CIRCUIT ARRANGEMENT FOR SWITCHING SWITCHES

Description

[0001] The present invention relates to a circuit arrangement for switching a switching element, comprising a control circuit which is configured to provide a variable pre-control voltage dependent on the switching state of the switching element. State of the art

[0002] Transistors such as IGBTs or other semiconductor switching elements are usually controlled with fixed voltages. This means in particular that a first voltage is applied to the gate terminal of a switching element to turn the switching element on, and a second voltage is applied to the gate terminal of the switching element to turn it off. As long as the switching state is not to change, the respective first or second voltage remains applied to the gate terminal. With a unipolar supply voltage, for example, 0 V is applied to the gate terminal to block or turn off a transistor, and +15 V is applied to turn on or turn on a transistor. With a bipolar supply, a negative voltage, e.g. -8 V or -15 V, is used, or in particular applied to the gate terminal to block the transistor, and +15 V to turn it on. The voltages are usually determined by external variables such asthe effective emitter inductance and the respective threshold voltage of the switching element.

[0003] Switching losses occur when switching elements are switched, particularly in the intermediate state between an on state and an off state, or vice versa. In particular, this reduces the performance of a circuit due to the heat generated and the reduced amount of energy available to the electrical load. This heat can also lead to faster aging of the switching elements, which may result in a shorter maintenance cycle for the devices in which they are used.

[0004] It is therefore an object of the invention to reduce the switching losses when switching the switching elements and to increase the economic efficiency.

[0005] Circuit arrangements for switching a switching element are known from the documents WO 2007 / 137268 A2, EP 2 632 048 A1 and US 2014 / 285241 A1. Disclosure of the invention

[0006] According to a first aspect, a circuit arrangement is proposed which has a drive circuit and a switching element, in particular a semiconductor component. The circuit arrangement is configured to switch between a first and a second switching state of the switching element. The drive circuit is configured to provide a variable pre-drive voltage dependent on the switching state of the switching element, wherein the pre-drive voltage is a voltage which is applied as a drive voltage to the control terminal of the switching element during one of the two switching states, and wherein the drive circuit is configured to vary the pre-drive voltage during a switching state without the switching state changing in the process, in particular from the first to the second switching state or vice versa.

[0007] In this disclosure, the term "phase" is used for the period of time during which the transistor is in a switching state, i.e., conducting or blocking. These phases are always interrupted when switching between intermediate states, which lie temporally between the on state and the off state, or vice versa. The pre-drive voltage is a voltage that can be used as a drive voltage, e.g., within one of the two phases. If it is used to turn the transistor on, this specific drive voltage is referred to herein as the on-drive voltage. If it is used to turn the transistor off, this specific drive voltage is referred to herein as the reverse drive voltage. The variable pre-drive voltage can, for example, be increased from a first voltage value to a second voltage value, or vice versa.Thus, the variability of the pre-control voltage, for example, refers to two voltage values ​​in two stages, but it can also be designed in three stages, multiple stages, or continuously variable. With increasing variability, the adjustment of the pre-control voltage to specific operating points of the switching element can be optimized, especially to minimize switching losses. Furthermore, the terms "semiconductor" and "semiconductor component" are used interchangeably.

[0008] The drive voltage applied to a control terminal of a switching element is, for example, the gate-emitter voltage of a transistor. The pre-drive voltage can be, for example, a reverse drive voltage which, when connected as a drive voltage, turns off the transistor. As long as the transistor is conductive, it is separated from the transistor and has no active function. During this conductive phase, a second, sufficiently positive pre-drive voltage, the on-drive voltage, is applied to the gate input. Switching losses can be reduced by introducing a pre-drive voltage which, for example, provides a reverse drive voltage. The reverse drive voltage is usually a non-positive voltage or a voltage below a switching threshold at the gate control input of the switching element, such as a transistor. It is only applied to the control terminal of a switching element when the switching element is supposed to turn off.Since the reverse drive voltage is separated from the control terminal of the switching element in the conducting phase, it can be conditioned or varied and preset in this phase, ie, it can be set a priori to reduce the switching loss when switching or switching to the reverse phase.

[0009] According to one embodiment, the control circuit is configured to change the pre-control voltage during the first switching state of the switching element, e.g. to reduce it, and to change the pre-control voltage during the second switching state of the switching element, e.g. to increase it. The first switching state can be a state in which the switching element is conductive. The second switching state can then be a state in which the switching element is blocking. If the switching element is conductive, for example, the blocking control voltage, which is not present at the control terminal of the switching element or gate control input during this phase, is reduced to ensure optimal turn-off of the transistor. While the switching element is blocking, the blocking control voltage, which is present at the control terminal of the switching element during this phase, is increased to ensure optimal turn-on. In this case, the blocking control voltage is conditioned.

[0010] To condition the conducting drive voltage, the conducting drive voltage is lowered during the conducting phase, in which it is applied to the control terminal of the switching element, to ensure optimal turn-off of the transistor. While the switching element is off, the conducting drive voltage, which is not applied to the control terminal of the switching element during this phase, is raised to enable optimal conduction.

[0011] According to one embodiment, the drive circuit is configured to reduce the pre-drive voltage from a first value to a second value during the first switching state of the switching element, and to increase the pre-drive voltage from the second value to the first value during the second switching state of the switching element. If the pre-drive voltage is a reverse drive voltage for blocking the switching element, the first value of the reverse drive voltage V_offa and the second value of the reverse drive voltage V_offb are in a range between V_th and V_min, for example, -20 V, where V_th is higher than or equal to V_offa, and V_offa is higher than V_offb. V_th is the switching threshold of the switching element, above which the switching element becomes conductive. V_min is the minimum permissible drive voltage of the switching element.If the pre-drive voltage is a conducting drive voltage for turning on the switching element, the first value of the conducting drive voltage V_ona and the second value of the reverse drive voltage V_onb are in a range between V_max and V_th, where V_max is higher than or equal to V_ona, and V_ona is higher than V_onb. V_max is the maximum allowable drive voltage of the switching element.

[0012] For example, the first value of the reverse drive voltage V_offa = 0 V and the second value of the reverse drive voltage V_offb = -8 V. During the second state, the off-state switching state of the switching element, the control circuit switches the reverse drive voltage from -8 V to 0 V in order to condition the switching to the on-state with a drive voltage V_ona, e.g., +15 V. By switching the drive voltage from 0 V to V_ona instead of from -8 V to V_ona, the switching loss is significantly reduced. Depending on the switching element or semiconductor type, the reverse drive voltage can also assume low positive values. For example, the voltage V_offa can be +1 V, at which the switching element continues to be off. In general, the value V_th, at which the switching element still blocks, can be found in the data sheet of the switching element. Another typical value for V_offb is -15 V, for example.A typical reverse drive voltage range can be specified as V_th > reverse voltage > V_min, for example -20 V.

[0013] The change in the variable pre-control voltage values ​​can also occur in several intermediate steps. The transition from one pre-control voltage value to another can be step-like, ramp-like, or curved within the physical limits.

[0014] According to a further embodiment, the control circuit comprises a switch configured to change the blocking control voltage from, for example, V_offa to V_offb, or vice versa, and to change the conducting control voltage from, for example, V_onb to V_ona, or vice versa. Switches are preferably understood here to be electronic switches, such as transistors. An electronic switch can also comprise an arrangement with multiple electronic components, e.g., a current source.

[0015] According to one embodiment, the control circuit is configured to switch the blocking drive voltage to V_offb, e.g., -8 or -15 V, during the conducting phase, in particular shortly after entering the conducting phase. Thus, the switching element is immediately ready for a conditioned switching into the blocking phase.

[0016] According to one embodiment, the control circuit is configured to switch the blocking control voltage to V_offa, e.g., 0 V, during the blocking phase, in particular shortly before entering the conducting phase. Thus, the switching element is reliably blocked at, e.g., -8 V or -15 V for a large part of the blocking phase.

[0017] The timing of the conduction drive voltage can also be selected accordingly. The preconditioning switching operations can also take place at other times during a conducting or blocking phase of the switching element.

[0018] According to another embodiment, the switching element or semiconductor component is a power transistor. For example, it is an IGBT (Insulated Gate Bipolar Transistor) or a FET (Field Effect Transistor), such as a MOSFET (Metal Oxide FET).

[0019] According to a second aspect, a method for controlling a switching element during operation is provided, wherein the switching element has two switching states, the different switching states being set by controlling the switching element with a control voltage. In particular, in at least one of the two switching states, a variable pre-control voltage is applied to the control terminal as the control voltage. In a first step, a first pre-control voltage and a second pre-control voltage are provided. In a second step, the second pre-control voltage is applied to a control terminal of the switching element in order to switch the switching element into a first switching state. In particular, the first pre-control voltage can be variable, and the second pre-control voltage can be variable or constant.In a third step, the first pre-drive voltage of the switching element is reduced while the switching element is in the first switching state. In a fourth step, the first pre-drive voltage is applied as a drive voltage to the control terminal of the switching element to switch the switching element to a second switching state. In a fifth step, the first pre-drive voltage is increased while the switching element is in the second switching state. In a sixth step, the second pre-drive voltage is applied as a drive voltage to the control terminal of the switching element.

[0020] According to one embodiment, the method can be applied for a variable reverse drive voltage, so that during the conduction phase, the reverse drive voltage V_off is reduced from, for example, 0 V to -15 V and in the blocking phase, when V_off is applied to the control terminal, it is increased from -15 V to 0 V. For example, the circuit arrangement for the variable reverse drive voltage has a switch in the negative branch for switching between V_offa and V_offb and, for example, a constant drive voltage V_on in the positive branch.

[0021] According to one embodiment, the method can be applied for a variable conducting drive voltage, so that during the conducting phase, the conducting drive voltage V_on is reduced from, for example, 15 V to 8 V and in the blocking phase, i.e., when V_on is not applied to the gate input, it is increased from 8 V to 15 V. For example, the circuit arrangement for the variable conducting drive voltage has a switch in the positive branch for switching between V_ona and V_onb and, for example, a constant voltage V_off in the negative branch.

[0022] According to one embodiment, both method variants can be combined. In this case, for example, a switch would be present in both the negative branch and the positive branch, so that variable drive voltages can be switched instead of the constant voltages V_on and V_off, respectively. Thus, the step of reducing the first pre-drive voltage of the switching element while the switching element is in the first switching state additionally comprises reducing the second pre-drive voltage of the switching element; and the step of increasing the first pre-drive voltage while the switching element is in the second switching state further comprises increasing the second pre-drive voltage.

[0023] According to a third aspect, an inverter is provided with a circuit arrangement for switching a switching element, comprising a drive circuit configured to provide a variable pre-drive voltage dependent on the switching state of the switching element. In particular, inverters used for high power outputs, such as in electric vehicles, have switching elements such as IGBTs, which switch high currents in the kHz range, for example. The switching losses occurring here can be reduced by approximately 10% by the circuit arrangement proposed here. Typically, an inverter has a plurality of switching elements or semiconductors, such as IGBTs, depending on the architecture and application.Inverters are DC-DC converters, AC-DC converters and DC / AC converters that are switched in a clocked manner in combination with windings or coils in order to convert the voltage level and / or the frequency.

[0024] According to a fourth aspect, a vehicle is provided with an inverter having a circuit arrangement for switching a switching element with a drive circuit configured to provide a variable pre-drive voltage dependent on a first or second switching state of the switching element. These are used, for example, to provide energy for an electric machine or to charge batteries for driving the vehicle. Electric vehicles can be motor vehicles, trucks, electric boats, aircraft, trains, work machines, etc.

[0025] Further measures improving the invention are presented in more detail below together with the description of the preferred embodiments of the invention with reference to figures. Examples of implementation

[0026] It shows: Fig. 1 a basic circuit arrangement for controlling a switching element according to an embodiment, Fig. 2 a diagram of the control voltage in the switching and control phases according to an embodiment, Fig. 2a, 2b, 2c, 2d Switch positions for the control voltage in the switching and control phases according to an embodiment, Fig. 3 a diagram of the control voltage in the switching and control phases according to another embodiment, Fig. 3a, 3b, 3c, 3d Switch positions for the control voltage in the switching and control phases according to another embodiment, Fig. 4 a flowchart of a method according to an embodiment, Fig. 5 a vehicle with an inverter according to an embodiment.

[0027] Fig. 1 shows a basic circuit arrangement 100 for controlling a switching element 101, with a control circuit 104. The Fig. 1 The controllable switching element 101 shown may, for example, be a field-effect transistor (FET) or a variant thereof, an IGBT or another transistor or high-power transistor type. Fig. 1 serves merely to clarify the functioning of the circuit arrangement 100 and in particular of the arrangement 104. In a real circuit, the battery voltage V_Batt would, for example, not be connected to ground, but to a consumer via a protective circuit.

[0028] Fig. 1 shows a simple principle from which it can be seen that three voltage levels can be switched using the two switches 103 and 102. Switch 103 is used to switch the states of the switching element (V_on, V_off), while switch 102 conditions or selects the reverse drive voltage (V_offa, V_offb), thus enabling a variable reverse drive voltage. The same arrangement could be used to condition, for example, the conducting drive voltage (V_ona, V_onb) with switch 102 and to set the switching state of the switching element 101 between V_on and a constant voltage V_off with switch 102.

[0029] Fig. 2 shows, by way of example, a curve of a control voltage V_T or gate-emitter voltage applied to the control terminal at switch 103 and the curve of the blocking voltage V_off at switch 102. Figuren 2a bis 2d show the phases of the voltage curve in Fig. 2 The switch positions of the switch arrangements correspond. For easier assignment of the switch arrangements of the Figuren 2a bis 2d to the phases of the voltage curve in Fig. 2 The voltage transitions are idealized as voltage jumps in the middle of a state phase. In this example, V_on is 15 V, V_offa is 0 V, and V_offb is -8 V. As already mentioned, the voltages can also assume other values.

[0030] Starting with the management phase in Fig. 2 and the switch arrangement according to Fig. 2a When switch 103 is in the up position, switch 102 is also initially switched up, so that V_offa = 0 volts is initially tapped at switch 102. This switch position of switch 102 is the switch position from the previous phase. Now, the current conducting phase is divided into two half-phases. In the second half-phase, switch 102 is switched down, so that V_offb = -8 V could be tapped or is present at the switch output. As soon as switch 103 is switched to the off-state phase, this voltage V_offb is applied as the control voltage V_T to the control terminal of switching element 101. Thus, in the conducting phase, the blocking control voltage, i.e., the voltage with which transistor 101 is switched off, is set or conditioned so that switching element 101 reliably blocks when switch 103 is switched. According to Fig. 2c then both switches 102, 103 are set down.

[0031] Now the blocking phase is also divided into two half-phases. In the second half-phase, switch 102 is Fig. 2d upwards, so that the blocking control voltage V_offa = 0 volts is applied to the control terminal of the switching element 101. This causes the switching losses when switching to the conducting phase, i.e. corresponding to the conducting phase in Fig. 2a , which is initiated by switching the positive voltage through switch 103, can be reduced compared to a voltage jump from -8 V to +15 V at the gate input.

[0032] Switches 102 and 103 can preferably be implemented electronically and controlled, for example, by a microcontroller. The pre-control can be implemented, for example, by current sources or switchable potentials.

[0033] The diagram in Fig. 3 , and the switching arrangements 3a to 3d with the corresponding switch positions show an example in which the control voltage for both V_on and V_off is variably set. The circuit arrangement now has a switch 104 in the positive branch, which can switch between V_ona = +15 V and V_onb = + 8 V. The switching of the voltages V_offa and V_offb with the resulting voltage V_off in Fig. 3 is carried out in the same way as i n Fig. 2a bis 2d In the conducting phase, the blocking phase is prepared by switching V_ona to V_onb, so that the control voltage V_T at the control terminal is now switched from 8 V to -8 V instead of +15 V. In the blocking phase, the control voltage V_T is switched back to 15 V, allowing a safe and rapid transition to the conducting state. It should be noted again that the specified voltage values ​​are only examples.

[0034] Fig. 4 shows a flowchart of a method according to an embodiment for controlling a switching element 101 during operation in which the switching element has a conducting and a blocking phase. In a first step 401, a reverse control voltage of 0 V is provided. In the next step 402, the switching element 101 is switched to a conducting phase with an active positive control voltage. Thus, the voltage at the control terminal, e.g., the gate voltage, merely jumps from 0 V to the positive voltage for switching the switching element 101, which can be e.g., 15 volts. In step 403, the provided reverse control voltage of the switching element is reduced during the conducting phase of the switching element. In this phase, the reverse control voltage is not present at the control terminal. The reduction serves for adjustment or conditioning, i.e., the preparation of the next switching phase of the switching element 101.In step 404, the provided, reduced blocking control voltage is applied to the control terminal as an active drive voltage to switch the switching element 101 into a blocking state. Since the voltage is well in the negative range, e.g., -8 V or -15 V, the switching element blocks optimally. In the next step 405, preparation for the next conducting phase of the switching element 101 takes place by raising the provided blocking control voltage, which at this point in time is still present at the control terminal as an active drive voltage, to 0 V. In step 406, a positive voltage is then applied to the control terminal as an active drive voltage, so that the switching element 101 switches to the conducting phase with less loss.

[0035] Step 403 may additionally comprise decreasing the second pre-drive voltage of switching element 101, and step 405 may further comprise increasing the second pre-drive voltage. Changing the two pre-drive voltages within a step may occur at different times within the state phase, i.e., during a switching state.

[0036] Fig. 5 shows a vehicle 500 with an inverter 501 according to an embodiment, which may have a circuit arrangement described above for controlling a switching element 101.

[0037] By conditioning the reverse drive voltage during the off-state phase of the switching element 101, the losses when switching to the conducting state are reduced, and on the other hand, by conditioning the reverse drive voltage during the conducting phase, it is ensured that the switching element 101 is switched to a safe off-state.

Claims

1. Circuit arrangement (100), having an actuation circuit (104) and a switching element (101), wherein the circuit arrangement (100) is designed to switch over between a first and a second switching state of the switching element (101); wherein the actuation circuit (104) is designed to provide a variable pre-actuation voltage that is dependent on the switching state of the switching element (101), wherein the pre-actuation voltage is a voltage that is applied to the control connection of the switching element (101) as the actuation voltage during one of the two switching states, and wherein the actuation circuit (104) is also designed to vary the pre-actuation voltage during a switching state without the switching state changing, wherein the first switching state is a state in which the switching element (101) is turned on and the second switching state is a state in which the switching element (101) is turned off; wherein the pre-actuation voltage is a turn-off actuation voltage V_off that is used to turn off the switching element (101) and that is disconnected from the control connection of the switching element as long as the switching element is turned on, and wherein the actuation circuit (104) is furthermore designed to change the turn-off actuation voltage V_off during the first switching state of the switching element (101), and to change the turn-off actuation voltage V_off during the second switching state of the switching element (101), wherein the actuation circuit (104) is furthermore designed to reduce the pre-actuation voltage from a first value to a second value during the first switching state of the switching element (101), and to increase the pre-actuation voltage from the second value to the first value during the second switching state of the switching element (101).

2. Circuit arrangement (100) according to Claim 1, wherein a first value of the turn-off actuation voltage V_offa and a second value of the turn-off actuation voltage V_offb are in a range between V_th and V_min, V_th is higher than or equal to V_offa and V_offa is higher than V_offb, wherein V_th is the switching threshold value of the switching element (101) and V_min is the minimum permissible actuation voltage of the switching element.

3. Circuit arrangement according to either of the preceding claims, wherein the actuation circuit (104) has a switch (102) that is designed to switch the turn-off actuation voltage over, in particular from a first value to a second value.

4. Circuit arrangement (100) according to one of the preceding claims, wherein the switching element (101) is a power transistor.

5. Use of the circuit arrangement (100) according to one of the preceding claims for reducing switching losses of a switching element (101).

6. Method for actuating a switching element (101) during operation, wherein the switching element has two switching states, wherein the different switching states are set by actuating the switching element with an actuation voltage, having the steps: providing (401) a first pre-actuation voltage and a second pre-actuation voltage; applying (402) the second pre-actuation voltage to a control connection of the switching element as the actuation voltage so as to switch the switching element (101) to a first switching state; reducing (403) the first pre-actuation voltage of the switching element (101) while the switching element (101) is in the first switching state, wherein the first pre-actuation voltage is disconnected from the control connection of the switching element; applying (404) the first pre-actuation voltage to the control connection of the switching element as the actuation voltage so as to switch the switching element (101) to a second switching state; increasing (405) the first pre-actuation voltage while the switching element (101) is in the second switching state; applying (406) the second pre-actuation voltage to the control connection of the switching element as the actuation voltage.

7. Method according to Claim 6, wherein the step of reducing (403) the first pre-actuation voltage of the switching element (101) while the switching element (101) is in the first switching state additionally includes reducing the second pre-actuation voltage of the switching element (101); and wherein the step of increasing (405) the first pre-actuation voltage while the switching element (101) is in the second switching state also includes increasing the second pre-actuation voltage.

8. Inverter (501) comprising a circuit arrangement (100) for switching a switching element (101) according to one of Claims 1 to 4.

9. Vehicle (500) comprising an inverter (501) that has a circuit arrangement (100) for switching a switching element (101) according to one of Claims 1 to 4.