DE102017124857A1 - Control method for an electric drive - Google Patents

Abstract

The invention relates to a control method for an electric drive, in particular a traction drive, a vehicle, in particular a mobile work machine, wherein the electric drive comprises a three-phase motor (208) having at least three phases, a controllable inverter (201) for supplying the phases with electrical energy from a power source (207), and a control device (211, 212) for the inverter (201), and is operated in a first operating range in a continuous pulse width modulation method and in a second operating range in a discontinuous pulse width modulation method by the control device, wherein the control device a control logic (212) configured to decide, based on resources of the power source, whether the inverter (201) is operating in the first operating region or in the second operating region.

Description

The invention relates to a control method for an electric drive, which is based in particular on different modulation methods of a frequency converter of a battery-powered vehicle and a corresponding vehicle, in particular a mobile work machine, and a control device for a controllable converter of an electric drive.

Furthermore, the invention relates to mobile electric drives with three-phase motors, which are powered by low-voltage power source; Electric drives of battery-operated vehicles, which are predominantly operated with a traction battery of limited capacity; mobile electric drives with frequency converters known as "three-phase pulse width modulation (PWM) frequency inverters"; Frequency converters and their control, which are used in modern drive systems with field-oriented control (vector control); modern control algorithms for mobile electric drives with frequency converters designed to increase the quality of torque and speed control as well as system efficiency in operational variations in battery voltage; and innovative modulation schemes of the drive designed to improve the handling quality of battery-powered vehicles with lowered battery voltage (due to low battery charge).

Frequency converters (inverters) that regulate or control the stator voltage and stator frequency of the electric motor are predominantly implemented in speed- and / or torque-controlled drives with three-phase machines. The frequency inverters use different methods of pulse width modulation (PWM). Basically, a distinction is made between three groups of modulation methods described below, which are often implemented in the PWM of the frequency converter.

The modulation methods from the first group ensure a very good harmonic spectrum of the stator current of the electric machine, since the current is almost sinusoidal. This method is known as "Sine-Triangle Modulation (SDM)". The best modulation of the inverter during the SDM, which is also described with a modulation index, reaches a maximum value of m = 0.785. The low modulation index results because this method does not use nearly the full voltage available. The modulation index is defined as the quotient of the voltage value of any modulation to the first harmonic of the block operation. Unfortunately, it is disadvantageous that the modulation methods of this group cause very high "voltage losses" in the converter and do not optimally utilize the energy source (traction battery) of the vehicle.

The modulation methods of the second group make better use of the vehicle's energy source, but not yet well enough. A modulation method of this group which is very often used is known as "balanced sine-triangle modulation (SSDM)". During SSDM the modulation index reaches the value m = 0.907. Disadvantages here are that the realization of the PWM is complicated because some additional signals are added to the sinusoidal reference voltage. There is no optimum spectrum of the stator currents of the electric motor.

A second modulation scheme of this group, which is more modern than the SSDM, achieves the same maximum modulation index (m = 0.907) and is referred to as space-vector modulation (RZM). The reference voltage of the RZM can be formed with two classical sine functions, which are described with the mathematical functions f1 = sin (π / 3-x) and f2 = sin (x) in each sector of the voltage level of the inverter. The voltage level of the inverter consists of six sectors. Advantages here are the simple trajectory of the reference voltage and a good spectrum of the stator currents.

The modulation methods of the third group use the power source of the vehicle very well. Such modulation methods of PWM are referred to as flat-top modulation (FTM). The modulation index can reach the value m = 1 during block operation during the FTM. The literature describes three flat-top modulation methods, each designed with a fixed flat-top angle (30 °, 60 °, 120 °) or with a fixed modulation index. Disadvantages of the FTM are the additional harmonics in the spectrum of the stator current; generating additional current heat and iron losses in the electric machine due to distorted currents and that the higher the modulation index, the worse the spectrum of the stator currents is generated.

To take advantage of all PWM methods in the drive system, one uses a combined drive of the drive, i. one uses SDM, SSDM or RZM methods with a stable voltage of the energy source (traction battery) and low or medium power of the drive; and FTM methods in the case of a lowered battery voltage of the power source or higher power of the drive.

A conventional solution that realizes a combined control of the converter is in 1 shown and below 1 described. The solution idea is that a sine commutation in the upper speed range in a flat-top modulation (block commutation) passes to better use the traction battery. However, occur in the drive system 100 according to 1 as well as in the conventional drive systems with switchable modulation methods of a pulse width modulation of the frequency converter in general, the problems described below.

After switching the modulation method to FTM, the conventional solution offers only a fixed modulation index, which corresponds to a block mode (m = 1). Such a sudden increase in the modulation index leads to additional losses in the drive system, which are caused by harmonics. The resulting harmonics not only cause the losses in the electric machine, but also ensure a non-circular course. The resulting harmonics and a rough course of the electric machine lead to deterioration of the torque-speed control in the drive system, poor efficiency of the drive system (Note: in the battery-powered vehicles, the increase in efficiency is particularly important), additional mechanical vibrations of the vehicle, which adversely affect the handling of the vehicle as well as on the life of the electrical machine and consequently to dissatisfaction of the customers or users.

Switching the modulation method to FTM does not take into account resources of the energy source (traction battery). At low battery voltage, which may occur at a higher drive power, the FTM in the inverter can not be activated. The reason for this is that the actual speed of the electric machine remains below a fixed switching speed, which in the block 111 parameterized. The described disadvantages limit the application of the conventional solution in the highly dynamic drive systems with FTM or in combination with FTW.

Other solutions known from the prior art somewhat mitigate these disadvantages by also offering a certain modulation index which is in the range (0.907 <m <= 1) (no block operation) with the aim of increasing the spectrum of the To improve stator current of the electric machine during the FTM. This is possible when the FTM reference voltage is represented by a synthesized trajectory. Often the trajectories of the FTM reference voltages are very complex, i. complicated, and are mostly formed by the addition of multiple reference trajectories. Disadvantages of the solutions, however, are that only a certain modulation index is used during the FTM, which limits the further optimization of the spectrum of the stator currents. The complexity of reference voltage trajectories: limits the application of drive systems to FTM. Intensive examinations, commissioning and parameterization of the inverter with FTM are necessary to find or define an "optimal" trajectory of the reference voltage. Furthermore, additional memory and computational resources of the arithmetic units / processors are needed in the case of the addition of several reference trajectories.

To mitigate disadvantages in switching the modulation method to FTM, solutions known in the art offer the possibility of some variation in the modulation index in FTM. In these solutions, the reference voltages are dynamically modified in FTM mode to better utilize drive resources. A disadvantage of this latter state of the art, however, is that the available resources in the drive system are not optimally utilized, because there is no possibility to specify a targeted, precise modulation index of the converter during the FTM. Characteristic curves which characterize the course of the modulation index as a function of the reference voltage in the complete range of the FTM are extremely nonlinear and mathematically difficult to analyze. The methods considered are predominantly implemented in drive systems with variable structures, which very often include commutators, multiplexers or switching components with a hysteresis effect. In this case, the traceability of the modulation index curve with the regular expressions in the mathematical sense is very problematic. Intensive examinations, commissioning and parameterization of the inverter can not be avoided with the methods described above.

After analyzing the prior art FTM solutions, it can be seen that without direct specification of a desired modulation index, the further optimizations of the drive system are very problematic. For example, an "overdriven" modulation index causes the additional losses in the electric machine, a non-round running behavior and a deterioration of the efficiency in the drive system. An "underdriven" modulation index limits the speed range of the electric machine or the power of the drive.

The present invention has for its object to provide a controller for an electric drive, in particular a battery-powered electric drive, with the drive below Use of available resources of the drive can work as lossless as possible.

This object is solved by the features of the independent claims. Advantageous forms of further education are the subject of the dependent claims.

According to a first aspect of the invention, the object is achieved by a control method for an electric drive, in particular a traction drive, a vehicle, in particular a mobile work machine, wherein the electric drive comprises a three-phase motor with at least three phases, a controllable inverter for the supply of the phases electrical energy from a power source, and a control device for the inverter, and is operated in a first operating range in a continuous pulse width modulation method and in a second operating range in a discontinuous pulse width modulation method by the control device, wherein the control device has a control logic, which is formed based on resources of the power source to decide whether the inverter is operated in the first operating range or in the second operating range.

Such a control method offers a high-precision control of a controllable converter with switching between a discontinuous pulse width modulation and a continuous pulse width modulation based on resources of the energy source. This can increase the quality of the regulation of battery-powered vehicles, especially with a fluctuating battery voltage.

The control method is associated with a significant increase in the quality of torque and speed control of battery powered vehicles during operation, without the need for additional hardware resources. As a result, no costs are incurred in the form of material purchases. The quality of the control, in particular precision of the vehicle handling improves and leads to improved customer satisfaction. The control method thus increases the range of the vehicle, resulting in improved dynamics and a higher end speed.

The solution is universal and transferable to all three-phase inverters with B6 bridges, especially those equipped with modern space vector modulation. The solution is particularly advantageous for mobile and self-sufficient electric drives with limited resources of the energy source.

According to an embodiment of the control method, the continuous pulse width modulation method comprises space vector modulation, RZM.

The space vector modulation uses the energy source of the drive very well and achieves a maximum modulation index of m = 0.907. The space vector modulation simply generates trajectories of the reference voltage and provides a good spectrum of stator currents.

According to one embodiment of the control method, the discontinuous pulse width modulation method comprises a flat-top modulation, FTM, with a predefinable modulation index.

Such a control method provides a high-precision modulation of an inverter with direct specification of its modulation index (as set value) during the flat-top modulation in order to increase the quality of the regulation of battery-operated vehicles with a fluctuating battery voltage.

According to one embodiment of the control method, in the case of a positive energy balance of the energy source, the control logic is designed to operate the converter in the first operating range and, in the case of a negative energy balance of the energy source, to operate the converter in the second operating range.

This offers the advantage that the state (state of charge) of the energy source (battery) is taken into account in order to realize optimum control of the electric drive.

According to an embodiment of the control method, the control logic is configured to switch the inverter based on a switching characteristic between the first operating range and the second operating range.

Such a switching characteristic allows easy switching between the two operating states of the inverter.

According to one embodiment of the control method, the switching characteristic assumes a first threshold value in a first rotational speed range of the three-phase motor, adopts a second threshold value in a second rotational speed range of the three-phase motor, and moves in a third rotational speed range of the three-phase motor between the first rotational speed range and the second rotational speed range of the first Threshold to the second threshold above.

The various areas of the switching characteristic make it possible to switch smoothly between the operating states so that the resources of the energy source can be optimally utilized.

According to one embodiment of the control method, the transition of the switching characteristic from the first threshold to the second threshold is monotonically increasing, in particular linear.

By a monotonically increasing switching characteristic, a good spectrum of the stator currents of the electric motor can be realized, i. E. a spectrum in which harmonics occur as subdued as possible.

According to one embodiment of the control method, the control logic is designed to operate based on the switching characteristic a modulation index of the discontinuous pulse width modulation method with proportional actual and set values.

The criterion of proportionality between the setpoint and actual values of the modulation index guarantees a desired degree of modulation of the inverter through the specified setpoint. The implementation of this criterion can be optimally performed by an algorithm as described below.

According to one embodiment of the control method, the control device is designed to operate the converter in the first operating range based on a predetermined reference voltage.

The specification of the reference voltage offers the advantage that a reference voltage present or predetermined in the system can be used without the need for further components in order to generate a specific reference voltage.

According to one embodiment of the control method, the control device is designed to operate the converter in the second operating range based on a scaling of the reference voltage.

This offers the advantage that a single reference voltage is sufficient, which can be used directly for the first operating range and can be used for the second operating range in scaled form.

According to one embodiment of the control method, the scaling of the reference voltage is performed based on a specifiable change, in particular increasing a modulation index of the discontinuous pulse width modulation method.

This offers the advantage that a desired degree of modulation of the converter can be realized by the specifiable change of the modulation index.

According to one embodiment of the control method, a scaling factor of the scaling of the reference voltage is determined based on the following algorithm: Kr = 1 + 0.01 * (exp (Δm / 0.036) -1) where Kr indicates the scaling factor and Δm the predeterminable change in the modulation index.

Such an algorithm ensures a precise match between the setpoint and actual values of the modulation index by the compensation of the extreme nonlinearity in the characteristic "reference voltage modulation index". This can be increased with a targeted degree of modulation of the inverter, the quality of the vehicle handling despite unstable battery voltage. The algorithm represents a practice-relevant solution, in particular for an FTM in the range 0.907 <m <= 1.

According to one embodiment of the control method, the scaled scaled reference voltage is limited based on a limitation.

This offers the advantage that overriding of the reference voltage can be prevented.

According to a second aspect of the invention, the object is achieved by a vehicle, in particular a mobile working machine, with an electric drive, a three-phase AC motor, a controllable inverter for supplying the phases with electrical energy from a power source, and a control device for the inverter, wherein the control device performs a control method according to the first aspect of the invention.

Such a vehicle, for example a mobile work machine, can be controlled with high quality, in particular with a fluctuating battery voltage. The work machine requires no additional hardware resources, so that no costs incurred in the form of material purchases. Due to the control device, the range of a vehicle equipped with such a vehicle increases. The vehicle has improved dynamics and a higher top speed.

According to a third aspect of the invention, the object is achieved by a Control device for a variable speed drive of an electric drive, in particular a traction drive, a vehicle, in particular a mobile work machine, wherein the electric drive comprises a three-phase motor having at least three phases, wherein the controllable converter is adapted to supply the phases with electrical energy from a power source and the control device is configured to operate the inverter in a first operating range in a continuous pulse width modulation method and in a second operating range in a discontinuous pulse width modulation method, the control device having control logic configured to decide, based on resources of the power source, whether the inverter is operated in the first operating range or in the second operating range.

Such a control device provides a high-precision modulation of a controllable converter with switching between a discontinuous pulse width modulation and a continuous pulse width modulation based on resources of the energy source. This can increase the quality of the regulation of battery-powered vehicles, especially with a fluctuating battery voltage.

The solution is universal and transferable to all three-phase inverters with B6 bridges, especially those equipped with modern space vector modulation. The solution is particularly advantageous for mobile and self-sufficient electric drives with limited resources of the energy source.

• 1 ein Blockschaltbild eines herkömmlichen Steuerungsverfahrens 100 eines elektrischen Antriebs eines Fahrzeugs,
• 2 ein Blockschaltbild eines erfindungsgemäßen Steuerungsverfahrens 200 eines elektrischen Antriebs eines Fahrzeugs,
• 3 ein schematisches Diagramm 300, das verschiedene Trajektorien der Referenzspannung für herkömmliche und erfindungsgemäße Steuerungsverfahren veranschaulicht und
• 4 eine schematische Darstellung eines erfindungsgemäßen Steuerungsverfahrens 400 eines elektrischen Antriebs eines Fahrzeugs.

Further advantages and details of the invention will be explained in more detail with reference to the embodiment shown in the schematic figures. This shows

• 1 a block diagram of a conventional control method 100 an electric drive of a vehicle,
• 2 a block diagram of a control method according to the invention 200 an electric drive of a vehicle,
• 3 a schematic diagram 300 which illustrates various reference voltage trajectories for conventional and inventive control methods, and
• 4 a schematic representation of a control method according to the invention 400 an electric drive of a vehicle.

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It should be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the concept of the present invention. The following detailed description is therefore not to be understood in a limiting sense. Further, it should be understood that the features of the various embodiments described herein may be combined with each other unless specifically stated otherwise.

Aspects and embodiments will be described with reference to the drawings, wherein like reference numerals generally refer to like elements. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects of the invention. However, it will be apparent to one skilled in the art that one or more aspects or embodiments may be practiced with a lesser degree of specific details. In other instances, well-known structures and elements are shown in schematic form to facilitate describing one or more aspects or embodiments. It is understood that other embodiments may be utilized and structural or logical changes may be made without departing from the concept of the present invention.

Furthermore, while a particular feature or aspect of an embodiment may have been disclosed in terms of only one of several implementations, such feature or aspect may be combined with one or more other features or aspects of the other implementations, as for a given or particular one Application may be desirable and advantageous. Furthermore, to the extent that the terms "contain,""have,""with," or other variants thereof are used in either the detailed description or the claims, such terms are intended to include such terms in a manner similar to the term "comprising." The terms "coupled" and "connected" may have been used along with derivatives thereof. It should be understood that such terms are used to indicate that two elements independently cooperate or interact with each other, whether they are in direct physical or electrical contact or are not in direct contact with each other. In addition, the term "exemplary" is to be considered as an example only, rather than the term for the best or optimal. The following description is therefore not to be understood in a limiting sense.

The 1 shows a block diagram of a conventional control method 100 an electric drive of a vehicle. The drive system after 1 includes the following blocks: Frequency converter 101 , "Sine" reference voltage for SSDM 102 , Flat-top reference voltage for FTM 103 , Selector of the reference voltages 104 , PWM driver 105 , Transistor Bridge of B6 Inverter 106, Traction Battery (Power Source) 107 , electric machine 108 , Speed sensor 109 , PWM setpoint generator 110 , Switching characteristic 111 and arithmetic unit 112 ,

The inverter 101 serves to supply a three-phase motor 108 via semiconductor bridges 106 or transistor bridges. The semiconductor bridges 106 and the inverter 101 become from a voltage source 107 , which in the present example is a traction battery, is supplied with power. The inverter 101 has a first reference voltage 102 for a sinusoidal commutation or continuous pulse width modulation and a second reference voltage 103 for a flat-top modulation or discontinuous pulse width modulation. About a selector 104 generates a PMW driver 105 the drive signals for the semiconductor bridges 106 , where the setpoints 110 for controlling the phases of the three-phase motor 108 be specified. A speed sensor 109 detects the actual speed of the three-phase motor 108 that make up a computing unit 112 the corresponding speed values are determined. A switching characteristic 111 specifies a system-specific threshold above which the selector 104 from a pulse width modulation based on the first reference voltage 102 to the second reference voltage 103 and thus switches from a sinusoidal commutation as a continuous pulse width modulation to a flat-top modulation as a discontinuous pulse width modulation.

The inverter 101 has two reference voltages 102 . 103 which can each ensure two maximum modulation indices of the inverter when switching the modulation methods. The first reference voltage according to block 102 is responsible for the sinusoidal commutation. During sinusoidal commutation, the drive control is limited to a maximum value (m = 0.907). The second reference voltage according to block 103 Generates a "flat-top" reference voltage for better utilization of the power source 107 , The modulation index in this operating state is a maximum value (m = 1).

The selector 104 selects the desired modulation method from the block using a switching command 111 , ie the switching characteristic off. The characteristic of the block 111 has a system-specific speed level, from which the switching command for the block 104 is activated. The PWM driver, ie block 105 determines the widths of the pulses that are generated by the comparison between setpoint (block 110 ) and selected reference voltage (block 104 ) arise. The transistor bridge of the inverter (block 106 ) supplies the required voltage (or power) for the electric machine (block 108 ). The arithmetic unit (block 112 ) determines the actual speed of the motor 108 using the speed sensor (block 109 ) and forms the digital commands for the block 104 ,

The drive system with the switching of the modulation method according to 1 offers the following advantages: At low motor speeds, the inverter ensures a very good spectrum of the stator current of the electr. Machine. In the higher speed range, the FTM ensures minimum "voltage drops" in the inverter and maximum drive performance.

2 shows a block diagram of a control method according to the invention 200 an electric drive of a vehicle. The block diagram includes the following blocks: Frequency converter 201 , Reference voltage 202 , eg sinusoidal (for example according to the SSDM, as above) 1 described), product block 203 , Limiter 204 the reference voltage, PWM driver 205 , Transistor bridge 206 of the inverter, battery (voltage source) 207 , electric machine 208 , Speed sensor 209 , PWM setpoint 210 , Switching characteristic (SSDM-FTM) 211 , Arithmetic unit 212 , Functional block 213 the scaling of the reference voltage trajectory (FBSR).

The frequency converter 201 advantageously contains only a classical sinusoidal reference voltage 202 whose trajectory corresponds to modern space vector modulation (RZM). The frequency converter 201 can reach the maximum value of the modulation index (m = 0.907) with this reference voltage. Depending on the available resources of the energy source 207 it is decided whether in the drive system either the space vector modulation (RZM) with the classical reference voltage 202 or FTM with specification of the desired modulation index is to be activated.

The selection decision comes from the commands of a computing unit 212 , The arithmetic unit 212 "Collects" or determines all important information about the drive resources (blocks 207 . 209 . 210 ) and in case of a positive energy balance becomes the output of the block 212 disabled. An inactive state of the block 212 delivers with the help of the block 211 ,, Switching characteristic (SSDM-FTM) "a NULL command (distance OA, 211 ). This Command corresponds to a PWM control of the inverter 201 which achieves a good spectrum of the stator currents of the electric motor. The function block 213 In this state, provides a scaling factor (Kr = 1) to pass the RZM reference voltage without modification or correction and to ensure a desired modulation index up to k = 0.907. The desired modulation index is classically controlled via the PWM setpoint (output of the block 210 ).

When Room Pointer Modulation (RZM) requires a required drive power due to the limited modulation of the drive 201 limited, activates the arithmetic unit (output of the block 212 ) using the switching characteristic (block 211 , Distance AB, 211b) the FTM mode in the inverter 201 (Range: 0.907 <m <= 1) by an additional scaling (blocks 203 . 213 ) of the RZM reference voltage 202 , The exit of the block 210 delivers in FTM mode of the inverter 201 always a maximum value corresponding to a maximum modulation (m = 0.907) during the RZM.

wobei Kr den Skalierungsfaktor der RZM-Referenzspannung darstellt (Ausgang des Blockes 213) und Δm eine Vorgabe einer Erhöhung des Modulationsindexes während der FTM (Ausgang des Blockes 211). Ein resultierender Modulationsindex des Umrichters 201 ergibt sich also zu m=0.907+ Δm, wobei m<=1. Das Resultat der Skalierung (Ausgang des Blockes 203) wird im Block 204 „Begrenzer der Referenzspannung“ limitiert (max. „1“, normiert).The scaling of the RZM reference voltage in FTM mode can be realized according to the criterion "Proportionality between the setpoints and actual values of the modulation index" in order to achieve a desired degree of control of the inverter 201 to achieve the given setpoint. The implementation of this criterion is guaranteed by the functional block 213 which provides the current scaling factor according to the following proposed algorithm: $$\text{Kr}=1+\mathrm{12:01}*\left(\text{exp}\left(\mathrm{\Delta }\text{m}/0036\right)-1\right).$$

where Kr represents the scaling factor of the RZM reference voltage (output of the block 213 ) and Δm a specification of an increase of the modulation index during the FTM (output of the block 211 ). A resulting modulation index of the inverter 201 This results in m = 0.907 + Δm, where m <= 1. The result of the scaling (output of the block 203 ) is in the block 204 Limiter of reference voltage limited (max. "1", normalized).

The algorithm presented above represents a key point of the control method 200 This practice-relevant mathematical algorithm for the FTM (range: 0.907 <m <= 1) ensures a precise match between the setpoint and actual values of the modulation index by compensation of the extreme non-linearity in the characteristic "reference voltage modulation index". This can be increased with a targeted degree of modulation of the inverter, the quality of the vehicle handling despite unstable battery voltage.

The highly dynamic adaptation of the degree of modulation of the inverter 201 provides adaptive control of the stator voltage of the electric motor 208 (Entrance of the block 208 ) in case of fluctuating battery voltage (block 207 ). The blocks 205 - 209 are identical to the blocks 105 - 109 that in the description of the conventional solution 100 according to 1 were explained.

The algorithm described above was synthesized using methods of numerical mathematics. The maximum deviation between the nominal and actual values of the modulation index is less than +/- 1%.

The proposed solution provides a high-precision modulation of a frequency converter with direct specification of its modulation index (as a setpoint) during the flat-top modulation in order to increase the quality of the regulation of battery-powered vehicles with a fluctuating battery voltage.

The solution is based on the following assumptions: Trajectory (s) of the reference voltage are classical; an addition of multiple trajectories is not accepted because of the complexity of the realization; the steady state and dynamic accuracy of the implementation of the given modulation index is high; a specification of the modulation index during the FTM is provided with a separate input; no commutators, multiplexers and switching components with hysteresis effects are used; and no intensive examinations and commissioning of the inverter are necessary.

This allows the following advantages to be achieved: The frequency converter 201 is always optimally controlled, ie there is always a correct stator voltage and stator frequency of the electric motor 208 with a best possible spectrum of stator currents. A "comfortable" specification of the modulation index during the FTM can be achieved, which is specified with a separate input. A simple realization of the algorithm "proportionality between the nominal and actual values of the modulation index" is possible, which is based on a classical exponential function. Furthermore, a simple realization and scaling of the reference voltage is possible. The solution offers a high quality of the torque and speed control of the electric motor or a high handling quality of the vehicle. No additional hardware resources are needed in the drive system. The reduction of the harmonics in the stator current reduces the losses in the electrical machine. A high efficiency of the drive system can be achieved. There is no or little additional mechanical vibration, so that A longer life of the machine can be guaranteed, which is associated with increased satisfaction of customers or users.

The proposed solution significantly increases the quality of the torque and speed control of the battery powered vehicles / drives during operation (without additional hardware resources). As a result, no costs are incurred in the form of material purchases. The quality of control (e.g., precision of vehicle handling or customer satisfaction) can be increased. There are savings, e.g. in the form of increased ranges, dynamics or top speed of the vehicle.

The solution is universal and transferable to all three-phase inverters with B6 bridges equipped with modern space vector modulation. The solution is particularly advantageous for mobile and self-sufficient electric drives in which the resources of the energy source are limited.

The solution described can be used for example in a frequency converter of battery-powered AGV (English: Automated Guided Vehicle, German: Driverless transport vehicle).

3 shows a schematic diagram 300 , which illustrates different trajectories of the reference voltage for a control method according to the invention. There will be exemplified three trajectories 301 . 302 . 303 the reference voltage (output of the block 204 gem. 2 ) for the different modulation indices of the inverter 201 shown.

The first trajectory 301 ensures a modulation index in the range 0 <= m <= 0.907. It corresponds to the classical space vector modulation (RZM), ie according to the distance OA of the switching characteristic 211 out 2 ,

The second trajectory 302 ensures a Modulaltionsindex (m = 0.95) while the FTM with the proportionality between the setpoint and actual values of the modulation index ensures (middle of the distance AB of the switching characteristic 11 ).

The third trajectory 303 ensures the modulation index m = 0.99 during the FTM with the proportionality between the setpoint and actual values of the modulation index (distance AB, near point B of the switching characteristic 211 ). In block mode (m = 1), the modified reference voltage is at the output of the block 204 always limited to "1", because the switching characteristic 211 requires a maximum increase of the modulation index with the value Δm = 0.1 (distance BC).

4 shows a schematic representation of a control method according to the invention 400 an electric drive of a vehicle, in particular a mobile work machine. The control process 400 serves to control an electric drive, in particular a traction drive of a mobile work machine, wherein the electric drive is a three-phase motor 208 with at least three phases, one variable speed drive 201 for supplying the phases with electrical energy from an energy source 207 , and a control device 211 . 212 for the inverter 201 has, as in 2 shown. The control process 400 is operated in a first operating range in a continuous pulse width modulation method and in a second operating range in a discontinuous pulse width modulation method by the control device 401 , The control device has a control logic 212 on how to 2 described, which is formed based on resources of the power source 207 to decide 402 whether the inverter 201 is operated in the first operating range or in the second operating range.

The continuous pulse width modulation method, in one embodiment, may include space vector modulation, RZM, such as the 1 and 2 described. The discontinuous pulse width modulation method may in one embodiment comprise a flat-top modulation, FTM, with a predeterminable modulation index, such as the 1 and 2 described.

The control logic 212 can in case of a positive energy balance of the energy source 207 the inverter 201 operate in the first operating range and in case of a negative energy balance of the energy source 207 the inverter 201 operate in the second operating range. The control logic 212 can the inverter 201 based on a switching characteristic 211 switch between the first operating range and the second operating range, such as above to 2 described.

The switching characteristic 211 can in a first speed range 211 the three-phase motor 208 assume a first threshold, in a second speed range 211c the three-phase motor 208 assume a second threshold, and in a third speed range 211b the three-phase motor 208 between the first speed range 211 and the second speed range 211c from the first threshold to the second threshold, such as above to 2 described. The transition of the switching characteristic 211 from the first threshold to the second threshold may be monotonically increasing, in particular linear, such as above to 2 described.

The control logic 212 may be formed based on the switching characteristic 211 To operate a modulation index of the discontinuous pulse width modulation method with proportional actual and setpoints. The control device 211 . 212 may also be configured, the inverter 201 in the first operating range based on a predetermined reference voltage 202 to operate, such as above to 2 described. The control device 211 . 212 may be formed, the inverter 201 in the second operating range based on scaling 203 . 213 the reference voltage 202 to operate, such as above to 2 described. The scaling 203 . 213 the reference voltage 202 can be based on a predeterminable change in particular increase a modulation index of the discontinuous pulse width modulation method, such as above to 2 described.

A scaling factor of the scaling 203 . 213 the reference voltage 202 can be determined, for example, based on the following algorithm: Kr = 1 + 0.01 * (exp (Δm / 0.036) -1), where Kr indicates the scaling factor and Δm the predeterminable change in the modulation index. The with the scaling 203 . 213 scaled reference voltage can be based on a limitation 204 be limited, such as above to 2 described.

The control process 400 can be performed by a control device of a vehicle, in particular a mobile work machine. Such a mobile work machine comprises an electric drive, which is a three-phase motor 208 with at least three phases, one variable speed drive 201 for supplying the phases with electrical energy from an energy source 207 , and the control device 211 . 212 for the inverter 201 , such as above to 2 described.

It is to be understood that the features of the various embodiments described herein by way of example may be combined with each other except as specifically stated otherwise. As shown in the specification and drawings, individual elements that have been shown to be related need not communicate directly with each other; Intermediate elements may be provided between the connected elements. Further, it is to be understood that embodiments of the invention may be implemented in discrete circuits, partially integrated circuits, or fully integrated circuits or programming means. The term "for example" is meant as an example only and not as the best or optimal. While particular embodiments have been illustrated and described herein, it will be apparent to those skilled in the art that a variety of alternative and / or similar implementations may be practiced instead of the illustrated and described embodiments without departing from the concept of the present invention.

Claims (15)

Control method (400) for an electric drive, in particular a traction drive, a vehicle, in particular a mobile work machine, wherein the electric drive comprises a three-phase motor (208) having at least three phases, a controllable converter (201) for supplying the phases with electrical energy a power source (207), and a control device (211, 212) for the inverter (201), and in a first operating range in a continuous pulse width modulation method and in a second operating range in a discontinuous pulse width modulation method by the control device operated (401) the controller comprises control logic (212) configured to decide (402) based on resources of the power source (207) whether the inverter (201) is operating in the first operating region or in the second operating region. Control procedure (400) Claim 1 wherein the continuous pulse width modulation method comprises space vector modulation, RZM. Control procedure (400) Claim 1 or 2 , wherein the discontinuous pulse width modulation method comprises a flat-top modulation, FTM, with a predetermined modulation index. A control method (400) according to any one of the preceding claims, wherein the control logic (212) is adapted to operate the inverter (201) in the first operating range in case of a positive energy balance of the power source (207) and in the case of a negative energy balance of the power source (207). to operate the inverter (201) in the second operating range. The control method (400) of any of the preceding claims, wherein the control logic (212) is configured to switch the inverter (201) between the first operating range and the second operating range based on a switching characteristic (211). Control procedure (400) Claim 5 wherein the shift characteristic (211) assumes a first threshold value in a first rotational speed range (211a) of the three-phase motor (208), assumes a second threshold value in a second rotational speed range (211c) of the three-phase motor (208), and in a third rotational speed range (211b) of the second Three-phase motor (208) between the first speed range (211a) and the second speed range (211c) transitions from the first threshold to the second threshold. Control procedure (400) Claim 6 wherein the transition of the switching characteristic (211) from the first threshold to the second threshold is monotonically increasing, in particular linear. Control method (400) according to one of Claims 5 to 7 wherein the control logic (212) is adapted to operate based on the switching characteristic (211) a modulation index of the discontinuous pulse width modulation method with proportional actual and set values. The control method (400) of any preceding claim, wherein the controller (211, 212) is configured to operate the inverter (201) in the first operating region based on a predetermined reference voltage (202). Control procedure (400) Claim 9 wherein the control device (211, 212) is configured to operate the inverter (201) in the second operating region based on a scaling (203, 213) of the reference voltage (202). Control procedure (400) Claim 10 wherein the scaling (203, 213) of the reference voltage (202) is based on a specifiable change, in particular increasing a modulation index of the discontinuous pulse width modulation method. Control procedure (400) Claim 11 wherein a scaling factor of the scaling (203, 213) of the reference voltage (202) is determined based on the following algorithm: Kr = 1 + 0.01 * (exp (Δm / 0.036) -1), where Kr is the scaling factor and Δm is the specifiable change of the modulation index. Control method (400) according to one of Claims 10 to 12 wherein the scaled reference voltage scaled (203, 213) is limited based on a limit (204). Vehicle, in particular a mobile working machine with an electric drive, comprising a three-phase motor (208) having at least three phases, a controllable converter (201) for supplying the phases with electrical energy from a power source (207), and a control device (211, 212) for the converter (201), in which the control device has a control method (400) according to one of the Claims 1 to 13 performs. Control device (211, 212) for a controllable converter (201) of an electric drive, in particular a traction drive, of a vehicle, in particular a mobile work machine, wherein the electric drive comprises a three-phase motor (208) having at least three phases, wherein the controllable converter (201 ) is adapted to supply the phases with electrical energy from a power source (207) and the control device (211, 212) is formed, the inverter (201) in a first operating range in a continuous pulse width modulation method and in a second operating range in a discontinuous pulse width modulation method wherein the controller comprises control logic (212) configured to decide, based on resources of the power source (207), whether the inverter (201) is operating in the first operating region or in the second operating region.

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