Control of asynchronous electrical machines

Abstract

The invention relates to a device for controlling the torque delivered by an asynchronous electric machine, comprising: - a rotary slip-ring collector system adapted to be connected to a rotor of an asynchronous electric machine and configured to collect or supply at least one winding of the rotor of the asynchronous electric machine so as to vary the impedance of the rotor and thus a torque delivered by the asynchronous electric machine; - a variable resistor connected to the rotary slip-ring collector system so as to control the rotary slip-ring collector system; - a processing unit configured to, from a frequency, a supply voltage of the asynchronous machine, a desired torque for the asynchronous electric machine and a corresponding rotor resistance, calculate a value for the variable resistor and thus control the supply voltage of the collector so that the asynchronous electric machine delivers the desired torque.Figure for the abbreviation: FIGURE 1.

Description

Title of the invention: Control of asynchronous electrical machines Technical field

[0001] The invention relates to the control of asynchronous electrical machines, particularly those used in a turbomachine of an aircraft. STATE OF THE ART

[0002] A turbomachine comprises, in addition to other components, systems which may comprise asynchronous electrical machines, for example a variable-timing system. These electrical machines are conventionally powered by the aircraft's on-board network which may be variable-frequency.

[0003] However, in a turbomachine, the torque, the speed and the power of the electric machine must be controlled to be constant for applications for which it is desired to have a fixed operating point at the output.

[0004] To do this, between the on-board network and the electrical machine to be powered, an electronic power box is placed comprising a rectifier and an inverter.

[0005] One problem with using such a housing is that it requires thermal management of its components. However, the volume and integration of such a housing on the turbomachine and its cost constitute other problems. Such management involves additional components which impact the sizing of the turbomachine. Statement of the invention

[0006] The invention makes it possible to do without an electronic power box while controlling a torque delivered by an asynchronous electrical machine.

[0007] To this end, the invention proposes, according to a first aspect, a device for controlling the torque delivered by an asynchronous electrical machine, comprising:

[0008] - a rotating ring collector system adapted to be connected to a rotor of a asynchronous electric machine and configured to collect or supply at least one winding of the rotor of the asynchronous electric machine so as to vary the impedance of the rotor and thus a torque delivered by the asynchronous electric machine;

[0009] - a variable resistor connected to the rotating ring collector system in a manner to drive the rotating ring collector system;

[0010] -a processing unit configured to, from a frequency of a supply voltage of the asynchronous machine, a desired torque for the asynchronous electrical machine and a corresponding rotor resistance, calculate a value for the variable resistance and thus control the supply voltage of the collector so that the asynchronous electrical machine delivers the desired torque.

[0011] The invention is advantageously completed by the following characteristics, taken alone or in any technically possible combination thereof:

[0012] - the processing unit determines the rotor resistance by means of the expression next:

[0013]

[0014] Tem: Desired torque in Nm

[0015] P: Number of pole pairs

[0016] mr • Number of rotor phases which is equal to the number of rotor bars for a asynchronous machine

[0017] ws • Stator electrical pulsation in rad / s which corresponds to the supply voltage of the asynchronous electrical machine

[0018] Zr( s) — Rr + jswsLr(r : Rotor impedance as a function of slip in Ohms

[0019] z2 = R2 + s2( due + L ) 2 • Rotor impedance modulus squared in Ohms at square

[0020] Rr: Rotor resistance in Ohms

[0021] Lra: Rotor inductance in Henri

[0022] 6: Sliding

[0023] Erk- RMS value of electromotive force in Volts.

[0024] - the electrical machine comprises a number of poles such that it makes it possible to achieve torque ranges greater than those required to drive the turbomachine element.

[0025] - the device comprises a voltage sensor or voltage measuring system configured to provide the processing unit with a measurement of a supply voltage of the asynchronous electrical machine, the processing unit being configured to implement a Fourier transform on the measurement to deduce the frequency of the supply voltage.

[0026] - the electric machine is powered by a voltage equal to 115 volts in a range variable frequency ranging from 360Hz to 800 Hz.

[0027] The invention proposes, according to a second aspect, a system for controlling an element of a turbomachine of an aircraft, comprising

[0028] - an asynchronous electric machine configured to provide a torque to an element of a turbomachine;

[0029] - a device according to the first aspect of the invention.

[0030] In the system according to the second aspect, the element of the turbomachine is a pump of a variable propeller pitch control system.

[0031] The invention makes it possible to control the slip of an asynchronous machine and its torque without power electronics.

[0032] In particular, the invention uses a relationship between the impedance of the rotor of the electric machine and the slip, which thus makes it possible to control the torque.

[0033] Consequently, and despite a variable electrical network frequency, it is possible to control the torque and rotation speed without power electronics.

[0034] PRESENTATION OF THE SINGLE FIGURE

[0035] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the single appended figure which illustrates a system for controlling an element of a turbomachine in accordance with the invention. DETAILED DESCRIPTION

[0036] [Fig.l] illustrates a system S for controlling an element E of a turbomachine of an aircraft, comprising an asynchronous electric machine 1 configured to provide torque to the element E of a turbomachine and a control device D

[0037] of the torque delivered by the electric machine 1. The electric machine 1 comprises a rotor 21 and a stator 22, the rotor 21 supplying the torque to the element E.

[0038] The turbomachine element E is advantageously an electrically actuated pump for variable propeller pitch setting. More generally, the element E is any type of pump integrated into a system for which the need is to provide a fixed flow rate (i.e. a fixed operating point).

[0039] The electric machine 1 is preferably an asynchronous electric machine with a wound rotor supplied in three-phase by an aircraft network delivering an alternating supply voltage V with variable electric frequency. The supply voltage V is for example equal to 115 volts in a variable frequency range from 360 Hz to 800 Hz.

[0040] Since the frequency of the voltage V is variable, the electric machine 1 provides a speed which is also variable.

[0041] Therefore, to maintain the rotation speed of the asynchronous electrical machine at a constant value and therefore its torque in order to maintain the element E at its ideal operating point, the system S comprises a device D for controlling the torque delivered by the electrical machine 1.

[0042] Such a device D comprises a collector 2 with rotating rings connected to the rotor 21 of the electric machine 1 in order to vary the impedance of the electric circuit of the rotor and thus the torque delivered by the electric machine.

[0043] Such a collector 2 is also known as a slip-ring collector. The collector 2 consists of at least two electrically conductive rings fixed by an insulating spacer on the axis of the rotor 21 of the Electric machine 1. The electrical connection is created between each ring and a fixed part by a brush. Preferably, the commutator 2 comprises three rings and three brushes. The commutator 2 is powered by a variable voltage U which makes it possible to control the rotor impedance and therefore the torque delivered by the asynchronous electric machine. Voltage V, which is the network voltage, powers the stator and voltage U powers the rotor.

[0044] To modify this voltage U, the device D comprises a variable resistor 3 whose value comes from a calculation implemented by a processing unit 4 of the device D.

[0045] Such a calculation makes it possible, from the frequency of the supply voltage V of the asynchronous machine, a desired torque Tem for the asynchronous electrical machine 2 and a corresponding rotor resistance Rr, to calculate a resistance value R for the variable resistor 3 in order to thus control the supply voltage U of the collector 2 so that the electrical machine 1 delivers the desired torque Tem.

[0046] In fact, the following relationship has been highlighted between the torque as a function of the slip and the resistance R, rotor:

[0047] T ( v \ ~ *____—____ ' J “ w, „?1 ,T \2^rk. R^(MX+Lm)

[0048] with

[0049] Tem: Electromagnetic torque in Nm

[0050] P: Number of pole pairs

[0051] mr ■ Number of rotor phases (equal to the number of rotor bars for an asynchronous machine)

[0052] ■ Stator electrical pulsation in rad / s which corresponds to the supply voltage V

[0053] Z^s) = Rr + jsœsLro : Rotor impedance as a function of slip in Ohms

[0054] Z2 — R? + +L )2 : Rotor impedance modulus squared (in the denominator in the equation) in Ohms squared

[0055] Rt: Rotor resistance in Ohms

[0056] Lrer: Rotor inductance in Henri

[0057] s: sliding

[0058] Erk: RMS (Root Mean Square) value of the electromotive force in Volts

[0059] This equation shows that by controlling the rotor resistance Rr, the slip is also controlled and thus the generated torque is brought under control.

[0060] Advantageously, the number of poles of the electric machine 1 is such that it makes it possible to achieve torque ranges greater than that required to drive the turbomachine element E. The device D will then limit the excess torque for proper operation, thus maintaining the machine at the correct speed and the correct torque. for the operation of element E.

[0061] In order to obtain the frequency of the supply voltage, a voltage measurement system 5 is connected to one phase and provides the processing unit 4 with a variation in the voltage to which a fast Fourier Transform is applied to obtain the frequency.

Claims

Claims

1. Device (D) for controlling the torque delivered by an asynchronous electrical machine (1), comprising: - a rotating ring collector system (2) adapted to be connected to a rotor (21) of an asynchronous electrical machine (1) and configured to collect or supply at least one winding of the rotor (21) of the asynchronous electrical machine (1) so as to vary the impedance of the rotor and thus a torque delivered by the asynchronous electrical machine (1); - a variable resistor (3) connected to the rotating ring collector system (3) so as to control the rotating ring collector system (2);- a processing unit (4) configured to, from a frequency (Cs) of a supply voltage (V) of the asynchronous machine (1), a desired torque (Tem) for the asynchronous electrical machine (2) and a corresponding rotor resistance (Rr), calculate a value (R) for the variable resistance (3) and thus control the supply voltage of the collector so that the asynchronous electrical machine delivers the desired torque (T^.;

2. Device according to claim 1, wherein the processing unit (4) determines the rotor resistance (Rr) by means of the following expression: 'T / < V _ 1' _____-E_____ 1 em\A ) ~ 2, v ,t \2nrk Tem: Desired torque in Nm P: Number of pole pairs mr ■ Number of rotor phases which is equal to the number of rotor bars for an asynchronous machine • Stator electrical pulsation in rad / s which corresponds to the supply voltage of the asynchronous electrical machine Zr(s) = Rr + jswsLra: Rotor impedance as a function of slip in Ohms Z2 - R2 + + Z ) 2: Rotor impedance modulus squared in Ohms squared R,: Rotor resistance in Ohms Lra; Rotor inductance in Henri 5: Slip Erk: RMS value of the electromotive force in Volts.

3. Device according to one of the preceding claims, in which the electrical machine (1) comprises a number of poles such that it allows to achieve torque ranges higher than those required to drive the turbomachine element (E).

4. Device according to one of the preceding claims, comprising a voltage sensor or voltage measurement system (5) configured to provide the processing unit (4) with a measurement of a supply voltage of the asynchronous electrical machine (1), the processing unit (4) being configured to implement a Fourier transform on the measurement to deduce therefrom the frequency of the supply voltage.

5. Device according to one of the preceding claims, in which the electrical machine (1) is supplied with a voltage equal to 115 volts in a variable frequency range from 360Hz to 800 Hz.

6. System (S) for controlling an element (E) of a turbomachine of an aircraft, comprising - an asynchronous electric machine (1) configured to supply torque to an element (E) of a turbomachine; - a device (D) according to one of the preceding claims.

7. System according to the preceding claim, in which the element (E) of the turbomachine is a pump of a variable propeller pitch setting system.

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