WO2020043353A1

WO2020043353A1 - Power converter with clamping diode

Info

Publication number: WO2020043353A1
Application number: PCT/EP2019/067306
Authority: WO
Inventors: Paul Mehringer; Neil Davies
Original assignee: Robert Bosch Gmbh
Priority date: 2018-08-29
Filing date: 2019-06-28
Publication date: 2020-03-05
Also published as: DE102018214579A1

Abstract

The invention relates to a power converter (11) comprising at least one power converter arrangement (12). The power converter arrangement (12) comprises an AC connection (13), at least one first transistor (14) and at least one second transistor (15). The first transistor (14) and the second transistor (15) are connected in series one after another in the power converter arrangement (12). The AC connection (13) is connected between the first transistor (14) and the second transistor (15). Known power converters with (MOSFET) transistors instead of conventional diodes have lower power losses but have only insufficient protection in the case of load shedding or in the case of voltage peaks. The invention provides a power converter (11) of the type mentioned above, characterized in that a clamping diode (22) is arranged between a gate contact (20) and the associated drain contact (21) of the first transistor (14). This achieves improved protection of the electronics system in the case of load shedding and in the case of voltage peaks.

Description

description

title

Converter with clamp diode

The present invention relates to a converter comprising at least one converter arrangement, the converter arrangement comprising one

AC connection, at least one first transistor and at least one second transistor, wherein the first transistor and the second transistor are connected in series in the converter arrangement, and wherein the AC connection is connected between the first transistor and the second transistor.

State of the art

Power converters are generally used to supply direct current systems from three-phase systems (for example the public three-phase network). These converters are usually built in a bridge circuit. As

Converter elements often serve diodes. The diodes do not require any further control circuitry, since they automatically switch to the conductive or blocking state at the right time. These 6-pulse bridge converters are also used as converters in automotive three-phase generators. These generators have a distinctive inductive one

Internal resistance. The converter has one through the diodes and one

Output current specified power loss. These losses can only be reduced insignificantly by means of circuitry measures (for example parallel connection of diodes).

A critical fault that must be considered when designing a power converter is load dump. This occurs when, with a correspondingly highly excited generator and a correspondingly high delivered current, the load on the generator suddenly decreases and not can be intercepted by capacitive elements in the vehicle electrical system (such as a battery). The generator can then continue to supply energy to the vehicle electrical system for up to 300-500 ms. This energy must be converted in the converter in order to protect electrical components that are connected to the generator from damage caused by overvoltage.

However, if the aforementioned diodes are replaced by active switches (for example MOSFET transistors) in order to significantly reduce the losses, new protection strategies have to be used in order to avoid damage to components connected to the load by load shedding. This applies to both active power converters and electronics, which allow generator and motor operation. There are solutions for 12 V for this

(.integrated starter generator '), for 48 V (boost recuperation machine) as well as higher voltage levels (> 200 V).

It is common in power converters (e.g. active inverters) in the event of a

Load shedding to set an active short circuit. This will short-circuit all currents coming from the machine. It can therefore not

damaging electricity flow more into the electrical system. For example, a capacitor connected in parallel to the vehicle electrical system is used for this purpose.

The problem with this approach is that a critical condition - in particular the presence of a load shedding - must first be recognized and then dealt with by setting an active short circuit. Control by a capacitor typically results in a dead time. Now no critical voltage threshold is allowed within this dead time

exceeded, which could damage the electronic components connected on the load side. The voltage rise occurs according to the formula:

Au / dt = 1 _c / C

Where lc is the current with which the capacitor is charged, C is the capacitance of the capacitor and Äu / dt describes the voltage rise across the capacitor. With a given capacitor, a charging current results in a detection threshold and a maximum permitted voltage threshold automatically a maximum allowed reaction time. If this response time cannot be observed, electronic components in the converter or in the vehicle electrical system can be damaged.

Now at high generator currents and / or low

Intermediate circuit components response times are required, which can no longer be solved conventionally via a circuit that is switched by means of a simple voltage threshold.

Disclosure of the invention

According to the invention, a converter of the type mentioned is used for

Provided, characterized in that a clamp diode is arranged between a gate contact and the associated drain contact of the first transistor.

Advantages of the invention

In the prior art, the voltage is usually bracketed via one or more Zener diodes which are connected in parallel to the load side and to the capacitor. This has the following disadvantages:

- The voltage level on conventional Zener diodes is difficult to set

- high power losses are concentrated in the Zener diodes,

- the Zener diodes are normally not used, but only for the rare and unusual case of load shedding,

- In the case of ordinary switching peaks, the Zener diodes may not have a clamp effect because they are inductively too far away from the generation of the switching tip, and thus there is no protection of the electronics in the entire voltage range of the circuit.

The solution according to the invention overcomes these disadvantages, since the at least one clamp diode is assigned to a single transistor. It can thus, for example, also protect the assigned transistor from switching peaks and at the same time enable a controlled short circuit with a sufficiently short reaction time in the event of a load shedding. The converter according to the invention preferably has both functionalities of a rectifier (in generator mode) and an inverter (for limiting switching peaks).

The converter can comprise a plurality of converter arrangements, which are preferably connected in parallel to one another. Each of the

Power converter arrangements can include their own AC connection. Each first transistor is then preferably provided with a clamp diode between the gate contact and the drain contact. The

Power converter arrangements preferably form a bridge circuit, the first transistors all being arranged on one side of the bridge circuit and the second transistors all being arranged on the other side of the bridge circuit.

The clamp diode preferably comprises a zener diode with a forward direction to the drain contact of the first transistor and a diode connected in series with a forward direction to the gate contact of the first transistor. The clamp diode then becomes transparent when the breakdown voltage of the zener diode is exceeded from the drain contact towards the gate contact. The breakdown voltage can be selected so that switching peaks can lead to a controlled short circuit and thus both

Surge damage caused by (rarely occurring) load shedding and switching peaks can be avoided.

It is preferred if the power converter has at least two

Includes converter arrangements that are connected in parallel, wherein the converter comprises two load connections that are connected in parallel to the at least two converter arrangements. It can do more

Power converter arrangements can be provided, for example three, four, five or more. Each first transistor preferably comprises a clamp diode between the gate contact and drain contact.

The converter preferably comprises at least one capacitor which is connected in parallel with the at least one converter arrangement. The The capacitor then serves to temporarily absorb a large part of the

Load current or the total load current in the event of a load shedding.

In a preferred embodiment, there is one between a gate contact and the associated drain contact of at least one second transistor

Bracket diode arranged. Damage caused by switching peaks can thus be avoided more effectively in the second transistor. The clamp diode can be connected to the via the AC connection of the converter arrangement

Drain contact of the second transistor may be connected.

It is preferred if the clamp diode comprises a zener diode with a forward direction to the drain contact of the second transistor and a diode connected in series with a forward direction to the gate contact of the second transistor. The clamp diode then becomes transparent when the breakdown voltage of the zener diode is exceeded from the drain contact towards the gate contact. The breakdown voltage can be selected so that switching peaks can lead to a controlled short circuit and thus both

It is preferred if at least one first transistor and / or at least one second transistor is a metal oxide semiconductor field effect transistor (MOSFET), preferably a normally blocking n-channel metal oxide semiconductor field effect transistor. All first transistors and / or all second transistors are preferably metal-oxide-semiconductor field-effect transistors, preferably normally blocking n-channel metal-oxide-semiconductor field-effect transistors.

When realizing a bracket function, especially in modern ones

MOSFET, it may be due to the negative temperature coefficient of the

Threshold voltage come to a so-called filament effect. In the bracket effect, the currents concentrate on individual cells of the MOSFET, which can then easily overheat. Whether this effect can occur depends on the MOSFET used, as well as on voltage, current and temperature. A so-called temperature-stable point is known from the literature here. At high currents there is better stability than at low temperatures. To reach this point faster, here are two Possibilities described to control only a part of the transistor cells (in particular the first transistor) in the bracket function and thus to artificially drive up the current.

At least one transistor preferably has a first gate contact and a second gate contact, the first gate contact being connected to all cells of the transistor and the second gate contact being connected only to some of the cells of the transistor, and where the to

corresponding transistor associated clamp diode is connected to the second gate contact. This is the first way to reach the temperature stable point faster. Only a part of the transistor cells is activated in the bracket function. Two gate connections are provided, all transistor cells (in particular all MOSFET cells) being driven across the entire area via the one gate connection. Only a selected part of the transistor cells (in particular the MOSFET cells) are controlled via the second gate contact. This second gate contact is connected to the associated clamp diode.

In a preferred embodiment, at least one transistor comprises a first cell type and a second cell type, the cell types having different doping, so that the first cell type has a lower threshold voltage than the second cell type. This is the second way to reach the temperature stable point faster. Individual transistor cells (in particular MOSFET cells) have a changed characteristic with a lower characteristic due to a changed doping

Threshold voltage compared to the rest of the transistor cells

(especially MOSFET cells). The first cell type has one

Control characteristic that begins to become conductive even at low gate voltages. The second cell type follows a different control characteristic. Here, a higher gate voltage is necessary in the lower area of the control characteristic in order to achieve a current flow. If a first (or second) transistor is now operated with a clamp diode according to the invention, the gate voltage is kept at a low level. This only controls the first cell type and increases the current density in these cells to such an extent that the transistor (in particular the MOSFET) operates above the temperature-stable point. At least one clamp diode is preferably integrated in the corresponding transistor.

Advantageous developments of the invention are specified in the subclaims and described in the description.

drawings

Exemplary embodiments of the invention are explained in more detail with reference to the drawings and the following description. Show it:

1 shows a converter of the prior art,

Figure 2 shows a first embodiment of a converter according to the invention, and

Figure 3 shows a second embodiment of a converter according to the invention. Embodiments of the invention

1 shows a power converter 1 of the prior art. The converter 1 here comprises five converter arrangements 2. Each

Converter arrangement 2 comprises an alternating current connection 3, a first transistor 4 and a second transistor 5. The first transistor 4 and the second transistor 5 are in the converter arrangement 2

connected in series. The AC connection 3 is connected between the first transistor 4 and the second transistor 5.

The converter 1 comprises a capacitor 6 which is parallel to the

Converter arrangements 2 is switched. The converter 1 comprises two load connections 7 which are connected in parallel to the converter arrangements 2. An electrical system load 8 is connected to the load connections 7 and is supplied with power by a generator 9 via the converter 1. A zener diode 10 is connected in parallel to the converter arrangements 2. This solution has the following disadvantages:

- The voltage level on the conventional Zener diode 10 is difficult to set

a high power loss is concentrated in the zener diode 10,

the Zener diode 10 is normally not used, but only for the rare and unusual case of load shedding,

- In the case of ordinary switching spikes, the zener diode 10 may not have a clamp effect because it is inductively too far away from the generation of the switching tip, and thus protects the electronics

(in particular in the on-board electrical system 8) in the entire voltage range of the converter 1 that does not occur.

In Figure 2 is a first embodiment of an inventive

Power converter 11 shown. The converter 11 comprises five

Converter arrangements 12. Each converter arrangement 12 comprises an AC connection 13, a first transistor 14 and a second transistor 15. The first transistor 14 and the second transistor 15 are connected in series in the converter arrangement 12. The

AC connection 13 is connected between the first transistor 14 and the second transistor 15.

The converter 11 comprises a capacitor 16, which is parallel to the

Converter assemblies 12 is connected. The converter 11 comprises two load connections 17 which are connected in parallel with the converter arrangements 12. A vehicle electrical system load 18 is connected to the load connections 17 and is supplied with power by a generator 19 via the converter 11.

A clamp diode 22 is arranged between a gate contact 20 and the associated drain contact 21 of the first transistor 14. Each first transistor 14 is preferably provided with a clamp diode 22 between the respective gate contact 20 and the respective drain contact 21.

The clamp diode 22 here comprises a zener diode 23 with a forward direction to the drain contact 21 of the first transistor 14 and a diode 24 connected in series with a forward direction to the gate contact 20 of the first transistor 14. The clamp diode 22 is then when the Breakdown voltage of the Zener diode 23 from the drain contact 21 in the direction of the gate contact 20 is permeable.

In Figure 3 is a second embodiment of an inventive

Power converter 11 shown. The same reference numerals designate the same

Elements for the first embodiment. All of the first

Embodiment of Figure 2 features disclosed also apply to the second embodiment.

In addition, a clamp diode 25 is also arranged here between a gate contact 20 and the associated drain contact 21 of the second transistor 15. In this way, damage in the second transistor 16 caused by switching peaks and load shedding can be avoided more effectively.

Here too, the clamp diode 25 also includes a zener diode 26

Forward direction to the drain contact 21 of the second transistor 15 and a diode 27 connected in series with the forward direction to the gate contact 20 of the second transistor 16. The clamp diode 25 is then from the drain contact 21 in the direction of the gate when the breakdown voltage of the Zener diode 26 is exceeded -Contact 20 permeable.

Both the first transistors 14 and the second transistors 15 are metal-oxide-semiconductor field-effect transistors in both embodiments

(MOSFET), in particular normally blocking n-channel metal-oxide-semiconductor field-effect transistors.

At least one transistor 14, 15 has a first gate contact 20 and a second gate contact 20, the first gate contact 20 being connected to all cells of the transistor 14, 15, and the second gate contact 20 being only part of the cells of the transistor 14, 15 is connected. The clamp diode 22, 25 belonging to the corresponding transistor 14, 15 is then connected to the second gate contact 20. This is the first way to reach a temperature stable point of the transistor faster. Only a part of the transistor cells is activated in the bracket function. Alternatively or additionally, at least one transistor 14, 15 comprises a first cell type and a second cell type, the cell types being one

have different doping, so that the first cell type has a lower threshold voltage than the second cell type. This is the second way to reach the temperature stable point faster. Separate

Transistor cells (in particular MOSFET cells) have a changed characteristic with a lower characteristic due to a changed doping

Threshold voltage compared to the rest of the transistor cells

(especially MOSFET cells).

Claims

Expectations

1. converter (11) comprising at least one converter arrangement (12), the converter arrangement (12) comprising:

- an AC connection (13),

- At least a first transistor (14), and

- at least one second transistor (15),

wherein the first transistor (14) and the second transistor (15) in the

Converter arrangement (12) are connected in series, and

the AC connection (13) being connected between the first transistor (14) and the second transistor (15),

characterized in that

a clamp diode (22) is arranged between a gate contact (20) and the associated drain contact (21) of the first transistor (14).

2. Power converter (11) according to claim 1, wherein the clamp diode (22)

Zener diode (23) with the forward direction to the drain contact (21) of the first transistor (14) and a series-connected diode (24) with the forward direction to the gate contact (20) of the first transistor (14).

3. converter (11) according to claim 1 or 2, wherein the converter (11)

comprises at least two converter arrangements (12) which

are connected in parallel, the converter (11) comprising two load connections (17) which are connected in parallel to the at least two converter arrangements (12).

4. The converter (11) according to claim 3, wherein the converter (11) comprises at least one capacitor (16) which is connected in parallel with the at least one converter arrangement (12).

5. Power converter (11) according to one of the preceding claims, wherein a clamp diode (25) is arranged between a gate contact (20) and the associated drain contact (21) of at least one second transistor (15).

6. converter (11) according to claim 5, wherein the clamp diode (25)

Zener diode (26) with the forward direction to the drain contact (21) of the second transistor (15) and a series-connected diode (27) with the forward direction to the gate contact (20) of the second transistor (15).

7. converter (11) according to any one of the preceding claims, wherein

at least one first transistor (14) and / or at least one second transistor (15) is a metal oxide semiconductor field effect transistor, preferably a normally blocking n-channel metal oxide semiconductor field effect transistor.

8. converter (11) according to any one of the preceding claims, wherein

at least one transistor (14, 15) has a first gate contact (20) and a second gate contact (20), the first gate contact (20) being connected to all cells of the transistor (14, 15), and wherein the second gate contact (20) is only connected to a part of the cells of the transistor (14, 15), and wherein the clamp diode (22, 25) belonging to the corresponding transistor (14, 15) is connected to the second gate contact ( 20) is connected.

9. converter (11) according to any one of the preceding claims, wherein

at least one transistor (14, 15) comprises a first cell type and a second cell type, the cell types having different doping, so that the first cell type has a lower threshold voltage than the second cell type.

10. converter (11) according to any one of the preceding claims, wherein

at least one clamp diode (22, 25) is integrated in the corresponding transistor (14, 15).