现代交流同步发电机常用自动电压调节器AVR这种电子部件调节励磁机定子磁场的强弱。虽然AVR的种类很多但性能大同小异都是实时采样主发电机的输出电压值与预先设定的值相比较,用比较的结果去调节脉冲宽度调制器PWM：输出电压值高则调制器输出脉冲宽度窄反之则宽。然后再用这些脉冲去调控大功率开关器件即三极管或场效应管控制送入励磁机定子线圈的电流的时间。从而使它的磁场强弱随着主柴油发电机输出电压的变化而相反变化;即输出电压升高则励磁机定子磁场减小输出电压降低励磁机定子磁场增强。从而达到负反馈调控的目的。
自动电压调节器是常用的一种AVR类型。取样自主发电机输出电压的信号从89两端输入到电压测量比较单元与内部预先设定的电压值(例如380V)相比较。比较结果以输出电压UA送入脉冲宽度调制单元PWM输出电压UC送入低频保护单元。电压测量比较单元的LSH是连接主发电机输出电压幅值调节电位器的三个端子。
脉冲宽度调制器由稳乐器输出的直流电乐UCC作为工作电源以确保其性能稳定。它的输出电压UB控制调制管VT3。若由电压测量比较单元送来的UA大表明主发电机输出电压升高,则大的UA就会使脉冲宽度调制器输出的脉冲UB的宽度变窄。窄的脉冲就会使VT3导通时间短通过的电流少。反之，主发电机电压降低UA变小脉冲宽度调制器输出的脉冲UB的宽度随之变宽从而使VT3导通时间变长,通过的电流增多。
励磁机定子线圈一端接在端子X1上另一端接在XX1端子上。由主发电机电枢送来的EA、EB、Ec三相电压经过三个二极管VD10、VD11、VD12整流后,电流从X1端流入励磁机的定子线圈由XX1流出再经过调制管VT3和XN端子流回主发电机电枢形成励磁机定子线圈的励磁电流通路。VT3是这个通路上的开关，它导通时间长则定子线圈流过电流时间长定子磁场强度大;VT3导通时间短，定子线圈电流少，定子磁场强度小。
AVR就是这样调控主发电机组的电压的:主发电机由于负荷原因输出电压升高，电压测量比较单元输出的UA随着升高，受UA控制的脉宽调制器输出脉冲UB宽度变窄，开关管VT3导通时间短，励磁机定子磁场减弱，转子电枢电压及旋转整流器输出电流随之减小，导致供给主发电机转子的励磁电流变小,则主发电机因其转子磁场的减小而使输出电压降低。反之，AVR的负反馈调控功能就会使主发电机的输出电压升高。
在主发电机因负荷超出额定值而输出极大电流时，柴油发动机也需随之输出巨大的动力以致导致其转速低于额定值。低频保护单元的作用就是在这种情况下，限制励磁机定子线圈里电流的超额增大。它以电阻和电容构成的充放电支路预先设定一个低频保护点，当主发电机负荷正常时，从电压测量单元来的UC小于低频保护点，则低频保护单元输出的电压Ud高，二极管VD8被截止，Ud到不了脉宽调制器,起不了作用。若主发电机超载则Ud变低VD8导通，Ud和UA就可同时作用于脉宽调制器,使其输出的脉冲UB随Ud的下降而变窄，调制管VT3导通时间随之变短，励磁电流减小励磁机定子磁场变弱，从而导致主发电机转子磁场减小。发电机输出电压下降、电流减小。低频保护单元起到了保护励磁机和主发电机的作用。
The commonly used electronic component in modern AC synchronous generators is the automatic voltage regulator (AVR), which regulates the strength of the stator magnetic field of the exciter. Although there are many types of AVRs, their performance is similar. They are real-time sampling of the output voltage value of the main generator and comparing it with a pre-set value. The comparison result is used to adjust the pulse width modulator PWM: if the output voltage value is high, the modulator's output pulse width is narrow; otherwise, it is wide. Then use these pulses to regulate the timing of the current sent to the stator coil of the excitation machine through high-power switching devices such as transistors or field-effect transistors. So that its magnetic field strength changes inversely with the output voltage of the main diesel generator; When the output voltage increases, the magnetic field of the exciter stator decreases, and when the output voltage decreases, the magnetic field of the exciter stator increases. Thus achieving the goal of negative feedback regulation.
Automatic voltage regulator is a commonly used type of AVR. The signal of sampling the output voltage of the autonomous generator is input from both ends of 89 to the voltage measurement comparison unit and compared with the pre-set voltage value (such as 380V) internally. The comparison result is sent to the pulse width modulation unit with the output voltage UA, and the PWM output voltage UC is sent to the low-frequency protection unit. The LSH of the voltage measurement comparison unit is connected to the three terminals of the main generator output voltage amplitude adjustment potentiometer.
The pulse width modulator uses the DC electric music UCC output from the stabilizing instrument as the working power supply to ensure its stable performance. Its output voltage UB controls the modulation tube VT3. If the UA sent by the voltage measurement comparison unit is large, it indicates that the output voltage of the main generator has increased, and the large UA will narrow the width of the pulse UB output by the pulse width modulator. A narrow pulse will result in a shorter conduction time for VT3 and less current passing through. On the contrary, when the voltage of the main generator decreases, the width of the pulse UB output by the pulse width modulator becomes wider, resulting in a longer conduction time of VT3 and an increase in the current passing through it.
One end of the exciter stator coil is connected to terminal X1, and the other end is connected to terminal XX1. The three-phase voltage of EA, EB, and Ec sent from the armature of the main generator is rectified by three diodes VD10, VD11, and VD12. The current flows into the stator coil of the excitation machine from the X1 terminal, flows out from XX1, and then flows back to the armature of the main generator through the modulation tube VT3 and XN terminal to form the excitation current path of the stator coil of the excitation machine. VT3 is the switch on this path, and if it conducts for a long time, the current flowing through the stator coil will last longer, resulting in a stronger stator magnetic field; VT3 has a short conduction time, low stator coil current, and low stator magnetic field strength.
AVR regulates the voltage of the main generator set in this way: due to load reasons, the output voltage of the main generator increases, and the UA output by the voltage measurement comparison unit increases. The pulse width modulator controlled by UA outputs a narrower pulse width UB, the conduction time of the switch tube VT3 is shorter, the stator magnetic field of the exciter weakens, the rotor armature voltage and the output current of the rotating rectifier decrease accordingly, resulting in a decrease in the excitation current supplied to the rotor of the main generator. As a result, the output voltage of the main generator decreases due to the decrease in its rotor magnetic field. On the contrary, the negative feedback control function of AVR will cause the output voltage of the main generator to increase.
When the main generator outputs a maximum current due to load exceeding the rated value, the diesel engine also needs to output a huge amount of power, resulting in its speed being lower than the rated value. The function of the low-frequency protection unit is to limit the excessive increase of current in the stator coil of the exciter in this situation. It uses a charging and discharging branch composed of resistors and capacitors to pre-set a low-frequency protection point. When the load of the main generator is normal and the UC from the voltage measurement unit is less than the low-frequency protection point, the output voltage Ud of the low-frequency protection unit is high, and the diode VD8 is cut off. Ud cannot reach the pulse width modulator and cannot function. If the main generator is overloaded, Ud will decrease and VD8 will conduct. Ud and UA can simultaneously act on the pulse width modulator, causing the output pulse UB to narrow as Ud decreases. The conduction time of the modulation tube VT3 will also become shorter, reducing the excitation current and weakening the stator magnetic field of the excitation machine, resulting in a decrease in the rotor magnetic field of the main generator. The output voltage and current of the generator decrease. The low-frequency protection unit plays a role in protecting the exciter and main generator.
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