JP3580753B2 - Power storage system - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power storage system that adjusts the supply and demand of active power of a three-phase AC system.
[0002]
[Prior art]
In order to transfer active and reactive power from the AC / DC converter of the power storage system to the three-phase AC system, the amplitude and phase of the output voltage of the AC / DC converter are adjusted relative to the system voltage. For this reason, it is necessary to detect the amplitude and phase of the three-phase AC system voltage. As a conventional general phase detection method, a PLL (Phase Locked Loop) circuit utilizing the fact that the point in time when the polarity of the three-phase AC voltage changes periodically occurs is used.
[0003]
As a protection control method against a system accident, for example, the line voltage of a three-phase AC voltage is used in accordance with the guidelines for grid connection requirements of the Agency for Natural Resources and Energy (Explanation: Guideline for Technical Requirements for Power System Interconnection, 1998, Electric Power Shimpo). The effective value of the signal is detected, and if any one of the effective values is less than the reference value, the power storage system is stopped.
[0004]
If the three-phase AC system is abnormal, for example, if two of the three phases are grounded and the phase voltage becomes zero, the protection control circuit of the transmission line will temporarily disconnect the grounded phase, and as early as 1 second Within a few seconds at the latest. If the system returns to normal within a few seconds, it is desirable to continue operating the power storage system. On the other hand, there is a case where a system abnormality in which power cannot be supplied continues for more than several seconds, such as a one-line three-phase ground fault. In such a case, it is necessary to provide a period for confirming that the protection of the system and the elimination of the accident have been completely performed on the system side, and thus it is necessary to immediately stop the protection of the power system in the event of an accident. In the current operation, protection is stopped when the system voltage falls to 80% of the rated value while the system is supplying power to the system according to the guidelines.
[0005]
[Problems to be solved by the invention]
The conventional power storage system is designed to stop the protection when the line voltage at the connection point drops to 80%. For this reason, even in the case of a system abnormality that does not require the system side to confirm the removal of the accident, the protection of the system is frequently stopped. In addition, since restarting takes a long time when the system is stopped, there is a problem that the power supply capability of the power storage system is lost immediately after the system returns to normal.
[0006]
The above-mentioned restriction on the operation of the power storage system is partly due to the phase detection accuracy of the PLL. It is part of the three-line ground fault that the operation of the power storage system cannot be continued due to restrictions on the equipment in order to avoid overcurrent, etc. in an AC system accident. The operation can be continued in the mode. However, in the event of a system failure, since the system voltage contains harmonics, the phase detection accuracy of the PLL is reduced, and stable control of the AC / DC power converter becomes difficult. For this reason, the present situation is that the margin of safe driving must be increased.
[0007]
Recently, the α-axis component and the β-axis component of the positive-phase voltage are calculated from the α component and the β component of each phase using the Fourier transform components of each of the three phases of the three-phase AC voltage, and based on these axis components, A method has been proposed in which a positive-phase voltage phase (△ θ) is obtained, and this △ θ is used as a phase difference between the system voltage phase θs and the reference phase θi to obtain the system voltage phase θs (Japanese Patent Laid-Open No. Hei 10-234135). If the phase detection by the discrete Fourier transfer (DFT) method is used, the operation range of the AC / DC converter at the time of a system fault can be safely extended.
[0008]
However, in the case of using phase detection by DFT, it is indispensable to properly recognize the safe operation range of the power storage system in the event of a system failure, in other words, an accident or timing of protection stop of the system. Furthermore, under the current situation where sodium-sulfur (NaS) battery systems are being put into practical use as small-scale power storage systems for general users, protection stoppage based on the judgment of the power storage system itself is not required, regardless of the stop command from the system. It has been demanded.
[0009]
It is an object of the present invention to provide a power storage system that overcomes the problems of the prior art, enhances the continuity of operation during a system accident, and that can promptly judge and stop when a protection stop is required. is there.
[0010]
[Means for Solving the Problems]
The present invention, which achieves the above object, employs a DFT method capable of accurately and reliably detecting a system voltage phase even in the event of an abnormality including a harmonic, thereby improving the continuity of operation during a system accident and requiring a protection stop. We have found a method that can properly judge an accident or timing, and have achieved it.
[0011]
The present invention includes an AC / DC power converter connected to a three-phase AC system, converting three-phase AC power to DC power or converting DC power to three-phase AC power, and a secondary battery connected to the converter. In the power storage system, in order to adjust AC power output from the AC / DC power converter, the AC / DC power converter with respect to a connection point voltage vector based on a connection point voltage phase at a connection point with the AC system. A power conversion control unit that controls an output voltage vector, performs a discrete Fourier transform by inputting the three voltage signals at the connection point, and performs a positive phase of the connection point voltage based on the converted real axis component and imaginary axis component. A positive-phase voltage detection unit that detects a positive-phase component phase and a positive-phase component phase, and outputs the positive-phase component phase to the power conversion control unit as the connection point phase; Based on the phase amplitude, it is monitored whether an abnormality that should stop the power storage system has occurred in the three-phase AC system, and when it is determined that an abnormality that requires a system stop has occurred, the system is stopped. A protection stop judging unit for outputting a signal is provided.
[0012]
In addition, the protection stop determination unit may be configured such that, when all phases of the three-phase AC system are normal, the amplitude of the positive-phase component is used as a unit value, and a 1/3 unit value is a lower limit and a 2/3 unit value is an upper limit. When the threshold value is arbitrarily set and the positive-sequence component amplitude is less than the predetermined threshold value, it is determined that an abnormality necessary to stop the system has occurred. I do.
[0013]
According to another aspect of the present invention, the power conversion control unit, the positive-phase voltage detection unit, an effective value detection unit that receives the three voltage signals and obtains three effective values, and the positive-phase voltage detection unit Based on the positive phase amplitude input from the and the voltage drop rate input from the effective value detection unit, monitor whether an abnormality to stop the power storage system has occurred in the three-phase AC system, the system A protection stop determination unit that outputs a system stop signal when it is determined that an abnormality that needs to be stopped has occurred.
[0014]
In this case, when the absolute value of the positive phase component amplitude is less than a first threshold value (upper limit of 単 位 unit value), the protection stop determination unit determines that the absolute value of the positive phase component amplitude is When the value is equal to or more than the first threshold value and less than the second threshold value (1/3 unit value is the lower limit), and all of the three effective values have the same value, the system needs to be stopped. Is determined to have occurred.
[0015]
Alternatively, a ratio of each effective value to a maximum value of the three effective values is calculated, and a voltage effective value decrease rate due to a synergistic value thereof is calculated. The protection stop determination unit determines that the absolute value of the positive phase component amplitude is When the absolute value of the positive-sequence amplitude is equal to or more than the first threshold and less than the second threshold, and the rate of decrease in the voltage effective value is equal to or less than the first threshold. If it is equal to or more than the threshold value of 3 (2/3 unit value is the lower limit), it is determined that an abnormality that requires the system stoppage has occurred.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram (functional block diagram) showing an embodiment of the power storage system of the present invention. An AC / DC power converter 2 (converter main circuit, hereinafter abbreviated as a converter) is connected to a connection point 8 of the three-phase AC system 1 via a connection reactor (or a connection transformer). A secondary battery 3 for power storage is connected. An instrument transformer PT is connected to the connection point 8, and a three-phase main circuit bus connecting the connection point 8 and the AC / DC converter 2 is connected to an instrument current transformer CT. The three-phase AC voltage (V1) based on each line voltage at the connection point is connected. , V2, V3) and three-phase AC currents (I1, I2, I3) based on the AC output current of the converter 2.
[0017]
The positive-phase voltage detector 4 adopts the DFT method, receives three-phase AC voltages V1, V2, and V3, and outputs the positive-phase amplitude (positive-phase voltage amplitude) Vs and the positive-phase partial phase (positive-phase voltage) of the connection point voltage. Phase) θs is calculated and output. The protection stop determination unit 5 inputs the positive-phase voltage amplitude Vs, and outputs a stop signal when it is determined that an accident requiring protection stop has occurred. The power converter control unit 6 inputs the three-phase AC voltages V1, V2, V3, the three-phase AC currents I1, I2, I3, and the positive-phase voltage phase θs, and converts these inputs into the active power command value and the reactive power command value. A vector (amplitude and phase) of the converter voltage command Vc * is calculated based on this, and a gate signal is generated so that the output voltage Vc of the AC power of the converter 2 follows the command Vc *. When a stop signal is output from the protection stop determination unit 5, the gate signal is shut off to stop the protection of the converter 2.
[0018]
FIG. 2 is a configuration diagram illustrating an embodiment of the power converter control unit. As is well known, when the active power command value set by a request from a higher-level (system side) is positive, the power converter control unit 6 operates the AC / DC power converter 2 as an inverter to reduce the DC power of the battery 3. Control to convert to three-phase AC power and supply it to the system. On the other hand, if the set active power command value is negative, the AC / DC power converter 2 operates as a converter to convert three-phase AC power from the system into DC power and charge the battery 3. In the following, the configuration using the positive-sequence voltage (Vs, θs) detected by the DFT method and the operation of the active power control for supplying power to the grid side will be mainly described in correspondence with the problem of the present invention.
[0019]
The power converter control unit 6 inputs the line voltages V1, V2, V3 at the connection point 8 and the AC currents I1, I2, I3 at the connection point, and the active power reactive power detection circuit 115 outputs the active power Psf and the reactive power Qsf. Is detected. The active power controller 113 inputs a difference between the active power command value Ps * of the active power command value setting unit 111 and the active power Psf, and outputs an active current command value Id *. The reactive power controller 114 inputs a difference between the reactive power command value Qs * of the reactive power command value setting unit 112 and the reactive power Qsf, and outputs a reactive current command value Iq *.
[0020]
The 3 / 2-phase number conversion unit 116 converts the AC currents I1, I2, and I3 into orthogonal two-phase signals, and outputs an α-axis current Iα and a β-axis current Iβ. The αβ / dq axis converter 117 receives the currents Iα and Iβ and the phase θs of the positive phase of the connection point voltage, and rotates the currents Iα and Iβ of the fixed coordinate system by the positive phase θs of the connection point voltage in the coordinate system. And an active current Idf having the same phase as the node voltage and a reactive current Iqf having a phase orthogonal to the node voltage by 90 ° are output. Note that Idf and Iqf perform DC operation.
[0021]
The 3 / 2-phase number converter 118 converts the connection point line voltages V1, V2, and V3 into orthogonal two-phase signals, and outputs an α-axis voltage Vα and a β-axis voltage Vβ. The αβ / dq axis conversion unit 119 receives the voltages Vα and Vβ and the positive phase phase θs, and converts the voltages Vα and Vβ of the fixed coordinate system into a coordinate system that rotates at the positive phase θs of the connection point voltage. Thus, an effective voltage Vd having the same phase as the connection point voltage and an invalid voltage Vq having a phase orthogonal to the connection point voltage by 90 ° are separated and output. Note that Vd and Vq perform DC operation.
[0022]
The effective current controller 121 receives the difference between the effective current command value Id * and the effective current Idf, and outputs an effective component voltage command addition value dVd * having the same phase as the connection point voltage. The adder 123 adds the effective voltage command addition value dVd * and the effective voltage Vd to obtain an effective voltage command Vd *. The reactive current controller 122 receives the difference between the reactive current command value Iq * and the reactive current Iqf, and outputs a reactive voltage command added value dVq * having a phase orthogonal to the connection point voltage by 90 °. The adder 124 adds the invalid voltage command addition value dVq * and the invalid voltage Vq to obtain an invalid voltage command Vq *.
[0023]
The dq / αβ axis converter 125 receives the effective voltage command Vd *, the ineffective voltage command Vq *, and the positive-phase voltage phase θs of the node voltage, and rotates in the positive-phase phase θs of the node voltage. Are converted into a fixed coordinate system to output converter voltage command values Vα * and Vβ * that operate AC at the frequency of the positive-phase phase θs of the connection point voltage. The 2 / 3-phase number conversion unit 126 converts the two-phase signals Vα * and Vβ * into three-phase signal converter voltage command values Vu *, Vv *, and Vw *, and outputs them.
[0024]
PWM pulse generator 127 receives converter voltage command values Vu *, Vv *, and Vw * and outputs a gate signal of converter 2 formed of a self-excited semiconductor device. When a stop command is input, the PWM pulse generator 127 immediately stops the gate signal, and the active power controller 113, the reactive power controller 114, the active current controller 121, and the reactive current controller 122 output the output immediately. , And the power storage system transitions to the protection stop state.
[0025]
FIG. 3 shows a configuration diagram of the positive-sequence voltage detection unit. The positive-phase voltage detector 4 receives the UV line voltage V1, the VW line voltage V2, and the WU line voltage V3 at the connection point 8, and the 3 / 2-phase number converter 211 outputs the α-axis voltage Vα and the β-axis voltage Vβ. Convert to The frequency reference signal generation circuit 212 generates a phase (reference phase) θ0 of a frequency reference signal having a system rated frequency (50 Hz or 60 Hz).
[0026]
The Fourier transform operation circuit (α-R) 213 obtains a projection component on the real axis when the voltage signal Vα is viewed from a coordinate system rotating at the reference phase θ0, and calculates a moving average value for one cycle of θ0. It calculates and outputs the α real axis component voltage VαR. The Fourier transform operation circuit (α-M) 214 obtains a projection component on the imaginary axis (θ0 + direction of fixed phase 90 °) when the voltage signal Vα is viewed from a coordinate system rotating at the reference phase θ0, and calculates this. A moving average value for one cycle of θ0 is calculated and an α-imaginary axis component voltage VαM is output. The Fourier transform operation circuit (β-R) 215 obtains a projection component onto the real axis when the voltage signal Vβ is viewed from a coordinate system rotating at “θ0 + fixed phase 90 °”, and calculates this for one period of θ0. The moving average value is calculated and the β real axis component voltage VβR is output. The Fourier transform operation circuit (β-M) 216 obtains a projection component on an imaginary axis (θ0 + direction of fixed phase 180 °) when the voltage signal Vβ is viewed from a coordinate system rotating at “θ0 + fixed phase 90 °”. Then, a moving average value for one cycle of θ0 is calculated, and a β imaginary axis component VβM is output.
[0027]
The fundamental frequency positive-phase voltage real axis component calculation circuit 217 receives VαR and VβR and outputs a positive-phase voltage real axis component VR. The fundamental frequency positive-phase voltage imaginary axis component calculation circuit 218 receives VαM and VβM and outputs a positive-phase voltage imaginary axis component VM. The absolute value calculation circuit 219 takes the square root of the sum of squares of VR and VM, and outputs the positive-phase voltage amplitude Vs of the connection point voltage. The phase difference calculation circuit 220 receives VR, VM, and Vs, obtains the phase difference Δθ between the positive-phase voltage phase θs of the connection point voltage and the reference phase θ0 from the calculation of Equation 1, and outputs the phase difference.
[0028]
(Equation 1)
VR / Vs = cos (θs−θ0)
VM / Vs = sin (θs−θ0)
Δθ = θs−θ0 = tan￣ ¹ (VM / Vs) / (VR / Vs)
The adder 221 adds the reference phase θ0 to the phase difference Δθ, and outputs a positive-phase voltage phase θs of the connection point voltage. Θs represents the connection point voltage phase not by the phase of the line voltage (V1, V2, or V3) but by the positive-phase voltage phase.
[0029]
FIG. 4 shows a vector diagram of the converter voltage command Vc *. (A) shows a vector when the positive-phase voltage phase θs by the DFT circuit is used as the connection point voltage phase in the present embodiment. Vc * is a vector sum of Vd * and Vq *, which are two-phase signals in a coordinate system rotating at the positive-phase voltage phase θs of the connection point voltage. In this coordinate system, the same direction as the connection point voltage phase θs is defined as a d-axis component, and the “θs + fixed phase 90 °” direction is defined as a q-axis component. As described above, Vd * is the sum of the d-axis component Vd of the connection point voltage and the effective component voltage command addition value dVd *. Vq * is the sum of the q-axis component Vq of the connection point voltage and the invalid voltage command addition value dVq *. As long as the connection point voltage phase θs is accurately detected without delay, Vd is a DC signal having a length of one unit value, and Vq is a DC signal having a length of zero.
[0030]
When this Vc * (= Vd * + Vq *) is converted into the dq axis / αβ axis, the two-phase signals Vα * and Vβ * in the fixed coordinate system are obtained. When this is converted into two-phase / three-phase, converter voltage commands Vu *, Vv *, and Vw *, which are three-phase signals, are obtained. The PWM pulse generator 127 outputs a gate signal from these signals, so that the AC / DC converter 2 generates an AC voltage Vc output to the system.
[0031]
FIG. 4B shows a vector when the phase θ1 of the voltage signal at the connection point (here, the line voltage V1) is used as the connection point voltage phase. Under normal conditions, θs and θ1 have the same value. However, if the system becomes abnormal, a phase shift or an amplitude change (decrease or 0) of V1 occurs, so that θ1 is erroneously detected and stable control becomes difficult. For example, when a two-phase ground fault of the UV phase occurs, V1 becomes zero, and control becomes impossible even if the W phase is sound.
[0032]
That is, if the absolute value of the true connection point voltage (for the positive phase) is defined as VL and its phase is defined as θL, the phase θ1 of the voltage V1 when the system is normal matches the θL, but the phase θ1 is erroneously detected at the time of an accident. And has a deviation from θL. As a result, the phase that determines the dq axes, θ1, deviates from the true phase, θL, so that the combining unit of Vd and Vq matches the true value, but dVd * and dVq * indicate different directions. become.
[0033]
Since the converter voltage command Vc * is a composite vector of the sum of Vd and Vq and the sum of dVd * and dVq *, the direction of dVd * and dVq * is shifted, so that the vector of Vc * shown by the solid line in the drawing becomes The output is different from the theoretical value shown by the broken line in the figure, and the output is controlled to be different from the expected output.
[0034]
On the other hand, in the case of (a) according to the present embodiment, the normal phase θs has only a slight deviation transiently due to detection delay even at the time of an accident, and substantially coincides with θL. As a result, the vector of the converter voltage command Vc * shown by the solid line in the figure slightly deviates from the theoretical value shown by the broken line in the figure, but is controlled to be almost the same as the expected output. Therefore, even if the AC voltage amplitude decreases due to the AC system fault, stable control based on the positive-phase voltage phase θs can be maintained, and the operation of the converter 2 can be continued without generating overcurrent or overvoltage. For example, even in a system failure where the positive-phase voltage amplitude is about 1/3 unit value, the interconnection operation can be continued without adding a special operation such as processing a phase signal.
[0035]
FIG. 5 shows a determination flow of the protection stop determination unit. The protection stop determination unit 5 receives the positive-phase voltage amplitude Vs of the connection point voltage, and determines whether Vs is smaller than a threshold value: LEVEL1 (s101). If it is less than LEVEL1, it is determined that a three-line ground fault has occurred (s102), and a stop signal is generated (s103). On the other hand, when Vs is equal to or higher than LEVEL1, system states such as a two-line ground fault, a one-line ground fault, and no accident are estimated (s104), but the process returns to the monitoring of Vs without doing anything.
[0036]
Here, the threshold value: LEVEL1 is a unit value (1.0 pu) of the positive-phase voltage amplitude of the connection point voltage when all three phases are normal, and a lower limit of 1/3 unit value and a 2/3 unit value Is arbitrarily set up to the upper limit. Note that the estimation of the accident type in steps s102 and s104 is not essential.
[0037]
FIG. 6 is an explanatory diagram showing the relationship between the positive-phase voltage amplitude at the fault point and the fault type. As described below, by observing the positive-sequence voltage amplitude at the fault point, it is possible to estimate the fault level or fault type occurring in the AC system.
[0038]
The figure (a-1) shows a case where the AC voltage is normal, and shows a U-phase voltage (vector U), a V-phase voltage (vector V), and a W-phase voltage (vector W) of the AC voltage. . The length of each vector indicates the rated voltage value (1 pu). In the illustration (a-2), the phase voltage vector (U, V, W) of (a-1) is geometrically symmetrically coordinated using the vector U as it is, and the vector V is rotated by + ２ππ. Then, the vector W is rotated by − ／ π, the three vectors are added, and the length is multiplied by 、 to obtain the amplitude value of the positive-phase voltage vector. As is clear from the figure, the positive-phase voltage amplitude is one unit value. That is, the positive-phase voltage amplitude value output from the positive-phase voltage detection unit 4 in FIG. 1 is one unit value.
[0039]
The illustration (b-1) shows the phase voltage vector of the AC voltage at the one-line ground fault point where the U phase is completely grounded. The lengths of the vectors V and W indicate one unit value, but the length of the vector U indicates 0 at a minimum. In the drawing (b-2), the positive-sequence voltage amplitude is obtained by geometrically using the symmetric coordinate method for the phase voltage vector of (b-1). When the phase voltage U is 0, the positive-phase voltage amplitude Vs has a minimum value of 2/3 unit value.
[0040]
The illustration (c-1) shows the phase voltage vector of the AC voltage at the two-line ground fault point where the V phase and the W phase of the AC system are completely grounded. The length of the vector U indicates one unit value, but the length of the vectors V and W indicates 0 at a minimum. In the figure (c-2), the positive-phase voltage amplitude is obtained by geometrically using the symmetrical coordinate method for the phase voltage vector of (c-1). When the phase voltages V and W are 0, the positive-phase voltage amplitude Vs has a minimum value of 1/3 unit value.
[0041]
(D-1) shows a phase voltage vector of an AC voltage in a three-wire ground fault in which the U phase, V phase, and W phase of the AC system are completely grounded. The lengths of the vectors U, V, and W indicate 0 at a minimum. In the drawing (d-2), the positive-phase voltage amplitude is obtained for the phase voltage vector of (d-1) by using the geometrically symmetric coordinate method. When the phase voltages U, V, and W are 0, the positive-phase voltage amplitude Vs has a unit value of 0 and a minimum value.
[0042]
FIG. 7 is an explanatory diagram showing a relationship between a distance from an accident point and an accident range in which protection stop can be determined. The characteristic shows that the residual value of the positive-phase voltage Vs at the time of a system fault changes depending on the fault type and the distance from the fault point. Here, the distance from the fault point is a relative distance of the system connection point to the distance to the system fault point.
[0043]
When a three-wire ground fault occurs, the phase voltage of the three wires drops to near zero at the point of the accident. At this time, the phase voltage may not become zero due to the short-circuit impedance, and a slight positive-phase voltage remains with zero as a lower limit. On the other hand, unless the protection of the AC / DC converter 2 is stopped, the converter output voltage Vc has a rated value (1 unit value = 1.0 pu) regardless of the accident. The connection point positive-phase voltage is determined by the proportional distribution of the total impedance value on the system side from the fault point to the connection point 8 and the impedance (impedance of the interconnection reactor) from the connection point 8 to the output voltage Vc. Therefore, the positive-phase voltage Vs observed at the connection point 8 has a smaller value (minimum value is 0 unit value) as the distance from the fault point to the connection point 8 is shorter, and a larger value (maximum value as the distance is longer). Is one unit value).
[0044]
Similarly, when a two-wire ground fault occurs, the phase voltage of the two wires drops to near zero at the point of the accident. At this time, the phase voltage may not become zero due to the short-circuit impedance, and a positive-phase voltage having a lower limit of 1/3 unit value remains at the fault point. The positive-phase voltage Vs observed at the connection point 8 has a smaller value (minimum value is 1/3 unit value) as the distance from the fault point is shorter, and a larger value (maximum value is 1 unit value) as the distance is longer. become. Also, when a one-line ground fault occurs, the phase voltage of one line drops to near zero at the point of accident. At this time, the phase voltage may not become zero due to the short-circuit impedance, and a positive-phase voltage having a lower limit of 2/3 unit value remains. The positive-phase voltage observed at the connection point has a smaller value (minimum value is 2/3 unit value) as the distance from the fault point to the connection point is shorter, and a larger value (maximum value is 1 unit value) as the distance is longer. )become.
[0045]
The accident estimation in the protection stop determination unit 5 is performed by observing how far the positive-phase voltage amplitude Vs of the connection point voltage decreases. That is, when Vs decreases to less than 1/3 unit value, it can be determined that a three-line ground fault has occurred regardless of the distance between the fault point and the connection point. If Vs falls from a value equal to or more than 1/3 unit value to a value less than 2/3 unit value, a two-wire ground fault occurred at a short distance or a three-wire ground fault occurred at a medium distance. Can be determined.
[0046]
According to the present embodiment, on the power storage system side, it is possible to substantially continue operation in most AC system accidents, and a part of the three-line ground fault in which the positive-phase voltage amplitude is less than 1/3 unit value is It is a target to be protected and stopped due to restrictions on the device side. If it is desired to stop protection of a three-line ground fault, if the threshold value LEVEL1 is temporarily set to 1/3 unit value, a short-range three-line ground fault can be detected, and a two-line ground fault can be erroneously detected. There is no detection. However, there are cases where a three-line ground fault that occurs at a medium distance cannot be detected. Therefore, if the set value is appropriately selected with the threshold value LEVEL1 set to a lower limit of 1/3 unit value and an upper limit of 2/3 unit value, a three-line ground fault at short distance and middle distance can be detected. It is to be noted that there is a possibility that a two-line ground fault at a short distance may be determined to be protection suspension.
[0047]
Next, another embodiment of the present invention will be described. FIG. 8 shows a configuration diagram of a power storage system according to the second embodiment. The same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. The difference between this embodiment and FIG. 1 is that an effective value detecting unit 7 for obtaining a line voltage effective value reduction rate Krms from the effective values of the line voltages V1, V2, and V3 at the connection point 8 is provided, and a protection stop determination unit. Reference numeral 5 'denotes that the input of the positive-phase voltage amplitude Vs and the line voltage effective value reduction rate Krms determines the necessity of protection stop while estimating the type of accident.
[0048]
The effective value detector 7 obtains effective values V1rms, V2rms, and V3rms from the line voltages V1, V2, and V3, and obtains a maximum value thereof: Vrms_max. Further, a line voltage effective value reduction rate Krms is obtained as an index for checking the degree of voltage reduction due to a system fault, and is passed to the protection stop determination unit 5 '. Formula 2 calculates the line voltage maximum value Vrms_max and the line voltage effective value reduction rate Krms.
[0049]
(Equation 2)
Vrms_max = max (V1rms, V2rms, V3rms)
Krms = V1rms / Vrms_max · V2rms / Vrms_max · V3rms / Vrms_max
FIG. 9 illustrates a determination flow of the protection stop determination unit according to the second embodiment. First, it is determined whether the positive-phase voltage amplitude Vs of the connection point voltage is smaller than a threshold value: LEVEL1 (s201). If it is less than 3, it is determined that a three-line ground fault has occurred (s202), and a stop signal is generated (s203). The threshold value: LEVEL1 is set arbitrarily with the positive-phase voltage amplitude of the connection point voltage when all three phases are normal as one unit value and the upper limit of １ ／ unit value.
[0050]
If Vs is equal to or higher than LEVEL1, it is determined whether Vs is lower than a threshold value: LEVEL2 (s204). LEVEL2 is arbitrarily set with a 1/3 unit value as a lower limit. The set upper limit of LEVEL2 is 1.0 pu in theory, but is practically about 0.8 pu, which is the current operation standard of protection suspension.
[0051]
If it is less than LEVEL2, it is determined whether or not the line voltage effective value decrease rate Krms is equal to or more than the threshold value: LEVEL3 (s205). If the line voltage effective value reduction rate Krms is LEVEL 3 or more, it is determined that a three-wire ground fault has occurred, a stop signal is generated, and no stop signal is generated under other conditions. LEVEL3 is arbitrarily set with a 2/3 unit value as a lower limit.
[0052]
FIG. 10 is an explanatory diagram showing the relationship between the distance from the accident point and the accident range in which protection can be stopped in the second embodiment. (A) shows the relationship between the distance to the fault point and the residual value of the positive-sequence voltage, and (b) shows the relationship between the distance to the fault point and the rate of decrease in the effective voltage between lines.
[0053]
As in the case of the first embodiment, by observing how far the positive-phase voltage amplitude Vs of the connection point voltage decreases, a system fault situation can be estimated considerably. When Vs decreases to less than 1/3 unit value, it can be determined that a three-line ground fault has occurred regardless of the distance between the fault point and the connection point. When Vs falls from a value equal to or more than the ３ unit value to a value less than the ２ unit value, it is determined that a two-wire ground fault occurred at a short distance or a three-wire ground fault occurred at a medium distance. I can judge.
[0054]
When it is desired to stop the protection of the three-line ground fault, the protection threshold LEVEL1 is set to an arbitrary value having an upper limit of 1/3 unit value, so that the short-range three-line ground fault can be detected. At this time, the two-line ground fault is not erroneously detected.
[0055]
Furthermore, in order to protect and stop the three-line ground faults at medium and long distances, the determination is made by paying attention to the difference between the effective values of the line voltages. In the case of a three-line ground fault, the effective value of the line voltage at the fault point is substantially the same for all three signals. For this reason, the line-to-line voltage effective value reduction rate at the fault point is almost one, and the voltage effective value reduction rate is almost one regardless of the distance from the fault point.
[0056]
As described above, when the line voltage effective value reduction rate Krms is approximately in the range of 2/3 unit value or more, the possibility of the one-line ground fault and the two-line ground fault is eliminated, and the three-line ground fault or the accident is not caused. Can be considered Therefore, if the positive-sequence voltage amplitude is in the range of 1/3 unit value or more in step s204 of FIG. 9 and it cannot be determined whether a three-wire ground fault or a two-wire ground fault has occurred, furthermore, in step s205, If it is determined whether the line voltage effective value reduction rate is in the range of 2/3 unit value or more, it is possible to determine a three-line ground fault at a medium distance.
[0057]
Alternatively, in the case of a three-line ground fault, the fact that the effective value of the line voltage at the fault point is substantially the same for all three signals may be used. That is, if the positive-sequence voltage amplitude is in the range of 1/3 unit value or more in step S204 and it is not possible to determine whether a three-wire ground fault or a two-wire ground fault has occurred, furthermore, in step S205, three lines are detected. It is checked whether the effective values of the inter-voltages are all the same value.
[0058]
According to the second embodiment, a three-line ground fault at a medium distance, which could not be reliably determined from the positive-sequence voltage in the first embodiment, is added with a determination using the line voltage effective value decrease rate as an index. By doing so, accurate discrimination became possible. As a result, the system can be reliably stopped in the event of a three-line ground fault, which is a request from the system, and operation can be continued in other accidents that do not need to be stopped.
[0059]
FIG. 11 shows a simulation result of the first embodiment. (A) is a model system diagram used for the analysis, which is a system composed of four voltage classes of 275 kV, 154 kV, 66 kV, and 6.6 kV. The NaS battery system is connected to a C substation 6.6 kV bus. We mainly analyzed various ground faults on 275 kV and 154 kV transmission lines. In FIG. 11, (1) and (2) indicate the occurrence points of the ground fault.
[0060]
(B) shows the analysis result. In each fault, the minimum value of the line voltage at the interconnection point of the NaS battery system (min), the positive-sequence voltage at the connection point, the maximum value of the converter current (max), the operation continuation (に よ る), and the stop ( ×). Assuming that the operation stop standard is 80% of the line voltage rating as in the past, the operation stops at 2LG of the 154 kV transmission line and at 2LG and 3LG of the 275 kV transmission line. When the operation stop reference is 45% of the positive-sequence voltage of the present embodiment, the operation continuation range can be extended to 2LG of the 154 kV transmission line and 2LG of the 275 kV transmission line. Further, in each of these cases, the overcurrent of the converter current is suppressed within a specified value.
[0061]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, while using a positive-phase voltage phase for the control of the AC / DC converter of the electric power storage system interconnected with an AC system, the stable operation continuation range at the time of a system failure is extended, Since the occurrence is determined based on the positive-sequence voltage amplitude, the operability in the event of an accident is improved, and there is an effect that the protection stop of the system necessary for system request or overcurrent prevention can be reliably performed.
[0062]
Furthermore, in addition to the above, the judgment of an accident that requires protection stop is also made based on the situation where the effective values of the three voltage signals at the connection point have decreased, so it is limited to three-phase ground faults that really need to be stopped. Protection stop can be performed, and unnecessary stop can be avoided.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a power storage system according to a first embodiment of the present invention.
FIG. 2 is a configuration diagram of a power converter control unit.
FIG. 3 is a configuration diagram of a positive-phase voltage detection unit.
FIG. 4 is an explanatory diagram showing a vector relationship of a converter voltage command Vc * for the present embodiment and a conventional example.
FIG. 5 is a flowchart showing a determination process of a protection stop determination unit according to one embodiment.
FIG. 6 is an explanatory diagram showing a relationship between a voltage vector diagram and a positive-phase voltage amplitude in a system fault.
FIG. 7 is an explanatory diagram showing a distance from an accident point and an accident range in which protection stop can be determined in the first embodiment.
FIG. 8 is a configuration diagram of a power storage system according to a second embodiment of the present invention.
FIG. 9 is a flowchart illustrating a determination process of a protection stop determination unit according to the second embodiment.
FIG. 10 is an explanatory diagram showing a distance from an accident point and an accident range in which protection stop can be determined in the second embodiment.
FIG. 11 is an explanatory diagram of a simulation result performed on the first embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... AC system, 2 ... AC / DC power converter (main circuit), 3 ... Secondary battery, 4 ... Positive phase voltage detector, 5, 5 '... Protection stop determination part, 6 ... Power converter controller, 7 ... Effective value detector 111, active power command value generator 112, reactive power command value generator 113, active power controller 114, reactive power controller 115, active power reactive power detector 116, 3 / 2-phase number conversion section, 117: αβ / dq axis conversion section, 118: 3/2 phase number conversion section, 119: αβ / dq axis conversion section, 121: active current controller, 122: reactive current controller, 123, 124: adder, 125: dq / αβ axis converter, 126: 2/3 phase number converter, 127: PWM pulse generator, 211: 3/2 phase number converter, 212: frequency reference signal generation circuit, 213 216: Fourier transform operation circuit, 217: Basic frequency positive phase power Pressure real axis component operation circuit, 218 ... fundamental frequency positive phase voltage imaginary axis component operation circuit, 219 ... absolute value operation circuit, 220 ... phase difference operation circuit, 221 ... adder.

Claims (4)

An AC / DC power conversion device connected to a three-phase AC system and converting three-phase AC power to DC power or converting DC power to three-phase AC power, and a power storage system including a secondary battery connected to the conversion device At
In order to adjust the AC power output from the AC / DC power converter, an output voltage vector of the AC / DC power converter is controlled with respect to a connection point voltage vector based on a connection point voltage phase at a connection point with the AC system. A power conversion control unit,
The discrete voltage Fourier transform is performed by inputting the three voltage signals at the connection point, and based on the converted real axis component and imaginary axis component, a positive phase component amplitude and a positive phase component phase of the connection point voltage are detected, A positive-phase voltage detection unit that outputs a positive-phase component phase to the power conversion control unit as the connection point voltage phase,
Based on the positive-sequence amplitude input from the positive-phase voltage detection unit, it is monitored whether an abnormality that should stop the power storage system has occurred in the three-phase AC system. A protection stop determination unit that outputs a system stop signal when it is determined that the
The protection stop judging section sets a threshold value having a 1/3 unit value as a lower limit and a 2/3 unit value as an upper limit, with the positive phase amplitude when all phases of the three-phase AC system are normal as a unit value. Is set arbitrarily, and when the amplitude of the positive-sequence component is smaller than the threshold value, it is determined that an abnormality that requires the system stoppage has occurred . An AC / DC power conversion device connected to a three-phase AC system and converting three-phase AC power to DC power or converting DC power to three-phase AC power, and a power storage system including a secondary battery connected to the conversion device At
In order to adjust the AC power output from the AC / DC power converter, an output voltage vector of the AC / DC power converter is controlled with respect to a connection point voltage vector based on a connection point voltage phase at a connection point with the AC system. A power conversion control unit,
The discrete voltage Fourier transform is performed by inputting the three voltage signals at the connection point, and based on the converted real axis component and imaginary axis component, a positive phase component amplitude and a positive phase component phase of the connection point voltage are detected, A positive-phase voltage detection unit that outputs a positive-phase component phase to the power conversion control unit as the connection point voltage phase,
An effective value detection unit that receives the three voltage signals and obtains three effective values;
On the basis of the positive phase component amplitude input from the positive phase voltage detection unit and the three effective values input from the effective value detection unit, an abnormality in which the power storage system should be stopped occurs in the three-phase AC system. A protection stop determination unit that outputs a system stop signal when it is determined that an abnormality requiring a system stop has occurred. In claim 2 ,
The protection stop determination unit includes: a first threshold having an upper limit of 1/3 unit value, with the amplitude of the positive-phase component as a unit value when all phases of the three-phase AC system are normal; A second threshold having a unit value as a lower limit is arbitrarily set, and the absolute value of the positive phase component amplitude is smaller than the first threshold value, If the absolute value is greater than or equal to the first threshold value and less than the second threshold value, and all of the three effective values have the same value, an abnormality that requires the system stoppage occurs. A power storage system characterized in that it is determined that there is a power storage system. In claim 3 ,
The effective value detecting unit calculates a ratio of each effective value to a maximum value of the three effective values, and determines a voltage effective value decrease rate due to a synergistic effect thereof,
The protection stop determination unit includes: a first threshold having an upper limit of 1/3 unit value, with the amplitude of the positive-phase component as a unit value when all phases of the three-phase AC system are normal; A second threshold having a unit value as a lower limit and a third threshold having a 2/3 unit value as a lower limit are arbitrarily set, respectively, and the absolute value of the positive phase component amplitude is equal to the second threshold. When the absolute value of the positive phase component amplitude is equal to or greater than the first threshold and less than the second threshold, and the voltage effective value decrease rate is equal to or less than the first threshold. A power storage system, wherein when the threshold value is equal to or more than 3, it is determined that an abnormality that requires the system stoppage has occurred.

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