WO2003090003A1

WO2003090003A1 - Universal variable-frequency resonant power supply

Info

Publication number: WO2003090003A1
Application number: PCT/US2003/010432
Authority: WO
Inventors: Sergiu Bucar
Original assignee: Olimex Group, Inc.
Priority date: 2002-04-17
Filing date: 2003-04-04
Publication date: 2003-10-30
Also published as: AU2003224843A1

Abstract

A novel power supply (100) provides power to various loads such as an electrolytic bath (200) for performing microarc oxidation, an arc welder (300) any other power-consuming (400), device or tool. The power supply (100) contains output circuitry having at least one adjustable element (106). The output circuitry forms, together with the load, a closed resonant circuit (108) providing a complete path for operating current of the load during the operation carried out by the load. The adjustable element (132) is used to tune the closed circuit to resonance (108) during the operation carried out by the load.

Description

UNIVERSAL VARIABLE-FREQUENCY RESONANT POWER SUPPLY

Field of the Invention

The present invention relates to power supplies, and more particularly, to a universal variable-frequency resonant power supply for providing power to various systems, devices, and tools, such as an electrolytic bath, an electric arc welder, an electric plasma generator, etc.

Background of the Invention

Processes performed by power-consuming systems, devices or tools depend on characteristics of respective power supplies. For example, power supplies may be used for supporting microarc oxidation processes that employ electrochemical deposition technique to form a ceramic coating on metals such as aluminum and its alloys.

U.S. patent No. 5,616, 229 describes a power supply supporting a process of forming a ceramic coating on a valve metal selected from the group consisting of aluminum, zirconium, titanium, and alloys of these metals. As illustrated in FIG. 1, the process involves immersing an article 12 made of the valve metal as an electrode in an electrolytic bath 14 comprising an electrolytic liquid 16 of water and a solution of an alkali metal hydroxide. The bath 14 is made of stainless steel and forms a second electrode. Agitation means 15 are provided to stir the electrolyte. The first electrode comprises the article 12 to be coated and conducting means 18 to suspend the article in the electrolytic liquid 16.

A 40,000 V-amp step-up transformer 20 designed to supply up to 1000 V is used as a source of AC voltage of at least 700 V. A capacitor bank 22 and connector elements 24 are provided to complete an electrochemical circuit. An operator control panel 26 is used to control processes in the electrolytic bath 14 arranged behind safety doors 28. A salt-containing feed hopper 30 having a solenoid-operated feed valve 32 is provided for adding salt 34 to the bath 14 during the electrochemical deposition.

After the article is immersed in the electrolytic liquid, an alternating current from the high- voltage source 20 is passed through a surface of the metal to be coated and the opposite electrode causing dielectric break-down, heating, melting and thermal compacting of a hydroxide film formed on the surface of the metal to form a ceramic coating. The composition of the electrolyte is being changed during the coating process by adding the salt 34 to the bath 14 to increase a film formation velocity.

However, conventional power supplies for supporting microarc oxidation processes do not take into account the electrochemical deposition condition. Therefore, conventional microarc oxidation processes are limited with respect to properties of ceramic coatings that can be achieved. For example, the conventional processes cannot provide sufficiently high uniform elasticity of ceramic coatings. Also, other properties of ceramic coatings formed using conventional microarc oxidation processes, such as density, thickness, corrosion resistance and hardness, are not uniform.

In addition, conventional microarc oxidation processes require high- voltage power sources with high power consumption.

Therefore, there exists a need for a power supply for microarc oxidation processes that would make it possible to form ceramic oxide coatings with properties superior to the properties of oxide coatings formed on metal or metal alloy layer employing conventional electrochemical deposition techniques. Also, it would be desirable to provide a power source with low power consumption for microarc oxidation processes.

Further, power supplies are used for electric arc welders used for joining metal workpieces. The arc welder includes a consumable electrode formed of coated rod or stick of metal. The electrode is placed adjacent to the workpieces being welded, and an arc is generated between the electrode and the workpiece. The heat of the arc transfers filler metal from the electrode to the workpiece, and a weld is formed to join the workpieces together.

A power source is electrically connected to the workpiece for generating the desired arc. The power source includes two output terminals, one of which is connected to the welding torch or electrode holder for providing the arc to the workpiece when positioned adjacent thereto. The other terminal is connected to the workpiece to complete a circuit with the power source.

For example, U.S. patent No. 6,091,612 discloses a power supply for arc welders. As shown in FIG. 2, the power supply PS includes a single phase input source 10, filter 12 and a full wave rectifier 14 controlled by a power factor correcting circuit 20 located between the rectifier and a load L, which is a high speed switching converter 30 having terminals 32, 34 for directing current across electrode 40 and workpiece 42 in accordance with a controlled direct-current

(DC) voltage across terminals 32, 34. The arc voltage is sensed by a sensor 50 and compared with a reference voltage in accordance with a signal on line 52 to provide an input voltage command signal in line 54 which controls the duty cycle of a pulse width modulated switching converter 30 to remove the high ripple of the voltage produced by the circuit 20.

However, conventional power supplies for arc welders do not take into account welding conditions. Therefore, physical properties of weld seams formed during arc welding supported by a conventional power supply may be unsatisfactory due to unstable arc. Also, the efficiency of welding supported by a conventional power supply may be low. Further, conventional power supplies for arc welders have high power consumption. Therefore, there is a need for a power supply with low power consumption that would enhance properties of weld seams and improve productivity of welding.

Accordingly, there is a need for a power supply with low power consumption that would improve properties of products produced by various loads, and enhance performed processes. Disclosure of the Invention

The present invention provides a novel power supply for providing power to a load such as an electrolytic bath for performing microarc oxidation, an arc welder or any other power-consuming system, device or tool. The power supply comprises output circuitry having at least one element adjustable for tuning the output circuitry to resonance during an operation carried out by the load. The output circuitry may provide resonance at various frequencies.

Specifically, the output circuitry may form, together with the load, a closed circuit providing a complete path for operating current of the load during the operation carried out by the load. This closed circuit may be an LC resonant circuit. The adjustable element may tune the closed circuit to resonance during the operation carried out by the load. Hence, the adjustable element may be used to control the operation carried out by the load.

For example, this element may be adjusted in accordance with conditions of a process performed by the load, and/or or to synchronize various phases of this process. Also, the adjustable element may be used to maintain a power factor equal to about 100% during the operation carried out by the load.

The output circuitry may support operations of different loads supplied by the power supply circuit. For example, the output circuitry may have separate adjustable elements for providing resonance to support different loads. Multiple closed circuits providing complete paths for operating currents of different loads may be formed by the output circuitry, together with the respective loads.

In implementing embodiments of the present invention, the power supply may include a voltage selector for selecting voltage supplied to the load, and a filter for suppressing noise transferred from the load.

In accordance with one aspect of the present invention, the power supply may provide power to an electrolytic bath. At least one adjustable element may be arranged to tune to resonance a closed circuit providing a complete path for operating current during a microarc oxidation process carried out in the electrolytic bath.

For example, the microarc oxidation process may be carried out to form a ceramic coating on at least one surface of an article made of a material selected from the group consisting of Al, Ti, Mg, Zr, V, W, Zn and their alloys.

In implementing this embodiment of the present invention, the output circuitry of the power supply may include inductive and capacitive elements connected in series and having values selected to achieve the resonance during the microarc oxidation process. The inductive elements may include at least one secondary winding of a transformer having a high level of magnetic leakage. This transformer may be used in the voltage selector. Additional inductance may be connected to the output circuitry to achieve the resonance during the microarc oxidation process. The capacitive elements may include multiple capacitors connectable in parallel to provide a total capacitance value required to achieve the resonance during the microarc oxidation process.

Another aspect of the present invention is a power supply for supplying AC power or DC power to an arc welder. At least one adjustable element may tune to resonance a closed circuit providing a complete path for welding current during an arc welding process carried out by the arc welder. The output circuitry of this power supply may include inductive and capacitive elements having values selected to achieve the resonance during the arc welding process.

In implementing the power supply for supplying AC power, the inductive elements may include at least one secondary winding of the transformer used in the voltage selector and having a high level of magnetic leakage. The capacitive elements may include multiple serially connectable capacitor chains, each of which is composed of multiple capacitors connectable in parallel. Total capacitance value of the capacitive elements may be selected to achieve resonance conditions for the welding current during the arc welding process. In the power supply for providing DC power to an arc welder, the output circuitry may include an inductor and a capacitor. The inductor may be adjusted to achieve resonance conditions for the welding current during the arc welding process. In accordance with a method of the present invention, the following steps are carried out to provide power to a load using a power supply: supplying power to the load to initiate an operation carried out by the load, and adjusting at least one element of the power supply to provide resonance conditions for operating current of the load during the operation.

The element may be adjusted to provide the resonance conditions at various frequencies in accordance with conditions of a process performed by the load. Hence, such an adjustment makes it possible to control the operation carried out by the load. Various objects and features of the present invention will become more readily apparent to those skilled in the art from the following description of a specific embodiment thereof, especially when taken in conjunction with the accompanying drawings.

Brief Description of the Drawings FIG. 1 illustrates a conventional system for forming a ceramic coating on a valve metal.

FIG. 2 illustrates a conventional power supply for arc welding. FIG. 3 is a block diagram of an exemplary power supply of the present invention. FIG. 4 is an exemplary circuit diagram illustrating the power supply of the present invention. Detailed Description of the Invention

In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures and entities are shown in schematic form in order to avoid unnecessarily obscuring the present invention.

A universal variable-frequency resonant power supply of the present invention is configured for providing power to various power-consuming systems, devices or tools. FIG. 3 shows an exemplary power supply 100, in which the present invention may be advantageously employed.

The exemplary power supply 100 operates in a microarc oxidation mode for providing power to an electrolytic bath 200, and in an arc welding mode for providing power to an arc welder 300. However, as one skilled in the art will realize, the power supply of the present invention may operate in multiple additional modes for providing power to various loads 400. For example, the universal power supply of the present invention may be configured to provide power to plasma generators and plasma guns for producing low-temperature plasma, to electroplating systems for electrochemical deposition of a metal or alloy from a suitable electrolyte solution, etc.

The universal variable-frequency resonant power supply 100 comprises an input power source 102, a filter 104, a supply voltage selector 106, a resonant circuit 108 for supporting a microarc oxidation mode of operation, and a resonant circuit 110 for supporting an arc welding mode of operation. Also, a rectifier 112 is coupled to the output terminals of the resonant circuit 110 to supply direct- current (DC) power to the arc welder 300 if a welding arc should be provided with direct current. In addition, the universal power supply 100 may contain multiple resonant circuits 1 14 configurable for supporting particular power- consuming devices 400. The input power source 102 may by a power line that provides input voltages of 110V or 220 V at frequencies of 50-60 Hz. The filter 104 is configured for suppressing noise, such as high-frequency oscillations transferred to the power supply circuitry from power-consuming devices during microarc oxidation or arc welding processes. The supply voltage selector 106 is provided for selecting supply voltage required to support a desired mode of operation.

The resonant circuits 108, 110 and 114 are adjustable to obtain resonance in circuitry including output circuitry of the power supply 100 and a load supplied by the power supply 100 during a process carried out by the load. The load may be any system, device or tool provided with power by the power supply 100.

In particular, the resonant circuits 108, 110 and 114 comprise adjustable inductive and capacitive elements. These elements are included in a closed circuit formed by the load and the output circuitry of the power supply 100 to provide a complete path for operating current of the load supplied by the power supply 100, and are adjusted during a process carried out by the load to obtain resonance in the closed circuit.

For example, adjustable capacitive elements of the resonant circuits 108, 1 10 and 114 may be connected in series with inductive elements of the respective resonant circuits to obtain series resonance in an LC circuit including a load supplied by the power supply 100 during a process carried out by that load.

The total capacitance of the respective resonant circuit may be selected so as to provide the voltage drop across the capacitive elements equal to the voltage drop across the inductive elements during a process carried out by a load supplied by the power supply 100: Ip2πfL = Ip/2πfC, where:

Ip is the value of the operating current, f is the frequency of the input power line, L is the total inductance of the closed circuit formed by the load and the output circuitry of the power supply 100 during a process carried out by the load, and

C is the total capacitance of the closed circuit formed by the load and the output circuitry of the power supply 100 during a process carried out by the load.

The resonance frequency of resonant circuits created by the power supply

100 during particular processes performed by the load is defined by values of inductive and capacitive elements engaged in the resonant circuit selected depending on processes being performed. Hence, the resonance frequency varies depending on conditions of process performed by the load.

MICROARC OXIDATION MODE OF OPERATION

The resonant circuit 108 supports a microarc oxidation process that may be carried out in the electrolytic bath 200. For example, the power supply 100 of the present invention may support a microarc oxidation process for producing an article comprising a metal with a ceramic coating on at least one surface thereof, typically a composite comprising a metal or metal alloy layer with an upper surface and a lower surface and a ceramic coating on the upper and lower surfaces. The ceramic coating is formed by electrochemical deposition in an electrolytic bath on metals selected from the group consisting of Al, Ti, Mg, Zr, V, W, Zn and their alloys

During microarc oxidation, the metal is subject to a high electrical current density while the metal is submerged in the electrolytic bath 200, which contains an electrolytic solution and includes a pair of electrodes 202 and 204 connected to output terminals 116 and 118 of the power supply 100. Voltage potential supplied by the power supply 100 is applied between the electrodes 202 and 204. Due to electrochemical reactions between the metal and the electrolytic solution, an oxide coating is being formed on the surface of the metal.

During the electrochemical deposition of the oxide coating, a closed electrical circuit including output circuitry of the power supply 100 and the electrolytic bath 200 is created. In particular, an operating current flowing between the electrodes 202 and 204 of the electrolytic bath 200 passes through the output circuitry formed inside the power supply 100 between the output terminals 116 and l l8.

Hence, the closed circuit providing a complete path for the operating current during the electrochemical deposition is formed by the electrolytic bath 200 and the output circuitry of the power supply 100. This closed circuit may be considered to be an LC circuit having inductance L equal to the total inductance of the closed circuit and capacitance C equal to the total capacitance of the closed circuit. In accordance with the present invention, during the electrochemical deposition, the closed circuit including the electrolytic bath 200 and the output circuitry of the power supply 100 is tuned to resonance. The resonance may be determined using a measuring instrument, such as an ammeter, or a voltmeter, appropriately connected to the closed circuit. For example, the value of capacitors included in the resonant circuit 108 may be selected to tune the closed circuit to resonance. As described in more detail below, inductors and capacitors of the resonant circuit 108 may be connected during the electrochemical deposition in a series resonant circuit to deliver a resonant voltage several times greater than the input voltage of the resonant circuit 108.

In a resonant circuit including the electrolytic bath 200, a change in the electrochemical deposition condition or electrical parameters of the coating during the microarc oxidation requires the elements of the resonant circuit 108 to be adjusted to maintain the resonance of the closed circuit including the electrolytic bath 200 and the output circuitry of the power supply 100. Hence, the resonant circuit 108 is adjustable depending upon the deposition condition.

Also, parameters of the resonant circuit 108 may be varied during the electrochemical deposition to synchronize different phases of the microarc oxidation process in order to obtain desired properties of the coatings, such as micro-hardness, thickness, porosity, adhesion to substrate, friction coefficient, electrical and corrosion resistance, etc.

The resonance maintained during the microarc oxidation process makes it possible to produce the coatings having high hardness, good adhesion to substrate, high electrical and good corrosion resistance.

During the electrochemical deposition in the electrolytic bath 200, the parameters of the resonant circuit 108 may be adjusted to maintain the power factor of the power supply 100 at a level close to 100%. As a result, the efficiency of the power supply 100 and the efficiency of the electrochemical deposition improve, and the micro-hardness of the coating increases.

The oxide coating formed in accordance with the present invention on such metals as aluminum and aluminum alloys exhibits various properties which are dramatically superior to the properties of oxide coatings formed on aluminum or aluminum alloys employing conventional electrochemical deposition techniques. For example, the ceramic oxide coating formed on aluminum or aluminum alloys exhibits a high degree of uniformity of thickness, an extremely high hardness, high insulating properties and high wear resistance. Typically, the hardness of the ceramic oxide coating formed on aluminum and aluminum alloys is about 1.5 to about 2 times that of the hardness of conventional ceramic oxide coatings formed on aluminum or aluminum alloys. The ceramic oxide coatings can be formed at a very reduced thickness, such as about 10 microns to about 25 microns, e.g., about 15 microns to about 20 microns up to any desired thickness, such as about 150 microns. The ceramic coating also exhibits high insulative properties and can withstand degradation, such as melting or decomposition, at temperatures up to 2,000°C.

Significantly, because of the particular electrochemical deposition technique employed, the properties of the coating are extremely uniform. Thus, ceramic coatings in accordance with the present invention exhibited high uniform elasticity, in that the elasticity of the aluminum substrate or aluminum alloy substrate can be increased by 10 fold. The ceramic coatings in accordance with the present invention also exhibit uniform density, uniform thickness, uniform corrosion resistance and uniform hardness.

The significant advantages of the present invention include ceramic coatings having an extremely high and uniform hardness, such as a hardness of about 1,000 to 1,100 Kg/mm², e.g., a hardness of about 1,050 Kg/mm². The ceramic coating in accordance with the present invention also exhibits superior insulative properties and can be used in high-temperature environments without decomposition or melting. Such electrical insulative properties find particularly utility in various industrial applications. In fact, the uniformity of thickness of the coatings formed in accordance with the present invention is particularly superior to conventional techniques. In accordance with the conventional techniques, the thickness of a ceramic coating can vary by as much as about 20%; whereas, in accordance with the present invention, the thickness of the ceramic coating does not vary by more than 5%. The superior properties in accordance with the present invention lends itself to numerous industrial applications. For example; articles containing ceramic coatings in accordance with the present invention can be employed in forming nonmagnetic substrates for magnetic recording, particularly those employing an aluminum or aluminum alloy layer with ceramic oxide coating on each surface thereof.

The high strength coatings of the present invention render the articles suitable for use in piping. The lack of friction and high hardness of the ceramic coatings in accordance with the present invention render the inventive articles suitable for use in pumps, transformers, engine components such as turbine blades, semiconductor manufacturing, engine housings, pipings, rings, abrasives, ship building, medical implants, food processing, chemical handling equipment and cookware. The significant use of the articles produced in accordance with the present invention is in jet fuel tanks which can be subjected to a higher pretreat temperature without rupturing thereby reducing overall fuel consumption. The ceramic coatings in accordance with the present invention render the composite articles suitable for use in automotive engines, particularly in components which would require high lubrication but, because of the reduced friction of the ceramic coatings of the present invention, such articles can be employed with minimum lubrication.

Articles produced in accordance with the present invention are also useful in fabricating missiles which due to reduced friction, can be employed for longer range targets.

The high hardness and wear resistance of the ceramic coatings render the inventive article suitable for use in magnetic pumps, the articles typically having a ceramic coating with a thickness of about 150 microns.

The articles having ceramic coatings produced by the inventive electrochemical deposition techniques find particular applicability in military hardware, such as structural components for military aircraft and particularly stealth type aircraft since the ceramic coatings have the ability to absorb rather than reflect radar, as well as missiles as previously mentioned.

ARC WELDING MODE OF OPERATION

The resonant circuit 1 10 supports an arc welding mode of operation of the power supply 100 to provide DC and AC power to the arc welder 300. In particular, during an arc welding process carried out by the arc welder 300, elements of the resonant circuit 110 are adjusted to tune to resonance a closed electrical circuit including the arc welder 300 and the output circuitry of the power supply 100.

The arc welder 300 includes a welding electrode 302 attached to an electrode holder. The welding electrode 302 may includes a core wire surrounded by a flux coating, which is usually applied to the core wire by an extrusion process. The flux coating is concentric with the core wire. The welding electrode provides filler metal for welding. A welding arc with a temperature of the order of 6,000°C is generated between the welding electrode 302 and a workpiece 304. As a result of the heat produced by the welding arc, the core wire of the electrode 302 melts and being transferred across the arc to coalesce with the molten metal of the workpiece 304 and form a bond which may be stronger than the workpiece. The flux covering of the electrode 302 melts more slowly than the core wire and a cup is formed at the electrode tip which assists in directing the molten droplets to the required spot.

The weld metal itself, as deposited, has a cast structure. Its composition is determined by the core wire, the flux coating of the electrode 302, and by the amount of pick-up of the workpiece 304 during welding. For example, a deposit of alloy steel no longer has just the properties expected from this alloy due to dilution with the workpiece.

Two connecting leads are required for welding. One lead, called the electrode lead, connects the power supply 100 to the electrode holder; and another lead, called the work or earth lead, connects the power supply 100 to the workpiece 304. The electrode holder provides electrical connection between the power supply lead and the electrode 302, and has insulated handles to avoid electric shocks and accidental arcing.

Both direct and alternating current may be used for arc welding. AC welding machines have several advantages over DC welding machines, among them being a lower cost, higher operating efficiency and negligible maintenance. However, AC welding machines are limited in that they will not satisfactory run many of the non-ferrous types of electrodes.

The power supply 100 has a pair of terminals 120 and 122 for providing alternating current, and a pair of terminals 124 (+) and 126 (-) for supplying direct current. When using alternating current, it does not matter to which terminal the electrode 302 and the workpiece 304 are attached, but when direct current is used more heat is produced at the positive pole with most electrode types.

With the welding of mild steel, it is usual for the workpiece 304 to be connected to the positive terminal 124, and the electrode to be connected to the negative terminal 126. The greater amount of heat generated at the workpiece in this way assists the welding operation, especially when the components have a heavy mass. Also, such a connection assures proper fusion and good penetration.

Most of the non-ferrous and stainless steel electrodes should be connected to the positive terminal 124. This connection provides greater arc stability. When the arc welder 300 is supplied with AC power during a welding operation, the welding current flows through the output circuitry formed between terminals 120 and 122 inside the power supply 100, and the welding arc generated between the electrode 302 and the workpiece 304. When DC power is provided to the arc welder 300 during a welding operation, the welding current passes through the output circuitry of the power supply 100 formed between the terminals 124 and 126, and the welding arc generated between the electrode 302 and the workpiece 304.

Hence, a closed electrical circuit providing a complete path for the welding current is formed during welding. As described in more detail below, capacitive and inductive elements of the resonant circuit 110 are included in this closed electrical circuit to form an LC resonant circuit. During the welding operation, values of these capacitive and inductance elements are being adjusted to tune the closed electrical circuit to resonance so as to provide resonant conditions for welding current flowing across the welding arc. As a result, a steady arc is provided.

Therefore, the resonant power supply 100 provides stable arc welding arc even at a low level of the open-circuit voltage. This is especially important for an AC welding machine, because in AC welders supplied by conventional power supplies, electrodes need a fairly high open-circuit voltage to prevent the arc cutting during welding.

Also, resonant oscillations of electric and magnetic fields produced in the LC circuit provide synchronization of processes taking place during arc welding to further increase operating efficiency, and improve properties of the weld seams. Further, in conventional DC welding machines, the arc, instead of playing steadily one spot, is deflected away from the point of welding due to the influence of surrounding magnetic fields created by welding currents flowing in the workpiece. Due to current resonance conditions provided by the resonant power supply 100 of the present invention, this problem is overcome. Hence, the present invention allows sputtering of metal during arc welding to be substantially reduced.

During the welding process, the power factor of the power supply 100 is maintained at a level of 90-96%. As a result, the power consumption of the power supply 100 in an arc welding mode is about 40% less than the power consumption of conventional power supplies for welding.

EXEMPLARY CIRCUIT DIAGRAM

FIG. 4 shows an exemplary circuit diagram of the resonant power supply

100. A connector X connects the power supply to a power line that may provide input voltages of 110V or 220 V at frequencies of 50-60 Hz. A switch Ql and a contactor may be used for applying the supply voltage to the power supply 100.

The filter 104 composed of inductances LI and L2, and capacitors CI, C2, C3 and C4 is configured for suppressing noise, such as high-frequency oscillations transferred to the power supply circuitry from power-consuming devices during microarc oxidation or arc welding processes.

The supply voltage selector 106 provided for selecting supply voltage required to support a desired mode of operation includes a switch Q2 which enables an operator to serially connect windings W2, W2' and W3, W3' to respective primary windings Wl, Wl' of an adjustable transformer Trl having a core-type magnetic circuit, and secondary windings W4, W4', and W5, W5'. The inductive resistance of the primary windings is selected to limit the open-circuit current to 1-10A depending on input voltage and power dissipation. Distance between the primary and secondary windings may be selected to provide a high level of magnetic leakage. For example, the supply voltage selector 106 may enable the power supply 100 to provide supply voltage of 220V, 380V or 780V at frequencies of 50-60Hz.

The secondary windings W4 and W5 are connected to capacitor chains 132 and 134. The capacitor chain 132 composed of n connected in parallel capacitors 132-1 to 132-n is used in a microarc oxidation mode of operation. Switch Q3 is used for connecting individual capacitors to the chain 134.

The capacitor chain 134 is composed of m serially connected chains 134-1 to 134-m, each of which is composed of k connected in parallel capacitors. For example, FIG. 1 shows capacitors 134-11 to 134-lk in the chain 134-1, and capacitors 134-ml to 134-mk in the chain 134-m. It is noted that n, m and k are integers exceeding 1. The capacitor chain 134 is used in an arc welding mode.

The inductor L4 and capacitor C5 are used in an arc welding mode when DC power is provided to a DC welder. These elements are connected to the rectifier 1 12 composed, for example, of multiple diodes. The inductance L3 is also connected to the rectifier 1 12.

The inductance L5 may be connected in an microarc oxidation mode if the inductance of the secondary windings is not sufficient to provide resonance. An ammeter PA and a voltmeter PV are connected to enable an operator to tune respective resonance circuits to resonance. In an microarc oxidation mode when the power supply 100 provides power to the electrolytic bath 200 during electrochemical deposition, operating current flows from the terminal 116, across the electrodes 202 and 204 used for electrochemical deposition in the electrolytic bath 200, to the terminal 118. From the terminal 118, the operating current passes through the windings W4', W5', W5, W4, the capacitor chain 132 and the measuring circuit of the ammeter PA to the terminal 116.

Hence, during electrochemical deposition, serially connected secondary windings W4', W5', W5, W4, and capacitor chain 132 are coupled into a closed electrical circuit including the electrolytic bath 200. A required number of capacitors may be connected into the chain 132 to adjust its total capacitance so as to tune the closed electrical circuit to resonance. The capacitance of the capacitor chain 132 is adjusted depending on deposition conditions in the electrolytic bath 200 to maintain resonance.

The series resonant circuit formed by the secondary windings and the capacitor chain 132 may deliver a resonant voltage several times greater than the input voltage. The operating current flowing in the resonant circuit across the electrodes 202 and 204 in the electrolytic bath 200 has practically sinusoidal shape. If the total inductance of the secondary windings is not sufficient to achieve resonance, the additional adjustable inductance L5 may be connected in series with the secondary windings and the capacitor chain 132.

Hence, the inductance as well as capacitance may be adjusted to achieve resonance.

In an arc welding mode when AC power is provided to the arc welder 300, welding current flows from the terminal 120 across the welding arc to the terminal 122. From the terminal 122, the current passes the secondary windings W5' and W5, and the capacitor chain 134 to the terminal 120.

Hence, the windings W5' and W5, and the capacitor chain 134 are connected into a closed electrical circuit. The total capacitance of the chain 134 may be adjusted to tune this closed circuit to resonance during welding. The arrangement of the capacitor chain 134 makes it possible to vary its total capacitance in a broad range depending on welding conditions. For example, the total capacitance may be adjusted from 7,000 mkF to 15,000 mkF to achieve resonance conditions for welding current.

When DC power is provided in the arc welding mode, welding current flows from the terminal 124 across the welding arc to the terminal 126. From this terminal, the current passes through the adjustable inductor L4 and capacitor C5 to the terminal 124.

Hence, the inductor L4 and capacitor C5 are connected in a closed electric circuit during welding carried out by a DC welding machine. The inductance value of the inductor L4 and/or capacitance value of the capacitor C5 are adjusted depending on welding conditions to achieve resonance in the closed circuit providing a path for the welding current, i.e. to achieve resonance conditions for welding current.

Accordingly, the universal variable- frequency power supply of the present invention enables an operator to control operations carried out by a load supplied with power, by adjusting values of capacitive and/or inductive elements of the power supply so as to achieve resonance in a closed circuit providing a complete path for operating current. Alternatively, the operations of the load may be controlled automatically by an automatic control system that adjusts parameters of the power supply in accordance with conditions of a process performed by the load to tune the closed circuit to resonance.

As a result, the power supply of the present invention improves properties of products produced by the load, and enhances performed processes. Also, the adjustment of power supply parameters makes it possible to substantially reduce the power consumption of the power supply.

Those skilled in the art will recognize that the present invention admits of a number of modifications, within the spirit and scope of the inventive concepts. For instance, the power supply 100 may be implemented in a number of different ways. While the foregoing has described what are considered to be preferred embodiments of the invention it is understood that various modifications may be made therein and that the invention may be implemented in various forms and embodiments, and that it may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim all such modifications and variations which fall within the true scope of the invention.

Claims

What is Claimed Is:

1. A power supply for providing power to a load, said power supply comprising output circuitry having at least one element adjustable for tuning the output circuitry to resonance during an operation carried out by the load.

2. The power supply of claim 1, wherein the output circuitry is configured to form, together with the load, a closed circuit providing a complete path for operating current of the load during the operation carried out by the load.

3. The power supply of claim 2, wherein said at least one element is configured to tune the closed circuit to resonance during the operation carried out by the load.

4. The power supply of claim 2, wherein said at least one element is adjustable to control the operation carried out by the load.

5. The power supply of claim 2, wherein said at least one element is adjustable to maintain a power factor equal to about 100% during the operation carried out by the load.

6. The power supply of claim 2, wherein said at least one element is adjustable in accordance with conditions of a process performed by the load.

7. The power supply of claim 2, wherein said at least one element is adjustable to synchronize various phases of a process performed by the load.

8. The power supply of claim 2, wherein the closed circuit is an LC resonant circuit.

9. The power supply circuit of claim 1, wherein the output circuitry is configured to support operations of different loads supplied by the power supply circuit.

10. The power supply circuit of claim 9, wherein the output circuitry has separate adjustable elements for providing resonance to support different loads supplied by the power supply circuit.

11. The power supply circuit of claim 9, wherein the output circuitry is configured to form, together with the different loads, multiple closed circuits providing complete paths for operating currents of the respective loads.

12. The power supply circuit of claim 1 , wherein the output circuitry is configured to provide the resonance at various frequencies.

13. The power supply of claim 1 , further comprising a voltage selector for selecting voltage supplied to the load.

14. The power supply of claim 1, further comprising a filter for suppressing noise transferred from the load.

15. The power supply of claim 1, wherein the load includes an electrolytic bath for performing an electrochemical deposition process.

16. The power supply of claim 15, wherein the output circuitry forms, together with the electrolytic bath, a closed circuit providing a complete path for operating current during the electrochemical deposition process.

17. The power supply of claim 16, wherein the output circuitry comprises a resonant circuit for supporting operations of the electrolytic bath.

18. The power supply of claim 17, wherein the resonant circuit is adjusted to tune the closed circuit to resonance during the electrochemical deposition process.

19. The power supply of claim 18, wherein the resonant circuit comprises reactive elements connected in series.

20. The power supply of claim 1, wherein the load includes a welder for performing an arc welding process.

21. The power supply of claim 20, wherein the output circuitry is connected to a welding electrode of the welder and to a workpiece to form a closed circuit providing a complete path for welding current during the arc welding process.

22. The power supply of claim 21, wherein the output circuitry comprises a resonant circuit for supporting operations of the welder.

23. The power supply of claim 22, wherein the resonant circuit is adjusted to provide resonance conditions for the welding current during the arc welding process.

24. Method of providing power to a load using a power supply, the method comprising the steps of: supplying power to the load to initiate an operation carried out by the load, and adjusting at least one element of the power supply to provide resonance conditions for operating current of the load during the operation.

25. The method of claim 24, wherein said at least one element is adjusted to control the operation carried out by the load.

26. The method of claim 24, wherein said at least one element is adjusted in accordance with conditions of a process performed by the load.

27. The method of claim 24, wherein said at least one element is adjusted to synchronize various phases of a process performed by the load.

28. The method of claim 24, wherein the power supply is adjusted to support operations of different loads.

29. The method of claim 24, wherein the power supply is adjusted to provide the resonance conditions at various frequencies.

30. The method of claim 24, wherein said step of adjusting is carried out during a microarc oxidation process performed in an electrolytic bath to form a ceramic coating on at least one surface of an article.

31. The method of claim 30, wherein the article is made of a material selected from the group consisting of Al, Ti, Mg, Zr, V, W, Zn and their alloys.

32. The method of claim 24, wherein said step of adjusting is carried out during an arc welding process to provide resonance conditions for welding cunent.

33. A power supply for providing power to an electrolytic bath, said power supply comprising at least one adjustable element for tuning to resonance a closed circuit providing a complete path for operating current during a microarc oxidation process carried out in the electrolytic bath.

34. The power supply of claim 33, wherein the microarc oxidation process is carried out to form a ceramic coating on at least one surface of an article.

35. The power supply of claim 34, wherein the article is made of a material selected from the group consisting of Al, Ti, Mg, Zr, V, W, Zn and their alloys.

36. The power supply of claim 34, wherein the power supply comprises output circuitry including said at least one adjustable element.

37. The power supply of claim 34, wherein the output circuitry includes inductive and capacitive elements connected in series and having values selected to achieve the resonance during the microarc oxidation process.

38. The power supply of claim 37, wherein the inductive elements include at least one winding of a transformer having a high level of magnetic leakage.

39. The power supply of claim 38, wherein additional inductance is connected to the output circuitry to achieve the resonance during the microarc oxidation process.

40. The power supply of claim 38, further comprising a voltage selector for selecting voltage supplied to the electrolytic bath.

41. The power supply of claim 40, wherein the voltage selector includes said transformer having a high level of magnetic leakage.

42. The power supply of claim 41 , wherein said at least one winding is a secondary winding of said transformer.

43. The power supply of claim 37, wherein the capacitive elements include multiple capacitors connectable in parallel to provide a total capacitance value required to achieve the resonance during the microarc oxidation process.

44. The power supply of claim 33, wherein a power factor equal to about 100% is maintained during the microarc oxidation process.

45. A power supply for supplying power to an arc welder, the power supply comprising at least one adjustable element for tuning to resonance a closed circuit providing a complete path for welding current during an arc welding process carried out by the arc welder.

46. The power supply of claim 45, wherein the power supply comprises output circuitry including said at least one adjustable element.

47. The power supply of claim 46, wherein the arc welder is supplied with AC power.

48. The power supply of claim 47, wherein the output circuitry includes inductive and capacitive elements having values selected to achieve the resonance during the arc welding process.

49. The power supply of claim 48, wherein the inductive elements include at least one winding of a transformer having a high level of magnetic leakage.

50. The power supply of claim 49, further comprising a voltage selector for selecting voltage supplied to the arc welder.

51. The power supply of claim 50, wherein the voltage selector includes said transformer having a high level of magnetic leakage.

52. The power supply of claim 51, wherein said at least one winding is a secondary winding of said transformer.

53. The power supply of claim 47, wherein the capacitive elements include multiple serially connectable capacitor chains, each of which is composed of multiple capacitors connectable in parallel.

54. The power supply of claim 53, wherein total capacitance value of the capacitive elements is selected to achieve resonance conditions for the welding current during the arc welding process.

55. The power supply of claim 46, wherein the arc welder is supplied with DC power.

56. The power supply of claim 55, wherein the output circuitry includes an inductor and a capacitor.

57. The power supply of claim 56, wherein the inductor is adjusted to achieve resonance conditions for the welding current during the arc welding process.