JP4175632B2 - Power compensation system for single-phase three-wire distribution system - Google Patents

Description

  The present invention relates to a multi-function power compensation system for a single-phase three-wire distribution system that is widely used in Japan. The current balance function, power factor improvement function, harmonic suppression function, power failure function of two systems The present invention relates to a system having all or part of a power supply function and a power storage function.

  Currently, three-phase high-voltage systems of 6 kV or more are distributed to consumers who consume large amounts of power, such as large factories, large-scale stores, and large office buildings. However, a unique single-phase three-wire low-voltage power distribution system is used for ordinary households, small stores, small office buildings, etc., which are overwhelmingly large in number. In the case of a three-phase load, a balanced current flows through the three-phase system in a steady state unless a failure occurs. However, all the loads connected to the single-phase three-wire distribution system are single-phase, and many single-phase loads are unspecifiedly connected to two single-phase power sources. Since these loads are arbitrarily operated for the convenience of the customer, the respective grid currents are not always balanced. In an extreme case, it is not uncommon for only the load group connected to one system to work and the other load group to be in a dormant state. For this reason, currently, a system is adopted in which a special transformer called a balancer is installed at the end of the single-phase three-wire distribution system to balance the system current.

  However, even if the grid current is balanced by the operation of the balancer, the current of the lead-in wire connected to each consumer remains unbalanced. For this reason, when the customer's power usage is extremely biased to the load group connected to one system, the breaker of the switchboard operates even within the contract power, and part of the load is shut down There are many cases where partial power failure occurs. In order to avoid this partial power failure, it is necessary to balance the currents of the two systems of each customer's service line.

  By the way, as a converter for converting alternating current into direct current, a rectifier circuit in which a bridge circuit is configured by a diode element has been used for a long time. However, this rectifier circuit is not preferable because it generates a large amount of harmonic components, and a sine wave of its input current is desired. Therefore, a single-phase three-wire type sine wave input single-phase rectifier circuit that forms a converter circuit including a plurality of active elements and rectifier elements and obtains a sine wave input current whose waveform follows this sine wave input voltage. It has been proposed for a long time to be applied to a power distribution system (for example, see Patent Document 1, Non-Patent Documents 1, 2, 3, and 4). However, these proposals relate to the control method of the converter itself, which is how to convert efficiently from AC to DC with high power factor (less waveform distortion).

Japanese Patent Laid-Open No. 10-337034 Masaaki Oshima, Eisuke Masada: “Constant-sampled PWM method in single-phase three-wire AC / DC converter”, 1999 IEEJ Industrial Application Conference, Vol. 3, pp. 143-146, August 1999 Kiyotake Hirofumi, Okada Hidehiko, Ishizaka Koichi, Ito Ryozo: “Characteristics of a single-phase voltage doubler rectifier with balanced capacitor voltage”, IEEJ Transactions Volume D, Vol.121-D, No.9, 964-969, Issued September 2001 Takayuki Fujita, Shoji Iida: “High power factor voltage rectifier circuit with balanced capacitor voltage characteristics”, Proceedings of the IEICE Industrial Application Division, Volume 2, page 1044, August 2002 Takayuki Fujita, Shoji Iida: “Reduction of DC Capacitor in High Power Factor Double Voltage Rectifier Circuit”, Proceedings of National Conference of the Institute of Electrical Engineers of Japan, pp. 69-70, September 2002

  The present invention has been made in view of the above-described circumstances, and is intended for a single-phase three-wire distribution system. Two-system current balance function, power factor improvement function, harmonic suppression function, power supply function during power failure, power An object of the present invention is to provide a multifunction power compensation system having a storage function and the like.

The power compensation system for a single-phase three-wire distribution system according to the present invention incorporates two sets of converters each sharing a capacitor in the system line of the single-phase three-wire distribution system, and the two sets of converters are half bridges that share a capacitor. Further, the neutral point connection line of the single-phase three-wire distribution system is shared, and one converter is reversely converted and the other is forward-converted at the same time. As a result, even if an imbalance occurs in many single-phase loads connected to the two systems of the single-phase three-wire power distribution system, the compensation current is supplied from the converter that performs reverse conversion operation to the large load side, and forward conversion operation is performed. By taking the compensation current from the system with the smaller load by the converter to be operated, it is possible to operate so that the currents of the two systems are balanced. Therefore, it is possible to balance the currents of the two systems of the single-phase three-wire power distribution system, maintain the current of the neutral line that is grounded to be almost zero, and to satisfy the requirements for the single-phase load connected to the two systems. A load current can be supplied.

  For example, when there is a load with a bad power factor, such as an electric motor load, a lead component is added to the compensation current if the load current is delayed, and a delay component is added to the compensation current if the load current is a lead. The power factor can be approximately 100%. In addition, even if the load groups of the two systems have different power factors, the phase of each compensation current can be individually controlled, so that the reactive power of each load current is compensated and the power factor of the two systems is 100% respectively. It is possible to maintain.

  Also, when the load is equipped with a DC power supply, a diode bridge type rectifier circuit is generally used for the DC power supply, so the input current becomes a pulsed AC current, and many low-order harmonics are generated. Including distorted wave current. If these harmonic currents flow into the grid, harmonic disturbances may occur. Even when such a load is connected, it is possible to eliminate the harmonic component of the load current by making the compensation current a waveform having a phase opposite to that of the distortion wave load current. That is, the two sets of converters of the present invention can have an active filter function. In addition, the waveform of each compensation current can be individually controlled, and the compensation current can be supplied to only one of the systems.

In addition, the power compensation system for a single-phase three-wire distribution system according to the present invention incorporates two sets of converters each sharing a storage battery in the system line of the single-phase three-wire distribution system, and reverse-converts or forward-converts each converter. You may make it make it . Thereby, in addition to the above-described functions, it is possible to provide a power supply function at the time of a power failure that continues to supply power to an important load even if the system fails, that is, an uninterruptible power supply function. Moreover, it can contribute to the load leveling of a system | strain by storing surplus electric power at night in a storage battery, and releasing this at the time of the electric power peak of the daytime.

  For example, the system power balance function allows contract power to be reduced, and the installed capacity can be reduced to match the average power of the two systems. In general, according to the present invention, it is possible to save energy in a single-phase three-wire distribution system, to reduce the cost of equipment and operation, and to reduce the cost of electricity.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, in each figure, the same code | symbol is attached | subjected to the member or element which has the same effect | action or function, and the overlapping description is abbreviate | omitted.

  The present invention relates to a system for connecting two sets of single-phase converters 1 and 2 sharing a capacitor to a single-phase three-wire distribution system and compensating for system current imbalance, power factor reduction, distortion, etc. caused by various loads. Is. Furthermore, instead of the capacitor shared by the converter, or by adding a storage battery group in parallel to the capacitor, the system can store power and make the single-phase three-wire distribution system uninterruptible and load leveling the power. Is also within the scope of the present invention.

  FIG. 1 is an embodiment of the present system when a half-bridge configuration is used as a single-phase converter. Reference numeral 1 denotes a system-side terminal of the single-phase three-wire distribution system, and the terminals 31, 32, and 33 correspond to service lines for supplying power from the system to the customer side. In general, the intermediate terminal 32 is a neutral wire grounded, and a single-phase voltage having the same phase is supplied between the terminals 31-32 and between the terminals 32-33 by a pole transformer or the like. The voltage between terminals 31-33 is double the voltage between terminals 31-32. Reference numeral 2 denotes load terminals 41, 42, 43 on the customer side, and various types of single-phase loads are connected between the terminals 41-42, between the terminals 42-43, or between the terminals 41-43 through the switchboard. Yes.

  Reference numerals 3 and 4 denote the multi-function power compensator of the present invention. 5, 7, 9, and 11 are self-extinguishing switching elements that can be freely turned on and off by signals. In the figure, it is represented by IGBT, but other switching elements having an on / off function such as a MOSFET can be applied. Reference numerals 6, 8, 10, and 12 denote diodes connected in antiparallel to these switching elements, and the built-in antiparallel diode can be used in the self-extinguishing type switching element having a module configuration. Reference numerals 13 and 14 denote capacitors, which serve to temporarily store DC energy converted by one converter. Reference numerals 15 and 16 denote AC reactors, and a compensation current having an arbitrary waveform can be caused to flow by adding a difference voltage between the system voltage and the converter input voltage to the reactor. Reference numerals 17 and 18 denote filter reactors, and reference numerals 19 and 20 denote filter capacitors, which play a role of removing high-order harmonic currents generated when the switching elements are turned on and off.

  The power compensator 3 of the present invention incorporates two sets of half-bridge converters that share capacitors 13 and 14 that store DC power. That is, the converter 1 constituted by the elements 5, 6, 7 and 8 sharing the capacitors 13 and 14 is constituted by the elements 9, 10, 11 and 12 sharing the capacitors 13 and 14 between the terminals 51-52. The converter 2 is incorporated between the terminals 52-53. These two sets of half-bridge converters 1 and 2 have a common connection line for not only the capacitor but also the terminal 52. Therefore, by connecting this to the neutral point 32 of the single-phase three-wire distribution system, the circuit configuration Can be greatly simplified. Further, since the neutral point 32 of the single-phase three-wire distribution system is generally grounded, the power compensation device 3 of the present invention can make the current of the neutral line substantially zero and balance the currents of the two systems. Therefore, it can be said that it does not generate common mode noise in principle and is effective for EMI (electromagnetic wave interference) countermeasures.

  When the multi-function compensator of the present invention is limited to the current balance function, the power factor improvement function, and the harmonic suppression function, only the power compensator 3 described above is sufficient. In order to have this, it is necessary to add the device 4 in FIG. 21 and 22 are two sets of storage battery groups. This is connected in place of the capacitors 13 and 14 of the power compensation device 3 or connected in parallel to these capacitors 13 and 14.

  Next, the operation of the multifunction power compensation system will be described. Of the two converters 1 and 2 incorporated in the power compensator 3 of the present invention, the converter 1 compensates for the power between the system terminals 31-32, and the converter 2 compensates for the power between the system terminals 32-33. To do. Each of these converters can not only perform a forward conversion operation or an inverse conversion operation, but can also perform a forward conversion operation on one side and an inverse conversion operation on the other side at the same time. The present invention uses this characteristic to perform power compensation for a single-phase three-wire system.

Here, it is assumed that the load group connected between the load terminals 41-42 in FIG. 1 is heavy and the load group connected between the load terminals 42-43 is light. That is, it is assumed that the load current I ₄₁ flowing into the load terminal 41 is large and the load current I ₄₃ flowing out from the load terminal ₄₃ is small. However, the arrow direction in FIG. 1 is the positive direction of each current. In this load state, the power compensator 3 of the present invention can balance the grid currents I ₃₁ and I ₃₃ by causing the converter 1 to perform the reverse conversion operation and simultaneously performing the forward conversion operation of the converter 2.

When the converter 1 is reverse-converted, the compensation current I _{51 at} the terminal 51 of the power compensator 3 flows out of the terminal 51 in the direction opposite to the arrow in FIG. Since the compensation current _{I 51} compensates a part of the load current _{I 41,} the system current _{I 31} is less than the load current _{I 41.} This reverse conversion operation can be executed by DC power (energy) stored in the capacitors 13 and 14. However, since a normal capacitor can store very little energy, the capacitor voltage drops instantaneously with only the converter 1, and the above-described reverse conversion operation cannot be maintained. For this reason, it is necessary to separately install a capacitor charging device, which makes the system more complicated. On the other hand, in the present invention, another set of converters 2 is incorporated, and this is a forward conversion operation. The capacitor voltage can be maintained at the set value by taking in the compensation current I ₅₃ from between the system terminals 32-33. Furthermore, since the system current I ₃₃ is the sum of the load current I ₄₃ and the compensation current I ₅₃ , the system current I ₃₃ can be larger than the load current I ₄₃ and equal to the system current I ₃₁ .

FIG. 2 shows the current waveform of each part when this system is operated. In the figure, (a) and (c) are actually measured waveforms, and (b) and (d) are computer-simulated waveforms. (C) As shown in (d), the compensation current I ₅₁ of the converter 1 that performs the reverse conversion operation is in reverse phase with respect to the compensation current I _{53 of the} converter 2 that performs the forward conversion operation. By appropriately controlling these compensation currents, as shown in (a) and (b), the system currents I ₃₁ and I ₃₃ are balanced and become the same current, and the system current I ₃₂ of the neutral line is almost zero. Become. That is, the power compensator 3 of the present invention can keep the system current of the lead-in line in balance even when the load group connected to the single-phase two systems is unbalanced.

Next, the configuration and operation of the control circuit will be described.
[Calculation of effective compensation current value]
The control method for the two sets of converters 1 and 2 shown in FIG. 1 differs greatly depending on what compensation function is provided to this apparatus. Even if only a current balance function is provided, various control methods are conceivable. Even if a control method is selected, a variety of configurations are conceivable for the control circuit that realizes this. FIG. 3 is an example of a control system for the current balance function which is the main object of the present invention.

First, the system currents I ₃₁ and I ₃₃ in FIG. 1 are detected. When a general current sensor or the like is used, an instantaneous value of a current that changes to a sine waveform is detected, and these are passed through effective value conversion circuits 61 and 62 to the respective system current effective values I _e31 and I _e33 . Convert. These are input to the average value calculation circuit 63, and an average value I _av = (I _e31 + I _e33 ) / 2 of both system currents is _obtained . In the following, assuming that the load connected between the load terminals 41-42 is heavy and the load between the load terminals 42-43 is light as described in the above example, I ₄₁ > I ₄₃ The operation of the control system that balances the grid current effective values I _e31 and I _e33 will be described.

First, I _av and I _e31 are input to the subtraction circuit 65 to calculate a deviation I _av −I _e31 between them, and at the same time, a subtraction circuit 66 _obtains a deviation between I _av and I _e33 . The outputs of these subtraction circuits have the same magnitude (absolute value: [I _av −I _e31 ] = [I _av −I _e33 ]), but when one is output as a positive value, the other is negative. Value. In the above load condition, since the system current immediately after the device was turned on is _{I e31> I e33,} the output _I av _{-I e31} of the subtraction circuit 65 is negative, subtracting circuit 66 is _I av _{-I e33} Output as> 0 (positive).

In the case of the load relationship described above, the converter 1 in the device 3 is reversely converted, and at the same time, the converter 2 is forwardly converted. If there is no loss in this apparatus, feedback control may be performed so that the compensation currents I ₅₁ and I ₅₃ of these converters have the same effective value as the output deviation of the subtraction circuit. Therefore, when there is no loss, the effective values of I ₅₁ and I ₅₃ are the same. However, in reality, due to loss in the apparatus, the same effective value results in a shortage of capacitor replenishment amount due to the forward conversion operation, the capacitor voltage decreases, and the apparatus cannot maintain normal operation. In order to avoid this, in the example of the control system shown in FIG. 3, the total voltage V _C of the two capacitors 13 and 14 is detected, and the deviation ΔV = V _C −V _Cref from the set capacitor voltage V _Cref is subtracted by the subtracting circuit 67. This deviation is converted by the PI control circuit 68 into a loss correction current ΔI.

This device is simply connected to the system, and the anti-parallel diodes 6, 8, 10, and 12 in the device 3 act and the capacitor voltage is charged to the maximum value (peak value) between the system line voltages 31-33. . However, because two converters of the apparatus operates stably, the capacitor voltage V _C is desirably maintained further √2 times the voltage of the maximum voltage between the line wires. That is, V _Cref is generally selected to be about twice the effective value of the system line voltage or more. For this reason, a signal is given to the switching elements 5, 7, 9, and 11, and the capacitor voltage immediately after the start of the apparatus is generally V _C <V _Cref , and therefore ΔV <0. As a result, the loss correction current ΔI output from the PI control circuit 68 is also output as a negative value.

This ΔI and the output I _av -I _e31 of the subtraction circuit 65 are input to the subtraction circuit 69. Since I _av −I _e31 <0 and ΔI <0 as described above, the output I _av −I _e31 −ΔI of the subtraction circuit 69 is a negative value, and its amplitude is smaller by ΔI than I _av −I _e31. Value. That is, when the converter 1 is operated in reverse conversion, the effective value of the compensation current I ₅₁ should be an effective value less than the average value deviation I _av -I _{e 31} by the loss correction current ΔI considering the loss. . At the same time, ΔI is input to the subtraction circuit 70, and a deviation I _av −I _e33 −ΔI from the output I _av −I _e33 of the subtraction circuit 66 is obtained. As described above, since I _av −I _e33 > 0 and ΔI <0, the output of the subtracting circuit 70 has a value that is larger by the loss correction current ΔI than the deviation I _av −I _e33 from the average value. Therefore, the converter 2 and the forward transform, by flowing a compensation current I ₅₃ so that only excess RMS current component corresponding to this loss, setting the capacitor voltage V _C in terms of the up for losses in the system The value V _Cref can be maintained.

[Compensation current reference waveform creation]
What has been described above is what compensation currents I ₅₁ and I ₅₃ should be supplied from the apparatus of the present invention in order to balance the system currents I ₃₁ and I ₃₃ with respect to the unbalanced load currents I ₄₁ and I ₄₃ . The effective value setting method. However, if the compensation current injected into the system is a distorted wave, a harmonic disturbance is caused. Therefore, the compensation current is preferably a sine waveform. Furthermore, in order to maintain a high power factor for the entire system, at least the fundamental wave power factor needs to be 100%. Therefore, as shown in FIG. 3, for example, the system voltage between the terminals 31-32 is detected, and a unit sine waveform having the same phase as this is generated by the sine wave generation circuit 71. After multiplying this by √2 and multiplying the outputs of the subtracting circuits 69 and 70 by the multiplying circuits 73 and 74, the reference waveform (command value) of the compensation current to be output by the converters 1 and 2 can be obtained. it can.

First, the converter 2 that performs the forward conversion operation will be described. Since the output of the subtracting circuit 70 is a positive value, the output of the multiplying circuit 74 is the same as the system voltage V _31-32 (FIG. 4A) between the terminals 31-32 as shown in FIG. It becomes a sinusoidal waveform in phase. On the other hand, the output of the subtraction circuit 69 is a negative value. Therefore, when the output of the subtracting circuit 69 is multiplied by a unit sine waveform (proportional to the system voltage in FIG. 4A), the polarity of the sine wave is inverted, and as shown in FIG. ° The phase of the current waveform is out of phase. That is, the waveform of the multiplication circuit 74 means a current during a forward conversion operation with a fundamental wave power factor of 100%, and the waveform of the multiplication circuit 73 is a current when an inverse conversion operation is performed with a fundamental wave power factor of 100%.

Further, the amplitude (maximum value) of the output sine waveform of the multiplication circuit 74 is √2 (I _av −I _e33 −ΔI). Therefore, the effective value of this waveform is equal to the effective value of the current that the converter 2 performs forward conversion and draws from the system. On the other hand, the output sine waveform of the multiplier circuit 73 has an amplitude of √2 (I _av −I _e31 −ΔI) on the negative polarity side. Therefore, the effective value of this waveform is applied to the system when the converter 1 performs the inverse conversion operation. It is equal to the effective value of the current to be injected. As described above, when the load current is I ₄₁ > I ₄₃ , the multiplier circuit 74 outputs the waveform of FIG. 4B, and the multiplier circuit 73 outputs the waveform of FIG.

In contrast to the above load state, when I ₄₁ <I ₄₃ , the multiplication circuit 73 outputs the waveform of FIG. 4B and the multiplication circuit 74 outputs the waveform of FIG. Therefore, if FIG. 4B is the compensation current reference waveform I _51ref of the converter 1, the converter 1 operates as a forward conversion circuit, and the compensation current I ₅₁ having the same phase and the same amplitude as that of FIG. Will be taken from. Similarly, the output of the multiplication circuit 74 in FIG. 4C is a compensation current reference waveform (command value) I _53ref of the converter 2, and a sine wave compensation current I ₅₃ having the same phase and the same amplitude as that of the converter 2 is systematized. It can be injected into. As described above, which converter performs the forward conversion operation (the other is the reverse conversion operation) is uniquely determined by the polarities of the two reference waveforms output from the multiplication circuits 73 and 74. .

[Current tracking control]
Various control methods are conceivable for obtaining a compensation current that satisfies the above-described reference waveform (command value). Hereinafter, the current tracking control method will be described. First, consider the operation of the converter 2 with the load condition I ₄₁ > I ₄₃ .

As shown in FIG. 3, the compensation current I ₅₃ is detected using a current sensor or the like. This I ₅₃ and I _{53 ref} which is the output of the multiplication circuit 74 are input to the comparison circuit 76. In the comparison circuit 76, as shown in FIG. _5A , a hysteresis width is provided in the reference waveform I _53ref . When the reference waveform is positive, if the detected I ₅₃ is less than or equal to the upper limit of the hysteresis width, the switching element 11 of the converter 2 is turned on. In this state, as shown in FIG. 6A, the voltage of the capacitor 14 and the system voltage between the terminals 32-33 are short-circuited through the AC reactor 16. Therefore, the compensation current I ₅₃ increases substantially linearly as shown in FIG.

When the signal of the switching element 11 is turned off at the time when this I ₅₃ reaches the upper limit of the hysteresis width, the diode 10 is turned on instead of the switching element 11, and as shown in FIG. -33) → diode 10 → the compensation current _{I 53} flows through the capacitor 13 → AC reactor 16. Since the two converters 1 and 2 in this device both operate as boost converters, the capacitors 13 and 14 in the steady state are charged to a higher voltage than the system (31-32) and system (32-33). Therefore, the compensation current I ₅₃ during this period decreases almost linearly as shown in FIG. When this I ₅₃ reaches the lower limit of the hysteresis width, a signal is sent to the switching element 11 to make the circuit of FIG. 6A again. As described above, in the reference waveform _{I 53Ref} positive polarity period, by turning on and off the switching element 11, as shown in FIG. 5 (a), the compensation current _{I 53} is _{I 53Ref} while repeating increase and decrease in the hysteresis width Can follow.

In the latter half of the period in which the reference waveform I _53ref has a negative polarity, the switching element 9 is turned on and off, so that I ₅₃ can follow I _53ref in the same manner. For this purpose, it is necessary to switch a switching element that gives an ON signal according to the polarity of the reference waveform. As one method, as shown in FIG. 3, the reference waveform I _53ref is input to the polarity discrimination circuit 78, and the switching element for sending the output of the signal generation circuit 80 is switched according to the polarity. That is, an ON signal is distributed to the switching element 11 of the lower arm when the reference waveform is positive, and to the switching element 9 of the upper arm when the reference waveform is negative.

Next, the operation of the converter 1 will be described. In the load state of I ₄₁ > I ₄₃ , the converter 1 is operated as an inverse conversion device, and the compensation current I ₅₁ following the reference current I _51ref in FIG. _4C flows into the load between the terminals 41-42. by, it is possible to reduce the system current I _31. For this purpose, the converter 2 may be controlled in substantially the same manner as the converter 1.

The compensation current I ₅₁ is detected, and this and the reference waveform I _51ref are _input to the comparison circuit 75. I _51ref is also input to the polarity discriminating circuit 77. When I _51ref is positive, the signal is distributed to the switching element 7 of the lower arm, and when I _51ref is negative, the signal is distributed to the switching element 5 of the upper arm. In the first half period of FIG. 4, the system voltage is positive, but the compensation current is negative. FIG. 5B shows the relationship between the compensation current I ₅₁ and the reference waveform I _51ref during this period, and FIGS. 7A and 7B _show the circuit states. Similar to the operation of the converter 2, the switching element 5 is turned on when the compensation current I ₅₁ reaches the lower limit (boundary with a small absolute value) within the hysteresis width provided in I _51ref . The circuit is as shown in FIG. 7A, and the voltage difference between the capacitor 13 and the system (31-32) is applied to the AC reactor 15. Since the capacitor voltage is higher than the system voltage, the compensation current I ₅₁ increases in the direction shown in the figure. When the switching element 5 is turned off when I ₅₁ reaches the upper limit (boundary with a large absolute value), the diode 8 is turned on, and the circuit becomes as shown in FIG. 7B, and the compensation current I _{51 in the} direction shown in FIG. Decrease. In the latter half period in which the reference current I _51ref of FIG. _4C is positive, the compensation current I ₅₁ can be controlled to follow the reference waveform I _51ref while operating as an inverse conversion device by _turning on and off the switching element 7. it can.

As described above, when the load state is I ₄₁ > I ₄₃ , the converter 1 automatically performs the inverse conversion operation by the control system of FIG. 3, and the sinusoidal compensation current I ₅₁ having the effective value I _av −I _e31 −ΔI. Inject. On the other hand, converter 2 automatically performs a forward conversion operation and takes in sine wave compensation current I ₅₃ having effective value I _av −I _e33 −ΔI from the system. As a result, even if unbalanced currents I ₄₁ and I ₄₃ flow through the load, the system currents both become (I ₄₁ + I ₄₃ ) / 2 + ΔI, and a current balance can be ensured.

Conversely, the same operation can be performed even when the load state is I ₄₁ <I ₄₃ . In this case, the reference waveform of FIG. 4B having the same phase as the system voltage is output from the multiplier circuit 73, and the converter 1 automatically performs forward conversion operation so as to follow this. On the other hand, the output of the multiplication circuit 74 becomes the reverse phase current of FIG. 4C, and the converter 2 performs the reverse conversion operation, whereby the balance of the system current can be maintained.

  Next, a power factor improvement function using the power compensation device 3 will be described. When using a load with a low power factor, such as a motor load, reactive power processing is required to maintain the stability of the system, and power is generated using a phase advance capacitor, phase adjuster, static reactive power compensator, etc. Rate improvements are made. However, these are cases of large consumers who consume large amounts of power in a three-phase system, and in small consumers using a single-phase three-wire distribution system, an example of implementing such power factor improvement is rare. In a single-phase three-wire distribution system, even if a single-phase load with a low power factor is used, if the power factor of the lead-in wire can be improved, the system current can be suppressed while maintaining the rated output, thus saving energy and reducing the electricity bill. Cost can be reduced.

  The description about the balance of the system current described above is a case where the power groups of the load groups connected between the load terminals 41-42 and between the load terminals 42-43 are the same. In particular, when the power factor is 100%, such as a resistive load, the quality of the system power can be maintained only by the current balance function. However, if all loads are inductive or capacitive, or if one load group is inductive and the other load group is capacitive, then each reactive power is compensated to improve the power factor of the system. There must be. In response to this requirement, the power compensation device 3 of the present invention can easily improve the power factor by controlling the phase of the compensation current. In other words, a lead component may be added to the compensation current if the load current is delayed, and a delay component may be added to the compensation current if the load current is a lead. In addition, even if the load groups of the two systems have different power factors, the phase of each compensation current can be individually controlled, so that the reactive power of each load current is compensated and the power factor of the two systems is 100% respectively. It is possible to maintain.

  Next, a harmonic suppression function using this compensation device will be described. Since electronic devices such as televisions, audios, and personal computers use a capacitor input type rectifier circuit as a power source, the input current is a pulsed alternating current, which is a distorted wave current containing many low-order harmonics. In order to prevent the harmonic disturbance caused by the flow of these harmonic currents into the system, it is desirable to install a filter in the interconnection part with the system. In the present invention, in addition to the above function, a function of suppressing this harmonic can be added. Note that an LC filter using resonance between a capacitor and a reactor cannot cope with a change in load, but the system of the present invention is characterized in that it operates as an active filter that can quickly respond to a change in load.

According to the compensation device 3, even if the load current is a distorted wave including harmonics, the harmonic component of the load current is eliminated by setting the compensation current to a waveform having a phase opposite to that of the distorted wave load current. Is possible. That is, the compensation device 3 of the present invention can have an active filter function. Moreover, it is a great feature that the waveform of each compensation current can be individually controlled. Thus, for example, even when the load terminals 41-42 strain wave generating load between is not connected, while the other load terminal 42-43 if sinusoidal load, is superimposed distortion wave of opposite phase to the compensation current I ₅₁ However, the compensation current I ₅₃ may be a sinusoidal current. As described above, since the compensation current can be individually controlled, complicated control such as three-phase to two-phase conversion is not required unlike a normal three-phase active filter.

  The active filter that has already been put into practical use mainly has the same harmonic suppression function as that of the present invention. Furthermore, some devices have the same reactive power compensation function as that of the present invention and also have the same current balance function as that of the present invention. However, these are all devices intended for a three-phase system, and not a single-phase three-wire system as in the present invention. In an existing active filter, in order to perform the above function in a three-phase system, complicated control such as three-phase to two-phase conversion is essential as described above. On the other hand, in the present invention, since the compensation current flowing through the single-phase two systems of the single-phase three-wire distribution system can be individually controlled, a function equivalent to that of the existing three-phase active filter is provided by a simple control method. be able to. As a result, the power quality of the single-phase three-wire distribution system can be improved, and the cost of electricity can be reduced for consumers.

  Next, a power supply function and a power storage function during a power failure using the compensation device 3 will be described. When IT equipment such as a computer is used as a load and important data processing is performed, it is recommended to install an uninterruptible power supply (UPS) to protect the data and maintain the program. In the present invention, by connecting a storage battery between the DC terminals, this uninterruptible power supply function, that is, a function of continuing to supply power to an important load by performing reverse conversion operation of the converters 1 and 2 even if the system fails. Also has.

  In addition, the load factor of power facilities in Japan has been on a downward trend year by year and has recently been below 55%, so there is a strong demand for power load leveling. For this reason, a power storage device has been developed that stores surplus power at night and discharges it during peak power hours in the daytime. In the present invention, as described above, by connecting the storage battery between the DC terminals, the converters 1 and 2 can be forward-converted and stored to operate as a power storage device.

  That is, in the power compensation system of the present invention, in the case of only the power compensation device 3, in order to keep the capacitor voltage constant, one of them must be reverse-converted and the other must be forward-converted. However, if the storage battery groups 21 and 22 of the device 4 of FIG. 1 are added in place of the capacitors 13 and 14 of the power compensation device 3 or in parallel with the capacitors 13 and 14, both converters are operated in reverse conversion. Is possible. Of course, it is also possible to charge the storage battery by performing a forward conversion operation on both converters simultaneously. It is also possible to supply power to the load by simultaneously reverse-converting both converters during a power failure in the system or during peak load during the day. As a result, this system can function as an uninterruptible power supply that supplies power to the load in the event of a power failure using the power of this storage battery, or as a power storage device that can be charged with surplus power at night and discharged during daytime power peaks. Functionality can also be added. And since the characteristic which can control each compensation current separately is not lost, the above-mentioned current balance function, power factor improvement function, and harmonic suppression function can be maintained.

  In addition, as for the power storage device using a battery, a large-capacity device for a three-phase system has been developed mainly by electric power companies. On the other hand, this system is intended for small-capacity equipment connected to a single-phase three-wire distribution system. Since it works as a kind of distributed power supply with a small capacity, if the number increases in the future, it will contribute to the load leveling of the system. On the other hand, customers can prevent power outage accidents due to temporary overcurrent by supplementing short-term peak power such as when starting a microwave oven or cooler with this system. Electricity costs can be saved by reducing power. Furthermore, by combining with other functions such as current balance, power factor improvement, and harmonic suppression, further energy saving and cost reduction can be expected.

  Although one embodiment of the present invention has been described so far, it is needless to say that the present invention is not limited to the above-described embodiment, and may be implemented in various forms within the scope of the technical idea.

It is a circuit diagram which shows the multifunctional power compensation apparatus of embodiment of this invention. It is a figure which shows the current waveform of each part. It is a block diagram showing an example of a control system for a current balance function. It is a wave form diagram which shows the relationship between a system voltage waveform and a compensation current reference waveform. It is a wave form diagram which shows that a hysteresis width is provided in a compensation current reference waveform, and a detection compensation current waveform is controlled within the range. FIG. 6 is a circuit diagram illustrating a compensation current path corresponding to the control illustrated in FIG. 5. FIG. 6 is a circuit diagram illustrating a compensation current path corresponding to the control illustrated in FIG. 5.

Explanation of symbols

1 System Terminal Group 2 Load Terminal Group 3 Power Compensation Device 4 Storage Battery Group 5, 7, 9, 11 Switching Element 6, 8, 10, 12 Reverse Parallel Diode 13, 14 Capacitor 15, 16 AC Reactor 17, 18 Filter Reactor 19, 20 Filter capacitors 21, 22 Storage battery groups 31, 32, 33 System terminals 41, 42, 43 Load terminals 51, 52, 53 Compensator output terminals 65, 66, 67, 69, 70 Subtractor circuits I ₃₁ , I ₃₂ , I ₃₃ System currents I ₄₁ , I ₄₂ , I ₄₃ Load currents I ₅₁ , I ₅₂ , I ₅₃ Compensation current I _51ref , I _53ref compensation current reference waveform I _e31 , I _e33 System current effective value I _av 2 Average of system current effective value V _C capacitor voltage V _Cref capacitor voltage reference value ΔI Loss correction current

Claims (5)

Two sets of converters with a shared capacitor are incorporated in the system line of the single-phase three-wire distribution system, respectively, and the two sets of converters have a half-bridge configuration with a shared capacitor, and the neutral point of the single-phase three-wire distribution system. A power compensation system for a single-phase three-wire distribution system, characterized in that a common connection line is shared and one converter is reversely converted and the other is forward-converted. Claim 1 single-phase three-wire power distribution system power compensation system of, wherein the added storage batteries in parallel before Kiko capacitor.   The system current in the single-phase three-wire distribution system is detected, and one set of converters is reverse-converted to supply compensation current to a system line with a large load, and the other set of converters is forward-converted. The power compensation system for a single-phase three-wire distribution system according to claim 1, further comprising a function of taking a compensation current from a system line with a small load and balancing the system current.   2. The power compensation system for a single-phase three-wire distribution system according to claim 1, wherein the converter has a function of supplying a compensation current for compensating a reactive current component of a load current of the system line.   2. The power compensation system for a single-phase three-wire distribution system according to claim 1, wherein the converter has a function of supplying a compensation current for compensating a distortion wave component of a load current of the system line.

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