An inductive power transfer, IPT, system primary converter comprising: a control means ; a push-pull resonant converter having a resonant frequency, the push-pull resonant converter comprising: a resonant circuit having a resonant frequency ; switching means comprising two switches (S p1 , S p2 ), the switching means being arranged to operate at a switching frequency below the resonant frequency of the resonant circuit , the control means being configured to provide a respective signal (D p1 , D p2 ) to respectively operate, by opening and closing, the switches of the switching means , characterised in that the push-pull resonant converter is configured to operate at a substantially fixed switching frequency and switch at zero voltage for a range of expected load levels, wherein the control means is configured to create a zero voltage period in which the resonant circuit is short-circuited, the zero voltage period comprising a time between which a voltage (V sp1 , V sp2 ) across an open switch (S p1 , S p2 ) of the switching means returns to zero and a time of a next rising edge of the respective signal (D p1 , D p2 ) and wherein the switching frequency is selected such that the zero voltage period is maintained for an expected range of fluctuations of the resonant frequency corresponding to the range of expected load levels. a control means ; a push-pull resonant converter having a resonant frequency, the push-pull resonant converter comprising: a resonant circuit having a resonant frequency ; switching means comprising two switches (S p1 , S p2 ), the switching means being arranged to operate at a switching frequency below the resonant frequency of the resonant circuit , the control means being configured to provide a respective signal (D p1 , D p2 ) to respectively operate, by opening and closing, the switches of the switching means , characterised in that the push-pull resonant converter is configured to operate at a substantially fixed switching frequency and switch at zero voltage for a range of expected load levels, wherein the control means is configured to create a zero voltage period in which the resonant circuit is short-circuited, the zero voltage period comprising a time between which a voltage (V sp1 , V sp2 ) across an open switch (S p1 , S p2 ) of the switching means returns to zero and a time of a next rising edge of the respective signal (D p1 , D p2 ) and wherein the switching frequency is selected such that the zero voltage period is maintained for an expected range of fluctuations of the resonant frequency corresponding to the range of expected load levels. a resonant circuit having a resonant frequency ; switching means comprising two switches (S p1 , S p2 ), the switching means being arranged to operate at a switching frequency below the resonant frequency of the resonant circuit , the control means being configured to provide a respective signal (D p1 , D p2 ) to respectively operate, by opening and closing, the switches of the switching means , characterised in that the push-pull resonant converter is configured to operate at a substantially fixed switching frequency and switch at zero voltage for a range of expected load levels, wherein the control means is configured to create a zero voltage period in which the resonant circuit is short-circuited, the zero voltage period comprising a time between which a voltage (V sp1 , V sp2 ) across an open switch (S p1 , S p2 ) of the switching means returns to zero and a time of a next rising edge of the respective signal (D p1 , D p2 ) and wherein the switching frequency is selected such that the zero voltage period is maintained for an expected range of fluctuations of the resonant frequency corresponding to the range of expected load levels. <EOS>