搭載低損耗整流器之車用發電機系統之自啟動轉速偵測方法

Rotational Speed Detection for the Automotive Alternator System with Low-Loss Rectifiers in Self-Start Function

游家崧(Chia-Sung Yu)

指導教授 ： 陳景然

國立臺灣大學/電機資訊學院/電機工程學研究所/博士(2022年)

https://doi.org/10.6342/NTU202201364

摘要

爪極式發電機系統廣泛應用於各種內燃機車型中作為主要電力來源，包含乘用車、混合動力車及商用車。發電機電壓調節器 (Alternator Voltage Regulator) 使用直流比較及計數電路，偵測發電機相電壓的振幅及頻率以估算發電機轉速，使發電機系統在引擎啟動後能進入發電模式對負載供電。自啟動功能 (Self-Start Function) 為發電機啟動訊號故障的備用機制，自啟動期間發電機的相電壓是透過轉子殘磁 (Residual Magnetism) 交鏈至定子線圈所產生，此時相電壓振幅微弱，無法滿足整流器的順向導通電壓，以及相電壓的直流位置受電瓶及整流器的漏電阻抗分壓效應影響而產生偏移，進而影響轉速偵測。習知技術在相電壓偵測電路增加一個下拉電阻以消除相電壓的直流位準偏移，使發電機系統可在發電機啟動訊號故障時，可透過自啟動功能進入發電模式。為了滿足降低二氧化碳的法規，新型式發電機經常使用低損耗整流器 (如：蕭特基二極體或場效應電晶體) 來取代傳統的 PN 接面二極體整流器，以降低整流橋的功率損耗。然而，伴隨低損耗整流器而來的是其較高的逆向漏電流，造成發電機相電壓浮動現象，影響電壓調節器在自啟動時從相電壓偵測發電機轉速的準確性。以致發電機系統在引擎啟動後無法正確進入發電模式，導致車輛耗光電瓶儲存之電能而拋錨。
為解決此問題，本文提出了一個偵測發電機轉速的方法，在不修改系統配線及額外零件成本的前提下，解決了搭載低損耗二極體時，發電機自啟動轉速偵測的問題。文中首先分析整流器漏電流對於相電壓直流位準偏移的現象，並對車用發電機的轉子及定子進行磁路分析，推導出轉子電壓的方程式作為由轉子電壓計算轉速的理論基礎，並透過 ANSYS Maxwell 模擬以驗證推導的有效性。最後，透過不同轉速及極端漏電流的實驗，驗證本文所提方法可用於自啟動時的發電機轉速偵測，避免相電壓直流位準偏移或電壓振幅衰減造成轉速偵測的問題。

關鍵字

車用發電機 ； 轉速偵測 ； 自啟動

並列摘要

The Lundell alternator is widely used as the main power source in the internal-combustion-engine (ICE) vehicles, such as passenger vehicles, hybrid vehicles and heavy-duty vehicles. the alternator voltage regulator (AVR) evaluates the alternator rotational speed (nR) by sensing the phase voltage with DC comparator and counter. Thus, the alternator system can enter regulation mode to supply electrical power to the loads after the engine is started. The self-start function, in which the phase voltage is generated by the residual magnetism of the rotor coupling to the stator winding, is a back-up function for ignition signal failure. During the self-start operation, the amplitude of phase voltage is too low to forward-bias the rectifiers. Therefore, phase voltage exists DC offset which is generated by the battery voltage divided by the leakage resistances of the rectifiers, and the rotational speed detection performance of AVR is impacted. Prior arts use the pull low resistor in phase detection circuit to mitigate the DC offset of phase voltage. Thus, the alternator system can enter regulation mode through the self-start function while the alternator ignition signal fails. In order to satisfy the regulations of CO2 reduction, the P-N junction diode rectifiers are generally replaced by low-loss rectifiers to reduce the power loss in rectification. However, the high reverse leakage current usually accompanying the low-loss rectifiers, often results in DC offset of phase voltage and reduces the accuracy of rotational speed detection. As a result, the alternator system fails to enter regulation mode and the vehicle crashes due to depletion of electrical energy stored in the battery.
In order to solve this issue, a novel alternator rotational speed detection method is proposed to solve detection issues for the self-start function with low-loss rectifiers. No extra wiring or external components are required. In this dissertation, phase voltage DC offset and verified the analysis by circuit simulation, then derived rotor field voltage vf by analyzing the magnetic circuit including rotor and stator of alternator to set the theoretical foundation for the proposed detection method for the self-start function. Eventually, the proposed method is experimentally verified to be effective for alternator rotational speed detection under different rotational speed and extreme leakage current conditions in self-start operation. Then, the rotational speed detection issues induced by the DC offset and attenuation effect of the phase voltage is prevented.

並列關鍵字

Automotive alternator ； rotational speed detection ； self-start function

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