An electrical converter system for power supply, comprising at least two similar cascaded modules (2410, 2420, 2430, 2440), wherein each module comprises at least 4 terminals and at least one module energy storage (2510; 2610) for energy storage, and the modules include switching elements (2535, 2540, 2545, 2550, 2555, 2560, 2565; 2635, 2640, 2645, 2650, 2655), and wherein the switching elements can switch the module energy storages of the modules both in series and in parallel, characterized in that the converter system comprises a control circuit, which controls the modules such that the module energy storages of modules, that are to be connected in parallel, can be added to the parallel connection one after the other, during operation of the converter, starting with a first module energy storage, wherein said adding of the modules to the parallel connection comprises the following steps: selecting the module energy storage among the module energy storages for the planned parallel connection that has the lowest voltage as the first module energy storage when a load current through the inverter charges said module energy storage, or selecting the module energy storage that has the highest voltage as the first module energy storage when a load current through the inverter discharges said module energy storage; selecting a module energy storage to be connected in parallel with the second lowest voltage when a load current through the inverter charges the first module energy storage, or selecting a module energy storage to be connected in parallel with the second highest voltage when a load current through the inverter discharges the first module energy storage; connecting said selected module energy storage to be connected in parallel to the first module energy storage, when the load current through the converter has charged or discharged the first module energy storage to the point that it has the same voltage as the selected module energy storage for connection in parallel; and repeating the previous two steps until all module energy storages that are to be connected in parallel have been connected in parallel with each other, wherein in case the converter system comprises three or more similar cascaded modules (2410, 2420, 2430, and 2440), the modules (2410, 2420, 2430, and 2440) are designed with respect to their switching elements that a parallel connection of module energy storages is possible even when the modules are not directly adjacent. selecting the module energy storage among the module energy storages for the planned parallel connection that has the lowest voltage as the first module energy storage when a load current through the inverter charges said module energy storage, or selecting the module energy storage that has the highest voltage as the first module energy storage when a load current through the inverter discharges said module energy storage; selecting a module energy storage to be connected in parallel with the second lowest voltage when a load current through the inverter charges the first module energy storage, or selecting a module energy storage to be connected in parallel with the second highest voltage when a load current through the inverter discharges the first module energy storage; connecting said selected module energy storage to be connected in parallel to the first module energy storage, when the load current through the converter has charged or discharged the first module energy storage to the point that it has the same voltage as the selected module energy storage for connection in parallel; and repeating the previous two steps until all module energy storages that are to be connected in parallel have been connected in parallel with each other, wherein in case the converter system comprises three or more similar cascaded modules (2410, 2420, 2430, and 2440), the modules (2410, 2420, 2430, and 2440) are designed with respect to their switching elements that a parallel connection of module energy storages is possible even when the modules are not directly adjacent.