Controlling a high voltage power supply for an electrostatic precipitator

A high voltage power supply for an electrostatic precipitator, said high voltage power supply comprising:

• a transformer-rectifier set comprising a high voltage transformer, a primary side of which is connectable to an AC industrial mains net having a line frequency, and a high voltage bridge rectifier connected to a secondary side of said high voltage transformer and configured to supply a rectified high voltage to said electrostatic precipitator;
• a semiconductor switch controller arranged at the primary side of said high voltage transformer and configured to control an output power level of the high voltage power supply;
• firing circuitry configured to provide firing pulses to said semiconductor switch controller;
• and
• a control unit configured to determine a firing angle of said firing pulses and to control said firing circuitry accordingly,
• wherein the control unit comprises:
• a breakdown detector configured to detect the occurrence of an electrical breakdown in said electrostatic precipitator;
• an interface circuit configured to measure, during normal operation of said electrostatic precipitator, a peak voltage value over said electrostatic precipitator in each half period of said line frequency and to measure, when a breakdown is detected, a residual voltage over the electrostatic precipitator;
• a memory configured to store said measured peak voltage value;
• and
• a calculation unit configured to determine a firing angle of a firing pulse to be provided to said semiconductor switch controller in the first half period after the occurrence of a breakdown, wherein the calculation unit is further configured to determine said firing angle from the latest stored measured peak voltage value and the measured residual voltage based on a predetermined relationship with said firing angle and the latest stored measured peak voltage value and the measured residual voltage.