As the core device of energy conversion, the efficiency of the motor directly depends on the collaborative working ability of the internal components, and the matching degree of the motor magnet and the coil is a crucial link. The two are like partners in precise cooperation. The performance parameters, spatial layout and even the matching degree of electromagnetic characteristics of each other will profoundly affect the loss and efficiency release of the motor during the energy conversion process, and then determine whether the motor can operate in an efficient and stable state.
The magnetic field matching between the magnet and the coil is the basic level that affects the efficiency of the motor. The motor magnet generates a constant magnetic field through its own permanent magnetic characteristics, and the coil forms an induced magnetic field after power is turned on. The interaction between the two drives the rotor to rotate. If the magnetic field strength of the magnet does not match the excitation capacity of the coil, the magnetic field coupling efficiency will be low. For example, when the magnetic flux density of the magnet is insufficient, the magnetic field generated by the coil cannot fully cut the magnetic lines of force, which weakens the electromagnetic induction intensity, reduces the driving torque obtained by the rotor, and the motor needs to consume more electricity to maintain operation, thereby reducing efficiency. On the contrary, if the magnetic field of the magnet is too strong and the coil power is insufficient, the excess magnetic field energy cannot be effectively utilized and will be wasted in the form of hysteresis loss, which also causes energy loss.
The spatial structure matching of the two also has a significant impact on the efficiency of the motor. The shape and size of the magnet, the winding method and the arrangement density of the coil jointly determine the uniformity of the magnetic field distribution. If the pole pitch of the magnet does not match the pitch of the coil, the air gap magnetic field distribution will be distorted and harmonic components will be generated. These harmonics will not only increase the iron loss and copper loss of the motor, but may also cause additional vibration and noise, further consuming energy. For example, in a permanent magnet synchronous motor, if the number of magnetic poles of the magnet is inconsistent with the number of winding poles of the coil, the alternating frequency of the magnetic field will be disordered, the electromagnetic resistance of the rotor will increase when it rotates, and the motor will be forced to draw more power from the power supply, and the efficiency will naturally decrease.
Whether the electrical parameters of the coil match the electromagnetic characteristics of the magnet reasonably is a key dimension affecting the efficiency of the motor. The number of turns, wire diameter and impedance characteristics of the coil need to be adapted to the parameters such as the residual magnetism and coercive force of the magnet. When the number of turns of the coil is too many, the inductance increases, causing the current to lag, and the magnetic field energy cannot be converted into mechanical energy in time. Instead, it is lost in the coil resistance in the form of Joule heat; if the number of turns is too few, the saturation of the magnetic circuit will increase, the magnetic resistance will increase, and the energy loss will also increase. In addition, if the wire material and cross-sectional area of the coil cannot match the working magnetic flux of the magnet, the eddy current loss will increase, especially in high-frequency working scenarios, this loss will increase significantly, further reducing the motor efficiency.
The matching stability under temperature environment is also a factor that cannot be ignored. During the operation of the motor, the coil will generate Joule heat when it is energized, and the magnet will drift in magnetic properties due to temperature changes. If the temperature characteristics of the two do not match, a vicious cycle may occur: the heating of the coil causes the ambient temperature to rise, the magnet demagnetizes at high temperature, the magnetic field strength decreases, and the coil has to increase the current to maintain the torque, thereby generating more heat. This repetition will cause the motor efficiency to deteriorate sharply with the increase in temperature. For example, the coercive force of NdFeB magnets decreases significantly at high temperatures. If the heat dissipation capacity of the matching coil is insufficient, the continuous temperature rise will cause the working point of the magnet to shift, and the motor efficiency will be greatly reduced or even unable to work normally.
The dynamic matching ability when the load changes also affects the motor efficiency performance. Under different working conditions, the load torque and speed of the motor will change, which requires the electromagnetic coupling relationship between the magnet and the coil to be adaptively adjusted. When the load increases, if the current adjustment range of the coil cannot match the magnetic field adjustment ability of the magnet, the motor may enter an overload state, the speed decreases, and the slip rate increases. At this time, the reactive current in the coil increases, the active power decreases, and the efficiency decreases accordingly. On the contrary, under light load conditions, if the magnetic field of the magnet fails to weaken accordingly, the excitation current of the motor will be too large, the "big horse pulling a small cart" phenomenon will occur, the power factor will decrease, and the efficiency will not be optimized.
The matching accuracy at the manufacturing process level will also indirectly affect the motor efficiency. Process problems such as the installation position error of the magnet and the winding uniformity of the coil may lead to uneven air gap or asymmetric magnetic field distribution. For example, the eccentricity of the magnet will cause the rotor to be subjected to uneven electromagnetic force, produce radial vibration, and increase mechanical loss; loose coil winding or poor interlayer insulation may cause local short circuits, resulting in uneven current distribution, local overheating, and increased energy loss. These seemingly subtle process differences will significantly reduce the overall efficiency of the motor when accumulated, especially in precision motors with extremely high precision requirements.
To achieve efficient matching between motor magnets and coils, full-process coordination is required from electromagnetic design, structural optimization, material selection to process control. By accurately calculating the magnetic performance parameters of the magnet and the electrical parameters of the coil, it is ensured that the two form an optimal coupling relationship in terms of magnetic field strength, spatial distribution, temperature characteristics and dynamic response. At the same time, advanced simulation technology is used to preview the motor operating status under different matching schemes, identify potential energy loss points in advance and improve them. Only in this way can the electromagnetic loss be minimized, the energy conversion efficiency of the motor be improved, and it can perform at its best in different application scenarios.
