Noise-corrected current measurement in an inverter

Abstract

A method is described for detecting currents flowing in an inverter (IN1, IN1') or between the inverter (IN1, IN1') and a multi-phase electrical machine (EM) connected to the inverter (IN1, IN1'). Currents (I1 - I3, I1' - I3') flowing in half-bridges (H1 - H3, H1' - H3') of the inverter (IN1, IN1') are detected. The inverter provides the currents as pulse-width-modulated phase currents for the electrical machine (EM). The detection can be performed by measuring at least one current (I1 - I3, I1' - I3') at the end of a detection period (E) and by estimating current values. The current values ​​are estimated to be currents that cannot be measured with a specified minimum accuracy due to disturbances during the detection period (E). The estimation is performed based on previously determined current values.The current (I1 - I3, I1' - I3') flowing in a half-bridge (H1) to be measured at the end of the detection period (E) is determined by estimation if the detection period (E) occurs less than a predetermined decay time (tA) after a switching edge (SF) in another half-bridge (H1 - H3, H1' - H3') of the inverter (IN1, IN1'). Otherwise, it is determined by measuring the current for the half-bridge (H1) to be measured. Furthermore, a method for controlling an electric traction drive and a current detection device are described.

Description

[0001] Electric-powered vehicles have a traction battery that powers an electric drive. The drive includes an inverter that generates current to generate a rotating field for an electric motor in the drive. This current is generated using pulse-width modulation, particularly to control the drive.

[0002] Controlling the drive requires knowledge of the actual phase currents, i.e. the currents flowing in the electrical machine. These are a direct result of the currents flowing in the inverter, particularly in the low-side section of the inverter's half-bridges, which, due to its low potential, is ideal for current measurement using a shunt. Due to the high switching speeds, it is important to ensure that the measurement is not performed at a single point in time, but rather during a measurement interval in which the current should not fluctuate significantly. In particular, no interference signal should occur during the current measurement, i.e. no interference that generates an interference signal should occur within the measurement interval, as otherwise a interference would lead to inaccuracies in the current measurement.

[0003] The task is therefore to show a way how current measurement in an electric drive can be carried out with high accuracy.

[0004] 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 figures.

[0005] It is proposed to consider the interference (interference voltages) caused by switching edges during phase current measurement. Interference voltages arise due to the switching edges that occur during pulse-width modulation to generate the phase currents. It has been recognized that the inductive and / or capacitive coupling between different windings or phases of the electrical machine can be taken into account in this way to increase accuracy and reduce distortions in current measurement.

[0006] In particular, it was recognized that crosstalk exists between the phases of the electrical machine (and thus between the connected half-bridges of the inverter), whereby interference voltage can be transferred from one half-bridge or phase to another half-bridge or phase due to the coupling effect of the star point. Measurements in a half-bridge that are subject to the interference signal due to the coupling of the interference signal from another half-bridge to the half-bridge being measured are suppressed or are not output, and in particular are not used as actual values ​​in a control system (of the electrical machine).

[0007] When currents are measured using a Kalman filter, those measurement points or current values ​​that fall within the time interval of a disturbance voltage (generated in a different phase, for example, by a switching edge) are considered incorrect measurements. Unlike valid measurements, such current values ​​are not used by the Kalman filter to correct the estimate within the Kalman filter. The time interval in which the disturbance voltage occurs, and during which measurements should not be taken in other phases, is determined by the modulation parameters (particularly the duty cycle) and the resulting switching times.

[0008] All but one phase or half-bridge can have current sensors. The current in the remaining phase is determined using the node rule, i.e. as the difference between the total current (e.g. measured at a DC voltage input of the inverter) and the sum of the currents measured in the individual phases. In general, currents can be recorded by measuring the currents, e.g. using a shunt resistor or a Hall sensor or another sensor, and can be recorded by determination, e.g. by calculation using the aforementioned difference analysis (node ​​rule), by calculating current values ​​in one winding system (or in the associated inverter) based on current values ​​from another winding system (or in the associated further inverter) or by applying a Kalman filter.The latter is particularly useful for detecting a current value when the Kalman filter outputs the current value, while the current cannot be measured with sufficient precision (free from interference) due to an interference signal. A motor control system uses these measured (using a current sensor), calculated (based on currents in another winding system / another inverter), determined (using the node rule), or detected (by estimation, e.g., using a Kalman filter) current values ​​as the input variable (actual value). The motor control system can also (temporarily) be based on current values ​​in only some of the windings or half-bridges to avoid the influence of interference. With multiple winding systems, current values ​​from phases of different winding systems can also be averaged to serve as the input variable for the motor control system.Preferably, primarily measured current values ​​are used; however, in the event of disturbances, values ​​from another winding system (adjusted by a phase shift if necessary) can be used instead. If these are also subject to disturbances, estimated values ​​can be used, and / or an update of the control system can be omitted, i.e., the input of actual values ​​can be suppressed (in order to prevent the undesirable influence of disturbed values ​​or values ​​that are incorrectly estimated due to disturbances).

[0009] A method is described for detecting currents flowing in an inverter or between the inverter and a multiphase electrical machine. Since the currents flowing in the inverter also flow identically or in combination in the windings of the electrical machine (as well as between the inverter and the electrical machine), no distinction is made in the following between currents within the inverter, currents flowing between the inverter and the electrical machine, and currents flowing in the electrical machine or its windings.

[0010] Currents are determined. In this context, “determination” is the generic term that includes measuring (using current sensors such as shunts), calculating using the node rule (as a difference), calculating based on currents from another winding system (e.g., by phase shifting), and estimating (e.g., using a Kalman filter or another estimation or prediction method). The currents flowing in half-bridges or, in general, phases of the inverter are determined. Since the electric machine is connected to the inverter, the phase currents are also determined. If the electric machine is designed in a star or delta configuration, the phase currents flowing in the electric machine are a direct, easily determined result from the currents flowing in the individual phases or half-bridges of the inverter. By determining the currents flowing between the inverter and the electric machine, orThe currents flowing in the windings or phases of the electric machine are also determined from the currents flowing in the inverter. The inverter provides pulse-width-modulated phase currents for the electric machine, for example, using (multiphase) pulse-width modulation (PWM), which is the actuator of a motor control system.

[0011] At least one current is measured in a detection period. A switch of the relevant half-bridge, in which the current sensor is located, is closed for current measurement. In particular, the switch of the half-bridge that is connected downstream of the current sensor is closed. If the current sensor is connected to a negative supply potential, the switch of the half-bridge that is connected to the negative supply potential via the current sensor is closed. This creates the current to be measured, which, however, requires amplification. This amplification is subject to a settling time during which the signal received from the current sensor (and amplified) is not yet stable (but is subject to errors due to settling). This makes it necessary to wait for this settling process until it has decayed, or until the settling process is negligible (i.e.until the errors / disturbances caused by transients are below a specified tolerance threshold). Measurement is therefore only taken at the end of or after the end of the transient response. This results in a detection period that begins with the start of the transient response (when the switch is closed) and can be sampled or measured at the end. If this effect occurring in the amplifier is viewed as an effect that generally affects the current sensor and its signal processing, then the detection period can be viewed as a time segment that begins with switching and ends with sampling. The detection period is thus characterized by a start (i.e. the start of the flow of the current to be measured), by a duration defined by the transient response of the signal processing of the current sensor, and by measuring at or after the end of the transient response.

[0012] The duration of the detection period is in particular predetermined and results, for example, from a settling time of a measuring circuit / amplifier circuit, which is necessary to achieve a desired level of precision. Preferably, at least one current is measured in each PWM period, i.e. the current in at least one half-bridge. Preferably, each PWM period has a detection period. The detection period preferably occurs at the beginning of each PWM period. The current is preferably measured by means of a shunt resistor which connects a lower (negative pole side) section of the half-bridge or the semiconductor switch present there to a negative potential of a supply voltage. This section is also referred to as the low-side section and corresponds in particular to a so-called base point measurement.

[0013] During or at the end of the detection period, the current of at least one phase is measured. The currents can also be estimated. It is therefore intended that the current values ​​for currents that cannot be measured with a specified minimum accuracy due to disturbances during the detection period (including the end of the detection period) are estimated. The estimate is based in particular on previously determined current values. The disturbances are, in particular, disturbances caused by switching edges of the pulse width modulation in a phase that are connected or coupled to the phase whose current is to be measured. The time of the disturbance can thus be determined. The disturbance occurs, due to ringing effects, for a certain period of time after the switching edge. This period corresponds to a decay time during which the disturbance significantly influences the measurement (i.e.leads to a precision worse than a minimum precision). After the decay time, measurements can be taken with a precision that is at least equal to or better than the minimum precision.

[0014] The current flowing in a half-bridge to be measured during or at the end of the detection period is determined by estimation if the disturbance caused by another half-bridge significantly influences the current measurement on the half-bridge to be measured. To avoid disturbances, estimation is carried out if the detection period takes place less than a predetermined decay time after a switching edge in another half-bridge of the inverter. The other half-bridge is coupled to the half-bridge whose current is being determined (by estimation) with regard to the disturbance, either by a common star point or inductively or capacitively coupled. The decay time can be changed depending on the strength of the coupling. If the strength of the coupling between the half-bridge causing the disturbance and the half-bridge to be determined (half-bridge whose current is to be determined) is low, then the decay time is shorter than for couplings where the coupling is greater in comparison.If the detection period is less than a predetermined decay time after a switching edge in another half-bridge of the inverter, then an estimation must be made, otherwise the current for the half-bridge to be measured is determined by measuring the current for this half-bridge, ie by measuring in this half-bridge or by measuring the current in other half-bridges and subsequent calculation using the node rule.

[0015] It can be provided that the fault-inducing half-bridge and the half-bridge to be determined are provided in the same winding system. In other words, it can be provided that the half-bridge to be measured and the other half-bridge are connected to different windings that are connected via a common star point or via a delta configuration. It can also be provided that the half-bridge to be measured and the other half-bridge belong to different winding systems that are provided in the same stator. In this case, the different winding systems or windings present in the different winding systems are coupled to one another via the common stator. This coupling is in particular a magnetic coupling and can also (additionally) comprise a capacitive coupling.

[0016] If a predetermined decay time has not yet ended after the last switching edge occurred, the current can only be determined incorrectly due to the disturbances that occur during the decay time and are introduced into the half-bridge to be measured. In this case, the relevant current for the determination period can therefore be estimated. This estimate preferably excludes the actual current of the half-bridge to be recorded, i.e. the current that would result from measurement and which can only be measured incorrectly due to the disturbance. An estimation algorithm, such as a Kalman filter, can be used for this purpose in order to reproduce the current flow for the relevant half-bridge or winding using a model (of the electrical machine and / or the inverter).If the detection period is less than a predetermined decay time after the last switching edge executed in the half-bridges, this is considered a measurement failure for the estimation algorithm, i.e. a measured value that was determined (fully or partially) during the decay time is not included in the estimation or model-based prediction. Instead, the last (valid, i.e. not influenced by disturbances) measured value, a moving average, or a result of the estimation algorithm (Kalman filter) for the relevant detection period can be used. Thus, if the detection period is less than a predetermined decay time after the last switching edge executed of all switching edges in the half-bridges of the inverter, the current is determined by estimation.In particular, it is provided that the current is determined by estimation if the detection period for the current detection in a half-bridge / winding is less than the predetermined decay time after the last switching edge of all switching edges in those half-bridges that are coupled to the half-bridge to be detected (by a common star point, by connection as a delta connection, or capacitively or inductively coupled). The decay time to be considered can depend on the degree of coupling between the interference-generating half-bridge (which executes the switching edge) and the half-bridge whose current is to be detected. If there is a direct connection via a star or delta connection, a longer decay time can be considered than if only a capacitive or inductive coupling exists.Preferably, an estimate is only made if the current cannot be obtained either by applying the node rule (sum of all currents = 0) in the winding system or by calculation from a second (phase-shifted) winding system of the same stator (without significant interference). If two winding systems are provided, they can be offset from each other by 180°. If n winding systems are generally provided, they can be evenly offset from each other by 360° / n. Due to the (rotationally) symmetrical current supply (in order to generate a uniform rotating field with the multiple winding systems), conclusions can be drawn about the current of a half-bridge or winding of another winding system from the current of a half-bridge or winding of one winding system. The underlying relationship results from the rotational symmetry, i.e. the phase shift between the winding systems.If this is 180° for two winding systems, then the current of the first phase or winding of the first winding system corresponds to the negative of the first phase or winding of the second winding system, the current of the second phase or winding of the first winding system corresponds to the negative of the second phase or winding of the second winding system and the current of the third phase or winding of the first winding system corresponds to the negative of the third phase or winding of the second winding system, etc. This also applies to the connected half-bridges. With two half-bridges this results in a phase shift of 180°, which in sinusoidal waves manifests itself as a change in polarity, i.e. by the formation of the negative current value. With a different number of winding systems a corresponding factor results.In general, the phase shift, by means of which the current value of one winding system can be deduced from the current value of another winding system that is phase-shifted by p, results from the cosine of p.

[0017] The detection period preferably begins with the PWM period (of the winding system or the half-bridges connected to the relevant winding system), i.e. it begins with the closing of the switch of the half-bridge which is connected to the current sensor. The detection period can be shifted relative to the start of the PWM period, for example to the end of the decay time after the last switching edge. The detection period can be shifted such that it does not occur before the end of the decay time which is to be taken into account for the half-bridge to be measured. The detection period is preferably not shifted into a switching edge. If the shift would result in a switching edge falling within the detection period, the disturbance from which is transferred from the half-bridge to be switched to the half-bridge to be measured, then no measurement is taken (orThe use of a measurement result is omitted—particularly in the sense of a measurement failure for the estimation algorithm. In this case, the relevant current value can be estimated, especially if it cannot be calculated using the node rule or can be obtained by calculation from a second (phase-shifted) winding system of the same stator (without significant interference). With a variable duty cycle (i.e., if two consecutive PWM periods have different duty cycles), the changed time of occurrence of the switching edge of the new PWM period must be taken into account.

[0018] The current flowing in a half-bridge to be measured during or at the end of the detection period is determined by measuring the current for the half-bridge to be measured, by measuring the current flowing through the half-bridge to be measured (and in particular, through the switch connected to the current sensor). This is done unless the release period extends into the detection period (i.e. the end of the release period falls within the detection period), and unless the detection period can be shifted (delayed) in such a way that no switching edge falls within the detection period. In this case, measurement is possible because the release period does not overlap with the detection period.the detection period can be shifted in such a way that neither the decay time after a switching edge of a preceding (first) PWM period extends into the detection period, nor a switching edge of a directly following (second) PWM period falls into the detection period.

[0019] If a half-bridge to be measured does not have a current sensor or if the measurement of this half-bridge is faulty, the current value for the half-bridge to be measured can be determined by applying the node rule and measuring in the other half-bridges of the winding system. The current of the half-bridge to be measured can be calculated as the difference between a total current and a residual total current. The residual total current is measured as the current flowing through all other half-bridges (of the winding system), i.e. as the sum of the currents flowing through the other half-bridges / phases. The total current is the current supplied to the winding system, for example a supply current for the inverter. This can also be measured in order to record the residual total current, i.e. the sum of the (measured) currents of the remaining half-bridges. For the measurement of the currents in the other half-bridges or the total current, it can also be the case that the measurement is carried out for one determination period (orat the end of a detection period), whereby the last switching edge that generates disturbances for one of the measurements should be at least the decay time before (the beginning of) the detection period.

[0020] As mentioned, currents can also be estimated as current values ​​if a measurement would be subject to a disturbance. Current values ​​​​corresponding to currents can be estimated based on previously determined current values. A model can be used for the estimation that characterizes the current flow in the inverter and the electrical machine connected to it. The estimation can be carried out using a Kalman filter that takes the model into account. Furthermore, the estimation can be carried out using a (moving) average or it can be assumed for the estimation that the previously measured current value corresponds to the current value to be determined currently, or previous current values ​​can be extrapolated to estimate the current value to be determined currently.

[0021] As mentioned, only undisturbed measured values ​​are preferably used for the estimation, and currents whose measurement is affected by a disturbance are masked out or suppressed. When estimating the current values, the previous (disturbance-free measured) current values ​​are preferably used, and those current values ​​that cannot be measured with a specified minimum accuracy due to disturbances during the determination period are excluded. This applies in particular to disturbances that occur due to switching edges of the PWM control of the half-bridges and are entered in the half-bridge to be measured. For this purpose, knowledge of the decay time is relevant, during which measurements are disturbed and which begins with the occurrence of a switching edge. The occurrence of the switching edge is determined based on the duty cycle of the pulse-width-modulated phase currents, in particular based on the duty cycle.When shifting / delaying the detection period (so that the decay time does not extend into the detection period and thus the detection period is subject to interference), it is preferable to ensure that a subsequent switching edge does not fall into the detection period. The detection period is therefore - if possible - not delayed or shifted so much that the switching edge of the current PWM period falls into the detection period and, in particular, does not coincide with the end of the detection period at which the measurement is performed. If the time between the last switching edge of the immediately preceding PWM period and the first switching edge of the current PWM period is shorter than the minimum duration of the detection period, then no measurement is taken for this detection period, but rather it is estimated or determined, for example, based on a measurement in a different, phase-shifted winding system or half-bridges connected to it.Since the time of occurrence of the first switching edge of the current PWM period is relevant here, the determination period is (also) planned taking into account the duty cycle of the current PWM period. This duty cycle can differ from the duty cycle of the previous PWM period if the duty cycle changes. The time of occurrence of the switching edge is preferably determined from the time of occurrence of the most recently occurring switching edge based on the largest duty cycle of the pulse-width-modulated phase currents. In particular, the largest duty cycle of all duty cycles of half-bridges connected to the same winding system is used to shift the determination period or to decide whether a measurement can be performed or whether a current value needs to be determined by other means (estimation, calculation, etc.).This prevents the last switching edge of another half-bridge (the half-bridge with the highest duty cycle) from disturbing the measurement in the half-bridge to be measured, whose last switching edge would allow a detection period after the decay time (neglecting the other half-bridges) due to a lower duty cycle.

[0022] The procedure described here can be used to operate an electric traction drive of a vehicle. A corresponding method for controlling an electric traction drive, which comprises an electric machine and an inverter, provides that the inverter provides pulse-width-modulated phase currents (generally: a PWM drive signal) for the electric machine. The electric machine is multi-phase and has one or more winding systems. The control (as a procedure) provides space-vector-based regulation of the electric machine. This is implemented using the inverter. The inverter can be a single-component device, for example, if the electric machine has only one winding system.If multiple winding systems of the electrical machine are to be controlled, the inverter can be considered a multi-component inverter, as the inverter comprises multiple groups of half-bridges, each group being connected to and operating a specific winding system. The pulse-width-modulated phase currents are generated according to the closed-loop control system. The closed-loop control system receives phase currents as feedback or input variables (actual variables). These are acquired according to the method described here and, in particular, derived from the currents that are acquired as described herein. The currents acquired in this way can be space-vector transformed in order to be processed as space-vector transformed variables in the closed-loop control system.

[0023] Furthermore, a current detection device is described which is designed to carry out the methods described here. In particular, the current detection device is designed to detect currents as described herein, in particular by measuring when no significant disturbance occurs due to switching edges, and by the calculation and / or estimation described here. The current detection device can have an input which is designed to receive signals that represent currents. The input can be a digital input which is designed to receive digital signals, or can be an analog input which is designed to receive analog signals, wherein in the latter case, an analog / digital converter is connected downstream of the input in order to convert the signal into a digital form. The input can be multi-part, i.e.can physically have several input connections, or can logically have several channels for receiving signals. The current determination device has an output which is set up to output the determined currents, in particular to output the currents as signals which represent the currents. This output can be designed as a physical output, but is preferably designed as a memory area in which values ​​which represent the currents are stored, wherein these values ​​can be retrieved from the memory area for further processing, for example to implement a control system, for example as actual variables of a control system. The current determination device can thus be part of a data processing device or control device which carries out further functions, preferably based on the current values ​​which are provided by the current determination device. The control device orThe current detection device can be implemented by a programmable circuit on which software code executes functions of the method described here (when executed on a processor). Software code that executes the method described here when executed on a processor also implements the current detection procedure described here. The Fig. 1, Fig. 2a and Fig. 2b serve to explain exemplary embodiments of the procedure and devices described here.

[0024] The Fig. Figure 1 shows an electrical machine EM with two winding systems WS, WS'. The winding systems each have three windings with the reference symbols 1, 2, 3 or 1', 2', and 3'. Thus, the electrical machine EM has two three-phase winding systems. The three-phase winding systems WS, WS' each comprise three windings, which are each connected to one another via a common star point. This results in three phase connections for each winding system WS, WS', whereby the phase connections of the winding system WS are designated U, V, W, and the phase connections of the second winding system WS' are designated U', V', and W'. The first winding system WS is connected to a first inverter IN1 via these phase connections U, V, W. The second winding system WS is connected to a second inverter IN1' via the phase connections U', V', W'.The two inverters IN1, IN1' can also be considered as parts of a common inverter, especially since they are supplied with the same voltage (between the potentials HV+ and HV-) of the accumulator AK.

[0025] Each part or each inverter IN1, IN1' has a half-bridge H1 - H3 or H1' - H3' for each phase (of the electric machine). Each half-bridge has two series-connected switches 11 - 23, with the connection point of the switches serving as the connection point for the phase connection U, V, W (U', V', W'). The first half-bridge H1 is formed by the series connection of switches 11 and 21, the second half-bridge H2 is formed by the series connection of switches 12 and 22, and the half-bridge H3 is formed by the series connection of switches 13 and 23. The half-bridges H1' to H3' of the second inverter IN1' are formed in the same way and are connected to the phases U', V', W' of the second winding system WS' via the connection points within the half-bridges.

[0026] To record the phase currents, where the current IU is shown as an example for phase U of the first winding system WS, currents I1, I2 and I3 are recorded in the half-bridges H1, H2 and H3. The same applies to the half-bridges H1', ​​H2' and H3', in which the currents I1', I2' and I3' flow. The respective currents in the half-bridges H1 - H3, H1' - H3' are shown at the base point, i.e. at a location between a negative potential HV- and the following low-side switch, for example 21, 22 or 23 of the first inverter I1 or the respective low-side switch LS of the second inverter I2. Current sensors for recording are preferably provided where the currents are recorded, i.e. at the locations designated by the reference numerals used for the currents. Based on the currents I1 to L3 and I1' to I3' measured at the base point, the phase currents IU can be determined or the currents in the windings 1 - 3 and 1' - 3' can be derived.

[0027] The half-bridges of inverters IN1, IN1' are controlled by a signal generated by pulse width modulation (PWM). For this purpose, the switches of the half-bridges have a control input symbolically represented by arrows. It is evident that, through the connection via the star point of the connected windings 1 - 3, a switching edge, such as that which occurs during pulse width modulation, can be transmitted from one half-bridge H1 to another half-bridge H2 or H3. If a switching edge occurs in half-bridge H1, the resulting disturbance is transmitted to half-bridges H2 and H3, which are connected to half-bridge H1 via the respective winding system. If half-bridge H2 or H3 is a half-bridge to be measured, it is potentially disturbed by switching edges in half-bridge H1. To illustrate this in more detail, the following Fig. 2a and Fig. 2b is examined in more detail.

[0028] The Fig. Figure 2a shows a section of a PWM signal, where the switching edge SF of a previous PWM period A(k-1) can be seen on the left, with the following PWM period A(k) beginning at point PB. Point PB marks the start of the following or current PWM period A(k). Point PB also corresponds to the end of the previous PWM period A(k-1), particularly assuming that the current period directly follows the previous period. It can be seen that the switching edge SF is further away from time PB than the switching edge of the following period A(k) is from the start of the period PB. This results from a variable duty cycle, where the duty cycle of the previous period A(k-1) is smaller than the duty cycle of the current or subsequent period A(k).

[0029] In the Fig. Figure 2a also symbolically shows that the switching edges SF cause a disturbance ST. The disturbance arises in the switching half-bridge or in the winding connected to it, and is transmitted via the star point, via inductive and / or capacitive coupling, to the other windings of the same winding system or half-bridges connected to the same winding system. Therefore, care must be taken to ensure that a disturbance originating from a first switching half-bridge does not lead to an incorrect or disturbed measurement in another half-bridge. The procedure described here therefore takes into account whether switching the half-bridge coupled via the winding system disturbs the measurements of another half-bridge.

[0030] The Fig. Figure 2b shows the respective PWM signals for two phases U, V for a previous period A U (k-1), A V (k-1) and a subsequent or current period AU (k), A V (k). A switching edge SF1 in the upper PWM signal (phase U) generates a disturbance (compare Fig. 2a), so that a subsequent determination period E would be set for this half-bridge, and using the measured current value, a minimum precision could not be achieved. If only the switching edges SF 1 occurred in the half-bridge and in the half-bridges connected to it or coupled to it, then after a decay time tA, the disturbance would no longer be relevant or would have decayed, and a measurement in this half-bridge or another half-bridge would be possible with a minimum precision. In this case, the decay time tA would begin at the onset of the disturbance with the switching edge SF 1.

[0031] It is the Fig. 2b that the switching edge SF 2 occurs later in the second phase V. This results in a disturbance for the indicated decay time tA not only for phase V (shown below), but also for the first phase U (shown above), since there is a coupling between the half-bridges or windings of the winding system, via which the disturbance is transmitted.

[0032] To measure the current, a detection period E is provided, within which the current is recorded, particularly at its end. Within this detection period E, an amplifier, for example, oscillates, so that no measurement can be performed during this settling period, but only at or after the end of the settling period. The earliest time for the end of the detection period E (i.e. for the measurement) is after the end of the disturbance or when a decay time tA has ended. The decay time tA describes the duration for which a disturbance can disrupt a measurement (on the same half-bridge or on a different half-bridge) in such a way that minimum precision cannot be guaranteed.

[0033] In the Fig. 2b and also in the Fig. In Figure 2a, a cross represents a possible point in time for which the current is measured. However, it must be taken into account that the decay time tA since the last disturbance or since the last switching edge must be taken into account, whereby the measurement at the end of the detection period E can only be carried out when the decay time tA has completely ended. Otherwise, the measurement at the end of the detection period E would be subject to a disturbance that persists throughout the entire decay time tA and is then considered to be over. According to the procedure described here, not only are the decay time and the switching edges present there for one phase taken into account, but a switching edge in a switching half-bridge is also taken into account during the measurement and when defining the detection period E if the current is to be measured in another half-bridge.This prevents a situation where, while a sufficient interval (decay time) is maintained since the last switching edge in the same phase to measure with a minimum of precision, the measurement result is nevertheless distorted by a later switching edge in a different phase, the disturbance of which is transmitted via the coupling to the half-bridge in which the measurement is performed. Fig. 2b, this would mean that even for a measurement in phase U (upper), the later edge SF2, rather than the earlier edge SF1, is to be considered. Based on the later edge SF2, the detection period E for the upper phase is defined, with the decay time tA beginning with the later edge, and the end of the decay time defining the earliest time at which the measurement can begin at the end of the detection period E.

[0034] However, it must be taken into account that a switching edge of the same or a different phase or half-bridge may occur in the thus shifted or delayed detection period E, which results in the following PWM period. Since this renewed switching edge in the following or current PWM period (A(k)) would disrupt the measurement at the end of the detection period E, a measurement is only performed during the detection period E if its start lies after the end of the decay time and if the end of the detection period E lies before the earlier of the switching edges (SF3, SF4) of the following PWM period. In this case, variable duty cycles that define the times of the switching edges must be taken into account. In addition, any dead times of the inverter must be taken into account. In the illustrated Fig.2b, the edge SF 4 is the earlier of the two edges SF 3 and SF 4 of the subsequent PWM period k. Therefore, the detection period E should end before the switching edge SF4 occurs. Since the detection period E itself has a minimum duration and can only be measured at the end of the minimum duration, an undisturbed measurement with steady-state data processing of the current sensor may not be possible. Therefore, instead of a measurement, the current is estimated or determined by another method.

[0035] In summary, the later switching edge SF2 of the switching edges SF1, SF2 of a preceding PWM period k-1 is the beginning of the decay time tA for all measurements in all half-bridges coupled to the half-bridge executing the later switching edge SF2. This coupling is particularly possible via a delta or star-point connection of the connected windings 1-3, 1'-3'. The end of the decay time tA defines the earliest possible time for the beginning of the detection period E for all half-bridges connected to the half-bridge executing the switching edges SF2 (= fault-triggering half-bridge). The measurement at the end of the detection period E is then passed on as a (valid) current value if the earliest of all subsequent switching edges SF3, SF4 occurs after the detection period E.In other words, measurements in a detection period E are not performed or discarded if the time of the measurement does not occur at least by the decay time after the last switching edge (of all switching edges of all coupled half-bridges) of a previous PWM period k-1, and if the end of the detection period E is before the earliest of all switching edges of all coupled half-bridges of a current PWM period k.

[0036] Half-bridges are coupled when they are connected to each other via a delta connection, a star-point connection, or a capacitive or inductive coupling of the connected windings. In particular, half-bridges are coupled when they belong to the same winding system or are connected to each other via a delta or star-point connection. The capacitive or inductive coupling can result from the delta or star-point connection.

[0037] If the measurement is not performed or rejected, an estimate can be made using a Kalman filter. However, if possible, a measured current of the corresponding phase of the other winding system is preferably used, for example, after changing the polarity of the current (i.e., forming the negative value) or otherwise taking into account the phase shift between the winding systems.

[0038] If this is not possible, for example because in the second winding system the detection period also begins too early after the last switching edge (i.e. still during the release period) or a switching edge of the following period would already fall into the detection period, then the current value can be determined by estimation, for example using a filter. When considering the second winding system WS', the coupling between the half-bridges H1' - H3' is also taken into account, in that the release period refers to the last of all switching edges in all half-bridges H1' - H3' of a previous PWM period k-1, and in that the earliest of all switching edges of all half-bridges H1' - H3' is taken into account for the current period k.the measurement for the half-bridges of the second inverter IN1' is suppressed or not carried out in the detection period E if the earliest of all switching edges of all half-bridges of the second winding system would fall into the detection period E or would coincide with the end of the detection period E (ie with the measurement time).

Claims

[1] Method for detecting currents flowing in an inverter (IN1, IN1') or between the inverter (IN1, IN1') and a multi-phase electrical machine (EM) connected to the inverter (IN1, IN1'), the method comprising: Determining currents (I1 - I3, I1' - I3') flowing in half-bridges (H1 - H3, H1' - H3') of the inverter (IN1, IN1'), which provides the currents as pulse-width modulated phase currents for the electrical machine (EM), by measuring at least one current (I1 - I3, I1' - I3') at the end of a detection period (E) and by Estimating current values ​​for currents that cannot be measured with a specified minimum accuracy at the end of the determination period (E) due to disturbances, based on previously determined current values, where the current (I1 - I3, I1' - I3') flowing in a half-bridge (H1) to be measured during the detection period (E) is determined by estimation if the end of the detection period (E) is less than a predetermined decay time (tA) after a switching edge (SF) in another half-bridge (H1 - H3, H1' - H3') of the inverter (IN1, IN1'), and otherwise is determined by measuring the current for the half-bridge (H1) to be measured. [2] Method according to claim 1, wherein the half-bridge to be measured and the other half-bridge (H1 - H3, H1' - H3') are connected to different windings (1, 2, 3) which are connected via a common star point or via a delta configuration, or wherein the half-bridge to be measured and the other half-bridge (H1 - H3, H1' - H3') belong to different winding systems (WS, WS') which are provided in the same stator. [3] Method according to claim 1, wherein the half-bridge to be measured and the other half-bridge (H1 - H3, H1' - H3') are provided in the same winding system (WS) and the current (I1 - I3, I1' - I3') flowing in a half-bridge (H1) to be measured during the detection period (E) is determined by phase-shifting a measured current of a half-bridge (H1') of another winding system (WS'), wherein the measured current is shifted by the complementary angle of the phase shift existing between the half-bridge (H1') of the other winding system (WS') and the half-bridge (H1) to be measured. [4] Method according to claim 1, 2 or 3, wherein, if the measurement at the end of the determination period (E) takes place less than a predetermined decay time (tA) after the last executed switching edge (SF2) of all switching edges (SF1, SF2) in the half-bridges (H1 - H3, H1' - H3') of the inverter (IN1, IN1'), the current is determined by estimation. [5] Method according to one of the preceding claims, wherein the current flowing in a half-bridge to be measured (H1 - H3, H1' - H3') during the detection period (E) is determined by measuring the current (I1 - I3, I1' - I3') for the half-bridge to be measured (H1 - H3, H1' - H3'), by measuring the current (I1) flowing through the half-bridge to be measured (H1), or by measuring the residual total current (I2 + I3) flowing through all other half-bridges (H2, H3), and the current of the half-bridge to be measured is calculated as the difference between a total current (I1 + I2 + I3) and the residual total current (I2 + I3). [6] Method according to one of the preceding claims, wherein the current values ​​associated with currents (I1 - I3, I1' - I3') are estimated on the basis of the previously determined current values ​​and a model which characterizes the current flow in the inverter (IN1, IN1') and the electrical machine (EM) connected thereto. [7] A method according to claim 6, wherein the current values ​​associated with currents are estimated by means of a Kalman filter taking into account the model. [8] Method according to one of the preceding claims, wherein the preceding current values ​​are used in estimating the current values ​​and those current values ​​are excluded which cannot be measured with a predetermined minimum accuracy due to disturbances (ST) during the determination period (E). [9] Method according to one of the preceding claims, wherein the time of occurrence of the switching edge (SF, SF1, SF2) is determined based on the duty cycle of the pulse-width modulated phase currents. [10] Method according to claim 9, wherein the time of occurrence of the switching edge (SF, SF1, SF2) is determined as the time of occurrence of the last occurring switching edge on the basis of the largest duty cycle of the pulse-width modulated phase currents. [11] Method for controlling an electric traction drive comprising an electric machine (EM) and an inverter (IN1, IN1') which provides pulse-width-modulated phase currents for these, wherein the controller provides a space vector-based control of the electric machine (EM) by means of the inverter (IN1, IN1') and the pulse-width-modulated phase currents are generated according to the control, and wherein the control is based on phase currents as an actual variable of the control and the phase currents are detected according to the method according to claim 1. [12] Current detection device with inputs arranged to receive signals representing currents, wherein the current detection device is arranged to carry out the method for detecting currents according to one of claims 1-10 and the current detection device has an output arranged to output the detected currents.

Images