3Phase Power Factor Correction Using Vienna Rectifier Approach and Modular Construction for ImprovWord文件下载.docx

1、1.0 Abstract:While applications for 1-Phase PFC are now familiar and prevalent, the same is not the case with 3-Phase PFC. Many equipments using kilowatts of power from 3-Phase mains should be candidates of 3-Phase power factor correction, because several advantages ensue, both to the user of the eq

2、uipment and to the utility. The Vienna Rectifier approach to achieve 3-Phase power factor correction offers many advantages and convenient, user-friendly features as compared to the two-level, six-switch boost PWM Rectifier. Amongst them are: continuous sinusoidal input currents with unity power fac

3、tor and extremely low distortion; no need for a neutral wire; reduction in voltage stress and switching losses of power semiconductors by almost 40%; immunity towards variation or unbalance in mains 3-Phase voltages or absence of one of the phases; wide mains voltage range: 320VAC to 575 VAC; very l

4、ow conducted common-mode EMI/RFI; very high efficiency of the order of 97.5%, say, for power levels of 10 KW and input line voltage of 400 VAC and short circuit immunity to failure of control circuit. The paper describes the Vienna Rectifiers power stage and control techniques, with particular empha

5、sis on modular construction. What is proposed in this paper is a new approach of employing Fuzzy Logic for building controller for Vienna Rectifier DCB Modules for 3-Phase AC to DC power conversion. 2.0 OverviewIn the past decade, there is growing awareness about line pollution and deteriorating pow

6、er factor due to all pervading inductive and non-linear loads. Utilities are as much concerned as the users. Passive power factor correction techniques are neither convenient nor economical; they need bulky components and are not adaptive to changing needs. Although many solutions were offered for 1

7、-Phase power factor correction, 3-Phase active power factor correction was seldom considered. As all high power equipments derive electrical power from 3-Phase mains, incorporating an active 3-Phase PFC front end can contribute significantly in improving overall power factor and reducing line pollut

8、ion.In addition to lowering power bill to the consumers, improved power factor also contributes towards conservation of energy and helps in reducing air pollution, by virtue of less fossil fuel required for generating same amount of electrical power. Other resultant effects are lower I2R losses, ste

9、adier terminal Voltages, released system capacity and reduced cable & switchgear sizes. Active PFC front ends also help meet the IEEE 519-92, IEC-555 and European EN 61000-3-2 standards for allowable harmonic contents of mains.2.1 Advantages Although there are some passive and active 3-Phase PFC sol

10、utions, Vienna Rectifier is unique by virtue of its embodiment of several advantages:1. It is a 3-Phase, three level PWM rectifier, utilizing three MOSFETS, with controlled output Voltage; three wire input, not requiring any connection to Neutral. 2. It is a dual boost type PFC with continuous sinus

11、oidal input current and unidirectional power flow3. It needs only three active switches, i.e. MOSFETS 4. It is Operational even in presence of unbalanced mains or only two phases. 5. Total switching losses are reduced by a factor of six, assuming switching frequency below 50 KHz.6. Any malfunction i

12、n control circuit does not manifest itself in short circuit of output or PFC front end.7. Sinusoidal input currents with Power Factor = 0.997, THD 97% are obtainable with current designs.As can be seen, Vienna Rectifier is the 3-Phase PFC solution that needs to be fully exploited. Readymade Vienna P

13、ower Semiconductor modules, embodying MOSFETS+ FREDS to make a stand alone Direct Copper Bonded Power Circuit, make it quite convenient and user-friendly. Powerful, yet inexpensive, microcomputers and DSPs make it attractive to design compact controllers for the Vienna Rectifiers. A new approach of

14、employing Fuzzy Logic for building embedded controller for Vienna rectifier for 3-Phase AC to DC power conversion is proposed here.3.0 ApplicationsA large number of industrial, telecom and computing equipments now use 3-Phase mains power. Salient amongst them are:1. A.C. and D.C Drives 2. Telecommun

15、ication Power Supplies3. Uninterruptible Power Supplies4. Air Conditioning Units5. Large Computer Installations6. Power supplies for all industrial uses such as welding, surface treating, motion control, large appliances and process control7. R.F. Transmitters and Radar Transmitters and repeater sta

16、tions8. Regulated and tracking +350V and 350VDC, for high power bidirectional servo amplifiers for driving heavy-duty critical loads such as Antenna Tracking and Positioning systems.All the above and many more such systems are good candidates for using Vienna Rectifiers for achieving performance imp

17、rovements as per the advantages listed in 2.1. 4.0 Vienna Rectifier4.1 Modus Operandi Vienna Rectifier as shown in Figure 1, was originally developed at the Technical University Vienna. It comprises a semiconductor switch, say, a MOSFET in each phase leg of a 3-Phase diode bridge. By adjusting the w

18、idth of the pulse that turns ON the MOSFET, corresponding line current is forced to be sinusoidal and in phase with the Voltage. When the MOSFET is turned ON the corresponding phase is connected, via the line inductor, to the center point between the two output capacitors. The phase current rises, t

19、hrough the MOSFET, during that pulse period, charging the capacitor. When the MOSFET is turned off, current tapers through the diode half bridge （upper or lower depending on direction of the current flow）. 4.2 Objective of Vienna RectifierIt is a highly efficient method of high current, 3-Phase AC t

20、o DC conversion and is particularly attractive for achieving unity power factor operation. In figure-1 ACR, ACY and ACB are 440V, 50Hz, 3-Phase sinusoidal line Voltages. -Vdc and +Vdc are the DC outputs connected to load. There are three semiconductor switches, corresponding to each phase T1, T2 and

21、 T3. These are switched continuously at around 25 KHz. The duty Figure 1 3-Phase Vienna Rectifier ConfigurationCycle of the pwm switching is so programmed that the current drawn from each phase is sinusoidal and in phase with the corresponding line Voltage, thus ensuring near unity power factor and

22、minimum total harmonic distortion. 4.3 Description In Vienna Rectifier configuration, as shown in figure-1, the output capacitor is split in two parts as two equal value capacitors, C1 and C2, connected in series. Across the output capacitors the Vdc and +Vdc are developed as 3-Phase peak detected o

23、utputs. A switch for each phase is connected, such that when “ON”, it connects the line phase to the center node of C1 and C2 through a series inductance. For a short switching period, （assuming 10 microseconds）, the capacitors charge linearly. This offsets -Vdc and +Vdc. The offset depends on the c

24、orresponding phase voltage and the switch “ON” time duration. The common node of C1 and C2 will have Voltage with triangular wave shape, having three times the mains frequency and its amplitude will be one quarter of the phase voltage. Figure 2 3-Phase line voltages red, yellow and blue with 12 time

25、 segments From 0 through 11 4.4 Vienna Rectifier ModulesLooking at Figure 1, it becomes apparent that if one were to assemble the entire 3-Phase Vienna Rectifier PFC circuit using discrete components, many different power semiconductors have to be connected together. This is not only inconvenient an

26、d costly, but also involves a degree of variation in performance from unit to unit. The lead inductances and parasitic capacitance may tend to oscillate, making its operation at high enough switching frequency a task by itself.Fortunately, readymade Vienna Rectifier power modules are available in DC

27、B （Direct Copper Bonding） ceramic base plate. These have a number of useful attributes:1. These modules have isolation voltage of 3600 Volts AC, ensuring personal and equipment safety and are U/L recognized. There is no need for external isolation. 2. Extremely low package inductance, facilitating h

28、igh speed switching3. Easy to mount on a printed circuit board for either wave soldering or manual soldering4. Kelvin source for reliable driver connections for the MOSFETS5. The MOSFET, built using HDMOS process has low RDS（on） and RGint and low RthJS and low input and output capacitances and low g

29、ate charge and rise fall times for low conduction and switching losses6. FREDS （Fast Recovery Epitaxial Diodes） have low VF and extremely low trr 7. Consistent and predictable performance from unit to unit4.5 Advantages of DCBThe Direct Copper Bonded substrates have a number of very attractive featu

30、res as given below:1. They have very good mechanical strength, hold stable shape with good adhesion and are corrosion resistant2. They have very good thermal conductivity, enhancing heat dissipation to heat sink. This allows very close packaging of chips, further reducing lead inductances and transl

31、ating more power per unit volume.3. Very good thermal cycling capability, giving reliable performance over many years4. The thermal expansion coefficient is close to that of silicon so no interface layers are required5. They feature good heat spreading thus leaving no hot spots during actual operati