RU2774841C1 - Method for smooth power control of a sectioned capacitor unit - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to the field of electrical engineering. The capacitor plant contains N main three-phase sections from a compensating capacitor and a thyristor contactor with a capacity of

, the branches of which are connected in a triangle. According to the method, the actual reactive power of the load is calculated and the thyristor contactors are switched in such a way that the total power of the main three-phase sections is as close as possible, but does not exceed the actual reactive power of the load. To achieve the effect, a correcting three-phase section with a power of Q₀ is introduced into the structure of a sectioned capacitor plant and pulse-phase control of lockable thyristors is carried out so that the current of each compensating capacitor of the correcting three-phase section has even symmetry with respect to the moments of transition through the zero value of the applied linear voltage of the three-phase electrical network for by turning on and off the lockable thyristors when the voltage of the compensating capacitor is equal to the linear voltage of the three-phase electrical network.

EFFECT: increasing the accuracy of power regulation of a sectional capacitor unit.

1 cl, 4 dwg, 2 tbl

Description

The invention relates to the field of electrical engineering and electric power industry and can be used to compensate for variable reactive power and increase the power factor of three-phase electricity consumers.

A known method for controlling the power of a partitioned capacitor plant containing N three-phase capacitor sections, the power of which is selected in the ratio 1:1:...:1, and N switching devices, which consists in the fact that the switching of three-phase capacitor sections is carried out using switching devices according to the N-bit unitary code a _N-1 …a ₁ a ₀ , each digit a _i =[0,1] of which controls one switching device and transfers to an adjacent control stage [1].

The disadvantage of the known method is the stepwise nature of the power control of the capacitor unit and, accordingly, the low accuracy of control, due to the fact that the number of control steps is equal to the number of three-phase capacitor sections, and the dead zone of the stepwise control characteristic is equal to the power of the three-phase capacitor section.

A known method of controlling the power of a partitioned capacitor plant containing N three-phase capacitor sections, the power of which is selected in the ratio 2 ⁰ :2 ¹ :…:2 ^N-1 devices according to the N-bit direct binary code a _N-1 …a ₁ a ₀ , each bit of which a _i =[0,1] controls one switching device [2].

The disadvantage of the known method is the stepwise nature of the power control of the capacitor unit with a dead zone equal to the power of the three-phase capacitor section with a minimum capacity, and limited control accuracy, determined by the number of three-phase capacitor sections.

In addition, the transition to an adjacent control stage must be ensured by the simultaneous switching of several three-phase capacitor sections, which increases the total number of switchings in the control process and reduces the service life of switching devices with a mechanical contact system.

Closest to the proposed is a method for controlling the power of a partitioned capacitor plant containing N main three-phase sections with a capacity of 2 ⁰ ·Q ₀ ;2 ¹ ·Q ₀ ;...;2 ^N-1 ·Q ₀ , the branches of which are connected in a triangle and formed by a series connection of a compensating capacitor and thyristor contactor, which consists in the fact that the actual reactive power of the load is calculated from the measured values of current and voltage and the thyristor contacts are switched using the N-bit direct binary code a _N-1 ... a ₁ a ₀ , each bit of which a _i = [0,1] controls the thyristor contactors of only one main three-phase section in such a way that the total power of the main three-phase sections included in the three-phase electrical network is as close as possible, but does not exceed the actual load reactive power [3].

The disadvantage of the known method is the stepwise nature of power regulation of a sectioned capacitor unit with a dead zone equal to the minimum power 2 ⁰ ·Q ₀ of the main three-phase section, and limited control accuracy, determined by the number of three-phase main capacitor sections.

The purpose of the proposed invention is to reduce the number of main three-phase sections and increase the accuracy of power control by forming a smooth control characteristic.

This goal is achieved due to the fact that a corrective three-phase section with a power of Q ₀ is introduced into the sectioned capacitor plant, the branches of which are connected in a triangle and formed by a series connection of a compensating capacitor and a thyristor contactor made on lockable thyristors, and pulse-phase control of lockable thyristors is carried out in such a way in such a way that the current of each compensating capacitor of the correcting three-phase section has even symmetry with respect to the moments of transition through the zero value of the applied linear voltage of the three-phase electrical network by turning on and off the lockable thyristors when the voltage of the compensating capacitor is equal to the linear voltage of the three-phase electrical network.

In FIG. 1 shows a functional diagram of a sectioned capacitor unit that implements the proposed method for smooth power control.

In FIG. Figure 2 shows the graphs of the instantaneous values of the line voltage of a three-phase electrical network and the compensating capacitor of the corrective three-phase section (a), the control pulses for turning on / off the lockable thyristors (b) and the currents of the lockable thyristors (c).

In FIG. 3 shows the adjustment characteristic of the corrective three-phase section.

In FIG. 4 shows the stepwise power control characteristic of the main three-phase sections and the smooth power control characteristic of a sectioned capacitor unit.

The sectioned capacitor plant contains N main three-phase sections 1.1,…,1.N, a corrective three-phase section 2 (one-line diagrams are shown in Fig. 1) and a control unit 3. The main three-phase sections 1.1,…,1.N contain thyristor contactors 4.1,… ,4.N and compensating capacitors 5.1,…,5.N. The power of the main three-phase sections 1.1,…,1.N is selected in the ratio 2 ⁰ :2 ¹ :…:2 ^N-1 , and the power of section 1.1 is selected to be minimal and equal to 2 ⁰ Q ₀ , and the power of section 1.N is selected to be maximum and equal to 2 ^N-1 ·Q ₀ . The corrective three-phase section 2 contains a thyristor contactor made on lockable thyristors 6.1 and 6.2, and a compensating capacitor 7. The power of the corrective three-phase section 2 is selected equal to Q ₀ .

The sectioned capacitor unit is connected to a three-phase active-inductive load 8, which is powered from a three-phase electrical network 9. The linear voltage of the three-phase electrical network 9 is measured by a voltage transformer 10, and the linear current of the three-phase active-inductive load 8 is measured by a current transformer 11.

The control unit 3 includes a module for calculating 12 reactive power Q _H of a three-phase active-inductive load 8, the inputs of which are connected to the secondary windings of the voltage transformer 10 and current transformer 11. The output of the module for calculating 12 reactive power Q _H is connected to the analog input of the N-bit analog -digital converter 13 and to the direct input "+" of the pulse-phase control module 14. The digital outputs of the N-bit analog-to-digital converter 13 are connected to the control inputs of the thyristor contactors 4.1, ..., 4.N, and the low-order bit "a ₀ " is connected to the control input of the thyristor contactor 4.1, and the most significant bit "a _N-1 " is connected to the control input of the thyristor contactor 4.N. The output of the pulse-phase control module 14 is connected to the control inputs of the lockable thyristors 6.1 and 6.2, and the inverse input "-" is connected to the output of the module for calculating 15 the power Q of the _COP of the main three-phase sections 1.1, ..., 1.N, connected by thyristor contactors 4.1, ..., 4.N to a three-phase active-inductive load 8. The digital inputs of the module for calculating 15 power Q _KS are connected to the same bits of the digital outputs of the N-bit analog-to-digital converter 13.

The proposed method for smooth power control of a sectioned capacitor unit is as follows.

Variations in the parameters of a three-phase active-inductive load 8, which is powered by a three-phase electrical network 9, are accompanied by a change in the amount of reactive power consumed. The module for calculating 12 the reactive power of a three-phase active-inductive load 8 generates, based on the instantaneous values of the secondary voltage u _C of the voltage transformer 10 and the secondary current i _N of the current transformer 11, an analog signal Q _N of the current consumption of reactive power according to the algorithm, which is determined by the known expression

where U _C is the effective value of the line voltage of a three-phase electrical network 9, calculated from the instantaneous values of the secondary voltage u _C , taking into account the transformation ratio of the voltage transformer 10; I _H is the effective value of the linear current of a three-phase active-inductive load 8, calculated from the instantaneous values of the secondary current i _H , taking into account the transformation ratio of the current transformer 11; φ _H is the phase angle between the curves of the instantaneous values of the secondary voltage u _C of the voltage transformer 10 and the secondary current i _N of the current transformer 11.

The analog signal Q _N of the module for calculating 12 reactive power of a three-phase active-inductive load 8 is converted by an analog-to-digital converter 13 into an N-bit direct binary code

a _N-1 …a ₁ a ₀

so that the amount

2 ⁰ ⋅а ₀ +2 ¹ ⋅а ₁ +…+2 ^N-1 ⋅а _N-1 = [Q _H /Q ₀ ]

was equal to the integer part of the ratio [Q _H /Q ₀ ], i.e. the ratio of the current value of reactive power Q _H of the three-phase active-inductive load 8 to the power Q ₀ of the main three-phase section 1.1. The bits of the N-bit direct binary code, taking a single value a _i \u003d 1, turn on the thyristor contactors 4.i of the main three-phase sections 1.i, and the bits, taking a zero value a _j \u003d 0, turn off the thyristor contactors 4.j of the main three-phase sections 1 .j As a result, the total power of 9 main three-phase sections connected to a three-phase electrical network is 1.1, ..., 1.N

Q _KS =Q ₀ ⋅[2 ⁰ ⋅а ₀ +2 ¹ ⋅а ₁ +…+2 ^N-1 ⋅а _N-1 ] (1)

will be less than the current value of the reactive power Q _N of the three-phase active-inductive load 8 by an amount not exceeding the power Q ₀ of the main three-phase section 1.1.

The module for calculating 15 the power of the main three-phase sections 1.1, ..., 1.N included in the N-bit direct binary code generates, in accordance with expression (1), an analog signal Q _KS , which is fed to the inverse input "-" of the pulse-phase control module 14. On direct input "+" of the pulse-phase control module 14 receives an analog signal Q _N of the current value of the reactive power of the three-phase active-inductive load 8.

The pulse-phase control module 14 converts the difference of analog signals (Q _H -Q _COP ) into a sequence of ON1, ON2 turn-on pulses and OF1, OF2 turn-off pulses of gated thyristors 6.1, 6.2 of the corrective three-phase section 2, as shown in FIG. 2b. The position of the ON1 on and off pulses of the lockable thyristor 6.1 is symmetrical with respect to the moments of zero-crossing of the line voltage u _C of the three-phase electrical network 9 from negative to positive values. The position of the ON2 on and off pulses of the lockable thyristor 6.2 is symmetrical with respect to the moments of zero-crossing of the line voltage u _C of the three-phase electrical network 9 from positive to negative values. In this case, turning on and off the lockable thyristors 6.1 and 6.2 is carried out at a zero value of the anode voltage, which excludes the possibility of current surges in the process of controlling the power of the corrective three-phase section 2, and the same value of the on / off angles (Fig. 2, a)

_αON =α _OF =α,

where α _ON is the turn-on angle of the turn-off thyristor 6.1(6.2); α _OF is the turn-off angle of the lockable thyristor 6.1(6.2).

After turning off the lockable thyristor 6.1(6.2), the voltage of the compensating capacitor 7 remains unchanged, as shown in Fig. 2,a, and equal to the value

until the next turn on of the lockable thyristor 6.2(6.1).

Under these conditions, the current curve i _6.1 (Fig. 2.c) of the lockable thyristor 6.1 acquires a piecewise sinusoidal shape, symmetrical with respect to the moment of zero crossing of the voltage u _C of the three-phase electrical network 9 from negative to positive values and therefore having even symmetry with respect to the amplitude value

where ω is the circular voltage frequency of the three-phase electrical network 9; C ₀ - capacitance of the compensating capacitor 7 of the corrective three-phase section 2.

Curve current i _6.2 lockable thyristor 6.2 also acquires a piecewise sinusoidal shape, but symmetrical with respect to the moment of transition through zero voltage u _C three-phase electrical network 9 from positive to negative values. The duration of the conduction interval λ of the lockable thyristor 6.1(6.2) is determined by the value of the on/off angle

λ=2⋅α

and the range of change of on/off angles will be

0≤α≤π/2.

When α=0, the lockable thyristors 6.1 and 6.2 are turned off, the corrective three-phase section 2 is disconnected from the three-phase electrical network 9 and does not participate in reactive power compensation of the three-phase active-inductive load 8. When α=π/2, the lockable thyristor 6.1(6.2) is in a conductive state during half the period (λ=π) of the voltage of the three-phase electrical network 9 and a sinusoidal current flows through the compensating capacitor 7 (thin line in Fig. 2, c), and the power of the corrective three-phase section 2 reaches its maximum value

At intermediate values of the on / off angles α of the lockable thyristors 6.1, 6.2, the current i _{7 of} the compensating capacitor 7

i ₇ \u003d i _6.1 +i _6.2

consists of two half-waves i _6.1 and i _6.2 , acquires a piecewise sinusoidal shape (bold line in Fig. 2, c) and, accordingly, a complex harmonic composition, which, taking into account the even symmetry of positive (i _6.1 ) and negative (i _6.2 ) half-waves, is determined by the expressions

where I ₇₍₁₎ , I _7(k) are the amplitudes of the main and higher harmonics of the current of the compensating capacitor 7.

Analysis of expression (4) shows that only odd harmonics in the current composition of the compensating capacitor 7 are different from zero, i.e. harmonics with serial numbers k=1,3,4,7,9,11,13… Relative values of the amplitudes I ^* _7(k) =I _7(k) /I _m higher current harmonics of the compensating capacitor 7 at different values of the switching angles/ switching off α lockable thyristors 6.1, 6.2 are presented in table 1.

Table 1

α, gr. 0 ten twenty thirty 40 fifty 60 70 80 90 I ^* ₇₍₃₎ 0 0.211 0.361 0.414 0.368 0.259 0.138 0.048 0.0066 0 I ^* ₇₍₅₎ 0 0.194 0.249 0.138 -0.375 -0.146 -0.138 -0.065 -0.01 0 I ^* ₇₍₇₎ 0 0.17 0.119 -0.069 -0.143 -0.041 0.069 0.065 0.0135 0 I ^* ₇₍₉₎ 0 0.141 0.0054 -0.124 0.01 0.092 0.0138 -0.049 -0.016 0 I ^* ₇₍₁₁₎ 0 0.109 -0.068 -0.055 0.087 -0.005 -0.055 0.024 0.017 0 I ^* ₇₍₁₃₎ 0 0.075 -0.091 0.039 0.03 -0.062 0.04 0.001 -0.017 0

The most significant third current harmonic I ^* ₇₍₃₎ , as well as the remaining harmonics of the zero sequence, are closed in the triangle of the branches of the corrective three-phase section 2 and do not affect the operation of the main three-phase sections 1.1, ..., 1.N.

At intermediate values of the on / off angles α of the lockable thyristors 6.1, 6.2, the power of the corrective three-phase section 2, which provides compensation for the proportional part of the reactive power of the three-phase active-inductive load 8, is determined only by the fundamental harmonic of the current I _{7(1) of} the compensating capacitor 7. Given this circumstance the power of the corrective three-phase section 2 will be determined by the expression

In FIG. 3 shows a graph of the relative power Q ^* _0(α) =Q _0(α) /Q ₀ of the corrective three-phase section 2 on the on/off angles α of the lockable thyristors 6.1, 6.2, built according to expression (5). Dependence Q ^* _0(α) =f(α) is the power control characteristic of the corrective three-phase section 2, which has a markedly non-linear form. Therefore, the practical range of regulation α=(0÷75) gr. noticeably less than theoretically possible (0÷90) gr., but provides an almost full range of power control Q ^* _0(α) = (0÷0.98) of the corrective three-phase section 2.

If the reactive power variations ΔQ _H of the three-phase active-inductive load 8 do not exceed the maximum power Q ₀ of the corrective three-phase section 2

∆Q _H ≤Q ₀ ,

the pulse-phase control module 14 by changing the on/off angles α of the lockable thyristors 6.1, 6.2 provides accurate compensation for variable reactive power

Q _H ±ΔQ _H =Q _KS +Q _0(α) (6)

without changing the N-bit direct binary code at the digital outputs of the analog-to-digital converter 13 and, accordingly, without switching the main three-phase sections 1.1, ..., 1.N.

If the reactive power variations ΔQ _H exceed the maximum power of the corrective three-phase section 2

∆Q _H >Q ₀ ,

then the analog-to-digital converter module 13 generates a new N-bit direct binary code, the bits a _j of which correspond to the changed reactive power value (Q _H ±ΔQ _H ) of the three-phase active-inductive load 8. In accordance with the new N-bit direct binary code, the and composition connected by thyristor contactors 4.1,…,4.N to a three-phase electrical network 9 main three-phase sections 1.1,…,1.N, the total power of which is less than the reactive power (Q _H ±ΔQ _H ) of the three-phase active-inductive load 8 by the value, not exceeding Q ₀ . There is a "rough" compensation, then the corrective three-phase section 2 ensures the fulfillment of condition (6) for accurate compensation of the changed reactive power of the three-phase active-inductive load 8.

The dependence of the total power Q _COP of the main three-phase sections 1.1,...,1.N on the values a _i =[0,1] of the individual bits of the N-bit direct binary code of the analog-to-digital converter 13 has a stepped character, as shown in FIG. 4. The main feature of the step characteristic Q _KS = f(a _N-1 a _N-2 ... a ₁ a ₀ ) is that the power of any two adjacent steps differs by the value of the maximum power Q ₀ of the corrective three-phase section 2. Therefore, for any the value of the N-bit direct binary code corrective three-phase section 2 allows for smooth power control within any step of the step characteristic Q _COP =f(a _N-1 a _N-2 …a ₁ a ₀ ). Thus, the control characteristic of the power Q _KU of a sectional capacitor unit as a whole

Q _KU =Q _KS +Q _0(α)

is formed by imposing on each step the power control characteristic of the main three-phase sections 1.1, ..., 1.N

Q _KS =f(a _N-1 a _N-2 …a ₁ a ₀ )

smooth control characteristic of the corrective three-phase section 2

Q _0(α) =f(α),

as shown in FIG. 4. As a result of the superposition, the stepwise power control characteristic of the main three-phase sections 1.1, ..., 1.N is converted into a continuous, smooth power control characteristic of a sectioned capacitor unit

Q _KU =f(a _N-1 a _N-2 …a ₁ a ₀ ,α),

which is shown in Fig. 4 as a wavy line and is a function of two parameters:

- digital, which is an N-bit direct binary code that provides "rough" reactive power compensation;

- analog, which is the on / off angle α, which provides accurate reactive power compensation.

With variations in the reactive power of a three-phase active-inductive load 8 in the range

0<Q _H ≤Q _H(max) =[(2 ⁰ +2 ¹ +…+2 ^N-1 ) Q ₀ +Q ₀ ]

stepless power characteristic

Q _KU =f(a _N-1 a _N-2 …a ₁ a ₀ ,α),

shown in FIG. 4, allows you to set an equal value for the power of a sectional capacitor bank, always providing mode (6) of full compensation.

The power Q ₀ of the corrective three-phase section 2 with a known value of the maximum reactive power Q _H(max) of the three-phase active-inductive load 8 is determined by the number N of the main three-phase sections 1.1, ..., 1.N. Table 2 shows the values

power of the corrective three-phase section 2 as a percentage of the maximum reactive power of the three-phase active-inductive load 8 with a different number N of the main three-phase sections 1.1,…,1.N.

table 2

N one 2 3 four 5 6 7 eight Q ^* ₀ , % fifty 25 12.5 6.25 3.125 1.5625 0.78125 0.390625

As you can see, already at N=4, the power of the corrective three-phase section 2 is only 6.25% of the maximum reactive power of the three-phase active-inductive load 8. Therefore, the number of main three-phase sections in the proposed sectioned capacitor plant can be limited to the specified value (N=4 and even N=3) while maintaining the ability to provide a full compensation mode for any variations in the reactive power of a three-phase active-inductive load 8.

Thus, the proposed invention makes it possible to obtain a positive effect, which consists in reducing the number of main three-phase sections and increasing the accuracy of power control of a sectioned capacitor plant due to the formation of a smooth control characteristic.

Sources of information used in the examination

1. Static reactive power compensators in electrical systems: Per. thematic Sat. Working Group of the Study Committee No. 38 CIGRE / Ed. I.I. Kartashev. – M.: Energoatomizdat, 1990. – 174 p. (Energy abroad).

2. Static reactive power compensators in power systems: Kartashev I.I., Chekhov V.I. / Ed. Yu.P. Ryzhov. - M .: Publishing House of MPEI, 1990. - 68 p.

3. Ivlev M.L., Cherevko A.I. Experimental setup for a discrete-type reactive power compensator // ELEKTRO. - 2005. - No. 3. - S. 30-32.

Claims (1)

A method for controlling the power of a partitioned capacitor plant containing N main three-phase sections with a power of 2 ⁰ Q ₀ ; 2 ¹ Q ₀ ;…2 ^N-1 Q ₀ , the branches of which are connected in a triangle and formed by a series connection of a compensating capacitor and a thyristor contactor, which consists in calculating the actual reactive power of the load from the measured values of current and voltage and switching the thyristor contactors, using an N-bit direct binary code a _N-1 …a ₁ a ₀ , each bit of which a _i =[0,1] controls the thyristor contactors of only one main three-phase section in such a way that the total power of the main three-phase sections included in the three-phase electrical network was as close as possible, but did not exceed the actual reactive power of the load, characterized in that a corrective three-phase section with power Q ₀ is introduced into the sectioned capacitor unit, the branches of which are connected in a triangle and formed by a series connection of a compensating capacitor and a thyristor contactor made on lockable thyristors, and implement they influence the pulse-phase control of lockable thyristors in such a way that the current of each compensating capacitor of the corrective three-phase section has even symmetry with respect to the moments of transition through the zero value of the applied linear voltage of the three-phase electrical network by turning on and off the lockable thyristors when the voltage of the compensating capacitor is equal to the linear voltage of the three-phase electrical network .

Images