JPH0251332A - Fault current compensator - Google Patents

Abstract

PURPOSE:To achieve an optimal design with respect to the capacity and the response of device by providing a current command means which weight the positive phase reactive component and negative phase component of a basic wave detected through a current detecting means and operating a current command for a power converter. CONSTITUTION:A PLL circuit 30A is synchronized in phase with the positive fundamental component of system voltage Vs while a PLL circuit 30B is synchronized in phase with the negative fundamental component of the system voltage Vs. With respect to the negative phase of the fundamental component, load current Ih is fed to 3-phase/2-phase converting section 21. The proportional gains ka, kb at amplifying sections 25A, 25B are set such that 1>=ka>kb. When the compensation degree of the reactive fundamental component is increased while that of the negative fundamental component is decreased, fluctuation of actual instantaneous power caused by the negative phase component is suppressed and the capacity of energy storing element in a power converter can be reduced resulting in the achievement of economic design of the entire compensator.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention provides a fault current system that compensates for a fault current included in a load current flowing through a power system with a compensation current supplied from a power converter. This invention relates to a compensation device.

(Prior Art) A load such as an arc furnace that generates a large amount of fault current such as reactive current, unbalanced current, or harmonic current and that fluctuates rapidly is undesirable because it causes disturbance in the power system. A fault current compensator using a self-excited inverter is attracting attention as an effective means of compensating for the fault current because it can control the output current at high speed.

FIG. 5 shows a power system equipped with a fault current compensation device using a self-excited inverter. A load 3 is connected to a power system 2 having an AC power source 1 . In order to compensate for the fault current included in the load current Ih flowing through the power system 2 and to prevent the fault current from being included in the supply current Is from the AC power supply 1, the fault current is transferred to the power system 2 via the transformer 4. A compensation device 5 is connected. The fault current compensator 5 includes a rectifier 6, a self-excited inverter 7, and a control device 8 that controls the inverter 7.

The load current 1h is detected by the current detector 51, and based on the detection result and the system voltage Vs, the fault current component to be compensated is detected in the control device 8, and the fault current component to be compensated for is sent from the inverter 7 via the control device 8 to compensate for it. A current 1c is supplied to the power system 2.

In order to control the compensation current 1c, it is detected by a current detector 52 on the output side of the inverter 7 and fed back to the control device 8.

FIG. 6 shows a detailed circuit configuration of the control device 8. Detection of fault current in this control device is based on the theory of instantaneous real power and instantaneous imaginary power (Transactions of the Institute of Electrical Engineers of Japan, Vol. 103).
(Refer to Volume B, No. 7, pp. 483-490). U, V of load current 1h.

W phase currents are respectively I hu, I hv,
I hv and each phase voltage of the system voltage Vs is V su and V sv, respectively.

As VSV, the following calculations are performed in the three-phase/two-phase converters 21 and 22, and the currents and voltages of the α phase and β phase, which are orthogonal to each other, are 1ha, Ihβ and Vsa,
Calculate Vsa.

...(1) ...(2) Based on the electric power 1fEIha, Ihβ and the voltages Vsα, Vsa obtained in this way, the instantaneous power calculation unit 2
3, instantaneous real power ph and instantaneous imaginary power Qh are calculated according to the following equations.

Now, assuming that the load current Ih is the 0th harmonic current, I hu −,,r2In 5in(n ωt−φ)I
hv=l]ln 5in(n (IJ t −2y
r/3-φ)... (5) I hv --P2In 5in(n ωt +2 y
r/3-φ)... (6) Define. Here, φ is an arbitrary phase difference.

Substituting equations (4) to (6) into equation (1), the current Iha,
Ihβ is It+a-(J″2/v′3) flhu-(1/2
) (Ihv+Ihv) 1 - J""J In fist5in (n (IJ -φ)
... (7) Ihβ-(1/2) (Thv-1hv) --J7
In φcos(n (L) t−φ) (8). Here, for simplicity, Vsa-sinωt.

Assuming Vsa--cosωt, the instantaneous real power Ph and the instantaneous imaginary power Qh are (7), Substituting equation (8) into equation (3), P h = (3In-cos ((n-1) ω) 1φ)Qh −J]Inφ5lnl(n-1)ω1φ)
becomes.

If the load current 1h is the fundamental wave, then (9).

Substituting n-1 into equation (10), Ph-J]l ”eO8φ , −(11
)Qlt −(”J I l・sinφ・(
12), and at this time, the electric powers Ph and Qh become constant values. Further, the powers Ph and Qh match the normal fundamental wave active power and fundamental wave reactive power.

The instantaneous real power ph and instantaneous imaginary power Qh obtained in this way are converted into instantaneous compensated real power Δph and instantaneous compensated imaginary power ΔQh via the bypass filter 24, respectively. As shown in FIG. 7, the bypass filter 24 has a function of cutting off the low frequency range below the frequency fp for the instantaneous real power and the frequency fq for the instantaneous imaginary power. has. The reason for this characteristic is that power system disturbances such as flicker are caused by fluctuating reactive currents, harmonic currents, unbalanced currents, etc., so it is necessary to compensate for a certain amount of fundamental active current and fundamental reactive current. This is because there is no need to do so.

To compensate for the instantaneous actual power, an energy storage element is required in the fault current compensator. For example, the rectifier 6 in FIG.
If the power conversion device consisting of the self-excited inverter 7 is equipped with a capacitor or an accelerator,
The capacitor or accumulator functions as an energy storage element, but a large capacitor or accumulator that can store a large amount of energy makes the power converter large and expensive. Therefore, as shown in the filter characteristics of Fig. 7, the cutoff frequency fp of the bypass filter for instantaneous real power is set to a higher value than the cutoff frequency fq of the bypass filter for instantaneous imaginary power, and the coordination between the compensation target and the equipment capacity is is measured.

The instantaneous compensated real power Δph and instantaneous compensated imaginary power ΔQh obtained through the bypass filter 24 are converted into an instantaneous actual power command Ph* and an instantaneous imaginary power command Qh' by passing through the proportional gain amplifier 25, and are further converted into a current command The signal is input to the calculation unit 26. Note that the cutoff characteristic of the bypass filter 24 and the proportional gain of the amplification section 25 are determined by the fault current generated by the load to be compensated and the performance of the power converter.

In the current command calculation unit 26, each phase current command 1 cu' I cv'', I cw' is calculated based on the instantaneous actual power command Ph* and the instantaneous imaginary power command Qh* according to the following equation.
(representatively indicated as ■c* in the figure) is required.

The current control system 27 is configured so that the output current of the inverter 7, that is, the compensation current Ic detected by the current detector 52, matches the current command lc* determined by equation (13).
and controls the fault current compensator 5 via the PWM control system 28.

(Problems to be Solved by the Invention) Assume that the load 2 in FIG. 5 is an arc furnace. Arc furnaces are highly variable loads and generate large amounts of unbalanced current. This unbalanced current contains a large amount of fundamental wave anti-phase components.

The load current Ih in Fig. 5 is a 0th order negative phase harmonic type...(
13) Assuming that I hu= J”Z In sin (n (IJ
t-φ)... (14) Ihv"v'T In・sin (n ωt +2/
3 yr-φ)... (15) Ihv"JfuIn0sin (nωt-2/3 y
r−φ)... (16) Then, the instantaneous real power ph and the instantaneous imaginary power Qh are Ph −−('I In−cos l(n +1 )
(JJ t−φ)... (17) Qh −−v”JIn・sin l(n+1) ωt−
φ)... (18) The instantaneous real power ph and instantaneous imaginary power Qh for the reverse phase component of the fundamental wave are n in equations (17) and (18).
As =1, Ph--,, /□11・cos (2ωt-φ)...
(19) Qh −−f d+ 1・sln (2ωt−φ)・・
・(20) becomes. In Equations (9) and (10), by considering the positive phase component of the third harmonic and substituting n-3, we get Ph −J13・cos (2(JJ −φ)・
・・(21) Qh −f d I3・cos (2ωt −φ)・・・・
(22) Therefore, the instantaneous real power ph and the instantaneous imaginary power Qh of equations (19) to (22) each have the same order, and the control device shown in FIG. 6 cannot separate and compensate for both. Furthermore, in the filter characteristics shown in FIG. 7, all high-order harmonic components are included as the instantaneous real power command and the instantaneous imaginary power command.

Due to constraints such as the capacity and responsiveness of power converters, when it is desired to compensate for a specific fault current, such as fundamental wave reverse phase generated by an arc furnace, conventional fault current compensators cannot compensate. The problem was that I couldn't do it.

Therefore, it is an object of the present invention to provide a fault current compensator capable of compensating for a specific fault current, for example, a negative sequence current component across a sample.

[Structure of the invention]

(Means for Solving the Problem) In order to achieve the above object, the present invention provides a fault current compensation device that compensates for a fault current included in a load current flowing in a power system with a compensation current supplied from a power conversion device. , current detection means for detecting positive-sequence reactive components and negative-phase components of the fundamental wave included in the load current, and power conversion by weighting the positive-sequence reactive components and negative-phase components of the fundamental wave detected by the current detection means. The present invention is characterized by comprising current command calculation means for calculating a current command for the device.

(Function) According to the above configuration, the positive phase reactive component and the negative phase component of the fundamental wave included in the load current are detected, and the positive phase reactive component and negative phase component of the fundamental wave are weighted and applied to the power converter. Since the current command is calculated, it is possible to achieve optimal design of device capacity, responsiveness, etc. by compensating only the desired component among both components.

(Embodiment) FIG. 2 is a block diagram showing an embodiment of the present invention in a format that is easy to compare and contrast with the conventional device shown in FIG. Second
In the figure, the three-phase/
It is assumed that the two-phase conversion section 21, the instantaneous power calculation section 23, the amplification section 25, and the current command calculation section 26 have substantially the same configurations as those with the same reference numerals in FIG. 6, respectively. Here, instead of the three-phase/two-phase converter 22 in FIG.
An L circuit 30 is provided, and a low pass filter 31 is provided in place of the bypass filter 24. Second
FIG. 1 shows the block diagram in more detail.

As shown in FIG. 1, the PLL circuit 30 actually consists of two PLL circuits 30A and 30B. The PLL circuit 30A is phase-locked to the positive phase component of the fundamental wave of the system voltage Vs, and
It is assumed that the LL circuit 30B is phase-locked to the fundamental wave velocity phase of the system voltage Vs. Regarding the instantaneous actual power,
By setting the proportional gain in the amplification section to zero, it can be easily excluded from the compensation target. As shown in FIG. 3, it is assumed that the low-pass filters 31A and 31B have a characteristic of cutting off a high frequency range equal to or higher than the cutoff frequency fc.

In FIG. 1, the path of instantaneous actual power is omitted.

For fundamental wave reverse phase, load current rh is (14) to (1
In formula 6), n-1 is 1 hu -(2-1
1 sin (ωt-φ) - (23) I hv-J 1 sin Cωt + 2/ 3 yr-φ)...
・(24) Ihv-fll 1sin ((IJ t-2/3 w
-φ)...(25) Substitute these into equation (1) to perform three-phase/two-phase conversion.

1 ha-('I I 1sin (ωt-φ) −
(26) Ihβ−f1tcos (ω is one φ)...
(27) The output of the PLL circuit 30B is Vsap, Vs
If IIp, Vsffp −5in (IJ t
−(28)Vsβp −cos ωt
...-(29) Substituting equations (26) to (29) into equation (3), Ph -fll lCo5 φ-(30)
Qh - Seed 1 □ S10 φ
... The DC component is obtained as (31).

In FIG. 1, the proportional gain k of the amplifier sections 25A and 25B
As an example of weighting a, k and b, 1≧
When ka > kb, the amount of compensation for the fundamental wave positive phase reactive component becomes larger than the fundamental wave velocity phase component. In other words, the former will take priority over the latter. In this way, it becomes possible to adjust the DC energy fluctuations of the self-excited inverter shown in FIG. Generally, when suppressing flicker generated from an arc furnace, it is not necessary to compensate for 100% of the power fluctuation, but an appropriate amount is controlled as a degree of compensation based on the flicker regulation value. Therefore, as mentioned above, if the degree of compensation for the fundamental wave reactive component is increased and the degree of compensation for the fundamental wave velocity phase component is decreased, and the overall compensation is performed, the variation in the instantaneous actual power due to the negative phase component is suppressed. Energy storage N of energy storage elements (capacitors and/or accelerators) in power converters
iA can be reduced, and economical design of the entire device can be achieved.

Note that the amplifying sections 25A and 25B (generally referred to as 25 in FIG. 1) are a low-pass filter 31 in the illustrated embodiment.
Although it is provided immediately after A and 31B, it may be provided anywhere in the control system. For example, as shown in FIG. 4, it may be provided after the current command calculation section 26.

〔Effect of the invention〕

As described above, according to the present invention, by specifying the instantaneous imaginary power for the positive phase of the fundamental wave, the instantaneous real power for the velocity phase of the fundamental wave, and the instantaneous imaginary power as compensation targets, and detecting these separately, The capacity and responsiveness of the power conversion device can be optimally designed.

Block diagram showing a modified embodiment regarding the arrangement of the width portion, No. 5
Figure 6 is a circuit diagram of a power system equipped with a fault current compensation device.
The figure is a block diagram of the main parts of a conventional fault current compensator.
This figure is a characteristic diagram showing the characteristics of the bypass filter used in the compensation device of FIG. 6.

1...AC power supply, 2...power system, 3...load,
4...Transformer, 5...Fault current compensator, 6...
Rectifier, 7...Self-excited inverter, 8...Control device, 21...3-phase/2-phase conversion section, 23, 23A, 23B
... Instantaneous power calculation section, 25.25A, 25B ... Amplification section, 26° 26A, 26B ... Current command calculation section, 3
0A, 30B...PLL circuit, 31A, 31B...
Low-pass filter, 51.52...Current detector.

[Brief explanation of the drawing]

Claims (1)

[Scope of Claims] A fault current compensator that compensates a fault current included in a load current flowing in a power system with a compensation current supplied from a power converter, comprising: The current detecting means detects a negative phase component, and the current command calculating means calculates a current command for the power conversion device by weighting the positive phase reactive component and the negative phase component of the fundamental wave detected by the current detecting means. A fault current compensator characterized by: