DE102016213276A1 - Method for controlling a semiconductor switch of a power converter, converter, electric drive arrangement - Google Patents

Abstract

Disclosed is a method for controlling at least one semiconductor switch (HS) of a power converter (WR) for providing phase currents for a rotating field machine (EM) with at least one pulse width modulated control signal (S), wherein a pulse (P1) in a signal period (T) of at least a control signal (S) is generated shifted from the center (t1) of the signal period (T) by a random offset (Δ).

Description

Technical area:

The invention relates to a method for controlling a semiconductor switch of a power converter for providing phase currents for a rotating induction machine, in particular an electric drive arrangement. Furthermore, the invention relates to a power converter and an electric drive arrangement with a said power converter.

State of the art and object of the invention:

Rotary electrical machines or induction machines are usually supplied with power by converters, in particular inverters, with phase currents. In this case, a converter or an inverter converts a DC current of an intermediate circuit into one or more phase currents. For this purpose, the power converter comprises half-bridges with semiconductor switches, which are controlled by pulse width modulated control signals alternately switched fully conducting or blocking.

Due to the system, the phase currents generated in this way have harmonics that can lead to problems with the acoustics as well as the electromagnetic compatibility (EMC) of the electric drive train.

Thus, the object of the present invention is to provide a possibility with which the above-mentioned problems can be avoided or the extent of the problems can be reduced.

Description of the invention:

This object is solved by subject matters of the independent claims. Advantageous embodiments are the subject of the dependent claims.

According to a first aspect of the invention, a method is provided for controlling at least one semiconductor switch of a power converter for providing at least one phase current for a rotary field machine having at least one pulse-width-modulated control signal.

According to the method, a pulse is shifted in at least one signal period of the at least one control signal from the middle of the signal period by a random offset, in particular by the random offset percentage angle or time shifted generated.

In particular, the method is used for controlling three-phase rotating field machines. The control of the induction machine is usually done using the space vector modulation ("SVM"). For the SVM, a duty cycle is calculated for a desired setpoint pointer and for each phase. The pulses are usually output mid-synchronous to the switching period, with a constant switching frequency. The linear combination of the individual zero and active voltage vector of a switching period results in magnitude and angle of the desired target voltage pointer at the time of the symmetry axis of the pulse pattern.

According to the method, a percentage offset Δ is defined from the center of the otherwise mid-synchronous PWM signal. The maximum permitted offset Δmax must not result in the pulse pattern being shifted beyond the limits of the associated switching period. As a result of the random displacement of the symmetry axis of the pulse pattern, a twisted setpoint voltage pointer results. For this twisted reference voltage pointer, the duty cycles are calculated for each phase and the pulses are output with the time delay shifted by the random offset. This ensures that the effect of the active voltage vector continues to optimally match the current rotor position.

Due to the required high power densities of three-phase machines in the application as a vehicle drive, the rotating field frequency is usually relatively high in the range of 0 to 2 kHz. Accordingly, the switching frequency of the PWM control is about 10 times higher than the rotating field frequency.

Due to the PWM control harmonics are generated, which lead to additional losses, EMC interference and acoustic emissions in the electric drive train. An increase in the switching frequency would reduce these effects, but this also increases the switching losses, which must be limited by the existing cooling capacity due to the system. In addition, an increase in the switching frequency also reduces the voltage utilization due to the existing dead times between switching off and on of the power semiconductors.

Due to the design, the sound level in electric cars is comparatively low compared to vehicles with internal combustion engines. In addition, since the noise level in the frequency range of 10-20 kHz is very low, acoustic emissions due to a constant switching frequency can be clearly perceived and bothersome.

Based on these findings, a solution was sought with which the acoustic emissions of the electric drive train can be reduced, avoided, or advantageously distributed in the frequency range. The aim of the invention is It is to spread the spectrum around the switching frequency so that the background noise in the vehicle is perceived more pleasantly. In addition, the solution offers a very low implementation effort, since the switching frequency can be left constant. A combinability with a variable switching frequency is still given. Since the greatest effectiveness of the invention is to be determined at low speeds, exactly the most critical case is covered when the ambient noise such as rolling noise in the electric vehicle is particularly low.

Based on these findings, the above-described method is provided for controlling at least one semiconductor switch of a power converter having at least one pulse width modulated control signal, wherein a (square) pulse in at least one signal period of the at least one control signal from the middle of said signal period by a random offset Δ (but within the aforementioned signal period) is generated shifted.

Thus, in the case of a continuous space vector modulation (CSVM) method, the underlying angle for computing the duty cycles of the respective control signals for the affected signal period is shifted by a shift angle. As a result, the symmetry axis of the active voltage pointer always exactly matches the discrete time or angle for the calculation of the duty cycles. Consequently, the effect of the active voltage pointers will not be corrupted and they will be set at the right time.

In the case of a Discontinuous Space Vector Modulation (DSVM) method, the mean zero voltage pointer is omitted within the affected switching period. In this case, the rectangular pulses may be shifted twice as far as compared with the aforementioned continuous space vector modulation ("CSVM") method.

For example, the random offset is an equally distributed random offset between a maximum offset and its counterpart, namely the negative number of the amount of the maximum (positive) offset.

Alternatively, the random offset is, for example, a normally distributed random offset between the maximum offset and its counterpart.

Alternatively, the random offset may be represented by a defined pattern, as this can be implemented very easily in a microcontroller system.

For example, the random offset Δ is proportional to a product of a constant k (depending on the modulation travel), a real random number from a real number interval [-1, 1] and a difference between a maximum possible modulation degree of the converter and a current modulation degree.

∆:

der zufällige Versatz [%];

k:

eine Zahl 1/4 (bei CSVM) oder 1/2 (bei DSVM);

rand:

die reelle Zufallszahl aus dem reellen Zahlenintervall [–1, 1];

m_max:

der maximal mögliche Modulationsgrad des Stromrichters;

m:

der aktuelle Modulationsgrad für eine aktuell bereitzustellende Phasenspannung des Stromrichters.

For example, the random offset is determined by the following equation: Δ = k · edge · (m_max-m), where are:

Δ:

the random offset [%];

k:

a number 1/4 (for CSVM) or 1/2 (for DSVM);

edge:

the real random number from the real number interval [-1, 1];

m_max:

the maximum possible degree of modulation of the converter;

m:

the current degree of modulation for a currently provided phase voltage of the converter.

For example, the current degree of modulation is proportional to a quotient between the currently provided phase voltage and an intermediate circuit voltage of the converter.

sqrt(6):

Quadratwurzel von der Zahl 6;

U_ph:

Effektivwert der aktuell bereitzustellenden Phasenspannung;

U_DC:

Zwischenkreisspannung des Stromrichters.

For example, the current degree of modulation of the converter is determined using the following equation: m = sqrt (6) · U_ph / U_DC, where are:

sqrt (6):

Square root of the number 6;

U_ph:

Rms value of the phase voltage currently to be provided;

U_DC:

DC link voltage of the converter.

For example, a current rotor position and a current angular speed of a rotor of the electric machine are detected at a current time (or measuring time) before the signal period mentioned. From the detected current rotor position and the detected current angular velocity, a future rotor position is determined at a reference instant of the pulse of said signal period, which is shifted (pulse) from the middle of the signal period by the previously determined random offset. The reference time is in particular the symmetry axis of the pulse.

α_next:

die zukünftige Rotorposition zu dem Bezugszeitpunkt tb des Impulses der genannten Signalperiode;

Tm:

ein Zeitabstand zwischen dem Anfang der nächsten Schaltperiode und dem Messzeitpunkt (bzw. dem aktuellen Zeitpunkt);

α_akt:

die aktuelle Rotorposition zum Messzeitpunkt tm;

ω_akt:

die aktuelle Winkelgeschwindigkeit zum Messzeitpunkt tm;

∆:

der zufällige Versatz;

T:

die Signalperiodendauer des Steuersignals in der Signalperiode.

For example, the future rotor position for the said signal period is determined by the following equation: α_next = α_akt + ω_akt · (Tm + T / 2 + Δ · T) where are:

α_next:

the future rotor position at the reference time tb of the pulse of said signal period;

tm:

a time interval between the beginning of the next switching period and the measurement time (or the current time);

α_akt:

the current rotor position at the time of measurement tm;

ω_akt:

the current angular velocity at the time of measurement tm;

Δ:

the random offset;

T:

the signal period of the control signal in the signal period.

From the determined as described above future rotor position for said signal period, for example, a duty cycle per phase for the current signal period is determined. In this case, the determination of the duty cycle is completed, for example, before the start time of said signal period.

In accordance with another aspect of the invention, there is provided a power converter for providing at least one phase current to a rotary electric machine.

The power converter comprises at least one semiconductor switch for providing the at least one phase current and at least one signal generator for generating the at least one pulse-width-modulated control signal. In this case, the at least one signal generator is further configured to generate the pulse shifted in at least one signal period of the at least one control signal from the center of the at least one signal period shifted by a random offset.

According to yet another aspect of the invention, an electric drive arrangement, in particular for driving a hybrid electric / electric vehicle, is provided.

The drive assembly comprises a rotating electrical machine, in particular for driving the hybrid / electric vehicle, and a previously mentioned power converter, which further comprises at least one phase current line and is electrically connected via the at least one phase current line to the electric machine and is arranged, the electric machine at least to provide a phase current.

Advantageous embodiments of the method described above are, as far as incidentally, transferable to the above-mentioned converter or to the above-mentioned drive arrangement, to be regarded as advantageous embodiments of the power converter of the drive assembly.

Brief description of the drawing:

In the following, an exemplary embodiment of the invention with reference to the accompanying drawings is explained in more detail. Showing:

1 a schematic representation of an electric drive assembly with an inverter according to an embodiment of the invention; and

2A . 2 B in respective signal flow diagrams in each case one signal period of a pulse width modulated control signal of the inverter according to the prior art and a signal period of a pulse width modulated control signal according to a method according to an embodiment of the invention.

Detailed description of the drawing:

1 shows a schematic representation of an electric drive assembly EA for driving a hybrid / electric vehicle.

The drive assembly EA comprises an electric machine EM for driving the hybrid / electric vehicle, which in this embodiment is designed as a permanent magnet synchronous machine with a stator having three stator phases and a rotor rotatable relative to the stator.

The electric drive assembly EA further includes an inverter (inverter) WR for providing phase currents to the electric machine EM, a rotation angle sensor DS for detecting the rotation angle, and the rotation speed of the rotor.

The electric drive arrangement EA further comprises a measuring arrangement MA for detecting an intermediate circuit voltage U_DC at the inverter WR, and a control arrangement RA for regulating a phase voltage U_ph, which the inverter WR is to provide for the operation of the electric machine EM.

The inverter WR includes a triple bridge circuit BS as one Power output stage for providing phase currents for the electric machine EM.

The bridge circuit BS comprises three half-bridges HB, which are connected in parallel between a positive supply current line V + and a negative supply current line V-. Each of the three half-bridges HB comprises in each case a positive-voltage-side semiconductor switch HS1 and in each case a negative-voltage-side semiconductor switch HS2, the two semiconductor switches HS1, HS2 of the respective half-bridges HB being connected to one another in series. The semiconductor switches HS1, HS2 are designed, for example, as power IGBTs (insulated gate power bipolar transistor) or as power MOSFETs (power metal oxide semiconductor field effect transistor).

The bridge circuit BS further comprises three phase current lines PL, which electrically conductively connect the respective electrical connection point VP of the positive voltage side and negative voltage side semiconductor switch HS1, HS2 of the respective half bridges HB to one of the three stator phases of the electric machine EM.

The inverter WR further comprises a signal generator SG for generating pulse width modulated control signals S1, S1 ', S2, S2', S3, S3 ', with which the respective semiconductor switches HS1, HS2 of the three half bridges HB are controlled.

Signal input side of the signal generator SG is signal-technically connected to a respective signal output of the rotation angle sensor DS, a signal output of the measuring arrangement MA and a signal output of the control arrangement RA.

Signal output side of the signal generator SG is electrically connected via a respective signal output to the control terminal of the respective semiconductor switches HS1, HS2 of the three half-bridges HB.

After the circuit topology of the electric drive assembly EA based 1 is described below, their function is in particular that of the inverter WR using 2A and 2 B described in more detail:
2A shows in a schematic signal flow diagram a signal period T of a generated according to the prior art pulse width modulated control signal S0, which lies between the times t0 and t2.

In this pulse width modulated control signal S0, the signal pulse P0 or the signal section with a high level is symmetrical to the middle t1 of the corresponding signal period T, so that the time duration T01, T02 of the signal pulse P0 in the two, equally long period sections between the times t0 and t1 or t1 and t2 of the same signal period T are the same length.

2 B shows in a further schematic signal flow diagram, an analog signal period T of another pulse width modulated control signal S1, which by means of in 1 illustrated inverter WR is generated according to a method according to an embodiment of the invention.

In this control signal S1, the signal pulse P1 is asymmetrically shifted to the middle t1 of the signal period T and by an offset Δ or a shift time period Δ · T from the middle t1 of the signal period T, respectively. Thus, the time duration T11, T12 of the signal pulse P1 in the two, equally long period sections between the times t0 and t1 or t1 and t2 the same signal period T are unequal length.

The determination of the offset Δ or of the shift time Δ ·T takes place as described below:
At the measurement time tm before the start time t0 of the signal period T, for which the offset Δ or the shift time Δ · T and a duty cycle D are determined, the rotation angle sensor DS determines a current rotor position α_akt and a current angular speed ω_akt of the rotor of the electric machine EM and transmits this to the signal generator SG.

Furthermore, the control arrangement RA determines a currently to be provided phase voltage U_ph and transmits this to the signal generator SG.

Analogously, the measuring arrangement MA determines an intermediate circuit voltage U_DC and transmits this to the signal generator SG.

The signal generator SG determines from the transmitted currently to be provided phase voltage U_ph and the transmitted intermediate circuit voltage U_DC and the following equation a current modulation degree m for the signal period T: m = sqrt (6) · U_ph / U_DC, where sqrt (6) means square root of 6.

Subsequently, the signal generator SG forms a difference (m_max-m) between a maximum possible modulation degree m_max and the determined current modulation degree m and uses a number generator from a real number interval [-1, 1] selects a uniformly or normally distributed real random number rand.

The maximum possible modulation degree m_max of the inverter WR is determined in advance based on the hardware properties of the inverter WR. Ideally, namely space vector modulation ("Space Vector Modulation") and the ideal inverter WR, the maximum possible degree of modulation is m_max 1, and normally 0.98, for example.

From the difference (m_max-m), the random number rand, as well as the period T of the signal period T, the signal generator SG calculates the random offset Δ using the following equation: Δ = k · edge · (m_max - m).

Here, the factor k is a number 1/4 or 1/2, which is determined depending on the modulation method used. In the continuous space vector modulation ("CSVM") method, the factor k is 1/4. In the discontinuous space vector modulation ("DSVM") method, the factor k is 1/2.

The random offset Δ thus determined is an equally or normally distributed random offset between a maximum possible offset Δmax and its counterpart -Δmax. The following relationship applies for the maximum possible offset Δmax: Δmax = k · m_max.

The maximum offset Δmax results when the duty cycle of a zero-voltage pointer at the edge of the switching period (signal period) becomes equal to 0 (in the case of an ideal inverter) or a hardware limit is reached (in the case of a real inverter).

Further, the signal generator SG determined from the previously determined random offset Δ, the current rotor position α_akt and the current angular velocity ω_akt using the following equation, a future rotor position α_next of the rotor at a reference time tb of the pulse P1, to which the shifted by the random offset Δ pulse P1 the symmetry axis has: α_next = α_akt + ω_akt · (Tm + T / 2 + Δ · T).

Tm is the time interval between the measurement time tm and the start time t0 of the signal period T.

From the determined, future rotor position α_next and the modulation degree m, the signal generator SG determines the duty cycle D1 for the signal period T in a manner known to those skilled in the art.

Subsequently, the signal generator SG generates the signal period T of the pulse-width-modulated control signal S1 with the pulse P1, which has the previously determined duty cycle D1 and by the means t1 of the signal period T by the previously determined random offset Δ and thus by a shift time Δ · T is time-shifted.

The above example described how the pulse width modulated control signal S1 is generated for driving one of the semiconductor switches HS1. The remaining control signals S2, S3 or S1 ', S2' and S3 'are generated in an analogous manner.

Claims (12)

Method for controlling at least one semiconductor switch (HS) of a power converter (WR) for providing at least one phase current for a rotary field machine (EM) with at least one pulse width modulated control signal (S), wherein a pulse (P1) in a signal period (T) of the at least one Control signal (S) from the center (t1) of the signal period (T) by a random offset (Δ) shifted generated. The method of claim 1, wherein the random offset (Δ) is an equally distributed random offset between a maximum offset (Δmax) and its counterpart (-Δmax). The method of claim 1, wherein the random offset (Δ) is a normally distributed random offset between a maximum offset (Δmax) and its counterpart (-Δmax). Method according to one of the preceding claims, wherein the random offset (Δ) is proportional to a product of a real random number (rand) of a real number interval [-1, 1] and a difference (m_max - m) between a maximum possible degree of modulation (m_max ) of the power converter (WR) and a current degree of modulation (m). Method according to claim 4, wherein the random offset (Δ) is determined by the following equation: Δ = k · edge · (m_max-m), where k is a number 1/4 or 1/2. Method according to Claim 4 or 5, wherein the current modulation factor (m) is proportional to a quotient between the phase voltage (U_ph) currently to be provided and an intermediate circuit voltage (U_DC) of the power converter (WR). Method according to claim 6, wherein the current modulation factor (m) of the power converter (WR) is determined by the following equation: m = sqrt (6) · U_ph / U_DC. Method according to one of the preceding claims, further comprising the following steps: - Detecting a current rotor position (α_akt) and a current angular velocity (ω_akt) of a rotor of the induction machine (EM) at a current time (tm) before the signal period (T); Determining a future rotor position (α_next) for the signal period (T) at a reference instant (tb) of the pulse (P1) shifted from the center (t1) of the signal period (T) by the random offset (Δ) from current rotor position (α_akt) and the current angular velocity (ω_akt). Method according to claim 8, wherein the future rotor position (α_next) for the signal period (T) is determined by the following equation: α_next = α_akt + ω_akt · (Tm + T / 2 + Δ · T); where Tm is the time interval between the current time (tm) and the start time (t0) of the signal period (T). The method of claim 8 or 9, wherein from the future rotor position (α_next) for the signal period (T) a duty cycle (D) for the signal period (T) is determined. Power converter (WR) for providing at least one phase current for a rotating field machine (EM), comprising: At least one semiconductor switch (HS) for providing the at least one phase current, - At least one signal generator (SG) for generating at least one pulse width modulated control signal (S) for controlling the at least one semiconductor switch (HS); - wherein the signal generator (SG) is further set up the pulse (P1) in at least one signal period (T) of the at least one control signal (S) from the center (t1) of the at least one signal period (T) by a random offset (Δ) time-shifted to generate. Electric drive arrangement (EA), in particular for driving a hybrid electric / electric vehicle, comprising: - An induction machine (EM), esp. To drive the hybrid electric / electric vehicle; - A power converter (WR) according to claim 11, which further comprises at least one phase current line and via the at least one phase current line to the induction machine (EM) is electrically connected and is arranged to provide the induction machine (EM) at least one phase current.

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