Control unit for a converter

A circuit for forming a periodic control signal having a predetermined pulse pattern for modulating a converter stage comprising:

• a memory for storing code words designating the position of switching pulse edges of a periodic control signal for a time interval, divided into increments, of up to one period of one of the AC input voltage and the output voltage of the converter, the memory having an address input, a memory advancing input, and a code word output comprising pulse patterns of a control signal for modulating a converter stage;
• a clock generator for generating clock pulses, each clock pulse representing one increment;
• a first counter coupled to the clock generator for counting the clock pulses and forming a count word;
• a digital comparator having a first input coupled to the code word output of the memory and a second input coupled to the counter word output of the counter, and the comparator generating an output signal upon each agreement of the code word and the count word;
• a pulse generator coupled to the signal at the output of the comparator and having an output coupled to the memory advancing input;
• and
• a second counter coupled to the output of the pulse generator and having an output signal coupled to the address input of the memory, the second counter generating a first subaddress upon each agreement of the code word and the count word;
• and
• a shift register having an output coupled to the memory address input, the shift register responsive to a modulation control signal for cyclically generating a second subaddress and supplying it to the memory.