Method for actuating an inverter and electronic control unit for carrying out the method

Abstract

The invention relates to a method for actuating an inverter (1), wherein the inverter (1) is connected on the input side to a DC voltage source (3) via an intermediate-circuit energy store (2) and comprises a plurality of inverter switches (T1HS, T1LS) actuated by drivers (4) in order to generate an AC voltage supplied to a load (6) from a DC voltage supplied by the DC voltage source (3), wherein the method comprises: a. receiving a request (A) that the intermediate-circuit energy store (2) is to be discharged; and b. actuating at least one of the drivers (4) of the inverter (1) such that the intermediate-circuit energy store (2) is discharged via the at least one driver (4).

Description

[0001] Description

[0002] Method for controlling an inverter and electronic control unit for carrying out the method

[0003] The invention relates to a method for controlling an inverter, in particular for discharging an intermediate circuit energy storage device connected to an input side of the inverter; and a control unit for carrying out the method.

[0004] Electric vehicles, such as fully electric or hybrid cars, are usually powered by three-phase synchronous motors, with the necessary drive energy drawn from a connected battery. To convert the direct current (DC) supplied by the battery into the required alternating current (AC), an inverter is connected between the motor and the battery.

[0005] Usually, an intermediate circuit capacitor is present in the intermediate circuit between the input side of the inverter and the battery connected there, which performs stabilization and buffer functions.

[0006] It is legally required that the intermediate circuit capacitor must be discharged within 10 seconds in the event of a crash or workshop repair.

[0007] In the prior art, discharge is achieved through a separate control circuit and a corresponding discharge resistor. These components required for discharge – the control circuit and the discharge resistor – incur costs and occupy valuable installation space.

[0008] Alternatively, it is known in the art to discharge the intermediate circuit capacitor via the inverter itself or the corresponding switches / transistors. However, this type of discharge leads to a heavy load and consequently to premature aging of the inverter.

[0009] Against this background, the object of the invention is to provide a method and a control unit that enable a fast, simple, and preferably gentle discharge of an intermediate circuit energy storage device. At a minimum, the object of the invention is to provide an alternative method and an alternative control unit.

[0010] This task(s) is / are solved by a method according to claim 1 and a control unit according to claim 9.

[0011] The method according to the invention involves controlling an inverter, wherein the inverter is connected on the input side to a DC voltage source via an intermediate circuit energy storage device and has a plurality of inverter switches controlled by drivers in order to generate an AC voltage supplied to a load from a DC voltage supplied by the DC voltage source, wherein the method comprises: a. receiving a request that the intermediate circuit energy storage device should be discharged; and b. controlling at least one of the drivers of the inverter such that the intermediate circuit energy storage device discharges via the at least one driver.

[0012] The intermediate circuit energy storage device is, for example, a capacitor or a multitude of capacitors. A power capacitor chip, or PCC for short, is particularly preferred as the intermediate circuit energy storage device.

[0013] The DC voltage source is in particular a high-voltage storage device (400V or 800V) of a vehicle, especially a motor vehicle or motorcycle.

[0014] Inverter switches are preferably semiconductor switches, such as MOSFET or IGBT transistors. The former can be n-channel or p-channel transistors of the enhancement or depletion type.

[0015] As discussed further below, the inverter is a three-phase inverter constructed from three half-bridges. Each half-bridge is assigned to one phase of a three-phase motor and contains the (two) inverter switches. Each inverter switch has a driver for control. The respective phase is connected to the center tap of the corresponding bridge circuit.

[0016] The three-phase motor preferably forms the aforementioned load and, for example, the electric drive unit of the vehicle. The requirement according to step a. is, for example, in the event of a crash or workshop visit of the corresponding vehicle, supplied to and received by the control unit according to the invention, wherein the control unit then executes step b. and controls the driver in such a way that the DC link energy storage is discharged via the driver and the HV power supply unit supplying it, which is supplied on the input side by the DC link.

[0017] A key feature of the method according to the invention is that, during normal operation, the drivers are used to control the inverter switches in order to generate the alternating voltage. For example, the control unit for generating the alternating voltage implements a corresponding pulse width modulation method by controlling the drivers accordingly.

[0018] Since the same drivers are used for the inventive method, components necessary for discharging the intermediate circuit energy storage are unnecessary. Furthermore, the inverter switches are subjected to no or only minimal stress.

[0019] Preferably, the method is designed such that the at least one driver includes a driver half-bridge made of driver switches which are switched accordingly to control the associated inverter switch; wherein in step b. the driver switches are switched such that the DC link energy storage is discharged via the driver switches.

[0020] As an alternative to the driver half-bridge, the driver can include a current source in its circuitry, which serves to control the associated inverter switch.

[0021] The driver switches are preferably field-effect transistors, but can also be bipolar transistors. The associated inverter switch is preferably connected with its control terminal, such as its gate terminal, to the center tap between the two driver switches.

[0022] Preferably, in step b of the inventive method, the driver switches can be switched such that the associated inverter switch retains its switching state. This allows the inventive method to be carried out in any operating state of the inverter.

[0023] Preferably, in step b. the driver switches can be operated as a power source.

[0024] Alternatively, in step b. at least one of the driver switches can be operated in pulsed mode.

[0025] In particular, both alternatives can prevent uncontrolled discharge of the DC link energy storage. This controlled discharge, however, is especially advantageous when the driver half-bridge is preferably connected to and supplied by a secondary side of a power supply, and a primary side of the power supply is supplied by the DC link energy storage; in this case, in step b., the driver switches are preferably configured such that the DC link energy storage is discharged by loading the secondary side.

[0026] The method according to the invention is particularly preferred for use in automobiles, wherein (i) the load is a three-phase motor,

[0027] (ii) the inverter has a half-bridge for each of the three phases, which is constructed from the inverter switches, one of which is a high-side inverter switch and another of which is a low-side inverter switch, and (iii) the drivers control the high-side inverter switches and / or the low-side inverter switches of the three half-bridges.

[0028] The other group of inverter switches, if present, which are not controlled by the drivers for discharging the DC link energy storage, are controlled by further drivers, the further drivers being preferably powered or supplied by a low-voltage battery of the vehicle or supplied by another power supply unit, which in turn is supplied by the DC link energy storage unit.

[0029] In step b., preferably one or a plurality of the drivers are controlled such that the DC link energy storage is discharged via the driver(s). Preferably, in step b., the discharge can additionally take place directly via the half-bridges and / or, particularly preferably, in the method according to the invention, the inverter is controlled in step b. such that the DC link energy storage is additionally discharged via at least one of the three phases and the corresponding windings of the motor.

[0030] This variant is particularly advantageous when the drivers only allow a load that is insufficient to achieve a certain discharge rate of the DC-circuit energy storage device. By distributing the discharge current across the driver(s) and the phases, a fast and component-friendly discharge can be achieved.

[0031] The invention also relates to a control unit for a vehicle, in particular a fully electric or hybrid powered motor vehicle / motorcycle, which is configured to execute the method according to one of claims 1 to 8 upon receipt of the requirement.

[0032] The invention is preferably used in vehicles, such as automobiles or motorcycles, but is not limited to these. It is suitable for any application where a cost-effective and system- and safety-relevant simple solution for discharging an intermediate circuit energy storage device via a control interface driver, such as a gate driver, is required.

[0033] In the following, a method according to the invention is explained with reference to the attached Figure 1.

[0034] Figure 1 shows an inverter connected to a load - a motor - of a motor vehicle, to a DC electrical power source (accumulator) and to a control unit, with the inverter being connected to the DC power source via an intermediate circuit energy storage device.

[0035] Figure 1 shows an arrangement to illustrate the method according to the invention. This arrangement is found in particular in a fully electric or hybrid powered motor vehicle / motorcycle.

[0036] An inverter 1 is connected at its input side to a DC voltage source 3 via an intermediate circuit energy storage device 2. The DC voltage source 3 is, in particular, a high-voltage battery that stores the energy required to power the motor vehicle / motorcycle. The DC voltage source provides, for example, an output voltage of 400 V or 800 V, which is applied to the intermediate circuit energy storage device 2 and the input side of the inverter 1. A preferred switch 31 is provided between the DC voltage source 3 and the intermediate circuit energy storage device 2, by means of which the DC voltage source 3 can be disconnected.

[0037] An electric motor 6, which for example forms the drive unit of the motor vehicle / motorcycle and represents a load, is connected to the output side of the inverter 1. The inverter 1 serves to convert the direct current supplied by the direct current source 3 into an alternating current necessary for the operation of the motor 6.

[0038] The control of the inverter 1 is carried out by the control unit 7 according to the invention, as shown in Figure 1. For example, the control unit 7 controls the inverter 1 according to a pulse width modulation method in order to carry out the aforementioned conversion.

[0039] The intermediate circuit energy storage device 2 is, for example, a capacitor or an array of capacitors, such as a power capacitor chip. The intermediate circuit energy storage device 2 performs stabilization and buffering functions during operation of the inverter 1 or the motor 6.

[0040] Inverter 1 comprises three parallel-connected half-bridges, each consisting of two inverter switches and each assigned to one of the phases U, V, W of the electric motor 6. In this embodiment, the inverter switches T1 HS, T1 LS, T2 HS, T2 LS, T3 HS and T3 LS are preferably n-channel field-effect transistors of the enhancement type.

[0041] The half-bridge associated with phase U consists of the high-side inverter switch T1 HS, which switches the high-voltage side HV+ of the DC voltage source 3, and the low-side inverter switch T1 LS, which switches a center tap of phase U relative to the ground side HV- of the DC voltage source 3. The half-bridge associated with phase V consists of the high-side inverter switch T2 HS, which switches the high-voltage side HV+ of the DC voltage source 3, and the low-side inverter switch T2 LS, which switches a center tap of phase V relative to the ground side HV- of the DC voltage source 3.

[0042] Ultimately, the half-bridge assigned to phase W is constructed from the high-side inverter switch T3HS, which switches the high-voltage side HV+ of the DC voltage source 3, and the low-side inverter switch T3LS, which switches a center tap of phase W opposite the ground side HV- of the DC voltage source 3.

[0043] Each of the inverter switches T1 HS, T1 LS, T2HS, T2LS, T3HS and T3LS is assigned a corresponding driver 4, 4', via which the control unit 7 can control or switch the respective assigned inverter switch.

[0044] The driver 4 shown is assigned to the low-side inverter switch T1 LS, whereby the control unit 7 can control this driver 4 via the signal Si1.

[0045] Each of the further low-side inverter switches T2LS and T3LS of the further half-bridges is assigned its own (not shown) driver 4, whereby the control unit 7 can individually control the drivers 4 of the low-side inverter switches T2LS and T3LS (not shown) via a respective (not shown) signal.

[0046] The construction of the drivers assigned to the low-side inverter switches T2LS and T3LS is preferably identical to the construction of the driver 4 assigned to the low-side inverter switch T1 LS shown, which is why reference is made to the corresponding descriptions.

[0047] The driver 4 associated with the inverter switch T 1 LS includes a control circuit 41 (GDU = Gate Drive Unit) and a driver half-bridge, which is constructed from switches S1 and S2. The control circuit 41 includes, for example, an operational amplifier to control the driver half-bridge or switches S1 and S2 accordingly.

[0048] The drivers 4 preferably form a current source for current-controlled operation of the associated inverter switch. Alternatively, the drivers can also implement voltage control. The control terminal – the gate terminal – of the inverter switch T1 LS is connected to the driver half-bridge at a center tap between switches S1 and S2.

[0049] When the inverter switch T1 LS is to be closed, the control unit 7 transmits the corresponding command to the control circuit 41 via the signal Si1, whereupon the control circuit 41 closes switch S1 and keeps switch S2 open. The inverter switch T1 LS then transitions to its closed or conducting state.

[0050] If the inverter switch T1 LS is to be opened again or switched to its non-conductive state, the control unit 7 transmits the corresponding command to the control circuit 41 via signal Si1. The control circuit 41 then opens switch S1 and closes the other switch S2, which results in the inverter switch T1 LS being opened or switching to its non-conductive state.

[0051] The driver 4 is connected to a secondary side of a power supply 5. The power supply 5 is, in particular, a DC / DC converter, whose primary side is connected to the DC voltage source 3 and the intermediate circuit energy storage device 2 connected in parallel. The power supply 5 converts the corresponding DC voltage to, for example, 30 V and supplies the driver 4 with electrical energy, in particular with a DC voltage. The power supply 5 is preferably a DC / DC converter.

[0052] The identical drivers 4 of the inverter switches T2LS and T3LS are preferably each assigned their own separate power supply 5.

[0053] Consequently, all low-side inverter switches T1 LS, T2LS, T3LS are preferably supplied with electrical energy indirectly via the power supplies 5 through the intermediate circuit energy storage 2.

[0054] The additional drivers 4', via which the control unit 7 individually controls the high-side inverter switches T1 HS, T2 HS and T3 HS, can preferably be identical in design to driver 4. The only preferred difference is that the drivers 4' are not powered / supplied via the intermediate circuit energy storage 2, but by a low-voltage DC voltage source LV, which can, for example, be a low-voltage battery.

[0055] The control unit 7 controls the additional driver 4', which is assigned to inverter switch T1 HS, via the SiT signal. The individual signals supplied to the additional drivers 4' of inverter switches T2 HS and T3 HS are not shown.

[0056] The control unit 7 is configured to control the drivers 4, 4' via their respective signals using a pulse-width modulation method, such that the DC voltage supplied by the DC voltage source 3 is converted into an AC voltage necessary for the operation of the motor 6. This type of control of the drivers 4, 4' corresponds to the normal (intended) control of the inverter 1.

[0057] In certain cases, it is necessary to discharge the intermediate circuit energy storage 2 as quickly as possible.

[0058] These cases include, for example, a vehicle crash or a workshop visit.

[0059] In both cases, the DC voltage source 3 is preferably disconnected by opening switch 31. Alternatively or additionally, the connection to the DC voltage source 3 can be disconnected by detonating an explosive charge.

[0060] Furthermore, in both cases it must be ensured that the intermediate circuit energy storage unit 2 does not pose a potential danger to occupants, rescuers, or workshop personnel. The fact that the intermediate circuit energy storage unit 2 needs to be discharged is signaled to the control unit 7 via the request signal A shown.

[0061] If the control unit 7 receives this request signal (step a.), it executes step b. of the inventive method for controlling the inverter 1.

[0062] It should be emphasized that the method according to the invention requires no additional equipment or components, but manages with the components already described that are necessary for the normal control of the inverter 1. The core idea of ​​the invention is to discharge the DC link energy storage device 2 via at least one of the drivers 4, which are assigned to the low-side inverter switches T1 LS, T2LS, T3LS. The corresponding discharge is explained with reference to the driver 4 shown.

[0063] The discharge of the intermediate circuit energy storage 2 takes place via the driver 4, in particular via the driver half-bridge, which is made up of the switches S1 and S2.

[0064] When the control unit 7 receives the request signal A (step a.), it signals the driver 4 via signal Si1 to short-circuit the secondary side of the power supply 5 by simultaneously closing switches S1 and S2. This leads to an increased load on the power supply 5 and thus to a discharge of the DC link energy storage 2. The power supply 5 preferably has a capacity sufficient to withstand this load.

[0065] The discharge of the intermediate circuit energy storage device 2 preferably occurs in less than 10 seconds using this method.

[0066] In the event of a short circuit on the secondary side of power supply 5, the inverter switch T1 LS inevitably switches to its non-conductive, open state. This means that an intended switching state of the inverter switch T1 LS cannot be maintained.

[0067] To eliminate this issue, the procedure can preferably be modified. This is done by having the control unit 7 signal a pulsed short circuit of the driver half-bridge instead of a continuous one.

[0068] Depending on the desired switching state of the inverter switch T1 LS, the control unit 7 decides which of the two switches S1 and S2 is operated in pulsed or static mode. The pulsed switch is preferably operated with an ON pulse duration that is insufficient to fully switch the switch into the ON state. In other words, the pulsed switch is not fully switched on due to the short duration of the ON state. The ON state is shorter than the time required to reach a fully ON state. Specifically, the pulsed switch operates linearly with a resistance greater than R_ON throughout the entire ON state (of pulsed operation). Therefore, switches S1 and S2 are in step b.The control circuit preferably does not involve a complete bridge short circuit, but rather a discharge via switches S1 and S2 is provided, at least one of which is in linear operation (with a resistance in the power path greater than the ON state in steady-state ON operation). This serves to maintain the supply voltage, for example to the control unit, which depends on the voltage of the DC voltage source. Alternatively, a further power supply can be provided, which is supplied by the intermediate circuit energy storage device and which supplies the control unit, but not the driver 4 or the switches S1 and S2. This allows the control unit to be continuously supplied via the further driver, while the discharge is carried out via the other power supply (and the respective switches / drivers). The design of the power supply / driver...The short-circuiting of the power supplies by switches S1 and S2 does not stress the voltage of the intermediate circuit energy storage in such a way that the control unit receives a supply voltage lower than the minimum supply voltage.

[0069] If the inverter switch T1 LS is to remain switched on, the switch S1 of the driver half-bridge is operated statically switched on and the switch S2 is switched in pulses.

[0070] If, however, the inverter switch T1 LS is to remain switched off, the switch S1 of the driver half-bridge is pulsed and the switch S2 is operated statically switched on.

[0071] The pulse and switching frequency of the pulsed switches is chosen so that the switching state of the inverter switch T1 LS does not change, but the intermediate circuit energy storage 2 preferably discharges as quickly as possible.

[0072] It is evident that in the method according to the invention, no discharge of the intermediate circuit energy storage device 2 takes place via the inverter switches T1HS, T1LS, T2HS, T2LS, T3HS and T3LS. Consequently, these are not subjected to any load and do not experience any aging.

[0073] The method according to the invention can be carried out with one, two or all drivers 4.

[0074] To accelerate the discharge of the DC link energy storage device 2, it is preferably possible to carry out part of the discharge via the inverter switches T1 HS, T1 LS, T2 HS, T2 LS, T3 HS, and T3 LS. For example, according to the inventive method, the discharge is carried out via the driver 4 shown, and the inverter switches T2 HS, T2 LS, T3 HS, and T3 LS of the other inverter half-bridges are additionally switched such that part of the discharge takes place via phases V and W. In the arrangement shown, the high-side inverter switches T1 HS, T2 HS, and T3 HS are controlled by the additional drivers 4', which are not supplied from the DC link energy storage device. The invention is not limited to this.The additional drivers 4' can also be supplied / powered from the intermediate circuit energy storage 2 like the driver 4 and are preferably constructed identically to the driver 4, whereby the control unit 7 can also control these additional drivers 4' for discharge according to the invention.

[0075] As an alternative to the described driver half-bridge, the corresponding switches S1 and S2 can also be implemented as a current source. As with the described pulsed short circuit, a desired limited discharge current can be set in this configuration.

Claims

Patent claims 1. Method for controlling an inverter (1 ), wherein the inverter (1) is connected on the input side via an intermediate circuit energy storage device (2) to a DC voltage source (3) and has a plurality of inverter switches (T1 HS, T1 LS) controlled by drivers (4) to generate an AC voltage supplied to a load (6) from a DC voltage supplied by the DC voltage source (3), wherein the method comprises: a. receiving a request (A) that the intermediate circuit energy storage device (2) should be discharged; and b. controlling at least one of the drivers (4) of the inverter (1) such that the intermediate circuit energy storage device (2) discharges via the at least one driver (4).

2. Method according to claim 1, wherein the at least one driver (4) comprises a driver half-bridge made of driver switches (S1, S2) which are switched accordingly to control the associated inverter switch (T1 LS); and in step b. the driver switches (S1, S2) are switched such that the DC link energy storage (2) is discharged via the driver switches (S1, S2).

3. Method according to claim 2, wherein in step b. the driver switches (S1 , S2) are switched such that the associated inverter switch (T1 LS) retains its switching state.

4. Method according to claim 3, wherein in step b. the driver switches (S1 , S2) are operated as a power source.

5. Method according to claim 3, wherein in step b. at least one of the driver switches (S1 , S2) is operated in pulsed mode.

6. Method according to any one of claims 1 to 5, wherein the driver half-bridge is connected to and supplied by a secondary side of a power supply (5), and a primary side of the power supply (5) is supplied by the intermediate circuit energy storage device. (2) is supplied; and in step b. the driver switches (S1 , S2) are switched so that the intermediate circuit energy storage (2) is discharged by loading the secondary side.

7. A method according to any one of the preceding claims 1 to 6, wherein the load (6) is a three-phase motor, the inverter (1) has a half-bridge for each of the three phases (U, V, W) constructed from the inverter switches (T1 HS, T1 LS; T2 HS, T2 LS; T3 HS, T3 LS), one of which forms a high-side inverter switch (T1 HS, T2 HS, T3 HS) and another a low-side inverter switch (T1 LS, T2 LS, T3 LS), and the drivers (4) control the high-side inverter switches (T1 HS, T2 HS, T3 HS) and / or the low-side inverter switches (T1 LS, T2 LS, T3 LS) of the three half-bridges; and in step b. one or a multitude of the drivers (4) are controlled in such a way that the intermediate circuit energy storage (2) discharges via the driver(s) (4).

8. Method according to claim 7, wherein in step b. the inverter (1 ) is controlled such that the intermediate circuit energy storage (2) is additionally discharged via at least one of the three phases (U,V,W) of the motor.

9. Control unit (7) for a vehicle which is configured to execute a method according to one of claims 1 to 8 upon receipt of a request.

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