SU1525841A1 - Device for controlling frequency converter with dc link - Google Patents

Abstract

The invention relates to converter technology and can be used to control adjustable power sources, for example, for induction heating of metals. The purpose of the invention is to increase the range of adjustment of the output voltage of the converter. The device comprises an adder 15, a null organ 18, a selector 19, a phase shifting circuit 17 of the output voltage of the converter, a polarity switch 16, a node 20 for limiting the maximum control angle of the inverter. The input of the first limiter 8 is connected to the output of the second regulator 13. The first input of the adder is connected to the output of the sensor 10 of the rectified current, the second input of the adder is connected to the output of the sensor 9 of the output voltage of the rectifier, the third input of the adder is connected to the voltage source of the minimum rectified current, the fourth input of the adder is connected to the output of the switch. The first input of the switch is connected to the phase-shifting circuit of the output voltage of the converter, and the second input is connected to the output of the converter. The zero output of the adder is connected to the first input of the selector, the second input of the selector is connected to the output of the inverter phase control system 7, the third input of the selector is connected to the output of the limiting node of the maximum inverter control angle, the output of the selector is connected to the inverter control pulse 6. 4 il.

Description

(21) 4135360 / 2A-07

(22) 10/20/86

(46) 11/30/89. Bksh. No. 44

(71) Production Association Tallinn Electrotechnical Plant them. M.I. Kalinina

(72) A.N.Yupegin, G.M.Mustafa and A.G. FAST

(53) 621.314.27 (088.8)

(56) USSR Author's Certificate No. 754610, cl. H 02 M 5/42, 1978.

(54) DEVICE FOR CONTROLLING A FREQUENCY CONVERTER WITH A DC CURRENT

(57) The invention relates to converter technology and can be used to control adjustable power sources, such as for induction heating of metals. The purpose of the invention is to increase the range of adjustment of the output voltage of the converter. The device comprises an adder 15, a zero-body 18, a selector 19, a phase-shifting circuit 17 of the output voltage of the converter, a polarity switch 16, a node 20 limiting the maximum control angle of the inverter. First limiter 8 input

itf.

(/)

fi f

connected to the output of the second regulator 13. The first input of the adder is connected to the output of the sensor 10 of the rectified current, the second input of the adder is connected to the output of the sensor 9 of the output voltage of the rectifier, the third input of the cy 1mator is connected to the voltage source of the setting of the minimum rectified current, the fourth the input of the adder is connected to the output of the switch. The first input of the switch is connected to the phase-shifting circuit of the output. The invention relates to electrical equipment, in particular to converter equipment, and can be used to control regulated power sources, for example, for induction heating of the metal.

The aim of the invention is to increase the range of adjustment of the output voltage of the converter.

Figure 1 shows the functional diagram of the device; figure 2 is a diagram of the output signals of the first and second limiters; figure 3 is a diagram of the switch signals; figure 4 is a diagram of the signal selector.

The device contains a rectifier 1, a filtering reactor 2 in the DC circuit, an inverter 3, a load 4, a block 5 of a pulse-phase control of a rectifier, a driver 6 of the inverter control pulses, a block 7 of the phase control of the inverter, a voltage limiter 8 at the minimum angle control of the inverter, sensor 9 of the output voltage of the high voltage, sensor 10 of the rectified current, sensor 11 of the output voltage of the converter, the first regulator 12, containing the node limiting the maximum output signal, the second regulator 13, voltage limiter 14 at the level of the minimum control angle of the rectifier, adder 15, polarity switch 16, phase-shifting circuit 17 of the output voltage of the converter, zero-body 18, selector 19, node 20 for limiting the maximum control angle of the inverter with a synchronous signal feed input the voltage of the converter, and the second input to the output of the converter. The output of the adder is connected via a null to the first input of the selector, the second input of the selector is connected to the output of the inverter phase control system 7, the third input of the selector is connected to the output of the node

limiting the maximum control angle of the inverter, the output of the selector is connected to the input of the driver 6 of the inverter control pulses. 4 sludge.

with inverter. Regulator 12 is connected by the first input to the source.

the voltage setting the output voltage of the converter, the second input to the sensor 11. The regulator 13 is connected by the first input to the output of the first controller 12, the second input to the output of the sensor 10, and the output through the limiter 8 to the input of the unit 7. The output of the second regulator torus 13 is also connected via a limiter 14 to the input of block 5. The adder 15 is connected by the first input to the output of the sensor 10, the second input to the output of the sensor 9, the third input to the voltage source of the minimum rectified current, the fourth

input - to the switch output 16. The switch 16 input is connected to the output of the phase-shifting circuit 17. The control input of the switch 16 is connected to the output of the converter.

The output of the adder 15 through the zero-body 18 is connected to the first input of the selector 19, the second input of which is connected to the output of block 7, and the third input to the output of the node 20. The output of the selector 19 is connected to the input of the imaging unit 6.

The device works as follows.

In steady-state mode with a constant voltage, the task to the input of the first regulator 12, which performs the function of a voltage regulator and can be integral or proportional-integral, the magnitude of a single voltage and a constant frequency frequency constant. The error signal at the inputs of the regulator 12 between the voltage of the ultrasonic signal and the signal

five

With brotherly communication from the sensor 11 1, the voltage of the converter voltage tends to zero. The output of regulator 12 is the reference signal for regulator 13, which can be proportional to integral or integral and performs the function of the current regulator. The error signal at the inputs of the second regulator 13 between the reference signal and the signal Ij from the sensor 10 also tends to zero. When the maximum limit of the running signal of the treadmill 12 is reached, the stabilized (limited) maximum rectified current of 1 1 mpx occurs.

The output signal U of the second regulator 13 enters the inputs of the limiters 8 and 14 and passes either to the output of the first limiter 8 (then the output of the second orpaHiiim body 14 is the level of restriction U - ogr) or to the output of the second limit.11tell 14 (then the output the first limiter 8, the limit level and, L orpi), which is provided by the characteristics of the limiters (Fig. 2).

Block 7 is adjusted so that the input control signal at the level of limitation U, Uogr i corresponds to the control angle (i) and the inverter 3 | LL and block 5 - so that the input control signal on ypoBiie limits Uj UQ ,. , corresponded to the minimum control angle of the straightener 1 oi ixi llia. Thus, by changing the control signal Ug at the output of the second regulator 13, either the inverter min is controlled, while the angle of the rectifier is limited. or adjustment of the rectifier (n while limiting the control angle of the inverter / 3 | / viHH)}} lm in both cases, the error signal at the inputs of the second controller 13 tends to tend to zero.

In the case when the control signal U (j at the output of the second regulator 13 corresponds to the mode. Cm can simultaneously occur at a sufficiently small power load, the stabilization mode C and the minimum rectified current in the case of throttling

258416

nt {by the inverter 3, where the adder 15 enters, the zero-organ 18, the selector 19, (shaper 6. The feedback signals to the first 1 m tor 15 come from the sensor 9, the sensor 10, the phase-shifting circuit 17 through the switch # 1 16. The adder 15 produces a control voltage Uunp which during the half-period of the inverter passes twice through zero.One of the two transitions (informational) sets the moment of switching on the inverter thyristors and is fixed by the zero-organ 18 as

j informational difference his vyghodno30

th logical signal F

2

1 is a voltage shifting circuit 17 of the output voltage of the converter; it forms the output signal U., sdg intiy 20 in phase with respect to the ideal sinusoidal sinusoidal output voltage of the converter by 90 (FIG. 3).

The switch 16 changes the polarity 25 of the signal U, with a negative voltage Uj, (, ix (phi, 3), which allows the single-channel control of the inverter to be realized.

The logical signal F-from the output of the zero-body 18 is fed to the input of the selector 19 and passes to its output without changing (Fig. 4a) in the case when the front of the signal F sets the angle of control of the inverter within

  f max P front 35 of the signal F comes earlier than the front of the signal F, from the output of block 7, but later than the front of the signal F from the output of node 20. If the front of the signal Fg comes before the front of the signal FJ, then the output of the selector l5 passes the signal F i.e. F F, which corresponds to the limitation of the maximum control angle / 3 / L 1.0x0 (Fig. 4, b). If the front of the signal F 45 arrives later than the front of the signal F, then the output of the selector 19 passes the signal F, i.e. F F, that corresponds to the limitation of the minimum angle of control of the min (figure 4, c).

On the front of the signal F, coming from the output of the selector 19 to the input of the driver 6, the opening imggles of the thyristors of the first or second diagonals of the inverter bridge 3 are formed.

Node 20 has an input to trigger a sync signal; and with an inverter, and generates a logic signal F, which sets the input voltage at each half-period of the input voltage and the resolution for the inverter control angle /). The resolution interval is the maximum allowable control angle of the inverter P о srr, choosing 1st according to the condition of stability in the control circuit of the undercurrent regulator — for the imitated sinusoidal output voltage of the inverter 90. The prohibition and resolution intervals of the signal F can be set with a potentiometer according to the known standby multivibrator circuit synchronized with the inverter.

The law of formation of the control voltage, p at the output of the adder 15, is based on the following.

In the steady-state mode, the average values of the inverter counter-emf voltage E (at the bridge input) and the output voltage of the rectifier Uj are: E Uj, the rectified current Ij due to filtering by the large inductance LJ of the reactor 2 is almost smoothed. The change in the rectified current Ij in transient conditions is determined by the difference in the average values of Uj – E and is proportional to the change interval and inversely proportional to the inductance LJ. Suppose that the UIi deviation of the rectified current Ij occurs from the specified minimum breakdown I

mn

e-blj Ij - Id

min

then, to compensate for the deviation of Ml, i.e. return the equality Ij Ij, for a time equal to one

To the inverter's luperiod T, it is necessary to create an opposite deviation -Qlj for the next half-period. To do this, you need to create a corresponding difference in the average (for the half period T) values:

F „, uld

 J - J T

With idealized sinusoidal output voltage of the converter and instantaneous switching of the thyristors of the inverter, the counter electromotive force K is determined by the formula

E-D-

,

where and is the voltage amplitude of 1 p., | y Before the next one) Thyristors of HHBayJTopa; there is a known deviation of -L1, which needs to be created in the next half-period T, the value Uj is known, it remains only to determine the required value E and, choosing the required angle p to produce the next inclusion of the inverter thyristors.

The inverter's counter electromotive force E is proportional to JQ and is equal to the cosine of the angle; therefore, the actual angle | 3 is determined using the cosine ramp voltage generated by circuit 17 and fed through

J5 switch 16. The instantaneous value of the sweep voltage and at the moment of switching on t c of the inverter thyristors is proportional to the value), therefore, also proportional to the value of the back electromotive force K;

E

...

),

where K is the proportionality coefficient.

Selecting one or another moment of switching on at the current half-period, simultaneously select the value) which is equivalent to choosing

- bm the most definable difference is E - Uj and creates a deviation of -D1., The condition for turning on the thyristors is determined by the expression

35

 Lj. T

Ld

.- d f-Id - l-V..H 0

0

five

Rights A part of the equality is an algebraic sum of four signals that is calculated

0 by adder 15 and, as a result, the control voltage is lost. Inverter thyristors are turned on when the control voltage and are passed. through zero. Ubie case 5 deviation rectified current

Ii from task Ij

/ min

(arising.

in particular, due to the ripple of the output voltage of the rectifier Uj), they are compensated with maximum speed — for one half-period of the inverter T, Task Ij is set close to zero, but sufficient so that the random deviations of the rectified current Ij do not interrupt it.

The frequency converter has three control zones.

Zone 1: regulation is performed by inverter 3, the angle of the controlled rectifier 1 is limited to the minimum value Regulated by either the output signals of the regulators 12 and 13, if there is no maximum limitation of the rectified current Ij, and the output voltage Ugf ,, is stabilized , the converter, or the output signal Ug of the second regulator 13 only, if the maximum limitation of the rectified current Ij Ij has come and the output voltage Ug ,, of the converter is reduced in comparison with the given one, then the output signal, qj of the first mode Str torus 12 is limited at the maximum value. The control action on the inverter is performed through the first limiter 8, block 7, the selector 19, the driver 6, and the angle restriction (xL pc d, (, c is specified by the second limiter 14.

Zone 2: regulation is performed by the rectifier 1, the control angle of the inverter 3 is limited to the minimum value of f min. Just as in zone 1, either the output signals Up of the regulators 12 and 13, or the output U of only the second regulator 13 are adjusted. The control action on the rectifier 1 is carried out through the second limiter 14 and block 5, and the limitation of the angle p ff is specified by the first limiter 8.

Zone 3: regulation is performed by rectifying 1, rectified current Ij is limited by inverter 3 at the minimum value I i Ij The control loop includes regulators 12 and 13, the second limiter 14, block 5, and the limit circuit

 I

min

- adder 15, zero-organ 18, selector 19, driver 6. The limiting circuit operates independently of the control loop and ensures that the rectified current Ij is equal to the value of the task at the input of the adder 15: Ij Ij "In the control loop the following occurs. The signal at the output of the pilot regulator 12 is adjusted so that the value of the signal I eo | becomes equal to the value of the signal I, from the sensor 10 of the rectified current and thereby equal to the value of the reference signal Ij, while the output signal and the second regulator 13 is adjusted so as to provide a signal from the sensor 1 1 of the output voltage of the converter equal to the reference signal Pzad from the input of the first regulator 12.

The transition from zone 1 to zone 2, then to zone 3 occurs with a gradual decrease in the signal for 1Cdd at the input of the first controller 12

The application of the proposed device provides for the stabilization of the output voltage in the control range of 10-100% and the use of the applicator for supplying the autonomous oscillating circuit of the electrothermal and other electrotechnological loads.

Claims (1)

Invention Formula A device for controlling a frequency converter with a DC link, containing an inverter control pulse driver, the outputs of which are intended for connection to inverter inverter valves, a phase I unit Inverter control, the input of which is connected to the output of the voltage limiter at the level of the minimum control angle of the inverter, sensor of the output voltage of the microphone, the first regulator containing the node limiting the maximum signal at the output of the first input of which is connected to the output voltage source converter voltage, the second input is to the output voltage sensor of the converter, the second regulator, the first input of which is connected to the output of the first regulator, the second input to the output of the sensor is downstream current, the output of the second regulator through the voltage limiter at the level of the minimum control angle of the rectifier is connected to the input of the pulsed-phase control unit of the rectifier, the outputs of which are intended for connection to the converter rectifier valves, characterized in that increasing the range of adjustment of the output voltage of the converter, it is equipped with an adder, a zero organ, a selector, containing an RCG element and the element I, a phase shifting circuit of the output voltage of the converter, polarity node limiting the maximum control angle of the inverter, having an input for supplying a synchronous signal and with an inverter, the input of the voltage limiter at the minimum control angle of the inverter connected to the output of the second regulator, the first input of the adder is connected to the output the voltage sensor is of direct current, the second input of the adder is connected to the output of the output voltage sensor of the rectifier, the third input from the matrix is intended to be connected to the voltage source to set the minimum rectified current, the fourth input of the adder is connected to the Bi- go to the ommutator polar Ut / d. x Fi.g Off whose input is connected to 1) the phase-shifting circuit of the output voltage of the converter, the control input is connected to the sensor input of the output voltage of the converter, the output of the adder is connected to the first input of the OR element of the selector, whose output is Q the first input of the element is And, the second input of the element OR of the selector is connected to the output of the phase control unit of the inverter, the second input of the element AND of the selector is connected to the output of the 5 LU node limiting the maximum control angle of the inverter, the output of the element AND selector and is connected to the input of the inverter control pulse generator.  / Fyg.Z FIG. C