Stober motor, Germany Stober model, Stober price

Stober motors are a type of electric motor powered by simultaneously connecting to 380V three-phase AC current (with a phase difference of 120 degrees). Because the rotor of a three-phase asynchronous motor rotates in the same direction but at a different speed than the stator's rotating magnetic field, there is slip, hence the name three-phase asynchronous motor. The rotor speed of a three-phase asynchronous motor is lower than the speed of the rotating magnetic field. The rotor windings generate electromotive force and current due to relative motion with the magnetic field, and interact with the magnetic field to produce electromagnetic torque, achieving energy conversion.

Stober motor speed control

Motor speed control: Principle of wound-rotor induction motor speed control implemented using a current-source PWM converter: The rotor electrical energy of the induction motor is converted from AC to DC by an uncontrollable rectifier composed of a diode bridge rectifier. Then, the current-source PWM converter converts the DC electrical energy into AC electrical energy with grid frequency, adjustable current amplitude, and adjustable phase. The converted energy is fed back to the grid for reuse through an autotransformer. This speed control scheme has the following characteristics while achieving speed regulation: (1) The transformer input and output can have a fixed transformation ratio as needed, and electrical isolation between input and output is not required. Therefore, this scheme uses an autotransformer, significantly reducing transformer costs. (2) The AC side output current of the current-source PWM converter is a pulse current containing several harmonics. To ensure normal operation of the power system and ensure that the energy fed back to the grid meets international harmonic standards, it is necessary to take appropriate filtering measures at the connection point between the PWM converter and the grid. (3) The AC side output current of the current-source PWM converter becomes sinusoidal after filtering, and the phase angle is controllable. Therefore, adopting an appropriate control scheme can solve the harmonic and power factor problems of the speed control system while achieving motor speed control. It has obvious advantages compared with thyristor cascade speed control. ① AC voltage regulation speed control; ② Rotor series resistance AC speed control; ③ AC cascade speed control. A wound-rotor induction motor is an induction motor whose primary winding on the stator is connected to the power supply, and whose rotor has a polyphase winding connected to slip rings. The three-phase symmetrical windings of the rotor can be connected in Y configuration or delta configuration. The characteristic of this rotor is that external resistors can be connected to the rotor windings to improve the starting performance of the motor or to adjust the speed.

Stober motor armature reaction

The effect of the motor armature current interfering with the magnetic flux generated by the magnetic field. The state varies depending on the phase difference between the armature voltage and the armature current. When the power factor is 1, the magnetic flux on the front side along the direction of pole rotation is enhanced, while the magnetic flux on the rear side is weakened. In the case of a motor, the magnetic flux advances beyond the rotor, and the magnetic flux pulls the rotor in the acceleration direction. Conversely, in the case of a generator, the magnetic flux lags behind the rotor, and the magnetic flux pulls the rotor in the deceleration direction. This corresponds to the torque generated by Maxwell stress based on the principle that "contractile force acts on magnetic lines of force." When the power factor is lagging, the magnetic flux acts in the direction of increasing magnetic flux. When the power factor is leading, its direction of action is to weaken the magnetic flux. In synchronous generators and synchronous motors, the leading/lagging of armature current relative to magnetizing/demagnetizing effects is opposite. This relationship can be unified by understanding whether weak excitation or strong excitation and reactive power are generated or absorbed. In weak excitation with reduced excitation current, the voltage generated by the synchronous motor (no-load induced electromotive force) is lower than the system voltage (armature voltage), and the synchronous motor absorbs lagging reactive power from the system. Hereinafter, lagging reactive power is simply referred to as reactive power. In this case, the armature reaction becomes a magnetizing effect. The load observed from a synchronous generator generates reactive power with a leading power factor (capacitive). From the perspective of the power source, a synchronous motor absorbs reactive power and has a lagging load (inductive). In strong excitation with large excitation current, the voltage generated by the synchronous motor (no-load induced electromotive force) is higher than the system voltage (armature voltage), and the synchronous motor supplies reactive power to the system. In this case, the armature reaction becomes a demagnetizing effect. The load seen from a synchronous generator absorbs reactive power with a lagging power factor (inductive). In the case of a synchronous motor, reactive power is generated by the load (capacitive) produced from the power source.

Stober motor performance

The construction of the motor stator is basically similar to that of a capacitor-split-phase single-phase asynchronous motor. Two windings positioned 90° apart are installed on the stator: one is the excitation winding Rf, which is always connected to the AC voltage Uf; the other is the control winding L, connected to the control signal voltage Uc. Therefore, AC servo motors are also known as two-phase servo motors. The rotor of an AC servo motor is usually made in a squirrel-cage style. However, to enable the servo motor to have a wide speed control range, linear mechanical characteristics, no "self-rotation" phenomenon, and fast response performance, it must have two characteristics compared with ordinary motors: high rotor resistance and low moment of inertia. There are two commonly used rotor structures: one is a squirrel-cage rotor made of high-resistivity conductive bars with high resistivity; to reduce the rotor's moment of inertia, the rotor is made slender. The other is a hollow cup-shaped rotor made of aluminum alloy; the cup wall is very thin, only 0.2-0.3mm. To reduce the magnetic reluctance of the magnetic circuit, a fixed inner stator is placed inside the hollow cup-shaped rotor. The hollow cup-shaped rotor has a very small moment of inertia, rapid response, and smooth operation, so it is widely adopted. When there is no control voltage, the AC servo motor has only the pulsating magnetic field generated by the excitation winding in the stator, and the rotor remains stationary. When there is a control voltage, a rotating magnetic field is generated in the stator, and the rotor rotates in the direction of the rotating magnetic field. Under constant load, the motor speed changes with the magnitude of the control voltage. When the phase of the control voltage is reversed, the servo motor will reverse.

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