IR2137 [INFINEON]

IGBT Protection in AC or BLDC Motor Drives; IGBT保护交流或直流无刷电机驱动器


型号：	IR2137
厂家：	Infineon
描述：	IGBT Protection in AC or BLDC Motor Drives IGBT保护交流或直流无刷电机驱动器驱动器电机双极性晶体管
文件：	总9页 (文件大小：89K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

International Rectifier • 233 Kansas Street, El Segundo, CA 90245 USA

IGBT Protection in AC or BLDC Motor Drives

byToshioTakahashi

The new IR2137 IGBT Gate Driver IC integrates Ground Fault and Over-Current Protection

with Soft Shutdown, thus providing a compact and comprehensive IGBT protection scheme.

1. INTRODUCTION

In the last decade, industrial AC drives have become more advanced in performance and more

compact in size. This is largely due to the rapid development of power silicon technology, including

the enhancement of IGBTs and of High Voltage Integrated Circuits. Additionally, this technological

growth has been particularly accelerated for low horsepower (< 5 Hp) AC Drives. Yet the ground fault

protection, a feature sought increasingly in motor drives of all power levels, is available widely only in

the high-end models due to the sensors and other circuitry involved. The market, however, continues

to demand a fully protected, yet inexpensive, system. To meet this demand, International Rectifier

has introduced the IR2137: a new generation 3-phase IGBT gate driver, featuring full IGBT protec-

tion and advanced soft shutdown features.

To understand traditional methods of IGBT protection, read Section 2. To understand the working of

the IR2137 skip to Section 3.

2.TRADITIONAL METHODS OF IGBT PROTECTION

2-1 Background Theory for Protecting Against Failure

One of the most common, and fatal, AC drive faults for IGBTs is the Over-Current condition. Table 1

outlines the causes for the three most common Over-Current modes.

Over-Current Mode

Potential Causes

Line-to-Line Short

Mis-wiring, Motor leads shorting, Motor phase-to-phase

insulation breaking down

Ground Fault

Motor phase-to-phase insulation breaking down

Shoot Through

False IGBT turn-on

Table 1: Potential Causes of Over-Current

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In order to protect IGBT devices effectively during an Over-Current condition, one needs to focus on

two factors.

First, one needs to detect the type of Over-Current mode and shut the system down. In both Line-to-

Line and Shoot Through mode, the short-circuit current flows from and to the DC bus capacitors

(Figures 1 and 3). Therefore, a shunt resistor in the ground path can detect these Over-Current

conditions. However in the Ground Fault mode, the current flows from the AC line input, through the

positive DC bus and high side IGBT, to the earth ground (Figure 2). Therefore, the Ground Fault

condition has to be detected either with a shunt resistor on the positive bus line or by detecting the

current in the output lines.

Second, one needs to look at the AC drive architecture.Protection circuitry needs to be built in a manner

that does not disrupt the drive system. For instance, Figure 4 shows a typical Floating Ground Refer-

ence Architecture in which the micro-controller (µC) is on the Floating Ground reference.Therefore, any

Over-Current detection circuit needs to be isolated. Alternate architecture may require reduced or no

isolation.

2-2 Traditional Methods of Over-Current Detection

Method 1

One can detect the Line-to-Line Short and Shoot Through currents by inserting a Hall Effect sensor

or a linear opto isolator across the shunt resistor. The device should be in series with the negative

DC bus line. For Ground Fault protection, an additional Hall Effect leakage current sensor could be

placed either on the AC line input or on the DC bus. The protection circuit is then implemented by

using fast comparators. The output of these comparators is ‘OR’d with the micro-controller or PWM

generator to initiate the shutdown of the gate signals.

Method 2

If located in the motor phase output, each Hall Effect sensor uses 2 comparators. This is done

because both positive and negative current polarities flow during a Line-to-Line Short condition.

Another important consideration is the total propagation delay for shutdown. The delay time associ-

ated with the optical isolators in the gate drive and the Hall Effect sensor is typically more than 2

microseconds. Therefore, regardless of protection circuitry implementation, this delay should be

added to the circuit delay, before matching it with the IGBT short circuit duration time. As shown in

Figure 4, the configuration requires 2 Hall Effect sensors and/or opto isolators in addition to the

protection circuit. The protection circuitry comprises of comparators (2), voltage references, capaci-

tors, and resistors.

Method 3

Another protection method is to use an IGBT de-saturation circuit. This discrete circuit can be con-

structed in the secondary side of the opto gate driver. (Opto isolated devices with in-built de-satura-

tion circuits can also be found in the market). This circuit detects voltage build-up across the collec-

tor and emitter while the device is fully on. If the voltage exceeds a specified limit, the associated

gate signal is shut off. A discrete circuit would require a comparator with voltage reference, a high

voltage diode, and various resistors and capacitors.

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2-3 Traditional Methods of Over-Current Shutdown

For shutting down an IGBT when an Over-Current condition is detected, a soft turn-off is preferred

because it reduces a high voltage spike across the collector and emitter of the IGBT device at fault.

Thus it provides a wider margin for the RBSOA limit during a short-circuit condition, allowing the

snubber circuit to be significantly minimized or even eliminated. When implemented in the discrete

circuit based on the floating ground reference architecture, a soft turn-off circuit can get very com-

plex. Each IGBT gate drive circuit requires an additional fast opto isolator and soft turn-off circuit with

the dedicated totem pole buffer transistors. Given circuit costs and complexities, a snubber circuit is

preferred to the discrete soft shutdown circuit. For low Hp devices, the snubber circuit can be imple-

mented with a high frequency type capacitor across the DC bus, near the IGBTs.

2-4 Problems with the Traditional Method

A. Circuit Control Problems

In a soft shutdown scheme, simultaneous shutdown of all 6 IGBTs is required to prevent a potential

false turn-on while the IGBTs are in the soft shutdown mode. If a high side IGBT is turned off softly

while the other IGBTs are in the middle of a switching transition within a PWM period, that IGBT can

unintentionally be turned back on. It is extremely difficult to synchronize simultaneous shutdown

using traditional architecture.

B. Part Count, Size, and Cost Problems

If the system requires full IGBT protection, including Ground Fault protection, and if it is based on the

floating ground reference architecture, then the gate drive and protection circuit require the following

major components (even without the soft shutdown feature):

•

6 fast opto isolators

2 fast Hall Effect sensors or fast linear opto isolators

2 comparators

4 floating 15V power supplies

Hall Effect sensors and opto isolators are relatively large and bulky, and require a lot more space

than a monolithic IC. In addition, if the system requires a soft shutdown function, 6 additional opto

isolators and 6 buffer circuits (with a provision for soft turn off capability) are required. Thus, whereas

low Hp AC drive systems are today moving toward smaller sizes, the above solutions provide neither

the simplicity nor the integration of the gate drive and protection circuitry that is needed.

The total cost, including assembly of the inverter system, is large due to the large number and

bulkiness of components. Furthermore, components such as the Hall Effect sensors are still subject

to manual assembly.

To circumvent these issues, a small, integrated IC device that is capable of performing all the above

functions is a necessity.

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IR2137: 3-PHASE GATE DRIVER WITH INTEGRATED IGBT PROTECTION

International Rectifier has now introduced the IR2137 to the AC drives market. This latest High

Voltage Integrated Circuit provides a monolithic solution to driving all six IGBT gate drivers, while

simultaneously providing full IGBT protection and soft shutdown. In contrast to the Floating Ground

Reference architecture discussed in the previous section, the IR2137 circuit enables a simple struc-

ture. The differences between the two architectures are summarized in Table 2.

Floating Ground System

Six Fast Optical Isolators

Two Hall Effect sensors and

Two comparators

IR2137 solution

IR2137

Gate Drive

IGBT Protection

IR2137 integrated function with a

shunt resistor and a comparator

Eliminated (boot strap power)

Four floating power supplies

Additional Circuits

Snubber circuit or discrete soft Eliminated by integrated soft shutdown

shutdown circuits

function

Brake IGBT drive circuit with

an optical isolator

Eliminated by integrated brake IGBT

driver circuit

Table 2: Solution Comparison of Gate Drive and IGBT Protection

For the IR2137 circuit, as shown in Figure 5, the IR2137 and a micro-controller (µC) share the same

ground potential – the negative DC bus potential. (This architecture is already the industry standard

in the micro AC inverter drive segment). Unlike its traditional counterpart, the IR2137 circuit requires

a single shunt resistor and associated comparator. With this, it can perform all modes of IGBT short

circuit protection.

Additionally, the IR2137 contains IGBT de-saturation logic in the circuit of each high-side gate drive,

as shown in figures 6 and 7. In the event of a Ground Fault condition, the DESAT pin is activated, and

the fault signal is transferred to the low side fault logic circuit. The low side fault logic then initiates the

simultaneous soft shutdown of all 6 IGBTs. When the soft shutdown signal is transferred back to the

high side, the active PMOS/NMOS transistor buffer goes into a high impedance mode and another

weak NMOS transistor becomes active to slowly drive the gate pin low. The shutdown softness can

be programmed by adding an external resistor to the SSD pin – thus allowing the user to optimize

softness for the specific gate charge of the IGBT. To eliminate the dv/dt induced false triggering of the

DESAT pin, there is a blanking filter delay of 2 microseconds at each high-side gate turn-on transi-

tion.

Figure 8 shows the oscillogram of the ground fault protection feature in the IR2137. In this measure-

ment, a size 4 IGBT, IRG4BC40KD, was used in conjunction with a turn-on resistor, Rg = 33Ω, turn-

off resistor, Rg = 16Ω, and soft turn off resistor, R_SSD= 500Ω. The top trace in Figure 8 is the IGBT

gate signal (10V/div), while the middle trace is the V_CEvoltage (100V/div), and the bottom trace is the

IGBT short circuit current (40A/div). No snubber circuit was used for this test. One can see that the

de-saturation protection activates quickly and the soft shutdown feature virtually eliminates the over-

shoot voltage across the collector and the emitter.

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For contrast, the oscillogram of a‘hard’shutdown is shown in Figure 9. The same IGBT, IRG4BC40KD,

and the same PCB pattern were used as in the example shown in Figure 8. The top trace is the IGBT

short circuit current and the bottom trace is the IGBT V voltage (100V/div). As can be seen in

Figure 9, the overshoot voltage reaches approximately 100V above the normal V voltage during

the turn-off transition.

In summary, the IR2137, a monolithic IC, provides excellent protection and soft shutdown features in

an extremely compact and cost-effective package.

Motor

Figure 1: Current Flow during Line-to-Line Short

Motor

Figure 2: Current Flow during Ground Fault

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Motor

Figure 3: Current Flow during Shoot Through Mode

M otor

O P TO

Figure 4: Overcurrent Protection in Floating Ground Reference System

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M otor

IR2137

3Phase G ate

Driver with

IGBT

DSP

protection

Figure 5: IR2137 Gate Driver with IGBT Overcurrent Protection

HO P

High Side G ate

LO P

SSD

2 us ec

Blan king

DE SAT

Desat Fault

3 50 ns ec

Filter

Soft Shutdow n

Im pedence =

500 ohm s

Figure 6: IR2137 High Side Circuit

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VB1

LATCH

HOP1

H IN 1

SOFT SHUTDOW N

DESAT

SCHMITT

TRIGGER INPUT

SHOOT

THROUGH

PREVENTION

SOFT

SHUTDOW N

D RIV ER

HIN1

LIN1

SOFT

SHUTDOW N

HON1

200nsec

D eadtim e

LEV E L

SH IFTE RS

DESAT

DETECTION

HSSD1

VS1

UV DETECT

DESAT1

VB2

LATCH

H IN 2

HOP2

HON2

SCHMITT

TRIGGER

HIN2

LIN2

SOFT

SHUTDOW N

D RIV ER

SOFT

SHUTDOW N

SOFT SHUTDOW N

200nsec

D eadtim e

LEV E L

SH IFTE RS

INPUT

SHOOT

THROUGH

PREVENTION

DESAT

DETECTION

HSSD2

VS2

DESAT

UV DETECT

DESAT2

VB3

LATCH

H IN 3

HOP3

HON3

HSSD3

VS3

SCHMITT

TRIGGER INPUT

SHOOT

THROUGH

PREVENTION

SOFT

SHUTDOW N

HIN3

LIN3

SOFT

SHUTDOW N

D RIV ER

SOFT SHUTDOW N

200nsec

D eadtim e

LEV E L

SH IFTE RS

DESAT

DETECTION

DESAT

UV DETECT

DESAT3

LOP1

D RIV ER

SOFT SHUTDOW N

LON1

LSSD1

LS1

SCHMITT

TRIGGER

LOP2

D RIV ER

LON2

LS2

SCHMITT

TRIGGER

ITRIP

LSSD2

F AUL T

LO G IC

SCHMITT

TRIGGER

FLTCLR

LOP3

LON3

D RIV ER

FAULT

VCC

LS3

LSSD3

BRIN

U V

D ETE CT

VSS

B R AK E

D RIV ER

COM

Figure 7: IR2137 Block Diagram

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Figure 8:

IR2137 Soft Shutdown

Figure 9:

Hard Shutdown

IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245 Tel: (310) 252-7105

IR EUROPEAN REGIONAL CENTRE: 439/445 Godstone Rd, Whyteleafe, Surrey CR3 0BL, United Kingdom

Tel: ++44 (0) 20 8645 8000

Data and specifications subject to change without notice. 2/28/2000

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IR2137 [INFINEON]

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