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Dart Profis - Richie Burnett - "Prince of Wales"Richard „Richie“ Burnett (* 7. Februar in Cwmparc, Rhondda) ist ein walisischer Dartspieler. wurde er Weltmeister der BDO gegen Raymond van. Marcel hat diesen Pin entdeckt. Entdecke (und sammle) deine eigenen Pins bei Pinterest. Finden Sie perfekte Stock-Fotos zum Thema Richie Burnett sowie redaktionelle Newsbilder von Getty Images. Wählen Sie aus erstklassigen Inhalten zum.
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The work coil is made to resonate at the intended operating frequency by means of a capacitor placed in parallel with it.
The parallel resonance also magnifies the current through the work coil, far higher than the output current capability of the inverter alone.
The inverter sees a sinusoidal load current. However, in this case it only has to carry the part of the load current that actually does real work.
The inverter does not have to carry the full circulating current in the work coil. This is very significant since power factors in induction heating applications are typically low.
This property of the parallel resonant circuit can make a tenfold reduction in the current that must be supported by the inverter and the wires connecting it to the work coil.
Conduction losses are typically proportional to current squared, so a tenfold reduction in load current represents a significant saving in conduction losses in the inverter and associated wiring.
This means that the work coil can be placed at a location remote from the inverter without incurring massive losses in the feed wires.
Work coils using this technique often consist of only a few turns of a thick copper conductor but with large currents of many hundreds or thousands of amps flowing.
This is necessary to get the required Ampere turns to do the induction heating. Water cooling is common for all but the smallest of systems. This is needed to remove excess heat generated by the passage of the large high frequency current through the work coil and its associated tank capacitor.
In the parallel resonant tank circuit the work coil can be thought of as an inductive load with a "power factor correction" capacitor connected across it.
The PFC capacitor provides reactive current flow equal and opposite to the large inductive current drawn by the work coil. The key thing to remember is that this huge current is localised to the work coil and its capacitor, and merely represents reactive power sloshing back-and-forth between the two.
Therefore the only real current flow from the inverter is the relatively small amount required to overcome losses in the "PFC" capacitor and the work coil.
There is always some loss in this tank circuit due to dielectric loss in the capacitor and skin effect causing resistive losses in the capacitor and work coil.
Therefore a small current is always drawn from the inverter even with no workpiece present. When a lossy workpiece is inserted into the work coil, this damps the parallel resonant circuit by introducing a further loss into the system.
Therefore the current drawn by the parallel resonant tank circuit increases when a workpiece is entered into the coil. Or simply "Matching".
This refers to the electronics that sits between the source of high frequency power and the work coil we are using for heating.
However this can be contrasted with the inverter that generates the high frequency power. The inverter generally works better and the design is somewhat easier if it operates at fairly high voltage but a low current.
Typically problems are encountered in power electronics when we try to switch large currents on and off in very short times.
The comparatively low currents make the inverter less sensitive to layout issues and stray inductance. We can think of the tank circuit incorporating the work coil Lw and its capacitor Cw as a parallel resonant circuit.
This has a resistance R due to the lossy workpiece coupled into the work coil due to the magnetic coupling between the two conductors.
See the schematic opposite. In practice the resistance of the work coil, the resistance of the tank capacitor, and the reflected resistance of the workpiece all introduce a loss into the tank circuit and damp the resonance.
Therefore it is useful to combine all of these losses into a single "loss resistance. This resistance represents the only component that can consume real power, and therefore we can think of this loss resistance as the load that we are trying to drive power into in an efficient manner.
When driven at resonance the current drawn by the tank capacitor and the work coil are equal in magnitude and opposite in phase and therefore cancel each other out as far as the source of power is concerned.
This means that the only load seen by the power source at the resonant frequency is the loss resistance across the tank circuit.
Note that, when driven either side of the resonant frequency, there is an additional "out-of-phase" component to the current caused by incomplete cancellation of the work coil current and the tank capacitor current.
This reactive current increases the total magnitude of the current being drawn from the source but does not contribute to any useful heating in the workpiece.
The job of the matching network is simply to transform this relatively large loss resistance across the tank circuit down to a lower value that better suits the inverter attempting to drive it.
There are many different ways to achieve this impedance transformation including tapping the work coil, using a ferrite transformer, a capacitive divider in place of the tank capacitor, or a matching circuit such as an L-match network.
In the case of an L-match network it can transform the relatively high load resistance of the tank circuit down to something around 10 ohms which better suits the inverter.
This figure is typical to allow the inverter to run from several hundred volts whilst keeping currents down to a medium level so that standard switch-mode MOSFETs can be used to perform the switching operation.
The L-match network consists of components Lm and Cm shown opposite. The L-match network has several highly desirable properties in this application.
The inductor at the input to the L-match network presents a progressively rising inductive reactance to all frequencies higher than the resonant frequency of the tank circuit.
This is very important when the work coil is to be fed from a voltage-source inverter that generates a squarewave voltage output. Here is an explanation of why this is so….
The squarewave voltage generated by most half-bridge and full-bridge circuits is rich in high frequency harmonics as well as the wanted fundamental frequency.
Direct connection of such a voltage source to a parallel resonant circuit would cause excessive currents to flow at all harmonics of the drive frequency!
This is because the tank capacitor in the parallel resonant circuit would present a progressively lower capacitive reactance to increasing frequencies.
This is potentially very damaging to a voltage-source inverter. It results in large current spikes at the switching transitions as the inverter tries to rapidly charge and discharge the tank capacitor on rising and falling edges of the squarewave.
The inclusion of the L-match network between the inverter and the tank circuit negates this problem. Now the output of the inverter sees the inductive reactance of Lm in the matching network first, and all harmonics of the drive waveform see a gradually rising inductive impedance.
This means that maximum current flows at the intended frequency only and little harmonic current flows, making the inverter load current into a smooth waveform.
Finally, with correct tuning the L-match network is able to provide a slight inductive load to the inverter. This significantly reduces turn-on switching losses due to device output capacitance in MOSFETs operated at high voltages.
The overall result is less heating in the semiconductors and increased lifetime. In summary, the inclusion of an L-match network between the inverter and the parallel resonant tank circuit achieves two things.
Looking at the previous schematic above we can see that the capacitor in the matching network Cm and the tank capacitor Cw are both in parallel.
In practice both of these functions are usually accomplished by a single purpose built power capacitor.
Most of its capacitance can be thought of as being in parallel resonance with the work coil, with a small amount providing the impedance matching action with the matching inductor Lm.
Combing these two capacitances into one leads us to arrive at the LCLR model for the work coil arrangement, which is commonly used in industry for induction heating.
This arrangement incorporates the work coil into a parallel resonant circuit and uses the L-match network between the tank circuit and the inverter.
The matching network is used to make the tank circuit appear as a more suitable load to the inverter, and its derivation is discussed in the section above.
Another advantage of the LCLR work coil arrangement is that it does not require a high-frequency transformer to provide the impedance matching function.
Ferrite transformers capable of handling several kilowatts are large, heavy and quite expensive. In addition to this, the transformer must be cooled to remove excess heat generated by the high currents flowing in its conductors.
The incorporation of the L-match network into the LCLR work coil arrangement removes the necessity of a transformer to match the inverter to the work coil, saving cost and simplifying the design.
However, the designer should appreciate that a isolating transformer may still be required between the inverter and the input to the LCLR work coil arrangement if electrical isolation is necessary from the mains supply.
This depends whether isolation is important, and whether the main PSU in the induction heater already provides sufficient electrical isolation to meet these safety requirements.
It is fed from a smoothed DC supply with decoupling capacitor across the rails to support the AC current demands of the inverter. However, it should be realised that the quality and regulation of the power supply for induction heating applications is not critical.
Full-wave rectified but un-smoothed mains can work as well as smoothed and regulated DC when it comes to heating metal, but peak currents are higher for the same average heating power.
There are many arguments for keeping the size of the DC bus capacitor down to a minimum. In particular it improves the power factor of current drawn from the mains supply via a rectifier, and it also minimises stored energy in case of fault conditions within the inverter.
The DC-blocking capacitor is used merely to stop the DC output from the half-bridge inverter from causing current flow through the work coil.
It is sized sufficiently large that it does not take part in the impedance matching, and does not adversely effect the operation of the LCLR work coil arrangement.
In high power designs it is common to use a full-bridge H-bridge of 4 or more switching devices. In such designs the matching inductance is usually split equally between the two bridge legs so that the drive voltage waveforms are balanced with respect to ground.
The DC-blocking capacitor can also be eliminated if current mode control is used to ensure that no net DC flows between the bridge legs.
If both legs of the H-bridge can be controlled independently then there is scope for controlling power throughput using phase-shift control.
See point 6 in the section below about "Power control methods" for further details. At still higher powers it is possible to use several seperate inverters effectively connected in parallel to meet the high load-current demands.
However, the seperate inverters are not directly tied in parallel at the output terminals of their H-bridges. Each of the distributed inverters is connected to the remote work coil via its own pair of matching inductors which ensure that the total load is spread evenly among all of the inverters.
These matching inductors also provide a number of additional benefits when inverters are paralleled in this way. Richie Burnett believes his darkest days are behind him as he bids to return to the top echelons of professional….
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Retrieved 15 December Archived from the original on 31 December Retrieved 21 December Archived from the original on 6 February Retrieved 3 February Retrieved 8 June Archived from the original on 10 June Retrieved 9 June Retrieved 9 December Archived from the original on 11 September Retrieved 25 October Archived from the original on 28 December Retrieved 14 September Retrieved 7 December Retrieved 8 December Retrieved 1 DecemberThis can be contrasted with the situation that would occur if the inverter were detuned on the low side of the work coil's Sunmaker Auszahlung frequency. Celebrity personalities from the worlds of sport, media, fashion, business, politics and entertainment. However, the control electronics now 20 Ab not need to track the resonant frequency so closely since the diminished Q gives a load current that shifts phase in a more Lotto6aus 49 manner. Richard „Richie“ Burnett ist ein walisischer Dartspieler. wurde er Weltmeister der BDO gegen Raymond van Barneveld mit Im folgenden Jahr verlor er mit das Finale gegen Steve Beaton. trat er erneut im Finale gegen Raymond van. Richard „Richie“ Burnett (* 7. Februar in Cwmparc, Rhondda) ist ein walisischer Dartspieler. wurde er Weltmeister der BDO gegen Raymond van. Richie Burnett wurde am 7. Februar in Cwmparc, Wales geboren. Gegenwärtig spielt Richie mit Darts der Marke Red Dragon. Der Waliser Richie Burnett wurde Weltmeister bei der BDO, spielt aber seit langer Zeit bei der PDC.