VEHICLE

The present invention relates to a switch driver system, as well as a switch leg, an inverter, an electric drive and a vehicle comprising such a switch driver system.

The European patent application EP 3 457 553 A1 describes an inverter comprising switching elements. Each switching element is driven by a driver unit having one terminal connected to a gate of the switching element through two electrical connections respectively dedicated to close and open the switching element.

An object of the invention is to provide means for driving a switching element.

The object of the invention is solved by means of a switch driver system comprising: two auxiliary switches connected to each other at a middle point intended to be connected to a control terminal of a main switch, the auxiliary switches having respective control terminals, called auxiliary control terminals; first and second resistances respectively connected to the two auxiliary control terminals; a driver having first and second terminals respectively connected to the first and second resistances, the driver being configured to selectively: provide, at its first terminal, a current flowing through the first resistance to at least one of the auxiliary control terminals, and drain, at its second terminal, a current from at least one of the auxiliary control terminals through the second resistance; a capacitance connected to the second terminal of the driver so as to provide a current to the second terminal when current is drained at the second terminal; and a third resistance connected between the first terminal of the driver and the capacitance so that the capacitance is charged through the third resistance when current is provided at the first terminal.

The two auxiliary switches may form a booster stage allowing to drive the main switch.

In some situations, a very high voltage may be applied to the main switch. For example, the main switch may be one of the two main switches of a switch leg, and the other switch of the switch leg may become damaged or destroyed and may act as a short circuit, so that the high voltage applied to the switch leg is then applied to the remaining main switch. In this case, the remaining main switch should be turned off in order to avoid a high current flowing through it, as a result from the high voltage. Indeed, this high current could damage or destroy the remaining main switch.

The turning off of the main switch should not be too fast in order to limit the overvoltage on the main switch. In order to obtain a slow turn off, usually called “soft turn off”, the driver may drain a low current at its second terminal. In particular, the drained current may be lower than during a normal turn-off. The soft turn off with a low current could work if the driver would be directly connected to the gate of the main switch. When using auxiliary bipolar switches, the current could still be too high and turn on these switches directly and therefore no soft turn off of the main switch could be achieved.

Thanks to the current provided by the capacitance, the current flowing from the auxiliary control terminals is lower than the current drained by the driver, thereby decreasing the risk for the main switch.

During normal switch on, a part of the current coming from the first terminal of the driver may be used to charge the capacitance, and thus not used to switch the auxiliary switches so that the switching time of the main switch could be long. Thanks to the third resistance through which the capacitance is charged, a fast charge of the capacitance may be achieved, at least faster than through the first and second resistances, so that the presence of the capacitance does not substantially increase the switching time and therefore does not substantially increase the switching losses in the main switch resulting from the switching time.

Preferably, the first and second resistances are each connected to both the auxiliary control terminals.

Preferably, the driver may be further configured to selectively provide a voltage at its second terminal so that a current flows to this second terminal from at least one of the control terminals of the auxiliary switches through the second resistance.

The driver may therefore carry out a normal turn-off through the second resistance, which may be of different value than the first resistance used for turn-on.

Also preferably, the switch driver system may comprise a diode connected between the control terminals of the auxiliary switches and the third resistance so as to prevent current from flowing from the control terminals of the auxiliary switches to the second terminal of the driver through the third resistance when the second terminal of the driver is connected to the electrical ground.

The diode may therefore ensure that the second resistance is used for normal turn off, instead, in particular, the first resistance.

Also preferably, the switch driver system may comprise a fourth resistance connected between the capacitance and the second terminal of the driver.

The fourth resistance may allow to control the discharge of the capacitance.

Also preferably, the third resistance is connected at a middle point between the capacitance and the fourth resistance.

The third resistance may allow to control the charge of the capacitance, while bypassing the fourth resistance.

Also preferably, at least one of the auxiliary switches comprises a bipolar transistor.

The invention also relates to a switch system comprising a main switch and a switch driver system according to the invention, for driving the main switch.

Preferably, the main switch comprises one amongst: a MOSFET and an IGBT.

The invention also relates to a switch leg comprising a high side controllable switch and a low side controllable switch connected to each other at a middle point and, for at least one of the high side and low side controllable switches, a switch system according to the invention, wherein the main switch of the switch system is the controllable switch.

The invention also relates to an inverter comprising input terminals, output terminals, at least one switch leg according to the invention, wherein the high side and low side controllable switches are connected to the input terminals and to the output terminals, and a control device configured to control the high side and low side controllable switches such that the high side and low side controllable switches convert a DC voltage present at the input terminals into an AC voltage to be present at the output terminals. The invention also relates to an electric drive comprising an inverter according to the invention and an electric motor driven by the inverter.

The invention also relates to a vehicle comprising wheels and an electric drive according to the invention for driving, at least indirectly, at least one of the wheels.

The present invention will be described more specifically with reference to the accompanying drawings, in which:

Figure 1 is a schematic view showing an embodiment of an automotive vehicle comprising an inverter according to the invention,

Figure 2 is an electric diagram of an embodiment of a switch driver system according to the invention, for driving a controllable switch of the inverter of figure 1 ,

Figure 3 is similar to figure 2, further illustrating current flow during a normal turn-on of the controllable switch,

Figure 4 is similar to figure 2, further illustrating current flow during a normal turn-off of the controllable switch, and

Figure 5 is similar to figure 2, further illustrating current flow during a soft turn-off of the controllable switch.

Referring to figure 1 , a vehicle 100 according to the invention will now be described. In the described example, the vehicle 100 is an automotive vehicle.

The vehicle 100 comprises wheels 102 and an electric drive 104 configured to drive at least one of the wheels 102 at least indirectly. The vehicle 100 further comprises a DC voltage source 106, such as a battery, for electrically powering the electric drive 104. The DC voltage source 106 is configured to provide a DC voltage E.

The electric drive 104 comprises an electric motor 108 and an inverter 110 configured to drive the electric motor 108, for instance by supplying electric power. For example, the electric motor 108 is a rotary electric motor comprising stator phases. In the described example, the electric motor 108 is a three-phase electric motor comprising three stator phases.

The inverter 110 comprises input terminals IT+, IT- connected to the DC voltage source 106 so that the DC voltage E is present at the input terminals IT+, IT-. More precisely, the input terminals IT+, IT- include a positive input terminal IT+ connected to a positive terminal of the DC voltage source 106 and a negative input terminal IT- connected to a negative terminal of the DC voltage source 106 and to an electrical ground GND.

The inverter 110 further comprises output terminals OT connected to the electric motor 108. An AC voltage is intended to be present at the output terminals OT for powering the electric motor 108. The AC voltage may be a single or a multiphase AC voltage. In the described example where the electric motor 108 is a three-phase electric motor, the AC voltage is a three-phase AC voltage.

The inverter 110 further comprises controllable switches Q, Q\ called main switches, connected to the input terminals IT+, IT- and to the output terminals OT. The main switches Q, Q’ may be semi-conductor switches comprising for example transistors. Each main switch Q, Q’ comprises for example one amongst: a Metal Oxide Semiconductor Field Effect Transistor (MOSFET), an Insulated Gate Bipolar Transistor (IGBT) and a Silicon Carbide MOSFET (SiC MOSFET).

In the described example, the inverter 110 comprises switch legs 114I- ₃ respectively associated to the stator phases of the electric motor 108. Each switch leg 114I- ₃ comprises a high side (HS) main switch Q’ connected to the positive input terminal IT+ and a low side (LS) main switch Q connected to the negative input terminal IT-. The HS main switch Q’ and the LS main switch Q are connected to each other at a middle point connected to the output terminal OT connected to the associated stator phase of the electric motor 108.

Each switch leg 114I- ₃ is intended to be controlled to commute between two configurations. In the first one, called high side (HS) configuration, the HS main switch Q’ is closed (on) and the LS main switch Q is open (off) so that the DC voltage E is essentially applied to the associated stator phase. In the second one, called low side (LS) configuration, the HS main switch Q’ is open (off) and the LS main switch Q is closed (on) so that a zero voltage is essentially applied to the associated stator phase.

The inverter 110 further comprises a control device 116 configured to control the main switches Q, Q’ such that the main switches Q, Q’ convert the DC voltage E into the AC voltage. In the described example, the control device 116 is configured to commute each switch leg 114 between the two configurations mentioned above. Referring to figure 2, an example of switch driver system 200 for driving the LS main switch Q of one of the switch legs 114 _I-3 will now be described in more detail.

Generally, the main switch Q comprises a control terminal G, called hereinafter main control terminal, and two current passing terminals C, E. The state of the main switch Q is defined by a control voltage VGE present at the main control terminal G relative to the current passing terminal E. The main switch Q is then controlled by modifying the control voltage VGE. In the described example, when the control voltage VGE is zero or negative, the main switch Q is open (off) so as to prevent current from flowing between the two current passing terminal C, E and, when the control voltage VGE is positive (e.g. higher than a threshold), the main switch Q is closed (on) so as to allow current to flow between the two current passing terminals C, E.

In the described example, the main switch Q is an IGBT comprising a gate, a collector and an emitter respectively forming the main control terminal G and the two current passing terminals C, E.

The switch driver system 200 comprises a booster stage including an auxiliary switch leg comprising two auxiliary switches q1 , q2 connected to each other at a middle point MP, this middle point MP being connected to the main control terminal G of the main switch Q. The high side auxiliary switch q1 is also connected to a supply voltage Vcc, while the low side auxiliary switch q2 is connected to the electrical ground GND.

Each auxiliary switch q1 , q2 comprises a control terminal b1 , b2, called hereinafter auxiliary control terminals b1 , b2, and two current passing terminals d , e1 and c2, e2. In the described example, the state of each auxiliary switch q1 , q2 is defined by a current present at the auxiliary control terminal b1 , b2. Each auxiliary switch q1 , q2 is then controlled by modifying this current. The two auxiliary switches q1 , q2 are connected in opposite directions and their control terminals b1 , b2 are connected together so that both auxiliary switch q1 , q2 may be controlled at the same time to switch in opposite states (one is open when the other is closed). When the auxiliary switch q1 is closed (and the auxiliary switch q2 is open), the main switch Q is closed. When the auxiliary switch q1 is open (and the auxiliary switch q2 is close), the main switch Q is open.

At least one of the auxiliary switches q1 , q2 may comprise a bipolar transistor. In the described example, both auxiliary switches q1 , q2 are bipolar transistors, so that the control terminals b1 , b2 and the current passing terminals d , e1 , c2, e2 are respectively formed by a base, an emitter and a collector of the bipolar transistor.

The switch driver system 200 further comprises resistances Ron, Roff each connected to both the auxiliary control terminals b1 , b2.

The switch driver system 200 further comprises a driver 202 having terminals Ton, Toff for respectively switching on the main switch Q (by switching on the auxiliary switch q1 and off the auxiliary switch q2) and switching off the main switch Q (by switching off the auxiliary switch q1 and on the auxiliary switch q2). To this end, the terminals Ton, Toff are respectively connected to the resistances Ron, Roff, so that they are both connected to the auxiliary control terminals b1 , b2 through respectively the resistances Ron, Roff. The driver 202 further comprises a DESAT terminal connected to the main switch Q, so as to detect a failure of the high side main switch Q’. In the described example, the DESAT terminal is connected to the collector C of the main switch Q.

The switch driver system 200 further comprises a resistance R1 connected to the terminal Toff of the driver 202, and a capacitance C1 connected between the resistance R1 and the electrical ground GND. In this manner, the capacitance C1 is connected to the terminal Toff through the resistance R1 .

The switch driver system 200 further comprises a resistance R2 connected between the terminal Ton of the driver 202 and the capacitance C1. In the described example, the resistance R2 is connected at a middle point between the capacitance C1 and the resistance R1 .

The switch driver system 200 further comprises a diode D connected between the control terminals b1 , b2 of the auxiliary switches q1 , q2 and the resistance R2.

An example of operation of the switch driver system 200 will now be described.

Referring to figure 3, for a normal turn on of the main switch Q, the driver 202 receives an ON command from the control device 116 and, in response, applies a positive voltage V at the terminal Ton, so that the terminal Ton provides, through the resistance Ron, a current Ion to the auxiliary control terminal b1 . The positive voltage V provided is for example derived from a supply voltage provided to the driver at supply pins (not shown). This current Ion closes the auxiliary switch q1 and opens the auxiliary switch q2, which in turn closes the main switch Q. A current I _d coming from the terminal Ton also charges the capacitance C1 through the resistance R2. In the absence of the resistance R2, the capacitance C1 would be charged through the resistances Ron, Roff, R1 whose sum could be very high leading to a very slow charge of the capacitance C1 . This would reduce the current Ion arriving to the auxiliary control voltage b1 , b2 so that the booster stage would open the main switch Q very slowly, thus leading to high throughput losses.

Therefore, the resistance R2 is preferably chosen much smaller (e.g. at least ten times smaller) than the sum of the resistances Ron and Roff. In the described example, the resistance R2 is chosen much smaller (e.g. at least ten times smaller) than the sum of resistances Ron, Roff and R1 .

Referring to figure 4, for a normal turn off of the main switch Q, the driver 202 receives an OFF command from the control device 116 and, in response, connects the terminal Toff to zero voltage, i.e. the electrical ground GND. The connection between terminal Toff and the electrical ground GND is a passive connection, i.e. no current is imposed by this connection. A current loff therefore flows to the terminal Ton from the auxiliary control terminal b2, through the resistance Roff. This current Ion makes the auxiliary switch q1 open and the auxiliary switch q2 close, which in turn opens the main switch Q. For example, the normal turn-off takes around 500 ns.

In other embodiments, terminal Toff could be connected to a negative voltage instead of the electrical ground GND for the normal turn off, for example when the driver 202 uses a bipolar supply instead of an unipolar supply.

Besides, the capacitance C1 discharges through the resistance R1 by providing a current I ’a flowing to the terminal Toff.

It will be appreciated that the diode D prevents current from flowing from the auxiliary control terminals b1 , b2 to the terminal Toff of the driver 202 through the resistance R2 and the resistance Ron. In this manner, the resistance Roff is used for normal turn off, instead of Roff and, in parallel to Roff, Ron, R2 and R1 if diode D were not present.

Referring to figure 5, when the driver 202 detects, through the DESAT terminal, a failure of the associated high side main switch Q’ leading for example this main switch Q’ to act as a short circuit, the driver 202 proceeds with an emergency turn-off of the main switch Q. This cannot be carry out by a normal turn-off because, with the main switch Q’ acting as a short circuit, a very high current passes through the main switch Q, the current entering the terminal Toff of the driver 202 would be too high for the main switch Q and could damage or destroy it. That is why the driver 202 uses instead a soft turn-off where the current from the auxiliary switches q1 , q2, is controlled to be less than during a normal turn-off.

To carry out the soft turn-off, the driver 202 ignores the commands coming from the control device 116 and for example carries out a current sink 502 at the terminal Toff. The current sink 502 drains a current ID at the terminal Toff. This current ID is imposed by the current sink 502. For instance, the imposed current ID is constant. For example, the current sink 502 comprises a transistor, such as a MOSFET, connected between the terminal Toff and the ground GND and saturated at a defined low current forming the current ID-

However, some drivers could be configured to drain a current ID still too high (for example in the range 100-200 mA, for example 130 mA). This current ID could therefore damage or destroy the main switch Q, which could lead to a destruction of the associated phase of the electric motor 108.

Thanks to the capacitance C1 , the current ID comprises a current ISTO coming from the auxiliary control terminal b2 through the second resistance Roff, as well as a current l”ci provided by the capacitance C1 through the resistance R1. In this manner, the current ISTO is equal to the current ID minus the current l”ci, so that the current ISTO is less than the current ID. The current ISTO drained from the auxiliary switch q2 is less than the current ID SO that the main switch Q is not likely to be damaged or destroyed. For example, the soft turn-off takes around 1 ps (instead of around 500 ns for a normal turn-off).

The diode D also prevents current from flowing from the auxiliary control terminals b1 , b2 to the terminal Toff of the driver 202 through the resistance R2 and the resistance Ron.

A drivers system similar to the driver system 200 may be used for driving the high side main switch Q’. In this case, the connection to ground GND may be replaced by connection to the middle point of the switch leg. It will be noted that the invention is not limited to the embodiments described above. It will indeed appear to those skilled in the art that various modifications can be made to the embodiments described above, in the light of the teaching which has just been disclosed. In the previous detailed description of the invention, the terms used should not be interpreted as limiting the invention to the embodiments presented in the present description, but should be interpreted to include all the equivalents within the reach of those skilled in the art by applying their general knowledge to the implementation of the teaching which has just been disclosed.