TECHNICAL FIELD

Embodiments presented herein generally relate to power electronics systems (PESs) and particularly to hybrid wireless-optical PES utilizing communication over both a wireless communication network and at least one fiber optical communication network.

BACKGROUND

PESs e.g. in the form of high voltage direct current (HVDC) power transmission has become increasingly important due to increasing need for power supply or delivery and interconnected power transmission and distribution systems. In a HVDC power system there is generally included an interface arrangement including, or constituting, a HVDC converter station, which is a type of station configured to convert high voltage Direct Current (DC) to Alternating Current (AC), or vice versa. A HVDC converter station may comprise a plurality of elements such as the converter itself (or a plurality of converters connected in series or in parallel), one or more circuit breakers, transformers, capacitors, filters, and/or other auxiliary elements. Converters, which often are referred to as 'converter valves', or simply 'valves', may comprise a plurality of solid-state based devices such as semiconductor devices and may be categorized as line-commutated converters (LCCs) or voltage source converters (VSCs), e.g. depending on the type of switches (or switching devices) which are employed in the converter. A plurality of solid-state semiconductor devices such as IGBTs maybe connected together, for instance in series, to form a building block, or cell, of a HVDC converter, or HVDC converter valve. HVDC converter valves may be arranged indoors, in so called converter valve halls. Elements which for example may be included in a converter, such as switches or switching devices, circuit breakers, transformers, capacitors, filters, and/ or other auxiliary elements, will in the following be referred to as power electronics components (PECs).

PECs, which for example may be included in converters, may be provided with communication means. Such communication means should preferably be robust and reliable and have a relatively low latency. Operation of PECs, such as, for example, IGBTs, maybe controlled by means of a controller by way of transmission of control signals, e.g., including switching commands or instructions, using multiple optical fiber (OF) communication links. OF communication links may however be expensive to fabricate, install and maintain, and may have a shorter lifetime and a higher rate of failure as compared with the PECs. Alternative solutions in the form of wireless communication links for replacing OF communication links have been proposed. Some benefits of using wireless communication links are reduction in material, installation and commissioning costs achieved by replacing the OF communication links between the controller and PECs by wireless communication links. The galvanic isolation between the controller and PECs is still achievable by the wireless communication links. However, in many applications, the distance between the controller and PECs may be desired or even required to be as long as up to a hundred meters, in particular in high voltage systems such as in HVDC converters and high voltage circuit breakers. Such a relatively long distance between the controller and PECs may make the use of wireless communication links between the controller and PECs difficult. For example, using wireless communication links between the controller and PECs where the distance between the controller and PECs is hundreds of meters, it may be difficult to implement a communicative connection between the controller and the PECs having a high reliability and high data rate. Wireless communication links may utilize radio frequency (RF) communication techniques or means. However, in case there is no direct line-of-sight between the controller and the PECs, for example due to components or obstacles being located between the controller and PECs such as metallic planes, dishes, columns, or beams, RF signals may be significantly distorted due to fading, reflection, and attenuation. This may make the use of wireless communication links between the controller and PECs even more difficult. PECs may be employed in applications other than HVDC power systems, such as, for example, in AC power systems such as a so-called flexible AC transmission system (FACTS).

One further limitation of using wireless communication links is represented by the scalability, i.e. preserving the required performance as the number of PECs and/ or control cards at the controller side becomes large (e.g. a few thousand PECs in one HVDC converter). Indeed, since the allocation of resources in the uplink (from PECs to controller) naturally scales with the number of PECs and the number control cards, existing schemes for wireless communication are unsuitable for providing sufficient network capacity and latency guarantees as the PES grows in size. Hence, there is still a need for an improved PES.

SUMMARY

An object of embodiments disclosed herein is to provide PESs that do not suffer from the above disclosed issues, or at least where the above disclosed issues are mitigated or reduced.

According to a first aspect there is presented a hybrid wireless-optical PES. The PES comprises a set of JV PECs. The PES further comprises a set of Q first wireless transceiver units. The PECs are operatively connected to the first wireless transceiver units over a first fiber optical communication network. The first wireless transceiver units are configured to communicate with a controller of the PES over a wireless communication network for facilitating communication of signals between the controller and the PECs.

According to some embodiments, the PES further comprises the controller, a set of M control cards operatively connected to the controller, and a set of P second wireless transceiver units. The control cards are operatively connected to the second wireless transceiver units over a second fiber optical communication network. The second wireless transceiver units are configured to communicate with the first wireless transceiver units over the wireless communication network for facilitating communication of signals between the controller and the PECs. According to a second aspect there is presented a hybrid wireless-optical PES. The PES comprises a controller. The PES further comprises a set of M control cards operatively connected to the controller. The PES further comprises a set of P second wireless transceiver units. The control cards are operatively connected to the second wireless transceiver units over a second fiber optical communication network. The second wireless transceiver units are configured to communicate with a set of first wireless transceiver units over a wireless communication network for facilitating communication of signals between the controller and a set of PECs.

Advantageously these PESs do not suffer from the above disclosed issues.

Advantageously these PESs provide efficient support for wireless connectivity in large-scale PESs, allowing significant cost savings compared to wired PESs. Advantageously these PESs are flexible in terms of redundancy configurations of the PESs.

Advantageously these PESs with wireless communication between controllers and PECs can be applied both in HVDC power systems and in other applications, e.g. in Flexible AC Transmission Systems (FACTSs).

Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, module, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, module, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which:

Figs. 1, 4, and 7 are schematic diagrams illustrating hybrid wireless-optical PESs according to embodiments;

Figs. 2 and 3 are schematic diagram illustrating a first fiber optical communication network communication network according to embodiments; and

Figs. 5 and 6 are schematic diagram illustrating a second fiber optical communication network communication network according to embodiments. DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional.

As disclosed above there is still a need for an improved PES, and an object of embodiments disclosed herein is to provide PESs that do not suffer from the above disclosed issues, or at least where the above disclosed issues are mitigated or reduced.

Reference is now made to Fig. l that schematically illustrates a hybrid wireless- optical PES 100a according to embodiments. The PES 100a comprises a set of JV PECs noa:iioN. The PES 100a further comprises a set of Q first wireless transceiver units 130a: 130Q. Each of the first wireless transceiver units 130a: 130Q is provided with one or more antennas 140a: 140Q (e.g., one or more RF antennas). The PECs 110a: 110N are operatively connected to the first wireless transceiver units 130a: 130Q over a first fiber optical communication network 120a, 120b. Each PEC 110a: 110N might be operatively connected to the first fiber optical communication network 120a, 120b over an electrical connection. The first wireless transceiver units 130a: 130Q are configured to communicate with a controller 200 (not shown) of the PES 100a over a wireless communication network 150 for facilitating communication of signals between the controller 200 and the PECs 110a: 110N. In this respect, the controller 300 and the PECs 110a: 110N are separately arranged. In some scenarios there are redundant controllers 200. That is, there could be two or more controllers 200. In such scenarios, the wireless communication network 150 is configured so that each redundant controller 200 is configured to communicate with all the PECs noa:iioN.

Such a PES 100a solves the scalability limitation of a fully wireless PES so that the cost saving obtained by using wireless communication links instead of optical communication links can still be achieved in large-scale PESs.

There could be different types of PECs 110a: 110N. In some non-limiting examples, each of the PECs noa:iioN is, or comprises, any of: an IGBT, IGCT, MOSFET, thyristor. In some examples, two or more of the PECs 110a: 110N are part of a power electronics element (PEE). The PEEs may for example comprise or be constituted by a converter configured to convert high voltage DC to AC, or vice versa. The converter may for example comprise one or even a plurality of PEEs. The converter may for example comprise or be constituted by a HVDC converter. There could be different types of signals. The controller 200 is configured to control the PECs 110a: 110N by means of transmitting at least one control signal to the PECs 110a: 110N. In some non-limiting examples, the signals therefore comprise firing commands, as issued by the controller 200, for the PECs 110a: 110N to execute.

According to the PES 100a, a first fiber optical communication network 120a, 120b can thus be used to operatively connect multiple PECs 110a: 110N to multiple first wireless transceiver units 130a: 130Q. By means of such a PES 100a, the stress on network capacity, especially for uplink communication, can be significantly decreased and thus improving the scalability of the PES 100a. Unlike current PES installations, fiber optical communication networks can be realized with short distance and low- cost plastic fibers, since the difference in electric potential between the nearby PECs noa:iioN and the first wireless transceiver units i3oa:i3oQ will be moderate. This allows to eliminate the long distance and high-cost glass fibers, similarly to a fully wireless network. Furthermore, the fiber optical communication networks can be pre assembled and tested during production, therefore avoiding the commissioning of cables, which is very time-consuming during the installation of a large-scale PES. For these reasons, the cost savings are comparable to a fully wireless PES, even though the PES 100a is hybrid wireless-optical PES.

In large-scale PES 100a, the value of JV can be as high as a few thousands. Further, there could be different relations between N and Q. According to an embodiment, Q < N. This enables a reduction in the needed number of first wireless transceiver units i30a:i30Q compared to the number of PECs noa:iioN. The total number of first wireless transceiver units 130a: 130Q can thus be smaller than the total number of PECs 110a: 110N, even when redundancy is considered in the PES 100a.

Each of the first wireless transceiver units 130a: 130Q may comprise an optical to wireless bridge. The optical to wireless bridge may for example employ or be based on RF-over- fiber technology, which as such is known in the art. However, the optical to wireless bridge could in alternative or in addition employ or be based on, for example, Gigabit Ethernet, EtherCat or proprietary optical communication technologies.

There could be different types of first fiber optical communication networks 120a, 120b. In some embodiments, the first fiber optical communication network 120a,

120b has a redundant star topology or a mesh topology.

Further aspects of the redundant star topology will now be disclosed with reference to Fig. 2. Fig. 2 schematically illustrates, according to the redundant star topology, how each PEC 110a: 110N, via individual optical fiber links of the first fiber optical communication network 120a, is operatively connected to at least two of the first wireless transceiver units 130a: 130Q.

Specifically, according to the redundant star topology in the example of Fig. 2, a certain number Aq of PECs 110a: 110N are operatively connected with individual optical fiber links to exactly two of the first wireless transceiver units 130a, 130Q. The required number of first wireless transceiver units 130a: 130Q can hence be estimated as Q = 2 \N/k and the number of individual optical fiber links to 2 N. One reason to have two first wireless transceiver units for each of the PECs 110a: 110N is to ensure redundancy in the PES 100a; if one of the first wireless transceiver units 130a: 130Q malfunctions, or experiences a communication fault, the other of the first wireless transceiver units 130a: 130Q can still carry out the operations as required.

Further aspects of the mesh topology will now be disclosed with reference to Fig. 3. Fig. 3 schematically illustrates how the PECs 110a: 110N are operatively connected to the first wireless transceiver units 130a: 130Q in a first fiber optical communication network 120b having a mesh topology. In this respect, according to the mesh topology, a certain number of the PECs 110a: 110N form a mesh optical network.

In some aspects, the mesh optical network includes two types of optical fiber links: normal optical fiber links deployed between neighboring PECs 110a: 110N and acceleration optical fiber links between some pairs of distant PECs 110a: 110N, where the latter type is used to increase the redundancy and to allow for faster communication by reducing the number of optical fiber link hops. That is, in some embodiments, according to the mesh topology, a first group of the PECs 110a: 110N are operatively connected to the first wireless transceiver units 130a: 130Q via optical fiber links of a first type, a second group of the PECs 110a: 110N are operatively connected to the first wireless transceiver units 130a: 130Q via optical fiber links of a second type. In some examples, the first group of the PECs 110a: 110N are placed farther away from the first wireless transceiver units 130a: 130Q than the second group of PECs 110a: 110N.

In the examples of Fig. 3, four first wireless transceiver units 130a: 130Q are attached to the mesh optical network in order to provide redundancy and fast communication. The required number of first wireless transceiver units 130a: 130Q can hence be estimated as Q = 4 \N /hi, whilst the number of low-cost fiber optical links is 4 plus all the optical fiber links in the first fiber optical communication network 120b, which depend on the density of acceleration links.

Reference is now made to Fig. 4 that schematically illustrates a hybrid wireless- optical PES 100b according to embodiments. The PES 100a comprises a controller 200. The PES 100b further comprises a set of M control cards 190a: 190M operatively connected to the controller 200. The PES 100b further comprises a set of P second wireless transceiver units 170a: 170P. Each of the second wireless transceiver units i30a:i30P is provided with one or more antennas i6oa:i6oP (e.g., two or more RF antennas). The control cards i9oa:i9oM are operatively connected to the second wireless transceiver units 170a: 170P over a second fiber optical communication network 180a, 180b. Each control card 190a: 190M might be operatively connected to the second fiber optical communication network 180a, 180b over an electrical connection. The second wireless transceiver units 170a: 170P are configured to communicate with a set of first wireless transceiver units 130a: 130Q (not shown) over a wireless communication network 150 for facilitating communication of signals between the controller 200 and a set of PECs noa:iioN (not shown). In some scenarios there are redundant controllers 200. That is, there could be two or more controllers 200. In such scenarios, the wireless communication network 150 is configured so that each redundant controller 200 is configured to communicate with all the PECs noa:iioN. Further, each controller 200 is operatively connected to all control cards i90a:i90M. Such a PES 100b solves the scalability limitation of a fully wireless PES so that the cost saving obtained by using wireless communication links instead of optical communication links can still be achieved in large-scale PESs.

According to the PES 100b, a second fiber optical communication network 180a, i8ob can thus be used to operatively connect multiple control cards i9oa:i9oM to multiple second wireless transceiver units i70a:i70P. By means of such a PES loob, the stress on network capacity, especially for uplink communication, can be significantly decreased and thus improving the scalability of the PES loob. Furthermore, the fiber optical communication networks can be pre-assembled and tested during production, therefore avoiding the commissioning of cables, which is very time-consuming during the installation of a large-scale PES. For these reasons, the cost savings are comparable to a fully wireless PES, even though the PES loob is hybrid wireless-optical PES.

There could be different relations between M and P. According to an embodiment, P < M. This enables a reduction in the needed number of second wireless transceiver units i70a:i70P compared to the number of control cards i90a:i90M. The total number of second wireless transceiver units 170a: 170P can thus be smaller than the total number of control cards i90a:i90M, even when redundancy is considered in the PES 100b. Each of the second wireless transceiver units i70a:i70P may comprise an optical to wireless bridge. The optical to wireless bridge may for example employ or be based on RF-over- fiber technology, which as such is known in the art. However, the optical to wireless bridge could in alternative or in addition employ or be based on, for example, Gigabit Ethernet, EtherCat or proprietary optical communication technologies.

There could be different types of second fiber optical communication networks 180a, 180b. In some embodiments, the second fiber optical communication network 180a, 180b has a redundant star topology or a mesh topology.

Further aspects of the redundant star topology will now be disclosed with reference to Fig. 5. Fig. 5 schematically illustrates, according to the redundant star topology, how each control card 190a: 190M is, via individual optical fiber links of the second fiber optical communication network 180a, 180b, operatively connected to at least two of the second wireless transceiver units 170a: 170P.

Specifically, according to the redundant star topology in the example of Fig. 5, a certain number k ₂ of control cards i90a:i90M are operatively connected with individual optical fiber links to exactly two of the second wireless transceiver units 170a: 170P. The required number of second wireless transceiver units 170a: 170P can hence be estimated as P = 2 \M/k ₂ and the number of individual optical fiber links to 2 M. One reason to have two second wireless transceiver units for each of the control cards i90a:i90M is to ensure redundancy in the PES 100b; if one of the second wireless transceiver units 170a: 170P malfunctions, or experiences a communication fault, the other of the second wireless transceiver units i70a:i70P can still carry out the operations as required.

Further aspects of the mesh topology will now be disclosed with reference to Fig. 6. Fig. 6 schematically illustrates how the control cards i9oa:i9oM are operatively connected to the second wireless transceiver units 170a: 170P in a second fiber optical communication network 180b having a mesh topology. In this respect, according to the mesh topology, a certain number l ₂ of the control cards i90a:i90M form a mesh optical network.

In some aspects, the mesh optical network includes two types of optical fiber links: normal optical fiber links deployed between neighboring control cards 190a: 190M and acceleration optical fiber links between some pairs of distant control cards i9oa:i9oM, where the latter type is used to increase the redundancy and to allow for faster communication by reducing the number of optical fiber link hops. That is, in some embodiments, according to the mesh topology, a first group of the control cards i9oa:i9oM are operatively connected to the second wireless transceiver units i70a:i70P via optical fiber links of a first type, a second group of the control cards i9oa:i9oM are operatively connected to the second wireless transceiver units i70a:i70P via optical fiber links of a second type. In some examples, the first group of the control cards i9oa:i9oM are placed farther away from the second wireless transceiver units i70a:i70P than the second group of control cards i90a:i90M. In the examples of Fig. 6, four second wireless transceiver units 170a: 170P are attached to the mesh optical network in order to provide redundancy and fast communication. The required number of second wireless transceiver units 170a: 170P can hence be estimated as P = 4 \M/l ₂ ], whilst the number of low-cost fiber optical links is 4 plus all the optical fiber links in the second fiber optical communication network 180b, which depend on the density of acceleration links.

Further aspects of the communication of signals over the wireless communication network 150, the first fiber optical communication network 120a, 120b, and the second fiber optical communication network 180a, 180b, as valid for both the PES 100a of Fig. 1 and the PES 100b of Fig. 4 will now be disclosed.

In some aspects, the signals are communicated in packets and packet aggregation is utilized for communication over the wireless communication network 150 by the first wireless transceiver units i30a:i30Q and/or the second wireless transceiver units i70a:i70P. In further detail, each of the first wireless transceiver units 130a: 130Q might aggregate uplink packets of the /cy or PECs 110a: 110N connected to it into one packet to be transmitted as unicast over the wireless communication network 150. That is, in some embodiments, the first wireless transceiver units 130a: 130Q are configured to transmit aggregated packets over the wireless communication network 150, where the aggregated packets comprise individual packets received from the

PECs noa:iioN over the first fiber optical communication network 120a, 120b.

Further, the second wireless transceiver units 170a: 170P might aggregate downlink packets coming from the control cards i9oa:i9oM into one packet to be transmitted as broadcast over the wireless communication network 150. That is, in some embodiments, the second wireless transceiver units i70a:i70P are configured to transmit aggregated packets over the wireless communication network 150, and the aggregated packets comprise individual packets received from the control cards i90a:i90M over the second fiber optical communication network 180a, 180b.

Such aggregation as performed by the first wireless transceiver units 130a: 130Q and/ or the second wireless transceiver units 170a: 170P allows for a more efficient transmission over the wireless communication network 150 since many common parts in the aggregated packets will not be replicated and some information can be compressed through suitable mapping schemes. This allows to improve the network capacity and latency of the communication of signals over the wireless communication network 150 with respect to prior art. In some aspects, when packet aggregation is utilized for communication over the wireless communication network 150 by the first wireless transceiver units i3oa:i3oQ and/or the second wireless transceiver units i70a:i70P, packet fragmentation is utilized at the other of the first wireless transceiver units i30a:i30Q and/or the second wireless transceiver units 170a: 170P during reception of the packets.

In further detail, the first wireless transceiver units 130a: 130Q might fragment received downlink packets if needed, for example selecting only the parts of the payload that are relevant for the corresponding PECs 110a: 110N. That is, in some embodiments, the first wireless transceiver units 130a: 130Q are configured to receive aggregated packets over the wireless communication network 150, to fragment each aggregated packet into individual packets, and to transmit the individual packets to the PECs 110a: 110N over the first fiber optical communication network 120a, 120b. In this way, communication over the first fiber optical communication network 120a, 120b can be faster by avoiding transmission of unnecessary information. Further, the second wireless transceiver units 170a: 170P might fragment received uplink packet into the k or l original individual packets and send them back to the control cards i90a:i90M. That is, in some embodiments, the second wireless transceiver units 170a: 170P are configured to receive aggregated packets over the wireless communication network 150, to fragment each aggregated packet into individual packets, and to transmit the individual packets to the control cards i90a:i90M over the second fiber optical communication network 180a, 180b.

The PECs 100a, 100b might require absolute synchronization between the clocks of the controller 200 and the PECs noa:iioN, for example to enable the switching of power devices at specific times. Internal synchronization of the first fiber optical communication network 120a, 120b and of the second fiber optical communication network 180a, 180b can be achieved by constantly measure the optical fiber link delays and clock offsets through the transmission of dedicated packets when the optical fiber links are idle.

In some aspects, synchronization is performed between the first wireless transceiver units i30a:i30Q and the second wireless transceiver units i70a:i70P over the wireless communication network 150. Such synchronization in the the wireless communication network 150 can be achieved by embedding synchronization-related information in signals exchanged over the wireless communication network 150. Therefore, in some embodiments, the aggregated packets comprise embedded synchronization information. In a first alternative, the first wireless transceiver units 130a: 130Q might record the timestamp of the last received downlink packet and the timestamp of the last transmitted uplink packet and embed this information in the uplink packet. The second wireless transceiver units 170a: 170P might then compare these timestamps with the timestamp taken at the transmission of the downlink packet and reception of the uplink packet and use the result to estimate continuously the propagation delays and the clock offsets. This information can then be sent in the next downlink packet so that the first wireless transceiver units 130a: 130Q can update their clocks.

In a second alternative, second wireless transceiver units 170a: 170P might record the timestamp of the last received uplink packet and the timestamp of the last received downlink packet and embed this information in the downlink packet. The first wireless transceiver units i30a:i30Q might then compare these timestamps with the timestamp taken at the transmission of the uplink packet and reception of the downlink packet and use the result to estimate continuously the propagation delays and the clock offsets. This information can then be sent in the next uplink packet so that the second wireless transceiver units 170a: 170P can update their clocks.

In both these alternatives, the embedded synchronization information of a given aggregated packet is provided as a timestamp of the last transmitted or received individual packet comprised in this given aggregated packet.

The synchronization accuracy of the first fiber optical communication network 120a, 120b and of the second fiber optical communication network 180a, 180b will depend on the percentage of idle link time; the higher this percentage, the more accurate the synchronization will be. For the wireless communication network 150 the synchronization accuracy will depend on the period with which downlink and uplink packets are transmitted; the higher this period, the more accurate the synchronization will be. These parameters can be tuned in order to meet the end-to- end synchronization requirement between the controller 200 and each PEC noa:iioN.

Reference is now made to Fig. 7 that schematically illustrates a hybrid wireless- optical PES 100c according to embodiments. The PES 100c is a combination of the PES 100a of Fig. 1 and the PES 100b of Fig. 4. The PES 100c thus comprises a set of JV PECs 110a: 110N. The PES 100c further comprises a set of Q first wireless transceiver units 130a: 130Q. Each of the first wireless transceiver units 130a: 130Q is provided with one or more antennas 140a: 140Q (e.g., RF antennas). The PECs 110a: 110N are operatively connected to the first wireless transceiver units 130a: 130Q over a first fiber optical communication network 120a, 120b. Each PEC noa:iioN might be operatively connected to the first fiber optical communication network 120a, 120b over an electrical connection. The first wireless transceiver units 130a: 130Q are configured to communicate with a controller 200 of the PES 100a over a wireless communication network 150 for facilitating communication of signals between the controller 200 and the PECs 110a: 110N. The PES 100c further comprises the controller 200. The PES 100c further comprises a set of M control cards i90a:i90M operatively connected to the controller 200. The PES 100c further comprises a set of P second wireless transceiver units i70a:i70P. Each of the second wireless transceiver units i30a:i30P is provided with one or more antennas i6oa:i6oP (e.g., two or more RF antennas). The control cards 190a: 190M are operatively connected to the second wireless transceiver units 170a: 170P over a second fiber optical communication network 180a, 180b. Each control card i90a:i90M might be operatively connected to the second fiber optical communication network 180a, 180b over an electrical connection. The second wireless transceiver units 170a: 170P are configured to communicate with the set of first wireless transceiver units i30a:i30Q over the wireless communication network 150 for facilitating communication of signals between the controller 200 and the set of PECs 110a: 110N. Further aspects, embodiments, and examples of the PES 100a, 100b apply equally for the PES 100c and a detailed description thereof is therefore omitted for brevity of this disclosure.

In summary, using a fully wireless communication network for the control of PECs 110a: 100N in a large-scale PES might significantly save cost but does not provide scalability when the number of PECs iioa:iioN and/or control cards i90a:i90M is large. The herein disclosed embodiments provides PESs 100a, 110b, 100c based on a hybrid wireless-optical network for communication between the controller 200 and the PECs iioa:iioN, and where wireless transceiver units i30a:i30Q, i70a:i70P are operatively connected to the PECs noa:iioN and/or the control cards i90a:i90M through fiber optical communication network 120a, 120b, 180a, 180b. Such PESs 100a, 100b, 100c allows for efficient increase of the total number of PECs noa:iioN and/or control cards i90a:i90M whilst maintaining most of the cost saving benefits of using a fully wireless communication network. In some scenarios there are redundant controllers 200. That is, there could be two or more controllers 200. In such scenarios, the wireless communication network 150 is configured so that each redundant controller 200 is configured to communicate with all the PECs 110a: 110N. Further, each controller 200 is operatively connected to all control cards i90a:i90M.

The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.