KR100683430B1 - System for Compensating Power Quality of Feeding equipment of Electric Railway - Google Patents

Abstract

The power quality compensating apparatus of the present invention comprises: a) a first inverter connected in parallel to a power source to compensate for harmonic currents and maintaining a constant DC link voltage, b) a second inverter connected in series to a power source to compensate for a voltage drop; c) a DC link voltage source shared by the first inverter and the second inverter to supply the DC link voltage to the first inverter and the second inverter, and d) a harmonic current compensation of the first inverter and a maintenance operation of the DC link voltage. It includes a control unit for controlling the voltage drop operation of the inverter. The power quality compensator according to the present invention not only improves control efficiency by sharing a DC link voltage between the parallel inverter and the serial inverter, but also compensates harmonic currents and provides effective power to compensate for voltage drop and improve the power factor. We can plan.

Description

System for Compensating Power Quality of Feeding equipment of Electric Railway}

1 shows the basic circuit of voltage compensation.

2 is for explaining a compensation vector according to the operation of the general SVC or STATCOM.

3 is a block diagram of a power quality compensation device according to the present invention.

4 is a block control diagram of a control unit for controlling a parallel inverter according to the present invention.

5 is a block control diagram of a controller for controlling a serial inverter according to the present invention.

Explanation of symbols on the main parts of the drawings

200: Scott transformer 210215: electric vehicle

310,330: parallel inverter 320,3400: serial inverter

350: DC link voltage source 410: PLL circuit

420 sine wave generator

The present invention relates to a power quality compensating apparatus, and more particularly, to a power quality compensating apparatus of an electric railway power supply system for compensating a voltage drop generated in a power feeding system.

The term power quality is used to refer to variations in voltage, current, frequency, etc. in the power system. In the past, power devices could operate well even when voltage, current, and frequency fluctuated in a relatively wide range, but many power devices used in recent industrial sites have many electronic devices for controlling, so that frequency, voltage, or current There is an increasing number of cases that cause a malfunction due to a very sensitive response to such a change. Accordingly, power quality problems in various power devices or power systems are gradually increasing.

Power quality issues are no exception to electrical railways. The vehicle load of electric railways continues to increase due to shortening of the driving time, high speed, and traction. This causes a large voltage drop because more current flows in the feeder line. The voltage drop not only hinders normal operation of the electric railway, but also causes voltage unbalance on the three-phase power side.

In the case of electric railway, when voltage unbalance due to load unbalance occurs, the voltage of one phase of the line voltage decreases, and the voltage of the other phase rises, causing damage by low voltage and high voltage at the same time. Damage can occur from the side.

As a solution to this, voltage compensation has been made by installing a power capacitor so far, but this has a disadvantage in that the response speed is slow and a transient phenomenon occurs due to the mechanical switching method. Afterwards, a power quality compensator was developed to quickly and accurately compensate for reactive power in the power system by connecting thyrister as a high-speed switch and connecting it to a capacitor and a reactor, which are passive elements. This is a static var compensator (SVC). to be.

SVC is used for the purpose of improving voltage stability, improving power factor, preventing flicker, and compensating for phase imbalance because of its low failure rate, easy maintenance and excellent dynamic performance. However, SVC has a disadvantage in that the compensation performance decreases in the form of squares for the voltage drop width in the V-I characteristic. In order to solve this problem, recently, inverter type reactive power compensation devices such as STATCOM (STATCOM) have been actively researched due to the development of power electronic technology.

Unlike SVC, STATCOM uses a synchronous voltage source with a semiconductor switch to quickly control the magnitude and phase of the output voltage. STATCOM consists of a voltage source inverter, a DC capacitor for energy storage, and a control circuit. The output voltage is continuously controlled to match the line voltage and phase.

STATCOM has high operation reliability, easy operation and maintenance, low vibration noise, and can continuously control reactive power from advanced reactive power to ground reactive power. In addition, since the installation area is as small as 70% of the SVC, and the opening and closing control can be performed at any time, the reactive power compensation is faster than the SVC, and the V-I characteristic is superior to the SVC.

1 illustrates a basic circuit of voltage compensation, and FIG. 2 illustrates a compensation vector according to an operation of a general SVC or STATCOM. In order to compensate the voltage drop due to the impedance of the feed line and the electric vehicle, the compensation device is usually located in the feed section. The compensation vector at this time is as shown in FIG.

In the vector diagram before compensation of FIG. 2, the voltage on the load side decreases due to the voltage drop caused by the impedance of the line. In order to compensate for this, the power quality compensator SVC or STATCOM causes the forward compensation current (IC) to flow on the line to separate the vector of the power supply current (I) from the load current (IL). The vector is newly set, and it can be seen from the vector diagram after the compensation that the voltage of the line can be compensated.

However, in the case of such a compensation device, when a large voltage drop occurs, the current compensating capacity increases accordingly since the compensating current IC of the forward phase must flow considerably. In addition, since the voltage compensation effect using the phase compensation current (IC) is seen, there is a disadvantage that direct compensation for voltage disturbance is also not achieved.

The present invention is to solve the problem of the conventional power quality compensation device, to provide a power quality compensation device that can improve not only the voltage drop compensation but also the power factor by increasing the control efficiency for voltage compensation and supplying active power. It is done.

In order to solve such a problem, the power quality compensator of the present invention includes: a) a first inverter connected in parallel to a power source to compensate for harmonic currents and maintaining a constant DC link voltage, b) a voltage drop connected in series with the power source. A second inverter for compensating for the voltage, c) a DC link voltage source shared by the first inverter and the second inverter to supply the DC link voltage to the first inverter and the second inverter, and d) a harmonic current compensation and DC link voltage of the first inverter. It includes a control unit for controlling the operation of maintaining and the voltage drop operation of the second inverter.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

3 is a configuration of a power quality compensation device according to the present invention. As shown in FIG. 3, the power quality compensator according to the present invention includes parallel inverters 310 and 330, series inverters 320 and 340, and a DC link voltage source 350.

The power quality compensating device according to the present invention has a structure in which the parallel inverters 310 and 330 and the serial inverters 320 and 340 share a DC link voltage source 350 that functions as a DC link. The parallel inverters 310 and 330 and the serial inverters 320 and 340 are installed on the secondary side of the Scott transformer 200.

The series inverters 320 and 340 compensate for the voltage by injecting a compensation voltage against the voltage disturbance of the feed line and the voltage drop caused by the electric vehicles 210 and 215.

The parallel inverters 310 and 330 compensate for the harmonic currents generated in the feeder lines due to the electric vehicles 210 and 215 serving as nonlinear loads, and the voltage of the DC link voltage source to cover the active power according to the voltage compensation of the series inverters 320 and 340. Vdc) is kept constant.

4 is a block control diagram of a control unit for controlling a parallel inverter according to the present invention. The parallel inverters 310 and 330 and the serial inverters 320 and 340 of the present invention are controlled by the gate signal output from the controller. As described above, in order for the controller to output the gate signals for controlling the parallel inverters 310 and 330 and the serial inverters 320 and 340, phase angle calculation is necessary to find the operation reference points of the parallel inverters 310 and 330 and the serial inverters 320 and 340. For the phase angle calculation, the controller includes a phase locked loop (PLL) circuit 410.

The PLL circuit 410 of the present invention generates one voltage that forms 90 ° with the M phase through a 90 ° phase delay filter (not shown) of the M phase line voltage (VMS) of the Scott transformer 200. The phase angle is calculated by simulating the phase voltage as the voltage on the stationary coordinate with the 90 ° difference obtained through Park's transformation. This phase angle calculation is the same on the T phase side.

The sinusoidal wave generator 420 included in the controller uses a phase angle calculated by the PLL circuit 410 to generate a reference sinusoidal wave for controlling the parallel inverters 310 and 330 and the serial inverters 320 and 340. The phase angle obtained through the above process determines the reference frequency of the AC voltage, and the T phase also determines the reference frequency of the AC voltage through the same method.

The control unit controls the harmonic compensation current supply operation of the parallel inverters 310 and 330 and the voltage drop compensation operation of the serial inverters 320 and 340 by using the reference sine wave generated by the PLL circuit 410 and the sinusoidal wave generator 420 of the controller. .

Next, a process of maintaining a constant DC link voltage by the parallel inverters 310 and 330 will be described in detail with reference to FIG. 4.

The control unit of the present invention includes a PI (Proportional Integration) control unit 430 to maintain a constant DC link voltage (Vdc). The PI controller 460 calculates a VLOSS component using the calculated proportional gain kP and integral gain kI as shown in Equation 1 below.

V _LOSS = k _PI (V'dc-Vdc)

V'dc: Reference voltage of DC link voltage

Vdc: Measured DC Link Voltage

V _LOSS : compensation voltage of DC link voltage

kPI: Proportional Integral Gain by Proportional Gain and Integral Gain

In this case, the reference voltage V'dc of the DC link voltage refers to a voltage that the DC link voltage source 350 must constantly supply. In addition, the low pass filter 440 is for removing noise mixed in the measured DC link voltage.

The processor 450 extracts a current component from the VLOSS component and multiplies the extracted current component by a reference sine wave output from the sinusoidal wave generator 420 to maintain a constant DC link voltage. Outputs (Idc).

Next, a process of supplying harmonic compensation currents by the parallel inverters 310 and 330 will be described in detail with reference to FIG. 4.

In order for the parallel inverters 310 and 330 to supply the harmonic compensation current, an operation for detecting the synchronization point with the line using the actual line voltages V _MS and V _TS measured in the line is required. The operation 410 and the sinusoidal wave generator 420 are performed.

The reference sinusoid output from the sinusoidal wave generator 420 is multiplied by the appropriate gain K1 and compared with the measured line current I _ML , I _TL . The harmonic current I _H to be injected by the parallel inverters 310 and 330 is calculated according to the difference between the reference sinusoid and the measured line current I _ML and I _TL .

Next, a process of forming a gate signal for operating the parallel inverter will be described in detail with reference to FIG. 4.

The calculated harmonic current IH is added to the calculated current component Idc for controlling the DC link voltage to generate a reference current I '= I _H + Idc to be injected by the parallel inverters 310 and 330. The reference current I 'refers to a current that the parallel inverters 310 and 330 must inject in order to compensate for harmonic currents and maintain a constant DC link voltage.

Therefore, for the operation of the parallel inverter according to the present invention, the control unit forms a gate signal such that the output currents I _MF and I _TF of the butters 310 and 330 which are actually parallel become the reference current I '.

The reference voltage V ′ of the parallel inverters 310 and 330 is a line voltage V _MS , which is a difference between the reference current I ′ of the parallel inverters 310 and 330 and the output currents I _MF and I _TF of the parallel inverters actually measured. It can be obtained by adding to V _TS ), and the current control can be expressed as follows through the following equation (2) and (3).

At this time, the inductance L _PF is for converting a current component into a voltage component.

The controller of the present invention converts the current component into a voltage component as shown in Equation 3 because the parallel inverters 331 and 333 of the present invention are voltage inverters. Equation 3 shows that the operation of the control unit operates like a proportional control unit having a gain K ₄ .

The pulse width modulation (PWM) circuit unit 460 receives the reference voltage V ₁ ′ and outputs a gate signal to control the output of the parallel inverters 310 and 330. In response to the gate signal, the parallel inverters 310 and 330 output a current I _MF for maintaining the harmonic compensation current and the DC link voltage constant.

The control unit controls the output current I _MF of the parallel inverter to follow the reference current I 'by continuously comparing the output current I _MF of the parallel inverter with the reference current I'.

Next, a control process of the serial inverters 320 and 340 according to the present invention will be described in detail with reference to the accompanying drawings.

5 is a block control diagram of a controller for controlling a serial inverter according to the present invention.

A general electric railway power supply system supplies 55 kV through the Scott transformer 200 in a bus of 154 kV. At this time, if a situation such as instantaneous step-down of the supply power occurs due to an unscheduled line short circuit or ground fault on the bus side, the power quality compensator according to the present invention performs a compensation operation by itself to stabilize the electric vehicles 210 and 215. Ensure driving

In addition, the power quality compensation apparatus according to the present invention can perform a stable operation by supplying a voltage from the series inverters 320 and 340 when the voltage is momentarily lowered according to the start after the electric vehicle 210 or 215 is stopped.

The operation of the control unit will be described with reference to the M phase only.

The reference line voltage (V ' _MS ) on M shall be maintained at 55 kV. To this end, the PLL circuit unit 410 of the controller receives the measured line voltage V _MS of M phase and calculates a phase angle.

The PLL circuit unit 410 generates one voltage that forms an M phase line voltage (V _MS ) 90 ° with the M phase through a 90 ° phase delay filter (not shown), and then converts the three phase voltage into Park's conversion. Calculate the phase angle by simulating the voltage on the static coordinates with the 90 ° difference obtained. The sine wave generator 420 determines the reference frequency of the line voltage using the phase angle calculated by the PLL circuit 410 and outputs the reference sine wave. The controller then multiplies the gain K ₂ by the reference sine wave to form a reference line voltage (V ' _MS ).

Thereafter, the controller calculates a difference (V _SUPPLY = V ' _MS -V _MS ) between the reference line voltage V' _MS and the measured line voltage V _MS . This difference V _SUPPLY is substantially the voltage that the series inverters 320 and 340 should inject into the line. This determines whether the series inverters 320 and 340 should supply or absorb the effective voltage to the line.

The control unit performs a control operation for efficiently supplying the supply required voltage V _SUPPLY to be injected by the serial inverters 320 and 340. To this end, the controller obtains the difference (V _SUPPLY -V _MF ) between the required supply voltage (V _SUPPLY ) and the output voltage (V _MF ) of the series inverter, and the series inverters 320 and 340 properly supply the supply required voltage (V _SUPPLY ). Check whether there is a PI control unit 510, this difference (V _SUPPLY -V _MF ) to follow the desired value.

Since the amount of calculation that has passed through the PI controller 510 is a reference current value that the series inverters 320 and 340 should output to compensate for the voltage drop, the difference is calculated by comparing the output current I _MSF of the series inverters 320 and 340 and the difference. The result of multiplying the gain K ₃ and the required supply voltage V _SUPPLY is added to finally output a result value V ₂ ′ of the voltage to be output by the series inverters 320 and 340.

The pulse width modulation (PWM) circuit unit 460 receives the result value V ₂ ′ and outputs a gate signal to control the output of the serial inverters 320 and 340.

As such, those skilled in the art will appreciate that the present invention can be implemented in other specific forms without changing the technical spirit or essential features thereof. Therefore, the above-described embodiments are to be understood as illustrative in all respects and not as restrictive.

The scope of the present invention is shown by the following claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention. do.

Such a power quality compensation device according to the present invention, the parallel inverter and the serial inverter share a single DC link voltage not only improves the control efficiency, but also can compensate for harmonic currents and supply the active power to compensate for the voltage drop and power factor Improvement can be aimed at.

Claims (11)

In the power quality compensation device of a power supply system for supplying power to a non-linear load, A first inverter connected in parallel to the power supply to compensate for harmonic currents and to maintain a constant DC link voltage; A second inverter connected in series with the power supply to compensate for a voltage drop; A DC link voltage source shared by the first inverter and the second inverter to supply a DC link voltage to the first inverter and the second inverter; And And a control unit controlling a harmonic current compensation and a DC link voltage holding operation of the first inverter and a voltage drop operation of the second inverter. The method of claim 1, The power source is an M phase power source and a T phase power source converted from a 3-phase power source by a Scott transformer, And the first inverter is installed in each of the M-phase power and the T-phase power, and the second inverter is installed in each of the M-phase power and the T-phase power. The method of claim 1, The controller includes a PLL circuit part and a sine wave generator, The PLL circuit unit receives a measured line voltage and calculates a phase angle, and the sinusoidal wave generator generates a reference sinusoidal wave using the calculated phase angle. And the control unit calculates harmonic currents to be injected by the first inverter based on a result of multiplying the reference sinusoid by a proper gain and the measured line current. The method of claim 1, The control unit, Power quality compensation, wherein the first inverter calculates a compensation voltage for keeping the DC link voltage constant by using a difference between the reference voltage of the DC link voltage and the DC link voltage measured at the DC link voltage source. Device. The method of claim 4, wherein The control unit includes a processor, When the processor extracts a current component from the compensation voltage, the controller calculates a current to be supplied by the first inverter to multiply the extracted current component by a reference sine wave to maintain the DC link voltage constant. Power quality compensation device. The method of claim 4, wherein The control unit, The power quality compensation device, characterized in that for calculating the compensation voltage for the first inverter to maintain the DC link voltage constant using the following equation. V _LOSS = k _PI (V'dc-Vdc) V'dc: Reference voltage of DC link voltage Vdc: Measured DC Link Voltage V _LOSS : compensation voltage of DC link voltage k _PI : Proportional integral gain by proportional gain and integral gain The method of claim 1, The control unit, PLL circuit section, sine wave generator and processor, The first inverter is injected according to a result of multiplying a phase gain calculated using the line voltage measured by the PLL circuit unit and the sinusoidal wave generation unit with a reference sine wave generated using the phase angle and an appropriate gain and the measured line current. Calculate the harmonic current to be Calculating a compensation voltage for the first inverter to keep the DC link voltage constant by using a difference between the reference voltage of the DC link voltage and the DC link voltage measured at the DC link voltage source, Calculating a current to be supplied by the first inverter in order to keep the DC link voltage constant by multiplying a current component of the compensation voltage extracted by the processor with the reference sine wave, Generating a reference current to be injected by the first inverter by adding the calculated harmonic current and the calculated current to maintain the DC link voltage, The power quality of claim 1, wherein the reference voltage of the first inverter is calculated by adding the difference between the reference current and the output current of the first inverter to be measured and the line voltage to generate a gate signal for controlling the first inverter. Compensator. The method of claim 7, wherein The reference voltage is a power quality compensation device, characterized in that calculated through the following equation.

V ₁ ': reference voltage, V _MS : measured line voltage, I': reference current, I _MF : output current of first inverter, L _PF : inductance for converting current components into voltage components, K ₄ : gain The method of claim 1, The controller includes a PLL circuit part and a sine wave generator, The PLL circuit unit receives a measured line voltage and calculates a phase angle, and the sinusoidal wave generator generates a reference sinusoidal wave using the calculated phase angle. And the control unit forms a reference line voltage through the reference sine wave and calculates a supply necessary voltage to be injected by the second inverter according to the difference between the reference line voltage and the measured line voltage. The method of claim 9, The control unit obtains a difference between the supply necessary voltage and the output voltage of the second inverter, and allows the difference to follow a desired value through a PI control unit. And forming a gate signal for controlling the second inverter using a control result for controlling the current output from the second inverter using the amount of computation passed through the PI controller. The method according to claim 3 or 7 or 9, The phase angle calculation of the PLL circuit part may generate a virtual voltage forming 90 ° with one line voltage, and calculate the phase angle by virtualizing the virtual voltage with the voltage on the static coordinate obtained through the conversion of the three-phase voltage. Power quality compensation device.

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