Algorithm for passive power factor compensation method with differential capacitor change and reduced line transient noise
A computer-implementable control algorithm that measures: 1) the reactive power; 2) the power factor; 3) the voltage; and 4) the line frequency. The algorithm calculates the differential compensation capacitance required that is either positive (capacitance to be added), or negative (capacitance to be removed). The new compensation capacitance is calculated from the sum or difference of the differential compensation capacitance and the current compensation capacitance. The algorithm compares the capacitor switching bit pattern for the current compensation capacitance and the capacitor switching bit pattern for the new compensation capacitance, and selects a capacitor switching bit map accordingly. The capacitor switch combination for the new compensation capacitance is switched in incrementally according to the capacitor switching bit map. To reach the selected capacitor switch combination, only one switch is switched at a time to minimize the line transient noise. This part of the algorithm continues to run until the PF is corrected, with the capacitor switches being switched on/off each delayed by a millisecond interval to minimize line transient noise.
1. A method for conducting passive power factor compensation based on differential capacitor change, comprising:
a. acquiring real time electrical power circuit measurements comprising: power factor, line voltage, line frequency, reactive power, and sign of reactive power;
b. determining a compensation capacitance required;
c. determining the states of each of capacitor switches for engaging or disengaging their corresponding capacitors for achieving a total capacitance closest to the compensation capacitance required;
d. forming a new capacitor combination according the states of each of the capacitor switches determined for the compensation capacitance required;
e. first disengaging currently engaged capacitors in current capacitor combination one by one in ascending order starting with the capacitor with lowest capacitance and ending with the capacitor with highest capacitance, and after all capacitors are disengaged, engaging capacitors in the new capacitor combination one by one in ascending order starting with the capacitor with lowest capacitance and ending with the capacitor with highest capacitance to minimize line transient noise; and
repeating above steps a-e every pre-determined time interval.
2. The method of claim 1 , wherein the determination of the compensation capacitance required comprises:
calculating
C_pfc
=
P_reactive
2
·
π
·
fl
Vac
2
,
where C_pfc is a differential compensation capacitance, P_reactive is the reactive power measured, Vac is the line voltage measured, and fl is the line frequency measured; and
if an absolute value of the differential compensation capacitance is larger than a predetermined limit value, then
adding, if the power factor measured is positive, or subtracting, if the power factor measured is negative, C_pfc to or from existing capacitance value, resulting in the compensation capacitance required.
3. The method of claim 2 , wherein the predetermined limit value being equal or larger than ½ of minimum capacitance step.
4. The method of claim 1 ,
wherein positions and the states of the capacitor switches are represented in binary form;
wherein the capacitor switches being positioned in descending order according to their corresponding the capacitor capacitance values with the capacitor switch corresponding to the capacitor with highest capacitance being positioned at most significant bit (MSB) and the capacitor switch corresponding to the capacitor with lowest capacitance being positioned at least significant bit (LSB).
5. The method of claim 1 , wherein each of engaging and disengaging of each capacitor being separated by a delay time interval.