A voltage source converter comprising first and second DC terminals for connection to a DC network , the voltage source converter including a plurality of limbs connected in series between the first and second DC terminals , each limb including: a phase element including a plurality of switching elements switchable to selectively interconnect a DC side voltage at a DC side of the phase element and an AC side voltage at an AC side of the phase element ; a DC side sub-converter connected to the DC side of the phase element , the DC side sub-converter configured to be operable as a waveform synthesizer to control the DC side voltage so as to form a DC voltage for presentation to the DC network ; and an AC side sub-converter connected to the AC side of the phase element , the AC side sub-converter configured to be operable as a waveform synthesizer to control the AC side voltage so as to form a or a respective AC phase voltage for presentation to a or a respective AC phase of an AC network , wherein the voltage source converter includes a controller programmed to selectively coordinate the operation of the DC and AC side sub-converters as the respective waveform synthesizers to simultaneously: synthesize one or more selected harmonic voltage components to control the or each DC side voltage so as to present a constant or substantially constant DC voltage to the DC network ; and cancel the or each selected harmonic voltage component from the or each AC side voltage so as to present a or a respective AC phase voltage free of the or each selected harmonic voltage component to the corresponding AC phase of the AC network , the voltage source converter being characterised in that each limb further includes a winding connected in series with the AC side sub-converter at the AC side of the corresponding phase element , each winding magnetically coupled to a respective one of a plurality of additional windings , and the plurality of additional windings are electrically interconnected in a daisy chain arrangement, preferably a delta arrangement. a phase element including a plurality of switching elements switchable to selectively interconnect a DC side voltage at a DC side of the phase element and an AC side voltage at an AC side of the phase element ; a DC side sub-converter connected to the DC side of the phase element , the DC side sub-converter configured to be operable as a waveform synthesizer to control the DC side voltage so as to form a DC voltage for presentation to the DC network ; and an AC side sub-converter connected to the AC side of the phase element , the AC side sub-converter configured to be operable as a waveform synthesizer to control the AC side voltage so as to form a or a respective AC phase voltage for presentation to a or a respective AC phase of an AC network , wherein the voltage source converter includes a controller programmed to selectively coordinate the operation of the DC and AC side sub-converters as the respective waveform synthesizers to simultaneously: synthesize one or more selected harmonic voltage components to control the or each DC side voltage so as to present a constant or substantially constant DC voltage to the DC network ; and cancel the or each selected harmonic voltage component from the or each AC side voltage so as to present a or a respective AC phase voltage free of the or each selected harmonic voltage component to the corresponding AC phase of the AC network , the voltage source converter being characterised in that each limb further includes a winding connected in series with the AC side sub-converter at the AC side of the corresponding phase element , each winding magnetically coupled to a respective one of a plurality of additional windings , and the plurality of additional windings are electrically interconnected in a daisy chain arrangement, preferably a delta arrangement. <EOS>