, a short-circuit fault, a turn-on over-voltage fault and a turn-off over-voltage fault.

9. The method as claimed in claim 8, further comprising, if the one or more series connected IGBTs comprise a number of redundant IGBTs, isolating the faulted IGBT or IGBTs from its gate driver or their gate drivers if the number of faulted IGBTs is less than or equal to the number of redundant IGBTs.

10. The method as claimed in claim 9, further comprising shutting down the gating signals to all the IGBTs if the number of faulted IGBTs is greater than the number of redundant IGBTs.

11. The method as claimed in claim 8, wherein the step of determining whether the IGBT is faulted and differentiating the fault type comprises: comparing:

(a) an interval ti between a rising edge of a first gating signal pulse and a rising edge of a first feedback signal pulse that immediately follows the rising edge of the gating signal pulse, with a maximum turn-on ack-wait time Ti;

(b) duration t.2 of the first feedback signal pulse, with a maximum turn-on ack time T2;

(c) an interval t3 between a falling edge of the first feedback signal pulse and a rising edge of a second feedback signal pulse that immediately follows the first feedback signal pulse, with a short-circuit blanking time T3.1 and an over-voltage blanking time T3.2;

(d) duration U of the second feedback signal pulse, with a maximum over-voltage time T4;

(e) an interval t5 between a falling edge of the first gating signal pulse or a second gating signal pulse and a rising edge of a third feedback signal pulse that immediately follows the falling edge of the first or second gating signal pulse, with a maximum turn-off ack-wait time T5; and

(f) duration t6 of third feedback signal pulse, with a maximum turn-off ack time T6; and diagnosing that: a gate driver fault occurs if ti>Ti; a failed turn-on fault occurs to the IGBT if tiT2; a short-circuit fault occurs to the IGBT if tiT4; a turn-off over-voltage fault occurs to the IGBT if ts>T5 and t$>T6.

12. The method as claimed in claim 11, wherein Ti, T2, T3-1, T3-2, T4, T5, and T6 are 160ns, 800ns, 6us, 500ns, 800ns, 550ns and Ins, respectively.