GB1584980A

GB1584980A - Drive circuit for driving hysteresis motors

Info

Publication number: GB1584980A
Application number: GB49843/77A
Authority: GB
Original assignee: Licentia Patent Verwaltungs GmbH
Current assignee: Licentia Patent Verwaltungs GmbH
Priority date: 1976-11-30
Filing date: 1977-11-30
Publication date: 1981-02-18
Also published as: NL186546C; NL186546B; DE2654734A1; NL7712118A; DE2654734B2; DE2654734C3

Description

(54) DRIVE CIRCUIT FOR DRIVING HYSTERESIS MOTORS (71) We, LICENTIA PATENT VER WALTUNGS G.m.b.H., of 1 Theodor Stern-Kai, 6 Frankfurt/Main 70, Federal Republic of Germany, a German body corporate, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a drive circuit for driving multiphase motors. Such a circuit comprises a mains-side rectifier, an intermediate circuit and a forced-commutation inverter with an output voltage for supply of high-speed multiphase e.g. three-phase motors, preferably constructed as hysteresis motors. Converters of the type described are known from the ETZ-A Volume 89 (1968) Book 5, pages 108 to 112.

Problems arise in the use of this type of intermediate circuit converter with hysteresis motors. Hysteresis motors are highspeed rotating-field machines (for example having a supply frequency of 1000 Hz) which can be operated under load both in synchronous and asynchronous operation.

Because of the high rotational speed the rotor comprises a steel disc which is entrained by the rotating field of the stator.

The rotor has a pronounced remanent field in synchronous operation. The rotor voltage and the stator loss voltage add up to the terminal voltage of the motor. While with no-load operation both component voltages are in phase. when loading the motor the load angle e occurs between the rotor and terminal voltages. This becomes greater with increasing load up to a certain limiting value eLim. If the limiting value e Grenz iS reached then the motor leaves the range of synchronous operation. With asynchronous operation the load angle 6um iS maintained. The motor thus develops a torque of the magnitude of the pull-out torquves which is dependent on the amount of the slip until the slight influence of the eddy currents sets in. The slip proportional rotor losses arise in the form of magnetic reversal (hysteresis) losses.

The hysteresis motor is distinguished substantially from an asynchronous motor by its capacity for self-excitation up to saturation.

The terminal voltage which can arise in these circumstances can far exceed the permitted value. Self excitation must therefore be prevented. Because of the high expense of pre- venting self-excitation, in many cases in the past the hysteresis motor has not been used.

As has been shown in practice particularly when starting up the motor under load and when reaching the slip frequency, the resonance frequency of the smoothing circuit present in the intermediate circuit is reached resulting in self-excitation of the hysteresis motor.

Attempts have been made to stabilize the direct current intermediate circuit used by control of the mains-side rectifier. This solution fails to work however because of the different operating frequencies of the rectifier and inverter; the responses of the rectifier is too slow.

The invention seeks to provide a drive circuit for an hysteresis motor by means of which self excitation of the motor is suppressed.

According to the invention, there is from vided a drive circuit for a hysteresis motor comprising an alternating current rectifier, an inverter having outputs for connection to the motor and driven from the alternating current rectifier through an intermediate circuit, and an acceptor circuit connected in parallel with the alternating current rectifier and the input to the inverter, which circuit provides a low impedance path at a resonant frequency substantially equal to the parallel resonant frequency of the intermediate circuit.

Preferably the intermediate circuit comprises a smoothing choke and associated capacitor. The acceptor circuit may comprise a series connection of an inductance, a capacitance and a resistance connected in parallel to the said associated capacitor and the resonant impedance of the series-tuned wave trap or acceptor circuit may be approximately equal to half the resonant impedance of the smoothing choke and associated capacitor and the attenuation factor of the series tuned wave trap or acceptor circuit being approximately equal to one.

Because of the stated dimensioning of the resonance frequency, the resonant impedance and the attenuation of the series-tuned acceptor circuit, the resonant area or pole of the output impedance of the intermediate circuit is reduced sufficiently without new resonant areas or poles being created and at a low cost. Starting up of the motor is possible without danger of self-excitation. The attenuation of the series-tuned acceptor circuit does not cause any additional losses since the self-excitation is safely prevented as a result of frequency tuning of the two circuits. Therefore, the elements of the seriestuned acceptor circuit can be kept relatively small.

In order that the invention and its various other preferred features may be understood more easily, an embodiment thereof will now be described, by way of example only, with reference to the drawing.

The drawing shows an intermediate circuit converter connected to a three-phase mains, which converter supplies a high-speed hysteresis motor M. The intermediate circuit converter comprises a rectifier GR and an inverter WR with a direct current intermediate circuit connecting them. The rectifier GR and inverter WR are equipped with semiconductor elements which may be controlled and which are not shown in greater detail.

The rectifier GR is operated preferably with gating control. The forced commutation inverter connects direct current blocks in sequence to the motor phases and at a desired frequency i.e. high frequency of appoximately 1000 Hz to the terminals of the motor M.

The direct current intermediate circuit has a smoothing choke Lo in known manner and an associated capacitor Co.

In order to avoid self-excitation of the hysteresis motor M when the slip frequency of the motor approaches the resonance frequency w

of the smoothing choke Lo and the capacitor Co, an additional series-tuned wave trap or acceptor circuit comprising the series connection of an inductance Ll, a resistance R and a capacitance C1 is provided in parallel with the capacitor Co between the output terminals A and B of the direct current intermediate circuit.

The resonance frequency of the seriestuned wave trap or acceptor circuit

is equal to the resonance frequency wo of the circuit made up of the capacitor C0 and the smoothing choke Lo; the resonant impedance of the series-tuned wave trap or acceptor circuit

is approximatel equal to half of the resonant impedance -. C1

ot the smoothing choke Lo and the capacitor C0 and the attenuation of the series-tuned circuit

Although the embodiment described relates to the drive of a three-phase motor it will be appreciated that the invention is also applicable to the drive of multiphase motors with any number of phases.

WHAT WE CLAIM IS: 1. A drive circuit for a hysteresis motor comprises an alternating current rectifier, an inverter having outputs for connection to the motor and driven from the alternating current rectifier through an intermediate circuit, and an acceptor circuit connected in parallel with the alternating current rectifier and the input to the inverter, which circuit provides a low impedance path at a resonant frequency substantially equal to the parallel resonant frequency of the intermediate circuit.

2. A circuit according to claim 1,wherein the intermediate circuit comprises a smoothing choke and an associated capacitor.

3. A circuit according to claim 2, wherein the acceptor circuit comprising a series connection of an inductance, a capacitance and a resistance is connected in parallel with said associated capacitor at the output of the intermediate circuit.

4. A circuit according to claim 3, wherein the resonant impedance of the series-tuned acceptor circuit is approximately equal to half the resonant impedance of the smoothing choke and associated capacitor and the attenuation factor of the series-tuned acceptor circuit is approximately equal to one.

5. A drive circuit for a hysteresis motor substantially as described herein with reference to, or as illustrated in, the drawing.

For the Applicants

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. capacitor. The acceptor circuit may comprise a series connection of an inductance, a capacitance and a resistance connected in parallel to the said associated capacitor and the resonant impedance of the series-tuned wave trap or acceptor circuit may be approximately equal to half the resonant impedance of the smoothing choke and associated capacitor and the attenuation factor of the series tuned wave trap or acceptor circuit being approximately equal to one. Because of the stated dimensioning of the resonance frequency, the resonant impedance and the attenuation of the series-tuned acceptor circuit, the resonant area or pole of the output impedance of the intermediate circuit is reduced sufficiently without new resonant areas or poles being created and at a low cost. Starting up of the motor is possible without danger of self-excitation. The attenuation of the series-tuned acceptor circuit does not cause any additional losses since the self-excitation is safely prevented as a result of frequency tuning of the two circuits. Therefore, the elements of the seriestuned acceptor circuit can be kept relatively small. In order that the invention and its various other preferred features may be understood more easily, an embodiment thereof will now be described, by way of example only, with reference to the drawing. The drawing shows an intermediate circuit converter connected to a three-phase mains, which converter supplies a high-speed hysteresis motor M. The intermediate circuit converter comprises a rectifier GR and an inverter WR with a direct current intermediate circuit connecting them. The rectifier GR and inverter WR are equipped with semiconductor elements which may be controlled and which are not shown in greater detail. The rectifier GR is operated preferably with gating control. The forced commutation inverter connects direct current blocks in sequence to the motor phases and at a desired frequency i.e. high frequency of appoximately 1000 Hz to the terminals of the motor M. The direct current intermediate circuit has a smoothing choke Lo in known manner and an associated capacitor Co. In order to avoid self-excitation of the hysteresis motor M when the slip frequency of the motor approaches the resonance frequency w of the smoothing choke Lo and the capacitor Co, an additional series-tuned wave trap or acceptor circuit comprising the series connection of an inductance Ll, a resistance R and a capacitance C1 is provided in parallel with the capacitor Co between the output terminals A and B of the direct current intermediate circuit. The resonance frequency of the seriestuned wave trap or acceptor circuit is equal to the resonance frequency wo of the circuit made up of the capacitor C0 and the smoothing choke Lo; the resonant impedance of the series-tuned wave trap or acceptor circuit is approximatel equal to half of the resonant impedance -. C1 ot the smoothing choke Lo and the capacitor C0 and the attenuation of the series-tuned circuit Although the embodiment described relates to the drive of a three-phase motor it will be appreciated that the invention is also applicable to the drive of multiphase motors with any number of phases. WHAT WE CLAIM IS:

1. A drive circuit for a hysteresis motor comprises an alternating current rectifier, an inverter having outputs for connection to the motor and driven from the alternating current rectifier through an intermediate circuit, and an acceptor circuit connected in parallel with the alternating current rectifier and the input to the inverter, which circuit provides a low impedance path at a resonant frequency substantially equal to the parallel resonant frequency of the intermediate circuit.

For the Applicants