【文章內(nèi)容簡(jiǎn)介】 he use of appropriate transformers, switching, and control inverters have no moving parts and are used in a wide range of applications, from small switching power supplies in puters, to large electric utility highvoltage direct current applications that transport bulk are monly used to supply AC power from DC sources such as solar panels or are two main types of 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 is simple and low cost and is patible with most electronic devices, except for sensitive or specialized equipment, for example certain laser pure sine wave inverter produces a nearly perfect sine wave output( Basic designsIn one simple inverter circuit, DC power is connected to a transformer through the centre tap of the primary 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 alternation of the direction of current in the primary winding of the transformer produces alternating current(AC)in the secondary electromechanical version of the switching device includes two stationary contacts and a spring supported moving spring holds the movable contact against one of the stationary contacts and an electromagnet pulls the movable contact to the opposite stationary current in the electromagnet is interrupted by the action of the switch so that the switch continually switches rapidly back and type of electromechanical inverter switch, called a vibrator or buzzer, was once used in vacuum tube automobile similar mechanism has been used in door bells, buzzers and tattoo they became available with adequate power ratings, transistors and various other types of semiconductor switches have been incorporated into inverter circuit designs Output waveforms The 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 Fourier analysis, periodic waveforms are represented as the sum of an infinite series of sine sine wave that has the same frequency as the original waveform is called the fundamental other sine waves, called harmonics, that are included in the series have frequencies that are integral multiples of the fundamental quality of output waveform that is needed from an inverter depends on the characteristics of the connected loads need a nearly perfect sine wave voltage supply in order to work loads may work quite well with a square wave Three phase inverters Threephase inverters are used for variablefrequency drive applications and for high power applications such as HVDC power basic threephase inverter consists of three singlephase inverter switches each connected to one of the three load 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 creates a linetoline output waveform that has six sixstep waveform has a zerovoltage step between the positive and negative sections of the squarewave such that the harmonics that are multiples of three are eliminated as described carrierbased PWM techniques are applied to sixstep waveforms, the basic overall shape, or envelope, of the waveform is retained so that the 3rd harmonic and its multiples are cancelled History Early inverters From the late nineteenth century through the middle of the twentieth century, DCtoAC power conversion was acplished using rotary converters or motorgenerator sets(MG sets).In the early twentieth century, vacuum tubes and gas filled tubes began to be used as switches in inverter most widely used type of tube was the origins of electromechanical inverters explain the source of the term ACtoDC converters used an induction or synchronous AC motor directconnected to a generator(dynamo)so that the generator39。s mutator reversed its connections at exactly the right moments to produce later development is the synchronous converter, in which the motor and generator windings are bined into one armature, with slip rings at one end and a mutator at the other and only one field result with either is ACin, an MG 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 MG set or rotary converter can be “run backwards”, converting DC to an inverter is an inverted Controlled rectifier inverters Since early transistors were not available with sufficient voltage and current ratings for most inverter applications, it was the 1957 introduction of the thyristor or siliconcontrolled rectifier(SCR)that initiated the transition to solid state inverter mutation requirements of SCRs are a key consideration in SCR circuit do not turn off or mutate automatically when the gate control signal is shut only turn off when the forward current is reduced to below the minimum holding current, which varies with each kind of SCR, through some external SCRs connected to an AC power source, mutation occurs naturally every time the polarity of the source voltage connected to a DC power source usually require a means of forced mutation that forces the current to zero when mutation is least plicated SCR circuits employ natural mutation rather than forced the addition of forced mutation circuits, SCRs have been used in the types of inverter circuits described applications where inverters transfer power from a DC power source to an AC power source, it is possible to use ACtoDC controlled rectifier circuits operating in the inversion the inversion mode, a controlled rectifier circuit operates as a line mutated type of opera