Method and device for monitoring and suppressing resonance
A method and device for monitoring and suppressing a resonance are provided, which are applied to a grid-connected generation system. A current sample voltage of a preset sample point of the grid-connected generation system is monitored in a real time manner; amplitudes of harmonics of the current sample voltage are acquired using a preset algorithm; it is verified whether a resonance occurs in the grid-connected generation system currently based on the acquired amplitudes of the harmonics; in a case that the resonance occurs in the grid-connected generation system, current corrections of parameters of inverters in the grid-connected generation system are acquired according to a preset rule and the parameters of the inverters are adjusted using the current corrections and a selected resonance suppressing algorithm.
1. A method for monitoring and suppressing a resonance applied to a grid-connected generation system, wherein the method comprises:
monitoring a current sample voltage of a preset sample point of the grid-connected generation system;
acquiring amplitudes of harmonics of the current sample voltage using a preset algorithm;
verifying whether a resonance occurs in the grid-connected generation system based on the acquired amplitudes of the harmonics; and
in a case that the resonance occurs in the grid-connected generation system, acquiring current corrections of parameters of inverters in the grid-connected generation system according to a preset rule, and adjusting the parameters of the inverters using the current corrections and a selected resonance suppressing algorithm until the resonance disappears in the grid-connected generation system,
wherein the adjusting the parameters of the inverters using the current corrections and a preset resonance suppressing algorithm comprises:
adjusting bandwidths of the inverters using the current corrections and a preset adjustment formula, wherein the preset adjustment formula is:
{
k
p
=
k
p
+
Δ
U
out
k
p
<
k
p
min
k
p
=
k
p
min
,
where K p indicates a proportion control parameter, ΔU out indicates the current corrections and K pmin indicates minimum allowable adjustment values of the bandwidths of the inverters,
adjusting active damping coefficients of the inverters using a pre-stored active damping algorithm and the current corrections; and
transmitting the current corrections to the inverters to control an inactive damping resistor to be connected to a respective one of the inverters.
2. The method according to claim 1 , wherein the acquiring amplitudes of harmonics of the current sample voltage using a preset algorithm comprises:
calculating frequency domain values corresponding to the harmonics of the current sample voltage using an FFT algorithm formula, wherein the FFT algorithm formula is:
x
(
l
)
=
∑
n
=
0
N
-
1
U
x
(
n
)
×
w
N
l
n
w
N
l
n
=
e
-
j
2
π
nl
/
N
,
l
=
0
,
1
,
…
,
N
-
1
,
where U x (n) indicates a discrete signal of the current sample voltage, x(l) indicates a frequency domain value corresponding to the current sample voltage after an FFT transformation is performed on the current sample voltage, N indicates the total number of sample points, W N ln indicates a weight for the FFT algorithm; and
calculating the amplitudes of the harmonics using the frequency domain values and a preset harmonic extracting formula, wherein the preset harmonic extracting formula is:
U amp ( k )=√{square root over ( X (2 k ) 2 +X (2 k+ 1) 2 )} k= 0,1, . . . , N/ 2−1,
where U amp (k) indicates an amplitude of the k-th harmonic, X(2k) indicates a value of a real part of the frequency domain value corresponding to a k-th harmonic, X(2k+1) indicates a value of an imaginary part of the frequency domain value corresponding to the k-th harmonic.
3. The method according to claim 2 , wherein the verifying whether a resonance occurs in the grid-connected generation system based on the acquired amplitudes of the harmonics comprises:
calculating valid values of the amplitudes of the harmonics within a preset resonance frequency band using the amplitudes of the harmonics and a preset valid value calculation formula, wherein the preset valid value calculation formula is:
U
r
=
1
N
1
∑
k
=
M
1
M
2
U
amp
(
k
)
2
,
where U r indicates the valid values of the amplitudes of the harmonics within the preset resonance frequency band [f min , f max ], N 1 indicates the total number of resonances occurred within the preset resonance frequency band, M 1 indicates the number of resonances corresponding to a minimum allowable resonance frequency f min , M 2 indicates the number of resonances corresponding to a maximum allowable resonance frequency f max , and U amp (k) indicates the amplitude of the k-th harmonic; and
verifying whether the valid values of the amplitudes of the harmonics are not less than a preset harmonic threshold,
wherein it is determined that the resonance occurs in the grid-connected generation system in a case that the valid values of the amplitudes of the harmonics are not less than the preset harmonic threshold.
4. The method according to claim 3 , wherein the acquiring current corrections of parameters of inverters in the grid-connected generation system according to a preset rule comprises:
calculating differences between the valid values of the amplitudes of the harmonics and the preset harmonic threshold to obtain input errors;
adjusting the input errors in proportion or proportion-integral to obtain current output controls; and
clipping amplitudes of the current output controls to obtain the current corrections of the parameters of the inverters in the grid-connected generation system.
5. The method according to claim 1 , wherein after the adjusting the parameters of the inverters using the current corrections and a preset resonance suppressing algorithm, the method further comprises:
controlling the inverters of the grid-connected generation system to stop operating in a case that the resonance does not disappear in the grid-connected generation system after a preset period of time.
6. The method according to claim 1 , wherein in a case that the resonance disappears in the grid-connected generation system, the method further comprises:
performing a power failure protection on the adjusted parameters of the inverters.
7. A device for monitoring and suppressing a resonance applied to a grid-connection generation system, wherein the device comprises:
a sample conditioning circuit connected to a preset sample point of the grid-connected generation system and configured to monitor a current sample voltage of the preset sample point;
a controller connected to the sample conditioning circuit and configured to acquire amplitudes of harmonics of the current sample voltage using a preset algorithm, verify whether a resonance occurs in the grid-connected generation system based on the acquired amplitudes of the harmonics, and acquire current corrections of parameters of inverters in the grid-connected generation system according to a preset rule in a case that the resonance occurs in the grid-connected generation system;
a communication bus connected to the controller and the inverters in the grid-connected generation system and configured to transmit the current corrections acquired by the controller to the inverters respectively; and
an adjusting module connected to the controller and the inverters and configured to adjust the parameters of the inverters using the current corrections and a preset resonance suppressing algorithm until the resonance disappears in the grid-connected generation system, wherein the adjusting module comprises a first adjusting unit configured to adjust bandwidths of the inverters using the current corrections and a preset adjustment formula, wherein the preset adjustment formula is:
{
k
p
=
k
p
+
Δ
U
out
k
p
<
k
p
min
k
p
=
k
p
min
,
where K p indicates a proportion control parameter, ΔU out indicates the current corrections and K pmin indicates minimum allowable adjustment values of the bandwidths of the inverters;
a second adjusting unit configured to adjust active damping coefficients of the inverters using a preset active damping algorithm and the current corrections; and
a third adjusting unit configured to transmit respectively the current corrections to the inverters to control an inactive damping resistor to be connected to a respective one of the inverters.
8. The device according to claim 7 , wherein the controller comprises:
a frequency domain calculation module configured to calculate frequency domain values corresponding to the current sample voltage using an FFT algorithm formula, wherein the FFT algorithm formula is:
x
(
l
)
=
∑
n
=
0
N
-
1
U
x
(
n
)
×
w
N
l
n
w
N
l
n
=
e
-
j
2
π
nl
/
N
,
l
=
0
,
1
,
…
,
N
-
1
,
where U x (n) indicates a discrete signal of the current sample voltage, x(l) indicates a frequency domain value corresponding to the current sample voltage after an FFT transformation is performed on the current sample voltage, N indicates the total number of sample points, and W N ln indicates a weight for the FFT algorithm;
an amplitude calculation module configured to calculate the amplitudes of the harmonics using the frequency domain values and a preset harmonic extracting formula, wherein the preset harmonic extracting formula is:
U amp ( k )=√{square root over ( X (2 k ) 2 +X (2 k+ 1) 2 )} k= 0,1, . . . , N/ 2−1,
where U amp (k) indicates an amplitude of the k-th harmonic, X(2k) indicates a value of a real part of the frequency domain value corresponding to a k-th harmonic, X(2k+1) indicates a value of an imaginary part of the frequency domain value corresponding to the k-th harmonic;
a valid value calculation module configured to calculate valid values of the amplitudes of the harmonics within a preset resonance frequency band using the amplitudes of the harmonics and a preset valid value calculation formula, wherein the preset valid value calculation formula is:
U
r
=
1
N
1
∑
k
=
M
1
M
2
U
amp
(
k
)
2
,
where U r indicates the valid values of the amplitudes of the harmonics within the preset resonance frequency band [f min , f max ], N 1 indicates the total number of resonances occurred within the preset resonance frequency band, M 1 indicates the number of resonances corresponding to a minimum allowable resonance frequency f min , M 2 indicates the number of resonances corresponding to a maximum allowable resonance frequency f max , and U amp (k) indicates the amplitude of the k-th harmonic;
a verifying module configured to verify whether the valid values of the amplitudes of the harmonics are not less than a preset harmonic threshold;
an error calculation module configured to calculate differences between the valid values of the amplitude of the harmonics and the preset harmonic threshold to obtain input errors;
a control acquiring module configured to adjust the input errors in proportion or proportion-integral to obtain current output controls; and
an amplitude clipping module configured to clip amplitudes of the current output controls to obtain the current corrections of the parameters of the inverters in the grid-connected generation system.