周波数変換器関連機器のサプライヤーは、周波数変換器が今日の産業生産において広く使用されていることをご承知おきください。周波数変換器で制御される機器は、ある程度のエネルギーを大幅に節約できるため、多くの産業メーカーから支持されています。
ソフトパーキング、ソフトスタート、無段階速度制御、あるいは速度の増減に関する特殊な要件などを実現するため、現代の非同期モータでは周波数変換器と呼ばれる速度制御装置が必要です。この装置の主回路は、動作周波数が0～400HzのAC-DC-AC回路を採用しています。低電圧汎用周波数変換器の出力電圧は380～460V、出力電力は0.37～400kWです。
適切な周波数変換器を選択する
周波数変換器の使用中に発生する異常動作、機器の故障など、生産停止や不必要な経済的損失につながる問題は、多くの場合、周波数変換器の不適切な選定と設置によって引き起こされます。したがって、生産およびプロセスの基本条件と要件をより適切に満たす、経済的で実用的な周波数変換器を選択する必要があります。
周波数変換器の主な駆動対象であるモータは、周波数変換器の種類を選択する際に、モータの動作パラメータに合わせて選択する必要があります。
（１）電圧整合：周波数変換器の定格電圧はモータの負荷電圧と整合する。
(2) Current matching: The capacity of the frequency converter depends on the rated current continuously output by the frequency converter. When selecting a frequency converter for motors that require speed regulation, it is necessary to choose a frequency converter with a continuous rated current greater than the rated current of the motor when operating at rated parameters, and with a quantitative margin; For general frequency converters with more than 4 poles, the selection cannot be based on the capacity of the motor, but on the current seat verification standard of the motor; Even if the load on the motor is relatively light and the current is less than the rated current of the frequency converter, the selected frequency converter cannot be too small in capacity compared to the motor.
(3) Capacity matching: Depending on the different load characteristics of the motor, there are different requirements for selecting the capacity of the frequency converter.
Control method of frequency converter
The main control methods of frequency converters currently include the following.
(1) The first generation used U/f=C control, also known as sine pulse width modulation (SPWM) control method. Its characteristics include a simple control circuit structure, low cost, good mechanical properties and hardness, which can meet the smooth speed regulation requirements of general transmission. However, this control method reduces the maximum output torque at low frequencies due to the lower output voltage, resulting in decreased stability at low speeds. Its characteristic is that without feedback device, the speed ratio ni is less than 1/40, and with feedback, ni=1/60. Suitable for general fans and pumps.
(2) The second generation adopts voltage space vector control (magnetic flux trajectory method), also known as SVPWM control method. It is based on the overall generation effect of three-phase waveforms, generating three-phase modulation waveforms at once and controlling them by cutting polygons to approximate circles. To eliminate the influence of stator resistance at low speeds, the output voltage and current are closed loop to improve dynamic accuracy and stability. Its characteristics: no feedback device, speed ratio ni=1/100, suitable for speed regulation in general industry.
(3) The third generation adopts vector control (VC) method. The practice of vector control variable frequency speed regulation essentially equates an AC motor to a DC motor, and independently controls the speed and magnetic field components. By controlling the rotor magnetic flux and decomposing the stator current to obtain two components, torque and magnetic field, orthogonal or decoupled control can be achieved through coordinate transformation. Its characteristics: speed ratio ni=1/100 without feedback, ni=1/1000 with feedback, and starting torque of 150% at zero speed. It can be seen that this method is applicable to all speed control, and when equipped with feedback, it is suitable for high-precision transmission control.
(4) Direct Torque Control (DTC) method. Direct torque control (DTC) is another high-performance variable frequency speed control mode that differs from vector control (VC). Obtain magnetic flux and torque data using magnetic flux simulation models and electromagnetic torque models, compare them with given values to generate hysteresis comparison state signals, and then switch the switch state through logic control to achieve constant magnetic flux control and electromagnetic torque control. It does not require imitation of DC motor control, and this technology has been successfully applied to the AC drive of traction electric locomotives. Its characteristics: without feedback device, the speed ratio ni=1/100, with feedback ni=1/1000, and the starting torque can reach 150% to 200% at zero speed. Suitable for heavy-duty starting and large loads with constant torque fluctuations.
Installation environment requirements
(1) Environmental temperature: The environmental temperature of the frequency converter refers to the temperature near the cross-section of the frequency converter. Due to the fact that frequency converters are mainly composed of high-power power electronic devices that are highly susceptible to temperature, the lifespan and reliability of frequency converters largely depend on temperature, generally ranging from -10 ℃ to+40 ℃. In addition, it is necessary to consider the heat dissipation of the frequency converter itself and the extreme situations that may occur in the surrounding environment, and a certain margin is generally required for temperature.
(2) Environmental humidity: The frequency converter requires a relative humidity of no more than 90% in its surrounding environment (with no condensation on the surface).
（3）振動と衝撃：周波数変換器の設置および運転中は、振動と衝撃を避けるよう注意する必要があります。周波数変換器の内部部品のはんだ接合部や緩んだ部品は、電気的接触不良や短絡などの重大な故障を引き起こす可能性があります。そのため、設置場所の振動加速度は通常0.6G以下に制限され、特別な場所には緩衝ゴムなどの耐震対策を施す必要があります。
（4）設置場所：周波数変換器の最大許容出力電流および電圧は、その放熱能力の影響を受けます。標高が1000mを超えると、周波数変換器の放熱能力が低下するため、一般的には標高1000m以下に設置する必要があります。
（５）周波数変換器の設置場所に対する一般的な要件は、腐食がなく、可燃性または爆発性のガスや液体がないこと、ほこりや浮遊繊維や金属粒子がないこと、直射日光を避けること、電磁干渉がないことなどである。
可変周波数速度制御の研究は、現在、電力伝送研究において最も活発かつ実用的に価値のある研究です。周波数変換器は空調、エレベーター、冶金、機械などの産業で広く利用されているため、その潜在力は計り知れません。可変周波数速度制御モーターとそれに対応する周波数変換器は、急速に発展するでしょう。