FR2468248A1 - NOISE SUPPRESSION CIRCUIT FOR AN ELECTRIC MOTOR CONTROL THYRISTORS - Google Patents

Abstract

The invention relates to a noise suppression circuit for an electric motor controlled by thyristors. The circuit comprises at least one thyristor bridge 14 and switching shock chokes 7, 8, 9 which protect thyristors 1, 6 against any excessive current peaks. At least one series resonance circuit 16 is connected in the circuit to the terminals of the motor 12 and the switching chokes 7, 8, 9 mounted in the circuit also function as damping chokes-series 15. Applications: electric motors for elevators.

Description

The present invention relates to a noise cancellation circuit for

  thyristor-controlled electric motor, such as a DC motor of an elevator, said circuit comprising at least one thyristor bridge and switching shock chokes protecting

  thyristors against excessive current peaks.

  Thyristors are today frequently associated with

  control of electric motors. It is possible

  particularly in alternating current lifts.

  in which squirrel cage motors are used as drive motors, for example to regulate the motor torque by means of

  shock connected in one or more phases. The thyris-

  tors act in the capacity of the shock elements and

  they are connected for this purpose, for example bypairs.

  Current elevator drive motors

  continuous have traditionally been Ward-motors

  Leonard. According to this commonly known technique, the DC motor is controlled by a DC generator. However, with the development of

  semiconductor technologies, it has become more economical

  replace the DC generator with

  a thyristor rectifier. The thyristor bridges

  designed to be used as rectifiers which are usually

  In particular, they are used in elevator technology, including three-phase motors with twelve thyristors and four sectors, although rectifiers employing a smaller number of thyristors have also been realized.

  The thyristor motor is suitable for use with

  as an elevator engine in every respect, but there was a problem with non-uniform tension

  from the thyristor control to the terminals of the

  tor. This variation of tension determines in the elevator motor a disturbing noise for the personnel who serves the elevator and for all the people in the vicinity of the latter, which undermines the

product quality.

  For example, the circuit shown in Figure 1 has been used to mitigate annoying noise, to provide a solution in the prior art. In

  this circuit, the thyristors constitute the bridge of

  required by the lift motor. In addition, thyroid

  The ristors are protected by switching shock chokes that are intended to protect the thyristors against excessive peak current at

  the current is switched from one thyristor to another. Ltamor-

  The sound is produced by an acoustic filter consisting of a choke connected to a terminal of the booster motor and a capacitor connected to the two terminals of the motor. This acoustic filter operates as a low-pass filter and the filtering improves at the same time as the inductance of the shock choke and the capacitance of the capacitor increases. This solution presents

  as disadvantages a high cost price and a function

  incomplete. Since the shock choke carries all the direct current of the motor and has

  a relatively high inductance, it is natural-

  very expensive. Moreover, it does not obtain with this assembly any complete suppression of the noise; a limitation is

  for example imposed by the fact that the capacitor

  should in principle be realized in unlimited dimensions.

  The present invention aims to eliminate

  the disadvantages mentioned in the

  thyristor driven electric motors, and provide the problem a solution that allows to effectively and advantageously remove the annoying noise. The

  noise suppression circuit of the invention is

  the fact that at least one resonance circuit

  The series is connected to the circuit at the motor terminals, and the switching shock chokes incorporated in the circuit additionally operate in series damping shock chokes. By its design, the invention offers the advantage of being able to operate

  the resonance-series circuit with relative values

  weaknesses of capacitance and inductance by comparison

  with those of the prior art mentioned above.

  above. It is therefore possible to use components

24M8248

  considerably less expensive. The shock chokes of com-

  mutation can also be extremely close to those already used in systems

  the prior art, but they still have to

  another function in the capacity of the shock-shock-series chokes for noise suppression. Another advantage is that since the resonant-series circuit constitutes a complete short circuit at a given frequency, which incorporates most of the annoying noise, the soundproofing will be

  more efficient than it was in the prior art

  in which the damping of the capacitor at the motor terminals was incomplete at

  any frequency. This solution is particularly

  advantageously in the case of a DC motor because for the damping of the fundamental frequency, which is the most troublesome frequency, a single resonant-series circuit is sufficient, if one is

  forced to damp multiple harmonic multiples of the frequency

  this fundamental, a single series-resonance circuit is also sufficient for each of them. In the case of

  DC lifts, it is recommended to

  to minimize annoying noise as the

  DC motors are in the main elements

  expensive, and therefore a very high level of

formance is required.

  An advantageous embodiment of the invention

  is characterized in that one or more series-resonance circuits which damp the harmonics of the fundamental frequency are connected in parallel

  with the resonance-series circuit that dampens the frequencies

  fundamentals. This gives the advantage of a

  even greater improvement of the soundproofing.

  Another embodiment of the invention is

  characterized in that the resonance of the resonant circuit

  nance-series is equal to n times the frequency of the supply network, n being equal to 2, 3, 6 or 12. Thus,

  the annoying resonant frequency is directly attenuated

  clouded by the resonance-series circuit.

  The invention will be described below from a

  more detailed reference with reference to the accompanying drawings, in which:

  FIG. 1 represents a device for eliminating

  noise generation of the prior art. Figure 2, the noise elimination circuit

according to the invention.

  Figures 3 and 4, using graphics, the

  waveform of the voltage delivered by the bridge of thy-

  ristors, and the corresponding form of the current of the armature. Figure 5, an equivalent simplified circuit

  in principle to the circuit of the invention.

  FIG. 6, an embodiment in which the harmonics are also damped, and

  FIG. 7, a device of the invention used

in a particular case.

  Although thyristor bridges in

  cations to elevators are usually

  at twelve thyristors, the drawings of this description

  represent, for better clarity, only one of the two bridges of six thyristors. This in no way modifies the character of the principle of this invention. In the device according to the prior art, device shown in FIG. 1, the same reference numbers were used as for the components represented.

  in the device of the present invention of the

  2, with a view to simplification and

  clarity. The same name can be used to refer to

  indicated by the same reference number, although these components do not have equivalent values or properties. The operating principle of devices made according to the prior art

  has already been described. In the drawing of the invention,

  2, the thyristors 1 to 6 constitute the rectifying bridge 14 necessary for the motor 12. The shock chokes 7, 8 and 9 are commonly known, they are switching shock chokes for bridges.

  thyristors whose function is to protect thyris-

  1 to 6 against the excessive peaks of current during

  current variations from one thyristor to another. This-

  while retaining the nature of the present invention.

  These shock chokes 7, 8 and 9 receive here another mission which will be described later in more detail. The resonance-series circuit 16 comprising the shock choke and the capacitor 11 interconnected in series, is connected to the terminals of the motor 12. The component 13, visible

  also in Figure 2, is the magnetization winding

  engine with which the magnetization of the engine

  is done in a well-known way.

  In order to facilitate the understanding of the invention,

  first of all, it is necessary to know more about

  The general nature of the voltage and current waveforms delivered by the thyristor bridge 14. FIGS. 3 and 4 serve to clarify this point. In FIG. 3, graph 17 represents the waveform of the voltage coming from the thyristor bridge 14 in the case where the back electromotive force 19 of the motor 12 is zero and the armature current is low. The

  Figure 4 represents the case in which, in order to

  swing the counter-electromotive force 19 of the engine 12,

  a higher voltage is required from the thyristor bridge.

  tor 14, so that the armature intensity 21 is also

  higher than in the previous case. However,

  the armature intensity does not depend on the level of

  it varies according to the load imposed.

  It can be seen from FIGS. 3 and 4 that the awkward voltage is an asymmetrical triangular wave.

  17 and 20. If the thyristor system in question

  on a 50 Hz mains supply, the components

  frequency of the voltage wave 17 and 20

  will be 300 Hz and multiples of this value. How-

  the 300 Hz component is the strongest, and therefore the annoying noise is almost exclusively

the frequency of 300 Hz.

  The present invention is based on the only suppression by filtering of the disturbing frequency of 300 Hz, thanks to the circuit of FIG. 2. The filtering is carried out by means of the resonance-series circuit 16

  constituted by the shock inductor 10 and the capacitor 11.

  Thus, at the same time, a new function is assigned to the shock chokes 7, 8 and 9. Shock chokes become series-connected elements for the damping of the harmful voltage and these elements can receive the name of shock chokes. 15. This is shown in more detail, though schematically,

  in FIG. 5. The shock inductor 22 is the balanced circuit

  Shock chokes 7, 8 and 9 are worth and it functions as a series-shock shock choke. With regard to the damping of the damaging voltage, one can also imagine the shock inductor 22 being connected between the thyristor bridge 14 and the motor 12. The short-circuit jumper 23 represents the resonance-series circuit 16 at a frequency of 300 Hz. It will therefore be clear, with reference to the figure, that the disturbing voltage at 300 Hz remains at the terminals

  of the shock inductor 22, and that this component is absent.

  in the voltage at the motor terminals.

  If the damping at 300 Hz is not enough in

  In a particular case, it is possible to improve the

  by connecting a second resonance circuit-

  series 24 in parallel with the resonance circuit-

16 series at 300 Hz.

  This case is illustrated by the circuit of figure 6. When the frequency of the sector is 50 Hz, the nearest harmonic giving rise to an annoying noise will be 600 Hz. Therefore, by correctly choosing the components for the resonance circuit series 24, this

  disturbing noise can also be amortized as

  tooth. The annoying noises coming from the nearest harmonic are already weak enough to be able to

to be practically neglected.

  It is obvious to a specialist that the various embodiments of the invention are not exclusively limited to the example presented above,

  and that they can vary without departing from

  vention. For example, the soundproofing circuit of the invention can also be used in ac motors in which the control of the drive motor has been effected by means of a thyristor circuit. In this case, it will suffice to note that a circuit

  equivalent to the series 16 resonance circuit shall be

  separately in each phase, as well as a circuit equivalent to the damping circuit-series 15. In addition,

  the soundproofing circuit of the invention may also be

  used in compound AC motors.

  tif and direct current. Such a case is shown in FIG. 7. The drive motor is a two-speed squirrel-cage motor 25, whose high-speed winding 26 is controlled by an AC power supply with a three-phase element. thyristors

  27, to produce the driving torque, and o the winding

  At low speed 28 is controlled by a bridge 29 of single-phase supply thyristors providing DC power to produce a braking torque. We then connected in parallel with the winding at low speed of

  28 operated by direct current, at least one circuit / reso-

  In addition, the power supply circuit includes a series-damping shock-inductance 31. There are now at least three series-resonance circuits 32 between the terminals of the three-phase winding of large size.

  speed 26, and there is furthermore a damping shock choke

  three-phase series in the supply circuit.

R E VE N DIC A T IO N S

  1.- Noise suppression circuit for an electric motor driven by thyristors, for example for a DC motor for an elevator, comprising at least one thyristor bridge (14) and switching shock chokes (7, 8, 9) which protect the thyristors (1-6) against any excessive current peaks, characterized in that at least one resonance-series circuit (16) and / or the chokes are connected in the circuit at the terminals of the motor (12).

  (7, 8 and 9) mounted in the circuit

  In addition, they are used as chokes;

(15). -

  2. A noise suppression circuit according to claim 1, characterized in that one or more series-resonant circuits damping the harmonics of the fundamental frequency are connected in parallel with the resonance-series circuit (16) which damps the

fundamental frequencies.

  3.- Noise canceling circuit according to

  any of claims 1 or 2, characterized

  in that the resonance of the resonance-series circuit (16) comprises n times the frequency of the supply network

  sector, the parameter n being equal to 2, 3, 6 or 12.