A control system for soft starting a dual-active-bridge direct current to direct current converter that comprises a transformer, a first H-bridge (H 1) connected to a primary winding of the transformer, and a second H-bridge (H 2) connected to a secondary winding of the transformer, the control system comprising a converter comprising the dual-active-bridge direct current to direct current converter, a current controller and a voltage controller, characterised in that the control system is configured to: perform a predefined control mode in which an outer phase-shift angle (β 0) is determined based on a predefined process, wherein the outer phase-shift angle (β) is a phase shift between the first voltage (v p) on the primary winding and a second voltage (v s) on the secondary winding; wherein, in the predefined control mode, a first duty cycle (d 1) is set to increase from an initial value to a nominal value (D 1), and wherein the first duty cycle is the duty cycle of a first voltage (v p) on the primary winding; determine that a first predefined event has occurred, wherein the first predefined event includes that the first duty cycle ( d 1) for the first voltage (v p) on the primary winding has reached a predetermined duty cycle value or that the DC current output from the second H-bridge (H 2) has reached a predetermined current threshold ( I 2,chg); in response to determining that the first predefined event has occurred, switch to a current control mode in which the outer phase-shift angle (β) is determined by the current controller based on a predefined reference current profile and a DC current output from the second H-bridge (H 2), determine that a second predefined event has occurred, the second predefined event including: a DC voltage at the output side of the second H-bridge (H 2) has reached a predetermined voltage level, or a predetermined amount of time has elapsed since the start of the current control mode; and in response to determining that the second predefined event has occurred, switch to a voltage-current control mode in which a reference current value ( i 2,ref) is determined by the voltage controller using a reference voltage value and a DC voltage output from the second H-bridge (H 2), and the outer phase-shift angle (β) is determined by the current controller using the reference current value ( i 2,ref) and the DC current output from the second H-bridge (H 2). perform a predefined control mode in which an outer phase-shift angle (β 0) is determined based on a predefined process, wherein the outer phase-shift angle (β) is a phase shift between the first voltage (v p) on the primary winding and a second voltage (v s) on the secondary winding; wherein, in the predefined control mode, a first duty cycle (d 1) is set to increase from an initial value to a nominal value (D 1), and wherein the first duty cycle is the duty cycle of a first voltage (v p) on the primary winding; determine that a first predefined event has occurred, wherein the first predefined event includes that the first duty cycle ( d 1) for the first voltage (v p) on the primary winding has reached a predetermined duty cycle value or that the DC current output from the second H-bridge (H 2) has reached a predetermined current threshold ( I 2,chg); in response to determining that the first predefined event has occurred, switch to a current control mode in which the outer phase-shift angle (β) is determined by the current controller based on a predefined reference current profile and a DC current output from the second H-bridge (H 2), determine that a second predefined event has occurred, the second predefined event including: a DC voltage at the output side of the second H-bridge (H 2) has reached a predetermined voltage level, or a predetermined amount of time has elapsed since the start of the current control mode; and in response to determining that the second predefined event has occurred, switch to a voltage-current control mode in which a reference current value ( i 2,ref) is determined by the voltage controller using a reference voltage value and a DC voltage output from the second H-bridge (H 2), and the outer phase-shift angle (β) is determined by the current controller using the reference current value ( i 2,ref) and the DC current output from the second H-bridge (H 2).