Circuit arrangement for switching a switching element

Abstract

The present invention relates to a circuit arrangement (100) having a control circuit (104) and a switching element (101) for switching between a first switching state and a second switching state. The control circuit (104) is configured to provide a variable pre-control voltage that depends on the switching state of the switching element (101). The pre-control voltage is a voltage that is applied to the switching element (101) as a control voltage during one of the two switching states. Furthermore, the control circuit (104) is configured to change the pre-control voltage during each of the switching states.

Description

Technical Field

[0001] The invention relates to a circuit arrangement for switching a switching element, comprising a control circuit which is designed to provide a variable pilot voltage which is dependent on the switching state of the switching element. Background Art

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

[0003] Switching losses occur, in particular, when switching or switching the switching element in an intermediate state between the on and off states, or vice versa. This reduces the efficiency of the circuit due to the heat generated and the reduced energy used by the load being powered. Heat can also lead to faster aging of the switching element, which can result in shorter maintenance cycles for the equipment that uses this heat.

[0004] Therefore, the object of the present invention is to reduce the switching losses during switching of the switching element and to improve the cost-effectiveness. Summary of the Invention

[0005] According to a first aspect, a circuit arrangement is provided, comprising a control circuit and a switching element, in particular a semiconductor module. The circuit arrangement is configured to switch the switching element between a first switching state and a second switching state. The control circuit is configured to provide a variable pre-control voltage that is dependent on the switching state of the switching element, wherein the pre-control voltage is a voltage that is applied to a control terminal of the switching element as a control voltage during one of the two switching states, and wherein the control circuit is configured to vary the pre-control voltage during a switching state without the switching state changing, in particular not changing from the first switching state to the second switching state or vice versa.

[0006] In this disclosure, the term "phase" refers to the duration during which a transistor is in a switching state, i.e., either on or off. These phases are always interrupted when transitioning from an intermediate state between the on and off states, or vice versa. The pre-control voltage is a voltage that can be used as a control voltage, for example, during one of the two phases. If it is used to turn the transistor on, this specific control voltage is referred to herein as the on-control voltage. If it is used to turn the transistor off, this specific control voltage is referred to herein as the off-control voltage. The variable pre-control 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 may, for example, involve two voltage values ​​in two stages, but it can also be designed as a three-stage, multi-stage, or continuously variable structure. Increased variability allows for optimal matching of the pre-control voltage to the specific operating point of the switching element, in particular to minimize switching losses. Furthermore, the terms "semiconductor" and "semiconductor module" are used interchangeably.

[0007] The control voltage applied to the control terminal of the switching element is, for example, the gate-emitter voltage of a transistor. The pre-control voltage can be, for example, a cutoff control voltage, which, when applied as the control voltage, cuts off the transistor. As long as the transistor is conducting, the pre-control voltage is isolated from the transistor and has no active function. During this conducting phase, a sufficiently positive second pre-control voltage, the conduction control voltage, is applied to the gate input. By introducing a pre-control voltage, such as one that provides the cutoff control voltage, switching losses can be reduced. The cutoff control voltage is typically a non-positive voltage or a voltage below the switching threshold at the gate control input of a switching element, such as a transistor. The cutoff control voltage is applied to the control terminal of the switching element only when the switching element is to be cut off. Because the cutoff control voltage is isolated from the control terminal of the switching element during the conducting phase, it can be adjusted or varied and pre-set, i.e., pre-set a priori, during this phase, thereby reducing switching losses during the transition or into the cutoff phase.

[0008] According to one embodiment, the control circuit is configured to change, for example, reduce, the pre-control voltage during a first switching state of the switching element, and to change, for example, increase, the pre-control voltage during a second switching state of the switching element. The first switching state can be the state in which the switching element is conductive. The second switching state can then be the state in which the switching element is blocked. If the switching element is conductive, for example, the cutoff control voltage, which is not present at the control terminal or gate control input of the switching element during this phase, is reduced to ensure optimal turn-off of the transistor. While the switching element is blocked, the cutoff control voltage, which is present at the control terminal of the switching element during this phase, is increased to ensure optimal turn-on. Thus, in this case, the cutoff control voltage is adjusted.

[0009] To adjust the on-state control voltage, the on-state control voltage is reduced during the on-state phase in which the on-state control voltage is applied to the control terminal of the switching element to ensure optimal turn-off of the transistor. During the off-state phase in which the switching element is blocked, the on-state control voltage, which is not applied to the control terminal of the switching element in this phase, is increased to enable optimal on-state switching.

[0010] According to one specific embodiment, the control circuit is configured to reduce the pilot control voltage from a first value to a second value during a first switching state of the switching element, and to increase the pilot control voltage from the second value to the first value during a second switching state of the switching element. If the pilot control voltage is a cut-off control voltage for cutting off the switching element, the first value V_offa of the cut-off control voltage and the second value V_offb of the cut-off control voltage are within a range between V_th and V_min, for example, -20 V, where V_th is greater than or equal to V_offa and V_offa is greater than V_offb. V_th is the switching threshold of the switching element, above which the switching element is conductive. V_min is the minimum permissible control voltage of the switching element. If the pilot control voltage is a conduction control voltage for turning on the switching element, the first value V_ona of the conduction control voltage and the second value V_onb of the cut-off control voltage are within a range between V_max and V_th, where V_max is equal to or greater than V_ona and V_ona is greater than V_onb. V_max is the maximum permissible actuation voltage of the switching element.

[0011] For example, the first value of the cutoff control voltage is V_offa = 0 V, and the second value of the cutoff control voltage is V_offb = -8 V. During this second state, i.e., the cutoff switching state of the switching element, the control circuit switches the cutoff control voltage from -8 V to 0 V to adjust for the transition to the conductive switching state using a control voltage V_ona, for example, +15 V. Switching the control voltage from 0 V to V_ona instead of from -8 V to V_ona significantly reduces switching losses. Depending on the switching element or semiconductor type, the cutoff control voltage can also have a low positive value. Thus, the voltage V_offa can be, for example, +1 V, while the switching element remains cutoff. Generally, the value V_th—at which the switching element remains cutoff—can be obtained from the switching element's data sheet. Another typical value for V_offb is, for example, -15 V. A typical range for the cutoff control voltage can be expressed as V_th > cutoff voltage > V_min, for example, -20 V.

[0012] The change of the variable pilot control voltage value can also be carried out in a plurality of intermediate steps. The transition from one pilot control voltage value to another pilot control voltage value can be carried out in a jump-shaped, ramp-shaped or curved manner within physical limits.

[0013] According to another embodiment, the control circuit includes a switch configured to change the off-state control voltage from, for example, V_offa to V_offb or vice versa, and to change the on-state control voltage from, for example, V_onb to V_ona or vice versa. The switch here is preferably an electronic switch, such as, for example, a transistor. The electronic switch can also include an arrangement having multiple electronic components, such as a power supply.

[0014] According to one embodiment, the control circuit is designed to switch the cutoff control voltage to V_offb, for example -8 or -15 V, during the on-phase, in particular shortly after entering the on-phase. The switching element is thus immediately ready for controlled switching into the cutoff phase.

[0015] According to one exemplary embodiment, the control circuit is designed to switch the cutoff control voltage to V_offa, for example 0 V, during the cutoff phase, in particular shortly before the onset of the conduction phase. The switching element is thus reliably blocked at, for example, −8 V or −15 V, for most of the cutoff phase.

[0016] The time for switching on the control voltage can also be selected accordingly. The pre-set switching process can also be performed at other times during the on- or off-phase of the switching element.

[0017] According to another embodiment, the switching element or semiconductor module is a power transistor, for example an IGBT (Insulated Gate Bipolar Transistor) or a FET (Field Effect Transistor), such as a MOSFET (Metal Oxide FET).

[0018] According to a second aspect, a method for controlling a switching element during operation is provided, wherein the switching element has two switching states, wherein the different switching states are 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 the control terminal of the switching element to switch the switching element into the 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-control voltage of the switching element is reduced while the switching element is in the first switching state. In a fourth step, the first pre-control voltage is applied to the control terminal of the switching element as the control voltage to switch the switching element into the second switching state. In a fifth step, the first pre-control voltage is increased while the switching element is in the second switching state. In a sixth step, the second pre-control voltage is applied to the control terminal of the switching element as the control voltage.

[0019] According to one exemplary embodiment, the method can be used for a variable cutoff control voltage, so that the cutoff control voltage V_off is reduced during the on-phase from, for example, 0 V to −15 V, and in the off-phase, i.e., when V_off is applied to the control terminal, is increased from −15 V to 0 V. For example, a circuit arrangement for a variable cutoff control voltage has a switch in the negative branch for switching between V_offa and V_offb and, for example, a constant control voltage V_on in the positive branch.

[0020] According to one exemplary embodiment, this method can be used for a variable on-state control voltage, so that the on-state control voltage V_on is reduced from, for example, 15 V to 8 V during the on-phase and increased from 8 V to 15 V in the off-phase, i.e., when V_on is not applied to the gate input. For example, a circuit arrangement for a variable on-state control 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.

[0021] According to one embodiment, the two method variants can be combined. In this case, for example, switches are present both in the negative branch and in the positive branch, so that a variable control voltage can be switched instead of a constant voltage V_on or V_off. Thus, the step of reducing the first pilot control voltage of the switching element while the switching element is in the first switching state additionally includes the step of reducing the second pilot control voltage of the switching element; and the step of increasing the first pilot control voltage while the switching element is in the second switching state additionally includes the step of increasing the second pilot control voltage.

[0022] According to a third aspect, an inverter is provided having a circuit arrangement for switching switching elements, the inverter having a control circuit configured to provide a variable pre-control voltage that depends on the switching state of the switching elements. Inverters, particularly for high power applications, such as in electric vehicles, have switching elements, such as IGBTs, that switch high currents, for example, in the kHz range. The switching losses that occur in this manner can be reduced by approximately 10% using the circuit arrangement presented herein. Typically, depending on the architecture and application, an inverter has multiple switching elements or semiconductors, such as IGBTs. Inverters are DC voltage converters, AC voltage converters, and DC / AC voltage converters that, in combination with windings or coils, are switched in a clocked manner to switch voltage levels and / or frequencies.

[0023] According to a fourth aspect, a vehicle is provided having an inverter, the inverter having a circuit arrangement for switching a switching element having a control circuit. The control circuit is configured to provide a variable pre-control voltage depending on a first or second switching state of the switching element. The pre-control voltage is used, for example, to provide energy for an electric motor or to charge a battery for driving the vehicle. The electric vehicle can be a motor vehicle, a truck, an electric boat, an aircraft engine, a train, a working machine, or the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Further measures for improving the invention are described in detail below with reference to the drawings together with the description of preferred exemplary embodiments of the invention.

[0025] Figure 1 shows a basic circuit arrangement for controlling a switching element according to an exemplary embodiment.

[0026] Figure 2 shows a diagram of the control voltage in the switching and control phases according to an exemplary embodiment,

[0027] Figure 2a 、 2b , 2c, 2d show the switch positions for the control voltage in the switching and control phases according to one exemplary embodiment,

[0028] Figure 3 shows a diagram of the control voltage in the switching and control phases according to another exemplary embodiment,

[0029] Figure 3a 、 3b , 3c, 3d show the switch positions for the control voltage in the switching and control phases according to another exemplary embodiment,

[0030] Figure 4 shows a flow chart of a method according to an embodiment,

[0031] Figure 5 A vehicle having an inverter according to one exemplary embodiment is shown. DETAILED DESCRIPTION

[0032] Figure 1 1 shows a basic circuit arrangement 100 for controlling a switching element 101, which has a control circuit 104. Figure 1 The controllable switching element 101 shown in FIG. 1 can be, for example, a field effect transistor (FET) or a variant thereof, an IGBT or another type of transistor or a high-power transistor. Figure 1 It is merely used to illustrate the mode of operation of the circuit arrangement 100 and in particular the arrangement 104. In a real circuit, the battery voltage V_Batt is not connected to ground, for example, but is connected to the load via a protective circuit.

[0033] Figure 1 This diagram illustrates a simple principle that allows three voltage levels to be switched using two switches 103 and 102. Switch 103 is used to switch the state of the switching element (V_on, V_off), while switch 102 adjusts or selects the cutoff control voltage (V_offa, V_offb), thereby achieving a variable cutoff control voltage. The same arrangement can be used to adjust the on-state control voltage (V_ona, V_onb), for example, using switch 102, and to adjust the switching state of switching element 101 between V_on and a constant voltage V_off using switch 102.

[0034] Figure 2 As an example, the curve of the control voltage V_T applied to the control terminal or the gate-emitter voltage at the switch 103 and the curve of the cut-off voltage V_off at the switch 102 are shown. Figures 2a to 2d shows the switching device with Figure 2 The switch position corresponds to the phase of the voltage curve. Figures 2a to 2d The switchgear is assigned to Figure 2The voltage transition is ideally shown as a voltage jump 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 voltage can also have other values.

[0035] exist Figure 2 The conduction phase and Figure 2a Starting with the switching device, in the switch position of switch 103 upward, switch 102 is first also switched upward, so that V_offa = 0 volt is first intercepted at switch 102. This switch position of switch 102 is the switch position from the previous phase. The current on-phase is now divided into two half-phases. In the second half-phase, switch 102 is switched downward, so that V_offb = -8 V can be intercepted or loaded at the switch output. As soon as switch 103 is switched in order to reach the cut-off phase, this voltage V_offb is loaded on the control terminal of the switching element 101 as the control voltage V_T. Therefore, in the on-phase, the cut-off control voltage, i.e. the voltage used to switch the transistor 101 in cut-off mode, is adjusted or regulated so that the switching element 101 is reliably cut off during the switching of switch 103. According to Figure 2c , both switches 102 , 103 are then adjusted downward.

[0036] However, the cut-off phase is now also divided into two half phases. In the second half phase, the switch 102 is Figure 2d is regulated upwards, so that the cutoff control voltage V_offa=0 volt is applied to the control terminal of the switching element 101. This results in the switching losses during the transition to the conduction phase, that is, the switching losses during the Figure 2a The conduction phase in , which begins with the switching on of the positive voltage via the switch 103 , is reduced relative to the voltage jump from −8 V to +15 V on the gate input.

[0037] The switches 102 and 103 can preferably be realized electronically and actuated, for example, by a microcontroller. The pilot control can be realized, for example, by a power supply or a switchable potential.

[0038] Figure 3 The diagram in FIG and the switching devices 3a to 3d with the corresponding switch positions show an example in which the control voltage can be variably adjusted both for V_on and for V_off. The circuit arrangement now has a switch 104 in the positive branch, which can be switched between V_ona = +15 V and V_onb = +8 V. Figure 3 The switching of the voltages V_offa and V_offb together with the generated voltage V_off is in accordance with the Figures 2a to 2dThis is done in the same way as in the on-phase. During the on-phase, the off-phase is now prepared by switching from 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 from +15 V to -8 V. During the off-phase, the control voltage V_T is switched back to 15 V, thus enabling a reliable and rapid transition to the on-state. It should be noted again that the voltage values ​​specified are merely exemplary.

[0039] Figure 4 A flow chart of a method for controlling a switching element 101 during operation, according to one embodiment, is shown. The switching element has an on-phase and a off-phase. In a first step 401, a blocking control voltage of 0 V is provided. In a next step 402, the switching element 101 is switched into the on-phase with an active, positive control voltage. As a result, the voltage at the control terminal, for example, the gate voltage, jumps only from 0 V to the positive voltage for switching the switching element 101, which can be, for example, 15 volts. In step 403, the provided blocking control voltage of the switching element is reduced during the on-phase of the switching element. During this phase, the blocking control voltage is not applied to the control terminal. This reduction is used to regulate or adjust, that is, to prepare for 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 the active control voltage to switch the switching element 101 into the off state. Because this voltage is clearly in the negative range, for example, -8 V or -15 V, the switching element is optimally blocked. In a next step 405, preparation for the next conduction phase of the switching element 101 is achieved by increasing the provided blocking control voltage, which is still present at the control terminal as the active control voltage at this moment, to 0 V. Then, in a step 406, a positive voltage is applied to the control terminal as the active control voltage, so that the switching element 101 switches to the conduction phase with low losses.

[0040] Step 403 can additionally include a step of reducing the pilot voltage of switching element 101, and step 405 can further include a step of increasing the second pilot voltage. The change of the two pilot voltages within one step can take place within this state phase, ie at different times during the switching state.

[0041] Figure 5 A vehicle 500 is shown according to one specific embodiment, having an inverter 501 , which may have the above-described circuit arrangement for actuating the switching element 101 .

[0042] Therefore, by adjusting the cut-off control voltage during the cut-off phase of the switching element 101, the loss when switching to the on state is reduced, but on the other hand, by adjusting the cut-off control voltage during the on phase, it is ensured that the switching element 101 is switched to a safe cut-off state.

Claims

1. A circuit arrangement (100) comprising a control circuit (104) and a switching element (101), the control circuit comprising a first switch and a second switch, and the switching element being electrically connected to the control circuit, The circuit arrangement (100) is configured to switch the switching element (101) between a first switching state and a second switching state by operating the first switch; wherein the control circuit (104) is configured to provide a variable pre-control voltage that is dependent on the switching state of the switching element (101), The pre-control voltage is a voltage which is applied to the control terminal of the switching element (101) as a control voltage during one of the two switching states, and wherein the actuation circuit (104) is further configured to change the pre-actuation voltage by actuating the second switch 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; The pre-control voltage is a cut-off control voltage V_off, which is used to cut off the switching element (101) and is disconnected from the control terminal of the switching element as soon as the switching element is switched on. and wherein the actuation circuit (104) is further configured to change a cut-off actuation voltage V_off during a first switching state of the switching element (101), and changing the off control voltage V_off during the second switching state of the switching element (101), wherein the control circuit (104) is further configured to reduce the pilot voltage from a first value to a second value by switching the second switch from a first position to a second position during the first switching state of the switching element (101), And during the second switching state of the switching element (101), the pilot voltage is increased from the second value to the first value by switching the second switch from the second position to the first position.

2. The circuit device according to claim 1 , wherein the first value V_offa of the cut-off control voltage and the second value V_offb of the cut-off control voltage are within a range between V_th and V_min, V_th being higher than or equal to V_offa and V_offa being higher than V_offb, wherein V_th is a switching threshold of the switching element ( 101 ) and V_min is a minimum permissible control voltage of the switching element.

3. The circuit arrangement according to claim 1 or 2, The control circuit (104) has a switch (102) which is designed to switch the cutoff control voltage from the first value to the second value.

4. The circuit arrangement (100) according to claim 1 or 2, wherein the switching element (101) is a power transistor.

5. The circuit arrangement (100) according to any one of claims 1 to 4, wherein the circuit arrangement is used to reduce switching losses of a switching element (101).

6. Method for controlling a switching element (101) during operation, The switching element has two switching states, wherein: The switch element is electrically connected to a control circuit, and the control circuit has a first switch and a second switch. The different switching states are set by actuating the switching element with an actuation voltage, The method comprises the following steps: Providing (401) a first pre-control voltage and a second pre-control voltage; Applying the second pre-control voltage as a control voltage (402) to the control terminal of the switching element by controlling the first switch in order to switch the switching element (101) into a first switching state; reducing (403) a first pre-control voltage of the switching element (101) by controlling the second switch while the switching element (101) is in the first switching state, wherein the first pre-control voltage is disconnected from a control terminal of the switching element; Applying the first pre-control voltage as a control voltage (404) to the control terminal of the switching element by controlling the first switch in order to switch the switching element (101) into a second switching state; increasing (405) the first pre-control voltage by controlling the second switch while the switching element (101) is in the second switching state; The second pilot control voltage is applied as a control voltage (406) to the control terminal of the switching element.

7. The method according to claim 6, The step (403) of reducing the first pre-control voltage of the switching element (101) while the switching element (101) is in the first switching state additionally comprises the step of reducing the second pre-control voltage of the switching element (101); and the step (405) of increasing the first pre-control voltage while the switching element (101) is in the second switching state additionally comprises the step of increasing the second pre-control voltage.

8. An inverter (501) comprising a circuit arrangement (100) for switching a switching element (101) according to any one of claims 1 to 4.

9. A vehicle (500) having an inverter (501) with a circuit arrangement (100) for switching a switching element (101) according to any one of claims 1 to 4.

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