TECHNICAL FIELD

The various aspects and embodiments thereof relate to a AC to DC converter, in particular to a three-phase AC to DC converter.

BACKGROUND

Conventional three-phase AC to DC converters employ transformers with wound coils for up or down conversion of a voltage, followed by a six-diode rectifier bridge and a capacitor for smoothing the output waveform.

With the arrival of power electronics, the three input phases are rectified and up or down conversion, followed by a buck or boost converter and an output filter for providing a smooth DC signal.

Whereas efficiency has gone up, AC to DC converters still are bulky devices that require significant cooling. This may be an issue in harsh and/or explosion safe and/or explosion proof environments. In explosion safe environments or explosion proof environments, a pressure-tight or flameproof cabinet, known as EX, is used. In the cabinet electronics and other equipment can be placed having a maximum, prescribed, power and heating development. Should there be an explosion inside of the cabinet, this explosion must remain inside of the cabinet. So, the flame or explosion must be cooled off on its way to the outside of the cabinet to ensure that the fire remains in the cabinet and cannot ignite the cabinet's direct

environment.

SUMMARY

It is preferred to provide an arrangement for converting three phase alternating current to direct current that is convenient to use.

A first aspect provides an arrangement for converting three phase alternating current having a first phase, a second phase and a third phase to direct current having a positive potential and a negative potential. The arrangement comprises a first phase input for receiving the first phase, a second phase input for receiving the second phase and a third phase input for receiving the third phase and a positive supply terminal and a negative supply terminal for providing direct current. The arrangement further comprises three alternating current to direct current converters. A first alternating current to direct current converter comprises a first input terminal connected to the first phase input, a second input terminal connected to the second phase input, a first positive output connected to the positive supply terminal and a first negative output connected to the negative supply terminal. A second alternating current to direct current converter comprises a first input terminal connected to the second phase input, a second input terminal connected to the third phase input, a second positive output connected to the positive supply terminal and a second negative output connected to the negative supply terminal. And a third alternating current to direct current converter comprises a first input terminal connected to the third phase input, a second input terminal connected to the first phase input, a third positive output connected to the positive supply terminal and a third negative output connected to the negative supply terminal.

By providing three single phase AC to DC converters, one provided between each pair of distinct phases, smaller components may be used compared to three phase AC to DC converters in which the three phases are rectified and one large DC to DC converter is used for down or up conversion. Use of smaller components may be employed for improved removal of dissipated heat, as smaller components have a higher outer surface/volume ratio compared to larger components. The smaller

components also allows for smaller building form factors and smaller footprint. Firstly in view of the size of the components and secondly in view of reduced requirements with respect to removal of heat. Furthermore, such system may be cheaper in maintenance. An important reason for this is that in case of failure, only one - smaller - single phase AC to DC converter may be replaced, instead of a larger three-phase component. The replacement may be physically, by taking a malfunctioning device out of the arrangement and replacing it by a new device.

Alternatively, the replacement may be functionally, by shutting down the malfunctioning device and using another AC to DC converter switched in parallel to the malfunctioning device.

In an embodiment, the alternating current to direct current converters comprise switched power converters comprising solid state switches. Such switches and switches comprising sihcon carbide or silicon active parts in particular, allow for efficient switching of power. Such switches may be MOSFETs, IGBTs, Triacs, other, or a combination thereof. Switches having a low or negligible switching current - like MOSFETs are preferred. Advantageously, the switched power converter has an operating frequency between about 40 kHz and about 60 kHz, preferably at about 45 kHz

An embodiment of the arrangement comprises a cabinet predominantly comprising metal, like (stainless) steel or aluminium, wherein the alternating current to direct current converters are provided in the cabinet such that the solid state switches are placed in thermal contact with an inner side of a first wall of the cabinet. Advantageously, the electric components, amongst which the solid state switches, are placed in direct thermal contact with a wall of the cabinet to improve heat dissipation. In an embodiment, het electronic components are mounted onto a wall of their casing, which in turn, is mounted in direct thermal contact with the wall of the cabinet to provide for heat dissipation to the outside of the cabinet.

In this embodiment, the cabinet may be used as a heat sink. If more heat removal capacity is required, the heatsink may be extended, for example, the heatsink may further comprise cooling fins, may be provided, preferably at an opposite side of the heatsink. This allows for static cooling and may remove the need for forced air cooling. This, in turn, provides more reliable operation. If the arrangement is to be used in high-reliability environments, like off-shore platforms, such reliability is very important. Furthermore, closed cabinets known so far and explosion safe cabinets in particular usually prevent proper removal of heat generated within the cabinet, as convection is not a reliable option and explosion safe cabinets are pressure-tight or flameproof, e.g. as required by regulation IEC-60079-1. On the other hand, this embodiment with semiconductor devices in direct thermal contact with the wall of the cabinet, improved heat removal is provided.

In this embodiment, the alternating current side of the converters are galvanically isolated from the direct current side of the converters. This allows for safer operation at the secondary side, where overload or other potential causes for malfunction, will not always and/or directly result in failure at the primary side. Such isolation may be provided by employing a forward based converter in the AC to DC converters.

A second aspect provides a system for converting three phase alternating current having a first phase, a second phase and a third phase to direct current having a positive potential and a negative potential, the system comprising a plurality of arrangements according to the first aspect connected in parallel at the input and at the output. By providing a plurality of arrangements, the system can relatively easily be scaled up, or down, depending on the power requirements. This provides for a modular system that can be tailored to the requirements defined by an operator and/or regulations.

An embodiment of this system further comprises a control circuit. The control circuit can be arranged to detect malfunction of an alternating current to direct current converter of a first of a first arrangement and a second arrangement and control a further alternating current to direct current converter of a second of the first arrangement and the second arrangement, parallel to the malfunctioning alternating current to direct current converter, to take over functionality of the malfunctioning alternating current to direct current converter in the first of the first arrangement and the second arrangement. Advantageously, the control circuit is mainly configured to detect malfunction of a converter and to rearrange the arrangement with a functioning, e.g. redundant or spare, converter.

Such system provides efficient redundancy in case of failure of a single phase AC to DC converter. Rather than replacing a full three phase converter arrangement, only a single converter is replaced. This improves the flexibility of the system and may reduce downtime as well as

maintenance cost. For example, in case one converter fails, a second, redundant, converter can take over the functionality of the failed first converter. Then, the first converter may be replaced by a different, functioning converter and/or may be repaired without impairment to the functioning of the system, thus reducing downtime.

Advantageously, each AC to DC converter may be provided individually, either fully or partially, in a casing, a so-called "converter module". Thus, to provide an arrangement with three alternating current to direct current converters, three converter modules are used for the arrangement. The converter module comprises the required electronic components to provide for the alternating current to direct current conversion, for example a power factor correction circuit - PFCC, a voltage converter and an output filter. Other and/or additional components may be provided in the converter module as well.

Further, each converter module comprises an input for alternating current, an output for direct current. Providing such a converter module is advantageous for manufacturing, installation, repair and/or maintenance. The converter modules can be manufactured in a controlled environment, such as a manufacturing hall, where they can be tested and controlled prior to leaving the factory. So, the converter module can be installed as a whole to form the arrangement, only connections to input, output. This allows easy installation and reduces the risk on mistakes and/or failures.

Also, in case of failure, the converter module can be easily removed from the arrangement and replaced by an other, functioning, converter module for which also only connections to input, output. This may allow for a cost reduction during the hfetinie of the system. Advantageously, the casings of the converter modules may have at least the same footprint and/or may have the same shape. As such, the converter modules are more easily interchangeable with one another.

A connection between a converter module and an other and/or adjacent converter module can be established via the control circuit.

Preferably, the arrangement comprises a cabinet, so the three converter modules forming the arrangement can be mounted in the cabinet, advantageously an explosion proof cabinet. The cabinet may be provided with seats corresponding with a footprint of the converter module, allowing for more easy mounting of the converter modules in the cabinet.

The invention further relates to a system for converting three phase alternating current comprising a plurality of the arrangements. This provides for relatively easy scahng up, e.g. when more current output is required. When converter modules are used, simply additional converter modules can be mounted to the system and can be connected to each other to provide for an arrangement of converters. In an embodiment comprising a cabinet, scaling up can be done relatively easy by providing one or more additional cabinets. The plurality of arrangements, for example a plurality of cabinets, can then be connected to each other to form a larger system for alternating current to direct current conversion. Scaling down of the system can of course be done as well.

Further, a cabinet for power supply is provided that comprises at least one of such arrangement of AC-DC converters. By providing a cabinet for power supply with at least one of such arrangement, a modular and efficient system is obtained. The arrangement is very energy efficient, in that it uses itself limited energy, but also, generates a limited amount of heat compared to conventional AC-DC converters. Due to the efficient layout of the arrangement, the AC-DC converter can be relatively compact. Preferably, a single cabinet is provided with three AC-DC converters according to the said arrangement, each converter having its associated controller. The AC-DC converters can be directly mounted onto a chassis. The chassis itself is preferably a relatively thin metal plate or a metal sheet such that heat can well transferred through the plate. The chassis can then be mounted to a back side of the cabinet. The back side of the cabinet is to that end machined to provide a receiving surface for receiving the chassis thereon and to enable a flush connection of the chassis to the receiving area such that heat can be transferred well through the chassis and the back side. The chassis may be machined as well on its side that mounts to the receiving area of the cabinet to improve connection, in particular heat connection. At the outer side of the cabinet, namely the outer side of the back side of the cabinet, a heat sink is mounted to the cabinet. The heat sink is a passive heat sink, such that active cooling of the cabinet can be obviated. The passive heat sink comprises multiple fins that extend transversally to the back side of the cabinet. As such, a compact cabinet module is obtained that can be prefabricated in a controlled environment, and can be mounted as such to a larger power system on site. Depending on the site environment, the cabinet can be an explosion proof cabinet, e.g. offshore, or can be a harsh environment cabinet, e.g. at a desert location. By providing such a pre-assembled cabinet comprising three AC-DC converters with the said arrangement and associated controllers, a modular power system can be obtained. This is in particular advantageous for sites that are difficult to reach or for which the environment to work is harsh and/or dangerous. Thus, the amount of man hours on site can be reduced. Such a modular system can be easily scalable.

As an example, if one cabinet comprises three AC-DC converters of each yKW, then, the cabinet has a power of 3ykW. When n cabinets are mounted in the system, the system provides for n times 3ykW. Thus, depending on the requirements of the power system, the number of cabinets to be mounted in the power system can be determined. The number of cabinets can be determined such that the required power is reached or exceeded. Additionally, some spare cabinets can be provided, to provide for

redundancy when a converter and/or a cabinet might fail. Further, a control unit can be provided comprised in a cabinet having the same dimensions as the power supply cabinets, but, for example, provided with a user interface to access the control unit locally and/or remotely. An additional advantage of the pre-assembled power supply cabinet, is that, during lifetime of the system, when upscaling or downscaling may be required, additional cabinets can be mounted to the system or cabinets may be removed from the system to adapt to changing requirements.

Further advantageous embodiments are explained in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects and embodiments thereof will now be discussed in further detail in conjunction with drawings. In the drawings:

Figure 1: shows an three-phase AC to DC converter;

Figure 2: shows a graph depicting normalized voltage or current amplitude vs. time for various nodes in the three-phase AC to DC converter; Figure 3: shows a single phase AC to DC converter

Figure 4: shows an explosion safe cabinet with the three- phase AC to DC converter; and

Figures 5a and 5b: shows a compound three-phase AC to DC converter;

Figure 6: shows a schematic view of an embodiment of a cabinet according to the invention comprising three AC-DC converters;

Figure 7 : shows an embodiment of a power system having two cabinets and two central control units with display interface.

DETAILED DESCRIPTION

Figure 1 shows a power supply system 100. The power supply system 100 comprises an alternating current to direct current - AC-DC - converting system 150 as an embodiment of the arrangement according to the first aspect and a three phase generator 110 as an alternating current electric energy supply. The generator 110 comprises a first excitation winding 112, a second excitation winding 114 and a third excitation winding 116. The three excitation windings provide alternating current in three phases, each 2/3 n rad or 120° apart in phase.

In Figure 1, the three phase generator 110 is schematically shown in star configuration. Optionally, the centre of the star may be connected to earth. Alternatively, the three phase generator 110 may be provided in a delta configuration. The power supply system 100 may be used for charging batteries for uninterrupted power supplies. Such uninterrupted power supplies may be found in power-critical environments, like data centres, offshore exploration platforms or other systems that require reliable power. Alternatively or additionally, the power supply system 100 may be used for powering further equipment like lighting, heating, electromotors or other actuators, other, or a combination thereof. The AC to DC converting system 150 comprises a first alternating current to direct current converter 300, a second alternating current to direct current converter 300' and a third alternating current to direct current converter 300". The AC to DC converters each comprise an input for receiving an alternating current power supply and an output 154 for providing a direct current supply. The AC to DC converting system 150 further comprises a control module 152 for controlling the operations of the AC to DC converters.

The voltage at the output 154 may be the substantially the same as the effective voltage provided by the three phases of the three phase generator 110, substantially higher or substantially lower. Also the current provided by the output 154 may be the substantially the same as the effective current provided by the three phases of the three phase generator 110, substantially higher or substantially lower. The output power available at the output 154 is preferably as close as possible to the power provided by the three phase generator 110.

The AC to DC converters are connected between two phases provided by the three phase generator 110. This means that neither input terminal of each AC to DC converter has a fixed potential relative to ground. This is elucidated by Figure 2. Figure 2 shows a graph 200 with waveforms of normalized amplitudes of voltages at various locations in the power supply system 100. Alternatively, they may represent normalized currents. The y-axis represents normalized values and the values at the horizontal axis are in radials. The lines Φ 1, Φ2, Φ3 provide voltage levels over each of the windings 112, 114, 116 of the three phase generator 110. The lines Θ1, Θ2, Θ3, provide voltage levels at each of the inputs of the AC to DC

converters 300, 300', 300". Θ 1 represents the difference between the voltages Φ1 and Φ2. Θ2 represents the difference between the voltages Φ2 and Φ3. Θ3 represents the difference between the voltages Φ3 and Φ 1. The AC-DC converters 300, 300', 300" then convert this input AC voltage to an output DC voltage 154.

From the graph 200 in figure 2, it may be deduced that the amplitude of the signals θ ΐ, Θ2, 63provided at the inputs of the AC to DC converters is proportional to the amplitude of the voltages over the windings Φ1, Φ2, Φ3 with a factor of cube root, in view of the three-phase generator 110.

The amplitude of the signals Φ 1, Φ2, 3at the windings 112, 114, 116 are each 2/3 n rad or 120° apart in phase, as well known for a three- phase generator. As a consequence, also the amplitude of the signals θ ΐ, Θ2, Θ3 at the input of the converters 300, 300', 300" are each 2/3 n rad or 120° apart in phase. Also, the input signals θ ΐ, Θ2, Θ3 are having a phase difference with respect to the winding signals Φ 1, Φ2, Φ3 due to their nature of representing a difference between the connected winding signals. A phase lag or lead of one or more of the phases will lead to higher or lower amplitudes at the inputs of the AC to DC converters. Therefore, the components of the AC to DC converters are preferably dimensioned such that they are able to withstand such fluctuations of amplitudes at the input side. Alternatively or additionally, the control module 152 is arranged to compensate for the phase changes of the input phases.

Figure 3 shows the first AC to DC converter 300 in further detail. The first AC to DC converter 300 comprises a power factor correction circuit - PFCC - 310, a voltage converter 320 and an output filter 330. Further, an input filter and a mains rectifier may be provided between the input 302 and the PFCC 310. An alternating current - or alternating voltage - signal is provided at an input 302 of the first AC to DC converter 300. The signal is firstly filtered by an EMC filter, and rectified by a mains rectifier to obtain a DC signal. This DC signal is offered to the PFCC 310 for correcting the power factor. The PFCC 310 works on a constant frequency and may comprise electronic components such as switch transistors or rectifier diodes. Further, to obtain a longer lifetime of the power factor correction circuit 310, a metal film condensator may be used as storage condensator, such that electrolytes can be obviated. This makes the PFCC more reliable and allows for a longer lifetime.

With the voltage converter 320 comprising various reactive components, including capacitors and/or inductances, voltage and current at the left side of the voltage converter 320 may not always be in phase. This is not preferred, as this may put a high strain on the three phase generator 110. The PFCC 310 is arranged to reduce and preferably minimize the difference in phase between voltage and current at the input 302. The PFCC may comprise first semiconductors switches 312.

In the voltage converter 320, an input voltage is converted down in this embodiment. In the examples discussed in this application, the input voltage has an amplitude of 340 Volt per phase - 240 Volt RMS - and preferably has a frequency between approximately 48 Hz and approximately 62 Hz, with a target frequency of about 50 Hz or about 60 Hz. In other embodiments, the amplitude may be higher. In further embodiments, a transformer or additional voltage converter may be provided between the three phase generator 110 and the AC-DC converting system 150. The voltage converter 320 preferably comprises a switched circuit for the voltage conversion, rather than a conventional transformer. In a preferred embodiment, the voltage converter 320 comprises forward converter, comprising second semiconductor switches 322. Advantageously, the converter 320 is an isolated full bridge forward converter with silicon carbide transistors. The converter can be controlled by a converter controller, which may be provided in a controller module, as discussed later.

The second semiconductor switches 322 are preferably field effect transistors, also known as FET, comprising silicon carbide and/or a gate comprising a material having a low dielectric constant. Such field effect transistors are available having a very low channel resistance. The second semiconductor switches 322 of the converter 320 preferably operate at a frequency between about 40kHz and about 60kHz, with a preferred frequency of approximately 45kHz. Whereas the second semiconductor switches 322 are referred to as a multiple, some embodiments may employ only one field effect transistor or other semiconductor switch in the voltage converter 320.

An advantage of use of a forward converter is that it is generally more efficient than a forward based converter. Further, the primary side and the secondary side are galvanically separated by means of a

transformer. Whereas use of transformers is not preferred at frequencies between about 48 Hz and about 62 Hz due to the inefficiencies of

transformers in that frequency range, transformers having a ferrite core provide high efficiency operation at frequencies between about 40kHz and about 60kHz.

The supply signal provided at the output of the voltage converter

320 is provided to the output filter 330. Between the converter 320 and the output filter 330, a rectifier can be provided. Such a rectifier can rectify the signal outputted by the converter 320 before supplying it to the output filter 330. The rectifier comprises active transistors, instead of passive diodes, to improve the efficiency of the rectifier. Alternatively, the rectifier may be implemented in front of the output filter. The output filter 330 may comprise various reactive elements for providing a smooth constant level of a DC power supply signal to an output of the first AC to DC converter 300. The output signal is preferably provided at approximately 24 Volt, with a maximum current of about 75 Ampere. With three AC to DC converters 300, 300', 300" provided in parallel, one for each phase, the AC to DC converting system 150 may provide a current of up to approximately 225 Ampere and may be rated at about 200 Ampere at continuous operation - at

approximately 4,8 kW. Whereas the channel resistance is relatively low - in the order of milli-Ohms or even tenths thereof -, the semiconductor switches still dissipate an amount of thermal energy that needs to be removed from the switches in particular and the AC to DC converter 300 in particular. An environment that is too hot quickly reduces life expectancy and/or performance of components , so removing the heat is very important.

As discussed above, the AC to DC converting system 150, as an embodiment of the arrangement according to the invention, is preferably used at an off-shore exploration platform. Such exploration platforms have strict requirements with respect to explosion safety. One important requirement is that electrical circuits are provided in a closed box or cabinet that is sealed in accordance with a particular standard. Hence, direct cooling of semiconductor devices by means of conventional measures - convection of air - is not possible.

Figure 4 shows an explosion safe cabinet 400 comprising the AC to DC converting system 150. The explosion safe cabinet 400 comprises a compartment 410 and a door 420. The door 420 is connected to the compartment 410 by means of hinges or other elements enabling to move the door 420 to open the compartment 410. The door and/or the

compartment 410 may be provided with seals for providing a pressure-tight or flameproof space in the cabinet 400 with the door 420 closed. Sealing may be provided in well known manners for EX-cabinets, such as using plane flanges or O-rings. To that purpose, the door 420 may be bolted to the compartment 410. Furthermore, the compartment 410 and the door 420 predominantly comprise a metal or a metal alloy, like aluminium or stainless steel. Figure 4 gives a very schematic representation, and is to be understood that the converters 300, 300', 300" are mounted to the cabinet 400, in particular to the cabinet back wall 412 with fastening elements, such as screws or bolts, or even may be welded to the back wall 412 or otherwise may be thermally connected to the back wall 412. Also, the door 420 may be provided with well known closing elements for providing an explosion proof closure of the cabinet 400. Also, in view of the schematic representation in figure 4, it is to be understood that the first and the second semiconductor switches 312, 322 are physically mounted in the converter 300, 300', 300".

In the compartment, the first AC to DC converter 300, the second

AC to DC converter 300' and the third AC to DC converter 300" are provided. The AC to DC converters 300, 300', 300" may be provided in the compartment 410 as fixed components, in which embodiment the output terminals of the individual converters are rigidly fixed to, for example, two common conductor rails that provide the DC output 154 (Figure 1) of the AC to DC converting system 150. In an alternative embodiment, the individual AC to DC converters are releasably mounted in the compartment 410, preferably in individual casings, that allow fast, convenient and efficient replacement of individual AC to DC converters.

The AC to DC converters 300, 300', 300" are placed in the compartment 410 such that they have a thermally conductive connection with a back wall 412 of the compartment 410. More in particular, the first semiconductor switches 312 and the second semiconductor switches 322 are placed in the compartment 410 such that they have a thermally conductive connection with a back wall 412 of the compartment 410. The cabinet is further provided with a heatsink 430. The heatsink 430 comprises in this embodiment, the back wall 412 of the compartment 410.

The heatsink 430 further comprises fins 432 for radiating thermal energy. The heatsink 430 is in thermal contact with the back wall 412 and is preferably provided over at least most of the area of the back wall 412. In an embodiment, the heatsink 430 comprises the back wall 412 and the fins 432 connected thereto. In this way, the heatsink 430 is in thermal contact with the first semiconductor switches 312 and the second semiconductor switches 322 for radiating thermal energy dissipated by these switches. If the heat radiation capacity of the back wall 412 is sufficient to ensure proper operation of the AC to DC system 150, the back wall 412 may be sufficient as the heatsink 430, and the fins 432 may be omitted. Alternatively, the heat sink may comprise a plate that is mounted to the back wall, at an outer side thereof, with, if required, fins connected to the plate. Many variants are possible.

Advantageously, the electric components of the arrangement 150 and of the converters 300, 300', 300" are mounted directly onto the back wall 412 of the cabinet 410, preferably with limited or preferably no additional thermally conductive layers in between. In another embodiment, the electric components of the converters 300, 300', 300" are mounted onto a back wall of their individual casing, which casing is mounted directly onto a wall, advantageously the back wall, of the cabinet 410. Advantageously, the footprint of the casing fits into a seat of the back wall such that a tight mounting is possible to improve the heat transport. As such, heat can be transported directly to the outside of the cabinet, while reducing the number of thermally conductive layers. Advantageously, to improve the heat dissipating capacity, the heat sink 430 may additionally be provided with fins 432 extending outwardly from the back wall 412.

Likewise, semiconductor switches and/or other semiconductor components of the second AC to DC converter 300' and the third AC to DC converter 300" are thermally conductively connected to the heatsink 430 via the back wall 412. Alternatively to the back wall 412, the heatsink 430 may be provided on another wall of the compartment 410 - as long as an efficient thermal connection with the relevant semiconductor circuit elements is provided.

For practical purposes, in particular with respect to cabinet size, individual converters (300, 300', 300") providing a current of 75 Ampere may be preferred - providing a total maximum current of about 200 Ampere per AC to DC system 150 as depicted by Figure 1. Systems for providing larger currents require larger cabinets, in particular considering heat dissipation and heat sink requirements. For loads requiring a higher current, multiple arrangements may be provided in parallel. Figure 5A shows the three phase generator 110 connected to a compound AC to DC converting system 500.

The compound system 500 comprises a first AC to DC

arrangement or converting system 150, a second AC to DC arrangement or converting system 156 and a third AC to DC arrangement or converting system 158. Each AC to DC converting system is preferably provided in a separate explosion safe cabinet. The first AC to DC converting system 150 comprises a first AC to DC converter 300, a second AC to DC converter 300' and a third AC to DC converter 300". The second AC to DC converting system 150' comprises a fourth AC to DC converter 306, a fifth AC to DC converter 306' and a sixth AC to DC converter 306". The third AC to DC converting system 150 comprises a seventh AC to DC converter 308, a eighth AC to DC converter 308' and a ninth AC to DC converter 308". The compound system 500 further comprises a system module 502 for controlling the various components of the compound system 500.

In this embodiment, the compound system 500 is designed such that the first AC to DC converting system 150 and the second AC to DC converting system 150' operate parallel to one another for providing approximately 400 Ampere maximum, at 24 Volts: 9.6 kW. Other values of voltage, current and power may be envisaged was well. The third AC to DC converting system 150" is arranged to be available in standby, as a redundant module. In this embodiment, the seventh AC to DC converter 308, the eighth AC to DC converter 308' and the ninth AC to DC converter 308" are designed as separate redundant module.

The redundancy principle is further elucidated by Figure 5 B. In Figure 5 B, the second AC to DC converter 300' is depicted as

malfunctioning. Hence, from the first and third phase provided by the three phase generator 110, about 150 Ampere may be provided, but from the second phase only 75 Ampere. This may lead to imbalance of the three phase generator 110 and/or overload of the fifth AC to DC converter 306'. Alternatively, the control module 502 switches the compound system 500 to secure mode, in which only half the amount of power may be provided.

As all of these three situations are all but preferred, the third AC to DC converting system 150" is arranged to be available in standby, as a redundant module. With the second AC to DC converter 300' failing, the eighth AC to DC converter 308' is switched on, controlled by the control module 502 that detects failure of the second AC to DC converter 300'. In this way, the compound system 500 can still provide the 9.6 kW power for which it has been designed.

In another embodiment, all individual AC to DC converters are operational and the maximum current to be provided by the individual AC to DC converters is limited below the actual maximum current they can provide. Such limitation may be controlled by means of the controller module 502. For example, the individual AC to DC converters may be operational at 80% of their operational power. In case of failure of one converter module, the remaining converter modules may then become operational at 100% of their power.

More in particular, the amount by which current supplied the individual AC to DC converters may be determined based on the total amount of individual AC to DC converters available per phase. If in total five individual AC to DC converters are available per phase, the maximum current to be provided may be set at 20% below the maximum current that each individual AC to DC converter can provide. In this way, if one individual AC to DC converter fails, the current initially provided by the malfunctioning or faihng individual AC to DC converter may be taken over by the other four AC to DC converters available on that particular phase.

Figure 6 shows a cabinet 400 that may be suitable for explostion proof environments and/or for harsh environments. The cabinet 400 is here shown without the door. The cabinet 400 has an inner compartment or inner space 410 and a back side or back wall 412. The power supply system 100 comprising the three AC-DC converters 300, 300', 300", can be mounted onto a chassis 414. Each AC-DC converter 300, 300', 300" has an associated controller 500, 500', 500", that may be mounted onto the chassis 414 as well. Alternatively, a single controller 152 may be provided for the converters 300, 300', 300" as shown in figure 1. The back wall 412 of the cabinet 400 is preferably machined to provide for a smooth receiving space for receiving the chassis 414. Advantageously, the side of the chassis 414 mating the receiving space of the back wall 412 can be machined as well. This is in particular advantageous for metal-metal contact, for which a simple bolt- connection may suffice. In case of a metal sheet chassis Then, the heat transfer can be optimized. Any heat generated by the converters 300, 300', 300" can then be optimally transferred to the heat sink 430, having fins 432, at an outer side of the back wall 412 of the cabinet 400. The heat sink 430 is preferably bolted to the outer side of the cabinet 400. In case of an

aluminium heat sink 430 that is to be mounted to a - usually - stainless steel cabinet, some pastry or other sealing may be used to obviate air between the heat sink and the cabinet.

Figure 7 shows an embodiment of a power system 600 comprising, here, two cabinets 400 which cabinets have the same dimensions. Also are provided two control unit cabinets 460 are provided from which the power system 600 can be controlled, either locally, e.g. via the display interface, or remotely when communication is provided in the control unit cabinet 460. Here, the system is provided entirely redundant, there is one spare cabinet 400 and one spare control unit cabinet 460. Since all cabinets have the same dimensions, they can easily be mounted together in a system 600, so the system can become scalable.

In summary, an AC to DC conversion system is disclosed, whereof between individual phases of a three-phase alternating current source, AC to DC converters are provided. The DC outputs of the converters are switched in parallel. The DC output may have the same effective voltage as the input, or higher or lower. The AC to DC converters preferably comprise electronic converters. In particular a forward based converter is preferred, as it provides a galvanic separation between the input side and the output side of the converter. The converters are provided in a steel or aluminium cabinet, preferably an explosion-safe cabinet. The switching components of the converters and other dissipating components are provided in thermal contact with one or more inner walls of the cabinet and at one or more outer walls of the cabinet, one or more heat sinks are provided. A module thus created provide a safe and flexible module for power supply on, for example, an offshore platform.

In the description above, it will be understood that when an element such as layer, region or substrate is referred to as being "on" or "onto" another element, the element is either directly on the other element, or intervening elements may also be present. Also, it will be understood that the values given in the description above, are given by way of example and that other values may be possible and/or may be strived for.

Furthermore, the invention may also be embodied with less components than provided in the embodiments described here, wherein a single component carries out multiple functions. Just as well may the invention be embodied using more elements than depicted in the Figures, wherein functions carried out by one component in the embodiment provided are distributed over multiple components.

It is to be noted that the figures are only schematic

representations of embodiments of the invention that are given by way of non-limiting examples. For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described. The word 'comprising' does not exclude the presence of other features or steps than those listed in a claim. Furthermore, the words 'a' and 'an' shall not be construed as limited to 'only one', but instead are used to mean 'at least one', and do not exclude a plurality.

A person skilled in the art will readily appreciate that various parameters and values thereof disclosed in the description may be modified and that various embodiments disclosed and/or claimed may be combined without departing from the scope of the invention.

It is stipulated that the reference signs in the claims do not limit the scope of the claims, but are merely inserted to enhance the legibility of the claims.