逆变器外文文献及翻译.docx

1、逆变器外文文献及翻译Inverter1 IntroductionAn inverter is an electrical device that converts direct current (DC) to alternating current (AC); the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits.Solid-state inverters have no mov

2、ing parts and are used in a wide range of applications, from small switching power supplies in computers, to large electric utility high-voltage direct current applications that transport bulk power. Inverters are commonly used to supply AC power from DC sources such as solar panels or batteries.The

3、re are two main types of inverter. The output of a modified sine wave inverter is similar to a square wave output except that the output goes to zero volts for a time before switching positive or negative. It is simple and low cost and is compatible with most electronic devices, except for sensitive

4、 or specialized equipment, for example certain laser printers. A pure sine wave inverter produces a nearly perfect sine wave output (3% total harmonic distortion) that is essentially the same as utility-supplied grid power. Thus it is compatible with all AC electronic devices. This is the type used

5、in grid-tie inverters. Its design is more complex, and costs 5 or 10 times more per unit power The electrical inverter is a high-power electronic oscillator. It is so named because early mechanical AC to DC converters were made to work in reverse, and thus were inverted, to convert DC to AC.The inve

6、rter performs the opposite function of a rectifier.2 Applications2.1 DC power source utilizationAn inverter converts the DC electricity from sources such as batteries, solar panels, or fuel cells to AC electricity. The electricity can be at any required voltage; in particular it can operate AC equip

7、ment designed for mains operation, or rectified to produce DC at any desired voltageGrid tie inverters can feed energy back into the distribution network because they produce alternating current with the same wave shape and frequency as supplied by the distribution system. They can also switch off a

8、utomatically in the event of a blackout.Micro-inverters convert direct current from individual solar panels into alternating current for the electric grid. They are grid tie designs by default. 2.2 Uninterruptible power suppliesAn uninterruptible power supply (UPS) uses batteries and an inverter to

9、supply AC power when main power is not available. When main power is restored, a rectifier supplies DC power to recharge the batteries.2.3 Induction heatingInverters convert low frequency main AC power to a higher frequency for use in induction heating. To do this, AC power is first rectified to pro

10、vide DC power. The inverter then changes the DC power to high frequency AC power. 2.4 HVDC power transmissionWith HVDC power transmission, AC power is rectified and high voltage DC power is transmitted to another location. At the receiving location, an inverter in a static inverter plant converts th

11、e power back to AC.2.5 Variable-frequency drivesA variable-frequency drive controls the operating speed of an AC motor by controlling the frequency and voltage of the power supplied to the motor. An inverter provides the controlled power. In most cases, the variable-frequency drive includes a rectif

12、ier so that DC power for the inverter can be provided from main AC power. Since an inverter is the key component, variable-frequency drives are sometimes called inverter drives or just inverters.2.6 Electric vehicle drivesAdjustable speed motor control inverters are currently used to power the tract

13、ion motors in some electric and diesel-electric rail vehicles as well as some battery electric vehicles and hybrid electric highway vehicles such as the Toyota Prius and Fisker Karma. Various improvements in inverter technology are being developed specifically for electric vehicle applications.2 In

14、vehicles with regenerative braking, the inverter also takes power from the motor (now acting as a generator) and stores it in the batteries. 2.7 The general caseA transformer allows AC power to be converted to any desired voltage, but at the same frequency. Inverters, plus rectifiers for DC, can be

15、designed to convert from any voltage, AC or DC, to any other voltage, also AC or DC, at any desired frequency. The output power can never exceed the input power, but efficiencies can be high, with a small proportion of the power dissipated as waste heat. 3 Circuit description 3.1 Basic designs In on

16、e simple inverter circuit, DC power is connected to a transformer through the centre tap of the primary winding. A switch is rapidly switched back and forth to allow current to flow back to the DC source following two alternate paths through one end of the primary winding and then the other. The alt

17、ernation of the direction of current in the primary winding of the transformer produces alternating current (AC) in the secondary circuit. The electromechanical version of the switching device includes two stationary contacts and a spring supported moving contact. The spring holds the movable contac

18、t against one of the stationary contacts and an electromagnet pulls the movable contact to the opposite stationary contact. The current in the electromagnet is interrupted by the action of the switch so that the switch continually switches rapidly back and forth. This type of electromechanical inver

19、ter switch, called a vibrator or buzzer, was once used in vacuum tube automobile radios. A similar mechanism has been used in door bells, buzzers and tattoo guns.As they became available with adequate power ratings, transistors and various other types of semiconductor switches have been incorporated

20、 into inverter circuit designs3.2 Output waveformsThe switch in the simple inverter described above, when not coupled to an output transformer, produces a square voltage waveform due to its simple off and on nature as opposed to the sinusoidal waveform that is the usual waveform of an AC power suppl

21、y. Using Fourier analysis, periodic waveforms are represented as the sum of an infinite series of sine waves. The sine wave that has the same frequency as the original waveform is called the fundamental component. The other sine waves, called harmonics, that are included in the series have frequenci

22、es that are integral multiples of the fundamental frequency.The quality of output waveform that is needed from an inverter depends on the characteristics of the connected load. Some loads need a nearly perfect sine wave voltage supply in order to work properly. Other loads may work quite well with a

23、 square wave voltage. 3.3 Three phase invertersThree-phase inverters are used for variable-frequency drive applications and for high power applications such as HVDC power transmission. A basic three-phase inverter consists of three single-phase inverter switches each connected to one of the three lo

24、ad terminals. For the most basic control scheme, the operation of the three switches is coordinated so that one switch operates at each 60 degree point of the fundamental output waveform. This creates a line-to-line output waveform that has six steps. The six-step waveform has a zero-voltage step be

25、tween the positive and negative sections of the square-wave such that the harmonics that are multiples of three are eliminated as described above. When carrier-based PWM techniques are applied to six-step waveforms, the basic overall shape, or envelope, of the waveform is retained so that the 3rd ha

26、rmonic and its multiples are cancelled4 History4.1 Early invertersFrom the late nineteenth century through the middle of the twentieth century, DC-to-AC power conversion was accomplished using rotary converters or motor-generator sets (M-G sets). In the early twentieth century, vacuum tubes and gas

27、filled tubes began to be used as switches in inverter circuits. The most widely used type of tube was the thyratron.The origins of electromechanical inverters explain the source of the term inverter. Early AC-to-DC converters used an induction or synchronous AC motor direct-connected to a generator

28、(dynamo) so that the generators commutator reversed its connections at exactly the right moments to produce DC. A later development is the synchronous converter, in which the motor and generator windings are combined into one armature, with slip rings at one end and a commutator at the other and onl

29、y one field frame. The result with either is AC-in, DC-out. With an M-G set, the DC can be considered to be separately generated from the AC; with a synchronous converter, in a certain sense it can be considered to be mechanically rectified AC. Given the right auxiliary and control equipment, an M-G

30、 set or rotary converter can be run backwards, converting DC to AC. Hence an inverter is an inverted converter. 4.2 Controlled rectifier invertersSince early transistors were not available with sufficient voltage and current ratings for most inverter applications, it was the 1957 introduction of the

31、 thyristor or silicon-controlled rectifier (SCR) that initiated the transition to solid state inverter circuits.The commutation requirements of SCRs are a key consideration in SCR circuit designs. SCRs do not turn off or commutate automatically when the gate control signal is shut off. They only tur

32、n off when the forward current is reduced to below the minimum holding current, which varies with each kind of SCR, through some external process. For SCRs connected to an AC power source, commutation occurs naturally every time the polarity of the source voltage reverses. SCRs connected to a DC pow

33、er source usually require a means of forced commutation that forces the current to zero when commutation is required. The least complicated SCR circuits employ natural commutation rather than forced commutation. With the addition of forced commutation circuits, SCRs have been used in the types of inverter circuits de