Motor control circuit

Abstract: The present invention is the improvement of the shunt type series excitation field driving circuit of the series excitation (or compound) motor, it is constituted by two sets of series excitation field windings, the one end of respectful series excitation winding is connected in parallel in same polarity to the armature jointly, there is one set of the series excitation field windings at least to be isolated in one way by means of a diode to receive the excitation of different power sources respectfully. The above series excitation field windings are used to replace conventional single set series excitation field winding, by means of the innovative design of the above specific magnetic field to facilitate the magnetic field of the series excitation motor to control the excitation current offset of one set of the excitation windings to improve the shortcoming of the dropping of efficiency in light load or overload of conventional series excitation motor.

Description: The invention relates to an improvement to a driving circuit for a series (or compound) motor. EP-A 0 129 319 describes a multi-range speed control system for a compound motor. The present invention provides a motor control circuit comprising a main power supply, an armature, a main series winding connected in series with the armature and the main power supply, and an auxiliary series winding connected in parallel between the mains series winding and an auxiliary power supply, a first end of the auxiliary series winding being connected to a first end of the main series winding, to the armature, and to one terminal of the auxiliary power supply, and a second end of the auxiliary series winding being connected by a first diode to a second end of the main series winding and by a second diode to a second terminal of the auxiliary power supply, the first and second diodes being biased such that the second end of the auxiliary series winding is connected to receive current from both the main and auxiliary power supplies and thereby increase the armature current for improved control at light loads and overload conditions. The invention will now be described in greater detail, by way of example, with reference to the drawings, in which:- Figure 1 is a schematic drawing of a driving circuit for a series (or compound) motor according to a preferred embodiment of the invention; and Figure 2 is a schematic drawing of a variation of the circuit shown in Figure 1, in which a feedback function is provided. In a conventional series excitation motor, efficiency decreases at light loads because of lower excitation current, and speed regulation becomes more difficult as the torque to revolving speed ratio becomes lower. In addition, efficiency is decreased during transient overload conditions as the magnetic field becomes saturated, i.e. as the excitation current passing through the series excitation field winding exceeds what is required for saturation and excitation, the excessive voltage drop resulting from excessive excitation current worsening the output power and efficiency of the motor. To solve this problem, as shown in Figure 1, the improved driving circuit includes at least two series excitation field windings, one end of each of the series excitation windings being jointly connected with the same polarity, to the armature, and at least one of the series excitation field windings is isolated by means of diodes so as to receive power from different power sources. The two series excitation field windings replace the conventional single series excitation field winding. In addition, a separately-excited field winding F101 can be added to provide a compound motor, which also includes the above pair of series excitation field windings. As shown in Figure 1, a main series excitation field winding S101 is in series with an armature A101, and is driven by a main power source CPS101. A blocking diode CR101 is connected in series between the power source end of the main winding S101 and an auxiliary series excitation field winding S102, with the polarity arranged so as to prevent an auxiliary excitation power source CPS102 from exciting the main winding S101, while allowing the auxiliary winding S102 to be excited by both the main power source CPS101 and the auxiliary power source CPS102. A diode CR102 is positioned in series between the auxiliary power supply CPS102 and the auxiliary winding S102. The main power source CPS101 can be either a storage battery, a solar energy converter, or a DC generator, or may be obtained from the rectification of an AC power source or other DC power source. The auxiliary power source CPS102 may also be a single voltage or variable output voltage DC power supply, such as a storage battery, a solar energy converter or a DC generator, or may be obtained from the rectification of an AC power source or other DC power source. The improved circuit of the embodiment of Figure 1 operates as follows:- (1) When the load is light, or to drive the series motor with a smaller main power source voltage (for example to provide a better control of speed), the excitation provided by the series excitation field winding S101 is supplemented by the excitation provided by the auxiliary excitation power source through the winding S102 to improve the efficiency of the motor and the regulation of speed. (2) The current of the motor rises with the load until the voltage drop of the power supply CPS101 across the main series excitation field winding S101 is larger than the voltage drop of the auxiliary excitation power supply CPS102 across the auxiliary series excitation field winding S102 (taking into account the value of the bias of the blocking diode CR101), at which time the current of the auxiliary excitation power supply decreases to zero, because the current of the armature A101 is the sum total of all series excitation currents. As shown in figure 2, the above circuit may also include components for detecting the state of operation of the motor, and the voltage and current of the power supply, and which are connected jointly to a central control circuit and to a control interface to form a more precise circuit system providing feedback functions. As shown in Figure 2, the improved driving circuit includes at least two series excitation field windings, one end of each of the series excitation windings being jointly connected, with the same polarity, to the armature, and at least one of the series excitation field windings is isolated by means of diodes so as to receive power from different power sources. The two series excitation field windings replace the conventional single series excitation field winding. In addition, a separately excited field winding F201 can be included to provide a compound motor, which also includes the above pair of series excitation field windings. As shown in Figure 2, a main series excitation field winding S201 is in series with an armature A201 and is driven by a main power source CPS201. A blocking diode CR201 is connected in series between the power source end of the main winding S201 and an auxiliary series excitation field winding S202 with the polarity arranged so as to prevent an auxiliary excitation power supply CPS202 from exciting the main series windings S201, while allowing the auxiliary winding S202 to be excited by the main power source CPS201 and the auxiliary power source CPS202. A diode CR202 is positioned in series between the auxiliary power supply CPS202 and the auxiliary winding S102. The main power source CPS201 can be either a single voltage or variable output voltage DC power source, such as a storage battery, a solar energy converter, or a DC generator, or may be obtained from the rectification of an AC power source or other DC power source. The auxiliary power source CPS202 may also be a single voltage or variable output voltage DC power supply, such as a storage battery, a solar energy converter, or a DC generator, or may be obtained from the rectification of an AC power source or other DC power source. The feedback detection components of this embodiment include one or more of the following components; a main power supply voltage detection component VD201, an armature current detection component ID201, an armature counter electromotive force (EMF) detection component EMFD201, a motor rotational speed detection component SD201, an auxiliary excitation voltage detection component VD202, an auxiliary excitation current detection component ID202, and a series excitation field voltage drop detection component VS201. Those skilled in the art will appreciate that all of these components, or at least one of them, may be selected according to the specific requirements of the motor with which the circuit is to be used. The above detection components may be of digital type or analogue type, with an appropriate command input device OP201, which allows the circuit to be controlled manually or by an electrical signal, and which is connected to a central control unit CCU201. The control unit CCU201, which may of the analogue type or digital type, includes electromechanical and/or solid state components for allowing control of the output voltages and currents of the main power source and the auxiliary excitation power source by referring to the setting of the input control unit and the signals from the feedback detection component in known fashion. In the embodiments if Figures 1 and 2, if a storage power battery or the like is used as the auxiliary power source, a current limiting adjustment element Z101, Z202 may be connected in parallel to the two ends of the blocking diode CR102 or to the current detector ID202 of the auxiliary power source and the auxiliary series excitation field winding. As the main excitation current increases, and the voltage drop across the two ends of the main series excitation winding exceeds the voltage provided by the auxiliary power source, a counter current will be formed which charges the auxiliary storage elements. The current limiting adjustment element allows adjustment of the counter current. The current limiting adjustment element Z201 of Figure 2 may be constituted by a resistance element, by an electromechanical or solid state element to be controlled by the central control unit CCU201 to adjust the charging current passing through the storage power element. While the basic operation of this circuit is essentially the same as that of Figure 1, the provision of the circuit limiting element does have the effect, on transient overload, that the current of the armature is the sum total of the current of various series excitation field windings, and of further increasing the charging current passing the storage power component. To sum up the above, the present invention is an innovative design, which raises the efficiency of a series excitation motor of the type used widely in the industrial world, and provides improved speed regulation.

Claims: A motor control circuit comprising a main power supply (CPS101, CPS201), an armature (A101, A201), a main series winding (S101, S201) connected in series with the armature and the main power supply, and an auxiliary series winding (S102, S202) connected in parallel between the main series winding and an auxiliary power supply (CPS102, CPS202), a first end of the auxiliary series winding being connected to a first end of the main series winding, to the armature, and to one terminal of the auxiliary power supply, and a second end of the auxiliary series winding being connected by a first diode (CR101, CR201) to a second end of the main series winding, and by a second diode (CR102, CR202) to a second terminal of the auxiliary power supply, the first and second diodes being biased such that the second end of the auxiliary series winding is connected to receive current from both the main and auxiliary power supplies and thereby increase the armature current for improved control at light loads and overload conditions. A motor control circuit as claimed in claim 1, further comprising a shunt field winding (F101, F201) to form a compound motor control circuit. A motor control circuit as claimed in claim 1 or claim 2, further comprising a central control unit (CCU201) arranged to vary an output of at least one of the main and auxiliary power supplies (CPS201, CPS202) in response to feedback from at least one detection component selected from the group consisting of a main power supply voltage detection component (VD201), an armature current detection component (ID201), an armature counter electromotive force detection component (EMFD201), a motor rotational speed detection component (SD201), an auxiliary excitation voltage detection component (VD202), an auxiliary excitation current detection component (ID202) and a series excitation field voltage drop value detection component (VS201). A motor control circuit as claimed in any one of claims 1 to 3, further comprising a current limiting adjustment element (Z101, Z201) connected between the auxiliary series winding (S102, S202) and the auxiliary power supply (CPS102, CPS202) to permit a charging current to flow between the main series winding (S101, S201) and the auxiliary power supply when the voltage drop across the main series winding exceeds the voltage provided by the auxiliary power supply.

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