Synchronized staggered operation of multiple inverters of an intermediate circuit to reduce ripple in the intermediate circuit

Abstract

If a vehicle has multiple inverters (IN1, IN2) supplied by the same intermediate circuit, the first inverter is controlled by a first control device (C1) with a first switching signal (1); the second inverter is controlled by a second control device (C2) with a second switching signal (2). The control devices are synchronized by transmitting a synchronization message (t0r) comprising a time stamp from the first control device (C1) to the second control device (C2) and returning a corresponding response message that indicates the time of receipt of the synchronization message (t0r) by the second control device (C2). This allows a synchronization time offset (OF) between the control devices to be calculated.By means of synchronization, alternating voltage components acting on the intermediate circuit can be generated (by the two inverters) in such a way that they at least partially cancel each other out. Furthermore, a corresponding control device and a computer program set as well as a multi-part vehicle drive are described.

Description

[0001] Electric vehicles are equipped with inverters that convert the direct current from a battery-supported intermediate circuit into an alternating current, for example, using pulse-width modulation. Each switching operation generates a voltage change in the intermediate circuit, which is partially absorbed by the assistance of an intermediate circuit capacitor. Significant voltage changes caused by the switching operations would lead to interference, so smoothing by an intermediate circuit capacitor is essential for the operation of the inverter. However, high switching currents or high traction power also require high capacitance values ​​from the intermediate circuit capacitor, which are associated with high costs. In addition, high alternating voltage components in the intermediate circuit lead to losses in the intermediate circuit capacitor, so that it ages more quickly with high alternating voltage components and unwanted heat loss is generated.

[0002] Document DE 10 2020 124 496 A1 describes a method for synchronizing inverters using an additional control signal that initializes clock synchronization. Document EP 1 906 518 A2 describes synchronizing multiple inverters using telecommunication messages based on counters within the message. Document DE 10 2004 006 023 A1 proposes obtaining clock signals for synchronous control from a common CAN bus. Document US 2023 / 0253910 A1 mentions the use of a separate synchronization line when operating multiple inverters.

[0003] These are possibilities for synchronization, whereby it was recognized that a comparatively high temporal precision is advantageous for the destructively interfering design of switching signals from inverters.

[0004] It is therefore a task to show a possibility with which AC voltage components in the intermediate circuit can be reduced by means of suitable time synchronization.

[0005] This problem is solved by the subject matter of the independent claims. Further properties, features, embodiments, and advantages are revealed by the dependent claims, the description, and the figure.

[0006] It is proposed to supply several inverters via the same intermediate circuit. These inverters are inverters of a vehicle and, in particular, are inverters of different drives of the same vehicle. The switching operations of the inverters thus generate an alternating voltage component in the same intermediate circuit, which is partially compensated for by the intermediate circuit capacitor present there. It is proposed to design the switching signals of the inverters so that they destructively interfere with one another (by mutually shifting the switching signals in time), so that the alternating voltage components generated by the two inverters at least partially cancel each other out. For example, a positive switching edge of one inverter can be executed simultaneously with a negative switching edge of the other inverter. In this way, the respective generated alternating voltage components can partially cancel each other out.This requires synchronization of the inverters to each other to enable essentially autonomous control for the two inverters, but the controls are synchronized to each other to enable the canceling or compensating effect.

[0007] Synchronization involves determining the runtime and response time between the two controllers using a message containing a timestamp and a time-related response. If this time is known, a common time base can be provided for both controllers, based on which the switching signals can be executed offset from one another. The offset enables at least partial (mutual) cancellation of AC voltage components resulting from the settings of the two inverters. The two switching signals are preferably periodic and, in particular, have the same period length in order to enable mutual compensation through an offset. For two control signals, the offset is 180°, for example, so that the two switching signals can be identical. However, this can also refer to only parts of the switching signals in order to enable individual control of the two drives.If the two control signals have different duty cycles, at least some of the edges of the two inverters can be executed synchronously with each other (with reversed polarity), for example, the switch-on edge of the first control signal can coincide in time with the switch-off edge of the second control signal, this being made possible by the aforementioned offset.

[0008] The CAN protocol is preferably used to synchronize the controls of the two inverters. The control of the two inverters is realized by control devices or by corresponding control steps.

[0009] A method for operating multiple inverters of a vehicle is thus proposed. The inverters are, in particular, traction inverters, preferably traction inverters of different drives of a vehicle, such as the two traction inverters of a front axle and a rear axle drive of a vehicle.

[0010] The inverters are supplied by the same intermediate circuit. The intermediate circuit itself is supplied by an accumulator circuit, for example a high-voltage accumulator circuit with a nominal voltage of more than 60 V, at least 200 V, 400 V or 800 V. The inverters are operated in a clocked mode. A first inverter is controlled by a first control device. For this purpose, the first control device generates a first switching signal, which is transmitted to the first inverter in a controlling manner. A second inverter is controlled by a second control device. For this purpose, the second control device generates a second switching signal, which is transmitted to the second inverter in a controlling manner. The alternating voltage components generated by the operation of the two inverters are found in the same intermediate circuit.It is proposed to synchronize the first control device with the second control device in order to be able to synchronize the first switching signal with the second switching signal. In particular, the first leap year is synchronized with the second switching signal in such a way that switching edges of different polarity can occur simultaneously in the two switching signals. The correspondingly generated AC voltage components compensate each other, thus reducing the load on the intermediate circuit (with AC voltage components).

[0011] The inverters are power inverters, in particular vehicle traction inverters, for example with power ratings of at least 50 kW, 100 kW, 200 kW, or more. Each inverter can be designed as a three-phase bridge, such as a BnC circuit, where n corresponds to twice the number of phases of the three-phase bridge. The inverters preferably have the same number of phases, but can also have different phase numbers. The switching signals are preferably pulse wave modulation (PWM) signals; the control devices are configured to generate them. The control devices can be part of a field-oriented control device or can represent this.The switching signals can be PWM switching signals of various types, such as SPWM (sinusoidal PWM), DPWM (discontinuous PWM), SVPWM (space vector-based PWM), THIPWM, THTRPWM (sinusoidal PWM with third harmonic injection), FHIPWM (sinusoidal PWM with fifth harmonic injection), THSDPWM (60° PWM with third harmonic injection), SDPWM (60° PWM), BCPWM (bus-clamping PWM), or combinations thereof. To offset according to a cancellation time offset (which leads to at least partial cancellation of the AC components of the various inverters in the DC link), the inverters can operate with the same PWM types, or it can be provided that different PWM types are selected for the inverters to achieve the cancellation time offset.

[0012] The control devices and the generation of the respective switching signals are synchronized. A synchronization message is transmitted from the first control device to the second control device. This synchronization message has a timestamp. The timestamp indicates the time at which the synchronization message was sent. The timestamp refers in particular to a local timer of the first control device. The first control device therefore has its own local timer. The second control device receives the synchronization message. The second control device determines the time at which the synchronization message was received from the second control device. This time refers to a local timer of the second control device.

[0013] The second device generates a response message. This includes time information that indicates the time at which the synchronization message (sent by the first control device) was received by the second control device. The response message is transmitted from the second control device to the first control device. The first control device is thus able to determine the time offset between the two local clocks. In particular, the time offset can be calculated, which indicates the time offset between the timestamp of the synchronization message and the current information of the response message. The time offset thus indicates the length of time required for a signal to be transmitted from the first control device to the second control device (or in the opposite direction).This means that at any time the offset reflects how synchronized the two control devices are with each other, so that this time offset is also called synchronization time offset.

[0014] The synchronization time offset thus affects the signal transmission or common mode between the two control devices. Separate from this is the cancellation time offset, i.e., a time offset between the switching signals to achieve at least partial (mutual) cancellation of AC voltage signals generated by the switching of the inverters in the intermediate circuit. The cancellation time offset is thus linked to the destructive interference between the switching signals of the two inverters, or rather, to the (partial) destructive interference that exists between the two AC voltage signals generated by the switching in the various inverters (in the intermediate circuit as voltage fluctuations).

[0015] The synchronization time offset is calculated, in particular, by the first control device that sends the synchronization message and receives the corresponding response message from the other control device. The synchronization time offset is preferably transmitted from the first control device to the second control device (or any further control device). The second control device can thus take this time offset into account when generating the second control signal, which is offset from the first control signal by the cancellation time offset.

[0016] The first inverter and the second inverter operate different electrical machines. The first inverter operates a first electrical machine and the second inverter operates a second electrical machine. The two electrical machines are preferably part of different drives of the same vehicle. The inverters are supplied from the same intermediate circuit. In particular, there is a power flow from the intermediate circuit to the DC voltage sides of the two inverters. The operation of the inverters provides for switching processes that feed back into the same intermediate circuit. The switching signals of the two control devices (which are synchronized after the exchange of the synchronization time offset) are offset from one another by a cancellation time offset. This is designed in such a way that at least partial mutual compensation or cancellation occurs for the AC voltage components generated by the (switched) operation of the inverters in the intermediate circuit.Cancellation or destructive interference results. The cancellation time offset can, for example, be designed such that at least one edge of a first direction of one of the two inverters (or one of the two switching signals) coincides with an edge of an opposite direction of the other inverter (the other switching signal).

[0017] If the inverters are driven with control signals of the same periodicity, the phase offset is preferably 180° of the period. In other words, the two inverters are operated in an interleaved manner to reduce voltage variations in the intermediate circuit (compared to non-interleaved operation).

[0018] Embodiments provide that a local timer is provided in each of the control devices. The control with the first switching signal and the control with the second switching signal provides that these switching signals are shifted relative to one another based on the time signals of the local timers and corrected by the synchronization time offset. The shift is carried out in particular by the second control unit, depending on the synchronization time offset determined by the first control device. Alternatively, the shift is carried out by the first control unit, depending on the synchronization time offset determined by this control unit.

[0019] It can be provided that the switching signals of the synchronized control devices (i.e. the first or second control device after exchange or calculation of the synchronization time offset) are emitted offset from one another by half a switching period (180°). This refers to the switching period of the first and second switching signals, which are preferably emitted with the same switching period duration. The switching signals are emitted with positive and negative switching edges. "Positive" and "negative" indicate the direction of the switching edge. This direction is also referred to as polarity. Preferably, the cancellation time offset is provided so that a plurality of the (consecutive) switching edges of the first switching signal of a (first) polarity coincide with the switching edges of the second switching signal of an opposite polarity.In this respect, “coincidence” means that one flank is not yet completed when a second one begins and vice versa.

[0020] The CAN protocol is preferably used for synchronization. The messages transmitted during synchronization (in particular the synchronization message and the response message) are preferably configured according to a CAN protocol. In particular, the transmission of these messages is also configured according to the CAN protocol. This applies, for example, to the first, second, third, and possibly also fourth layers of the ISO-OSI reference model.

[0021] The control devices each preferably have a microprocessor or a microcontroller. Some embodiments provide that the interrupts of these components are used for sequence control. In particular, the offsetting of the switching signals from one another (i.e. the offset by the cancellation time offset, optionally combined with the synchronization time offset) is carried out completely or partially by means of the interrupts of these components. For example, an interrupt request (IRQ) can be issued in order to specifically achieve a delay of the first and / or second control signal. As part of the temporal offsetting of the switching signals from one another, at least one interrupt is set or issued according to a predetermined cancellation time offset (approximately corresponding to 180° or corresponding to half a signal period of a switching signal). In this case, the synchronization time offset is taken into account in particular.

[0022] It can be provided that, as part of the offsetting of the two switching signals relative to one another, an actual cancellation time offset between the switching signals is adjusted to a predetermined cancellation time offset over several periods of the switching signal. In other words, the synchronization of the two switching signals (taking the synchronization offset into account) can occur not only through a single temporal change, but can be changed stepwise or essentially continuously over a certain period of time, in particular over a plurality of periods, until the target offset (the cancellation time offset) is reached. The target offset can also be referred to as the predetermined cancellation time offset.

[0023] Furthermore, a control device for an inverter is described, which can in particular perform the function of the second control device. The control device has a data interface, in particular a CAN interface. The data interface is configured to receive a synchronization message from another control device. In particular, the data point is configured to receive a synchronization message as sent by the first control device. The synchronization message has a timestamp. The timestamp indicates a point in time that originates from a local timer of the entity (control device) that sends the synchronization message. The timestamp indicates when the synchronization message was sent. The timestamp refers to the local timer of the control device that sends the synchronization.

[0024] The control device itself also has a local timer. The control device is configured to output a response message to the data interface in response to the receipt of the synchronization message. In particular, the control device is capable of sending the response message to another control device (entity) via the data interface. Preferably, the control device is configured to send the response message via the data interface to the entity or control device from which the synchronization message was received. The response message is provided with time information that indicates the time of receipt of the synchronization message. The time information relates to the local timer of the control device that receives the synchronization message. The control device is capable of providing the response message with this time information.Thus, the response message also has a timestamp, which, however, is referred to as time information to avoid any confusion. This timestamp refers to the local timer of the (second) control device and indicates the time at which the control device received the synchronization message. The representation of this time refers to the local timer of the (second) control device. The time contained in the synchronization message thus refers to the time count in the first control device, while the time contained in the response message refers to the time count within the second control device. The control device described here, which has the data interface for receiving the response message, corresponds to the second control device that is represented within the method.

[0025] The first control device represented within the framework of the method corresponds to a time master, i.e., a predetermined unit that determines the underlying time horizon of the synchronization or the switching signals, while the second control device represented within the framework of the method corresponds to a controlled unit or a time slave. The second control device thus follows the time specifications of the first control device.

[0026] The (second) control device has a calculation device. This is configured to calculate the synchronization time offset. This time offset represents the time offset between the timestamp of the synchronization message and the time information of the response message. Alternatively, the synchronization time offset is based on information received by another control device (first control device) from the (second) control device whose interface receives the synchronization message. Thus, instead of a calculation device, the interface therein can also be configured to receive a signal that represents the synchronization time offset. Using this time offset, the control device is able to output a signal synchronized to the entity from which the time offset originates.

[0027] The control device further has a control output. This is configured to control the inverter; the control output can in particular be configured for connection to a driver that controls the relevant inverter. The control device is configured to output a switching signal at the control output that is offset from the local clock by the synchronization time offset and by a predetermined cancellation time offset. In particular, the switching signal output by the control device is offset in time by a combination of the synchronization time offset and the cancellation time offset, wherein this combination (depending on the sign) can correspond to an addition or a subtraction. If the synchronization time offset and the cancellation time offset correspond to a time offset in opposite directions, the synchronization time offset is subtracted from the cancellation time offset.If the synchronization time offset and the cancellation time offset correspond to a temporal offset in the same direction, the cancellation time offset is added to the synchronization time offset. The resulting offset is the temporal offset by which the control signal output by the control device must be offset from the local clock of this control device in order to achieve at least partial compensation.

[0028] A central timer may also be provided, which outputs a central time signal to at least one of the control devices described here. The control device described here (the first and / or the second) may be configured to receive a central time signal at its data interface.

[0029] The procedure described here can be implemented by means of a computer program set which, when executed on microprocessors or microcontrollers in two control devices, is set up to carry out the method described here. In particular, the computer program set can have a first computer program which, when executed in the first control device, carries out the steps of controlling the first inverter (or emitting the first switching signal), transmitting the synchronization message, receiving the response message and calculating the synchronization time offset. The first computer program can further be set up to carry out further functions or steps which are carried out by the first control device. The computer program set can have a second computer program which carries out the steps of transmitting a response message and controlling the second inverter (orOutput of the second switching signal). The first computer program can further implement the local timer of the first control device. The second computer program can also implement the local timer of the second control device. The computer programs can also be provided individually.

[0030] The procedure described here can also be implemented using a multi-part vehicle drive. This has a first and a second electric machine. The vehicle drive also has a first and a second inverter. These are connected to the corresponding electric machines in a controllable manner. This results in two parts of the vehicle drive, a first part having the first electric machine, which is operated by the first inverter, and a second part having the second electric machine, which is operated by the second inverter. Both inverters are connected to the same intermediate circuit. In other words, the DC side of the two inverters is connected to the same intermediate circuit and thus to the same intermediate circuit capacitor. In order to reduce the load on the intermediate circuit caused by the switching operations, the vehicle drive has a first and a second control device, as described herein.

[0031] The control devices are connected to the inverters for control purposes. The first control device is connected to the first inverter, and the second control device is connected to the second inverter. The control devices are configured to output a first and a second switching signal, respectively. The control devices are connected for signal transmission and are configured to carry out the method as described herein, including the steps of synchronizing, transmitting the messages, and calculating the synchronization time offset.

[0032] The multi-component vehicle drive can have different vehicle outputs, such as a rear axle drive and a front axle drive. The first electric machine can be connected to the front axle drive or the rear axle drive for transmitting torque. The second electric machine can be connected to the rear axle drive or the front axle drive for transmitting torque. Both parts of the vehicle drive are powered by the same intermediate circuit.

[0033] The Fig. 1 shows a multi-part vehicle drive and serves to explain by way of example embodiments of the methods and objects described here.

[0034] The Fig. 1 shows a vehicle drive FA with a first inverter I1, which supplies an electric machine EM1 with current and thereby operates it. Fig.Figure 1 also shows a second inverter I2 of the vehicle drive FA, which supplies an electric machine EM2 with current and thereby operates it. Both inverters I1, I2 are supplied by the same intermediate circuit ZK. This, in turn, is connected to a battery B. Battery B can be a high-voltage traction battery with a nominal voltage of more than 60 V, of at least 200 V, 400 V, or 800 V.

[0035] There is a first control device C1, which outputs a first switching signal 1 to the first inverter I1. As a result, the first control device C1 is connected to the first inverter I1 in a controlling manner. There is a second control device C2, which outputs a second switching signal 2 to the second inverter I2. As a result, the second control device C2 is connected to the second inverter I2 in a controlling manner. In the embodiment shown, the first electric machine EM1 belongs to a first output AB1 of the vehicle drive, for example a front axle drive, while the second electric machine EM2 belongs to a second output AB2 of the vehicle drive, for example a rear axle drive.

[0036] The first control device C1 has a first timer T1. The second control device T2 has a second timer T2. The timers T1, T2 are each local timers of the respective control device C1, C2. In the illustrated embodiment, the second control device C2 has a calculation device B for calculating a synchronization time offset OF. Other embodiments provide that the first control device C1 has such a calculation device, represented by the calculation device B'. In the latter case, the second control device C2 is configured to receive the synchronization time offset OF determined by the calculation device B'.

[0037] A synchronization SY is performed between the two control devices C1 and C2. For this purpose, the first control device C1 sends a synchronization message t0r to the second control device C2 (or to its data interfaces S). This message t0r contains a timestamp. This time stamp indicates the time at which the first control device C1 sends the synchronization message t0r. The time refers to the time horizon of the first control device C1, i.e., to the local clock T1 of the first control device C1.

[0038] This message t0r is received by the second control device C2 at a specific time. The second control device C2 generates a response message t1r (in response to the synchronization message). This response message t1r contains time information. This indicates when the second control device C2 received the synchronization message t0r or when the response message was sent by the second control device C2. This time information (corresponding to a timestamp) refers to the time horizon of the second control device C2, i.e., to the local clock T2 of the second control device C2. From the temporal relationship between the timestamp in the message t0r and the second fraction in the message t1r, the first control device C1 (in particular its calculation unit B') calculates the synchronization time offset OF. This is preferably transmitted to the second control device.The transmission of these messages is represented by arrows between the two control devices C1, C2.

[0039] Furthermore, the synchronization time offset OF is taken into account when generating switching signals 1 and 2, which are offset from each other by a cancellation time offset. To ensure that this cancellation time offset actually exists and that the disturbances in the switching processes in the inverter can partially cancel each other out (in the common intermediate circuit ZK), it is important that both switching signals 1 and 2 refer to the same time horizon or are synchronized with each other. The synchronization time offset OF serves to correct deviations in the individual time bases of the two control devices C1, C2 in order to achieve a common time horizon or to achieve mutually aligned (synchronized) time bases for the two control devices C1, C2.

Claims

[1] Method for operating several inverters (IN1, IN2) of a vehicle, comprising the steps: Controlling a first of the inverters with a first control device (C1) with a first switching signal (1); Controlling a second of the inverters with a second control device (C2) with a second switching signal (2); Synchronizing (SY) the first control device (C1) with the second control device (C2) by - transmitting a synchronization message (t0r) comprising a time stamp from the first control device (C1) to the second control device (C2); - in response to the receipt of the synchronization message (t0r), transmitting a response message (t1r) from the second control device (C2) to the first control device (C1), wherein the response message (t1r) comprises time information that reflects the time of receipt of the synchronization message (t0r) by the second control device (C2), and - Calculating the synchronization time offset (OF), which represents the time offset between the time stamp of the synchronization message (t0r) and the time information of the response message (t1r), by the first control device (C1) and transmitting the synchronization time offset (OF) from the first control device (C1) to the second control device (C2); wherein the first and the second inverter operate different electrical machines (EM1, EM2) and are supplied by the same intermediate circuit (ZK), and wherein the switching signals (1, 2) of the synchronized control devices (C1, C2) are offset from one another by a cancellation time offset such that the AC voltage components resulting from the operation of the inverters (I1, I2) in the intermediate circuit (ZK) at least partially cancel each other out. [2] Method according to claim 1, wherein a local timer (T1, T2) is provided in each of the first and the second control devices (C1, C2), and wherein the actuation with the first switching signal (1) and with the second switching signal (2) provides for shifting these switching signals (1, 2) against each other based on the time signals of the local timers, corrected by the synchronization time offset (OF). [3] Method according to claim 1 or 2, wherein the switching signals (1, 2) of the synchronized control devices (C1, C2) are emitted offset from one another by half a switching period or are emitted with positive and negative switching edges, wherein a plurality of the switching edges of the first switching signal (1) of a first polarity coincide with the switching edges of the second switching signal (2) of a polarity opposite to the first polarity. [4] Method according to one of the preceding claims, wherein the messages transmitted during the synchronization are designed according to a CAN protocol and are transmitted according to this CAN protocol. [5] Method according to one of the preceding claims, wherein the control devices (C2) comprise a microprocessor or microcontroller whose sequence control comprises interrupts, wherein the offsetting of the switching signals (1, 2) relative to one another provides for setting these interrupts according to the predetermined cancellation time offset between the switching signals (1, 2). [6] Method according to one of the preceding claims, wherein the offsetting of the switching signals (1, 2) relative to one another provides for an actual cancellation time offset between the switching signals (1, 2) to be adjusted to a predetermined cancellation time offset over a plurality of periods of the switching signals (1, 2). [7] Method according to one of the preceding claims, wherein the offsetting of the switching signals (1, 2) relative to one another provides for the switching signals (1, 2) to be output at different switching frequencies until a predetermined cancellation time offset is reached. [8] Control device (C2) for an inverter (IN2), wherein the control device (C2) - a data interface (S) configured to receive a synchronization message (t0r) from another control device, wherein the synchronization message (t0r) comprises a time stamp; - has a local timer (T2), wherein the control device (C2) is configured to output a response message (t1r) to the data interface (S) in response to the receipt of the synchronization message (t0r), wherein the control device (C2) is configured to provide the response message (t1r) with time information which represents the time of receipt of the synchronization message (t0r) detected by the local timer (T2); - a calculation device (B) which is arranged to calculate the synchronization time offset (OF), which represents the time offset between the time stamp of the synchronization message (t0r) and the time information of the response message (t1r), and - has a control output (A) which is configured to control the inverter (IN2), wherein the control device (C2) is configured to output a switching signal (2) at the control output (A) which is offset by the synchronization time offset (OF) and by a predetermined cancellation time offset with respect to the local timer (T2). [9] A computer program set which, when run on microprocessors or microcontrollers in two control devices, is arranged to carry out the method according to any one of claims 1-7. [10] Multi-part vehicle drive with a first and a second electrical machine (EM1, EM2) and a first and a second inverter (IN1, IN2), which are connected in a driving manner to one of the electrical machines and which are connected to the same intermediate circuit, wherein the vehicle drive has a first and a second control device (C1, C2), which is connected in a driving manner to one of the inverters (IN1, IN2) and is designed to output a first and a second switching signal (1, 2), respectively, wherein the control devices (C1, C2) are connected to one another in a signal-transmitting manner and are designed to carry out the method according to one of claims 1-7. [11] Multi-part vehicle drive according to claim 10, wherein the first and second electric machines (EM1, EM2) are connected to different vehicle outputs (AB1, AB2).

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