- 4—Solid-state transformer (SST)
- 11—First module (converts HV AC to HV DC signal)
- 12—Second module (voltage scaling/transformation)
- 13—Sub-module
- 14—DC to AC converter (medium frequency)
- 15—Medium frequency transformer (MFT)
- 16—AC to DC converter (low voltage)

The solid state transformer 4 shown in FIG. 3 consists of two modules 11 and 12. The first module 11 converts typical HV AC signal into HV DC signal or backwards. The second module 12 consists of several, in series connected, sub-modules 13. Each submodule 13 converts a HV DC signal into a HV AC signal through a DC to AC converter 14, then provides galvanic insulation within a medium frequency transformer 15 and converts the medium frequency AC signal into DC signal at a low voltage level. The output of all sub-modules 13 is connected in parallel either within the SST 4 and then goes into the LV switchgear 5, or connection of sub-modules 13 is done within the LV switchgear 5.

Another mechanism by which the solid-state transformer (SST) can target higher power applications is to use plurality of second modules 12 connected in parallel. This is illustrated in FIG. 4, which shows schematics of an SST architecture with multiple second modules with DC output. In this case, each parallel second module 12 branch can serve different applications, but the first module 11 is designed to be able to carry the full total power of the SST 4.

The SST 4 can be configured to convert DC to AC power, in order that it can be connected to LV AC applications, and therefore is not limited to the DC only. Nevertheless, also for this case, the high-level topology of the described converter station 1 can remain the same, with an additional block of DC to AC conversion 30. As shown in FIG. 5 the DC to AC conversion 30 can be added to the SST or as shown in FIG. 6 the DC to AC conversion 30 can be connected to one or more of the outputs from LV switchgear 5, or can if necessary be located close to the application 6.

In FIG. 6, a reference numeral is shown which represents the following: 30-LV DC to AC conversion unit

Depending on power requirements of different applications, power flow through at least a portion of the AC/DC converter station (power conversion system) 1 can be set. An advantage of utilizing a LV switchgear (SWG) 5 to connect the applications 6 is that the LV SWG 5 can freely configure the energy flow for each particular application 100, 101 and/or 102, based on the power available. Furthermore, all types of mentioned connected devices 6 might not always be connected.

Examples of possible scenarios for power flow are shown in FIGS. 7a-7c.

Unidirectional power flow as shown in FIG. 7a) is applicable in cases where energy storage 100 and energy consumption 101 devices are powered from the HV/MV network 2 through the AC/DC converter station (power conversion system) 1. An example of the energy storage device 100 can be for example battery storage or any other kind of technology for energy storage, which is, in this case, being charged from HV/MV network 2. An example of an energy consumption device 101 can be for example datacenters, charging station of electric vehicles or any other type of devices that need to be powered using LV DC signal.

Another type of unidirectional power flow, but going in opposite direction, is shown in FIG. 7b). This represents a situation when the energy storage device 100 is at least partly charged and thus can supply power into the HV/MV network 2 when there is a high need. The same can be done with energy originating within the energy generation devices 102, such as wind turbines or solar power plants.

Advantage of the power conversion system 1 are further shown in the configuration shown in FIG. 7c), d) and e).

In the situation where there is a high amount of power available from the energy generating devices 102, capable of powering the actual needs of energy storage devices 100 and/or energy consuming devices 101, the power does not need to flow into the HV/MV network 2 or not even to any part of the solid-state transformer 4, but can flow only through the LV switchgear 5. This case is represented by FIG. 7c). If necessary the excess of energy available from the energy generating devices 102, or energy storage 100 when charged, can be transferred though the solid-state transformer 4 and HV/MV switchgear 3 into the HV/MV network 2.

Situations with high power demand are represented in FIG. 7d). In these cases, energy generating devices 102 are capable of providing only a portion of the power required by the other devices 6 connected to the LV switchgear 5. The remaining power can then be supplied through the solid-state transformer 4 and HV/MV switchgear 3 from the HV/MV network 2.

In situation when the connected devices 6 are each connected through the LV switchgear 5 to the single second module 12 or submodule 13, the power mix can be done within the solid-state transformer 4 as well.

Thus, in a detailed embodiment an AC/DC converter station 1, also termed a power conversion system, has a solid-state transformer 4. The solid-state transformer 4 is build out of several modules. A first module 11 of the SST 4 is for converting a HV AC signal into a HV DC signal and it is designed for maximum parameters of the solid state transformer 4. At least one second module 12 of the SST 4 is used for voltage scaling, comprising at least one sub-module 13 containing a DC/AC converter 14, medium frequency transformer 15 and AC/DC converter 16. The AC/DC converter station 1 also has a high voltage switchgear 3 that is connected to the input of the solid-state transformer 4, with at least one switching and/or protection device. The AC/DC converter station 1 also has a low voltage switchgear 5, connected to the output of the solid-state transformer 4, with plurality of switches, each connected to a different users or applications 6. The AC/DC converter station 1 also has an overall control system 8 with data acquisition and communication, and an auxiliary power supply 7 for control and/or communication circuits

In this detailed embodiment the solid-state transformer