GB1594367A - Static converter for variable reluctance machine - Google Patents

Description

(54) STATIC CONVERTER FOR VARIABLE RELUCTANCE MACHINE (71) We, ENGINS MATRA, a French Society, of 4 rue de Presbourg, Paris, France, 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 static converters for variable reluctance machines and specifically variable frequency converters associated with vernier-type variable reluctance machines, i.e. whose shaft rotation speed is a submultiple of the rotation speed of the magnetomotive force.

Although known, variable reluctance machines have not been used to any significant extent industrially in view of their relatively poor performance when supplied at fixed frequency. As a result of the development of power semiconductors permitting the construction of variable frequency static converters and the improvement of the dynamic characteristics obtained by the automatic control of variable reluctance machines, it is now possible to produce machines having exceptional performance characteristics and whose torque or speed can be controlled in the four quadrants of the torque/speed diagrams, that is to say both in motor operation and in generator operation with in the latter case recuperation of the electrical power produced by the machine.

According to the invention there is provided a variable frequency static converter for a vernier-type variable reluctance machine comprising: a power supply having control electronics and operable both as a generator and as a receiver while being controlled as a function of the desired speed or torque of the machine: and at least one pair of identical series mounted elementary switching networks.

each network having two individual branches connected in parallel to the supply by one of their ends and connected by their other ends to a common point with the corresponding ends of the other identical series mounted switching network or networks, the common point being the only direct connection between the networks, each of the branches being adapted to supply a respective elementary field coil of the variable reluctance machine, and having a thyristor and a diode mounted in series in the conductive direction towards the field coil, and each network having a capacitor connected between the junctions of the thyristor and the diode of the two branches, and the thyristors of the networks being controlled by a control electronics controlled by an internal coder and synchronised with the control electronics of the power supply.

Embodiments of the invention will now be described by way of example with reference to the accompanying illustrative drawings in which: -Fig. 1 shows diagrammatically a first embodiment of a converter according to the invention; Fig. 2 shows a second embodiment of a converter according to the invention; -Fig. 3 shows part of the switching circuits used in constituting the converters according to Fig. 1 or 2.

Figs I and 2 respectively show two embodiments of static converters according to the invention, both being associated with a variable reluctance maFhine 100 which, in the present case, is-a machine having two pairs of complwentary poles 1, 3 and 2, 4, that is to say four elementary poles and a Vernier ratio of 1/4. This machine is shown in highly diagrammatic manner by its four field coils 1, 2, 3, 4, whose junction point carries the reference numeral 101.

P both cases, the static converter comprises two main parts namely on the one hand a power supply 102, 102', which is unidirectional and is able to function either as a generator or as a power receiver by polarity reversal and on the other hand a switching circuit 103 which is able to switch the field coils of the machine to a power supply 102 or 102'. In the two embodiments shown in Figs 1 and 2, the switching circuits are identical and are consequently given, the same reference numeral 103.

However, power supply 102 in- FIg 1 is different from power supply 102' in Fig 2. In the case of the embodiment of Fig 1, the power supply 102 essentially comprises a three-phase rectifier-inverter having thyristors 1021 and a smoothing choke 1022.

Control electronics 1023 receiving the signals necessary for its operation from a current loop 1024 controls the six thyristors TH5 and TH 10 of the rectifier-inverter as a function of the torque or speed data applied to an input 1025. In the case of the embodiment of Fig 2.

however, power supply 102' substantially comprises an auxiliary d.c. voltage source constituted by a bank of accumulators 1021' which can be charged from the mains by a rectifier-charger 1022' and is associated with two choppers 1023' and 1024' as well as with two free wheel circuits 1025' and 1026' permitting the recuperation on the bank of accumulator 1022' of the electric power produced by the reluctance machine 100 functioning as a generator. Control electronics 1027' which receives the power necessary for its operation from a current loop 1028' controls the choppers 1023' and 1024' as a function of the torque and feed data applied to an input 1029' for regulating the motive power or the braking power.

Power supplies 102 and 102' are of conventional design and are known per se. Thus, it is unnecessary to show them and describe them in greater detail. The invention is based on the association of the known power supplies with the switching circuit 103, common to both the embodiments shown, and which will be explained in greater detail with reference to Fig 3.

Fig 3 shows a circuit 103a constituting the upper part of the switching circuits 103.

Circuit 103a receives a current I from the power supply or restores current I to the power supply. It comprises two branches 1031 and 1032 which lead to the junction point 101 and on each of which are respectively mounted in series in the conductive direction towards the junction point 101 a thyristor TH, or TH3, a diode D, or D3 and a winding I or 3 of the variable reluctance machine. Between said two branches 1031 and 1032 is provided a capacitor C,3, whose terminals are respectively placed between thyristor TH, and diode D, and between thyristor TH3 and diode D3.

The circuit 103 described hereinbefore operates in the following manner: As thyristor TH, is in the conductive state and capacitor C13 is charged in accordance with the polarity indicated in Fig 3, thyristor TH3 is fired. This firing has the effect of applying the voltage of capacitor C,1 to the terminals of thyristor TH1, which is blocked.

Capacitor C,3 then discharges into the winding I via diode D1. Towards the end of this discharge, polarity is reversed at the terminals of capacitors C,3 and the total current I received or transmitted by the circuit flows via diode D1 into winding 3, whilst diode D, prevents the return of the current into branch 1031. At the same time. capacitor C,3 is recharged with a polarity which is the opposite to that shown in Fig 3. Thus. the switching of current I of winding 1 towards winding 3 is completed and capacitor C, is charged in order to permit in accordance with the reverse procedure to that described hereinbefore the subsequent switching of current I from winding 3 towards winding 1 by simply firing thyristor TH,.

It should be noted that under established operating conditions the charging voltage obtained at the capacitor terminals is only dependent on current I and is repetitive from one switching operation to the next.

On returning to Figs I and 2, it can be seen that a circuit 103b. which is symmetrical to circuit 103a with respect to the junction point 101, is provided to ensure under conditions identical to those described hereinbefore the switching of current I between the windings 2 and 4 of the variable reluctance machine.

Each of the assemblies respectively formed by elementary field coils 1 and 3 on the one hand and 2 and 4 on the other hand constitutes a pair of complementary windings. Thus, the sum of the currents passing through windings 1 and 3 is constant. The same applies regarding windings 2 and 4.

The circuits such as 103a or 103b which switches a pair of complementary windings is an elementary switching modular network.

In addition to the elementary switching modular networks 103a and 103b, the switching assembly 103 has a control electronics 1033 for the elementary switching modules controlled by an internal coder 1034. Control electronics 1033 is connected to control electronics 1023 (Fig 1) or to control electronics 1027' (Fig 2) by a synchronization loop 104.

It should be noted that the identical switching circuits of Figs 1 and 2 are constituted by the placing in series of two elementary modular networks 103a and 103b and ensure the switching of a reluctance machine having two pairs of complementary windings, i.e. four elementary windings in all, with a Vernier ratio of 1/4.

The switching arrangement according to the invention can however be extended to the control of a reluctance machine having more than two pairs of complementary field coils, namely 3, 4, 5, 6 or n pairs of complementary field coils or 6, 8, 10, 12 or 2n elementary field coils and with a Vernier ratio of 111 1 1 , - -, or - 6 8 10 12 2n by arranging in series 3, 4, 5, 6, or n elementary switching modular networks. The number of elementary modules arranged in series is only limited by the maximum voltage of the power supply which must at all times remain above the sum of the counterelectromotive forces of the machine.

Even if in theory, a Vernier-type variable reluctance machine can comprise two pairs of complementary windings, it has in practice a radial symmetry of random order.

Each system of 2n windings of a machine whose Vernier ratio is 2n is repeated a certain number of times at the periphery of the machine, the current circulating in the 2n windings being at all times identical from one system to the next. Two windings taken from different systems but at all times traversed by the same current are "homologous" windings. A machine with a Vernier ratio of 2n and a shaft symmetry p comprises 2n groups with in each case p homologous windings.

The homologous windings which are to be traversed by the same current can be supplied in series by one branch of the switch.

Thus, for a machine with a Vernier ratio of 1/4, the diagram would remain the same as that of Figs 1 and 2, but each of the windings therein would be replaced by two homologous windings in series.

In Vernier-type variable reluctance machines, the homologous windings can be very easily coupled. It is thus possible to separately supply each of the p systems of 2n windings. In this concept, each system is supplied by n elementary switching modular network, this being reproduced p times. The switches are associated in series or in parallel on the power supply.

Such an arrangement offers the following advantages: It facilitates the construction of the machine windings, both with regard to the cross-section and insulation of the conductors.

It obviates the need for having semiconductors in series or in parallel.

It permits an easy modular extension of controllable power ratings in an almost unlimited manner, using standard components.

The diagram of Fig I is suitable more particularly for all industrial applications in which it is necessary to obtain high torques at low speed and involving braking phases whose duration is by no means negligible compared with the motive cycle. Such problems are encountered in the iron and steel industry, in hoisting and lifting technologies and in propulsion.

The diagram of Fig 2 has the same characteristics as that of Fig 1, but in this case the braking energy is stored in a bank of accumulators which may or may not discharge to the network.

It is particularly interesting with respect to the problems of propulsion with an airborne power supply or when it is necessary to continue to ensure service in the case of a mains failure (restarting a lift in an emergency for example).

Obviously, the invention is not limited to the embodiments described and represented hereinbefore and various modifications can be made thereto without passing beyond the scope of the invention.

The described and illustrated embodiments of the invention provide a variable frequency static converter for a variable reluctance machine which under optimum power efficiency conditions can be accompanied by the constant control of the speed or torque which permits either the supply of the windings of the machine acting as a motor or the recuperation of the electric power produced in the windings of the machine operating as a generator.

These embodiments relate to a converter characterised in that it essentially comprises, associated with a per se known power supply which is able to operate both as a generator and as a receiver, whilst being controlled as a function of the speed or torque of the machine, at least one pair of identical seriesmounted elementary switching modular networks, one elementary modular network having two branches in parallel to the source by one of their ends and connected by their other ends to a common point with the homologous ends of the other identical series-mounted switching modular network, each of the branches supplying respectively one elementary field coil of the variable reluctance machine and having a thyristor and a diode mounted in series in the conductive direction towards the field coil, the armatures of one capacitor being respectively connected to each of the branches between the thyristors and the diodes, the thyristors of the two elementary modules being controlled by a control electronics controlled by an internal coder and synchronized with the control electronics of the power supply.

WHAT WE CLAIM IS:- 1. A variable frequency static converter for a Vernier-type variable reluctance machine comprising: a power supply having control electronics and operable both as a generator and as a receiver while being controlled as a function

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

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. number of elementary modules arranged in series is only limited by the maximum voltage of the power supply which must at all times remain above the sum of the counterelectromotive forces of the machine. Even if in theory, a Vernier-type variable reluctance machine can comprise two pairs of complementary windings, it has in practice a radial symmetry of random order. Each system of 2n windings of a machine whose Vernier ratio is 2n is repeated a certain number of times at the periphery of the machine, the current circulating in the 2n windings being at all times identical from one system to the next. Two windings taken from different systems but at all times traversed by the same current are "homologous" windings. A machine with a Vernier ratio of 2n and a shaft symmetry p comprises 2n groups with in each case p homologous windings. The homologous windings which are to be traversed by the same current can be supplied in series by one branch of the switch. Thus, for a machine with a Vernier ratio of 1/4, the diagram would remain the same as that of Figs 1 and 2, but each of the windings therein would be replaced by two homologous windings in series. In Vernier-type variable reluctance machines, the homologous windings can be very easily coupled. It is thus possible to separately supply each of the p systems of 2n windings. In this concept, each system is supplied by n elementary switching modular network, this being reproduced p times. The switches are associated in series or in parallel on the power supply. Such an arrangement offers the following advantages: It facilitates the construction of the machine windings, both with regard to the cross-section and insulation of the conductors. It obviates the need for having semiconductors in series or in parallel. It permits an easy modular extension of controllable power ratings in an almost unlimited manner, using standard components. The diagram of Fig I is suitable more particularly for all industrial applications in which it is necessary to obtain high torques at low speed and involving braking phases whose duration is by no means negligible compared with the motive cycle. Such problems are encountered in the iron and steel industry, in hoisting and lifting technologies and in propulsion. The diagram of Fig 2 has the same characteristics as that of Fig 1, but in this case the braking energy is stored in a bank of accumulators which may or may not discharge to the network. It is particularly interesting with respect to the problems of propulsion with an airborne power supply or when it is necessary to continue to ensure service in the case of a mains failure (restarting a lift in an emergency for example). Obviously, the invention is not limited to the embodiments described and represented hereinbefore and various modifications can be made thereto without passing beyond the scope of the invention. The described and illustrated embodiments of the invention provide a variable frequency static converter for a variable reluctance machine which under optimum power efficiency conditions can be accompanied by the constant control of the speed or torque which permits either the supply of the windings of the machine acting as a motor or the recuperation of the electric power produced in the windings of the machine operating as a generator. These embodiments relate to a converter characterised in that it essentially comprises, associated with a per se known power supply which is able to operate both as a generator and as a receiver, whilst being controlled as a function of the speed or torque of the machine, at least one pair of identical seriesmounted elementary switching modular networks, one elementary modular network having two branches in parallel to the source by one of their ends and connected by their other ends to a common point with the homologous ends of the other identical series-mounted switching modular network, each of the branches supplying respectively one elementary field coil of the variable reluctance machine and having a thyristor and a diode mounted in series in the conductive direction towards the field coil, the armatures of one capacitor being respectively connected to each of the branches between the thyristors and the diodes, the thyristors of the two elementary modules being controlled by a control electronics controlled by an internal coder and synchronized with the control electronics of the power supply. WHAT WE CLAIM IS:-

1. A variable frequency static converter for a Vernier-type variable reluctance machine comprising: a power supply having control electronics and operable both as a generator and as a receiver while being controlled as a function

of the desired speed or torque of the machine; and at least one pair of identical series mounted elementary switching networks.

each network having two individual branches connected in parallel to the supply by one of their ends and connected by their other ends to a common point with the corresponding ends of the other identical series mounted switching network or networks, the common point being the only direct connection between the networks. each of the branches being adapted to supply a respective elementary field coil of the variable reluctance machine, and having a thyristor and a diode mounted in series in the conductive direction towards the field coil.

and each network having a capacitor connected between the junctions of the thyristor and the diode of the two branches, and the thyristors of the networks being controlled by a control electronics controlled by an internal coder and synchronised with the control electronics of the power supply.

2. A converter according to claim 1, comprising several pairs of series-mounted elementary switching networks. characterised in that the pairs of elementary networks are associated in parallel on the power supply.

3. A converter according to claim 1, comprising several pairs of series-mounted elementary switching networks, characterised in that the pairs of elementary networks are associated in series on the power supply.

4. A converter according to claim 1, comprising several pairs of series-mounted elementary switching networks, characterised in that the pairs of elementary networks are associated in series/parallel on the power supply.

5. A converter according to claim 1, characterised in that the power supply essentially comprises a rectifier with thyristors.

6. A converter according to claim 1, characterised in that the power supply essentially comprises two choppers and two free wheel circuits associated with a bank of accumulators.

7. A variable frequency static converter substantially as herein described and shown in Figures 1 and 2 of the accompanying drawings.

8. An elementary switching circuit in a variablc frequency static converter as defined in claim I substantially as herein described and shown in Figure 3 of the accompanying drawings.