The present invention relates to an electronic AC/AC power converter apparatus, that allows, in a reliable, stable, simple, and inexpensive way, to regulate power transferred to a load, in particular from a single phase or three-phase power supply (preferably at 230/380 Volt and at 50/60 Hz), the apparatus having limited size and weight.

The electronic apparatus that is the subject matter of the present invention, due to its field of application, belongs to the class of the electronic power converters which are found wherever it is necessary to modify the electrical energy "form", e.g. for modifying voltage, current or frequency. Said electronic converters present the characteristic to have a power range variable from some milliwatts (as in cellular telephones) to hundreds of megawatts (as in HVDC transmission systems). It is known that in "classical" electronics, the electric current and the voltage are used for transporting information, whereas in power electronics they are used for transporting power. The main aim of power electronics is, hence, to control the electrical parameters of the loads connected to an energy source allowing a variation of the functions of the same.

Apparatuses exploiting power electronics take the name of converters.

Power conversion systems may be classified depending on the type of input and output power: - from AC to DC (rectification),

- from DC to AC (reversal),

- from DC to DC (conversion), and

- from AC to AC (conversion).

Power electronics systems are virtually found in every electronic device.

In particular, AC-DC converters, also called rectifiers, are the most typical tools of power electronics. They are in many electronic equipments, as in televisions, personal computers, battery charger, etc.

The power range usually varies from tens of watts to several hundreds of watts. In industry, the most common application is the speed regulator used for controlling electric motors, the power of which usually varies from some hundreds of watts to tens of megawatts. Since efficiency is one of the most important aim of electronic power converters, power leakages of electronic devices must be minimised. As it is known, instant power dissipated by a device is equal to the product of the voltage across it by the current flowing through it. For this reason, it is to be noted that power losses are minimised when voltage is close to zero (condition occurring in the ON or power up state of the devices), or when no current flows through the device (condition occurring in the OFF or interdiction state). Thus an electronic power converter is made with one or more devices which operate by switching between the ON state and the OFF state. With such structure, energy is transferred from the input to the output of the converter.

DC/AC converters, also called inverters, are used, e.g., when a dc power generation electronic device (such as, for instance, a photovoltaic panel) has to transfer the generated power to an ac mains.

DC/DC converters are used in most part of mobile instruments (such as cellular telephones, etc.) for maintaining the voltage fixed at a certain level, whatever the load of the battery. These converters are also used for electronic insulation and power factor correction.

AC/AC converters are used for modifying both the voltage level and the frequency (such as the international power adaptors, etc.). In power distribution networks, AC/AC converters may be used for exchanging power between distribution networks at 50 Hz and those at higher frequency.

The first devices of the power electronics used for making such converters were mercury vapour rectifiers. In modern systems, the conversion is carried out with semiconductor materials like diodes, thyristors and transistors.

With reference to AC/AC converters, basically in the prior art there exist three process in order to be able to vary the power in ac current provided to a load: - phase partialisation (or phase cut) control;

- wave train (or complete wave cycle) control; and

- pulse width modulation or PWM control.

As shown in Figure 1a, phase partialisation control, the triac

101 used by the AC/AC converter (represented as two SCRs or thyristors connected in anti-parallel) is triggered in each half-wave of the power supply by means of a control pulse, generated by a control device 102. As shown in Figure 1b, the current flows through the triac 11 from this power up instant up to the passage through the natural zero of each sinusoidal half-wave. Moving the control pulse within the voltage half-wave it is possible to vary the voltage across the load 100 in a practically continuous way and in this way power transferred to the load 100 is regulated. The setting range, within which the voltage pulse may be moved, is between phase values of 0° and 180°, where 0° corresponds to the maximum driving level, i.e. full voltage. The trigger point (or trigger angle) is also called as partialisation angle α or control angle α.

This way of operation is equally adapted for use with ohmic, ohmic-inductive and inductive loads. The advantages of this way of operation consist in the capability to set up in a continuous way, in the possibility of fine dosing and in the short reaction time of the energy transfer to the load. In particular, a dynamic limitation of the current is possible only with this way of operation. However, the disadvantages of the phase partialisation control consist in fast raising edge of the clipped power supply half-waves and in the related high frequency disturbance resulting from the harmonics which derive.

The occurrence of a reactive power also in case of ohmic loads is also disadvantageous. In order to meet EMC requirements suitable filters must be installed before the phase partialisation control power converters. In general, these filters are already integrated into the triac (or thyristor) low power converters, whereas they must to be provided as external filters connected before the triac (or thyristor) converters in case of high power.

With reference to Figure 2, it may be observed that in wave train control (or complete wave cycle control) complete power supply half- waves are allowed to pass as "wave packets" with pauses of variable duration between one train and the next. The power value is provided by means of the insertion ratio (duty-cycle), equal to the ratio between insertion time T _Θ jn and insertion period duration T. Due to the fixed duration of the period of the given power supply frequency, there is a limit in the resolution of the power to the load and hence also in the dynamics of the

^• whole system. In the wave train control, it is advantageous that the current across the load is purely sinusoidal and thus no harmonic is generated and (with ohmic load) no reactive power arises. Also the radiofrequency disturbance are minimised since the thyristors (or triacs) are triggered in correspondence with the passage of the voltage through zero.

The disadvantages are due to the fact that, due to the cyclic stress on the power supply, weak voltage fluctuations may arise in the power supply which may cause cumbersome fluctuations, e.g. in lighting equipments luminous flux fluctuations, also called voltage flickers.

Moreover, direct insertion at each cycle normally limits this way of operation to applications with resistive loads, since in presence of inductive elements (e.g. transformers) or loads with a large difference cold-R/hot-R (e.g. infrared projectors) high insertion currents would occur at each insertion.

In PWM control, the following are used: a rectifier which the initial current enters, a dc connecting bus (DC Bus), and a final, generally three-phase, inverter producing the output current, that is then used in the required application. Such devices are part of an apparatus called inverter.

In the inverter, the initial rectifier transforms the input power supply ac current in dc current, or if it is already dc it keeps it as constant, which current is then kept uniform by the capacitors constituting the DC

Buses. After all the inverter generates the variable frequency power supply depending on the needs.

Noise in the frequency of the wave generated by the inverter occurs when, due to frequency peaks of the input wave harmonics, the output wave is different from the desired one. This phenomenon obviously encumbers on the apparatus efficiency and this will be lower. The simplest and most common form of inverter is constituted by an oscillator controlling a transistor, which operates for generating a square wave by opening and closing a circuit. The wave is sent to a transformer that smooths these peaks thus generating the desired variable frequency at the output of the instrument. Possible presence of diodes in the rectifier acts to maintain the square wave as rectangular as possible. The used transistors are generally insulated gate bipolar transistors or IGBTs which are often controlled via software.

Instead, electronic inverters use pulse width modulations for making the output wave as sinusoidal as possible. This can be obtained through the use of capacitors and inductors levelling the transformer current.

The choice of one of the prior art three controls of the AC/AC converters illustrated above essentially depends on the type of load and on the regulation dynamics of the system. By way of example, phase

■ partialisation control is employed when fast regulation processes are required, e.g. as in operations for fans/pumps, for luminous flux regulators, and also in thermotechnical pro cesses wit h high thermal dynamics or heating elements with large variations of the cold-R/hot-R ratio (i.e.: cold resistance/hot resistance). On the contrary, the wave train control is adapted to the use in presence of thermal time constants of high value, e.g. as in case of smelting furnaces, industrial furnaces, etc. (having high temperature time constants).

In this context, the solution proposed according to the present invention is introduced, allowing to overcome all the aforementioned drawbacks of prior art AC/AC converters.

It is therefore an object of the present invention to allow in a reliable, stable, simple, and inexpensive way, to regulate power transferred to a load, in particular from a single phase or three-phase power supply.

It is specific subject matter of this invention an electronic AC/AC power converter apparatus for regulating power transferred to a load from a power supply having at least one phase, comprising:

- at least two units for rectifying respective waveforms drawn from the power supply, characterised in that it comprises, for each one of said at least two rectifying units: - means for detecting zero-crossing of the respective waveform, connected to the respective rectifying unit;

- amplitude regulating means, connected to the respective rectifying unit, that outputs an amplitude regulated power supply to the load, to which it is further connected; the apparatus further comprising electronic processing and controlling means that controls, on the basis of at least one detection signal received from each one of said detecting means, said regulating means and switching means, in such a way that said switching means assumes a configuration such that it closes at least one circuit loop to which the power supply, a rectifying unit and the respective regulating means, and the load belong and such that it opens at least one loop to which the power supply, another rectifying unit and the respective regulating means, and the load belong.

Always according to the invention, said amplitude regulating means and said switching means may include solid state power electronic devices, preferably selected from the group comprising triacs, thyristors, SCRs, and IGBTs.

Still according to the invention, said waveforms drawn from the power supply may be power supply voltage waveforms and said amplitude regulating means may be capable to regulate a voltage amplitude of said waveforms. Furthermore according to the invention, said regulating means may comprise voltage step-down devices, i.e. buck-type regulator devices. Always according to the invention, said electronic processing and controlling means may comprise at least one microcontroller.

Still according to the invention, said power supply may be a single phase power supply, preferably of sinusoidal-type, more preferably at 230 or 380 V and at 50 or 60 Hz, said rectifying units may be two and said waveforms drawn from the power supply may be one positive half wave and one negative half wave, said switching means may comprise two switches, preferably connected between a respective end of the load and the power supply, said electronic processing and controlling means alternatively closing the two switches.

Furthermore according to the invention, said power supply may be a three-phase power supply, the load may be a three-phase load comprising three sections, preferably balanced, more preferably either delta or star connected, said rectifying units may be three and said waveforms drawn from the power supply may be the three phases of the power supply, said switching means may comprise three switches, preferably connected to an output of respective regulating means and to a circuit common ground. The electronic AC/AC power converter apparatus according to the invention belongs to the class of the AC/AC converters, being connectable to the (ac) power supply. Such apparatus does not modify the sinusoidal behaviour nor the power supply signal frequency, but it varies the amplitude of the same signal, that will be provided as power supply for the load connected thereto.

The apparatus according to the invention causes the power supply voltage that is stabilised at the output to the load to carry out the regulation between the nominal value and a minimum value compatible with the type of load that is used.

The apparatus according to the invention allows supplied power to be regulated through an operation of linear reduction of the supply voltage, through solid state switches which allow to carry out a completely static control and regulation.

The apparatus according to the invention, that has very compact size and much reduced weight, outputs a voltage, starting from the input one directly drawn from the power supply voltage, that is perfectly sinusoidal, since it maintains its characteristics, in particular power supply frequency and behaviour, unaltered.

Moreover, by applying a signal variable within 0-10 V to a control terminal board at the input of the apparatus, it is possible to obtain a regulation of the output voltage from 1 % to 100%. Thanks to the characteristics of the output signal, the apparatus according to the invention allows the regulation of capacitive, inductive, electronic and mixed loads.

The advantages offered by the electronic AC/AC power converter apparatus according to the invention with respect to conventional, electromechanical or electronic, conversion systems are numerous: very compact size; significantly lower total weight (less than 1 kg); high performance in economical terms; efficiency higher than 97% at full power; stability of the regulation level; reduced production costs; obtainment of output, single phase or three-phase, voltages with variable effective value starting also from few volts, thus perfectly allowing a gradual supply; in case of three-phase plant, the three single phase voltages may be also independently regulated in amplitude for obtaining different reductions of luminous flux on each phase; from a manufacture point of view moving electromechanical components (such as relays and brushes) are eliminated, allowing maintenance costs to be decreased; in the case where light sources are connected to the output, it allows an extension of lamp life, a stability of efficiencies, a drastic reduction of maintenance interventions, an abatement of operation costs, an energetic saving from 25% to 50 %, benefits for environment (lower emission of CO2 and of light pollution), a stabilisation of the power supply voltage, and a simple and advantageous maintenance, installation and assistance, thanks to the modularity of the apparatus. The application fields of the electronic AC/AC power converter apparatus according to the invention are many, including: public lighting systems, such as commercial centres, hypermarkets and supermarkets, industrial and service sale areas, state, private and industrial buildings, sports facilities, parking places, squares, stations, and stores; industrial furnaces, such as electric furnaces and induction furnaces; smelting

• furnaces; IR radiators (desiccation); infrared projectors; evaporators, die heating systems, extruders; heating cables and resistors; luminous flux regulators (dimmers); fan systems; preheating systems; air heating, room heating; electroforming and electroplating techniques; zootechny, aviculture, greenhouses; chemical and food industries.

The present invention will be now described, by way of illustration and not by way of limitation, according to its preferred embodiments, by particularly referring to the Figures of the enclosed drawings, in which:

Figure 1 shows a prior art phase partialisation control circuit (Fig. 1a) and the related graphs of power supply voltage, power up pulses, and voltage across the load (Fig. 1b);

Figure 2 shows the graphs of the power supply voltage, power up pulses, and voltage across the load of a prior art wave train control;

Figure 3 shows a first embodiment of the apparatus according to the invention; and

Figure 4 shows a second embodiment of the apparatus according to the invention. In the Figures, identical reference numbers are used for alike elements.

Figure 3 shows a first embodiment of the electronic AC/AC power converter apparatus, generally indicated with reference number 1 , for regulating power transferred to a load 100, operating through a single phase power supply voltage, preferably at 230/380 volts and at 50/60 Hz,

^■ drawn from a power supply 2.

The apparatus 1 comprises a unit 3 for rectifying a positive half- wave and a unit 8 for rectifying a negative half-wave, connected to the single phase power supply 2. A first and a second units 4 and 9 for detecting zero-crossing are connected, respectively, to the rectifying units 3 and 8. A first and a second units 5 and 10 for regulating the voltage amplitude, preferably of buck type, are also connected, respectively, to the rectifying units 3 and 8, and they output the supply voltage to a load 100 connected thereto.

First and a second switches 6 and 11 for closing the circuit towards the positive and negative, respectively, half-waves are connected after the load 100, which switches are connected to the power supply 2 through respective circuit closing lines 7 and 12.

A microcontroller 13 receives from the detecting units 4 and 9 the respective signals of detection of zero-crossing of the positive and negative, respectively, half-waves and it controls, alternatively, the regulator units 5 and 10 and the closing switches 6 and 11.

In particular, the units 3 and 8 for rectifying the positive and negative, respectively, half-waves draw the sinusoidal-like signal (preferably at 230/380 V and at 50/60 Hz) from power supply 2. The unit 3 operates for rectifying the positive half-wave, whereas the unit 8 operates for rectifying the negative half-wave.

The positive half-wave rectifying unit 3 directly transfers the positive half-wave signal drawn from the power supply 2 to the respective unit 4 for detecting zero-crossing and to the respective regulator unit 5. Similarly, the negative half-wave rectifying unit 8 directly transfers the negative half-wave signal drawn from the power supply 2 to the respective unit 5 for detecting zero-crossing and to the respective regulator unit 10.

The unit 4 for detecting zero-crossing detects the passage through zero of the positive half-wave coming from the positive half-wave rectifying unit 3, whereas the unit 9 for detecting zero-crossing detects the passage through zero of the negative half-wave coming from the negative half-wave rectifying unit 8.

The buck regulator units 5 and 10, also called step-down, produce an output voltage lower than the input voltage. In fact, the function of these apparatuses is to regulate, through their intrinsic operation characteristics, the amplitude of the input signal coming from the positive and negative, respectively, half-wave rectifying units 3 and 8. Such buck regulator units 5 and 10 receive the command of power up/power down from the microcontroller 13, that operates to adequately synchronise and drive such units 5 and 10. The microcontroller 13 also receives from the units 4 and 9 for detecting zero-crossing the signal of passage through zero of the positive and negative, respectively, half-waves. In this way, the microcontroller is capable to also drive the switches 6 and 11 of closing the circuit towards the positive and negative, respectively, half-waves.

Once it has exited the buck regulator units 5 and 10, the signal is transferred to the load 100, that, alternatively through the switches 6 and 11, closes its own electrical circuit. In this regard, the switches 6 and 11 of closing the circuit towards the positive and negative, respectively, half-waves alternatively close depending on the control signal received from the microcontroller 13, that is conditioned by zero-crossing as detected by the units 4 and 9. Once it has exited the switches 6 and 11 of closing the circuit towards the positive and negative, respectively, half-waves, the signal is transmitted to the lines 7 and 12 for closing the electrical circuit.

Other embodiments of the apparatus according to the invention, for single phase applications, may provide that the switches 7 and 12 are in different position along the respective loops; preferably, they could be located between the respective buck regulator unit 5 or 10 and the load 100.

Figure 4, immediately understandable by those skilled in the art, shows a portion of a second embodiment of the electronic AC/AC power converter apparatus, generally indicated with the reference number 1', for regulating power transferred to a three-phase load 100A, 100B, and 100C (that is preferably, but not necessarily, balanced) from a three-phase power supply voltage, drawn from a power supply 2'. In particular, although the three sections 100A, 100B, and 100C of the load are delta connected, it is immediate for those skilled in the art to apply the apparatus of Figure 4 to different connections of the three-phase load, e.g. star connections.

In this case, the apparatus according to the invention comprises three sections, each one connected to a respective phase of the supply voltage. Each section comprises a unit (3A, 3B, 3C) for rectifying the respective phase, the output of which is connected to a, preferably buck, regulator unit (5A, 5B, 5C), the output of which is connected to two sections (respectively 100A and 100B, 100A and 100C, and 100B and 100 C) of the three-phase load and to a circuit closing switch (6A, 6B, 6C). A microcontroller, not shown in Figure 4, receives signals of detection of zero-crossing of the three phases and it consequently controls the three regulator units 5A, 5B, and 5C and the three closing switches 6A, 6B, and 6C, similarly to the microcontroller 13 of the embodiment of the apparatus of Figure 3.

It is immediate for those skilled in the art to make, on the basis of the teaching described above with reference to single phase and three- phase supply, embodiments of the apparatus according to the invention usable with two-phase supply or supply having any number of phases.

The preferred embodiments have been above described and some modifications of this invention have been suggested, but it should be understood that those skilled in the art can make variations and changes, without so departing from the related scope of protection, as defined by the following claims.