現(xiàn)代交流同步發(fā)電機常用自動電壓調(diào)節(jié)器AVR這種電子部件調(diào)節(jié)勵磁機定子磁場的強弱。雖然AVR的種類很多但性能大同小異都是實時采樣主發(fā)電機的輸出電壓值與預(yù)先設(shè)定的值相比較,用比較的結(jié)果去調(diào)節(jié)脈沖寬度調(diào)制器PWM：輸出電壓值高則調(diào)制器輸出脈沖寬度窄反之則寬。然后再用這些脈沖去調(diào)控大功率開關(guān)器件即三極管或場效應(yīng)管控制送入勵磁機定子線圈的電流的時間。從而使它的磁場強弱隨著主柴油發(fā)電機輸出電壓的變化而相反變化;即輸出電壓升高則勵磁機定子磁場減小輸出電壓降低勵磁機定子磁場增強。從而達到負反饋調(diào)控的目的。

  自動電壓調(diào)節(jié)器是常用的一種AVR類型。取樣自主發(fā)電機輸出電壓的信號從89兩端輸入到電壓測量比較單元與內(nèi)部預(yù)先設(shè)定的電壓值(例如380V)相比較。比較結(jié)果以輸出電壓UA送入脈沖寬度調(diào)制單元PWM輸出電壓UC送入低頻保護單元。電壓測量比較單元的LSH是連接主發(fā)電機輸出電壓幅值調(diào)節(jié)電位器的三個端子。

  脈沖寬度調(diào)制器由穩(wěn)樂器輸出的直流電樂UCC作為工作電源以確保其性能穩(wěn)定。它的輸出電壓UB控制調(diào)制管VT3。若由電壓測量比較單元送來的UA大表明主發(fā)電機輸出電壓升高,則大的UA就會使脈沖寬度調(diào)制器輸出的脈沖UB的寬度變窄。窄的脈沖就會使VT3導(dǎo)通時間短通過的電流少。反之，主發(fā)電機電壓降低UA變小脈沖寬度調(diào)制器輸出的脈沖UB的寬度隨之變寬從而使VT3導(dǎo)通時間變長,通過的電流增多。

  勵磁機定子線圈一端接在端子X1上另一端接在XX1端子上。由主發(fā)電機電樞送來的EA、EB、Ec三相電壓經(jīng)過三個二極管VD10、VD11、VD12整流后,電流從X1端流入勵磁機的定子線圈由XX1流出再經(jīng)過調(diào)制管VT3和XN端子流回主發(fā)電機電樞形成勵磁機定子線圈的勵磁電流通路。VT3是這個通路上的開關(guān)，它導(dǎo)通時間長則定子線圈流過電流時間長定子磁場強度大;VT3導(dǎo)通時間短，定子線圈電流少，定子磁場強度小。

  AVR就是這樣調(diào)控主發(fā)電機組的電壓的:主發(fā)電機由于負荷原因輸出電壓升高，電壓測量比較單元輸出的UA隨著升高，受UA控制的脈寬調(diào)制器輸出脈沖UB寬度變窄，開關(guān)管VT3導(dǎo)通時間短，勵磁機定子磁場減弱，轉(zhuǎn)子電樞電壓及旋轉(zhuǎn)整流器輸出電流隨之減小，導(dǎo)致供給主發(fā)電機轉(zhuǎn)子的勵磁電流變小,則主發(fā)電機因其轉(zhuǎn)子磁場的減小而使輸出電壓降低。反之，AVR的負反饋調(diào)控功能就會使主發(fā)電機的輸出電壓升高。

  在主發(fā)電機因負荷超出額定值而輸出極大電流時，柴油發(fā)動機也需隨之輸出巨大的動力以致導(dǎo)致其轉(zhuǎn)速低于額定值。低頻保護單元的作用就是在這種情況下，限制勵磁機定子線圈里電流的超額增大。它以電阻和電容構(gòu)成的充放電支路預(yù)先設(shè)定一個低頻保護點，當(dāng)主發(fā)電機負荷正常時，從電壓測量單元來的UC小于低頻保護點，則低頻保護單元輸出的電壓Ud高，二極管VD8被截止，Ud到不了脈寬調(diào)制器,起不了作用。若主發(fā)電機超載則Ud變低VD8導(dǎo)通，Ud和UA就可同時作用于脈寬調(diào)制器,使其輸出的脈沖UB隨Ud的下降而變窄，調(diào)制管VT3導(dǎo)通時間隨之變短，勵磁電流減小勵磁機定子磁場變?nèi)?，從而?dǎo)致主發(fā)電機轉(zhuǎn)子磁場減小。發(fā)電機輸出電壓下降、電流減小。低頻保護單元起到了保護勵磁機和主發(fā)電機的作用。

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.