A multi- step changeover type series (or compound) field winding for shunt motor speed control circuit having transient storage effect

Abstract: The present multi-step changeover type series (or compound) field winding for shunt motor speed control circuit having transient storage effect relates to a series field winding having plural intermediate taps, series with a choke diode between with the power supply and parallel connnecting an energy storage diode, capacitor, etc., and a shunt switch device for carrier control is parallel connected between the power supply and each tap, when the controlled switch device is broken circuit, motor armature current will pass by the series field winding in full; when the switch device is conducted the power supply current will be shunted by the controlled switch device leading to the armature through the other series windings or directly, leading to the armature while the field is excited continuously with the storage element in order to advance armature voltage under much stable flux intensity depending on the ratio of conducting time to broken circuit cycle by the control of each shunt switch device and further to control the speed of motor. Some part of series winding may be parallel connected to the shunt switch device and the remainings maintain series with armature in order to meet a flexible requirement, or a plural series field winding taps matching a plural shunt switch device in order to select turn ratio of relatively controlled winding; in addition shunt ratio can be controlled with the feedback signal of current or running speed. The shunt switch device required by the present design may comprise matured thyristor or switch transistor.

Description: The present invention relates to a shunt-type motor speed control circuit. Known motor speed control circuits are described in DE-A-2605561 and CH-A-445629. A shunt-type motor speed control circuit according to the preamble of independent claims 1 is disclosed in DE-A-2 605 561. The present invention provides a shunt-type motor speed control circuit comprising a direct current motor armature; a series field winding having first and second ends, the second end being connected to the armature; a tap on the series field windinq, a switch beinq connected between the tap and the power supply terminal ; and control means for controlling the switch selectively to connect the tap to the power supply terminal, and thereby change the effective turn ratio of the series field winding; characterised by a diode connected in series between the power supply terminal and the first end of the series field winding and transient energy storage means connected in parallel with the series field winding for enabling the series field winding to maintain a stable excitation field during switching of the switch. Advantageously, the series field winding has a plurality of intermediate taps, the series field winding being connected in series with a choke diode between a power supply and the motor armature, and in parallel with an energy storage element in the form of a diode or a capacitor. A shunt switch device is connected in parallel between the power supply and each tap, such that, when the switch device is open, the motor armature current passes through the series field winding; and, when the switch device is closed, the power supply current is shunted by the switch device to the armature through the associated tap, while the field is excited continuously by the energy storage element in order to increase the armature voltage with a much more stable flux intensity depending on the ratio of on-to-off times according to which each shunt switch device is controlled, and thereby provide improved control of the speed of the motor. A part of the series winding may be connected in parallel with the shunt switch device, with the remaining part maintained in series with the armature in order to provide flexibility, permitting selection of the turn ratio of the relatively controlled winding. In addition, the shunt ratio of the motor can be controlled by feeding back a signal representative of the armature current or running speed. The shunt switch device required by the present design may be a thyristor or a switch transistor. The invention will now be described in greater detail, by way of example, with reference to the drawing, in which: Figure 1 is a circuit diagram showing a preferred embodiment of the invention. The series (or compound) motor has been widely applied to various kinds of household appliances, electrical loaders and other machines, because it possesses such desirable characteristics as easy speed control and an excellent current/torque ratio. However, for various kinds of speed control circuits for series motors, the series field shunting method is advantageous for increasing the armature voltage without changing flux intensity as a greater motor output is achieved. However, when the shunt element is a linear impedance, such as a resistance or a linear power element, a power loss and decrease of field excitation occurs, which can be significant when the motor has a large horsepower. The present multi-step series (or compound) field shunt control circuit, in contrast, provides a transient storage effect by utilising a series field winding having plural intermediate taps, and connected in series with a choke diode between the power supply and the motor armature, a parallel-connected energy storage device such as a diode or a capacitor, and a shunt switch device connected in parallel between the power supply and each tap; such that, when the controlled switch device is open to break the circuit, the motor armature current will pass through the series field winding; and, when the switch device is closed or conductive, the power supply current will be shunted by the controlled switch device to the armature through the other series windings or directly to the armature as the field is being excited continuously by the storage element in order to increase the armature voltage while maintaining a stable flux intensity depending on the on/off (or conducting/nonconducting) time ratio according to which each shunt switch device is controlled, thereby providing improved control of the speed of the motor. A part of the series winding may be connected in parallel with the shunt switch device, with the remaining part maintained in series with the armature in order to provide flexibility. In addition, the shunt ratio can be controlled by a feedback signal representative of the current or running speed. The shunt switch device required by the present design may include a thyristor or a transistor switch. Referring to Figure 1, the preferred circuit includes a series field winding S101 for a series (or compound) motor. The series field winding S101 has at least one intermediate tap, and is connected in series between an armature A101 and a power supply, and in parallel with a flywheel diode CR102, and further in parallel with a storage capacitance C101. Optionally, a flywheel diode CR103 may be connected in parallel with the armature A101. A choke diode CR101 is positively connected in series with the series field winding S101, the positive terminal of the power supply being connected to the series field winding via the choke diode CR101, with the armature A101 being connected in series between the series field winding S101 and the negative terminal of the power supply. At least one solid state switch device Q101, Q102... Qn, which may be in the form of a solid state switch transistor or thyristor, is connected such that its positive end, which positively conducts current, is directly parallel-connected to the positive terminal of the power supply, and its output end is connected to the connection between the series field winding S101 and the armature A101 or to the intermediate tap of the series winding. In the case of plural series field winding taps, plural shunt switch devices may be provided in order to select the turn ratio of the series winding. Optionally, the solid state switch device Q101 may be jointly connected in series with an auxiliary excitation winding F101. The state of the switches Q101, QW102... Qn is controlled by a central control unit CCU101 to provide cyclic driving signals or pulses, for example in response to setting and feedback values, so as to control any selected one of the solid state switch devices, ie to select any of the switch devices Q101 Q102...Qn for relatively cyclic ON/OFF driving, or alternative ON/OFF driving by two more switch devices in order to reduce series field current pulsation. The feedback element can, for example, be a speed detector SD101 made up of analogue or digital sensing elements, and coupled to the armature A101 for sending respective analogue or digital signals representative of armature speed back to the control unit CCU101. Alternatively, the speed detector SD101 could be replaced by an armature EMF detector EMFD101 for providing a speed reference signal, or by a load current detector ID101, which can also transmit analogue or digital signals to the control unit CCU101. Also included is an operation interface OP101 for manual or communication signal inputs to the speed control operation of the control unit CCU101 and the power switch device Q101. The preferred circuit thus may be manually controlled, or controlled with feedback signal(s) from a load current detector, a speed detector, or an EMF detector, or by a combination of two or more of the above-mentioned means. In addition to series motors, the preferred circuit is applicable to compound motors having series windings. In summary, the preferred shunt motor speed control circuit uses a transient storage effect in order to reduce thermal loss relative to conventional linear power elements or resistances by means of a cyclic changeover of a series field winding having intermediate taps and a shunt switch device; and, by virtue of a storage element and choke diode, resulting in improved motor performance and suitability.

Claims: A shunt-type motor speed control circuit comprising a direct current motor armature (A101); a series field winding (S101) having first and second ends, the second end being connected to the armature; a tap on the series field winding, a switch (Q101) being connected between the tap and the power supply terminal; and control means (CCU101) for controlling the switch selectively to connect the tap to the power supply terminal, and thereby change the effective turn ratio of the series field winding; characterised by a diode (CR101) connected in series between the power supply terminal and the first end of the series field winding and transient energy storage means (C101) connected in parallel with the series field winding for enabling the series field winding to maintain a stable excitation field during switching of the switch. A circuit as claimed in claim 1, wherein the transient energy storage means is a capacitor (C101) A circuit as claimed in claim 1 or claim 2, wherein the switch (Q101) is controlled in response to a feedback signal representative of the motor speed. A circuit as claimed in claim 3, wherein the feedback signal is generated by a speed detector. A circuit as claimed in claim 3, wherein the feedback signal is generated by an EMF detector (EMFD101). A circuit as claimed in claim 1 or claim 2, wherein the switch is controlled in response to feedback from a load current detector (ID101). A circuit as claimed in any one of claims 1 to 6, further comprising a flywheel diode (CR102) connected in parallel with the series field winding (S101) and the transient energy storage means. A circuit as claimed in any one of claims 1 to 7, wherein the series field winding (S101) has a plurality of taps, a corresponding plurality of switches (Q101, Q102...Qn) being connected between the taps and the said power supply terminal, and the control means (CCU101) includes means for cycling between the switches. A circuit as claimed in any one of claims 1 to 8, wherein the motor is a compound motor, and further comprises a shunt winding connected in parallel with said circuit. A circuit as claimed in any one of claims 1 to 9, further comprising a field winding (F101) connected between the power supply terminal and the or each switch.

Inventors: YANG TAI-HER, YANG, TAI-HER
Applicants: YANG TAI HER, YANG, TAI-HER
Application year: 1993
Main classification: H02P5
IPC codes: H02P7