電氣外文翻譯--一種用于消除pwm逆變器輸出共模電壓的有源電路

1、<p>　　中文4700字，2900單詞，15500英文字符</p><p>　　出處：Ogasawara S, Ayano H, Akagi H. An active circuit for cancellation of common-mode voltage generated by a PWM inverter[J]. IEEE Transactions on Power Electronics

2、, 2002, 13(5):835-841.</p><p><b>　　英文文獻(xiàn)</b></p><p>　　AN Active Circuit for Cancellation of</p><p>　　Common-Mode Voltage Generated by a PWM Inverter</p><p>　

3、　Satoshi Qgasawara, Hideki Ayano and Hirofumi Akagi</p><p>　　Department of Electrical Engineering Okayama University</p><p>　　3-1-1 Tsushima-Naka, Okayama, 700 .JAPAN</p><p><b&g

4、t;　　Abstract</b></p><p>　　This paper proposes an “Active Common-noise Canceller (ACC)” that is capable of eliminating the common-mode voltage produced by a PWM inverter. An emitter follower using compl

5、ementary transistors and a common-mode transformer are incorporated into the ACC, the design method of which is also presented in detail. A prototype ACC designed and constructed in this paper verifies the viability and

6、effectiveness in a 3.7kW induction motor drive using an IGBT inverter. Some experimental results show tha</p><p>　　I. INTRODUCTION</p><p>　　An emergence of high-speed switching devices such as

7、IGBT’s has enabled to increase, a carrier frequency of voltage source PWM inverters, thus leading to much better operating characteristics. High-speed switching, however, can accompany the following serious problems orig

8、inating from a steep change in voltage and/or current:</p><p>　　o. ground current escaping to earth through stray capacitors inside motors[1]-[2]</p><p>　　o .conducted and radiated EMI[3]-[6]<

9、;/p><p>　　o. bearing current and shaft voltage [7]-[9] </p><p>　　o. shortening of insulation life of motors and transformers[10]-[13]</p><p>　　The voltage and/or current change caused

10、by high-speed switching produces high-frequency oscillatory common-mode and normal-mode currents at the instant of every switching, because parasitic stray capacitors inevitably exist inside an ac motor. The oscillatory

11、currents with a frequency range of 100 kHz to several MHz can create a magnetic field, and radiate Electro-Magnetic Interference (EMI) noises throughout, thus producing a bad effect on electronic devices such as AM radio

12、 receivers and medi</p><p>　　Generally, common-mode chokes and EMI filters, based on passive elements, could not solve the problems perfectly. The authors have proposed a common-mode transformer with an addi

13、tional winding shorted by a resistor [2]. It can damp the oscillatory ground current, but a small amount of a periodic ground current still remains. Some attempts introducing active circuits have been made to eliminate t

14、he ground current or common-mode voltage [14][15].</p><p>　　This paper proposes an “Active Common-noise Canceller (ACC)” that is able to eliminate the common-mode voltage produced by a PWM inverter. The ACC

15、superimposes a compensating voltage on the inverter output. The compensating voltage applied by the ACC has the same amplitude as, but the opposite polarity to, the common-mode voltage produced by the PWM inverter. As a

16、result, the common-mode voltage applied to a load is canceled completely.</p><p>　　A prototype ACC, constructed in this paper, verifies the viability and effectiveness in a 3.7 kW induction motor drive using

17、 an IGBT inverter. Some experimental results show that the proposed ACC makes significant contributions to reducing the common-mode current, i.e., the ground current, and the conducted EMI. The ACC can also prevent an el

18、ectric shock from being received when some-one touches a non-grounded motor frame. Furthermore, the ACC can suppress a motor shaft voltage stemming from the</p><p>　　II. PRINCIPLE OF ACTIVE COMMON-NOISE CA

19、NCELLER</p><p>　　Fig.1 shows the configuration of an experimental system including an active common-noise canceller proposed in this paper. A voltage-source PWM inverter using IGBTs drives an induction motor

20、 of 3.7kW through three feeder wires, and the motor frame is connected to an earth terminal on a switch board. A shaft voltage is measured between the frame and a carbon brush touching to the motor shaft. Measurement of

21、conducted EMI is performed by using a LISN and a spectrum analyzer. The ACC is connected b</p><p>　　A common-mode current ic , flows to the earth terminal through stray capacitors between the windings and th

22、e frame of the motor, because a zero-sequence output voltage of the inverter, i.e., a common-mode voltage, varies every switching of the inverter. The ACC aims to cancel this common-mode voltage perfectly, so that no com

23、mon-mode current flows, i.e., ic= 0.</p><p>　　Fig.2 shows a common-mode circuit equivalent to the experimental system. Here, C means the stray capacitor between the motor windings and the frame, and the tota

24、l common-mode inductance and resistance are shown as Lc and Rc , respectively. In the equivalent circuit, the voltage-source inverter is modeled by a step voltage source V inv, because switching operation in one phase of

25、 the inverter causes step change in the common-mode voltage by 1/3 of the dc link voltage. If no ACC is connected, the </p><p>　　Combination of a voltage-controlled voltage source and an inductor, which are

26、surrounded by a dotted line, corresponds to the ACC. The emitter follower, along with the three capacitors, is represented as the voltage-controlled voltage source due to the following characteristics; a voltage gain clo

27、se to unity, a high input impedance, and a low output impedance. On the other hand, the common-mode transformer is the same as a conventional common-mode choke, except for connecting a tightly coupled a</p><p&

28、gt;　　The purpose of the Y-connected capacitors in Fig. l is to detect the common-mode voltage produced by the inverter. The emitter follower applies the same voltage as the detected voltage to the common-mode transformer

29、. The three primary windings of the common-mode transformer with the polarity shown by the dots in Fig.1 are connected between the output terminals of the inverter and the feeder wires. Therefore, the polarity of the com

30、pensating voltage Uc is opposite to the common-mode voltage gener</p><p>　　Fig.1 System configuration</p><p>　　III. DESIGN OF ACTIVE COMMON-NOISE CANELLER</p><p>　　Power Dissipati

31、on in the Emitter Follower</p><p>　　The voltage-controlled voltage source in Fig.2 requires the following properties; </p><p>　　o a wide frequency bandwidth up to several MHz,</p><p&

32、gt;　　o a low output impedance for eliminating any influence of the output current on the compensating voltage,</p><p>　　o a high input impedance to minimize the capacitance of C1.</p><p>　　The p

33、ush-pull emitter follower using complementary transistors satisfies the requirements. Table I shows the absolute maximum ratings of the transistors that are operated in the active region.</p><p>　　If Lm were

34、 infinity in Fig.2, the magnetizing current would be zero, so that no power loss would occur in the voltage-controlled voltage source, i.e., the emitter follower. In practice, the magnetizing current is supplied from the

35、 emitter follower rather than from the inverter, due to the low output impedance of the emitter follower.</p><p>　　Fig.3 shows waveforms of the triangular magnetizing current and the rectangular common-mode

36、voltage, in which all three phases are being switched simultaneously at a switching frequency fsw = l/T. As a result, the amount of power dissipation is the maximum.</p><p>　　In intervals II and III, the mag

37、netizing current is positive so that it flows, not through Tr2, but through Tr1. During interval II, the common-mode voltage is Ed/2 so that no collector dissipation occurs in both transistors, because the emitter-collec

38、tor voltage of Tr1 equals zero. However, an amount of power dissipation appears in Tr1 during interval III. Therefore, the average power dissipation of one transistor can be calculated by:</p><p><b>　　

39、(III-1)</b></p><p>　　In the experimental system, the PWM period and the dc link voltage of the inverter are T =100μs and Ed =282V, respectively. Since the absolute maximum power dissipation of both tra

40、nsistors is rated at 15W, the magnetizing inductance should be greater than 8.3 mH.</p><p>　　Design of the Common-Mode Transformer</p><p>　　Table II shows the specifications of the ferrite core

41、used. The common-mode transformer should be designed so as not to cause magnetic saturation. Therefore, the product of the stack number k of core and the number of turns N satisfies：</p><p><b>　　(III-2

42、)</b></p><p>　　In the experimental system, four toroidal ferrite cores(k=4)are used for the common-mode transformer in consideration of margin, and the number of turns is selected as N =22. Therefore,

43、the magnetizing inductance of the common-mode transformer is given by：</p><p><b>　　(III-3)</b></p><p>　　In this case, the power dissipation Pc, the maximum magnetizing current Immax

44、and the maximum flux density Bmax , are calculated as follows:</p><p><b>　　(III-4)</b></p><p>　　The power dissipation in both transistors corresponds to 0.26 % of the rated power of

45、the induction motor.</p><p>　　DC-Side Capacitors</p><p>　　A dc component included in the output voltage of the emitter follower may cause an excessive current flowing to the common-mode transfor

46、mer, and the transistors may break down. In order to remove the dc component, two dc-side capacitors CO are connected as shown in Fig.1. The smaller the capacitance or CO, the larger the variation of the neutral 1 point

47、potential vo. Because the voltage variation amounts to a voltage error in the compensating voltage, a large variation result in imperfect cancel</p><p>　　Fig.2 Common-mode equivalent circuit Fig.3 Va

48、riation of magnetizing current</p><p>　　TABLE I Absolute maximum ratings of transistors TABLE II Specification of toroidal ferrite core</p><p>　　IV. EFFECT ON GROND CURRENT</p><p>

49、　　Fig.4 shows experimental waveforms of the common-mode current and voltage without ACC. The common-mode voltage v inv is measured between the neutral points of the Y-connected capacitors and the dc-side capacitors. It i

50、s shown that a non-negligible amount of the common-mode current, i.e., the ground current, leaks to earth every switching of the PWM inverter. The common-mode current ic oscillates at 290 kHz and the amplitude reaches 0.

51、4A(peak value). It may cause incorrect operation of an earth l</p><p>　　In reference[2], the authors have proposed an equivalent circuit for the ground current, which forms an LCR series resonant circuit as

52、shown in Fig2 .The damped and oscillatory current in Fig.4 is similar to the current waveform after a step voltage is applied to the equivalent resonant circuit. The equivalent circuit provides a simple way for analyzing

53、 the ground current with a sufficient accuracy. It is considered that the equivalent circuit is the same as the reduced-order common-mode model f</p><p>　　Fig.5 shows an experimental result with the ACC. The

54、se waveforms indicate that the ACC is capable of suppressing the common-mode current almost completely. A mere common-mode current remains due to a control delay of the emitter follower every switching. The ACC is effect

55、ive in reduction of the common-mode or ground current.</p><p>　　Fig.4 Ground current without ACC Fig.5 Ground current with the ACC (a) Ground current (b)Common-mode voltage (a) Ground cu

56、rrent (b)Common-mode voltage</p><p>　　V. EFFECT ON CONDUCTED EM1</p><p>　　Fig.6 shows conducted EMI, measured in a frequency range from 10kHz to 30MHz.In a range from 10 kHz to 150kHz, it turns

57、 into a sequence of impulse spectra at intervals of the switching frequency of 10 kHz, where the spectrum analyzer used for measurement, has a resolution bandwidth of 200Hz. Since the resolution bandwidth is changed to 9

58、 kHz in a range from150kHz to 30MHz, it turns into a continuous spectrum. It is shown that conducted EMI beyond 100dBµV occurs at the maximum point.</p><p>　　The frequency at the maximum point coincides

59、 with the oscillation frequency of the ground current shown in Fig.4.This fact indicates that the conducted EMI is affected by the common-mode current. The conducted EMI is measured as a voltage drop when the common-mode

60、 current flows through a resistor in the LISN. Therefore, analysis of the conducted EMI can be achieved by using a common-mode equivalent circuit combined with the LISN.</p><p>　　Fig.7 shows a conducted EMI

61、when the ACC is connected. The experimental result indicates that the ACC decreases the conducted EMI by about 20dB in a frequency range from10kHz to3MHz. The ACC proposed in this paper makes great contributions to reduc

62、ing the conducted EMI in a wide frequency range.</p><p>　　Fig.6 Conducted EMI without ACC Fig.7 Conducted EMI with the ACC</p><p>　　VI. EFFECT ON PREVENTION OF ELECTRIC SHOCK</p

63、><p>　　In Japan, a safety standard to prevent an electric shock from being received on an accessible metal part of non-grounded electric apparatus is enacted, which is a similar standard to the IEC 335. A measu

64、ring circuit complying with the Japanese standard is shown in Fig.8. The measuring circuit is connected between a non-grounded motor frame and an earth terminal, and a rms value of voltage between output8 terminals 1-2 i

65、s measured. It is judged that there is no danger of an electric shock when th</p><p>　　Fig.8 Measuring circuit Fig.9 Terminal voltage of measuring circuit without ACC</p><p>　　Analysis o

66、f the Terminal Voltage</p><p>　　Fig9 shows waveforms of the common-mode current, the terminal voltage of the measuring circuit and the common-mode voltage when no ACC is connected. The rms value of the termi

67、nal voltage v12 is 3.54V. Since the rms value exceeds 1V, the motor frame has the potential of an electric shock.</p><p>　　The terminal voltage waveform is analyzed by using a circuit simulator. The simulati

68、on circuit is shown in Fig.11.Here, Cc means a stray capacitor between the windings and frame of the motor and the value is measured by an LCR meter. The equivalent circuit with focus the common-mode voltage and current

69、is represented by capacitor Cc because the common-mode impedance included in both feeder wires and grounding conductor is negligible, compared with that of the measuring circuit. The amplitude of </p><p>　　F

70、ig.10 Expanded waveforms of Fig.9 Fig.11 Simulation circuit</p><p>　　Fig. 10 and 12 show expanded waveforms of Fig.9 and a simulation result, respectively. Although the motor is dealt with as

71、 capacitor Cc, the simulated waveforms of ic and v12 coincide with the experimental waveforms. The larger Cc the larger the rms value of the terminal voltage. Hence, reduction of Cc is effective in mitigation of an elect

72、ric shock on the motor frame.</p><p>　　Fig.12 Simulated waveforms</p><p>　　B. In Case of the Connecting common-mode Transformer</p><p>　　Fig.13 shows waveforms of the common-mode c

73、urrent, the terminal voltage and the common-mode voltage when the common-mode transformer proposed in reference[2]is connected to output terminals of the inverter. Here, the secondary winding of the common-mode transform

74、er is shorted by a resistance of 1k. Compared with Fig.9, it is shown that the common-mode current, decreases and that the overshoot of the terminal voltage occurring every switching is mitigated. The reason is that the

75、common-mode trans</p><p>　　Fig.13 Terminal voltage of measuring circuit Fig.14 Terminal voltage of measuring circuit </p><p>　　when connecting the common-mode transformer w

76、hen connecting the ACC</p><p>　　C. In Case of Connecting the ACC </p><p>　　Fig.14 shows waveforms of the common-mode current, the terminal voltage and the common-mode voltage in the case of conn

77、ecting the ACC to the output terminals of the inverter. Compared with Fig.9, it is indicated that the common-mode current ic and the terminal voltage v12 are well reduced because the ACC cancels the common-mode voltage a

78、lmost perfectly. The rms value of the terminal voltage, 0.1V, is much smaller than the prescribed value 1V. Therefore, the ACC can remove any danger of an electr</p><p>　　VII. EFFECT ON MOTOR SHAFT VOLTAGE&

79、lt;/p><p>　　Fig.15 shows experimental waveforms of a common-mode voltage and a motor shaft voltage when no ACC is connected. A motor shaft voltage of 2V(peak value)occurs every PWM period of the inverter. It is

80、 concluded that the motor shaft voltage is caused by the common-mode voltage, because shapes of the two waveforms are similar. The shaft voltage results from a capacitive coupling between the stator and rotor. It may ind

81、uce electric field breakdown of a thin oil film existing between a bearing rate an</p><p>　　Fig.16 shows experimental waveforms when the ACC is connected. Compared with Fig.15, the motor shaft voltage is sup

82、pressed sufficiently. Therefore, the ACC produces a welcome side effect, i.e., “no flow of bearing current.”</p><p>　　Fig.15 Motor shaft voltage without ACC Fig.16 Motor shaft voltage with the ACC</p

83、><p>　　VIII. CONCLUSIONS</p><p>　　In this paper, an active common-mode canceller(ACC)has been proposed, which is capable of canceling a common-mode voltage generated by a PWM inverter. A prototype

84、 ACC has been constructed and tested to verify the effectiveness in a 3.7kW induction motor drive using an IGBT inverter. As a result, it is shown that the ACC can suppress a ground current almost perfectly. Moreover, th

85、e effect on prevention of an electric shock is confirmed by using a measuring circuit complying with a Japanese standa</p><p><b>　　中文翻譯</b></p><p>　　一種用于消除PWM逆變器輸出共模電壓的有源電路</p>

86、<p><b>　　摘要</b></p><p>　　本文提出了一種可以消除由PWM逆變器產(chǎn)生的共模電壓的有源共模噪聲消除器(ACC)。在ACC中使用了一個(gè)采用互補(bǔ)晶體管的發(fā)射極跟隨器和一個(gè)共模變壓器，并且對設(shè)計(jì)方法也進(jìn)行了詳細(xì)的交代。本論文中設(shè)計(jì)和建造的這個(gè)原型ACC驗(yàn)證了在用一個(gè)IGBT逆變器驅(qū)動的3.7kW異步電機(jī)的可行性和有效性。一些實(shí)驗(yàn)結(jié)果表明：ACC對降低漏電流和傳

87、導(dǎo)的電磁干擾(EMI)有著重要的貢獻(xiàn)。另外，ACC還可以防止在非接地電動機(jī)框架觸電和抑制電動機(jī)軸電壓觸電。</p><p><b>　　I 緒 論</b></p><p>　　高速開關(guān)裝置即IGBT的出現(xiàn)，使得電壓型PWM逆變器的載波頻率能夠增加，這樣可以導(dǎo)致產(chǎn)生更多更好的操作特性。盡管如此，高速開關(guān)可能伴隨下列嚴(yán)重的問題：來自急劇變化的電壓和/或電流：</

88、p><p>　　o.通過電動機(jī)內(nèi)部的雜散電容流到大地的漏電流。</p><p>　　o.傳導(dǎo)和輻射的電磁干擾。</p><p>　　o. 軸承電流和軸電壓。</p><p>　　o. 電機(jī)和變壓器絕緣壽命的縮短。</p><p>　　由于在交流電動機(jī)內(nèi)部不可避免地存在著寄生的雜散電容，因而，高速開關(guān)引起的電壓和/或電流變化

89、在每一個(gè)開關(guān)的瞬間產(chǎn)生高頻震蕩共同模式和正常模式的電流。這個(gè)振蕩電流的頻率從100 kHz到3MHz之間，可以形成一個(gè)磁場，同時(shí)輻射電磁干擾(EMI)噪音，這樣就會對諸如AM收音機(jī)接收器和醫(yī)療設(shè)備等電子產(chǎn)品產(chǎn)生一個(gè)壞的影響。</p><p>　　一般地，基于無源元件的共模扼流圈和電磁干擾過濾器不能很好的解決這個(gè)問題。作者提出了一種共模變壓器，這種變壓器有一個(gè)被電阻短接的附加線圈。它可以抑制振蕩接地電流，但是少量的

90、周期漏電流依然存在。引進(jìn)有源電路的一些嘗試已經(jīng)被用來消除漏電流和共模電壓了。</p><p>　　本論文提出了一種“有源共模噪聲消除器(ACC)”，它能夠消除由PWM逆變器產(chǎn)生的共模電壓，也可以對逆變器的輸出產(chǎn)生一個(gè)補(bǔ)償電壓。由ACC產(chǎn)生的補(bǔ)償電壓和由PWM逆變器產(chǎn)生的共模電壓振幅相同，極性相反。結(jié)果，輸出到負(fù)載的共模電壓就被完全地消除。</p><p>　　本論文中設(shè)計(jì)和建造的這個(gè)原型A

91、CC驗(yàn)證了在用一個(gè)IGBT逆變器驅(qū)動的3.7kW異步電機(jī)的可行性和有效性。一些實(shí)驗(yàn)結(jié)果表明ACC對減少共模電流即漏電流和傳導(dǎo)的電磁干擾有著重要的貢獻(xiàn)。當(dāng)有人接觸到非接地電動機(jī)框架時(shí)，ACC也可以防止觸電。同時(shí)，它也能抑制來自PWM逆變器引起的共模電壓的電動機(jī)軸電壓。</p><p>　　II 有源共模噪聲消除器（ACC）的原理</p><p>　　圖1顯示了一個(gè)包括有本論文提出的有源共模

92、噪聲消除器的一個(gè)實(shí)驗(yàn)系統(tǒng)裝置。一個(gè)采用IGBT的電壓型PWM逆變器通過三條連接線驅(qū)動一個(gè)功率為3.7kW的異步電動機(jī)，并且，在開關(guān)板上，電動機(jī)外殼被連接到一個(gè)接地端。在外殼和接觸到電動機(jī)軸的一個(gè)碳刷之間軸電壓被測量到。通過一個(gè)LISN和一個(gè)頻譜分析儀可以完成對電磁干擾傳導(dǎo)的測量。ACC連接在逆變器輸出端和三條連接線之間，包括以下元件：一個(gè)采用互補(bǔ)對稱的插撥式晶體管發(fā)射極跟隨器，一個(gè)共模變壓器，三個(gè)探測出現(xiàn)在逆變器輸出端共模電壓的電容，還

93、有兩個(gè)用來阻止在共模變壓器附加線圈中流動的直流電流的直流側(cè)電容。</p><p>　　由于逆變器的一個(gè)零序輸出電壓即共模電壓在逆變器的每個(gè)開關(guān)處不同，這時(shí)一個(gè)共模電流 ic通過電動機(jī)外殼和線圈之間的雜散電容流到了地端，ACC的目的就是完全地取消這個(gè)共模電壓，這樣就不會存在共模電流了，即ic = 0。</p><p><b>　　圖1 系統(tǒng)結(jié)構(gòu)</b></p&g

94、t;<p>　　圖2顯示了一個(gè)等效于實(shí)驗(yàn)系統(tǒng)的共模電路，這兒C相當(dāng)于電動機(jī)線圈和框架之間的雜散電容，用Lc 和 Rc分別地表示總的共模電感和電阻，在等效電路中，由于在單相逆變器中的開關(guān)操作在共模電壓中引起的步進(jìn)變化可以達(dá)到直流滲透電壓的1/3，如果沒有ACC連接在電路中，那么步進(jìn)變化將會引起一個(gè)流到地端的振蕩共模電流ic。</p><p>　　用虛線圈起來的一個(gè)電壓控制電壓源和一個(gè)電感的組合與ACC

95、相對應(yīng)，發(fā)射極跟隨器，以及三個(gè)電容器代表電壓控制電壓源，主要是有以下特征: 電壓增益接近飽和,一個(gè)高輸入阻抗，一個(gè)低輸出阻抗。另一方面，除了連接一個(gè)緊密耦合的附加繞組(次要繞組)到發(fā)射極跟隨器的輸出端，共模變壓器與傳統(tǒng)的共模扼流圈是一樣的。因此，在等效電路中，共模變壓器可認(rèn)為是一個(gè)磁化電感Lm，從而忽略掉漏感。</p><p>　　在圖1中的將電容進(jìn)行Y連接的目的是檢測逆變器產(chǎn)生的共模電壓，發(fā)射極跟隨器產(chǎn)生的電壓

96、與在共模變壓器檢測到的電壓一樣。在圖1顯示中，極性由虛點(diǎn)表示出來的共模變壓器的三個(gè)主要的繞組連接在逆變器的輸出端和連接線之間。因此，補(bǔ)償電壓Uc的極性與逆變器產(chǎn)生的共模電壓的極性相反。結(jié)果，共模電壓的消除完全地獲得實(shí)現(xiàn)，因此，沒有共模電流流動。</p><p>　　圖2 有源共模噪聲消除器（ACC） 圖3 磁化電流的變化波形</p><p>　　表1 晶

97、體管的絕對最大等級 表2 鐵氧體磁芯規(guī)格</p><p>　　III 有源共模噪聲消除器（ACC）的設(shè)計(jì)</p><p>　　A.發(fā)射極跟隨器的功耗</p><p>　　圖示2中電壓控制電壓源要求以下性能：</p><p>　　o.在較寬的頻率帶寬高達(dá)數(shù)兆赫。</p><p&

98、gt;　　o.可以消除任意在補(bǔ)償電壓下輸出電流影響的低輸出阻抗。</p><p>　　o.使得電容C1最小的高輸入阻抗。</p><p>　　采用互補(bǔ)晶體管的插拔式發(fā)射極跟隨器滿足以上要求。表I表明晶體管的絕對最大值在活動區(qū)能夠操作。如果圖2中的電感Lm是無窮大，那么磁化電流將是零，因此在電壓控制電壓源即發(fā)射極跟隨器中將沒有電能損失。事實(shí)上，由于發(fā)射極跟隨器的低輸出阻抗，磁化電流來自發(fā)射極

99、跟隨器而不是逆變器。</p><p>　　圖3顯示了在開關(guān)頻率f sw = l/T時(shí)，三個(gè)開關(guān)同時(shí)閉合時(shí)，三角磁化電流和矩形共模電壓的波形，結(jié)果，此時(shí)，電功耗達(dá)到最大。</p><p>　　在II和III間隔，磁化電流為正，因此，此電流只流過Tr1 而不流經(jīng)Tr2，在時(shí)間間隔II中，因?yàn)門r1集射電壓為零，共模電壓為Ed/2，從而在兩個(gè)晶體管不會有集電極耗散。盡管如此，在時(shí)間III間隔中，

100、Tr1會有一定的電耗散，因此，一個(gè)晶體管的平均電耗散可以通過以下式(3-1)計(jì)算：</p><p><b>　　(3-1)</b></p><p>　　在實(shí)驗(yàn)系統(tǒng)中，PWM的周期和逆變器的直流電壓分別是100µs 和282V，因?yàn)閮蓚€(gè)晶體管的額定絕對電耗散最大值都是15W，所以磁化電感值應(yīng)大于8.3 mH。</p><p>　　B.共