DE102011003566A1 - Method and device for calibrating at least one current sensor - Google Patents

Abstract

The invention relates to a method and a device for calibrating a current sensor (7-U; 7-V; 7-W), which is used to detect a phase current (I_U; I_V; I_W) of an electrical machine (1) controlled by an inverter (2) ) serves. For this purpose, a control unit (5) switches the electric machine (1) into a short-circuit mode in which at least one actual value of the phase current (I_U; I_V; I_W) is detected by the current sensor (7-U; 7-V; 7-W). is detected. An evaluation unit (6) compares the detected actual value or a quantity derived from the at least one detected actual value with a predefinable desired value and determines a deviation of the at least one current sensor (7-U.) As a function of a deviation of the actual value or the quantity derived therefrom 7-V; 7-W) from a standard state.

Description

The invention relates to a method and a device for calibrating at least one current sensor, which serves for detecting a phase current of an electric machine controlled by an inverter.

State of the art

For the drive in hybrid or electric vehicles electrical machines in the form of induction machines are usually used, which in conjunction with inverters - often referred to as inverter - are operated. The electrical machines are operated either in motor or generator mode. During engine operation, the electric machine generates a drive torque which, when used in a hybrid vehicle, supports an internal combustion engine, for example in an acceleration phase. In generator mode, the electric machine generates electrical energy that is stored in an energy storage such as a battery or a super-cab. Operating mode and power of the electrical machine are set via the inverter.

Known inverters comprise a series of switching elements with which the individual phases (U, V, W) of the electric machine are selectively switched to a high supply voltage potential or to a low supply voltage potential. In each case, two series-connected switching elements form a half-bridge branch, wherein a first switching element with the high supply voltage potential and a second switching element with the low supply voltage potential are connected. Each phase of the electrical machine is then connected to one half-bridge branch each. The switching elements are controlled by an external control unit, which calculates a desired operating point for the electric machine as a function of the driver's request (acceleration or braking). The inverter is connected to the control unit and receives from this the corresponding operating data or control commands.

For this purpose, current sensors are provided, which are usually arranged in the connecting lines between the inverter and the electric machine and detect the currents in the individual phases of the electric machine (phase currents).

However, the current sensors can scatter due to manufacturing tolerances and / or drift depending on temperature, current amount and / or aging. However, such variations (offsets) and drifts have a negative effect on the accuracy of a torque control of the electrical machine, so that a calibration of the current sensors is required.

Disclosure of the invention

The invention provides a method for calibrating at least one current sensor, which is used for detecting a phase current of an inverter controlled by an electric machine, in which the electric machine is switched to a short-circuit mode, in which all connected to a high supply voltage potential switching elements of the inverter closed and all switching elements of the inverter connected to a low supply voltage potential are opened, or all of the switching elements of the inverter connected to the high supply voltage potential are opened, and all of the switch elements of the inverter connected to the low supply voltage potential are closed. In the short-circuit mode, at least one actual value of the phase current is then detected. Subsequently, the detected actual value or a variable derived from the at least one detected actual value is compared with a predefinable desired value and a deviation of the at least one current sensor from a standard state is determined as a function of a deviation of the actual value or the quantity derived therefrom.

The invention also provides an apparatus for calibrating at least one current sensor which serves to detect a phase current of an electrical machine controlled by an inverter. In this case, the device comprises a control unit which switches the electric machine into a short-circuit mode in which all switching elements of the inverter connected to a high supply voltage potential are closed and all switching elements of the inverter connected to a low supply voltage potential are open or all switching elements connected to the high supply voltage potential of the inverter open and all connected to the low supply voltage potential switching elements of the inverter are closed. The at least one current sensor detects at least one actual value of the phase current in the short-circuit mode. The device further comprises an evaluation unit which compares the detected actual value or a quantity derived from the at least one detected actual value with a predefinable desired value and a deviation of the at least one current sensor from a nominal value depending on a deviation of the actual value or the quantity derived therefrom Standard state determined.

Advantages of the invention

In order to be able to calibrate current sensors, one needs at least one reference point to which the current flow through a sensor in the standard state is known. In the short-circuit mode of the electric machine, phase currents set in, the values of which are essentially influenced only by the electrical machine and the temperature and which are consequently known in advance. The invention is based on the basic idea of using these known current values in order to determine deviations of a current sensor which detects the phase current from a standard state. The method according to the invention and the method according to the invention offer the advantage that the calibration takes place "under load", which makes it possible to calibrate a current sensor even with different amounts of current and resulting rotational speeds. This, in turn, is particularly advantageous because the deviations of a current sensor from a standard state, ie the offsets and drifts via temperature, current amount and aging, are not linear. In addition, the calibration according to the invention in the short-circuit mode also offers the possibility of not only evaluating a deviation from a standard value, but also of taking into account the sign of the deviation.

In order to increase the accuracy of the calibration method according to the invention, it is provided according to an embodiment of the invention to detect actual values of the phase current over at least one full period, to integrate the detected actual values, to compare the resulting current integral or a quantity derived therefrom with a desired value and depending on a deviation of the current integral or a quantity derived therefrom, the deviation of the at least one current sensor from a standard state can be determined from the desired value.

In a short circuit mode, which is often referred to as an active short circuit, the phase currents oscillate around the zero point. If one integrates the acquired actual values of a phase current over one or more full periods, eg. B. triggered by a zero crossing of a rising edge, the current integral must be zero. The value "zero" thus represents the desired value. If a value deviating therefrom results for the current sensor to be calibrated, a measured value of the current sensor can be corrected according to the magnitude and sign of this deviation and thus the current sensor can be calibrated.

If, in each case, a current sensor for detecting the respective phase current is provided for each phase of the electrical machine, a summation current of the current sensors can also be used for the calibration. For this purpose, at least one actual value of the respective phase current is detected by each current sensor in the short-circuit mode of the electrical machine. The detected actual values are then summed up and the resulting summation current is compared with a predefinable setpoint value. Depending on a deviation of the summation current from the desired value, the deviation of the current sensors from a standard state is then determined.

Since the phase current to be detected by the current sensor in the short-circuit mode is dependent on the rotational speed of the electric machine, it is provided according to an embodiment of the invention that in the short-circuit mode, a variable characterizing the rotational speed of the electric machine is detected and the target value in dependence is specified by the detected speed.

In addition, the phase current to be detected by the current sensor in the short-circuit mode is also dependent on a temperature in the region of the current sensor. Therefore, it is advantageous to detect a temperature in the region of the at least one current sensor and to specify the desired value as a function of the detected temperature.

A particularly simple realization results when the speed and / or temperature-dependent setpoints are specified in the form of characteristic curves which are stored in an evaluation unit.

To further increase the accuracy of the calibration, the deviation of the current sensors from a standard state can also be determined at at least two different rotational speeds and / or temperatures.

Advantageously, an offset in the de-energized state of the electrical machine can additionally be determined for the at least one current sensor. If a current sensor for detecting the respective phase current is provided for each phase of the electrical machine, this can be done concretely in that at least one actual value of the respective phase current is detected by each current sensor in the de-energized state and the detected actual values are added up. In the de-energized state, a summation current of "zero" must result in the standard state of the current sensors. In this respect, the resulting summation current can be interpreted as the total offset of the current sensors.

Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the accompanying figures.

Brief description of the drawings

Show it:

1 3 is a schematic block diagram of an electrical machine controlled by an inverter;

2 a flowchart of a calibration method according to the invention.

Description of the embodiments

1 shows a schematic representation of a three-phase electric machine 1 which can be designed, for example, as a synchronous, asynchronous or reluctance machine, with an inverter connected thereto in the form of a pulse-controlled inverter 2 , The pulse inverter 2 includes switching elements 3a - 3f in the form of circuit breakers, which with individual phases U, V, W of the electric machine 1 are connected and the phases U, V, W switch either against a high supply voltage potential T + or a low supply voltage potential T-. The switching elements connected to the high supply voltage potential T + 3a - 3c are also called "high-side switch" and connected to the low supply voltage potential T- switch 3d - 3f referred to as "low-side switch" and can be embodied for example as Insulated Gate Bipolar Transistor (IGBT) or as Metal Oxide Semiconductor Field-Effect Transistor (MOSFET). The pulse inverter 2 further includes a plurality of free-wheeling diodes 4a - 4f , which in each case parallel to one of the switching elements 3a - 3f are arranged. The switching elements 3a and 3d . 3b and 3e such as 3c and 3f each form a half bridge 10a . 10b respectively. 10f , which in each case one of the phases U, V, W of the electrical machine 1 assigned.

The pulse inverter 2 determines the power and operating mode of the electric machine 1 and is of a first control unit shown only schematically 5 which also in the inverter 2 can be integrated, driven accordingly. The electric machine 1 can be operated either in motor or generator mode.

Parallel to the pulse inverter 2 is a so-called DC link capacitor 6 arranged, which also in the pulse inverter 2 can be integrated and which essentially serves to stabilize a voltage of an energy storage, so for example a battery voltage.

In the connecting lines between the pulse inverter 2 and the electric machine 1 is each a current sensor 7-U respectively. 7 V respectively. 7-W arranged, which detects the phase currents I_U, I_V and I_W in the phases U and V and W of the electric machine 1 serve. Output signals of the current sensors 7-U . 7 V and 7-W become the control unit 5 supplied and taken into account in the control of the pulse inverter.

The electric machine 1 is designed in the illustrated embodiment, three-phase, but may also have fewer or more than three phases.

To ensure sufficient accuracy in the regulation of the torque of the electric machine 1 through the control unit 5 to ensure the current sensors 7-U . 7 V and 7-W calibrated. The calibration method according to the invention will be described below with reference to FIG 2 explained.

In a first step S1, the electric machine is actively switched to a short-circuit mode. This is done by the control unit 5 all connected to the high supply voltage potential T + switching elements 3a - 3c of the pulse inverter 2 (High-side switch) closed and all connected to the low supply voltage potential T- switching elements 3d - 3f of the pulse inverter 2 (Low-side switch) open or all high-side switches 3a - 3c open and all low-side switches 3d - 3f of the inverter closed.

In a second step S2, through each of the current sensors 7-U . 7 V and 7-W in each case at least one actual value of the respective phase current I_U or, I_V or, I_W is detected. In addition, a speed of the electric machine 1 characterizing size and a temperature in the range of the current sensors 7-U . 7 V and 7-W detected.

In a third step S3, the detected actual values are evaluated by an evaluation unit 8th which is in the control unit 5 can be integrated or can be implemented as a separate unit, each compared with a predetermined target value. The setpoints are in speed and temperature-dependent form in the evaluation unit 8th deposited in the form of characteristic curves. Depending on the resulting deviations of the actual values from the respective nominal values, the deviations of the individual current sensors then become 7-U . 7 V and 7-W determined by a standard state. The current sensors are calibrated and the deviations determined by the control unit 5 in the processing of the output signals of the current sensors 7-U . 7 V and 7-W each be taken into account.

Alternatively or additionally, actual values of the phase currents I_U, I_V and I_W can also be detected in each case over one or more periods in step S2. In this case, the actual values are first integrated in step S3 for each of the phase currents I_U, I_V and I_W. Subsequently, the resulting current integrals are compared with corresponding (integral) setpoint values and, depending on the comparison results, the deviations of the individual current sensors 7-U . 7 V and 7-W determined by the standard state. Since the phase currents I_U, I_V and I_W oscillate in the short-circuit mode around the zero point, the current integral when integrated over one or more full periods, z. B. triggered by a zero crossing of a rising edge, zero. The value "zero" thus represents the desired value in this case.

In addition to the individual currents in phases U, V and W, a summation current of the phases can also be used for calibration. Thus, as an alternative or in addition to the described evaluation method in step S3, the actual values of the individual phase currents I_U, I_V and I_W can also be added up and the total current can be compared with a corresponding (sum) setpoint.

The setpoint values for evaluating the current integral and the total current can of course also be stored in the evaluation unit in the form of speed-dependent and temperature-dependent characteristic curves.

In order to increase the quality of the calibration, the steps S1 to S3 are advantageously repeated at different operating points, that is to different rotational speeds and / or temperatures.

In addition, in the de-energized state of the electric machine also 1 an offset of the current sensors 7-U . 7 V and 7-W be determined. This is the electrical machine 1 initially switched to a freewheel mode, in which all switches 3a - 3f of the pulse inverter are open. In this de-energized state is through each of the current sensors 7-U . 7 V and 7-W again at least one actual value of the respective phase current I_U or, I_V or, I_W detected. These recorded actual values are then added up. If a total current different from "zero" results, this becomes the total offset of the current sensors 7-U . 7 V and 7-W interpreted.

Claims (10)

Method for calibrating at least one current sensor ( 7-U ; 7 V ; 7-W ), which is used to detect a phase current (I_U; I_V; I_W) by an inverter ( 2 ) controlled electric machine ( 1 ), in which - the electric machine ( 1 ) is switched to a short-circuit mode in which all switching elements connected to a high supply voltage potential (T +) ( 3a - 3c ) of the inverter ( 2 ) and all switching elements connected to a low supply voltage potential (T-) ( 3d - 3f ) of the inverter ( 2 ) are open or all switching elements connected to the high supply voltage potential (T +) ( 3a - 3c ) of the inverter ( 2 ) and all switching elements connected to the low supply voltage potential (T-) ( 3d - 3f ) of the inverter ( 2 ), at least one actual value of the phase current (I_U; I_V; I_W) is detected, the detected actual value or a variable derived from the at least one detected actual value is compared with a predefinable desired value and depending on a deviation of the actual value or the quantity derived therefrom, a deviation of the at least one current sensor ( 7-U ; 7 V ; 7-W ) is determined by a standard state. Method according to one of the preceding claims, wherein - actual values of the phase current (I_U; I_V; I_W) are detected over at least one full period, - the detected actual values are integrated, - the resulting current integral or a quantity derived therefrom is compared with a desired value and as a function of a deviation of the current integral or a quantity derived therefrom, the deviation of the at least one current sensor ( 7-U ; 7 V ; 7-W ) is determined by a standard state. Method according to one of claims 1 or 2, wherein for each phase (U; V; W) of the electrical machine ( 1 ) each a current sensor ( 7-U ; 7 V ; 7-W ) is provided for detecting the respective phase current (I_U; I_V; I_W) and wherein - of each current sensor ( 7-U ; 7 V ; 7-W ) in the short circuit mode of the electric machine ( 1 at least one actual value of the respective phase current (I_U; I_V; I_W) is detected, the accumulated actual values are summed up, the resulting summation current is compared with a predefinable desired value, and depending on a deviation of the summation current from the desired value, the deviation of Current sensors ( 7-U . 7 V . 7-W ) is determined by a standard state. Method according to claim 1, wherein in the short-circuit mode the rotational speed of the electric machine ( 1 ) characterizing size is detected and the setpoint is specified as a function of the detected speed. Method according to one of claims 1 or 2, wherein a temperature in the region of the at least one current sensor ( 7-U ; 7 V ; 7-W ) is detected and the setpoint is specified in dependence on the detected temperature. Method according to one of claims 2 or 3, wherein speed-dependent and / or temperature-dependent desired values in the form of characteristic curves in an evaluation unit ( 8th ) are deposited. Method according to one of claims 4 to 6, wherein the deviation of the current sensors ( 7-U ; 7 V ; 7-W ) is determined by a standard condition at at least two different speeds and / or temperatures. Method according to one of the preceding claims, wherein for the at least one current sensor ( 7-U ; 7 V ; 7-W ) In addition, an offset in the de-energized state of the electrical machine ( 1 ) is determined. Method according to claim 8, wherein for each phase (U; V; W) of the electrical machine ( 1 ) each a current sensor ( 7-U ; 7 V ; 7-W ) is provided for detecting the respective phase current (I_U; I_V; I_W) and wherein - of each current sensor ( 7-U ; 7 V ; 7-W ) in the de-energized state at least one actual value of the respective phase current (I_U; I_V; I_W) is detected, - the detected actual values are summed up, - the resulting summation current is the total offset of the current sensors ( 7-U . 7 V . 7-W ) is interpreted. Device for calibrating at least one current sensor ( 7-U ; 7 V ; 7-W ), which is used to detect a phase current (I_U; I_V; I_W) by an inverter ( 2 ) controlled electric machine ( 1 ), with - a control unit ( 5 ), which the electrical machine ( 1 ) switches to a short-circuit mode in which all switching elements connected to a high supply voltage potential (T +) ( 3a - 3c ) of the inverter ( 2 ) and all switching elements connected to a low supply voltage potential (T-) ( 3d - 3f ) of the inverter ( 2 ) are open or all switching elements connected to the high supply voltage potential (T +) ( 3a - 3c ) of the inverter ( 2 ) and all switching elements connected to the low supply voltage potential (T-) ( 3d - 3f ) of the inverter ( 2 ) are closed, - the at least one current sensor ( 7-U ; 7 V ; 7-W ), which detects at least one actual value of the phase current (I_U; I_V; I_W), and - an evaluation unit ( 6 ) which compares the detected actual value or a variable derived from the at least one detected actual value with a predefinable desired value and, depending on a deviation of the actual value or the quantity derived therefrom, a deviation of the at least one current sensor (FIG. 7-U ; 7 V ; 7-W ) determined by a standard state.

Images