JP2007110894A - Electric power conversion system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect an individual operation of an electric power converter linked to a system by a simple control unit or by a control method. <P>SOLUTION: A frequency component is added to an output voltage command value of an electric power converter, and the amplitude width of the frequency component is detected from a voltage that the system outputs. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power conversion system that is connected to a grid and absorbs or discharges power, and a control device therefor.

  In the control device for a power converter described in Japanese Patent Laid-Open No. 10-248168, an n-th order current source is connected to the system, a change in system impedance during the independent operation of the private power generation facility is detected, and the private power generation facility is disconnected. To do.

JP-A-10-248168

  As described above, since the n-th order current source is installed in the prior art, when a distributed power source such as a voltage source inverter for interconnection is installed, a current source for detection and a control device are separately required. .

  An object of the present invention is to provide a power conversion system suitable for detecting an isolated operation of a power converter and a control device therefor.

  In the power conversion system according to the present invention, the power converter and the power system are interconnected, and an AC voltage or an AC current in the interconnecting unit is detected. From the detected AC voltage or AC current, a frequency component having a frequency different from the frequency of the system, that is, a harmonic component, is obtained by calculation or the like. When the power flowing into the system from the power converter increases as in isolated operation, the amplitude of the frequency component increases. Therefore, the isolated operation of the power converter can be detected based on the frequency component.

  The frequency component is obtained by adding an alternating voltage command having a frequency component frequency to an output voltage command created by calculation or the like using a control device or a control method for controlling the output voltage of the power converter. Further, the frequency component may be a harmonic component output from the power converter. With such frequency components, it is possible to detect islanding with high accuracy by a relatively simple control device or control method.

  According to the present invention, the magnitude of the frequency component superimposed on the output voltage of the power converter is detected by adding the AC voltage command to the output voltage command. Moreover, the harmonic component which a power converter outputs is detected. Therefore, the control device or the control method can be simplified.

Example 1
A power conversion system according to a first embodiment of the present invention will be described below with reference to FIG.

  In FIG. 1, the power converter is connected to the interconnection transformer 3a. The interconnection transformer 3a is connected to the power system via the circuit breaker 1a. A secondary battery 4a is installed in the DC circuit portion of the power converter. The power converter is used for the secondary battery, and the control device 11a absorbs / discharges the active power P / reactive power Q to / from the power system via the interconnection transformer 3a.

  The control device 11a of the power converter converts the active power P and reactive power Q output to the system into the output (AC current) of the current detector (current detection means) 2b and the output (AC voltage) of the voltage detector (voltage detection means) 5a. ) From the power detector. The active power P and the reactive power Q thus obtained are input to the active power regulator and the reactive power regulator, respectively, and the powers P and Q are matched with the command values Pref and Qref by the active power regulator and the reactive power regulator. The current command values Id * and Iq * are calculated and output to the current regulator.

The phase detector outputs phase signals Vcos and Vsin that follow the phase of the system voltage. The phase signals Vcos and Vsin are input to the coordinate converter. The current of the converter is detected by the current detector 2a, the current detection value Icnv is coordinate-converted by the coordinate converter, and the two-axis current detection values Id and Iq as the conversion results are input to the current regulator. The current regulator controls the current of the power converter so as to match the command values Id * and Iq *. Outputs Vd * and Vq * of the current regulator are input to the coordinate converter, and the coordinate converter outputs voltage command values Vuo *, Vvo *, and Vwo * to the adders 15a, 15b, and 15c.

  The detected interconnection point (interconnection part) voltage Vac is input to a feedforward (FF) voltage calculator, the magnitude is adjusted, and feedforward voltage command values Vuf, Vvf, Vwf are added to adders 15a, 15b, 15c. Output to.

  The adders 15a, 15b, and 15c are voltage command values (output voltage commands) Vu * of the power converter that are the addition results of the voltage command values Vuo *, Vvo *, and Vwo * and the feedforward voltage command values Vuf, Vvf, and Vwf. , Vv *, Vw * are output to the adders 15d, 15e, 15f.

  The n-order harmonic voltage calculator calculates n-order three-phase voltage command values Vun, Vvn, Vwn (AC voltage commands) and outputs them to adders 15d, 15e, 15f.

  The adders 15d, 15e, and 15f are voltage command values Vu1, Vvl, and Vw1 of the power converter that are the addition results of the voltage command values Vu *, Vv *, and Vw * and the n-order three-phase voltage command values Vun, Vvn, and Vwn. Is output to the PWM calculator, and the PWM calculator outputs a gate pulse GP based on the voltage command values Vu1, Vvl, and Vw1 of the power converter to the power converter.

  The accuracy is further improved by using, for example, an even order as an order that is not included in the grid side without being output by the converter as an nth order frequency component to be superimposed on the voltage command of the power converter.

  Further, when the interconnection transformer has a delta winding, multiple harmonics of 3 do not flow out to the system, and therefore, other than multiple harmonics of 3 are used as the n-order component to be superimposed on the voltage command value.

  The output of the interconnection point voltage detector is input to the nth-order harmonic detector 14a, the voltage amplitude is calculated by the nth-order harmonic detector 14a, and the isolated operation is detected by sudden change or increase / decrease in the amplitude. A signal Sa for operating the circuit breaker 1a is output to disconnect the conversion device from the system.

  FIG. 2 shows the configuration of the nth-order harmonic detector 14a in FIG. 1 in detail. The detected voltage detection value Vac at the connection point is input to the three-phase two-phase converter, and the three-phase two-phase converter calculates the voltage components for the positive phase and the reverse phase by the symmetric coordinate method, Va and Vb, respectively. Is output.

  The voltage components Va and Vb are input to the fundamental wave calculation means and the adders 15g and 15h, respectively. The fundamental wave calculating means detects fundamental wave components VaR and VbR (power supply frequency components) of the inputted signals Va and Vb by Fourier transform and outputs them to an adder.

  The adders 15g and 15h output VaS and VbS, which are the results of subtracting the outputs VaR and VbR of the fundamental wave calculation means, from the outputs Va and Vb of the three-phase to two-phase converter, to the nth-order harmonic component detector. The n-order harmonic component detector performs Fourier transform on the input signals Vas and Vbs with the n-order component as a reference, detects the n-order components VaN and VbN, and outputs them to the amplitude calculator. The amplitude calculator calculates a square sum route of VaN and VbN and outputs an nth-order voltage amplitude value Vn to the level determiner 10a. When the n-th order voltage amplitude Vn becomes equal to or higher than a predetermined value, the level determination unit 10a determines that the operation is independent, and disconnects the system from the system and stops it.

  As the set level of the level determination device 10a, the value at the start of operation is detected in advance and stored, and this is set to several percent on the basis of this.

  Further, the isolated operation may be detected from the values of the distortion magnitudes of all the harmonic voltages obtained by the square sum route of VaS and VbS.

  FIG. 3 shows a circuit in which the power supply Vso of the system, the line impedance Z2 of the system, the impedance Z1 up to the connection point with the power converter system, and the load Z3 are connected. The power converter system superimposes the n-th order voltage Vn for detecting an isolated operation. If attention is paid only to the n-th order voltage at this time, the power supply Vso of the system may be considered to be short-circuited, and the voltage Vn ′ at the connection point of the system decreases by the voltage drop due to Z1, and is expressed by the equation (Equation 1) Is done.

Generally, the capacity of a power storage system having a power converter and a secondary battery is small compared to the capacity of the power system, and therefore Z2 is a small value compared to Z1. Moreover, Z3 becomes a large value compared with Z2 on the conditions that independent operation is materialized. Therefore, Expression (Equation 2) and Expression (Equation 3) hold.
(Equation 2)
| Z2 | << | Z1 | (Formula 2)
(Equation 3)
| Z3 | >> | Z2 | (Equation 3)
Therefore, Expression (Expression 4) is obtained from Expression (Expression 3).

  Further, Expression (Formula 5) is obtained from Expression (Formula 2).

  Therefore, the n-th order voltage at the interconnection point is almost zero.

  Next, when considering a state in which the power system is disconnected, a circuit in which the switch SW is opened in FIG. 3 is formed, and the power storage system supplies power to the load and enters a single operation state. At this time, since the impedance of the system is no longer Z2, for example, when a load Z equivalent to the system capacity is connected, 100% impedance is connected, and the impedance viewed from the system is larger than before the single operation. Therefore, the n-order voltage Vn ′ observed at the interconnection point is expressed by the equation (Equation 6).

  Assuming that Z1 is the sum of the transformer leakage and the internal impedance of the system and is about 15%, for example, Vn ′ is calculated by substituting into the above equation (Equation 6), Vn ′ = 0.87 Vn. .

  Thus, when it becomes independent operation, the nth-order voltage of a connection point changes a lot, and the change can be caught easily.

  In addition, an n-th order current may be used for detecting an isolated operation. However, if the frequency of the superimposed n-order voltage is compared with the current control response and a higher order than the response is used, the magnitude of the n-order current is difficult to be suppressed by the current control system, and the change before and after the single operation transition is detected greatly. Accuracy is improved.

  In the present embodiment, the level determination is used for the determination of the isolated operation, but the isolated operation may be detected based on the rate of change.

  In the present embodiment, the method of always adding the n-th order voltage has been described. However, the isolated operation may be detected by superimposing the n-th order voltage once in 100 ms, for example, using a time pattern. In this case, erroneous detection can be prevented by individually setting patterns for a plurality of converter systems.

  Further, detection accuracy can be improved by detecting a harmonic spectrum that is stopped, automatically selecting an order having a small harmonic from the detection result, and adding the order having a small harmonic during operation to the voltage command value.

  In addition, using the detected n-th order harmonic amplitude detection value during operation, the amplitude value of the n-th order harmonic added to the voltage command value is automatically adjusted to affect the effect of voltage harmonics on the system when multiple units are installed. Can be small.

  According to this embodiment, since the nth-order harmonic voltage component is superimposed on the output voltage of the converter and the magnitude of the nth-order voltage component output by the system is detected, the change in system impedance is By utilizing the influence on the n-order voltage, the isolated operation state can be detected from the change, and the system can be stopped safely.

(Example 2)
Next, another embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to an equivalent component through each figure, and detailed description is abbreviate | omitted.

  FIG. 4 is a second embodiment of the power conversion system according to the present invention.

  In this embodiment, the addition of the n-order voltage command value in the first embodiment is eliminated.

  According to the present embodiment, the isolated operation is detected using the harmonic component (for example, the 5th and 7th orders) output in principle by the power converter using the same nth-order voltage detection method as in the first embodiment. This makes it possible to simplify the control configuration.

(Example 3)
FIG. 5 shows a third embodiment of the power conversion system according to the present invention.

  In this embodiment, an n-order current amplitude detector is added to the n-order voltage amplitude detector of the second embodiment.

  FIG. 6 shows the configuration of the nth-order voltage / current amplitude detector 100a. By using the input of the n-th order voltage amplitude detector described in the first embodiment as a current, the n-th order current amplitude can be detected. When either the change in the n-th order current amplitude or the change in the n-th order voltage amplitude exceeds the set value, the isolated operation is detected and a breaker open command is output. Further, the rate of change in amplitude may be used for the determination of the isolated operation.

  Alternatively, the impedance may be calculated from the current and voltage, and the single operation may be determined from the change in the calculated impedance.

  According to the present embodiment, in addition to the same effects as those of the first or second embodiment, the isolated operation state can be detected from the nth-order current, so that it can be detected more reliably.

  Although the case where the present invention is mainly applied to the control device and the control method of the second embodiment has been described here, the control device and the control method described in other embodiments may be used.

Example 4
FIG. 7 shows an embodiment in which a reactive power compensator (SVC) is applied to the power storage converter using the secondary battery 4a of the second embodiment. A capacitor 6 is installed in the DC portion of the power converter of the reactive power compensator, and the reactive power compensator exchanges reactive power with the system in response to a command from the control device 11f.

  In the present embodiment, it becomes possible to prevent a single operation of the power generating device including the SVC.

  Moreover, a solar power generation device as shown in FIG. 8 is also applicable. The solar cell panel 7 is installed in the direct current portion of the power converter of the solar power generation device, and the power is released to the system by a command from the control device 11c.

  A superconducting power storage device as shown in FIG. 9 can also be applied. A superconducting coil 8 is installed in the DC portion of the power converter of the superconducting power storage device, and power is absorbed from the system or released to the system in response to a command from the control device 11d.

  A wind power generator as shown in FIG. 10 can also be applied. The output of the wind turbine generator is once converted into direct current by the power converter, and power is supplied to the system by the power converter.

  Although the case where the present invention is mainly applied to the control device and the control method of the second embodiment has been described here, the present invention may be used for the control device and the control method described in other embodiments.

1 is a power conversion system according to a first embodiment of the present invention. The figure explaining the structure of FIG. The figure explaining the effect of a 1st Example. The figure explaining the 2nd Example of this invention. The figure explaining the 3rd Example of this invention. The figure explaining the structure of FIG. The figure explaining the modification of the 2nd Example of this invention. The figure explaining the modification of the 2nd Example of this invention. The figure explaining the modification of the 2nd Example of this invention. The figure explaining the modification of the 2nd Example of this invention.

Explanation of symbols

1a, 1b, 1c, 1d, 1e, 1f ... circuit breaker, 2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h, 2i, 2j, 2k, 2l ... current detector, 3a, 3b, 3c, 3d , 3e, 3f ... interconnection transformer, 4a, 4b ... secondary battery, 5a, 5b, 5c, 5d, 5e, 5f ... voltage detector, 6 ... capacitor, 7 ... solar cell, 8 ... superconducting coil, 9 ... wind power generator, 10a ... level judgment unit, 11a, 11b, 11c, 11d, 11e, 11f ... power converter control device, 14a, 14b, 14c, 14d, 14e, 14f, 100a ... n-order voltage detector, 15a , 15b, 15c, 15d, 15e, 15f, 15g, 15h, 15i, 15j, 15k, 15l, 15m, 15n, 15o, 15p, 15q, 15r, 15s, 15t, 15u, 15v, 15w ... adder, Iac Link point current detection value, Vac ... Link point voltage detection value, Icnv ... Converter current detection value, Pref ... Active power command value, Qref ... Reactive power command value, P ... Active power, Q ... Reactive power, Id * ... active current command value, Iq * ... reactive current command value, Id ... active current detection value, Iq ... reactive current detection value, Vcos, Vsin ... phase signal, Vd * ... active current command value,
Vq * ... reactive current command value, Vuo *, Vvo *, Vwo * ... voltage command value, Vuf, Vvf, Vwf ... feedforward voltage command value, Vun, Vvn, Vwn ... n-order voltage command value, Vu *, Vv *, Vw *, Vu1, Vvl, Vw1 ... Converter output voltage command value, GP ... Gate pulse, Vdc ... DC voltage detection value, Vdcref ... DC voltage command value, Sa ... Circuit breaker operation signal, Va ... Voltage α component, Vb: Voltage β component, VaR: Fundamental wave component of voltage α component, VbR: Fundamental wave component of voltage β component, VaS: Harmonic voltage α component, VbS: Harmonic voltage β component, VaN: nth harmonic voltage α Component, VbN: n-order harmonic voltage β component, Vn: n-order voltage amplitude, Vso: system voltage.

Claims (7)

  In a power conversion system comprising: a power converter linked to a grid; a voltage detection means for detecting an AC voltage in the linkage section; and a control means for calculating an output voltage command of the power converter. Means for calculating an AC voltage command having a different frequency from the output voltage command, the AC voltage command is added to the output voltage command, and the frequency component of the frequency of the AC voltage command is detected from the AC voltage detected by the voltage detection unit. A power conversion system comprising: means for calculating a voltage amplitude; and means for detecting a single operation of the power converter from the voltage amplitude.   In a power conversion system comprising a power converter linked to a grid, current detection means for detecting an alternating current in the grid, and a control means for calculating an output voltage command of the power converter, the frequency of the grid voltage A means for calculating an AC voltage command having a frequency different from that of the output voltage command. A power conversion system comprising: means for calculating the power converter; and means for detecting a single operation of the power converter from the current amplitude.   3. The power conversion system according to claim 1, wherein the frequency of the AC voltage command is an integral multiple of the frequency of the system voltage.   The power conversion system according to claim 2, wherein the frequency of the AC voltage command is higher than the current control response.   3. The power conversion system according to claim 1, wherein the frequency of the AC voltage command is added in a time pattern.   In the power conversion system, comprising: a power converter linked to the grid; a voltage detection means for detecting an AC voltage in the interconnection section; and a control means for calculating an output voltage command of the power converter. A power conversion system comprising: means for calculating a voltage amplitude of a harmonic component output from the power converter from the AC voltage detected by the step, and detecting a single operation of the power converter from the voltage amplitude.   In the power conversion system, comprising: a power converter linked to the grid; a current detection means for detecting an alternating current in the interconnection section; and a control means for calculating an output voltage command of the power converter. The power converter includes means for calculating a current amplitude of a harmonic component output by the power converter during normal operation from the alternating current detected by, and detecting a single operation of the power converter from the calculated current amplitude. Power conversion system.

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