JPH0833786B2 - Reactive power regulator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a reactive power adjusting device for a three-phase AC circuit for preventing voltage flickering, improving power factor, and reducing harmonic components.

[Conventional technology]

It is well known to connect a lead current supply circuit composed of a capacitor, or a parallel circuit of a capacitor and a reactor, between each of the three-phase AC power supply lines in order to prevent flicker and / or improve the power factor. Further, Japanese Laid-Open Patent Publication No. 56-159936 (Japanese Patent Application No. 55-61600) discloses that an instantaneous active current and an instantaneous reactive current are obtained and the power failure compensation circuit is controlled based on the obtained instantaneous active current and instantaneous reactive current. Further, in Japanese Patent Application No. 60-137499, the applicant of the present application has proposed a method for easily achieving power factor improvement of a three-phase unbalanced load based on line current detection. Also,
A method of controlling a reactive component using a three-phase PWM converter composed of transistors has already been proposed.

[Problems to be solved by the invention]

However, the above-mentioned Japanese Patent Application No. 60-137499 does not disclose a method for removing harmonic components. Further, the method of using the transistor three-phase PWM converter has a drawback that it is difficult to increase the capacity.

Therefore, an object of the present invention is to provide a device capable of easily achieving a medium or large capacity reactive power adjustment.

[Means for solving problems]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention for achieving the above-mentioned object will be described with reference to the reference numerals of the drawings showing an embodiment. And a three-phase reactive current fundamental wave component supply circuit (3a) (3b) configured to adjust the magnitude of the reactive current fundamental wave component
And a three-phase pulse width modulation conversion circuit (12) connected to the three-phase AC power supply line and configured to supply a harmonic component of a reactive current by on / off control of a semiconductor switch, Line current detection for detecting the line currents (I _U , I _V , I _W ) of the first, second and third phases of the approximately three-phase balanced load (2) connected to the three-phase AC power supply line. Bowl (4a) (4b)
(4c) and the first, second and third phase line currents (I _U , I _V ,
Instantaneous reactive current of all three phases based on _IW ) The average value (Iqa) of the instantaneous reactive currents (Iq) of the three-phase batch is calculated for each section corresponding to one cycle of the AC voltage of the three-phase AC power supply line, and the average value (Iqa) is reduced. As described above, the reactive current fundamental wave component supply circuit (3a)
(3b) is controlled, and the instantaneous reactive current (I
q) fluctuation (ΔIq) is calculated, and the fluctuation (ΔIq) is converted into three-phase line current components (ΔI _U q, ΔI _V q, ΔI _W q) to reduce the fluctuation (ΔIq). Pulse width modulation (PW) based on the line current components (ΔI _U q, ΔI _V q, ΔI _W q)
M) The present invention relates to a reactive power adjusting device which comprises a calculation and control means for forming a control signal and controlling the three-phase pulse width modulation conversion circuit (12).

The calculation and control means are, for example, reference numeral 5 in FIG.
6, 7, 8, 6a, 9, 10, 11 are circuits or microcomputers.

[Action]

In the above invention, since the load (2) is a substantially balanced three-phase load, the zero-phase current can be ignored. Therefore, the instantaneous reactive current Iq (hereinafter referred to as an instantaneous imaginary current) for all three phases can be easily calculated. Since the instantaneous imaginary current Iq is obtained as a direct current, it can be used to easily form a signal for controlling the fundamental wave component supply circuits (3a) (3b) of the reactive current. The PWM conversion circuit (12) has a function of removing not only the fundamental wave component of the reactive current but also the harmonic component. However, in order to compensate all the fundamental wave components, a large self-erasing type switching element such as a transistor or GTO is required, which is unavailable or expensive. Therefore,
In the present invention, the PWM conversion circuit (12) mainly compensates for harmonic components, and the fundamental wave components are provided by separately provided fundamental wave component supply circuits (3a) and (3b). However, the fundamental wave component of under-compensation or over-compensation in the fundamental wave component supply circuit (3a) (3b)
Compensate with the PWM conversion circuit (12) if necessary. This makes it possible to easily and satisfactorily achieve suppression of harmonic current, prevention of flickering, and power factor improvement.

〔Example〕

Next, a reactive power adjustment method for a three-phase AC circuit according to an embodiment of the present invention will be described with reference to the drawings.

(Explanation of FIG. 1) In FIG. 1, a first phase (U phase), a second phase (V phase),
A three-phase balanced load (2) is connected to the power supply lines (Iu, Iv, Iw) of the third phase (W phase). (3a) and (3b) are fundamental wave component supply circuits of the forward reactive current for power factor adjustment, which are connected to three-phase power supply lines (Iu) (Iv) (Iw). Configured the fundamental component supply circuit reactive current (3a) (3b) is selectively connected through the thyristor S ₁ to S ₆ of a plurality of capacitors C ₁ -C ₆ as an AC switch between each line Has been done. Reactive current fundamental wave component supply circuit (3a)
If the advance current supplied in (3b) is adjusted according to the fluctuation of the load (2), the power factor of the three-phase AC circuit is compensated and the voltage fluctuation (flicker) is also prevented. Although only two fundamental wave component supply circuits (3a) and (3b) are shown in FIG. 1, more fundamental wave component supply circuits having the same configuration are actually provided.

(4a) (4b) (4c) are current detectors, and the line current I _U ,
Each power line (Iu) (Iv) (Iw) to detect I _V and I _W
It is connected to the.

(5) is a first arithmetic circuit for obtaining an instantaneous imaginary current component, which outputs an instantaneous imaginary current Iq of each phase corresponding to the line currents I _U , I _V , and I _W as a direct current. The specific configuration of the arithmetic circuit (5) will be described later.

(6) is the average value Iq of the instantaneous imaginary current Iq for one cycle of the commercial frequency
It is an average value circuit for obtaining a and is connected to the first arithmetic circuit (5). The average value Iqa obtained from this is a direct current corresponding to the fundamental wave component of the reactive current.

(7) is a capacitor stage number determination circuit, which is connected to the average value circuit (6). Here, in order to compensate the average value Iqa, the optimum number of connection stages of the capacitors C _{1 to} C ₆ , that is, the _one to be turned on among the fundamental wave component supply circuits (3a) (3b) is determined. If, when selecting the first fundamental wave component supply circuit (3a) generates an on command signal of the thyristor S ₁ to S _3.

Reference numeral (8) is a control circuit, which is connected to the capacitor stage number determination circuit (7). The control circuit (8) in response to determining capacitor stages, thyristors S ₁ to S ₃ or S ₄ ~
Generates ON control signals for S ₆ or both. The thyristors S _{1 to} S ₃ are controlled simultaneously, and S _{4 to} S ₆ are also controlled simultaneously.

Reference numeral (9) is a fluctuation extraction circuit, which is connected to the first arithmetic circuit (5) and the fundamental wave compensation amount signal generation circuit (6a). The fluctuation amount ΔIq output by the fluctuation amount extraction circuit (9)
Corresponds to the harmonic component contained in the instantaneous imaginary current Iq, and is basically obtained from the instantaneous imaginary current Iq obtained from the first arithmetic circuit (5) and the average value circuit (6). It corresponds to the difference from the average value Iqa. If almost all of the fundamental wave components can be compensated by the fundamental wave component supply circuits (3a) and (3b), the average value signal Iqa obtained from the average value circuit (6) is used as a variation extraction circuit ( 9) You can input directly. However, in this embodiment, the fundamental wave component is stepwisely compensated, and shortage or excess of compensation occurs. Therefore, this shortage or excess is compensated by the PWM conversion circuit (12).
In order to enable this compensation, a fundamental wave compensation amount signal generation circuit (6a) is provided between the capacitor stage number determination circuit (7) and the fluctuation amount extraction circuit (9). This fundamental wave compensation amount signal generation circuit (6a) includes a capacitor stage number determination circuit (7)
The signal Iqb indicating the amount of fundamental wave compensation that can be supplied with the number of capacitor connection stages determined in step 1 is output. Capacitor C
_Since the capacities of _{1 to} C ₆ are known, the compensating fundamental wave component can be easily determined.

(10) is a second arithmetic circuit for returning the variation to the three-phase line currents ΔI _U q, ΔI _V q, ΔI _W q, and is connected to the variation extraction circuit (9). This second arithmetic circuit (10) is a variation amount Δ of the three-phase batch obtained from the variation amount extraction circuit (9).
It is a circuit that obtains a signal indicating variations ΔI _U q, ΔI _V q, and ΔI _W q in the line current of each phase (U, V, W) based on Iq.

(11) is a control signal forming circuit, which is a current detector (13) (14) for detecting the current supplied by the second arithmetic circuit (10) and the PWM conversion circuit (10) for harmonic component compensation. (15)
Connected to and, the transistors Q _{1 to} Q of the PWM conversion circuit (12)
Generates a signal to control ON / OFF of ₆ .

The harmonic conversion current supply PWM conversion circuit (12) includes transistors Q _{1 to} Q ₆ as bridge-connected self-arc-extinguishing semiconductor switch elements, and an AC voltage is applied to the connection point of each pair of transistors Q _{1 to} Q _6. Power supply lines (Iu, Iv, Iw) are connected, and a reactor (16) is connected as a load to the transistors Q _{1 to} Q ₆ of each pair. Bases of the transistors Q ₁ to Q ₆ is connected to the control signal forming circuit (11), each of the transistors Q ₁ to Q ₆ is driven pulse width modulation (PWM), for supplying a desired harmonic compensation current. Note that capacitors C ₁₁ , C ₁₂ , and C ₁₃ are connected between the input lines of the PWM conversion circuit (12).

(Explanation of Iq and FIG. 2) The instantaneous reactive current is described in the above-mentioned Japanese Patent Laid-Open No. 56-159936.

The three-phase AC power supply voltages V _U , V _V , and V _W are represented by the following equations, assuming that they are balanced three-phase AC voltages having a maximum value Vm and an angular frequency ω.

Now, when the three-phase load currents I _U , I _V , and I _W are coordinate-transformed by a transformation matrix that rotates by ω and are represented by Ip and Iq, the following equation is generally established when there is no zero-phase current.

Here, since only the instantaneous reactive current Iq is calculated, (2)
If Ip = 0 in the equation, the following equation is obtained.

In the present invention, Iq in the above equation (4) is defined as an instantaneous imaginary current. This instantaneous imaginary current Iq corresponds to the instantaneous reactive current component of all three phases as is clear from the above equation.

FIG. 2 shows the first arithmetic circuit (5) of FIG. 1 in detail. Lines (21) (22) (23) connected to the current detectors (4a) (4b) (4c) of FIG. 1 are multipliers (24) (25) (2).
6) Each is connected to one of the input terminals. The other input terminals of the multipliers (24) (25) (26) have sin ωt generation circuit (27), sin (ωt-2π / 3) generation circuit (28), s
The in (ωt-4π / 3) generation circuits (29) are connected to each other. The output of each multiplier (24) (25) (26) is connected to the adder (30). A coefficient unit (31) is provided on the output line of the adder (30). This coefficient unit (31)
Is the coefficient at the output of the adder (30) And outputs the instantaneous imaginary current Iq of equation (4).

(Explanation of Average Value Circuit) As shown in FIG. 3, the average value circuit (6) of FIG. 1 is composed of an integrating circuit (32) and a sample hold circuit (33). The integrator circuit (32) is connected to the first arithmetic circuit (5) and reset in response to a power source zero-point pulse indicating the start of one cycle of the commercial AC voltage of the power source lines (Iu, Iv, Iw),
The instantaneous imaginary current Iq for one cycle of the commercial frequency is integrated. The sample hold circuit (33) samples and holds the integrated value of one cycle in response to the power source zero point pulse, and outputs it as the average value Iqa. This average value Iqa corresponds to the fundamental wave component of the instantaneous reactive current.

_{(ΔIq, ΔI U q, ΔI} V q, ΔI W q and description of FIG. 4) variation extraction circuit (9), Iq-Iqb as shown in FIG. 4
And outputs a signal corresponding to the harmonic component of the instantaneous reactive current as the variation ΔIq. The second arithmetic circuit (10) of FIG. 1 is a circuit for returning the fluctuation amount ΔIq of the three-phases to the three-phase line current, and is configured as shown in FIG. The following functions exist between the line currents I _U , I _V , and I _{W of} each phase, and the instantaneous reactive current (imaginary current) Iq and the instantaneous active current I _P of the three phases collectively.

If I _P = 0 in order to obtain the relationship between I _U , I _V , and I _W and the instantaneous reactive current Iq, the following equation holds.

The relational expression between the line currents I _U , I _V , and I _W and the instantaneous reactive current Iq is created based on the equation (6), and the relational expression is as follows.

ΔIq corresponds to Iq, and each line current of ΔIq ΔI _U q, ΔI _V q, Δ
Since I _W q corresponds to I _U , I _V , and I _W , the following equation holds.

In order to perform the calculation of the above equation (8), in the circuit of FIG. 4, the coefficient unit (34) is connected to the output line of the variation extraction circuit (9).
Is connected, Is multiplied. The output of the coefficient multiplier (34) is the multiplier (3
5) (36) (37) is connected to one input terminal, and the other input terminal has sin ωt generation circuit (38) and sin (ωt-2
It is connected to the π / 3) generation circuit (39) and the sin (ωt-4π / 3) generation circuit (40).

(Description of PWM Control Signal Forming Circuit) The PWM control signal forming circuit (11) includes a hysteresis comparator (42) and a logic circuit (43) as shown in FIG. The second arithmetic circuit (10) is connected to one input terminal of the hysteresis comparator (42), and the fluctuation U-phase line current ΔI _U q shown in FIG. 6 (A) is input to the second arithmetic circuit (10). The other input terminal of the comparator (42) is in contact with the current detector (13) of FIG. 1, and the detected current value I _CT shown in FIG. 6 (A) is input. The comparator (42) obtains two hysteresis levels V _L and V _H based on the line current ΔI _U q, compares these with the current detection value I _CT, and I _CT is V _L ,
The output is inverted every time V _H is reached, and the comparison output shown in FIG. 6 (B) is obtained. That, I _CT is directed to the level V _L from the level V _H t ₂ ~t ₃ comparison output in a section is low, I _CT level V
It goes high during the period t ₃ to t ₄ from _L to V _H.

The logic circuit (43) is a transistor based on the comparison output.
This is a circuit that forms the PWM control signals for Q ₁ and Q ₂ . The control signal of the transistor Q ₁ shown in FIG. 6 (C) is the line current ΔI _U
By selecting the comparison output of FIG. 6 (B) as it is from t ₁ to t ₅ of the first half cycle of q, and inverting the comparison output of FIG. 6 (B) from t ₅ to t ₆ of the second half cycle. Is formed. The control signal of the transistor Q _{2 in} FIG. 6 (D) is an inversion of the control pulse in FIG. 6 (C). ΔI _V q
And the second and third phase transistors Q _{3 to} Q based on ΔI _W q
The control signal of ₆ is also formed in exactly the same manner as the first phase.

(Operation) When the line currents I _U , I _V , and I _W including harmonic components and reactive components are flowing through the load (2) in FIG. 1, the current detector (4
a) (4b) and (4c) are detected and sent to the first arithmetic circuit (5). The first arithmetic circuit (5) is for each line current I _U , I _V , I _W
The instantaneous reactive current of the three phases, that is, the instantaneous imaginary current Iq is output. The average value circuit (6) outputs the average value ΔIqa corresponding to the effective value of the fundamental wave component of the instantaneous reactive current of the three-phase batch. The capacitor stage number determination circuit (7) and the control circuit (8) control the thyristors S _{1 to} S ₆ so that a current for compensating the average value ΔIqa, that is, a current to be canceled flows. Since the fundamental wave component supply circuits (3a) and (3b) are provided in a plurality of stages, the compensation current (fundamental wave advance current) required by the selected one or the selected combination is supplied.

On the other hand, the harmonic compensating PWM conversion circuit (12) compensates for the component which cannot be compensated by the fundamental wave component supply circuits (3a) (3b) of the reactive current. That is, since the fundamental wave component supply circuits (3a) and (3b) of the reactive current compensate the fundamental wave component of the reactive current and cannot compensate the harmonic component, the variation extraction circuit (9) The variation ΔIq including the wave component information is extracted and the transistor is used to compensate for it.
It drives the PWM conversion circuit (12) consisting of Q _{1 to} Q ₆ . Since the transistor Q ₁ ~Q ₆ is a self-extinguishing semiconductor switch,
This on / off can be performed at a frequency higher than the commercial frequency, and the harmonic component can be compensated. Therefore, according to the method of FIG. 1, flickering prevention, power factor improvement,
And suppression of harmonic currents is achieved.

(Modification)

The present invention is not limited to the above-described embodiments, and the following modifications are possible, for example.

(1) The fundamental wave component supply circuits (3a) and (3b) in FIG. 1 can have a circuit configuration as shown in FIG. In Fig. 7, the triangular connection circuit of capacitors C ₁ , C ₂ and C ₃ and the reactor
L _1, L _2, and a triangle connection circuit of L ₃ are connected in parallel, the triangle connection circuit of the reactor and phase control (conduction angle control) thyristor S ₁ to S _3, equivalently continuously controlled capacitance Is configured. In this case, the fundamental wave compensation amount signal generation circuit (6a) is not required, and 1qa is directly input to the variation extraction circuit (9).

(2) As shown in FIG. 8, thyristors S _{1 to} S ₃ may be connected in series to capacitors C _{1 to} C ₃ in the fundamental wave component supply circuit.

(3) A capacitor may be connected instead of the reactor (16) of the PWM conversion circuit (12). Also, the transistor Q ₁ ~
A high speed switching device such as FET or GTO may be used instead of Q ₆ .

(4) The thyristors S _{1 to} S ₆ may be SCRs connected in antiparallel instead of being triaced.

(5) The arithmetic circuits (5) and (10) may be configured by a microcomputer.

〔The invention's effect〕

 The present invention has the following effects.

(A) The pulse width modulation conversion circuit has a function of compensating for the fundamental wave component. If the pulse width modulation conversion circuit is configured to compensate all the fundamental wave components, it becomes necessary to use a large capacity semiconductor switch, which increases the cost of the device. Therefore, in the present invention, in addition to the pulse width modulation conversion circuit, a fundamental wave component supply circuit including a capacitor or a reactor connected to a three-phase AC power supply line via a switch is provided, whereby all or one of the fundamental wave components is provided. The department is compensated. Since the switch of the fundamental wave component supply circuit does not have to continue at high speed, when compared with the same current capacity, the cost is lower than that of the semiconductor switch of the pulse width modulation conversion circuit. Therefore, according to the present invention, the cost of the reactive power adjusting device can be reduced.

(B) If both the fundamental wave component supply circuit and the pulse width modulation conversion circuit are controlled based on the arithmetic processing specified by the present invention, the predetermined control can be achieved relatively easily.

[Brief description of drawings]

FIG. 1 is a block diagram showing a three-phase reactive power adjusting device according to an embodiment of the present invention, FIG. 2 is a block diagram showing a first arithmetic circuit of FIG. 1, and FIG. 3 is an average value of FIG. FIG. 4 is a block diagram showing a circuit, FIG. 4 is a block diagram showing the second arithmetic circuit of FIG. 1, FIG. 5 is a block diagram showing a part of the control signal forming circuit of FIG. 1, and FIG. Waveform diagrams showing the states of the respective parts in the figure, and FIGS. 7 and 8 are circuit diagrams showing modifications of the fundamental wave component supply circuit. (Iu) (Iv) (Iw) …… Power line, (2) …… Load, (3
a) (3b) ... fundamental wave component supply circuit of reactive current, (4a)
(4b) (4c) ... current detector, (5) ... first arithmetic circuit, (6) ... average value circuit, (8) ... gate control circuit, (9) ... variation extraction circuit , (12) …… PWM conversion circuit.

Claims (1)

[Claims] 1. A capacitor or a reactor is connected to a three-phase AC power supply line via a switch to supply a fundamental wave component of a reactive current and adjust the magnitude of a fundamental wave component of the reactive current. A three-phase reactive current fundamental wave component supply circuit (3a) (3b) configured and supplying a reactive current harmonic component by ON / OFF control of a semiconductor switch connected to the three-phase AC power supply line. And a three-phase pulse width modulation conversion circuit (12) configured to enable the first phase, the second phase and the third phase of the substantially three-phase balanced load (2) connected to the three-phase AC power supply line. Phase line currents (I _U , I _V ,
Line current detector for detecting an I _W) and (4a) (4b) (4c ), said first, second and third phase line current (I _U, I _V, the three-phase on the basis of the I _W) Instantaneous reactive current The average value (Iqa) of the instantaneous reactive currents (Iq) of the three-phase batch is calculated for each section corresponding to one cycle of the AC voltage of the three-phase AC power supply line, and the average value (Iqa) is reduced. As described above, the reactive current fundamental wave component supply circuit (3a)
(3b) is controlled, and the instantaneous reactive current (I
q) fluctuation (ΔIq) is calculated, and the fluctuation (ΔIq) is converted into three-phase line current components (ΔI _U q, ΔI _V q, ΔI _W q) to reduce the fluctuation (ΔIq). Pulse width modulation (PW) based on the line current components (ΔI _U q, ΔI _V q, ΔI _W q)
M) A reactive power adjusting device which comprises a calculation means for forming a control signal and controlling the three-phase pulse width modulation conversion circuit (12).