This invention relates to circuits for driving an electric motor from a DC (direct current) power supply.

Various motor drive circuits are known, for example from US9099947 and US9099888.

Some drive circuits are configured to manage the rate at which power is drawn from the power supply, for example, by returning power to the power supply in regenerative braking or similar arrangements. Often such drive circuits rely on inverters or other relatively complex circuit configurations. A simpler circuit configuration may be desirable for reasons of cost as well as reliability.

It is a general object of the present invention to provide a drive circuit which, at least in some embodiments, can be implemented with a relatively simple circuit configuration to drive an electric motor from a DC power supply while managing the rate at which power is drawn from the supply. in a first aspect the present invention provides a drive circuit for supplying DC power from a DC power supply to a power connection arrangement of an electric motor. The power supply has a positive pole and a negative pole, with the power connection arrangement being configured to supply power from the drive circuit to windings of the motor. The power connection arrangement and windings are configured to provide a fluctuating impedance in the drive circuit in use; which is to say, the fluctuating circuit impedance may be due to the operation of either the power connection arrangement, or the windings, or both the power connection arrangement and the windings.

The drive circuit comprises a first inductor, a second inductor, a transformer, and a blocking element. The transformer comprises first and second windings, each winding having a first end and a second end. The first and second windings are inductively coupled such that, if the first winding were connected across a power source and the second winding were connected across a load, then a rise in current flowing into the first end of the first winding would induce a voltage in the second winding to cause a current to flow out of the first end of the second winding,

The first inductor, the first winding, and the power connection arrangement of the motor are electrically connected in series across the positive and negative poles of the power supply to form a first circuit loop, with the second inductor, the second winding, and the blocking element being electrically connected in series across the positive and negative poles of the power supply to form a second circuit loop. The first end of the first winding is arranged in the first circuit loop between the second end of the first winding and the positive pole of the power supply, with the first end of the second winding being arranged in the second circuit loop between the second end of the second winding and the positive pole of the power supply.

The blocking element is arranged to permit current to flow in the second circuit loop in a direction away from the negative pole of the power supply and towards the positive pole of the power supply, and to prevent current from flowing in the second circuit loop in a direction away from the positive pole of the power supply and towards the negative pole of the power supply.

In a related aspect the invention provides an apparatus comprising the novel drive circuit and an electric motor having a power connection arrangement configured to supply power from the drive circuit to windings of the motor, and to provide a fluctuating impedance in the drive circuit in use. The power connection arrangement may comprise a brushed commutator or an electronic commutator.

In a further aspect the invention provides a method of driving an electric motor, including supplying DC power from the DC power supply via the novel drive circuit to a power connection arrangement, and supplying power from the drive circuit via the power connection arrangement to windings of the motor. The power connection arrangement is configured to provide a fluctuating impedance in the first circuit loop of the drive circuit.

Further, more particular objects and advantages will become apparent from the illustrative embodiments of the invention which will now be described, purely by way of example and without limitation to the scope of the claims, and with reference to the accompanying drawings, in which;

Fig. 1 shows a first drive circuit driving a permanent magnet DC motor with a brushed commutator, in accordance with a first embodiment;

Figs. 2 and 3 show the flow of current in the first drive circuit, respectively at first and second time instants, wherein the motor windings and brushed commutator forming the power connection arrangement present a relatively lower impedance at the first time instant (Fig. 2} and a relatively higher impedance at the second time instant (Fig. 3);

Figs. 2A and 3A are enlarged views of the brushed commutator, respectively at the first time instant (Figs. 2, 2A) and the second time instant (Figs. 3, 3A);

Fig. 4 shows a variant of the first drive circuit; and

Fig, 5 shows the current flow in a nominal circuit arrangement illustrating the polarity of the first and second transformer windings.

Reference numerals and characters appearing in more than one of the drawings indicate the same or corresponding parts in each of them.

Referring to Fig. 1, a first drive circuit 1 is configured to supply DC (Direct Current) power from a DC power supply 20 to a power connection arrangement 31 of an electric motor (M) 30. The motor 30 drives a load (L) 50 via the motor shaft 51. The power supply 20 has a positive {+) pole 21 and a negative (-) pole 22. in this specification, references to polarity and current flow are in accordance with

conventional current notation.

The DC power supply 20 may comprise or consist of a rechargeable battery (comprising for example multiple cells connected together to function as a single battery), as illustrated in the variant example of Fig. 4, or may be any other arrangement suitable for supplying DC power and, preferably, also capable of accepting energy which is returned to the power supply via the first and second inductors and the transformer, as further discussed below. For example, the DC power supply could be a rectified DC output from an AC power supply.

Optionally, a switch 10 may be provided to disconnect the power supply 20 from the motor 30; the following description assumes that the switch 10 is closed.

The power connection arrangement 31 is configured to supply power from the drive circuit 1 to windings 34 of the motor 30, and the power connection arrangement 31 and windings 34 are configured to provide a fluctuating impedance in the first circuit loop 7 of the drive circuit, which in turn governs the current flowing in the first circuit loop 7 so that pulsed DC flows through the drive circuit 1 in use.

For example, the motor may be a permanent magnet motor with a wound stator or a wound rotor, or may have both a wound stator and a wound rotor. The power connection arrangement may comprise an electronic commutator or a brushed commutator, as exemplified by the illustrated embodiment.

In a motor with multiple (e.g. two or more) windings, different ones of the windings may be alternately disconnected and reconnected across the supply as the rotor rotates. Typically also, in a motor with one or multiple windings, the polarity of the supply across the or each winding may be reversed as the motor rotates. The cyclical connection and disconnection of the inductive motor windings causes fluctuating impedance (principally, inductive reactance) across the motor and power connection arrangement in use.

Typically in a brushed DC motor the brush or brushes at each of the positive and negative sides of the supply will span more than one segment of the commutator as the motor rotates. For example, the brush or brushes may span two or three segments of the commutator as the motor rotates. Thus, more than one winding of the motor may be connected through the brushes of the commutator in parallel across the supply at the same instant, and the number of windings connected across the supply may vary with the rotational position of the rotor. The impedance (principally, the inductive reactance) of the motor windings across the supply thus fluctuates as the motor windings are periodically connected and disconnected with the action of the commutator.

The motor windings may also be interconnected between the commutator segments so that the brushes connect the windings across the supply, alternately in a series configuration and in a single or parallel configuration, again presenting a fluctuating impedance (principally, inductive reactance) in the drive circuit 1 across the alternately connected motor windings as the rotor rotates.

In the illustrated embodiment, the motor 30 Is a permanent magnet DC motor with a stator comprising a pair of permanent magnets 32, and a rotor 33 with multiple rotor windings 34. For clarity, in Figs. 2, 2A, 3 and 3A only a small number of the multiple rotor windings and commutator segments are shown. The power connection arrangement 31 comprises a rotating commutator 35, with each of the rotor windings 34 being connected between an opposite pair of the commutator segments 36. The power connection arrangement 31 is connected to the first circuit loop at the positive and negative terminals of the commutator, comprising a pair of commutator brushes 37, each of which makes sliding contact simultaneously with either two or three adjacent segments 36 of the commutator depending on the momentary angular position of the rotor 33.

Alternatively, the motor may be a brushless or electronically commutated DC motor - which is to say, a motor powered from a DC supply and equipped with an electronic commutator, i.e. an electronic circuit which is arranged in use to supply the windings of the motor with a varying current, e.g . by periodically connecting and disconnecting the windings of the motor with constant or reversing polarity across the supply.

Electronic commutators are well known in the art and may be arranged to present a fluctuating impedance across the supply, with simiiar effect to a brushed commutator. For example, the electronic commutator may periodically connect and disconnect different numbers of windings across the supply, to direct the current to flow alternately through a single winding, and then through two windings in parallel; or, for example, to flow through two windings in parallel, and then through three windings in parallel; or to connect different ones of the windings alternately in different

series/parallel configurations; or in any other desired configuration to provide a fluctuating impedance across the motor and power connection arrangement. The fluctuating impedance presented by the electronic commutator may represent the inductance of the windings or the internal inductance, capacitance or resistance of any other component of the electronic commutator.

Referring again to Fig. 1, the drive circuit 1 comprises a first inductor 2, a second inductor 3, a transformer 6, and a blocking element 9.

The transformer 6 comprises a first winding 4 having a first end 4' and a second end 4", and a second winding 5 having a first end 5' and a second end 5",

Fig. 5 shows a nominal circuit configuration in which the transformer 6 is connected with its first winding 4 across a power source, represented by AC supply 40, and its second winding 5 across a load, represented by a resistor 41, with the arrows representing momentary current flowing at the same instant in the two resulting circuits. The nominal circuit illustrates the relative polarity of the first and second windings 4, 5, which are inductively coupled such that, if the first winding 4 were connected across the power source 40 and the second winding 5 were connected across the load 41, then a rise in current flowing into the first end 4' of the first winding 4 would induce a voltage in the second winding 5 to cause a current to flow out of the first end 5' of the second winding 5. The polarity relationship between the windings is also indicated by the conventional dot notation, with the dots indicating the first ends 4', 5' of the two windings, it will be understood of course that the nominal circuit configuration of Fig. 5 purely serves to illustrate how the transformer 6 is arranged, and does not form part of the novel drive circuit 1.

Referring again to Fig. 1, the first inductor 2, the first winding 4, and the power connection arrangement 31 of the motor 30 are electrically connected in series across the positive and negative poles of the power supply 20 to form a first circuit loop 7.

The second inductor 3, the second winding 5, and the blocking element 9 are electrically connected in series across the positive and negative poles of the power supply 20 to form a second circuit loop 8.

The first and second circuit loops 7, 8 are connected in parallel across the positive and negative poles 21, 22 of the power supply 20. Thus, it will be understood that the first inductor 2, the first winding 4, and the power connection arrangement 31 of the motor 30 are not included in the second circuit loop 8, while the second inductor 3, the second winding 5, and the blocking element 9 are not included in the first circuit loop 7.

The first end 4' of the first winding 4 is arranged in the first circuit loop 7 between the second end 4" of the first winding 4 and the positive pole 21 of the power supply 20.

The first end 5' of the second winding 5 is arranged in the second circuit loop 8 between the second end 5" of the second winding 5 and the positive pole 21 of the power supply

20.

Thus, if each of the first and second circuit loops 7, 8 is considered as having a positive end at the positive pole 21 of the power supply and a negative end at the negative pole 22 of the power supply, then it will be appreciated that the first end 4', S' of each of the first and second windings 4, 5 will be connected to face towards the positive end of the respective circuit loop, while the second end 4", 5" of each of the first and second windings 4, 5 will be connected to face towards the negative end of the respective circuit loop, as shown in Figs, 1 - 4.

The blocking element 9 is arranged to permit current to flow in the second circuit loop 8 in a direction away from the negative pole 22 of the power supply 20 and towards the positive pole 21 of the power supply, and to prevent current from flowing in the second circuit loop 8 in a direction away from the positive pole 21 of the power supply and towards the negative pole 22 of the power supply.

The blocking component 9 may consist of a single diode as shown, or may consist of a group of diodes, or may comprise any other suitable circuit configuration, optionally including one or more diodes.

In this and other embodiments, the first and second inductors are not inductively coupled with each other or with the transformer, Preferably the first and second inductors are of substantially equal inductance.

The inductance of each of the inductors may be equal to that of each of the transformer windings. Alternatively the inductance of each of the inductors may be greater or lesser than that of each of the transformer windings.

Preferably the transformer has a 1:1 turns ratio, which is to say, the first and second windings have a siibstantially equal number of turns.

Preferably the first and second inductors are formed by coils with high permeability (e.g. iron) cores.

Preferably also the transformer has a high permeability (e.g. iron) core.

In various embodiments of the invention, the respective components of each of the first and second circuit loops may advantageously be arranged in the series configuration as illustrated, or may be arranged in an alternative series configuration. in accordance with a first, preferred configuration as exemplified by the illustrated embodiments, the first inductor 2 and the first winding 4 are arranged in the first circuit loop 7 between the power connection arrangement 31 of the motor 30 and one respective pole of the power supply 20.

In said first, preferred configuration, the second winding 5 and the second inductor 3 are arranged in the second circuit loop 8 between said one respective pole of the power supply 20 and the blocking element 9. in said first, preferred configuration, the second winding 5 may be arranged between the second inductor 3 and said one respective pole of the power supply 20. In this case, the second winding 5 and the second inductor 3 may be arranged in the second circuit loop 8 between said one respective pole of the power supply 20 and the blocking element 9, again as illustrated. In said first, preferred configuration, the first inductor 2 may be arranged in a yet further preferred configuration between the first winding 4 and said one respective pole of the power supply 2Q _; as illustrated.

In said yet further preferred configuration, the second winding 5 and the second inductor 3 may be arranged in the second circuit loop 8 between said one respective pole of the power supply 20 and the blocking element 9, as illustrated.

In said yet further preferred configuration, the second winding 5 may be arranged between the second inductor 3 and said one respective pole of the power supply 20, as illustrated. In this case, the second winding 5 and the second inductor 3 may be arranged in the second circuit loop 8 between said one respective pole of the power supply 20 and the blocking element 9, again as illustrated.

In each of the references above to one respective pole of the power supply 20, said one respective pole of the power supply 20 may be the positive pole 21 of the power supply, as in the illustrated arrangement. Alternatively, said one respective pole of the power supply 20 may be the negative pole of the power supply.

Fig. 4 illustrates an alternative embodiment in which each of the first and second inductors 2, 3 comprises a respective pair of inductors arranged in parallel, with the power supply 20 being configured as a rechargeable battery. The Fig, 4 embodiment is found to operate generally as described with reference to the embodiment of Figs. 1, 2 and 3.

Referring now to Figs. 2, 2A, 3 and 3A, it can be seen that as the rotor 33 rotates from the angular position of Figs. 2 and 2A to that of Figs. 3 and 3A, one of the three adjacent commutator segments 36 bridged by the brushes in the initial position is disconnected, leaving the remaining two commutator segments 36 in the circuit; thus, the circuit impedance changes from the relatively lower value of Figs. 2 and 2A, in which three rotor windings are connected in parallel across the supply, to the relatively higher value of Figs, 3 and 3A, in which only two rotor windings are connected in parallel across the supply.

Tests suggest that the energy returned to the power supply 20 under conditions of fluctuating impedance in the novel drive circuit 1 may result in more energy efficient operation of the motor.

The arrows in Fig, 2 illustrate how current flows from the power supply 20 via the first circuit loop 7 through the rotor windings 34 to drive the rotor in rotation, with a rise in current in the first circuit loop storing energy in the first inductor 2 and the transformer 6.

The arrows in Fig. 3 illustrate the current induced in the second winding 5 and second circuit loop 8 by the change in current in the first winding 4 of the transformer responsive to the increased impedance of the motor windings 34 and power connection arrangement 31. The rise in current flowing through the blocking device 9 in the second circuit loop 8 stores energy in the second inductor 3.

A portion of the energy stored in the drive circuit 1 is thus returned to the power supply 20.

Preferably the power connection arrangement 31 and the windings 34 of the motor are configured to provide unbroken electrical continuity in the first circuit loop 7 during operation of the motor - which is to say, the current flows continuously in the first circuit loop 7 through the motor windings 34, This can be achieved for example by configuring the brush or brushes 37 forming each pole of the commutator of a DC motor to extend across more than one segment 36 of the commutator, as exemplified by the illustrated embodiment and best seen in Figs. 2A and 3A, so that the input and output terminals of the power connection arrangement 31 are always connected through one or more motor windings 34. A similar arrangement can be obtained in brushless or electronically commutated arrangements by suitably configuring the circuitry of the power connection arrangement.

While the invention is not bound by theory, it is believed that an arrangement of unbroken continuity may facilitate partial recovery of the energy stored in the electromagnetic field of each motor winding 34 by linkage of the flux with the remaining, connected windings 34 as the motor transitions from a lower impedance state (Figs. 2, 2A) to a higher impedance state (Figs, 3, 3A). Further, it is believed that the resulting current induced in the first circuit loop 7 (corresponding to the arrows of Fig. 2) may augment the current flowing in the second loop 8 (as shown by the arrows in Fig. 3). The recovered energy is stored in and released from the first and second inductors 2, 3 at the frequency of the fluctuating impedance of the motor 30 and power connection arrangement 31, providing a balanced or resonant circuit which manages the rate at which power is drawn from the power supply by returning to the power supply a portion of the recovered energy as a pulsed DC current at the rotational frequency of the motor 30.

Thus, the novel drive circuit may be used to actively manage, control or regulate the power supply. For example, if the power supply is a battery, then the novel drive circuit can be used to manage the charge state or rate of discharge of the battery.

In operation it is further observed that when driving the same load, the motor may rotate more slowly than when powered from the same power supply 20 without the novel drive circuit 1. Thus, for a given load, by appropriately selecting or adjusting the inductance of the inductors 2, 3 and transformer windings 4, 5 relative to the inductance of the motor windings 34, the inductive reactance of the drive circuit 1 may be selected to govern the rotational frequency of the motor 30 or to adjust the rotational frequency of the motor 30. The novel drive circuit 1 may thus provide a convenient means for regulating or controlling the speed of the motor 30 for any given load. If for example the load 50 is an alternator, then the novel drive circuit 1 can be used to regulate or control the frequency of the power supplied from the alternator.

In summary, a drive circuit 1 comprises first and second circuit loops 7, 8 connected in parallel across a DC power supply 20 to deliver pulsed DC to the power connection arrangement 31 of an electric motor 30 which is arranged to provide a fluctuating impedance in the first circuit loop 7. The first circuit loop 7 includes a first inductor 2 arranged in series with the first winding 4 of a transformer 6, while the second circuit loop 8 includes a second inductor 3 arranged in series with the second winding 5 of the transformer 6. The first and second windings 4, 5 of the transformer 6 are inductively coupled such that, if the first winding 4 were connected across a power source 40 and the second winding 5 were connected across a load 41, then a rise in current flowing into a first end 4 ^; of the first winding 4 would induce a voltage in the second winding 5 to cause a current to flow out of a first end 5' of the second winding 5. The first ends 4', 5' of both windings are arranged between the respective winding and the positive pole

21 of the power supply. A blocking element 9 is arranged to prevent current from flowing through the second circuit loop 8 from the positive pole 21 to the negative pole

22 of the power supply 20.

In the above and other embodiments, the load (L) 50 could be an electric generator or any other useful machine. In yet further embodiments the motor could be a linear rather than rotary motor.

The illustrated embodiment presents a simple implementation of the novel drive circuit. Thus, the novel drive circuit may consist essentially of the elements as described above which are electrically connected together without other circuit components. The elements of each circuit loop 7, 8 may be connected in the series configuration as illustrated or in a different series configuration. Alternatively or additionally, other circuit components may be included to incorporate the novel drive circuit into a more complex circuit arrangement as required for the intended application.

Many further adaptations are possible within the scope of the claims.

In the claims, reference numerals and characters are provided in parentheses purely for ease of reference and should not be construed as limiting features.