JPH06274237A - Device for compensating reactive power for single phase - Google Patents

Abstract

PURPOSE:To compact a filter capable of reducing the generation of higher harmonics and fixing the contents of each higher harmonic. CONSTITUTION:An inverter 2 having serial triple structure is connected to a system 1 through a reactor L1, the reactive power QL of a load and the reactive power Qi of the inverter 2 are detected and a deviation between both the reactive power signals QL, Qi is amplified by an amplifier 6. The amplifier result is converted into frequency by a voltage control oscillator 7, the frequency is divided by a counter 8 and a gate generating circuit 9 controls the inverter 2 at conduction width 120 deg.. If the reactive power QL is increased when the load has a delay phase, the frequency of the oscillator 7 is reduced, the inverter 2 is controlled by the delay phase, active power is allowed to flow from the system 1 into the inverter 2, DC voltage Ed and output voltage are changed, and the reactive power is controlled at Qi=QL. Since the inverter 2 is controlled by the conduction width 120 deg., the 3rd higher harmonic is not generated and the contents of higher harmonic in each order is fixed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single-phase reactive power compensator for compensating the reactive power generated by an electric vehicle or the like.

[0002]

2. Description of the Related Art A reactive power compensator has an inverter 2 connected to a power system 1 via a reactor L as shown in FIG. 5, and an inverter voltage V _I in phase with a system voltage V _S as shown in FIG. As a result, the reactive power is compensated by controlling its size.

(1) If the inverter voltage V _I has the same phase and voltage as the system voltage, the current I does not flow between the inverter 2 and the system 1.

(2) The phase is the same and the inverter voltage V _I
Is lower than the system voltage V _S , as shown in FIG. 6A, V _S = V _I + ΔVx, so ΔVx = jωL ·
I, I = -j (ΔVx / ωL) to the inverter current I
Is a current delayed by 90 ° from the voltage phase. That is, the delayed reactive power flows into the inverter 2, and the inverter equivalently functions as an inductance to function to compensate the advanced reactive power of the load of the system 1.

(3) When the phase is the same and the inverter voltage V _I is higher than the system voltage, as shown in FIG.
_{Since S} = V _I −ΔVx, −ΔVx = jωL · I, I
= J (ΔVx / ωL), the current I of the inverter is 90 ° ahead of the voltage phase.

That is, since the leading reactive power flows into the inverter 2, the inverter equivalently functions as a capacitance and can compensate the delayed reactive power of the load of the system 1.

However, by raising or lowering the inverter 2 voltage V _I relative to the system voltage V _S , it becomes possible to compensate for the delayed and advanced reactive power.

Conventionally, small capacity, high efficiency, low distortion, low cost and high reliability have been required for large capacity converters of several thousand KVA or more. Therefore, a GTO element (gate turn-off thyristor) is generally widely used as a switching element used in a large capacity converter.

However, there is a separately-excited inverter type static var compensator (SVC) using a thyristor as a device for compensating the reactive power of a single-phase large power load such as an electric vehicle. Excited inverter type single-phase reactive power compensator is not yet available.

There is an application of a self-excited inverter type reactive power compensator (SVC) for a three-phase circuit, which has a proven track record as a self-excited inverter type single-phase reactive power compensator, to a single-phase circuit. When a large-capacity conversion device is configured by using a GTO element for this SVC, it is necessary to reduce the amount of harmonics and improve efficiency. Therefore typically multiplexed square wave voltage V ₁ ~V ₃ single machine inverter 2 ₁ to 2 ₃ of the series single-phase triple inverter 2 shown in FIG. 2 (a) in the transformer TR ₁ to Tr _3, further In order to reduce the snubber loss which increases in proportion to the GTO switching circuit, the switching circuit is held as much as possible once or several times in one cycle.

To control the amount of reactive power, the output voltage of the inverter may be adjusted, but the PWM method is generally adopted as the output voltage adjusting method.

The loss as shown in FIG. 7 is minimized 1
When the pulse PWM method is adopted, the third high frequency is not generated in the 120 ° flow width, but if the flow width for changing the voltage is 120 ° or more or 120 ° or less, the third harmonic is generated. Resulting in. (The third harmonic does not occur in a three-phase circuit).

Therefore, there is a 3-pulse PWM system as shown in FIG. 8 as a system in which the third harmonic is not generated and the number of switching circuits is small. The third harmonic components a, a'and b, b'of the waveform of the output voltage RS have the same area and are on the plus side and the minus side.
The harmonic component becomes 0 and does not appear in the output waveform.

[0014]

However, when the single-phase triple-voltage self-exciting inverter (FIG. 2 (a)) adopts the n-pulse PWM system (n = integer of 2 or more), there are the following drawbacks. .

(1) The snubber loss is n compared to the one-pulse system.
Efficiency is reduced.

(2) When the 120 ° flow width is constant, the order of the generated harmonics is the same, but the content is large.

(3) When the output voltage is adjusted, the flow width is changed, but when the harmonic content is required because the content of the harmonic changes with the change in the flow width, the harmonic filter needs to be changed. Design becomes difficult.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to reduce the number of times of switching, improve efficiency, reduce the generation of harmonics, and reduce harmonics of each order. It is an object of the present invention to provide a single-phase reactive power compensator in which the wave content is constant and the filter can be easily downsized.

[0019]

In order to achieve the above object, a single-phase reactive power compensator according to the present invention is a large-capacity single-phase reactive power compensator using a self-excited inverter. Is a serial multiplex configuration, and the control circuit compares the reactive power of the load with the output of the inverter to adjust the phase difference of the output voltage of the inverter with respect to the system voltage phase and to fix the conduction angle of the inverter constant. It was done.

A single-phase reactive power compensator for suppressing voltage fluctuations is a large-capacity single-phase reactive power compensator for suppressing voltage fluctuations by generating reactive power by a voltage-type self-exciting inverter. The main circuit has a serial multiplex structure, and the control circuit compares the power supply voltage setting value with the power supply voltage detection value to adjust the phase difference of the output of the inverter with respect to the phase angle of the power supply and to keep the conduction angle of the inverter constant. It is configured to be fixed.

[0021]

Since the main circuit of the inverter has a serial multiplex structure and the flow angle is fixed and controlled, the harmonic content rate of the output voltage waveform of the inverter with respect to the fundamental effective value can be controlled to be constant.

Since the phase difference of the output voltage of the inverter with respect to the grid voltage phase is adjusted by comparing the reactive power signal of the inverter with the load reactive power signal of the grid, the active power flowing from the grid to the inverter is controlled and the DC voltage is controlled. Is changed to change the output voltage and the reactive power of the inverter is controlled to be equal to the reactive power of the load.

Further, in the case of the reactive power compensator for suppressing the voltage fluctuation, since the set value of the power supply voltage and the power supply voltage signal are compared, the active power flowing from the grid is controlled and the direct current voltage is varied to disable the reactive power. Electric power is generated and controlled so that the power supply voltage becomes equal to the set power supply voltage.

[0024]

Embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 In FIG. 1, 1 is a power system (power source), 2 is a series single-phase triple inverter with a flow width of 120 ° connected to the system 1 via a reactor L ₁ (see FIG. 2), 3 Is the voltage transformer P
Reactive power detector for detecting a T ₁ and current transformers reactive power flows from the current ip flowing in the detected inverter CT ₁ system voltage detected by V _S and current transformer CT ₂ to the load and the inverter device of the system Q _L and Qi vessel.

[0026] 6 is disabled from a reactive power detector 3 power Q _L
Deviation amplifier for amplifying the difference between Qi and Qi, 7 is deviation amplifier 6
Of the voltage controlled oscillator 8 to which the output of is input to determine the phase of the inverter 2, 8 is a counter that divides the output of the voltage controlled oscillator 8, and 9 is the pulse width from the counter 8 that is input to the series single phase triple inverter 2 It is a gate generation circuit that outputs a gate signal of 120 °.

Next, the operation of this embodiment will be described with reference to the vector of FIG. The inverter 2 and the system 1 are transformers for multiplexing the inverter 2 (TR ₁ to TR _{3 in} FIG. 2),
If they are connected by a series reactor L ₁ etc. and the resistance component γ of these transformers and the series reactor is very small and can be ignored, the effective component current ip flowing from the system 1 to the inverter 2 is the voltage V _I of the inverter 2 and the system 1. And the phase angle θ of V _S , and the reactive power Qi flowing through the inverter 2 is determined by the voltage difference V _I −V _S between the inverter 2 and the grid 1.

If the flow width of the inverter 2 is constant, the relationship between the DC voltage Ed and the induced voltage V _I of the inverter 2 is directly proportional. Therefore, if the DC voltage Ed is controlled, the induced voltage V _I can be controlled. It becomes, it becomes possible to control the reactive power Q _L flowing into the first path. The deviation amplifier 6 takes a difference so that the reactive power Q _L of the system is a set amount and the reactive power Q _I of the inverter 2 is a detected amount, and amplifies the difference and outputs it to the voltage controlled oscillator 7 which determines the phase of the inverter. To do.

[0029] Thus when the reactive power Q _L is the delay power load, a direction to decrease the output voltage of the deviation amplifier 6, reduces the frequency of the voltage controlled oscillator 7, the operating frequency of the inverter 2 is delayed from the phase of the low strain is controlled to, because it is controlled to raise the DC voltage Ed captures real power from the grid, the inverter 2 is the effective power uptake from the always reactive power Q _L = line so as to maintain the DC voltage such that Qi invalid The power can be controlled.

At this time, the serial single-phase triple inverter 2 is controlled by a gate signal having a distribution width of 120 °, which is generated by the gate generator 9 by dividing the output of the voltage controlled oscillator 7 by the counter 8. Therefore, the power is taken in to compensate the reactive power so that the fundamental wave content rate and the harmonic wave content rate become constant.

Embodiment 2 Referring to FIG. 4, 4 is a power supply voltage detector connected to a voltage transformer PT ₁ for detecting a power supply (system) voltage V _S , 5 is a power supply voltage setting device, and 6 is a power supply voltage detector 4 Source voltage V _{S from}
Is a deviation amplifier that amplifies the difference between the voltage setting Vset from the power supply voltage setting device 5. Since the other configurations are the same as those of the first embodiment (FIG. 1), the same parts are designated by the same reference numerals and the duplicate description will be omitted.

Next, the operation of this embodiment will be described. Since the flow width of the inverter 2 is fixed at 120 ° by dividing the output of the voltage oscillator 6 by the counter, the DC voltage Ed and the device output voltage V _I have a positive relationship, so the DC voltage Ed is If controlled, the amount of reactive power flowing into the power supply 1 can be adjusted, and thus the fluctuation of the power supply voltage V _S can be suppressed.

The deviation amplifier 6 receives the power source voltage V from the detector 4.
Amplify the difference between _S and the voltage setting Vset from the setting device 5,
The output is output to the voltage controlled oscillator 7 which determines the phase of the inverter 2.

However, when the inverter 2 supplies the delayed reactive power to the power supply 1 to increase the power supply voltage V _S , the output of the deviation amplifier 6 decreases, the frequency of the voltage controlled oscillator 7 decreases, and the phase of the inverter 2 is changed to the power supply. It is controlled so as to be delayed from the voltage, the effective voltage is taken in from the power supply 1, the DC voltage Ed is increased, and the reactive power Q _I is supplied from the inverter 2 to the power supply 1 as a DC voltage such that the voltage V _S = Vset. Control _S constant.

In this case, the serial single-phase inverter 2 is the same as the first embodiment.
Similarly, since the distribution width is controlled at 120 °, the fundamental wave content rate and the harmonic content rate are constant.

[0036]

Since the present invention is configured as described above, it has the following effects.

(1) The number of times of switching of each inverter constituting the multiple inverter is once per cycle, so that the efficiency of the inverter can be improved.

(2) The content of each order of the high frequency generated by the inverter is constant, and the filter design is easy.

(3) The generated high frequency is smaller than that of the conventional method, and the filter can be downsized.

(4) In the second aspect of the present invention, when the feeder wire of the railway is long, the impedance drop of the feeder wire can be compensated by providing a device at the end of the feeder wire.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an inverter control system according to a first embodiment of the present invention.

FIG. 2A is a configuration diagram showing a main circuit of a series single-phase triple inverter. (B) is a vector diagram of a single inverter of the same inverter.

FIG. 3A is an explanatory diagram showing current flows of an inverter and a system. (B) is a vector diagram of the inverter and the system.

FIG. 4 is a configuration diagram showing an inverter control system according to a second embodiment.

FIG. 5 is a circuit diagram illustrating the principle of reactive power compensation.

6 (a) and 6 (b) are vector diagrams when the grid and the inverter are in phase.

FIG. 7 is an explanatory diagram of a 1-pulse PWM 120 ° flow method,
(A) is a circuit diagram of an inverter, (b) is a voltage waveform diagram of an inverter.

8A and 8B are explanatory diagrams of 3-pulse PWM, FIG. 8A is a circuit diagram of an inverter, and FIG. 8B is a voltage waveform diagram of the inverter.

[Explanation of symbols]

1 ... line (power supply, the feeder) 2 ... inverter 2 ₁ to 2 ₃ ... single machine inverter 3 ... reactive power detector 4 ... supply voltage detector 5 ... power supply voltage setter 6 ... deviation amplifier 7 ... voltage-controlled oscillator 8 ... counter 9 ... gate generator V _S ... line (power supply, the feeder) voltage V _I ... inverter voltage Ed ... DC voltage ip ... inverter active current Q _I ... inverter reactive power Q _L ... load reactive power L ₁ ... reactor

Claims (2)

[Claims] 1. A large-capacity single-phase reactive power compensator using a self-excited inverter, wherein the main circuit of the inverter is configured as a series multiplex, and the control circuit compares the reactive power of a load with the output of the inverter. The output voltage of the inverter is controlled by adjusting the phase difference of the output voltage of the inverter with respect to the grid voltage phase and by fixing the conduction angle of the inverter to a constant value. A reactive power compensator characterized by compensating for reactive power. 2. A large-capacity single-phase reactive power compensator that suppresses voltage fluctuations by generating reactive power by a voltage-type self-excited inverter, wherein a main circuit of the inverter has a serial multiplex configuration, and its control circuit is a power supply. It controls the active power flowing from the grid to the inverter by comparing the voltage setting value and the detected value of the power supply voltage to adjust the phase difference of the output of the inverter with respect to the phase angle of the power supply and to fix the conduction angle of the inverter constant. The single-phase reactive power compensator is characterized by varying the DC voltage to generate reactive power so that the power supply voltage fluctuation is constant.