2023年全國碩士研究生考試考研英語一試題真題(含答案詳解+作文范文)_第1頁
已閱讀1頁,還剩5頁未讀 繼續(xù)免費(fèi)閱讀

下載本文檔

版權(quán)說明:本文檔由用戶提供并上傳,收益歸屬內(nèi)容提供方,若內(nèi)容存在侵權(quán),請進(jìn)行舉報(bào)或認(rèn)領(lǐng)

文檔簡介

1、International Journal of Scientific those are a) Voltage-source inverter and b) Current-source inverter. The gain of the inverter can be controlled by using pulse width modulation. Different PWM techniques are devised t

2、o control these inverters. PWM control technique also reduces harmonic distortion in the output signal and improves the performance of the inverter. PWM with third harmonic injection method eliminates third harmonic comp

3、onent from output waveform and also provides higher range of modulation index than regular PWM modulation technique. These PWM waveforms can be generated using analog circuits using active and passive components or it ca

4、n be generated digitally using microprocessor and microcontroller [4]. Fig. 1 Traditional voltage source inverter Figure.1 shows the traditional three-phase voltage-source inverter. The dc voltage source connected at the

5、 input side across a large capacitor. DC link voltage produced across this capacitor feeds the main three-phase bridge. The input dc supply can be a battery or fuel cell stack or diode rectifier, and/or capacitor. Three

6、phase bridge inverter circuit consists of six switches; each is composed of a power transistor and an anti-parallel diode to provide bidirectional current flow and reverse voltage blocking capability. Figure 2 shows the

7、traditional current-source inverter (CSI). The DC current source is formed by a large dc Inductor fed by a voltage source such as a battery or fuel-cell stack or diode rectifier or converter etc. Like VSI three phase bri

8、dge inverter circuit consists of six switches; each is composed of a switching device with reverse block capability such as a gate-turn-off thyristor and SCR or a power transistor with a series diode to provide unidirect

9、ional current flow and bidirectional voltage blocking. For voltage source inverter and current source inverter the on/off time the switching devices is controlled by applying control voltage (PWM) to the control terminal

10、 i.e. gate of the device. Fig. 2 Traditional current source inverter Traditionally in most of industries these voltage-source inverter and current-source inverter are used in adjustable speed drives. But these tradit

11、ional inverters have many limitations as summarized below: 1) They are either a buck or a boost converter and cannot be a buck–boost converter [1]. That is, the output voltage is either greater or smaller than the input

12、voltage. The output International Journal of Scientific B = T / (T1 – T0) = 1 / (1 – 2T0/T) ≥ 1 (3) is the boost factor resulting from the shoot-through zero state. Fig. 4 Equivalent circuit of Z-Sourc

13、e inverter with inverter in active state The peak dc-link voltage is the equivalent dc-link voltage of the inverter. On the other side, the output peak phase voltage from the inverter can be expressed as; Vacp = M Vip /

14、2 (4) In above equation M is the modulation index of PWM waveform, Vacp is output peak phase voltage and Vip is peak dc link voltage across bridge inverter. Using (2) and (4)

15、 peak phase voltage can be expressed as Vacp = M B Vdc / 2 (5) For the traditional V-source PWM inverter, the output peak phase voltage is given by Vacp = M Vdc / 2. Where Modula

16、tion index M is always less than unity hence in traditional inverter the output voltage is always less than input dc voltage. Equation (5) shows that in Z-Source inverter the output voltage can be stepped up and down by

17、choosing an appropriate buck–boost factor BB. The buck–boost factor is determined by the modulation index M and boost factor B. For Z-source inverter the boost factor is always greater than or equal to unity. When boost

18、factor is equal to unity the Z-source inverter acts like traditional inverter. The boost factor B as expressed in (3) can be controlled by varying shoot-through duty cycle T0/Tof the inverter PWM input. 3 MAXIMUM CONSTAN

19、T BOOST PWM WITH THIRD HARMONIC INJECTION CONTROL METHOD In order to reduce the volume and cost, the shoot-through duty ratio must be kept constant [2]. At the same time, a greater voltage boost for any given modulation

20、 index is desired to reduce the voltage stress across the switches. The maximum constant boost control achieves the maximum voltage gain while always keeping the shoot-through duty ratio constant. Maximum Constant boost

21、control with third harmonic injection method is devised to produce the maximum constant boost while minimizing the voltage stress. Shoot-through pulses are generated as shown in fig.7. These shoot-through pulses can be

22、generated by using triangular waveform generator and comparator. Shoot-through time is decided by the two reference levels called shoot-through level. When triangular carrier wave exceeds above upper shoot-through level

23、or below lower shoot-through level a shoot-through pulse is generated. Shoot-through time remains almost constant from switching cycle to switching cycle. These shoot-through pulses are evenly spread in traditional PWM w

24、aveform to obtain PWM waveform with shoot-through. Figure 8 shows third harmonic injected PWM with shoot-through and the control method is referred as maximum constant boost control with third harmonic injection. The th

25、ird and higher harmonic component can be injected into fundamental to reduce harmonic distortion in the output waveform [8]. The third harmonic component with 16.6% of the fundamental component is injected into the modul

26、ating signals. From the figure 8, it can be seen that the upper shoot-through level is always equal to or higher than the maximum value of the reference signals, and the lower shoot-through level is always equal to or lo

27、wer than the minimum value of the reference signals. Therefore, the shoot-though states only occur during the traditional zero states. As a result, this control method maintains the output voltage waveform. As shown in F

28、ig.8, at an angle of π/3 of modulating signal the third harmonic component crosses zero and then increases towards negative peak. Therefore at π/3 Va reaches its peak value (√3/2)M while Vb is at its minimum value -(√3/2

29、)M. In this method only two straight lines are needed to control the shoot-through time with the third harmonic injection. The boost factor depends up on the shoot-though duty cycle. If the shoot-through duty cycle is ke

溫馨提示

  • 1. 本站所有資源如無特殊說明,都需要本地電腦安裝OFFICE2007和PDF閱讀器。圖紙軟件為CAD,CAXA,PROE,UG,SolidWorks等.壓縮文件請下載最新的WinRAR軟件解壓。
  • 2. 本站的文檔不包含任何第三方提供的附件圖紙等,如果需要附件,請聯(lián)系上傳者。文件的所有權(quán)益歸上傳用戶所有。
  • 3. 本站RAR壓縮包中若帶圖紙,網(wǎng)頁內(nèi)容里面會有圖紙預(yù)覽,若沒有圖紙預(yù)覽就沒有圖紙。
  • 4. 未經(jīng)權(quán)益所有人同意不得將文件中的內(nèi)容挪作商業(yè)或盈利用途。
  • 5. 眾賞文庫僅提供信息存儲空間,僅對用戶上傳內(nèi)容的表現(xiàn)方式做保護(hù)處理,對用戶上傳分享的文檔內(nèi)容本身不做任何修改或編輯,并不能對任何下載內(nèi)容負(fù)責(zé)。
  • 6. 下載文件中如有侵權(quán)或不適當(dāng)內(nèi)容,請與我們聯(lián)系,我們立即糾正。
  • 7. 本站不保證下載資源的準(zhǔn)確性、安全性和完整性, 同時(shí)也不承擔(dān)用戶因使用這些下載資源對自己和他人造成任何形式的傷害或損失。

評論

0/150

提交評論