GB969598A - Improvements in direct-current motors - Google Patents

Abstract

969,598. Electric motors. SIEMENS & HALSKE A.G. June 22, 1962 [June 22, 1961], No. 24078/62. Heading H2A. Motor construction.-A D.C. motor comprises a permanent magnet rotor L and a wound stator Sp which is connected to supply G through a forward biased tunnel diode T which acts in place of the commutator. In a modification a number of stator coils, which may be constructed as multi-turn field coils and connected to produce opposed north and south poles, are used, each coil serially connected to a tunnel diode to form a group and having the groups connected in parallel across the supply. In a further modification a wound rotor may be connected to the supply through a tunnel diode either alone when a permanent magnet stator is used or in series with the stator coils when a wound stator is used. Motor operation.-In a normal D.C. motor the commutator reverses the current in the armature coil after every half revolution (for a 2-pole machine) so that the torque on the rotor is unidirectional. In this machine, however, the current in the coil remains unidirectional but changes from a high value to a low one every half revolution, the rotor torque therefore reverses every half revolution. The current is obtained by operating a tunnel diode on the " reverse slope " portion of its forward current/voltage characteristic. The static load line is derived in the normal way from the value of the static current and supply voltage and intersects the curve at Po, in the lower half of this part of the curve. At a given speed of rotation the internal E.M.F. generated with alternately boost and buck the supply voltage to give the dynamic load lines II and III, intersecting the curves in points P<SP>1</SP> and P<SP>11</SP> respectively, the speed being such that the operating lines lie within the boundaries a, b on the curve. The operating points are adjusted, by altering the position of Po, so that the forward torque taken over a whole revolution equals the sum of the load, friction and braking torque taken over a whole revolution, so that the motor will continue to run. The motor will require manual starting, or a special starting circuit, to ensure that reliable operation in the correct direction is obtained. It is preferable that the circuit resistance is chosen to give a single intersection Po, as shown. Connection of the motor armature coils.-If a number of coils are used these are connected in parallel across the supply, with each coil serially connected to a forward biased tunnel diode. In another modification, a pair of multi-turn field coils are connected together in series opposition, each coil pair and its associated tunnel diode being connected in parallel across the supply. Due to the requirement for low operating voltage with these diodes it may be preferable to operate groups of coil/diode circuits in series but this is impracticable due to possible instability and the power loss incurred in a series resistor. This is overcome by having a capacitor associated with each group of serially connected coil/diode units so that the whole system acts as a capacitive potentialdivider and the voltage developed across each unit is the supply voltage divided by the number of units. A further resistor in parallel with each unit may be used to set the desired operating point on the tunnel diode characteristic. The capacitors further act to prevent interaction between each coil/diode unit.