JPH0641348U - Injection circuit type active filter - Google Patents

Abstract

(57) [Abstract] [Purpose] To prevent harmonics when installing multiple injection circuit type active filters in the system to suppress harmonics, a fixed phase advance capacity depending on the operating conditions of the load Automatically adjust the number of active filter connections with. At the same time, the active filters connected are combined and controlled to obtain a higher compensation rate than the independent compensation rate of each active filter. [Configuration] The number of active filter connections to the grid is increased or decreased according to the priority order of connections so that the reactive power of the grid does not exceed the set range. At the same time, the current signal input to each active filter as a compensation target is
Seen in the order of priority of the connection, the first stage has a total current value on the load side, and the subsequent stages have a current value obtained by subtracting the active filter output from the previous stage from the total current value.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 This invention provides an automatic on / off sequence circuit to prevent the system from over-advancing when multiple injection circuit type active filters are installed, and the overall compensation rate is higher than the individual compensation rate. The purpose is to provide a control method that can be performed.

[0002]

[Prior art]

As shown in FIG. 4, the injection circuit type active filter 1 has a system bus 2 in which a capacitor C and a reactor L are serially connected in this order, and the capacitor C is passed through the capacitor C from the inverter 3 to the harmonics on the load side. intended for flowing current I _AF to cancel the harmonic current I _LH generated by source 4, thereby, the power source side Inpi - suppressing harmonics to be flowed through the dance X _L to a power source 5.

This injection circuit system has the feature that the capacity of the inverter can be reduced and at the same time the power factor of the system can be improved.

This characteristic is obtained by the following principle. In FIG. 4, the impedance 1 / jωC of the capacitor C and the impedance jωL of the reactor are set to 1 / jωC = 100% and jωL = 8% with respect to the fundamental wave of the system, for example. Under this condition, the relationship of 1 / jωC> jωL for the fundamental wave and 1 / jωC <jωL for the harmonic wave holds, and the fundamental wave component is mainly borne by the capacitor C and the harmonic wave component is the reactor. You will have to pay.

The voltage output of the inverter 3 is given to both ends of the reactor L. Therefore, when the inverter 3 tries to output a compensating current to the grid, its output voltage may correspond to a harmonic voltage that is as small as a few percent of the fundamental voltage, and the output capacitance of the inverter 3 (Voltage x current) can be reduced to, for example, 25% as compared with the case where the inverter 3 is made to bear the entire voltage of the system bus with the same compensation capacity.

Also, since the capacitor C bears most of the fundamental wave component of the system voltage, this capacitor capacity supplies a phase advance amount to the system and functions as a power factor improving capacitor.

According to the above-mentioned principle, the injection circuit type active filter 1 calculates a harmonic wave (I _LH ) to be suppressed from the load current I _L detected by CT ₀ , and an arithmetic unit 6 including a Fourier transform circuit and the like. Are separated and combined in step S3, and this is given to the inverter circuit 3 as a command value, and the canceling current I _AF flows out to the power supply side to suppress harmonics.

In the above system, when the compensation capacity is insufficient with one active filter due to the addition of load equipment or the like, a plurality of active filters 1 are installed as shown in FIG. The load current signal to be input to 6 is given according to the burden (in the example shown in the figure, two active filters 1 are provided, and the burden of the compensation amount is set to 1/2, I _L Enter / 2).

Here, each active filter 1 has its inverter capacity and capacitor capacity determined in accordance with the load on the load. In other words, if the burden is 1/2 of the full load, the inverter capacity is the capacity necessary to cancel the harmonic current generated by the 1/2 load, and the capacitor capacity is the lagging power generated by the 1/2 load. Correspond to the quantity.

[0010]

[Problems to be solved by the device]

 As shown in FIG. 5, consider the compensation rate when a plurality of active filters 1 are installed in parallel.

The individual compensation rate of each active filter 1 is generally about 80% due to a calculation error or the like. Even if a plurality of units are installed in parallel, each active filter 1 compensates for the burden, so the overall compensation rate is the same 80%.

Also, consider improvement of the power factor.

At the maximum load when all the loads are in the operating state, even if all the active filters 1 are connected to the system, the total capacity of the capacitors C corresponds to the lagging power generated by the load during operation, Helps improve power factor. However, in the light load state, the lagging phase power is reduced in proportion to this, and if all the capacitors C are connected to the system bus 2, there is a possibility that the lagging phase state will occur.

In view of this, the present invention automatically switches the number of active filters 1 connected so that the power factor of the system does not become an excessively advanced phase, and effectively operates the active filters 1 being connected to compensate. It is an object of the present invention to provide a control method that improves the rate over individual compensation rates.

[0015]

[Means for Solving the Problems]

 In this device, a capacitor C and a reactor L are connected to the system in this order, and the harmonic current that cancels the harmonic current generated on the load side is generated by the inverter 3 and is supplied to the system through the capacitor C. When multiple circuit type active filters 1 are installed in the system,

A first configuration provided with a capacitor automatic injection relay 7 that increases / decreases / controls the number of connections of the active filter 1 to the system according to the priority order of the connections so that the reactive power of the system does not exceed the set range. When,

Further, looking at the current signals input to each active filter 1 as a compensation target in the order of priority of the above connection, the first stage is the total current value on the load side, and the subsequent stages are from this total current value to the previous stage. A second configuration is provided in which a compensation amount determination circuit 8 for setting the current value obtained by subtracting the output of the active filter up to is added to the first configuration.

[0018]

With the above-described first configuration, the connection of the plurality of active filters 1 to the system is performed stepwise by the automatic capacitor relay 7 that monitors the reactive power of the system. By this, the over-advanced phase state can be avoided and the power factor can be maintained in the optimum state.

In the second configuration, the compensation amount determination circuit 8 connects the current signal input to the calculation unit 6 as the compensation target to the active filter 1 connected to the system by the relay 7. When viewed in order of priority, the active filter 1 in the first stage inputs the total current I _L detected on the load side, and in the second and subsequent stages, the residual amount (I _L −Σ I _AFk ) left uncompensated up to the previous stage is input. . In this control method, the active filter 1 of the second and subsequent stages compensates for the residual components of the compensation up to the preceding stage, so that the absolute amount of calculation error is reduced and the compensation rate of the entire system can be improved as compared with the conventional system.

[0020]

【Example】

FIG. 1 shows a basic circuit embodying the first and second configurations of the present invention. This is the system bus 2, a plurality of active filters 1 controlled in the manner of this invention, which was connected, the system bus 2, the power supply side Inpi - from the power supply 5 of varying power stations or the like through dance X _L Power is supplied and the harmonic generation source 4 is connected to the load side.

A plurality of active filters 1 installed in parallel in the system are prioritized for connection to the system (in the illustrated example, the leftmost one is the highest priority, and the second and third filters are directed rightward below. Are ranked)).

The automatic capacitor closing relay 7 receives the load current I _L detected by the current transformer CT ₀ and the system voltage V _S detected by the transformer PT ₀ to calculate the reactive power Q, which is set by the setter 9. The number of active filters 1 to be applied is increased or decreased so as to fall within the set reactive power range (for example, defined by the center set value and the lead / lag setting range). Then, according to the priority order of the connection, the relay sequence circuit 10 connects / disconnects the active filter 1 (capacitor C of the active filter) to / from the system bus 2. This connection / disconnection is performed by the hysteresis control that is performed when the calculated reactive power Q attempts to exceed the upper limit / lower limit of the above-mentioned setting range, so that unnecessary connection / disconnection operations do not occur.

The current signal input to each active filter 1 as a compensation target is given by the compensation amount determination circuit 8. The compensation amount determination circuit 8 is _composed of current transformers CT _{1 to} CT _n that detect the output currents I _{AF1 to} I _AFn of the active filters 1 and adders 11 _{1 to} 11 _n . This configuration, seen in order of priority connections, harmonic active filter 1 of the first stage the total load current I _L, 2-stage and subsequent detected by current transformer CT ₀ on the load side, remaining scratches compensated by front This is to enter the residual wave. The calculation of this residual component is performed by the adders 11 _{1 to} 11 _n subtracting the total sum ΣI _AFk of the output currents from the previous stage to the full load current I _L. In this way, the current signal input to the calculation unit 6 of each active filter 1 has a value obtained by subtracting the output harmonic components up to the preceding stage, including the calculation error.

Then, the operation unit 4 of the active filter in the second and subsequent stages determines the compensation command value I _REF of the harmonic current for this residual amount and outputs it to the inverter 3. In each active filter 1, the output current I _{AFk with} respect to the current signal input as a compensation target has a calculation error of about 80%. However, since a calculation error occurs with respect to the compensation residual value up to the preceding stage, when the number of stages increases, the absolute error sharply decreases, and the overall compensation rate is significantly higher than when operating individually. improves.

Next, a more specific embodiment of the present invention will be described.

FIG. 2, the active filter 1 _1, 1 ₂ of the two, so also configured this invention, capacitors automatic insertion relay 7, similar to those described in FIG. 1, a current transformer C T ₀ And the reactive power Q is calculated from the load current I _L detected by the transformer PT ₀ and the system voltage V _S, and the second stage active filter 1 ₂ is turned on so that this value does not fall within the set range and does not become an advanced phase.・ Determine the separation.

The compensation amount determination circuit 8, the current transformer CT ₁ detect the first-stage output current I _AF1 of the active filter 1 _1, constituted by the adder 11 _1.

The current signal input to the arithmetic circuit 6 of the active filter 1 _{1 in} the first stage as a compensation target is the full load current I _L detected by the current transformer CT ₀ on the load side. The current signal is input to the arithmetic unit 6 of the active filter 1 ₂ of the second stage I _L 'is the compensation amount determination circuit 8, the calculated I _L' = a I _L -I _AF1.

[0029] Incidentally, the reactor L of the active filter 1 _1, 1 ₂ in Figure 2, reactor integrated with associated transformer inverter - uses a transformer 12.

The arithmetic unit 6 and the inverter 3 have a common configuration for the _two active filters 1 ₁ and 1 ₂ .

The internal configuration of the active filter 11 of the _first stage will be described below. The operation unit 6 separates and synthesizes the harmonic current I _LH to be suppressed from the current signal input as the compensation target in the compensating harmonic current detection circuit 13 having a Fourier transform circuit and the like, which will be described later. The compensation command value I _REF obtained by adding the correction signals is given to the inverter control circuit 14. Then, the switching element 15 of the inverter 8 is PWM controlled to output the compensation current I _AFK corresponding to the compensation command value I _REF to the system bus 2.

The inverter 3 includes a DC power supply unit 16, a switching element 15, and a switching frequency removing filter 17. In this inverter, a control current transformer CT _INV and a correction current transformer CT _T are provided on the output side of the switching element 15 and the output side of the filter 17, respectively.

The output I _INV of the control current transformer CT _INV is given to the adder 18 in the preceding stage of the inverter control circuit 14, and the compensation command value I _REF is subtracted by this value and output to the hysteresis comparator 19. To be done. In this way, inverter control by PWM modulation is performed.

The output of the current transformer CT _T for correction is returned to the calculation unit 6 together with the output current I _AF1 of the active filter 1 ₁ detected in CT ₁ . This correction is performed because a part of the harmonic current output from the inverter 3 flows to the ground side through the reactor L, and the inverter output needs to be increased by this amount.

That is, the adder 20 calculates I _T −I _AF1 to detect a current (including a fundamental wave and a harmonic wave) flowing to the ground side through the reactor L. Next, the fundamental wave voltage component detected by the bandpass filter 21 is input to the divider 22 having a predetermined impedance value as a divisor, and the fundamental wave component of the current flowing through the reactor L is obtained. When these differences are obtained by the adder 23, the harmonic current I _RH flowing in the reactor L can be detected. Therefore, this is used as a correction value, and the adder 24 adds the harmonic current I _LH to the compensation command. _Let it be the value I _REF .

Next, consider the compensation rate when the _two active filters 1 ₁ and 1 ₂ are controlled by the control system of the present invention as shown in FIG.

FIGS. 3 (a) and 3 (b) show the compensation rate obtained with the configuration of FIG. 2 of the present invention in comparison with the conventional configuration shown in FIG. This is because the compensation ratio of each active filter is generally 0.8, and the output capacitance ratio of the harmonic current I _AF of the _two active filters 1 ₁ and 1 ₂ is I ₁ : I ₂ = 1: 1. And (1 PU of the maximum value of the harmonic current I _LH to be compensated is 0.5 PU, respectively) and I ₁ : I ₂ = 5: 1.

When operated independently as shown in FIG. 5, each active filter bears 1/2 I _LH , so that the compensation rate is 0.5 × 0.8 × 2 = 0.8. It is a fixed value. On the other hand, as shown in FIG. 2, when the total current I _LH is input to the first stage active filter and this compensation remaining amount is input to the second stage active filter, the output current of the first stage active filter is I _AF1 = I _LH × 0.8, the output current of the second-stage active filter is I _AF2 = (I _LH −I _AF1 ) × 0.8 = 0.16 I _LH , and the compensation current of the whole active filter is I _AF = I _AF1 + I _AF2 = 0.96 I _LH .

However, the compensation rate is limited by the output capacitance of the _first active filter 1 ₁ . When the output capacity ratio is I ₁ : I ₂ = 1: 1, I _AF1 = 0.4I _LH (MAX) when the harmonic current I _LH on the load side to be suppressed exceeds 0.5 PU. , The compensation rate decreases from 0.96 and becomes 0.8 when I _LH = 1 PU. When the output capacity ratio is I ₁ : I ₂ = 5: 1, the compensation rate of 0.96 can be maintained until I _LH reaches 0.83 PU.

[0040]

[Effect of device]

 According to this invention, when a plurality of injection circuit type active filters are installed, the overall compensation rate can be made higher than the individual compensation rate while maintaining the condition that the system is not in the advanced phase.

[Brief description of drawings]

FIG. 1 is a basic circuit diagram of an injection circuit type active filter embodying the first and second configurations of the present invention.

FIG. 2 is a circuit diagram showing an embodiment of the present invention using two active filters.

FIG. 3 is a characteristic diagram showing a compensation rate improvement effect in the configuration of FIG. 2 in comparison with a conventional case.

FIG. 4 is a diagram showing a general configuration of an injection circuit type active filter.

FIG. 5 is a circuit diagram showing a conventional configuration in which two active filters are provided in a system.

[Explanation of symbols]

 1 Injection circuit type active filter 2 System bus 3 Inverter 4 Harmonic generation source (load) 5 Power supply 6 Arithmetic unit 7 Automatic capacitor closing relay 8 Compensation amount determination circuit

Claims (2)

[Scope of utility model registration request] 1. An injection circuit active filter having a structure in which a capacitor and a reactor are connected in this order to a system, a harmonic current that cancels a harmonic current generated on the load side is generated by an inverter, and is supplied to the system through the capacitor. When multiple units are installed in the system, it is equipped with a capacitor automatic closing relay that increases / decreases / controls the number of active filter connections to the system according to the connection priority order so that the reactive power of the system does not exceed the setting range. The injection circuit type active filter characterized by the above. 2. The injection circuit active filter according to claim 1, wherein the current signals input to each active filter as a compensation target are viewed in connection priority order, and the first stage is the total current value on the load side, and the subsequent stages and thereafter. Is an injection circuit type active filter characterized by comprising a compensation amount determination circuit for setting a current value obtained by subtracting the output of the active filter from the previous stage from the total current value.