Method for solving for converter valve states and valve currents based on valve-side current timing characteristics

A method for determining a converter valve state and a valve current based on temporal features of a valve side current, for use in fault analysis and control and protection optimization of DC project, characterized in that, the calculation method comprises following steps:

• S1. collecting three-phase AC currents ia, ib, ic, and DC currents idH, idN on a converter valve side of a DC transmission system, and trigger pulses FP1, FP2, FP3, FP4, FP5, FP6 of converter valves;
• S2. according to a topology structure of the converter of the DC transmission system, establishing a node current equation Ai=y of the three-phase AC currents ia, ib, ic, the DC currents idH, idN and valve currents iVTm on the valve side;
• {
• i
• VT
• ⁢
• 2
• +
• i
• VT
• ⁢
• 4
• +
• i
• VT
• ⁢
• 6
• =
• i
• dH
• i
• VT
• ⁢
• 1
• +
• i
• VT
• ⁢
• 3
• +
• i
• VT
• ⁢
• 5
• =
• i
• dN
• i
• VT
• ⁢
• 4
• -
• i
• VT
• ⁢
• 1
• =
• i
• a
• i
• VT
• ⁢
• 6
• -
• i
• VT
• ⁢
• 3
• =
• i
• b
• i
• VT
• ⁢
• 2
• -
• i
• VT
• ⁢
• 5
• =
• i
• c
• (
• G1
• )
• wherein
• ⁢
• ⁢
• A
• =
• [
• 0
• 1
• 0
• 1
• 0
• 1
• 1
• 0
• 1
• 0
• 1
• 0
• -
• 1
• 0
• 0
• 1
• 0
• 0
• 0
• 0
• -
• 1
• 0
• 0
• 1
• 0
• 1
• 0
• 0
• -
• 1
• 0
• ]
• ,
• i
• =
• [
• i
• VT
• ⁢
• 1
• i
• V
• ⁢
• T
• ⁢
• 2
• i
• V
• ⁢
• T
• ⁢
• 3
• i
• V
• ⁢
• T
• ⁢
• 4
• i
• V
• ⁢
• T
• ⁢
• 5
• i
• VT
• ⁢
• 6
• ]
• ,
• y
• =
• [
• i
• dH
• i
• dN
• i
• a
• i
• b
• i
• c
• ]
• ,
• is a valve current coefficient matrix, i is a valve current vector, y is a current vector at both ends of the valve side, iVTm are respective six converter valve currents, m is a number of six converter valves, m=1, 2, 3, 4, 5, 6;
• S3. according to the trigger pulses FP1, FP2, FP3, FP4, FP5, FP6 of the converter valves obtained in step S1, when detecting a rising edge of a trigger pulse of a converter valve, latching the number m of the converter valve into a register;
• S4. according to the trigger pulses FP1, FP2, FP2, FP4, FP5, FP6 of the converter valves obtained in step S1, and amplitude characteristics of the AC currents and characteristics of AC variations, to perform a conducting state and a blocking state judgment of valve states, and obtaining six valve states of the converter valves SVT1, SVT2, SVT3, SVT4, SVT5, SVT6;
• S5. according to the valve states obtained in step S4, constructing a valve state matrix S:
• S
• =
• [
• s
• VT
• ⁢
• 1
• s
• VT
• ⁢
• 2
• s
• VT
• ⁢
• 3
• s
• VT
• ⁢
• 4
• s
• VT
• ⁢
• 5
• s
• VT
• ⁢
• 6
• ]
• ;
• (
• G
• ⁢
• 2
• )
• in the formula (G2):
• SVT1, SVT2, SVT3, SVT4, SVT5, SVT6 are the valve states of the six converter valves;
• S6. by calculating a product of an upper valve state and a lower valve state of each phase, judging whether each phase has a bypass state, valve bypass states Sa, Sb, Sc of each phase are:
• {
• S
• a
• =
• s
• VT
• ⁢
• 1
• ×
• s
• V
• ⁢
• T
• ⁢
• 4
• S
• b
• =
• s
• VT
• ⁢
• 3
• ×
• s
• VT
• ⁢
• 6
• S
• c
• =
• s
• VT
• ⁢
• 2
• ×
• s
• VT
• ⁢
• 5
• (
• G3
• )
• in the formula (G3):
• Sa represents a valve bypass state of phase a, Sb represents a valve bypass state of phase b, Sc represents a valve bypass state of phase c, Sk=1 represents a bypass, Sk=0 represents no bypass, and k is serial numbers of a, b, and c phases;
• S7. summing the valve bypass states of the three phases to judge a number of bypass phases, where a number of bypass phases Stotal is expressed as follows:
• Stotal=Σ(Sa+Sb+Sc) (G4);
• in the formula (G4):
• Stotal represents the number of bypass phases in the three phases abc;
• S8. according to the number of bypass phases and corresponding phases obtained in step S7, supplementing a bypass loop voltage equation Cpi=Dp;
• wherein Cp is a coefficient matrix of the bypass loop voltage equation, i is a valve current vector, Dp is a constant vector, and p is serial number of the bypass phases;
• S9. according to step S2 and step S8, and in conjunction with step S4, calculating the valve currents iVTm:
• S10. when the valve currents iVTm calculated in step S9<0, considering a one-way conductivity of the converter valves, correcting the valve states, correcting the valve states to blocking state SVTm=0, otherwise, do not correct;
• S11. repeating steps S5 to S10 until the valve currents iVTm≥0 is calculated;
• and
• S12. coordinating control of the converter valves, based on the corrected valve states and the calculated valve currents.