CN111371103A - Capacitance split type static compensator circuit with zero sequence voltage-sharing bridge arm and method - Google Patents

Abstract

The invention discloses a capacitor split type static compensator circuit and method with a zero-sequence voltage equalizing bridge arm, and relates to a compensation technology for a three-phase low-voltage power distribution system. A static compensator circuit, including a low-voltage distribution network, a capacitor-split static compensator, a zero-sequence equalizing inductor L ₀ , and a zero-sequence equalizing bridge arm; the zero-sequence equalizing bridge arm is connected to the positive bus of the static compensator Between p and negative busbar n; the zero-sequence balancing inductor L ₀ is connected between the midpoint o 1 of the split capacitor C ₁ and the split capacitor C ₂ and the midpoint o ₂ of the zero-sequence balancing bridge arm _; the two split _The midpoint o1 _of capacitors _C1 and C2 is connected to the neutral point of the low voltage distribution network. The capacitor-split static compensator circuit with zero-sequence equalizing bridge arms and the equalizing method of the present invention solve the problems of voltage imbalance and fluctuation on two split capacitors caused by zero-sequence compensation current.

Description

A capacitive split static compensator circuit and method with zero-sequence equalizing bridge arm

technical field

The invention relates to a three-phase low-voltage power distribution system compensation technology, in particular to a capacitor-split static compensator circuit with a zero-sequence voltage equalizing bridge arm for a three-phase four-wire low-voltage power distribution system and a voltage equalizing method.

Background technique

At present, in the three-phase AC power distribution system, most electrical equipment not only draws active power from the grid to do work, but also absorbs a large amount of reactive power from the grid to maintain the normal operation of the inductive equipment. These reactive powers do not do work, but are exchanged back and forth between the power supply and the electrical equipment through the power grid, which increases the load current flowing through the power grid, and thus produces significant power loss in the power grid, reducing the transmission and distribution of the power grid. electrical efficiency. To this end, the power standard requires power users to compensate the reactive power required by the electrical equipment through the nearby reactive power compensation equipment, reduce the reactive power demand for the power supply, and achieve the purpose of energy saving and consumption reduction in the power grid.

Static compensator is a new type of advanced dynamic reactive power compensation equipment based on power electronic technology. In low-voltage power distribution systems, static compensators are divided into three-phase three-wire static compensators and three-phase four-wire static compensators. The three-phase three-wire static compensator is mainly used in industrial power applications where three-phase electrical equipment is the main component. It cannot compensate for the zero-sequence reactive power generated by single-phase loads. For civil or commercial buildings where single-phase electrical equipment is the main electrical equipment, or for industrial electrical applications where single-phase electrical equipment occupies a certain proportion, in order to compensate for the zero-sequence reactive power generated by single-phase electrical equipment, it is necessary to use Three-phase four-wire static compensator.

Capacitor split static compensator is a kind of three-phase four-wire static compensator, but the zero-sequence current of the compensation output will cause serious voltage imbalance on the two split capacitors on the DC side of the static compensator and large fluctuations in the split capacitor voltage , which will adversely affect the performance of the compensator and the life of the split capacitor, and limit the application of the capacitive split static compensator.

Therefore, it is necessary to propose a voltage equalization circuit of two split capacitors on the DC side of a capacitor-split static compensator and a control method thereof.

SUMMARY OF THE INVENTION

The main purpose of the present invention is to provide a capacitor split static compensator circuit and method with zero-sequence voltage balancing bridge arms, which can solve the problem of voltage imbalance and fluctuation on two split capacitors caused by zero-sequence current.

According to one aspect of the present invention, a capacitor-split static compensator circuit with a zero-sequence voltage equalizing bridge arm is provided, including a low-voltage distribution network, a capacitor-split static compensator, a zero-sequence voltage equalizing inductance L ₀ , a zero-sequence voltage equalizing inductance L 0 , sequence equalizing bridge arm;

The zero-sequence balancing bridge arm is connected between the positive busbar p and the negative busbar n of the static compensator;

The zero-sequence balancing inductor L ₀ is connected between the midpoint o 1 of the split capacitor C ₁ and the split capacitor C ₂ and the midpoint o ₂ of the zero-sequence balancing bridge arm _;

The midpoint o1 _of the _two split capacitors _C1 and C2 is connected to the neutral point of the low voltage distribution network.

Further, the static compensator adopts a three-phase two-level converter topology, including six switch tubes T ₁ , T ₂ , T ₃ , T ₄ , T ₅ , T ₆ ; wherein the switch tubes T ₁ , T ₂ In series connection, switch _{tubes T 3} and T ₄ are connected in series, and switch tubes T ₅ and T ₆ are connected in series _.

Further, the zero-sequence voltage equalizing bridge arm includes two switch tubes T ₇ and T ₈ , and the switch tubes T ₇ and T ₈ are connected in series and form a positive electrode p, a negative electrode n and a midpoint o ₂ .

According to yet another aspect of the present invention, a method for a capacitive split static compensator with a zero-sequence balancing bridge arm is provided, comprising the following steps:

Step 1: The expected value of the neutral line current i _n of the three-phase four-wire static compensator is obtained by summing the three-phase compensation current command value of the static compensator:

Among them, i _a.ref , i _b.ref and i _c.ref are the command values of the compensator A-phase, B-phase and C-phase compensation current respectively, and i _n.exp is the expected value of the neutral line current of the compensator;

At the same time, the expected value of the neutral line current is used as the command value of the zero-sequence balancing inductor current i ₀ :

；

;

Among them, i _n.exp is the expected value of the neutral line current of the compensator, and i _0.ref is the command value of the equalizing inductor current;

Step 2: Subtract the zero-sequence equalizing inductor current command value and the zero-sequence equalizing inductor current actually detected to obtain the zero-sequence current compensation error and send it to the tracking control link of the zero-sequence current; the tracking control can use proportional Integral control, proportional resonance control or repetitive control; the output of the tracking control link is output to the comparator after being limited by the limiter;

Step 3: The comparator compares the limited control signal of the current tracking control with the bipolar triangular carrier, and outputs PWM switching signals of 0 and 1; when the value of the control signal is greater than the value of the triangular carrier signal, the output is 1, otherwise output is 0;

Step 4: The switching signal output by the comparator is sent to the PWM driving circuit to form a driving signal that can be directly applied to the gate of the switching device to control the opening or closing of the switching device; one signal output from the comparator is driven by PWM and sent to zero The upper switch tube T ₇ of the sequence balancing bridge arm, the other signal output by the comparator is driven by the inverter and PWM and then sent to the lower switching tube T ₈ of the zero-sequence balancing bridge arm.

Advantages of the present invention:

The capacitor-splitting static compensator circuit with zero-sequence equalizing bridge arms of the present invention includes a low-voltage distribution network, a capacitor-splitting static compensator, a zero-sequence equalizing inductor, a zero-sequence equalizing bridge arm, and a zero-sequence equalizing bridge. The arm is connected to the positive bus (p) and the negative bus (n) of the static compensator, and the zero-sequence balancing inductor is connected between the midpoint (o ₁ ) of the split capacitor and the mid-point (o ₂ ) of the zero-sequence balancing bridge arm , while the split capacitor midpoint (o ₁ ) is connected to the neutral point of the low-voltage distribution network. The capacitor-split static compensator circuit with zero-sequence balancing bridge arms has the characteristics of independent control of four bridge arms, small deviation and fluctuation of the voltage of the two split capacitors, and good robustness of unbalanced current control, and has good application prospects.

In the method of the present invention, the zero-sequence current of the capacitor-split static compensator is provided by the zero-sequence balancing bridge arm, so that the split capacitor no longer provides the zero-sequence current in the neutral line, and the original capacitor split static compensation is eliminated. The large fluctuation of the capacitor voltage and the unbalance of the two capacitor voltages caused by the zero-sequence current compensation in the device. In addition, even if there is a large error in the control of the zero-sequence balancing inductor current or even the zero-sequence balancing bridge arm is out of operation, it will not significantly affect the compensation performance or normal operation of the static compensator, and the overall system stability is good.

In addition to the objects, features and advantages described above, the present invention has other objects, features and advantages. The present invention will be described in further detail below with reference to the drawings.

Description of drawings

The accompanying drawings constituting a part of the present application are used to provide further understanding of the present invention, and the exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

1 is a circuit schematic diagram of a capacitive split static compensator with a zero-sequence balancing bridge arm according to an embodiment of the present invention;

2 is a schematic diagram of a split capacitor voltage equalization control method for a capacitor split static compensator circuit with a zero-sequence voltage equalizing bridge arm according to an embodiment of the present invention;

Figure 3 is a simulation diagram of the control effect of the capacitor-split static compensator circuit when there is no zero-sequence balancing bridge arm (or the zero-sequence balancing bridge arm is not put into operation);

4 is a simulation diagram of a control effect of a split capacitor voltage equalization control method of a capacitor split static compensator circuit with a zero-sequence voltage equalization bridge arm according to an embodiment of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Example 1

Referring to Figure 1, as shown in Figure 1, a capacitor-split static compensator circuit with a zero-sequence voltage equalizing bridge arm includes a low-voltage distribution network, a capacitor-split static compensator, a zero-sequence voltage equalizing inductor L ₀ , Zero-sequence equalizing bridge arm;

The zero-sequence balancing bridge arm is connected between the positive busbar p and the negative busbar n of the static compensator;

The zero-sequence balancing inductor L ₀ is connected between the midpoint o 1 of the split capacitor C ₁ and the split capacitor C ₂ and the midpoint o ₂ of the zero-sequence balancing bridge arm _;

The midpoint o1 _of the _two split capacitors _C1 and C2 is connected to the neutral point of the low voltage distribution network.

The capacitor-splitting static compensator circuit with zero-sequence equalizing bridge arms of the present invention includes a low-voltage distribution network, a capacitor-splitting static compensator, a zero-sequence equalizing inductor, a zero-sequence equalizing bridge arm, and a zero-sequence equalizing bridge. The arm is connected to the positive bus (p) and the negative bus (n) of the static compensator, and the zero-sequence balancing inductor is connected between the midpoint (o ₁ ) of the split capacitor and the mid-point (o ₂ ) of the zero-sequence balancing bridge arm , while the split capacitor midpoint (o ₁ ) is connected to the neutral point of the low-voltage distribution network. The capacitor-split static compensator circuit with zero-sequence balancing bridge arms has the characteristics of independent control of four bridge arms, small deviation and fluctuation of the voltage of the two split capacitors, and good robustness of unbalanced current control, and has good application prospects.

The static compensator circuit adopts a three-phase two-level converter topology, including six switch tubes T ₁ , T ₂ , T ₃ , T ₄ , T ₅ , T ₆ ; wherein the switch tubes T ₁ and T ₂ are connected in series, The switch tubes T ₃ and T ₄ are connected in series, and the switch tubes T ₅ and T ₆ are connected in series; the intermediate ends of the three groups of switch tubes connected in series are respectively connected to the three-phase power supply through filter inductors _La , L _b and L _c .

The zero-sequence _balancing bridge arm includes two switch tubes T ₇ and T ₈ , which are connected in series and form a positive electrode _{p, a negative electrode n and a midpoint o 2 .}

The eight switching devices used in the static compensator and the zero-sequence voltage equalizing bridge arm are fully-controlled voltage switching devices, such as IGBT and MOSFET.

The three-phase compensation current control of the static compensator and the zero-sequence compensation current control of the zero-sequence voltage equalizing bridge arm both adopt a current tracking control strategy and a bipolar SPWM modulation strategy.

Example 2

Referring to Figure 2, as shown in Figure 2, a method for a capacitor split static compensator with a zero-sequence balancing bridge arm, that is, a split capacitor voltage balancing control method, controls the zero-sequence balancing bridge arm to make the compensator The zero-sequence current is completely provided by the zero-sequence balancing inductance branch and has nothing to do with the split capacitor current, so that the zero-sequence current no longer affects the voltages of the two split capacitors; it specifically includes the following steps:

Step 1: The expected value of the neutral line current i _n of the three-phase four-wire static compensator is obtained by summing the three-phase compensation current command value of the static compensator:

Among them, i _a.ref , i _b.ref and i _c.ref are the command values of the compensator A-phase, B-phase and C-phase compensation current respectively, and i _n.exp is the expected value of the neutral line current of the compensator;

At the same time, the expected value of the neutral line current is used as the command value of the zero-sequence balancing inductor current i ₀ :

；

;

Among them, i _n.exp is the expected value of the neutral line current of the compensator, and i _0.ref is the command value of the equalizing inductor current;

Step 2: Subtract the zero-sequence equalizing inductor current command value and the zero-sequence equalizing inductor current actually detected to obtain the zero-sequence current compensation error and send it to the tracking control link of the zero-sequence current; the tracking control can use proportional Integral control (PI control), proportional resonance control (PR control) or repetitive control (RC) strategy; the output of the tracking control link is output to the comparator after being limited by the limiter;

Step 3: The comparator compares the limited control signal of the current tracking control with the bipolar triangular carrier, and outputs PWM switching signals of 0 and 1; when the value of the control signal is greater than the value of the triangular carrier signal, the output is 1, otherwise output is 0;

Step 4: The switching signal output by the comparator is sent to the PWM driving circuit to form a driving signal that can be directly applied to the gate of the switching device to control the opening or closing of the switching device; one signal output from the comparator is driven by PWM and sent to zero The upper switch tube T ₇ of the sequence balancing bridge arm, the other signal output by the comparator is driven by the inverter and PWM and then sent to the lower switching tube T ₈ of the zero-sequence balancing bridge arm.

In the voltage equalization control method of the present invention, the zero-sequence current of the capacitor-split static compensator is provided by the zero-sequence voltage-equalizing bridge arm, so that the split capacitor no longer provides the zero-sequence current in the neutral line, and the original capacitor split is eliminated. The large fluctuation of the capacitor voltage and the unbalance of the two capacitor voltages caused by the zero sequence current compensation in the static compensator. In addition, even if there is a large error in the control of the zero-sequence balancing inductor current or even the zero-sequence balancing bridge arm is out of operation, it will not significantly affect the compensation performance or normal operation of the static compensator, and the overall system stability is good.

The switching control of the two switching tubes of the voltage-balancing bridge arm makes the current of the voltage-balancing inductor must have switching ripple or harmonic components, and the inductance value of the voltage-balancing inductor and the switching frequency of the voltage-balancing bridge arm are appropriately selected. The harmonic components of , can be ignored. At this time, the equalizing inductor current i ₀ is equal to the neutral line current i _n of the three-phase four-wire static compensator.

According to the principle of Figure 1 and Figure 2, a static compensator simulation example system for three-phase four-wire unbalanced load reactive power compensation is established. The AC side filter inductor is 1.0mH, the DC side split capacitor is 2200uF, the zero-sequence equalizing inductor is 1.0mH, and the triangular carrier frequency for SPWM modulation is 20kHz. It is assumed that the three-phase inductive load is balanced before 0.505 seconds, and a single-phase load suddenly increases into an unbalanced load at 0.505 seconds. Figure 3 shows the simulation results when the zero-sequence balancing arm is not put into operation, and Figure 4 shows the simulation results after the zero-sequence balancing arm is put into operation under the same conditions. Figures 3 and 4 are divided into three sub-waveform diagrams, upper, middle and lower. The upper diagram shows the grid phase A voltage ( u _a ) and the three-phase four-wire current output by the static compensator ( i _a , i _b , i _c , i _n ) ), the middle picture is the difference between the neutral line current of the static compensator and the zero-sequence balancing inductor current ( i _n - i ₀ ) and the zero-sequence balancing inductor current ( i ₀ ), and the lower picture is the DC voltage ( u _dc ) and the two split capacitor voltages ( u _c1 , u _c2 ) and the difference between the two split capacitor voltages ( u _c1 - u _c2 ).

Comparing Fig. 3 and Fig. 4 can show the application effect of the present invention.

Figure 3 shows that the two split capacitor voltages ( u _c1 , u _c2 ) are stationary and equal since the zero-sequence current ( i _n ) on the neutral line of the static compensator is zero during the balance compensation phase before 0.505 seconds ; however, during the unbalance compensation phase after 0.505 seconds, the power frequency zero-sequence current ( i _n ) on the neutral is supplied by the two split capacitor branches, resulting in two split capacitor voltages ( u _c1 , u _c2 ) appearing Severe power frequency fluctuation, especially the phase of the two split capacitor voltage fluctuations is opposite, making the difference between the two split capacitor voltages ( u _c1 - u _c2 ) larger.

Figure 4 shows that the two split capacitor voltages ( u _c1 , u _c2 ) are stationary and equal in the balance compensation phase before 0.505 s since the zero-sequence current ( i _n ) on the neutral line of the static compensator is zero , this stage is consistent with Figure 3; however, in the unbalance compensation stage after 0.505 seconds, the power frequency zero-sequence current ( in ) on the neutral line is completely determined by the zero-sequence balancing inductor current ( i _{0 )} Provided, the difference between the neutral line current and the voltage-sharing inductor current ( i _n - i ₀ ) is substantially zero, that is, the two split capacitor branches no longer provide zero-sequence compensation current, so that the difference between the two split capacitor voltages ( u _c1 - u _c2 ) tends to zero, eliminating the potential imbalance at the midpoint of the split capacitor caused by the zero-sequence unbalance compensation, and achieving the purpose of equalizing voltage and reducing capacitor voltage fluctuations.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (4)

1. a capacitor split type static compensator circuit with zero-sequence equalizing bridge arm, is characterized in that, comprises low-voltage distribution network, capacitor split type static compensator, zero-sequence equalizing inductance L ₀ , zero-sequence equalizing voltage bridge arm; the zero-sequence balancing bridge arm is connected between the positive busbar p and the negative busbar n of the static compensator; The zero-sequence balancing inductor L ₀ is connected between the midpoint o 1 of the split capacitor C ₁ and the split capacitor C ₂ and the midpoint o ₂ of the zero-sequence balancing bridge arm _; The midpoint o1 _of the _two split capacitors _C1 and C2 is connected to the neutral point of the low voltage distribution network. 2. The capacitor-split static compensator circuit with zero-sequence balancing bridge arm according to claim 1, wherein the static compensator adopts a three-phase two-level converter topology, comprising six switch tubes T ₁ , T ₂ , T ₃ , T ₄ , T ₅ , T ₆ ; wherein the switch tubes T ₁ and T ₂ are connected in series, the switch tubes T ₃ and T ₄ are connected in series, and the switch tubes T ₅ and T ₆ are connected in series; The middle ends of the switch tubes of the group are respectively connected to the three-phase power supply through filter inductors L _a , L _b and L _c . 3 . The capacitor-split static compensator circuit with zero-sequence voltage-balancing bridge arm according to claim 1 , wherein the zero-sequence voltage-balancing bridge arm comprises two switch tubes T ₇ , T ₈ , the switch tube T ₇ , T ₈ are connected in series and form a positive electrode p, a negative electrode n and a midpoint o ₂ . 4. a method for a capacitive split static compensator with zero-sequence balancing bridge arm, is characterized in that, comprises the following steps: Step 1: The expected value of the neutral line current i _n of the three-phase four-wire static compensator is obtained by summing the three-phase compensation current command value of the static compensator:

Among them, i _a.ref , i _b.ref and i _c.ref are the command values of the compensator A-phase, B-phase and C-phase compensation current respectively, and i _n.exp is the expected value of the neutral line current of the compensator; At the same time, the expected value of the neutral line current is used as the command value of the zero-sequence balancing inductor current i ₀ :

; Among them, i _n.exp is the expected value of the neutral line current of the compensator, and i _0.ref is the command value of the equalizing inductor current; Step 2: Subtract the zero-sequence equalizing inductor current command value and the zero-sequence equalizing inductor current actually detected to obtain the zero-sequence current compensation error and send it to the tracking control link of the zero-sequence current; the tracking control can use proportional Integral control, proportional resonance control or repetitive control; the output of the tracking control link is output to the comparator after being limited by the limiter; Step 3: The comparator compares the limited control signal of the current tracking control with the bipolar triangular carrier, and outputs PWM switching signals of 0 and 1; when the value of the control signal is greater than the value of the triangular carrier signal, the output is 1, otherwise output is 0; Step 4: The switching signal output by the comparator is sent to the PWM driving circuit to form a driving signal that can be directly applied to the gate of the switching device to control the opening or closing of the switching device; one signal output from the comparator is driven by PWM and sent to zero The upper switch tube T ₇ of the sequence balancing bridge arm, the other signal output by the comparator is driven by the inverter and PWM and then sent to the lower switching tube T ₈ of the zero-sequence balancing bridge arm.

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