RU2249896C2 - Single-phase instant-power passive component corrector - Google Patents

Abstract

FIELD: electrical engineering; correction of instant-power passive components associated with characteristics features of load.

SUBSTANCE: proposed corrector uses circuit arrangement of single-phase voltage inverter in the form of transistor bridge incorporating inverted diodes with storage capacitor connected across two diagonally opposite dc terminals and two diagonally opposite ac terminals connected through choke to supply mains in parallel with load; choke has sectionalized coil, that is it is made of two sections with output lead in-between; corrector is provided with newly introduced switch built around two thyristors and used to connect one section of choke coil during discharge of storage capacitor and both sections during its charge.

EFFECT: enlarged adjustment range of instant-power passive components; enhanced reliability of corrector.

1 cl, 2 dwg

Description

The present invention relates to electrical engineering, the field of devices that increase the efficiency of energy consumption, in particular reactive power and distortion power compensation devices, which in some sources are called “passive components of instantaneous power” [1].

The most common compensation devices are capacitor banks, connected in parallel with the load and providing the passive components of instantaneous power required by the load at the place of consumption, without loading the network with the corresponding current component. The disadvantages of such devices are associated with the requirements for regulating the capacitance of a capacitor bank.

Another type of compensators are devices based on bridge circuits of voltage inverters on two-operational keys with reverse diodes and storage capacitance in the diagonal of a DC bridge. Such a device [2] was proposed in the form of a series connection with a load to form a sinusoidal current in it. Such a connection has a very limited field of application, since it violates the regime of the method of energy consumption natural for a given load. Connecting such a device parallel to the load, and therefore parallel to the power source, makes it quite versatile, since it does not violate the mode of natural consumption of the load current, but can unload the power source from reactive currents, as well as higher harmonics currents, which is required to increase energy efficiency, that is, increasing the power factor of the power source. In connection with this prototype of the invention is the compensator of passive components of instantaneous power considered in article [1].

The disadvantage of the existing compensator circuit based on the voltage inverter is its tendency to gradually decrease the average voltage value of the storage capacitor, which ultimately leads to disruption of the discharge-charge process and a violation of the conditions for generating the compensation current i _to (t) of the required shape and size. This is because in order to ensure the stability of the discharge-charge process of the capacitor, the oscillatory circuit from the inductor and capacitor with the active resistances of the semiconductor devices, inductor and wires introduced into it must have a high quality factor, which is rather difficult to achieve for power devices, which include the compensator in question . The technical result obtained from the present invention consists in overcoming the indicated drawback, that is, in improving the reliability of the compensator by eliminating the possibility of disruption of the discharge-charge process of the storage capacitor during surges in the load current and, as a result, expanding the range of regulation of the compensation current.

The scheme of the invention is shown in figure 1.

In this diagram:

1, 2, 3, 4 - compensator transistors connected by a bridge circuit and providing its inverter mode;

5, 6, 7, 8 - reverse diodes, also forming a bridge circuit, through them the charge of the capacitor 9;

9 - storage capacitor;

10 - inductor (inductance), which, unlike the prototype, is sectioned, that is, the entire winding consists of two sections and has an output in the middle;

11, 12 - the key on two thyristors, one of which is connected to the output of the second section of the inductor by an anode, its cathode is connected to the anode of the other thyristor, the cathode of which is connected to the output of the first section of the inductor, and the control electrodes are connected to the control unit 24;

13 - load current sensor;

14 - sensor current consumed from the network;

15 - load voltage sensor matching the mains voltage;

16 - load;

17 is a compensator driver that generates a signal for setting the current consumed from the network and a signal for setting the form of the compensation current;

18 is a device for comparing the signals for setting the consumed current and its measured value;

19 - network current regulator;

20 - modulator of the duration of the control pulses of the transistors 1-4 compensator;

21 - shaper and pulse amplifier control transistors 1-4 compensator;

22 and 23 - pulse distributors control pairs of transistors 1, 4 and 2, 3;

24 - thyristor control unit 11 and 12.

The compensator according to the scheme of figure 1 is a system for automatically controlling the compensation current i _to (t) from the condition of consumption of the minimum current from the network i _c (t).

Figure 2 shows the timing diagrams of changes in the main coordinates of the compensator for the case of a “non-distorting” form of the load current. The curves of Fig. 2, a show the load current i _n (t), lagging behind the mains voltage e _s by an angle φ, and its components: i _a (t) - active, coinciding in phase with the mains voltage, and i _p (t) - reactive, shifted from e _with an angle π / 2.

The main purpose of the compensator is to form a current i _к (t) = i _р (t). Then the reactive component of the load current will not be consumed from the network, but will be produced at the place of consumption, and the network (power source) is unloaded from it. This makes it possible to increase the efficiency of electricity consumption, since losses in the transmission line will be reduced by an amount determined by reactive currents.

Power loss in the line without a compensator is determined by the expression

where I _n , I _a , I _p are the effective values, respectively, of the load current and its active and reactive components;

ΔР _l , ΔР _la , ΔР _лр - total power losses in the line (power supply network) and their components from active and reactive currents;

R _l - the total active resistance of the power supply network from the power source e _s to the point of electricity consumption by the load.

Power loss in line with compensator

Since the active I _a and reactive I _p components of the current I _n are commensurate, a decrease in the line loss by ΔР _lr turns out to be very effective: not only the losses are reduced, but the line capacity also increases due to the possibility of connecting other loads.

Figure 2, b shows the voltage variation curves across the storage capacitor U _ck (t) and the emf modules network | e _with | in the stationary mode of formation of the desired value of the compensation current i _to (t) (Fig.2, c). Figure 2, d shows the curve of the change in the emf inductor self-induction 10 e _L (t), which is determined by the state of the thyristors 11 and 12:

if thyristor 12 is open, and 11 is closed, then the current i _к (t) flows through the first section of the inductor 10 and

if thyristor 11 is open, and 12 is closed, then the current i _к (t) flows through both sections of the inductor 10, which are included according to, while e _L (t) is determined by the expression

All coordinates of the compensator i _к (t), U _ck (t), e _L (t) consist of average values (“smooth components”) i _k0 (t), U _cк0 (t), e _L0 (t) and variables Δi _k , ΔU _ck0 , Δe _L

The average values vary with the frequency of the network f _c = 1 / T _c , where T _c is the period of change of the supply voltage e _s (t), and the variable components change with the switching frequency of the transistors 1-4 compensator (switching frequency)

f _P = 1 / T _P ,

where T _P - the period of switching transistors.

At this switching period, the transistors have an open state interval εТ _П and a closed state interval (1-ε) Т _П ,

where ε = t _in / T _P - the relative duration of the open state (duty cycle) of the transistors.

Changing the duty cycle ε and allows you to form the compensation current i _to (t) the desired size and shape.

The switching frequency of the transistors f _P is set by the carrier frequency generator included in the block 21.

The compensator according to the scheme of figure 1 works as follows.

After the compensator is connected to the network, the initial charge of the storage capacitance 9 occurs through both sections of the inductor 10 (thyristor 11 is open, and 12 is closed) and reverse diodes 5-8 to a voltage close to double the amplitude value of the emf. network e _c (t). This process begins strictly from the moment e _c = 0, which is ensured by the operation of block 24, and takes the duration of a time interval of no more than a half-period T _c / 2 (not shown in FIG. 2).

Depending on the nature of the load 16, i.e. from the magnitude and shape of the consumed current i _n (t), the driver 17, using the current sensor 13 and the voltage sensor 15, generates a set value of the compensation current i _к0 (t), the deviation from which by an acceptable value Δi _{cdop is} controlled by the current regulator 19. The output signal link 19 and the signal to set the shape of the compensation current from the master 17 determines the output signal at the output of the block 20 of the modulator duration of the control signals of transistors 1-4. The discharge process of the capacitor 9 in the stationary mode starts from the moment of time, the angular estimation of which corresponds to the value θ ₁ = ωТ _s / 2 = π / 2, where ω = 2πf _c is the angular frequency of the supply voltage; θ = ωt is the angular measurement of the current time.

At this moment, the corresponding pair of transistors 1-4 or 2-3 opens and the current i _k (t) begins to increase in the time interval εT _П (Fig. 2, c). When it deviates from the set value i _к0 (t) by an acceptable value, the transistors close and in the interval (1-ε) T _{P, the} current begins to decrease, tending to a negative steady-state value. When deviating from i _к0 (t) in the negative direction by the permissible value Δi _{cdop, the} pair of transistors turns on again and the current begins to increase. Further, such processes are repeated with a frequency f _P and a changing duty cycle ε.

With a positive half wave of current i _k (t), when it goes from the compensator to the network, the voltage across the capacitor 9 U _ck (t) decreases (discharge of the capacitor), and with a negative half wave i _k (t), when it goes from the network to capacitor (capacitor charge), - voltage U _ck (t) increases.

The change in all coordinates of the compensator of figure 1 obey the equations

where rΣ = r _k + Σr _pp is the total active resistance through which the switching current i _k is closed;

r _to - the resistance of the inductor;

Σr _pp - the total resistance of semiconductor devices;

LΣ = L _l + L _k - inductance of the network and inductor.

Finding solutions to equations (5) and extracting mean values (smooth components) from them, we obtain

Therefore, the average over the period of the carrier frequency value of the emf self-induction of the inductor 10 e _L0 is in phase with the voltage of the power source e _s , and the average value of the variable component of the voltage ΔU _sko on the storage capacitor 9 is in antiphase with e _s (θ). The expression for the current value of the current i _ko (θ) in the inverter mode of the compensator (capacitor discharge 9) can be written as follows:

k=0, 1, 2, ..., ∞.Where

k = 0, 1, 2, ..., ∞.

The expression for the current value of the current i _ko (θ) in the rectifier mode of the compensator (capacitor charge 9) is written as follows:

k=0, 1, 2, ..., ∞.Where

k = 0, 1, 2, ..., ∞.

From the expressions (7) and (8) it follows that in the inverter mode, when the current i _ko goes from the capacitor to the network through transistors 1-4, the absolute value | U _ck (θ) | should be greater than the total value | e _c + e _L0 |, and in the rectifier mode, when the current i _ko goes to the capacitor 9 through the inverse diodes, the sum of the emf | e _c + e _L0 | must be greater than the absolute value of the voltage across the capacitor | U _ck (θ) |. Since the value of e _c (θ) cannot be changed, to obtain the desired ratio between | U _ck (θ) | and | e _c + e _L0 | it is advisable to change the value of e _L0 : in the inverter mode it should be made less than in the rectifier mode. This is the essence of the invention: in the inverter mode, when e _L0 prevents the formation of current i _к (θ), its value should be made small, and in the rectifier mode, when e _L0 contributes to the flow of current i _к (θ), it should be made large . This is achieved by making the inductor 10 two-sectional (double-winding) and switching according to the included sections using thyristors 11 and 12, which switch the inductor from one winding to two series-connected depending on the direction of the current i _to (θ). The use of the present invention eliminates the main disadvantage of existing compensator circuits with a single-wound choke, namely that situations often arise when switching loads on and off when a condition

In this case, the process of charging the capacitor 9 is disrupted and the compensator ceases to fulfill its function - to generate a compensation current

i _to (θ) = i _p (θ).

With a correctly executed control system and the occurrence of condition (9), the following process should begin: the capacitor 9 should be discharged to almost zero by properly controlling the pairs of transistors 1-2 and 3-4 (which in normal mode do not turn on in such combinations), then the initial charge of the capacitor to the maximum voltage and the subsequent control of the pairs of transistors 1-4 and 2-3 to ensure a normal compensation mode. However, such a procedure is accompanied by the appearance of a time interval with the loss of current compensation i _p (θ) and the corresponding additional losses in the power supply network _{ΔР рл} .

The application of the present invention eliminates the possibility of the occurrence of the described situations, and therefore, increase the reliability of the compensator and expand the range of regulation of the current of the compensator i _to (θ).

Sources of information

1. Labuntsov V.A., Zhang Daizhong. Single-phase semiconductor compensators for passive components of instantaneous power // Electricity. 1993. No. 12. S.20-32.

2. A.S. 1128350. Adjustable AC-to-AC converter / Zinoviev G.S., Konovalov A.N., Krasikov N.A.// Discovery. Inventions 1984. No. 45.

Claims (1)

A single-phase compensator of passive components of instantaneous power, the power circuits of which are made on four transistors with reverse diodes, a storage capacitor is included in the DC diagonal, the AC diagonal is connected to the mains parallel to the load through the inductor, and the compensator control system consists of current and voltage sensors, the network current sensor, contains a driver of the compensator, which generates a signal for setting the current consumed from the network, and a signal for setting the current shape compensation, the input of which is connected to voltage and load current sensors, a node for comparing the current setting signal with the signal of the network current sensor, the network current regulator that controls the deviation of the network current from the set value, the output signal of the current regulator and the signal for setting the form of the compensation current from the master the output signal of the modulator of the pulse width of the control transistor of the compensator, characterized in that the inductor winding is sectioned, the compensator is equipped with a key for two thyristors ax and a control unit, moreover, the anode of one thyristor is connected to the output of the second section of the inductor, and its cathode is connected to the anode of the second thyristor and to the diagonal of the AC compensator, the cathode of the second thyristor is connected to the output of the first section of the inductor, and the control electrodes of the thyristors are connected to the control unit them, the input of which receives the signal to set the shape of the compensation current.

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