Small Power Invetrer Type Induction Heating Power

Industrial heating occupies a seat on an important position in the modern industrialprocessing technology. In the production of many products，for example， the processof forging metal and plastic products，the heating process is necessary. Usually，theburning of combustible material，which can generate heat so as to achieve the purposeof heating on the heated object，is used in the traditional heating mode of production.Although these heating methods are widely used in various fields，but there are a lot ofproblems about them, such as space， low efficiency and serious pollution of theenvironment during the heating process. Of course， in modern industry， heating byelectric is also very extensive， but it is a contact heating that will cause the metaloxidized and result in uneven heating，ect.，The generation of new heating method isinevitable in such circumstances.This new way of heating is induction heating, belonging non-contact heating filed.The induction heating, which will not cause the metal oxidized, hates the workpiece byusing high-frequency electric or magnetic field of it. It is able to satisfy therequirements of the high efficiency of modern industrial production. At the same time,the induction heating, which has great advantage to save energy, reduce industrialenvironmental pollution and destruction, has a very broad market prospects.The electromagnetic induction principle have been earliest used in motors,generators and transformers, but the conductor in an alternating magnetic field will notonly produce the induced current, but also generate heat. People treat this hate as loss ofenergy and leave no stone unturned to reduce this heat. Late19th century, scientiststruly appreciated the value of its application after the in-depth discussion and researchon the eddy current effect. The theoretical basis of the induction heating was slowlybuilt up. China began to use the induction heating technology in industrial production atearly1950s and began to work on the development of the Medium Frequency PowerSupply at the end of1960s. China’s first Medium Frequency Power Supply was born inZhejiang University, and has been widely used in production. In the1980s, super audiopower (50kW/50kHz) was developed successfully; in the1990s, the current IGBTinduction heating power(50kW/50kHz) and the MOSFET induction heating power(30kW/300kHz) were put into production.With the advent of the thyristor, the modern power electronics began rapiddevelopment with solid-state semiconductor devices as the core. Later, a new type ofshutdown of electronic component, such as the MOS thyristor, insulated gate bipolartransistors (IGBT), static induction transistor, MOSFET field-effect transistors, etc,rised and was widespread used. It set off another a revolution in the field of highfrequency induction heating. At present, Induction heating technology is developingtoward the greater power and the higher frequency field. In the near future, theinduction heating power supply will be computerized, automated and fully equipped.This paper design is small power inverter type induction heating power supply.The working principle of the inverter power supply is to change alternating current of220V to direct current by the means of rectification circuit and filter circuit, then inputto the main circuit of inverter. Under the function of pulse of Control circuit, the fieldeffect transistor MOSFET in the main circuit of inverter conduction or close accordingto the certain frequencies. Then Output must frequency of alternating current. Thisalternating current must be changed by the transformer to suitable voltage and current.Then input to the load circuit. The parameters of induction heating power in this paperis: Output oscillation frequency:=100~250kHz; Output oscillating current: I2=100~200A; Output oscillation power: P2=4KVA; Efficiency: η=80%; Load durationfactor: FSe＝50％; Cooling water requirements:0.2MPa-5L/min.Because the induction heating power supply designed in this thesis has higherfrequency, requires conducting switches frequently, and needs to make the current never turned off, I chose the series resonant inverter structure. The field-effect transistorMOSFET is chosen as a power switching device because its many advantages, such assmaller drive power, faster switching speed, higher operating frequency, better thermalstability and better anti-jamming capability, suitable for smaller power occasions.Calculation according to the given design parameters shows that a pair of ferrite coremodels for the EE55was used for the transformer. Its primary side turns is31, with35diameter of0.41mm enameled wire parallel wound; and its secondary side turns is two,using four parallel hollow brass tubes, whose outer radius is8.69mm while the innerradius is8.03mm. This can avoid the skin effect effectively and reduce the temperatureof the output coil in time. The main circuit includes the buffer starting circuit, the filtercircuit and the MOSFET field effect transistor inverter main circuit. The inductionheating power supply designed in this thesis is low-power, so I chose the single-phasecontrolled rectifier circuit. After processing of filter circuit, the rectified un-smoothvoltage waveform can become a smooth DC with310V voltage that can be supplied forinverter main circuit. It is worth mentioning that the buffer circuit, which can avoid thesurge current producing at the closing moments causing damage to the individualcapacitors in the circuit, is set in the circuit. Turning on the power, the current limitingresistor will be shorted to prevent power loss after the inverter main circuit worksproperly. The buffer time is very short. Three MOSFET taken in the inverter maincircuit are paralleled as a bridge arm switch tube, which can increase the power outputcapacity. At the same time, capacitance and resistance are paralleled at both ends of theswitch in order to avoid the instantaneous voltage is too large to damage it.Control circuit is the heart of the Induction heating power. Its affect is to producepulse providing to the driving circuit, making the field effect transistor MOSFETconduction or close. The pulse is produced by the KA3525of the pulse widthmodulator. In this process, Simultaneous tracking load loop is very important. In orderto prevent load characteristics caused by the resonance frequency drift. In this circuit,current feedback circuit and output power adjustment are necessary. Through changing the pulse frequency to adjust Output power. On the other hand, current transformerreceive current signal to regulate pulse frequency. The most important thing is the maincontrol circuit equipped with dead time in order to avoid shoot through of the fieldeffect transistor MOSFET. There are many protection circuits in the control circuit tomake sure the Induction heating power work stably. Of course, control circuitincludes of power circuit、 start and show circuit to ensure the basic functions of thecircuit.In the last, we perform an experiment to the Induction heating power. During theexperiment,we measured the triggering pulse waveform of KA3525、MOSFET andthe output voltage waveform of transformer under different frequency. Through theanalysis of the waves, proved the power circuits designed in this paper meet to thedesign requirements.