DANFOSS motor Germany DANFOSS model DANFOSS price

DANFOSS motor refers to the engine that controls the operation of mechanical components in a servo system; it is an auxiliary motor indirect speed change device. Servo motors can control speed with very accurate position precision, converting voltage signals into torque and rotational speed to drive controlled objects. The rotor speed of the servo motor is controlled by the input signal and responds quickly. In automatic control systems, it serves as an actuator, featuring small electromechanical time constants and high linearity, converting received electrical signals into angular displacement or angular velocity output on the motor shaft. It is divided into two major categories: DC and AC servo motors. Its main characteristics are that there is no self-rotation phenomenon when the signal voltage is zero, and the rotational speed decreases uniformly as the torque increases.

DANFOSS motor working principle

The motor stator winding is powered by a single-phase power supply, and the rotor is an armature winding with a commutator short-circuited by brushes. The brushes can be moved to any position relative to the stator winding as needed. By moving this position, the rotation direction, mechanical characteristics, and operating speed of the rotor can be changed. When the brush deviates counterclockwise from the geometric neutral line, the rotor rotates clockwise; when the brush deviates clockwise from the geometric neutral line, the rotor rotates counterclockwise. Due to this phenomenon where the rotation direction is opposite to the brush deviation direction, it is called a repulsion motor. It has similar mechanical characteristics to a series-wound DC motor and is used to drive mechanical loads with heavy starting requirements. It is suitable for occasions requiring single-phase power supply, speed regulation, and reversal of rotation direction. Some motors are equipped with overload protection devices to protect the motor from burning out due to excessive current during overload. This component, composed of bimetal, expands when heated to open the contacts and cut off the circuit. When the overload is eliminated and the motor cools down, the contacts close again. The rotor coil is connected to the commutator and is not connected to the external circuit. The short-circuited brushes press against the commutator, inclined at an angle to the central axis of the stator magnetic field. When energized, the stator magnetic field induces the armature to generate an armature magnetic field. The poles of this magnetic field are near the brushes. The polarity of the armature magnetic field at this location is the same as that of the adjacent stator pole, generating mutual repulsion between them and causing the armature to rotate.

DANFOSS motor control principle

Regarding the motor control principle, first, the control unit must determine the sequence for turning on the power transistors in the inverter based on the position of the motor rotor sensed by the hall-sensor, according to the stator winding. This involves AH, BH, CH (these are called upper-arm power transistors) and AL, BL, CL (these are called lower-arm power transistors) in the inverter, causing current to flow through the motor coils in sequence to generate a forward (or reverse) rotating magnetic field, which interacts with the rotor magnets, thereby enabling the motor to rotate clockwise or counterclockwise. When the motor rotor rotates to a position where the hall-sensor senses another set of signals, the control unit turns on the next group of power transistors. By cycling in this manner, the motor continues to rotate in the same direction until the control unit decides to stop the rotor by turning off the power transistors; to reverse the rotor, the sequence of turning on the power transistors is reversed. Basically, the switching of power transistors can be exemplified as follows: AH and BL as one group → AH and CL as one group → BH and CL as one group → BH and AL as one group → CH and AL as one group → CH and BL as one group. However, AH and AL, or BH and BL, or CH and CL must never be turned on simultaneously.

DANFOSS motor structure

The motor body is similar to a Permanent Magnet Synchronous Motor (PMSM); the rotor uses permanent magnets, often rare-earth permanent magnet materials, but lacks cage windings and other starting devices. Its stator winding operates as an AC winding, generally supporting multi-phase (three-phase, four-phase, or five-phase), and the rotor is composed of permanent magnet steel with a specific number of pole pairs (2P=2,4,6…). The design requires obtaining a trapezoidal wave with a top width of 120° in the stator winding; therefore, the winding arrangement often adopts full-pitch, concentrated, or near full-pitch, concentrated forms to retain other harmonics in the magnetic flux density. Brushed DC motors rely on mechanical commutators to convert DC current into AC current approximating a trapezoidal wave to supply the armature winding, while Brushless DC Motors (BLDCM) rely on electronic commutators to input square wave currents sequentially into each phase of the stator armature winding according to a certain phase sequence. When a phase of the stator winding of a brushless DC motor is energized, the magnetic field generated by the current in that phase interacts with the magnetic field produced by the rotor permanent magnets to generate torque, driving the rotor to rotate. Position sensors convert the rotor magnet position into electrical signals to control the electronic switch circuit, thereby conducting the various stator windings in a certain order, ensuring that the stator phase current commutes in the correct sequence as the rotor position changes. This allows the electronic magnetic field to change continuously with the rotor's rotation, generating a rotating magnetic field synchronous with the rotor speed, and keeping the spatial angle between the stator magnetic field and the rotor magnetic field at approximately 90°, pushing the rotor to rotate with maximum torque. Since the conduction sequence of the electronic switch circuit is synchronous with the rotor angle, it performs the commutation function of a mechanical commutator, ensuring that the stator and rotor magnetic fields remain basically perpendicular during operation to improve efficiency. Therefore, in terms of basic structure, a brushless DC motor can be considered a 'self-synchronous motor system' composed of electronic switch commutation current, a permanent magnet synchronous motor, and position sensors, which will not lose synchronism during operation. The rotor structure of permanent magnet brushless motors (BLDCM) includes both traditional inner rotor structures and new structural forms such as disc-type, outer rotor, and linear structures.

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