JP4218835B2 - Apparatus and method for compensating voltage imbalance in distribution system - Google Patents

Description

  The present invention relates to a distribution system unbalance compensation apparatus and method for compensating for a three-phase unbalance in a distribution system.

  Due to the liberalization of electric power, the interconnection of distributed power sources (for example, photovoltaic power generation systems) to the electric power system is increasing. Usually, a distributed power source is often connected to a single-phase 200V distribution system by converting generated direct current into single-phase alternating current by a single-phase inverter. Currently, the total capacity of single-phase distributed power sources connected to each other is small, so the effect of unbalancing the voltage and current of the distribution system, which is a three-phase alternating current, is small, but when there are more distributed power sources connected The influence of unbalance on the distribution system cannot be ignored. When a three-phase imbalance occurs in the distribution system, the output torque of the three-phase induction machine, which is a three-phase load, fluctuates, or an increase in power loss or a decrease in voltage occurs during transmission and distribution due to voltage and current imbalance. May occur.

Therefore, compensation for a three-phase unbalanced state by controlling a single-phase inverter of a distributed power source has been studied. For example, the amount of evaluation of a single-phase unbalanced state based on the instantaneous real power and instantaneous imaginary power of the interconnection system is derived, and the reactive power output control of the distributed power source is performed so that the evaluation amount is minimized. Some have achieved balance compensation (see, for example, Non-Patent Document 1).
Electrical Engineering D, Vol.124, No.2, 2004, p215-p221 “System interconnection method for single-phase photovoltaic power generation system considering three-phase voltage imbalance”

  However, in the non-patent document 1, the transformer for receiving and transforming the distribution system is examined under the condition that the impedance is balanced on the assumption that the impedance is balanced. For this reason, in the output control of the single-phase inverter by the method of Non-Patent Document 1, when the impedance is three-phase unbalanced, unbalance compensation cannot be realized. In a power distribution system, power is often supplied to a load by V-connection using two single-phase transformers, and the capacity of the two transformers constituting the V-connection is often different. In other words, a transformer with three-phase unbalanced impedance is often used. Therefore, when the transformer for receiving and transforming the distribution system is a V-connection transformer, the method of Non-Patent Document 1 cannot be applied as it is to compensate for the three-phase imbalance in the distribution system.

  An object of the present invention is to provide an unbalance compensation apparatus and method for a distribution system that can compensate for the unbalance occurring in the distribution system even if the impedance and load of the transformer for receiving and transforming the distribution system are unbalanced.

  The unbalance compensation device for a distribution system according to the invention of claim 1 is connected between any two phase terminals of the three phase terminals of the secondary system of the V-connection transformer of the distribution system, and converts direct current into alternating current. Based on the single-phase inverter connected to the distribution system, the voltage of the V-connection transformer, the impedance of each transformer constituting the V-connection transformer, and the load connected to the V-connection transformer, The target value calculation unit that calculates the target value of the output current of the single-phase inverter where the unbalance evaluation amount for evaluating the degree of unbalance is zero or the minimum, and the output current of the single-phase inverter are obtained by the target value calculation unit And an output control unit that controls the single-phase inverter so as to achieve the set target value.

  An unbalance compensation method for a distribution system according to the invention of claim 2 is a single-phase power conversion from a direct current to an alternating current between any two phase terminals of the three-phase terminals of the secondary system of the V-connection transformer of the distribution system. Evaluate the degree of unbalance in the three phases of the distribution system based on the voltage of the V-connection transformer, the impedance of each transformer constituting the V-connection transformer, and the load connected to the V-connection transformer. It calculates the target value of the output current of the single-phase inverter where the unbalanced evaluation amount to achieve zero or the minimum, and controls the single-phase inverter so that the output current of the single-phase inverter becomes the target value .

  The unbalance compensation apparatus for a distribution system according to the invention of claim 3 is connected between any two phase terminals of the three-phase terminals of the secondary system of the V-connection transformer of the distribution system, and converts DC power into AC power. The distribution system based on the single-phase inverter connected to the distribution system, the voltage of the V-connection transformer, the impedance of each transformer constituting the V-connection transformer, and the load connected to the V-connection transformer A target value calculation unit for calculating a target value of the output reactive power of the single-phase inverter with which the unbalance evaluation amount for evaluating the degree of unbalance of the three phases is zero or minimum, and output invalidity of the single-phase inverter And an output control unit that controls the single-phase inverter so that electric power becomes a target value obtained by the target value calculation unit.

  The unbalance compensation method for the distribution system according to the invention of claim 4 is a single-phase power conversion from a direct current to an alternating current between any two phase terminals of the three phase terminals of the secondary system of the V-connection transformer of the distribution system. Three-phase imbalance in the distribution system based on the voltage connected to the inverter, the voltage of the V-connection transformer, the impedance of each transformer constituting the V-connection transformer, and the load connected to the V-connection transformer A target value of the output reactive power of the single-phase inverter that calculates zero or the minimum unbalanced evaluation amount for evaluating the degree of power is calculated, and the single-phase inverter output reactive power becomes the target value. It is characterized by controlling the phase inverter.

  According to the present invention, the three-phase fault of the distribution system based on the voltage of the V-connection transformer, the impedance of each transformer constituting the V-connection transformer, and the load connected to the secondary system of the V-connection transformer. Since the unbalanced evaluation amount for evaluating the degree of balance is calculated and the output current of the single-phase inverter is controlled so that the unbalanced evaluation amount is zero or minimum, the transformer impedance is unbalanced or unbalanced. Even when a balanced load is connected, an unbalance occurring in the distribution system can be suppressed.

  Embodiments of the present invention will be described below. FIG. 1 is an explanatory diagram of an unbalance compensator according to the first embodiment of the present invention, FIG. 1 (a) is a connection diagram of a V-connection transformer, and FIG. 1 (b) is a configuration of the unbalance compensator. FIG.

  In FIG. 1 (a), a V-connection transformer is obtained by connecting two single-phase transformers with a V-connection, for example, between the uv phase of the uvw phase on the upper system side and between the vw phase and the abc phase on the lower system side. The primary side and the secondary side of two single-phase transformers are connected between the ab phase and the bc phase. Assume that the impedance X of the two single-phase transformers is the same.

FIG.1 (b) is the block diagram which connected the unbalance compensation apparatus 11 to the secondary side of the V connection transformer, and has shown the case where the three-phase balanced load Z is connected. The unbalance compensator 11 is connected between the bc phases of the V-connection transformer, converts the direct current of the distributed power source 12 into an alternating current by the single-phase inverter 13 and supplies it to the distribution system. The single-phase inverter 13 is controlled by the output control unit 14 and outputs an output current I _OUT so as to compensate for an unbalance occurring in the distribution system. That is, the output control unit 14 feeds back the output current I _OUT of the single-phase inverter 13 detected by the current detector 16 and controls the target value I _OUT1 obtained by the target value calculation unit 15. Thereby, the output current I _OUT of the single-phase inverter 13 is controlled by the output control unit 14 so as to be the target value I _OUT1 obtained by the target value calculation unit 15.

The target value calculation unit 15 is connected to the primary side voltage E (E _uv , E _vw ) of the V connection transformer, the impedance X of each transformer constituting the V connection transformer, and the secondary side system of the V connection transformer. The target value I _OUT1 of the output current I _OUT of the single-phase inverter 13 is calculated based on the load Z. The target value I _OUT1 of the output current I _OUT is an _{unbalanced expression} expressed as an alternating current component of instantaneous real power and an alternating current component of instantaneous imaginary power obtained from the primary voltage E (E _uv , E _vw ) of the distribution system and the output current. The unbalanced evaluation amount ξ for evaluating the degree is calculated to be zero.

  FIG. 2 is a general representation of a three-phase AC system, and the unbalance evaluation amount will be described below using this.

In general, the unbalanced evaluation amount ξ is expressed by equation (1-1). In the following mathematical formula, “·” at the top of the character indicates a complex vector, and the notation “·” is omitted in the text.

The unbalanced evaluation amount ξ is the square of the AC component | P _a | of the instantaneous real power p and the square of the AC component | Q _a | of the instantaneous imaginary power q as shown in the equation (1-1). It is indicated by the square root of the sum of

The AC component | P _a | of the instantaneous real power p of the three-phase AC system and the AC component | Q _a | of the instantaneous imaginary power q are expressed by the three-phase voltage V of the three-phase AC system, as shown in Equation (1-2). It is expressed by voltage V _α , voltage V _β , current I _α , and current I _{β obtained} by two-phase conversion of _ab , V _bc , V _ca and three-phase currents I _a , I _b , I _c . That is, as shown by the equations (1-3) and (1-4), it is obtained from the alternating current components of the instantaneous real power p and the instantaneous imaginary power q expressed by the three-phase-two-phase converted voltage-current.

However, three-phase voltage _V ab of the three-phase AC _system, V _{bc, V ca} and three-phase currents _{I a,} I b, a three-phase _{I c} - two-phase voltage is converted two-phase V _alpha, V _beta, two-phase current The instantaneous real power p and the instantaneous imaginary power q represented by I _α and I _β are a frequency that is twice the DC component and the AC system frequency as shown in the equations (1-3) and (1-4). Can be divided into the sum of alternating current components that vibrate. The AC components oscillating at twice the frequency are defined as AC component | P _a | of instantaneous real power p and AC component | Q _a | of instantaneous imaginary power q, respectively.

Here, as the power quality related to the three-phase unbalance in the power system, the voltage unbalance rate and the current unbalance rate shown in the equations (1-5) and (1-6) are defined. In the formulas (1-5) and (1-6), V ₁ is a positive phase voltage, V ₂ is a negative phase voltage, I ₁ is a positive phase current, and I ₂ is a negative phase current. On the other hand, when the unbalanced evaluation amount ξ represented by the equation (1-1) is expressed by the positive phase voltage V ₁ , the negative phase voltage V ₂ , the positive phase current I ₁ and the negative phase current I ₂ , the equation (1-7) is obtained. The unbalance evaluation amount ξ is an amount that includes the voltage unbalance rate and the current unbalance rate at the same time.

Next, a condition for balancing the unbalanced evaluation amount ξ to zero, that is, a three-phase voltage and current is considered. When formula (1-1) is modified, formula (2-1) is obtained. The condition for making the equation (2-1) zero is expressed by the equation (2-2).

Next, returning to FIG. 1, in order to make the unbalanced evaluation amount ξ zero, the output current I _OUT supplied to the secondary side of the V-connection transformer is derived from the single-phase inverter 13 of the unbalance compensation device 11. As shown in FIG. 1B, the primary voltage E (E _uv , E _vw ) of the V-connection transformer and the secondary voltages V _ab , V _bc of the V-connection transformer constitute the V-connection transformer. It is assumed that the load connected to the impedance X and V-connection transformer of each transformer is a three-phase balanced load Z. The output current supplied from the single-phase inverter 13 to the secondary side of the V-connection transformer is I _OUT1 . In this case, the secondary side voltages V _ab and V _bc are expressed by equation (3-1), and the circuit equation in the secondary circuit is expressed by equation (3-2). The secondary currents I _a and I _c of the secondary circuit are expressed by the formula (3-3) from the formulas (3-1) and (3-2).

When the secondary currents I _a and I _c of the secondary circuit are three-phase to two-phase converted, the α-phase current and the β-phase current are expressed by equations (4-1) and (4-2).

The condition for making the unbalanced evaluation amount ξ zero, that is, the condition for making the equilibrium state by the output of the single-phase inverter 13 can be obtained by substituting various quantities corresponding to the equation (2-2). However, the equation regarding the voltage in the equation (2-2) is established because the primary side voltage E (E _uv , E _vw ) of the V-connection transformer is balanced. Therefore, when the expressions (4-1) and (4-2) are substituted into the expression relating to the current among the expressions (2-2), the expression (4-3) is obtained. The expression (4-3) is established when the expression (4-4) is established. Therefore, the output current I _OUT of the single-phase inverter 13 is changed to the output current I _OUT1 satisfying the expression (4-5). If controlled, complete balancing is achieved.

Thus, in order to make the unbalanced evaluation amount ξ zero by considering the impedance X of the transformer, the output current I _OUT of the single-phase inverter 13 is controlled to the output current I _OUT1 satisfying the expression (4-5). do it.

Therefore, the target value calculation unit 15 of the unbalance compensator 11 includes the primary voltage E (E _uv , E _vw ) of the V connection transformer, the impedance X of each transformer constituting the V connection transformer, and the V connection transformer. The target value I _OUT1 of the output current I _OUT of the single-phase inverter 13 expressed by the equation (4-5) is calculated based on the load Z connected to. The output control unit 14 controls the output of the single-phase inverter 13 so that the output current I _OUT of the single-phase inverter 13 becomes the target value I _OUT1 calculated by the target value calculation unit 15.

  In addition, when the primary side voltage E of a V connection transformer cannot be measured directly, it can be calculated from the secondary side voltage / current and the transformer impedance X according to the first equation (3-1). Further, when the load impedance Z cannot be measured in advance, it can be calculated from the secondary side voltage / current value according to the equation (3-2). However, it is necessary to measure the transformer impedance X in advance.

According to the first embodiment, the primary side voltage E (E _uv , E _vw ) of the V-connection transformer, the impedance X of each transformer constituting the V-connection transformer, and the V-connection transformer are connected. Based on the three-phase balanced load Z, an unbalanced evaluation amount ξ for evaluating the degree of unbalance of the three phases of the distribution system is calculated, and the output current of the single-phase inverter 13 is set so that the unbalanced evaluation amount ξ becomes zero. Since I _OUT is controlled, even if the impedance of the transformer is a three-phase unbalance, the unbalance of the distribution system can be suppressed.

  If the capacity of the single-phase inverter 13 is smaller than the single-phase inverter output where the unbalanced evaluation amount ξ is zero, complete balancing cannot be performed, but the unbalance is within the capacity range of the single-phase inverter 13. By outputting a current that minimizes the evaluation amount ξ, unbalance can be reduced.

Next, a second embodiment of the present invention will be described. FIG. 3 is a configuration diagram of an unbalance compensation apparatus for a distribution system according to the second embodiment of the present invention. This second embodiment is different from the first embodiment shown in FIG. 1 in that three-phase unbalanced loads Z ₁ and Z ₂ are used in place of the three-phase balanced load Z, and the transformer impedances are not changed. The balanced impedances X ₁ and X ₂ are used. The same elements as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted.

The unbalance compensator 11 is connected between the bc phases on the secondary side of the V-connection transformer, converts the direct current of the distributed power source 12 into alternating current by the single-phase inverter 13 and supplies it to the distribution system. V is the ab phase of connection transformer on the secondary side is loaded Z ₁ is connected, the bc phase of the secondary side of the V connection transformer load Z ₂ are connected.

The single-phase inverter 13 is controlled by the output control unit 14 and outputs an output current I _OUT so as to compensate for an unbalance occurring in the distribution system. That is, the output control unit 14 feeds back the output current I _OUT of the single-phase inverter 13 detected by the current detector 16 and controls the target value I _OUT1 obtained by the target value calculation unit 15. Thereby, the output current I _OUT of the single-phase inverter 13 is controlled by the output control unit 14 so as to be the target value I _OUT1 obtained by the target value calculation unit 15.

The target value calculation unit 15 is connected to the primary voltage E (E _uv , E _vw ) of the V-connection transformer, the impedances X ₁ and X _{2 of} each transformer constituting the V-connection transformer, and the V-connection transformer. Based on the three-phase unbalanced loads Z ₁ and Z ₂ , the target value I _OUT1 of the output current I _OUT of the single-phase inverter 13 is calculated. The target value I _OUT1 of the output current I _OUT evaluates the degree of unbalance indicated by the AC amount of the instantaneous real power and the instantaneous imaginary power obtained from the primary voltage E (E _uv , E _vw ) of the distribution system and the output current. The unbalanced evaluation amount ξ is calculated to be zero or minimum.

Here, in order to make the unbalance evaluation amount ξ zero, the output current I _OUT supplied to the secondary side of the V-connection transformer is derived from the single-phase inverter 13 of the unbalance compensation device 11. As shown in FIG. 3, the primary side voltage E (E _uv , E _vw ) of the V-connection transformer and the secondary side voltages V _ab and V _bc of the V-connection transformer are used to form the V-connection transformer. Is assumed to be X ₁ and X ₂ , and the three-phase unbalanced load connected to the V-connection transformer is Z ₁ and Z ₂ . The target value of the output current supplied from the single-phase inverter 13 to the secondary side of the V-connection transformer is defined as I _OUT1 .

In this case, the secondary side voltages V _ab and V _bc are expressed by equation (5-1), and the circuit equation in the secondary circuit is expressed by equation (5-2). The secondary currents I _a and I _c of the secondary circuit are expressed by the equation (5-3) from the equations (5-1) and (5-2).

When the secondary currents I _a and I _c of the secondary circuit are three-phase to two-phase converted, the α-phase current and the β-phase current are expressed by equations (6-1) and (6-2). The condition for making the unbalanced evaluation amount ξ zero is obtained by substituting various amounts corresponding to the equation (2-2). However, the equation regarding the voltage in the equation (2-2) is established because the primary side voltage E (E _uv , E _vw ) of the V-connection transformer is balanced. Therefore, when the expressions (6-1) and (6-2) are substituted into the expression relating to the current among the expressions (2-2), the expression (6-3) is obtained.

The expression (6-3) is established when the numerator on the left side of the last line of the expression (6-3) becomes zero. When the numerator on the left side of the last line of the expression (6-3) is expanded, the expression (7-1) is obtained, and the conditional expression for setting the unbalanced evaluation amount ξ to zero is the expression (7-2). The output current I _OUT1 of the single-phase inverter 13 that establishes the equation (7-2) is expressed by the equation (7-3).

In this way, the primary voltage E (E _uv , E _vw ) of the V-connection transformer, the unbalanced impedances X ₁ and X ₂ and the three-phase unbalanced loads Z ₁ and Z of each transformer constituting the V-connection transformer. _In order to reduce the unbalanced evaluation amount ξ to zero in consideration of ₂ , the output current I _OUT of the single-phase inverter may be controlled to the output current I _OUT1 that satisfies the equation (7-3).

Therefore, the target value calculation unit 15 of the unbalance compensator 11 includes the primary voltage E (E _uv , E _vw ) of the V-connection transformer, the impedances X ₁ , X _{2 of} each transformer constituting the V-connection transformer, and Based on the loads Z ₁ and Z ₂ connected to the V-connection transformer, the target value I _OUT1 of the output current I _OUT of the single-phase inverter 13 expressed by the equation (7-3) is calculated. The output control unit 14 controls the output of the single-phase inverter 13 so that the output current I _OUT of the single-phase inverter 13 becomes the target value I _OUT1 calculated by the target value calculation unit 15.

In addition, when the primary side voltage E of a V connection transformer cannot be measured directly, it can be calculated from the secondary side voltage / current and the transformer impedance X according to the first equation (5-1). Further, when the load impedances Z ₁ and Z ₂ cannot be measured in advance, the load impedances Z ₁ and Z ₂ can be calculated from the secondary side voltage / current value by the equation (5-2). The transformer impedances X ₁ and X ₂ need to be measured in advance.

  According to the second embodiment, based on the primary voltage of the V-connection transformer, the unbalanced impedance of each transformer constituting the V-connection transformer, and the three-phase unbalanced load connected to the V-connection transformer. Since the unbalanced evaluation amount ξ for evaluating the unbalance of the three-phase voltage and current of the distribution system is calculated and the output current of the single-phase inverter is controlled so that the unbalanced evaluation amount becomes zero, the impedance of the transformer is Even when unbalanced or unbalanced loads are connected, it is possible to suppress unbalance in the distribution system.

  When the capacity of the single-phase inverter 13 is smaller than the single-phase inverter output required for complete balancing, by outputting a current that minimizes the unbalanced evaluation amount ξ within the capacity range of the single-phase inverter. , Three-phase AC imbalance can be reduced.

  Next, a third embodiment of the present invention will be described. In the first embodiment and the second embodiment, the output current of the single-phase inverter 13 is adjusted to compensate for the imbalance that occurs in the distribution system, but the output reactive power of the single-phase inverter 13 is adjusted. It is also possible to compensate for the imbalance that occurs in the distribution system. That is, in the first embodiment and the second embodiment, since the output current of the single-phase inverter 13 is adjusted without taking active power and reactive power into account, not only reactive power but also active power is adjusted. May also vary. In the third embodiment, while maintaining the output of active power, even when the impedance of the transformer is unbalanced or when an unbalanced load is connected, the distribution system unbalance is compensated. It is.

FIG. 4 is a configuration diagram of an unbalance compensation apparatus for a distribution system according to the third embodiment of the present invention. A V-connection transformer in which two single-phase transformers are connected by a V-connection is a primary side and a second side between the uv phase of the uvw phase on the upper system side and between the uv phase and the vw phase, and between the ab phase and the bc phase of the lower system side. The next side is connected. Assume that the impedances of the two single-phase transformers are unbalanced impedances X ₁ and X ₂ , and currents flowing through the secondary windings are I _a and I _c . Further, the currents flowing through the load impedances Z ₁ and Z ₂ are I ₁ and I _2, and the output current of the single-phase inverter 13 is I _OUT .

The unbalance compensator 11 is connected between the bc phases on the secondary side of the V-connection transformer, converts the direct current of the distributed power source 12 into alternating current by the single-phase inverter 13 and supplies it to the distribution system. The load current I ₁ flows in the load ab phases of V connection transformer on the secondary side, and the load current I ₂ flows through the load bc phases on the secondary side of the V connection transformer.

The single-phase inverter 13 is controlled by the output control unit 14 and outputs an output current I _OUT so as to compensate for an unbalance occurring in the distribution system. That is, the output control unit 14 feeds back the output current I _OUT of the single-phase inverter 13 detected by the current detector 16 and controls the target value I _OUT1 obtained by the target value calculation unit 15. Thereby, the output current I _OUT of the single-phase inverter 13 is controlled by the output control unit 14 so as to be the target value I _OUT1 obtained by the target value calculation unit 15.

The target value calculation unit 15 calculates the target value I _OUT1 of the output current I _OUT of the single-phase inverter 13 for adjusting the reactive power to compensate for the voltage / current imbalance. The unit 17 includes a reactive power target value calculation unit 18 and an output current setting unit 19.

The active power target value calculation unit 17 calculates the active power target value P ^* based on the output voltage Vd and output current Id of the distributed power source 12. For example, when the distributed power source 12 is a solar power generation system, the solar cell output characteristic curve and the maximum possible output are determined by the amount of solar radiation, and thus the active power target value of the single-phase inverter 13 can be determined by the amount of solar radiation. However, since the operation becomes unstable at the time of transient such as when the distributed power source 12 is started or when the amount of solar radiation changes, the distributed power source is multiplied by the output voltage V _d of the distributed power source 12 and the output current I _d. 12 actual output powers are obtained, and based on this, the active power target value P ^* is obtained.

For example, when the output voltage _Vd decreases, the active power target value P ^* is set lower than the actual output power, and then the active power target value P ^* is calculated so that the operating point is brought to the maximum output point. To do. Thus, the active power target value P ^* varies depending on the operating state of the distributed power supply 12.

The reactive power target value calculation unit 18 includes a primary voltage E (E _uv , E _vw ) of a V-connection transformer, impedances X ₁ and X _{2 of} each transformer constituting the V-connection transformer, and a load of the V-connection transformer. A reactive power target value Q ^* is calculated based on the currents I ₁ and I ₂ .

The reactive power target value Q ^* is an unbalanced value indicated by the AC amount of instantaneous real power and instantaneous imaginary power obtained from the primary voltage E (E _uv , E _vw ) of the distribution system and the output current I _OUT of the single-phase inverter 13. The unbalanced evaluation amount ξ for evaluating the degree is calculated to be zero or minimum. In this case, the reactive power target value Q ^* is obtained so that the unbalanced evaluation amount ξ becomes zero or minimum by adjusting only the output reactive power Q while maintaining the output of the active power at the active power target value P ^*. It is done.

The output current setting unit 19 includes an active power target value P ^* obtained by calculating the output current I _OUT of the single-phase inverter 13 by the active power target value calculating unit 17 and a reactive power target value calculated by the reactive power target value calculating unit 18. A target value I _OUT1 that becomes Q ^* is calculated and output to the output control unit 14. As a result, the output control unit 14 controls the output current I _OUT of the single-phase inverter 13 to be the target value I _OUT1, and the active power output of the distributed power source 12 holds the active power target value P ^*. Compensates for voltage and current imbalances in the distribution system.

The reactive power target value Q ^* for adjusting only the output reactive power Q to make the unbalanced evaluation amount ξ zero or minimum is derived as follows. As shown in FIG. 4, the primary side voltage E (E _uv , E _vw ) of the V-connection transformer and the secondary side voltages V _ab and V _bc of the V-connection transformer are used to form the V-connection transformer. Are assumed to be X ₁ and X ₂ , and the load currents of the V-connection transformer are I ₁ and I ₂ . Further, the reactive power target value output from the reactive power target value calculation unit 18 is defined as Q ^* .

In this case, the secondary side voltages V _ab and V _bc are expressed by equation (8-1), and the secondary currents I _a and I _c of the V-connection transformer are expressed by equation (8-2). Further, the two-phase currents I _α and I _{β obtained} by converting the secondary currents I _a and I _c into three-phase to two-phase are expressed by the formula (8-3).

Next, the output power of the single-phase inverter 13 is expressed by the equation (9-1), and the secondary side voltage _Vbc and the output current I _OUT of the single-phase inverter 13 are expressed by a real part and an imaginary part (9-2). It is shown by the formula. Thereby, the active power P and the reactive power Q of the output power of the single-phase inverter 13 are represented by the formula (9-3). Further, when the load current I ₂ is expressed by a real part and an imaginary part, and the real part and the imaginary part of the secondary side voltage V _bc are expressed by the primary side voltage E of the V-connection transformer and the impedance X ₂ of the transformer, The active power P of the output power of the phase inverter 13 is represented by the formula (9-4), and the reactive power Q of the output power of the single phase inverter 13 is represented by the formula (9-5).

Next, the real part I _OUTR and the imaginary part I _OUTI of the output current I _OUT of the single-phase inverter 13 are obtained from the expressions (9-4) and (9-5). The real part I _OUTR of the output current I _OUT is shown in (10-1) below, the imaginary part I _OUTI of the output current I _OUT is represented by (10-2) below. The real part I _OUTR and the imaginary part I _OUTI of the output current I _OUT are expressed as a function of the active power P and the reactive power Q of the output power of the single-phase inverter 13.

The unbalanced evaluation amount | ξ | ² is obtained by substituting various amounts corresponding to the equation (2-1). On the other hand, since the voltage on the higher system side is balanced, equation (11-1) is established. Accordingly, the unbalanced evaluation amount | ξ | ² is expressed by the equation (11-2), and expressed by the equation (11-3) when expressed by the real part and the imaginary part of the two-phase currents I _α and I _β .

The real part I _αR and the imaginary part I _αI of the two-phase current I _α are represented by the real part I _1R and the imaginary part I _1I of the load current I ₁ as shown in the equation (12-1), and the two-phase current I _β the real part I _{[beta] R} and an imaginary part I _{beta I} as shown in (12-2) above, the load current _{I 1} of the real part _{I 1R} and an imaginary part _{I 1I,} the load current real part of _{I 2 I 2R} and the imaginary part I _2I , the real part I _OUTR and the imaginary part I _OUTI of the output current I _OUT of the single-phase inverter 13. When the equations (12-1) and (12-2) are substituted into the equation (11-3), the unbalanced evaluation amount | ξ | ² is expressed by the equation (12-3).

As can be seen from the equation (12-3), the unbalanced evaluation amount | ξ | ² is represented by a function of the real part I _OUTR and the imaginary part I _OUTI of the output current I _OUT . Since the real part I _OUTR and the imaginary part I _OUTI of the output current I _OUT are expressed as a function of the active power P and the reactive power Q, the unbalance evaluation amount | ξ | ² is a function of the active power P and the reactive power Q. is there.

Therefore, the reactive power Q that minimizes the unbalanced evaluation amount | ξ | ² with respect to the active power P of the single-phase inverter 13 is obtained. Now, the active power P of the single-phase inverter 13 is a constant. As can be seen from the equation (12-3), the unbalanced evaluation amount | ξ | ² is a quadratic function of the output current I _OUT (real part I _OUTR , imaginary part I _OUTI ) that is a function of the reactive power Q, Since the sign of the next term is positive, the unbalanced evaluation amount | ξ | ² is a downward convex function and is minimum when it is an extreme value.

Differentiating both sides of the equation (12-3) with the reactive power Q yields the equation (13-1), and when ordering, the equation (13-2) is obtained. When the derivative of the unbalanced evaluation amount | ξ | ² expressed by the equation (13-2) is 0, an extreme value is obtained, and the unbalanced evaluation amount | ξ | ² is minimized.

Since the primary side voltage E of the V-connection transformer is not 0 during normal operation, the condition that the derivative of the unbalanced evaluation amount | ξ | ² expressed by the equation (13-2) is 0 is (14-1 ).

Since the real part I _OUTR of the output current I _OUT of the single-phase inverter 13 is expressed by the equation (10-1), when both sides of the equation (10-1) are differentiated by the reactive power Q, the equation (14-2) is obtained. It is done. Similarly, since the imaginary part I _OUTI of the output current I _OUT is expressed by equation (10-2), when both sides of equation (10-2) are differentiated by reactive power Q, equation (14-3) is obtained. When (10-1), (10-2), (14-2), and (14-3) are substituted into (14-1), (14-4) is obtained. When the reactive power Q is obtained from the equation (14-4), the reactive power Q is expressed by the equation (14-5).

The reactive power Q represented by the equation (14-5) represents the reactive power Q that minimizes the unbalanced evaluation amount | ξ | ² , and is referred to as a reactive power target value Q ^* . The reactive power target value calculation unit 18 substitutes the active power target value P ^* calculated by the active power target value calculation unit 17 into the equation (14-5) indicating the reactive power Q in order to obtain the reactive power target value Q ^*. To do. That is, the reactive power Q expressed by the equation (14-5) is expressed as a function of the active power P (for example, B, D, and F are functions of the active power P as shown in [Equation 10]). Then, the reactive power target value Q ^* is obtained by substituting the active power target value P ^* into the equation (14-5).

The output current setting unit 19 inputs the reactive power target value Q ^* and the active power target value P ^* calculated by the active power target value calculation unit 17 and inputs the target value of the output current I _OUT of the single-phase inverter. I _OUT1 is calculated and output to the output control unit 14. As a result, the output control unit 14 controls the output current I _OUT of the single-phase inverter 13 to be the target value I _OUT1 . That is, by controlling the reactive power Q to the reactive power target value Q ^* , the output of the active power of the distributed power source 12 is maintained at the active power target value P ^*, and the voltage / current imbalance of the distribution system is compensated. .

Here, the real part I _OUTR and the imaginary part I _OUTI of the output current I _OUT are (10−) with respect to the reactive power Q that minimizes the unbalanced evaluation amount | ξ | ² expressed by the equation (14-5). As shown in the formulas (1) and (10-2), there are two. Since the target value I _OUT1 of the output current I _OUT is one, it indicates which of the two is below.

For the real part I _OUTR of the output current I _OUT , substituting the reactive power Q obtained by the equation (14-5) into the equation (10-1), the two output currents I _OUT are obtained as shown in the equation (15-1). The real part I _{OUTR of} is obtained.

On the other hand, the unbalanced evaluation amount | ξ | ² expressed by the equation (12-3) is differentiated by the real part I _OUTR of the output current I _OUT , and the derivative of the unbalance evaluation amount | ξ | ^{2 by} the real part I _OUTR is When a condition of 0 (a condition that minimizes the unbalanced evaluation amount | ξ | ² ) is obtained, equation (15-2) is obtained, and a real part I _{OUTR of} one output current I _OUT is obtained.

Therefore, the real part I _OUTR of the output current I _OUT with respect to the value of the reactive power Q that minimizes the unbalanced evaluation amount | ξ | ² is expressed by the equation (15-2), and the equation (15-1) in one of the real part I _OUTR of the two output currents I _oUT shown, it can be seen that the real part I _OUTR code under decoding.

  According to the third embodiment, the reactive power target for maintaining the output of the active power of the output power of the single-phase inverter 13 and changing only the reactive power to compensate for the voltage / current imbalance of the distribution system. Since the reactive power target value calculation unit 18 for calculating the value is provided, the output of the active power of the output power of the single-phase inverter 13 is maintained and the impedance of the transformer is unbalanced or an unbalanced load is connected. Even if it is a case, the imbalance of a power distribution system can be suppressed.

Next, a fourth embodiment of the present invention will be described. FIG. 5 is a configuration diagram of an unbalance compensation apparatus for a distribution system according to the fourth embodiment of the present invention. In the fourth embodiment, a power calculation unit 20 that detects the output power of the single-phase inverter 13 is provided with respect to the third embodiment shown in FIG. The reactive power target value Q ^* is obtained using the active power P obtained by the power computing unit 20 instead of the active power target value P ^* obtained by the target value computing unit 17. The same elements as those in FIG. 4 are denoted by the same reference numerals, and redundant description is omitted.

The output voltage V _bc of the single phase inverter 13 is detected by the voltage detector 21, and the output current I _OUT of the single phase inverter 13 is detected by the current detector 16 and input to the power calculation unit 20.

As described above, the reactive power target value calculation unit 18 calculates the reactive power target value Q * that minimizes the unbalanced evaluation amount | ξ | ² , and the reactive power target value Q * is the value of the active power P. Indicated by function. Therefore, the reactive power target value calculation unit 18 uses the actual active power P calculated by the power calculation unit 20 in order to set the active power P that is actually output from the single-phase inverter 13 as the active power P to be held. Reactive power target value Q ^* is obtained.

That is, the reactive power Q expressed by the equation (14-5) is expressed as a function of the active power P (for example, B, D, and F are functions of the active power P as shown in [Equation 10]). Then, the reactive power target value Q ^* is obtained by substituting the active power P actually output from the single-phase inverter 13.

The output current setting unit 19 calculates the active power P and the reactive power Q obtained by the power calculation unit 20 by the active power target value P ^* and the reactive power target value calculation unit 18 calculated by the active power target value calculation unit 17. The target value I _OUT1 is calculated so as to be the reactive power target value Q ^* and is output to the output control unit 14.

As a result, the output control unit 14 controls the output current I _OUT of the single-phase inverter 13 to be the target value I _OUT1, and the active power output of the distributed power source 12 holds the active power target value P ^*. It compensates for voltage and current imbalances in the distribution system.

According to the fourth embodiment, the active power P and reactive power Q output from the single-phase inverter 13 are detected by the power calculation unit 20, and match the active power target value P ^* and the reactive power target value Q ^* . Therefore, even when the transformer impedance is unbalanced or an unbalanced load is connected, the active power P output from the single-phase inverter 13 is maintained at the active power target value P ^*. Distribution system imbalance can be suppressed.

Explanatory drawing of the unbalance compensation apparatus of the distribution system concerning the 1st Embodiment of this invention. Explanatory diagram of unbalanced evaluation quantity in three-phase AC system The block diagram of the unbalance compensation apparatus of the power distribution system concerning the 2nd Embodiment of this invention. Explanatory drawing of the unbalance compensation apparatus of the power distribution system concerning the 3rd Embodiment of this invention. The block diagram of the unbalance compensation apparatus of the power distribution system concerning the 4th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Unbalance compensator, 12 ... Distributed type power supply, 13 ... Single phase inverter, 14 ... Output control part, 15 ... Target value calculating part, 16 ... Current detector, 17 ... Active power target value calculating part, 18 ... Invalid Power target value calculation unit, 19 ... output current setting unit, 20 ... power calculation unit, 21 ... voltage detector

Claims (4)

A single-phase inverter connected between any two-phase terminals of the three-phase terminals of the secondary system of the V-connection transformer of the distribution system and converting the direct current into an alternating current to connect to the distribution system; and the V-connection transformer An unbalance evaluation for evaluating the degree of unbalance of the three phases of the distribution system based on the voltage of the transformer, the impedance of each transformer constituting the V connection transformer, and the load connected to the V connection transformer A target value calculation unit that calculates a target value of the output current of the single-phase inverter whose amount is zero or minimum, and the output current of the single-phase inverter becomes the target value obtained by the target value calculation unit An unbalance compensation device for a distribution system, comprising an output control unit for controlling a single-phase inverter. A single-phase inverter that converts direct current to alternating current is connected between any two phase terminals of the three-phase terminals of the secondary system of the V-connection transformer of the distribution system, and the voltage of the V-connection transformer, the V The unbalance evaluation amount for evaluating the degree of unbalance of the three phases of the distribution system is zero or minimum based on the impedance of each transformer constituting the connection transformer and the load connected to the V connection transformer. A distribution system unbalance compensation method, comprising: calculating a target value of an output current of the single-phase inverter, and controlling the single-phase inverter so that an output current of the single-phase inverter becomes the target value. A single-phase inverter connected between any two-phase terminals of the three-phase terminals of the secondary system of the V-connection transformer of the distribution system and converting the direct current into an alternating current to connect to the distribution system; and the V-connection transformer An unbalance evaluation for evaluating the degree of unbalance of the three phases of the distribution system based on the voltage of the transformer, the impedance of each transformer constituting the V connection transformer, and the load connected to the V connection transformer A target value calculation unit that calculates a target value of output reactive power of the single-phase inverter whose amount is zero or minimum, and an output reactive power of the single-phase inverter becomes a target value obtained by the target value calculation unit And an output control unit for controlling the single-phase inverter. A single-phase inverter that converts direct current to alternating current is connected between any two phase terminals of the three-phase terminals of the secondary system of the V-connection transformer of the distribution system, and the voltage of the V-connection transformer, the V The unbalance evaluation amount for evaluating the degree of unbalance of the three phases of the distribution system is zero or minimum based on the impedance of each transformer constituting the connection transformer and the load connected to the V connection transformer. Calculating a target value of the output reactive power of the single-phase inverter, and controlling the single-phase inverter so that the output reactive power of the single-phase inverter becomes the target value. Method.

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