DE102023202008A1 - Method for optimizing a pulse pattern for controlling an inverter - Google Patents

Abstract

The present invention relates to a method for optimizing a pulse pattern for controlling a preferably multi-phase inverter (100), in particular with synchronous clocking, wherein the inverter (100) for energizing an electrical machine (14) with a plurality of coil windings has an intermediate circuit to which an intermediate circuit voltage is applied and a phase (104, 106, 108) for each coil winding with a plurality of power switches (S1-S6) which form a high-side device and a low-side device of a half-bridge, the method comprising:
- Reading in an inverter voltage as a function of a switching angle of the inverter (100), wherein the inverter voltage is provided by means of a phase (104, 106, 108) of the inverter (100) and based on the intermediate circuit voltage;
- reading in a voltage induced in the electrical machine (14) based on the inverter voltage;
- Determining several harmonics of a difference between the inverter voltage and the corresponding induced voltage, preferably by means of Fourier expansion;
- Determining several values of the switching angle at which a sum of the determined harmonics is at a minimum;
- Generating a pulse pattern based on the determined values of the switching angle for switching the circuit breakers (S1-S6).

Description

The invention relates to the energization or control of an electrical machine or a rotating field machine. In particular, the invention relates to a method for optimizing a pulse pattern for controlling a DC/AC inverter, a control method and a corresponding control device for the DC/AC inverter in an at least partially electrified vehicle. The invention also relates to a computer-readable (storage) medium.

Pure electric vehicles and hybrid vehicles are known in the prior art, which are driven exclusively or with the support of one or more electric machines as drive units. In order to supply the electric machines of such electric vehicles or hybrid vehicles with electrical energy, the electric vehicles and hybrid vehicles comprise electrical energy storage devices, in particular rechargeable electric batteries. These batteries are designed as direct voltage sources, but the electric machines usually require alternating voltage. Therefore, power electronics with a so-called DC/AC inverter are usually connected between a battery and an electric machine (electric machine) of an electric vehicle or a hybrid vehicle in order to convert the DC input voltage into an AC output voltage to power the electric machine.

Such inverters use half-bridges to set predetermined voltages on the strings or phases of the electrical machine or rotating field machine. In each half-bridge, two semiconductor-based power switches (high-side power switches and low-side power switches) are connected in series between different potentials of an intermediate circuit voltage. Where the two power switches are connected to each other, the corresponding phase is contacted. If the two power switches are opened and closed alternately with a predetermined duty cycle, the desired voltage is set on the phase. Methods for controlling inverters are known from the prior art, which can be carried out using a control device in order to switch the power switches accordingly.

Such a control device and associated control method are known, for example, from EN 10 2016 208 801 A1 concerning dead time compensation for a rotating field machine with a pulse inverter.

The disadvantage of the control methods known from the state of the art is that power losses, noise and torque fluctuations of the energized electrical machine, which are due to harmonics (also called harmonic waves), cannot be sufficiently reduced or minimized.

It is an object of the invention to provide a method for optimizing a pulse pattern for controlling a DC/AC inverter, a corresponding control method and control device in order to at least partially eliminate the disadvantages mentioned above.

This object is achieved according to the invention by the method for optimizing a pulse pattern, the control method, the control device and the computer-readable (storage) medium according to the independent patent claims. Advantageous embodiments and further developments of the invention emerge from the dependent patent claims.

In a first aspect, the present invention relates to a method for optimizing a pulse pattern for controlling a DC/AC inverter. The inverter is used to supply current to an electrical machine with several coil windings, in particular to convert a DC input voltage provided by a vehicle drive battery into an AC output voltage. For this purpose, the inverter has an intermediate circuit (or commutation circuit) with an intermediate circuit capacitor to which an intermediate circuit voltage is applied. The intermediate circuit capacitor can comprise a single capacitor or an arrangement of several capacitor modules. The inverter also has a phase for each coil winding of the electrical machine. The inverter can be single-phase, i.e. with a single phase, or preferably multi-phase, i.e. with several phases. Each phase comprises several semiconductor-based power switches that form a half bridge. In each half-bridge, a high-side device consisting of one or more parallel-connected power switches (high-side power switches) and a low-side device consisting of one or more parallel-connected power switches (low-side power switches) are connected in series between different potentials of the intermediate circuit voltage. Where the high-side device and the low-side device are connected to each other, the corresponding phase is contacted. If the high-side and low-side power switches are opened and closed alternately with a predetermined duty cycle, the desired voltage (inverter voltage) is set at the phase, which is to be supplied to the corresponding coil winding. The predetermined duty cycle is specified by a pulse pattern, which is specified in a pulse pattern table. (for example in the form of a look-up table, LUT). The control unit, which controls the inverter for switching the power switches, can access the pulse pattern table in order to extract the predetermined duty cycle from it and to carry out a so-called pulse width modulation (PWM) of the power switches.

• - Einlesen einer Wechselrichterspannung in Abhängigkeit von einem Schaltwinkel des Wechselrichters, wobei die Wechselrichterspannung mittels einer Phase des Wechselrichters und basierend der Zwischenkreisspannung bereitgestellt ist;
• - Einlesen einer basierend auf der Wechselrichterspannung in der elektrischen Maschine induzierten Spannung;
• - Ermitteln mehrerer Oberschwingungen einer Differenz zwischen der Wechselrichterspannung und der zugehörigen induzierten Spannung, vorzugsweise mittels Fourierentwicklung;
• - Bestimmen mehrerer Werte des Schaltwinkels, bei denen eine Summe der ermittelten Oberschwingungen im Minimum liegt;
• - Generieren eines optimierten Pulsmusters (Engl.: Optimized Pulse Pattern, OPP) basierend auf den bestimmten Werten des Schaltwinkels zum Schalten der Leistungsschalter.

According to the invention, the pulse pattern is optimized with the following steps:

• - Reading in an inverter voltage depending on a switching angle of the inverter, wherein the inverter voltage is provided by means of a phase of the inverter and based on the intermediate circuit voltage;
• - Reading a voltage induced in the electrical machine based on the inverter voltage;
• - Determining several harmonics of a difference between the inverter voltage and the corresponding induced voltage, preferably by means of Fourier expansion;
• - Determining several values of the switching angle at which a sum of the determined harmonics is at a minimum;
• - Generating an optimized pulse pattern (OPP) based on the determined values of the switching angle for switching the circuit breakers.

The inverter voltage is thus generated from the intermediate circuit voltage (corresponding to the DC input voltage of the vehicle drive battery) by switching the phase power switches. The inverter voltage depends on the switching angle of the inverter or can be described mathematically as a function of the switching angle. The switching angle is a phase angle (or electrical angle) of the electrical machine at which the high-side power switches and the low-side power switches of the phase are switched (i.e. the high-side power switches are opened/closed while the low-side power switches are closed/opened at the same time). Each phase angle/electrical angle defines an operating point of the electrical machine. The pulse pattern determines at which phase angles/electrical angles the power switches are switched. The shape (or the temporal progression) of the inverter voltage therefore depends on the values of the switching angle.

Based on the inverter voltage, a coil winding of the electrical machine that is electrically connected to the phase is energized. The time-varying inverter voltage generates a time-varying current in the associated coil winding, which induces a counter voltage in the rotor (or in a rotor bar) of the electrical machine. Both the inverter voltage and the induced voltage can be expressed mathematically, for example according to Fourier expansion, as the sum of oscillation elements, namely a fundamental oscillation (zero-order oscillation) and several harmonics (higher-order oscillations).

The inverter voltage is usually not equal to the induced voltage, but is higher in magnitude than the latter. After the inverter voltage and the associated induced voltage have been read in, the difference between these two voltages can be determined. The difference (or differential voltage) can also be described mathematically as the sum of fundamental and harmonic oscillations. In this way, the harmonics of the difference between the inverter voltage and the associated induced voltage can be determined.

The harmonics can be summed. Since the inverter voltage depends on the switching angle, the sum of the harmonics also depends on the switching angle. Therefore, those values of the switching angle at which the sum of the harmonics of the differential voltage is at a minimum can be determined by minimizing the sum. Based on the values of the switching angle determined in this way, an optimized pulse pattern can be generated in order to switch the circuit breakers according to the generated pulse pattern.

The method according to the invention for optimizing the pulse pattern can be carried out by a device separate from the control unit, such as a processing unit or an on-board computer in the vehicle. Alternatively, the control unit itself can carry out the optimization of the pulse pattern. The pulse pattern is preferably optimized before the inverter is operated (i.e. "offline") according to the above steps and is only used to control the inverter when the inverter is operated (i.e. "online") by a control unit integrated in the vehicle. In particular, the pulse pattern optimized "offline" can be pre-stored in a pulse pattern table in the form of a look-up table (LUT), which the control unit accesses when the inverter is operating. Alternatively or additionally, the values of the switching angle determined "offline" as described above can be included in a switching angle table (e.g. LUT). The control unit can read the values of the switching angle to operate the inverter and the pulse pattern optimized based on this. generate. The LUT for the optimized pulse pattern and/or the switching angle values can preferably be stored in a storage medium integrated in the control unit or an external storage medium that is connected to the control unit for communication purposes. The optimized pulse pattern is preferably used to control the inverter with synchronous clocking.

According to the invention, a method for optimizing the pulse pattern has been created in which, in contrast to the methods known from the prior art, the harmonics of the voltage induced in the electrical machine are taken into account. In this way, the overall harmonic content of the phase currents can be reduced or certain harmonics can be eliminated. This is therefore a controlled measure for suppressing current harmonics, which cause undesirable losses and noise. Such controlled compensation of the current harmonics is particularly advantageous compared to regulated compensation, which is difficult or even impossible at high speeds due to the limited bandwidth/sampling frequency of the current measurement.

wobei α den Schaltwinkel, u_(v)(α) die Wechselrichterspannung, e_(v) die der Wechselrichterspannung zugehörige induzierte Spannung, v eine Ordnungszahl der Oberschwingungen beschreiben. Durch Minimieren der Zielfunktion insbesondere gemäß der folgenden Form (Glg. 2) lassen sich die Werte des Schaltwinkels bestimmen: $$\underset{\alpha \in {\left[0;\frac{2\pi }{n}\right]}^k}{\text{min}}{J}_e\left(\alpha \right)$$

wobei k die Anzahl der zu bestimmenden Werte des Schaltwinkels und _n einen Symmetriegrad des Pulsmusters beschreiben.To optimize the pulse pattern, according to one embodiment, an objective function J _e (α) dependent on the switching angle is used, which takes the following form (Eq. 1): $$J_e\left(\alpha \right)={{\displaystyle \sum _{v=\mathrm{5,7,11,}\dots }\left(\frac{u_{\left(v\right)}\left(\alpha \right)-e_{\left(v\right)}}{v}\right)}}^2$$

where α is the switching angle, u _(v) (α) the inverter voltage, e _(v) the induced voltage associated with the inverter voltage, v an order number of the harmonics. The values of the switching angle can be determined by minimizing the objective function, in particular according to the following form (Eq. 2): $$\underset{\alpha \in {\left[0;\frac{2\pi }{n}\right]}^k}{\text{min}}{J}_e\left(\alpha \right)$$

where k describes the number of switching angle values to be determined and _n describes a degree of symmetry of the pulse pattern.

Durch diese zusätzliche Bedingung neben Minimieren der Zielfunktion wird das Pulsmuster mit höherer Zuverlässigkeit und breiterer Einsatzbarkeit optimiert.According to a further embodiment, an amount of a fundamental oscillation of a peak value of the inverter voltage (û ₍₁₎ (α)) at the specific values of the switching angle corresponds to a predefined modulation level (m) of the inverter. The modulation level indicates the ratio between the peak value of the fundamental oscillation of the inverter voltage and the intermediate circuit voltage and depends on the operating point of the electrical machine. Preferably, the amount of the fundamental oscillation is equal to the modulation level (Eq. 3): $${\widehat{u}}_{\left(1\right)}\left(\alpha \right)=m.$$

This additional condition, in addition to minimizing the objective function, optimizes the pulse pattern with higher reliability and wider applicability.

wobei k die Anzahl der zu bestimmenden Werte des Schaltwinkels und _n einen Symmetriegrad des zu optimierenden Pulsmusters beschreiben. Der Symmetriegrad kann vorzugsweise die Werte 4, 2 oder 1 annehmen, die einer Viertelwellensymmetrie, Halbwellensymmetrie oder Periodizität jeweils entsprechen.According to a further embodiment, the following condition (Eq. 4) is fulfilled for the determined values of the switching angle: $$0\le {\alpha }_1\le {\alpha }_2\le \cdots \le {\alpha }_k\le \frac{2\pi }{n}$$

where k is the number of switching angle values to be determined and _n describes a degree of symmetry of the pulse pattern to be optimized. The degree of symmetry can preferably assume the values 4, 2 or 1, which correspond to a quarter-wave symmetry, half-wave symmetry or periodicity, respectively.

Preferably, the above three conditions (equations 2 to 4) are met simultaneously for the specific values of the switching angle. Using the values of the switching angle determined under these conditions, an improved optimization of the pulse pattern can be achieved, in which the spectrum of the current harmonics as a whole or the total harmonic distortion (THD) of the phase currents can be reduced or minimized.

wobei î einen Scheitelwert des Differenzstroms, v_i eine i-te Ordnungszahl der Oberschwingungen und g_i den der i-ten Ordnungszahl zugehörigen vordefinierten Schwellenwert beschreiben, wobei g_i den Wert Null annehmen kann. Die Bedingung kann für eine oder mehrere Ordnungszahlen bzw. Oberschwingungen gelten. Im Fall meherer Oberschwingungen handelt es sich hierbei um eine Mehrzahl von Optimierungsrandbedingungen, durch die sich einzelne Stromoberschwingungen mit den Ordnungszahlen v_i unter bzw. auf den vordefinierten Schwellwert g_i senken lassen.According to a further embodiment, a current intensity of a differential current generated by the difference between the inverter voltage and the associated induced voltage falls below or is equal to a predefined threshold value at the specific values of the switching angle. Preferably, the following condition (Eq. 5) is additionally met for the specific values of the switching angle: $${\widehat{l}}_{\left(v_i\right)}\left(\alpha \right)\le G_i$$

where î describes a peak value of the differential current, v _i an i-th order number of the harmonics and g _i the predefined threshold value associated with the i-th order number, where g _i can take the value zero. The condition can apply to one or more order numbers or harmonics. In the case of several harmonics, this is a plurality of optimization boundary conditions through which individual current harmonics can be compared with the order numbers. numbers v _i can be reduced below or to the predefined threshold g _i .

Preferably, the above four conditions (equations 2 to 5) are met simultaneously for the specific values of the switching angle. Consequently, the optimization produces a modified pulse pattern which is characterized by the fact that its losses, noise emissions and/or torque fluctuations are lower than those of the prior art. The optimization result or the conditions underlying it depend on the respective properties of the electrical machine (or electric motor) or its harmonic content and thus differ from motor type to motor type. According to the invention, an individually optimized pulse pattern can therefore be generated for each motor type.

According to a further embodiment, a degree of anisotropy of the electrical machine to be energized is also taken into account to determine the values of the switching angle. The anisotropy indicates how much the d and q components of the inductances of an electrical machine differ from one another. To take the anisotropy into account, both the inverter voltage and the induced voltage of the electrical machine are preferably broken down into their corresponding d and q components according to the dq representation (for example using Clarke/Park transformation). In this way, with the help of the inductances of the electrical machine in the d and q directions (or with the help of the d and q components of the inductances), the current harmonics (i.e. the harmonics of the current caused by the difference voltage between the inverter voltage and the induced voltage of the electrical machine or the associated coil winding) can also be determined. The determined current harmonics are minimized in order to optimize the pulse pattern. Alternatively or additionally, a winding resistance of the electrical machine to be powered can be taken into account when converting the harmonics of the inverter voltage and the induced voltage into the current harmonics.

The invention further relates to a control method and a corresponding control device for an inverter. The control method comprises switching several power switches of the inverter according to the pulse pattern optimized according to the method according to one of the embodiments of the present invention. The control device comprises a processing unit which is designed to carry out the control method according to the invention. The invention further relates to a computer-readable (storage) medium comprising commands which, when executed by a computer, cause the computer to carry out the steps of the method for optimizing the pulse pattern and/or the control method according to one of the embodiments of the present invention. This results in the advantages already described in connection with the method according to the invention for optimizing the pulse pattern also for the control method according to the invention, the control device according to the invention and the (storage) medium according to the invention.

The invention is explained below by way of example using embodiments shown in the figures.

• 1 eines schematisches Schaltbild eines mehrphasigen (insbesonere dreiphasigen) Wechselrichters zum Bestromen einer elektrischen Maschine;
• 2 eine schematische Darstellung eines Steuerverfahrens zum Ansteuern des Wechselrichters mittels eines Steuergerätes;
• 3 eine schematische Darstellung eines Verfahrens zum Optimieren eines Pulsmusters, welches durch das Steuergerät zum Ansteuern des Wechselrichters verwendet wird.

They show:

• 1 a schematic circuit diagram of a multi-phase (especially three-phase) inverter for supplying current to an electrical machine;
• 2 a schematic representation of a control method for controlling the inverter by means of a control device;
• 3 a schematic representation of a method for optimizing a pulse pattern used by the control unit to control the inverter.

Identical objects, functional units and comparable components are designated with the same reference symbols across all figures. These objects, functional units and comparable components are identical in terms of their technical features, unless the description explicitly or implicitly indicates otherwise.

1 shows a schematic circuit diagram of a multiphase, here for example three-phase DC/AC inverter 100 for supplying current to an electrical machine 14 (such as a rotating field machine) in an at least partially electrified vehicle (not shown). The inverter 100 has an intermediate circuit (commutation circuit) with an intermediate circuit capacitor 102, into which a DC input voltage is fed via a voltage input 12 of the inverter 100, which is determined by a 2 schematically shown DC voltage supply 11 (in particular a vehicle drive battery). The electrical voltage applied to the intermediate circuit thus corresponds essentially to the DC input voltage. The inverter 100 also has a power electronics consisting of several, here for example three, phases 104, 106, 108. Each phase 104, 106, 108 is designed as a half-bridge, which comprises a high-side device and a low-side device electrically connected thereto. In the example shown here the high-side devices each have, purely by way of example, a single high-side power switch S1, S3, S5, while the low-side devices also have, purely by way of example, a single low-side power switch S2, S4, S6. However, this is in no way limiting for the present invention. Each high-side or low-side device can comprise a plurality of power switches connected in parallel. A voltage output U, V, W is connected to the respective node 105, 107, 109 between the high-side device and the low-side device of each phase 104, 106, 108 in order to supply the AC output voltage of each phase 104, 106, 108 to the electrical machine 14 to be powered, in particular to the associated coil winding of the electrical machine 14.

The power switches S1-S6 each comprise a transistor, such as MOSFET, HEMT, IGBT, based on a semiconductor material. The semiconductor material can be silicon, or a so-called wide bandgap semiconductor (WBS) such as silicon carbide (SiC) or gallium nitride (GaN). The phases or the half-bridges 104, 106, 108 can be designed in a modular manner, for example in such a way that each half-bridge 104, 106, 108 comprises several half-bridge modules, each of which has a module high side and a module low side. The module high sides are connected in parallel and form the high side device of the phase, with the module low sides being connected in parallel and forming the low side device of the phase. The intermediate circuit capacitor 102 can also have a single capacitor or several capacitor modules. The number of half-bridge and/or capacitor modules used in the inverter can be selected depending on the power class of the electrical machine or vehicle to be powered.

The AC output voltage (alternating voltage) can be generated from the DC input voltage (direct voltage) using the inverter 100. This is done by specifically switching the power switches S1-S6. A control unit 10 is used for this purpose, or to control the inverter 100. The control unit 10 is shown purely schematically and as an example in 2 and comprises a processing unit 18 which is designed to impress a pulse pattern on the inverter 100. The pulse pattern contains a duty cycle with which the high-side power switches S1, S3, S5 and the low-side power switches S2, S4, S6 are alternately opened and closed so that a desired voltage (inverter voltage) is established at the voltage output of the respective phase. The pulse pattern can be predetermined “offline”, i.e. before or after operation of the electrical machine 14, and then pre-stored in a pulse pattern table (for example in the form of a look-up table, LUT). The pulse pattern (or the pulse pattern table) can be stored in a storage medium 16 integrated in the control unit 10 or alternatively in an external storage medium 17. The processing unit 18 can access the storage medium 16, 17 "online", ie when the electrical machine 14 is operating, to control the inverter 100 and read the pulse pattern stored there in advance in order to switch the power switches S1-S6 accordingly. The pulse pattern is used to provide pulse width modulation (PWM), preferably for synchronous clocking or synchronous modulation of the power switches S1-S6.

• - Einlesen einer Wechselrichterspannung in Abhängigkeit von einem Schaltwinkel des Wechselrichters 100, wobei die Wechselrichterspannung mittels einer Phase 104,106,108 des Wechselrichters 100 und basierend der Zwischenkreisspannung bereitgestellt ist;
• - Einlesen einer basierend auf der Wechselrichterspannung in der elektrischen Maschine 14 induzierten Spannung;
• - Ermitteln mehrerer Oberschwingungen einer Differenz zwischen der Wechselrichterspannung und der zugehörigen induzierten Spannung, vorzugsweise mittels Fourierentwicklung;
• - Bestimmen mehrerer Werte des Schaltwinkels, bei denen eine Summe der ermittelten Oberschwingungen im Minimum liegt;
• - Generieren eines optimierten Pulsmusters (Engl.: Optimized Pulse Pattern, OPP) basierend auf den bestimmten Werten des Schaltwinkels zum Schalten der Leistungsschalter S1-S6.

The pulse pattern can be optimized by means of a method according to the invention, which can preferably be carried out offline. 3 shows the method for optimizing the pulse pattern in a purely schematic and exemplary representation. The method comprises the following steps:

• - Reading in an inverter voltage as a function of a switching angle of the inverter 100, wherein the inverter voltage is provided by means of a phase 104,106,108 of the inverter 100 and based on the intermediate circuit voltage;
• - Reading in a voltage induced in the electric machine 14 based on the inverter voltage;
• - Determining several harmonics of a difference between the inverter voltage and the corresponding induced voltage, preferably by means of Fourier expansion;
• - Determining several values of the switching angle at which a sum of the determined harmonics is at a minimum;
• - Generating an optimized pulse pattern (OPP) based on the determined values of the switching angle for switching the circuit breakers S1-S6.

The inverter voltage depends on the switching angle of the inverter or can be described mathematically as a function of the switching angle. The switching angle is a phase angle (or electrical angle) of the electrical machine 14 at which the high-side power switches S1, S3, S5 and the low-side power switches S2, S4, S6 of phase 104, 106, 108 are switched (i.e. the high-side power switches S1, S3, S5 are opened/closed while the low-side power switches S2, S4, S6 are closed/opened at the same time). Each phase angle/electrical angle defines an operating point of the electrical machine 14. The pulse pattern determines at which phase angles/electrical angles the power switches S1-S6. Thus, the shape (or the temporal progression) of the inverter voltage depends on the values of the switching angle.

Based on the inverter voltage, a coil winding of the electrical machine 14 that is electrically connected to phase 104, 106, 108 is energized. The time-varying inverter voltage generates a time-varying current in the associated coil winding that induces a counter voltage in the rotor (or in a rotor bar) of the electrical machine 14. Both the inverter voltage and the induced voltage can be described mathematically, for example according to Fourier expansion, as the sum of oscillation elements, namely a fundamental oscillation (zero-order oscillation) and several harmonics (higher-order oscillations).

The inverter voltage is usually not equal to the induced voltage, but is higher in magnitude than the latter. After the inverter voltage and the associated induced voltage have been read in, the difference between these two voltages can be determined. The difference (or differential voltage) can also be described mathematically as the sum of fundamental and harmonic oscillations. In this way, the harmonics of the difference between the inverter voltage and the associated induced voltage can be determined.

The harmonics can be summed. Since the inverter voltage depends on the switching angle, the sum of the harmonics also depends on the switching angle. Therefore, those values of the switching angle at which the sum of the harmonics of the differential voltage is at a minimum can be determined by minimizing the sum. Based on the values of the switching angle determined in this way, an optimized pulse pattern can be generated.

As already mentioned above, the pulse pattern optimized in this way can be stored as a LUT and pre-stored in the storage medium 16, 17. In this case, the control unit 10 reads the offline generated pulse pattern and controls the inverter 100 according to the optimized pulse pattern. Alternatively, the individual values of the switching angle, which are determined by minimizing the sum of the differential voltage, can also be stored as a LUT and pre-stored in the storage medium 16, 17. In the latter case, the control unit 10 reads the offline determined values of the switching angle from the storage medium 16, 17 and generates an optimized pulse pattern based on the switching angle values, which can be done offline or online.

wobei α den Schaltwinkel, u(_v)(α) die Wechselrichterspannung, e_(v) die der Wechselrichterspannung zugehörige induzierte Spannung, _v eine Ordnungszahl der Oberschwingungen beschreiben. Durch Minimieren der Zielfunktion insbesondere gemäß der folgenden Form (Glg. 2) lassen sich die Werte des Schaltwinkels bestimmen: $$\underset{\alpha \in {\left[0;\frac{2\pi }{n}\right]}^k}{\text{min}}{J}_e\left(\alpha \right)$$

wobei k die Anzahl der zu bestimmenden Werte des Schaltwinkels und _n einen Symmetriegrad des Pulsmusters beschreiben.To optimize the pulse pattern, an objective function J _e (α) dependent on the switching angle is preferably used, which takes the following form (Eq. 1): $$J_e\left(\alpha \right)={{\displaystyle \sum _{v=\mathrm{5,7,11,}\dots }\left(\frac{u_{\left(v\right)}\left(\alpha \right)-e_{\left(v\right)}}{v}\right)}}^2$$

where α is the switching angle, u( _v )(α) is the inverter voltage, e _(v) is the induced voltage associated with the inverter voltage, _{and v} is an order number of the harmonics. The values of the switching angle can be determined by minimizing the objective function, in particular according to the following form (Eq. 2): $$\underset{\alpha \in {\left[0;\frac{2\pi }{n}\right]}^k}{\text{min}}{J}_e\left(\alpha \right)$$

where k describes the number of switching angle values to be determined and _n describes a degree of symmetry of the pulse pattern.

Der Modulationsgrad gibt das Verhältnis zwischen dem Scheitelwert der Grundschwingung der Wechselrichterspannung und der Zwischenkreisspannung an und hängt vom Betriebspunkt der elektrischen Maschine 14 ab.The fundamental oscillation of a peak value of the inverter voltage (û ₍₁₎ (α)) at the specific values of the switching angle corresponds to a predefined modulation level (m) of the inverter 100 or is equal to it (Eq. 3): $${\widehat{u}}_{\left(1\right)}\left(\alpha \right)=m.$$

The degree of modulation indicates the ratio between the peak value of the fundamental oscillation of the inverter voltage and the intermediate circuit voltage and depends on the operating point of the electrical machine 14.

wobei k die Anzahl der zu bestimmenden Werte des Schaltwinkels und _n einen Symmetriegrad des zu optimierenden Pulsmusters beschreiben. Der Symmetriegrad kann vorzugsweise die Werte 4, 2 oder 1 annehmen, die einer Viertelwellensymmetrie, Halbwellensymmetrie oder Periodizität jeweils entsprechen.In addition, the following condition (Eq. 4) is fulfilled for the specific values of the switching angle: $$0\le {\alpha }_1\le {\alpha }_2\le \cdots \le {\alpha }_k\le \frac{2\pi }{n}$$

where k is the number of switching angle values to be determined and _n describes a degree of symmetry of the pulse pattern to be optimized. The degree of symmetry can preferably assume the values 4, 2 or 1, which correspond to a quarter-wave symmetry, half-wave symmetry or periodicity, respectively.

With the help of the switching angle values determined under these conditions (equations 2 to 4, which corresponds to a condition group I), an improved optimization of the pulse pattern can be achieved, in which the spectrum of the current harmonics in its entirety or the harmonics total harmonic distortion (THD) of the phase currents can be reduced or minimized.

wobei î einen Scheitelwert des Differenzstroms, v_i eine i-te Ordnungszahl der Oberschwingungen und g_i den der i-ten Ordnungszahl zugehörigen vordefinierten Schwellenwert beschreiben, wobei g_i den Wert Null annehmen kann. Die Bedingung kann für eine oder mehrere Ordnungszahlen bzw. Oberschwingungen gelten. Im Fall meherer Oberschwingungen handelt es sich hierbei um eine Mehrzahl von Optimierungsrandbedingungen, durch die sich einzelne Stromoberschwingungen mit den Ordnungszahlen v_i unter bzw. auf den vordefinierten Schwellwert g_i senken lassen.In addition, when optimizing the pulse pattern, it can be taken into account that a current intensity of a differential current generated by the differential voltage between the inverter voltage and the associated induced voltage falls below or is equal to a predefined threshold value at the specific values of the switching angle. Preferably, the following condition (Eq. 5) is also met for the specific values of the switching angle: $${\widehat{l}}_{\left(v_i\right)}\left(\alpha \right)\le G_i$$

where î describes a peak value of the differential current, v _i an i-th order number of the harmonics and g _i the predefined threshold value associated with the i-th order number, where g _i can assume the value zero. The condition can apply to one or more order numbers or harmonics. In the case of several harmonics, this is a plurality of optimization boundary conditions through which individual current harmonics with the order numbers v _i can be reduced below or to the predefined threshold value g _i .

If the conditions (equations 2 to 5, which corresponds to a condition group II) are met at the same time, the optimization produces a modified pulse pattern which is characterized by the fact that its losses, noise emissions and/or torque fluctuations are lower than those of the prior art. The optimization result or the conditions underlying it depend on the respective properties of the electrical machine 14 (or electric motor) or its harmonic content and thus differ from motor type to motor type. According to the invention, an individually optimized pulse pattern can therefore be generated for each motor type.

To determine the values of the switching angle, a degree of anisotropy of the electrical machine 14 to be energized can also be taken into account. The anisotropy indicates how much the d and q components of the inductances L of the electrical machine 14 differ from one another. To take the anisotropy into account, it is preferable to break down both the inverter voltage and the induced voltage of the electrical machine 14 into their corresponding d and q components according to the dq representation (for example using Clarke/Park transformation). In this way, with the help of the inductances L of the electrical machine 14 in the d and q directions (or with the help of the d and q components of the inductances L), the current harmonics (i.e. the harmonics of the current caused by the difference voltage between the inverter voltage and the induced voltage of the electrical machine 14 or the associated coil winding) can also be determined. The current harmonics determined are minimized in order to optimize the pulse pattern. Alternatively or additionally, a winding resistance of the electrical machine 14 to be powered can be taken into account when converting the harmonics of the inverter voltage and the induced voltage into the current harmonics.

Reference symbol

10

Control unit

12

Voltage input

14

electric machine

16

integrated storage medium

17

external storage medium

18

Processing unit

100

Inverter

102

DC link capacitor

104,106,108

Phases/Half Bridges

105,107,109

Nodes

S1-S6

Circuit breaker

U, V, W

Voltage outputs

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• DE 102016208801 A1 [0004]

Claims (10)

Method for optimizing a pulse pattern for controlling a preferably multi-phase inverter (100), in particular with synchronous clocking, wherein the inverter (100) for energizing an electrical machine (14) with a plurality of coil windings has an intermediate circuit to which an intermediate circuit voltage is applied and a phase (104, 106, 108) for each coil winding with a plurality of power switches (S1-S6) which form a high-side device and a low-side device of a half-bridge, the method comprising: - reading in an inverter voltage depending on a switching angle of the inverter (100), wherein the inverter voltage is provided by means of a phase (104, 106, 108) of the inverter (100) and based on the intermediate circuit voltage; - reading in a voltage induced in the electrical machine (14) based on the inverter voltage; - Determining several harmonics of a difference between the inverter voltage and the associated induced voltage, preferably by means of Fourier expansion; - Determining several values of the switching angle at which a sum of the determined harmonics is at a minimum; - Generating a pulse pattern based on the determined values of the switching angle for switching the circuit breakers (S1-S6). Procedure according to Claim 1 , where the values of the switching angle are determined by means of an objective function J _e (α) that depends on the switching angle and takes the following form: $$J_e\left(\alpha \right)={{\displaystyle \sum _{v=\mathrm{5,7,11,}\dots }\left(\frac{u_{\left(v\right)}\left(\alpha \right)-e_{\left(v\right)}}{v}\right)}}^2$$

where α is the switching angle, u( _v )(α) is the inverter voltage, e _(v) is the induced voltage associated with the inverter voltage, v is an ordinal number of the harmonics. Procedure according to Claim 2 , where the values of the switching angle are determined by minimizing the objective function according to the following form: $$\underset{\alpha \in {\left[0;\frac{2\pi }{n}\right]}^k}{\text{min}}{J}_e\left(\alpha \right)$$

where k describes the number of switching angle values to be determined and _n describes a degree of symmetry of the pulse pattern. Procedure according to one of the Claims 1 until 3 , wherein an amount of a fundamental oscillation of a peak value of the inverter voltage at the specific values of the switching angle corresponds to a predefined degree of modulation of the inverter (100), preferably is equal to it, and/or wherein the following condition is met for the specific values of the switching angle: $$0\le {\alpha }_1\le {\alpha }_2\le \cdots \le {\alpha }_k\le \frac{2\pi }{n}$$

where k describes the number of switching angle values to be determined and _n describes a degree of symmetry of the pulse pattern. Procedure according to one of the Claims 1 until 4 , wherein a current intensity of a differential current generated by the difference between the inverter voltage and the associated induced voltage is less than or equal to a predefined threshold value at the specific values of the switching angle. Method according to one of the Claims 1 until 5 , whereby the following condition is additionally fulfilled for the specific values of the switching angle: $${\widehat{l}}_{\left(v_i\right)}\left(\alpha \right)\le G_i$$

where î describes a peak value of the differential current, v _i an i-th order number of the harmonics and g _i the predefined threshold value associated with the i-th order number. Procedure according to one of the Claims 1 until 6 , wherein a degree of anisotropy and/or a winding resistance of the electrical machine (14) to be energized are additionally taken into account for determining the values of the switching angle. Control method for a preferably multiphase inverter (100), comprising switching several power switches (S1-S6) of the inverter (100) according to one of the Claims 1 until 7 defined procedure optimized pulse pattern. Control device (10) for a preferably multiphase inverter (100), with a processing unit (18) which is designed to carry out the control method according to Claim 8 to execute. Computer-readable (storage) medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method according to one of the Claims 1 until 8 to execute.

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