WO2023041382A1

WO2023041382A1 - System and method for controlling an electric machine

Info

Publication number: WO2023041382A1
Application number: PCT/EP2022/074762
Authority: WO
Inventors: Gerhard HÜBNER; Mark Mclaren
Original assignee: Rolls-Royce Deutschland Ltd & Co Kg
Priority date: 2021-09-16
Filing date: 2022-09-06
Publication date: 2023-03-23
Also published as: DE102021124021A1

Abstract

The invention relates to a system (1) comprising an electric machine (10), a rotor (11), a gearing mechanism (12) via which the rotor (11) is coupled to the electric machine (10), and a control unit (13) comprising: a computer (130) which is designed to a) detect values of required torques and measurement values which are indicative of rotational speeds and calculate performance values therefrom as output values or b) detect values of required performances and measurement values which are indicative of rotational speeds and calculate torque values therefrom as output values; and a change rate limiter (131) which is designed to obtain the calculated output values and limit a change of the calculated output values over time to a maximum value in order to obtain a change rate-limited output value, wherein the control unit (13) is designed to control the electric machine (10) on the basis of the change rate-limited output value.

Description

System and method for controlling an electric machine

Description

More particularly, the present disclosure relates to a system and method for controlling an electric machine.

In the case of electric motors and other electrical machines that are coupled to a rotor via a gear, vibrations can occur, particularly when the load changes. On the one hand, such vibrations can be annoying, for example for passengers of a vehicle, in particular an aircraft, with the electrical machine. Furthermore, such vibrations can also lead to increased wear and accelerated aging of the transmission, the electrical machine or other components. Furthermore, it is generally often desirable to reduce noise emissions, which can be a result of vibrations in particular, as much as possible.

The object of the present invention is to reduce vibrations during operation of electrical machines coupled to rotors via gears.

According to one aspect, a system is provided that includes an electric machine, a rotor, a transmission via which the rotor and the electric machine are coupled to one another, and a control unit. The control unit includes a computer (eg in the form of a power computer) which is set up to record values of requested torques and measured values of the system indicative of speeds and to calculate power values (as initial or output values) from them. Furthermore, the control unit comprises a rate-of-change limiter, which is set up to receive the calculated power values and to limit a change in the calculated power values over time to a maximum value in order to obtain a power value with a rate-of-change-limit. The control unit is set up to control the electric machine based on the rate-of-change-limited power value.

Alternatively or additionally, the control unit includes a computer (e.g. in the form of a torque calculator) which is set up to record values of required power and measured values of the system indicative of speeds and to calculate torque values (as initial or output values) from them. Furthermore, the control unit then comprises a rate-of-change limiter which is set up to receive the calculated torque values and to limit a change in the calculated torque values over time to a maximum value in order to obtain a rate-of-change-limited torque value. In this case, the control unit is set up to control the electric machine based on the rate-of-change-limited torque value.

This is based on the finding that vibrations can be counteracted particularly effectively by first converting a torque requested, for example via a throttle position, into a requested power, for example engine power, based on the speed. Vibrations, in particular torsional vibrations, are impressed on the rotational speed (or generally on a value indicative thereof, for example an angular velocity or the like) which is measured continuously (eg with a predetermined frequency or continuously). By using the measured values of the rotational speed as a feedback signal, the electrical machine can be subjected to an oscillation signal that is phase-shifted with respect to the vibrations caused by the measurement, thereby enabling an effective reduction in the oscillations. As a result, can also Noise emissions are reduced. In particular, the control unit works continuously and determines the calculated power values (or torque values), for example with a specified frequency of, for example, 1 Hz or less, 10 Hz or less, 100 Hz or less, 1 kHz or less or more than 1 kHz. If the difference between two successive calculated power values exceeds the maximum value, then, for example, the rate-of-change-limited power value is set equal to the sum of the previously calculated power value and the maximum value. If the difference is less, then the rate-of-change-limited power value is set equal to the new calculated power value, for example. The system may include a closed loop control.

The system may include a tachometer for taking readings of the speed. The tachometer therefore measures the speed and provides corresponding measured values.

For example, the tachometer measures the speed of the electric machine or the rotor.

The electrical machine is designed, for example, in the form of an electric motor, in particular in the form of a drive motor of a vehicle, such as an aircraft. Alternatively (or additionally), the electrical machine is designed in the form of a generator and/or set up in the system to be operated as such. For example, the system is part of a wind turbine.

The rotor includes, for example, a turbomachine, in particular a propeller. Rotor blades or vanes, for example, are mounted on the rotor.

Optionally, the turbomachine includes rotor blades or vanes with an adjustable angle of attack. The angle of attack is the angle between the direction of the oncoming fluid and the chord of a profile of each of the rotor blades or vanes. For example, the control unit is set up to specify the angle of attack. In this way, the speed (on average, i.e. apart from the imposed variation as a result of the vibrations) can be kept approximately constant, while a thrust and an associated torque are adjusted via the angle of attack. For example, the gear is a reduction gear. The transmission can translate a higher speed of the electric machine into a comparatively lower speed of the rotor.

The rate-of-change limiter is set up, for example, to determine the change over time in a calculated power value by comparing it with at least one previously calculated power value.

The controller may further include a divisor configured to calculate a modified torque value based on the rate-of-change limited power value and the speed measurements. This can be converted, e.g. by the control unit, into an electrical current with which the electrical machine is then operated.

The control unit can also include an extreme value limiter, which is set up, for example, to receive the respectively calculated output value (e.g. power value) from the (power) computer, to limit it by a maximum output value and/or a minimum output value and to send the respective limited output value output the rate of change limiter. It can thus be prevented that the absolute value of the power/torque assumes a value that is too large or too small (in particular in generator operation).

The maximum value of change over time of each of the calculated rate-of-change limiter power values may be based on one or more previously calculated rate-of-change limited power values. In this way, for example, a maximum relative increase or decrease in power can be implemented. This allows a particularly good reduction of vibrations with good system performance at the same time.

Furthermore, the control unit can include a multiplier which is set up to receive a respective rate-of-change-limited power value from the rate-of-change limiter and to multiply it by a predetermined or predeterminable factor. The value obtained in this way is, for example, the maximum value of the temporal change. The factor can be the same for all calculated power values.

For example, the predetermined factor is less than 1. For example, the predetermined factor is 10% or less.

According to one aspect, a vehicle, in particular an aircraft, is specified, comprising the system according to any configuration described herein, in particular as a drive system. With regard to the advantages, reference is made to the above information on the system. The vehicle can also be a land vehicle or a watercraft, for example a submarine. Furthermore, the system can be used in a wind turbine. There, transient operating conditions can be caused by changes in wind conditions as well as changes in load absorption, which directly affects the generator torque.

According to one aspect, a method for controlling an electric machine coupled to a rotor via a transmission is specified. The method includes detecting, by means of a control unit, values of requested torques (or power) and of measured values indicative of speeds, calculating, by means of the control unit, power values (or torque values) from the values of requested torques (or power) and the values for the speeds are indicative measured values. The method also includes limiting, by means of the control unit, a change over time in the calculated power values (or torque values) to a maximum value in order to obtain a power value (or torque value) that is limited by the rate of change, and controlling, by means of the control unit, the electric machine based on the rate-of-change limited power (or torque) value. With regard to the advantages, reference is again made to the above information on the system.

The electric machine used in the method, the rotor, the gearbox and the control unit can be part of the system according to any of the configurations described herein. Exemplary embodiments will now be described with reference to the figures; show in the figures:

Figure 1 shows an aircraft in the form of an airplane with a system for

control of an electrical machine of the aircraft;

FIG. 2 shows a block diagram of a control unit of the system according to FIG

Figure 1;

Figure 3 is a graph of plotted against engine speed

Torques when accelerating from a standing start with and without activation of a control by means of the control unit according to FIG. 2; and

FIG. 4 shows the result of a frequency analysis with and without activation of a controller using the control unit according to FIG.

FIG. 1 shows an aircraft 2 in the form of an electrically powered aircraft. The aircraft 2 comprises a system 1 with an electric machine 10, a rotor 11 and a gearbox 12.

The electric machine 10 can be operated as an electric motor (alternatively or additionally as a generator) and is operatively connected to the rotor 11 via the transmission 12 . In the present case, the electric machine 10 drives the rotor 11 via the transmission 12 .

The transmission 12 has an input shaft and an output shaft. The input shaft is coupled to the electric machine 10 . The output shaft is coupled to the rotor 11 . The gear 12 is a reduction gear and translates a predetermined speed of the input shaft into a lower speed of the output shaft. The transmission 12 includes several transmission elements, in particular gears. For example, the gear 12 is designed in the form of a planetary gear. For example, the electric machine drives a sun wheel of the transmission 12, which is coupled to a ring gear via planet wheels. The rotor 11 is, for example, non-rotatably connected to the ring gear or a planet carrier. The planet gears can be rotated on the planet carrier assembled.

The rotor 11 includes a propeller 110 with multiple rotor blades. The rotor blades have a changeable angle of attack, and the rotor blades can also be fixed to a hub.

The system 1 also includes an energy source, here in the form of an electric battery 14. The electric machine 10 is supplied with energy by the battery 14. Optionally, the system 1 further includes a generator 16 and, for example, a gas turbine 15 for driving the generator 16. The generator 16 feeds the battery 14 with electrical energy. Alternatively or additionally, the generator 16 provides electrical energy directly to the electrical machine 10 .

Furthermore, the system 1 comprises a control unit 13. The control unit 13 can consist of one module or be divided into several modules which can be arranged at the same place and/or at a distance from one another and can, for example, be communicatively connected to one another. The control unit 13 is communicatively connected to the electric machine 10 (e.g. a power supply unit thereof). In the example shown, the control unit 13 is also communicatively connected to the rotor 11, specifically for setting an angle of attack of the rotor blades. Optionally, the control unit 13 is also communicatively connected to the battery 14, the gas turbine 15 and/or the generator 16. The communicative connections are established, for example, via appropriate cable connections and/or wirelessly.

Furthermore, the system 1 includes one (or more) tachometer 17. The tachometer 17 is arranged in such a way that it acquires measured values that indicate a speed of the electric machine 10. For example, the tachometer 17 measures the speed of a shaft, z. B. an output shaft, the electric machine 10 or the input shaft of the transmission 12. Alternatively or additionally, the tachometer 17 (or another tachometer) can be arranged at another location, e.g. on an output shaft of the transmission 12 to measure the speed of this output shaft or on the rotor 11 for measuring the speed of the rotor 11. The (or) tachometer 17 is (are) connected to the control unit 13 communicatively connected.

Figure 2 illustrates some components of the control unit 13. In particular, the control unit 13 comprises a computer in the form of a power computer 130, which is set up to acquire values of requested torques and measured values indicative of speeds, which are, and to calculate power values therefrom, and a rate of change limiter 131, which is set up to receive the calculated power values and to limit a change in the calculated power values over time (in particular a change in the power values between two consecutive computing cycles) to a maximum value in order to obtain a power value with a rate-of-change-limited power value. The control unit 13 is set up to control the electric machine 10 based on the rate-of-change-limited power value.

If, for example, a motor controller of the electrical machine 10 requires the provision of a power signal as a control variable, torque values and power values can be interchanged in the calculation described with reference to FIG.

The values of the requested torques are entered at an input E1 of the control unit 13 . For example, the values of the requested torques are provided by a thrust lever at input E1.

The measured values, which are indicative of rotational speeds, are entered at an input E2 of the control unit 13 and made available to the power computer 130 . These measured values are provided by the tachometer 17 at the input E2. These measured values are (optionally) made available to a multiplier 134 of the performance computer 130 from the input E2. The multiplier 134 (optionally) multiplies the measured values by a constant, eg pi/30, for subsequent determination of the requested shaft power in watts. The multiplication result of the multiplier 134 is provided to an (optional) maximum value selector 135 of the performance calculator 130 . This is also given a constant, for example the value 1. The maximum value selector 135 selects the larger value from the two values provided at the same time. This avoids dividing by zero, for example when the The thrust lever is in a position that requires no thrust and therefore no torque.

The value selected by maximum value selector 135 is provided to a multiplier 134 of power computer 130, as is the requested torque provided at input E1. This multiplier 134 of the power calculator 130 multiplies these two values and thus calculates the power corresponding to the requested torque, i.e. a power value.

The power value calculated by the power calculator 130 is provided to an (optional) extreme value limiter 133 . At input E3, this also receives a value for a maximum output power of electrical machine 10 in motor operation and at input E4 a value for a maximum input power of electrical machine 10 in generator operation. If the calculated power value exceeds the maximum power output or if the calculated power value falls below the maximum power input (the power input is considered here as an example with a negative sign), then the extreme value limiter 133 outputs the value of the maximum power output or the maximum power input . Otherwise, the peak limiter 133 outputs the power value calculated by the power calculator 130 .

The calculated power value (optionally limited by peak limiter 133 ) is provided to rate of change limiter 131 . The rate of change limiter 131 includes a buffer memory in which at least one previously calculated power value is stored. If the difference between the power value currently calculated and present at the input of the rate-of-change limiter 131 and the stored power value exceeds a maximum value, then the rate-of-change limiter 131 outputs the sum of the stored power value and the maximum value. If the difference between the power value currently calculated and present at the input of the rate-of-change limiter 131 and the stored power value falls below the maximum value (with the opposite sign), then the rate-of-change limiter 131 outputs the sum of the stored power value and the maximum value (again with the opposite sign). Otherwise the Rate of change limiter 131 from the present, currently calculated power value.

The maximum value is calculated relatively in each case. For this purpose, the output of the rate-of-change limiter 131 is provided to a multiplier 134 via an (optional) delay 136 . This multiplier 134 also receives a predetermined value of a maximum relative change over time, which is present at an input E5. This predetermined factor is e.g. 1% (ie 0.01) or less, 5% (ie 0.05) or less, 10% (ie 0.1) or less or 20% (0.2) or less. In the example shown, the value provided at input E5 is 10%. The input E5 can also represent an internal memory of the control unit 13 . The multiplier 134 thus calculates a proportion (e.g. 10%) of the rate-of-change-limited power value output at the output of the rate-of-change limiter 131 and provides this as a maximum value to the rate-of-change limiter 131 for the subsequent computing cycle. An optionally interposed maximum value selector 135 selects the larger value from this value and a constant, e.g. to enable starting from a standstill. A sign changer 137 outputs the maximum value of the change over time with the sign reversed to a further input of the rate-of-change limiter 131 for comparison with falling power values.

The rate of change limiter 131 can also be supplied with a reset signal via an input E6 in order to clear the buffer memory and enable a start from standstill.

The value based on the measured value indicative of the speed, which is also already provided to the multiplier 134 of the power calculator 130 , is also provided to a divisor 132 . The value output at the output of the rate-of-change limiter 131 is also provided to the divisor 132 . From this, the divisor 132 calculates a modified value of the requested torque by dividing it. This is provided at an output A and output, for example, to a motor controller of the electrical machine 10 (which can be integrated into the control unit 13 or designed separately therefrom). Electric machine 10 is operated based on this value. For example, the electrical machine 10 is subjected to a current intensity corresponding to this value.

Since the vibration in the form of torsional vibrations is included in the readings indicative of the speeds, this control applies a correction that counteracts the vibration.

FIG. 3 shows the result of a measurement in which two drive systems were operated in parallel, one without the components of the control unit 13 shown in FIG. 2 (curves K1 to K4) and one with the control unit 13 according to FIG. 2 (curves K5 to K8). The torque values of each of the four different curves were measured against the engine speed in the same way using strain gauges at the same positions between each two components of the transmission 12 . The significantly smoother curves K5-K8 of the measurement with the activated control unit 13 according to FIG. 2 are clearly visible. For better illustration, one coil winding of the electrical machines 10 was deactivated in each case. It is evident that even such a disturbance could be smoothed out by the control unit 13 according to FIG. Thus, the proposed power rate limited torque control solution can control the vibrations even in the event of a failure of individual coil windings.

FIG. 4 shows the result of a frequency analysis (using FFT, fast Fourier transformation) of both drive systems. The left half reflects the result of the drive system without the components of the control unit 13 shown in Figure 2, the right half the result of the drive system with the components of the control unit 13 shown in Figure 2 Reduction of 20 dBm visible.

It should be noted that a reduction in vibrations is particularly important in a transient operating state (eg acceleration or deceleration), but also, for example, in stationary operating states in which the vibrations themselves cause changes in the rotational speed. It should be understood that the invention is not limited to the embodiments described above, and various modifications and improvements can be made without departing from the concepts described herein. Any of the features may be employed separately or in combination with any other feature, provided they are not mutually exclusive, and the disclosure extends to and encompasses all combinations and sub-combinations of one or more features described herein. It should be noted, for example, that the blocks shown in FIG. 2 can be implemented in the form of hardware and/or in the form of software.

Furthermore, it is possible to use a parallel hybrid drive instead of a fully electric drive or a serial hybrid electric drive, in which a gas turbine or another internal combustion engine and an electric machine both drive mechanically.

Reference List

1 system

10 electric machine

11 rotors

110 propellers

12 gears

13 control unit

130 Performance Calculator

131 rate of change limiter

132 divisor

133 peak limiter

134 multiplier

135 maximum value selector

136 retarders

137 sign changer

14 battery

15 gas turbine

16 alternators

17 tachometer

2 aircraft

A exit

E1-E6 input

K1-K8 curve

Claims

Expectations

1. System (1), comprising an electric machine (10), a rotor (11), a transmission (12), via which the rotor (11) is coupled to the electric machine (10), and a control unit (13) with: a computer (130), which is set up to a) record values of required torques and measured values indicative of speeds and calculate power values therefrom as starting values or b) values of required performances and measured values indicative of speeds and use them to record torque values as starting values and a rate-of-change limiter (131) that is set up to obtain the calculated output values and to limit a change in the calculated output values over time to a maximum value in order to obtain a rate-of-change-limited output value, the control unit (13) being set up to to control the electric machine (10) based on the rate of change limited output value.

2. System (1) according to claim 1, further comprising a tachometer (17) for detecting the indicative of speeds measured values.

3. System (1) according to claim 2, wherein the tachometer (17) is adapted to measure the speed of the electric machine (10).

4. System (1) according to any one of the preceding claims, wherein the electrical machine (10) is designed in the form of an electric motor.

5. System (1) according to any one of the preceding claims, wherein the rotor (11) comprises a turbomachine, in particular a propeller (110).

6. System (1) according to claim 5, wherein the turbomachine comprises rotor blades or vanes with adjustable pitch.

7. System (1) according to any one of the preceding claims, wherein the transmission (12) translates a higher speed of the electric machine (10) into a comparatively lower speed of the rotor (11).

8. System (1) according to one of the preceding claims, wherein the change rate limiter (131) is set up to determine the change over time in a calculated output value in each case by a comparison with at least one previously calculated output value.

9. System (1) according to any one of the preceding claims, wherein the control unit (13) further comprises a divisor (132) which is set up to calculate a modified torque value based on the rate-of-change-limited power value as an output value and the measured values indicative of speeds.

10. System (1) according to one of the preceding claims, wherein the control unit (13) comprises an extreme value limiter (133) which is set up to obtain the respectively calculated output value from the computer (130) by a maximum output value and/or a constrain the minimum output value and output the constrained output value to the slew rate limiter (131).

11 . The system (1) of any preceding claim, wherein the maximum value of the slew rate limiter (131) is based on a previously calculated slew rate limited output value.

12. System (1) according to claim 11, wherein the control unit (13) comprises a multiplier (134) which is set up to receive a rate-of-change-limited power value as an output value from the rate-of-change limiter (131) and to multiply it by a predetermined or specifiable factor.

13. System (1) according to claim 12, wherein the predetermined factor is less than 1, optionally 0.1 or less. - 16 - Vehicle, in particular aircraft (2), comprising the system (1) according to one of the preceding claims as a drive system. Method for controlling an electric machine (10) coupled to a rotor (11) via a transmission (12), comprising:

- detecting, by means of a control unit (13), a) values of requested torques and measured values indicative of speeds and calculation of power values as output values therefrom or b) values of requested power and measured values indicative of speeds and calculation of power values as output values therefrom,

- limiting, by means of the control unit (13), a change over time in the calculated output values to a maximum value in order to obtain an output value with a rate-of-change limitation, and

- Controlling, by means of the control unit (13), the electrical machine (10) based on the rate-of-change-limited output value. The method of claim 15, wherein the electric machine (10), the rotor (11), the transmission (12) and the control unit (13) are part of the system (1) according to any one of claims 1 to 13.