JPS60226778A - Controller of regenerative converter - Google Patents

Abstract

PURPOSE:To control the change rate of a regenerative current substantially constantly by using the difference between a regeneration starting voltage produced by adding the prescribed value to the peak value of an interphase voltage and a DC voltage as a regenerative current command. CONSTITUTION:A voltage setter 26 detects the peak value of an interphase voltage of received AC voltage, and outputs a regeneration starting voltage E0 added with the prescribed value to the peak value. When a DC voltage E becomes higher than the voltage E0, a voltage error amplifier 14 generates a regenerative current command value I0. A deviation between the value I0 and a regenerative current detected value I is compared through a current error amplifier 18 with a triangular wave from a triangular wave generator 20. The output of the compared result is input together with the output of a phase detector 25 to AND gates 37-39 to control ON or OFF the switching transistors 61-66 of a regenerative converter.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a control device for a converter capable of power regeneration (hereinafter simply referred to as a regenerative converter), and particularly to a control device for a converter capable of power regeneration (hereinafter simply referred to as a regenerative converter), and in particular, regeneration control that is stable even against fluctuations in AC voltage on the power supply side. The present invention relates to a control device for a regenerative converter that can perform the following steps.

[Background of the invention]

Regenerative converters are used to rectify AC power and supply DC power to inverters and DC motors that drive AC motors. When these motors decelerate, power is returned from the motor side to the converter. Therefore, the regenerative converter control device has a function of controlling the converter so as to return this to the input AC power supply side.

Figure 1 shows the main circuit configuration diagram of the regenerative converter.
A three-phase AC power supply is applied to one end of the switching elements 61 to 66 (for example, a transistor) via an AC reactor 2 as shown in the figure, and a smoothing capacitor 3 is inserted between the other terminals of the switching elements 61 to 66. DC terminal 6.
Connected to 7.

The diodes 71-76 are normally built-in diodes in the transistors 61-66, but if the current capacity is insufficient, rectifying diodes 81-86 are provided separately as shown in the figure. These diodes 71-76 and 81-86
act as a rectifying element when DC current is being supplied from the AC power supply 1 to the load, while transistors 1 to 66 are turned on when power is regenerated from the load to the AC power supply 1 and transfer the regenerated current to the power supply side. Flow. The DC voltage E between the terminals 6 and 7 is detected by the voltage detector 5, and the DC current is detected by the current detector 4, both of which are used for converter control during regenerative operation. A control signal is given to the pace of.

There are control methods for regenerative converters, such as one that sets the power factor to 1, and another called the 120° overcurrent method, but the 120° current-carrying method is advantageous for small-capacity, compact, and low-priced ones. The present invention relates to improvements to this method. Figure 2 is a block diagram showing the configuration 2 of a conventional control device using the 1206 overcurrent method, where the DC voltage E detected by the voltage detector 5 is such that power is fed back from the load side. Sometimes it always rises. Therefore, first, the difference between the DC voltage E and the regeneration start voltage setting value E is taken by the subtracter 13 and inputted to the voltage error amplifier 14 to obtain the current command value 1o'l.

Here, the input/output characteristics of the subtracter 13 and the voltage error amplifier 14 are as shown in FIG. It has the characteristic of being saturated at . Next, the difference between the current I detected by the current detector 4 and the current command value ro is calculated by the subtractor 1.
7 and the difference thereof is amplified by a current error amplifier 18. Further, the output of the amplifier 18 is compared with the triangular wave output from the triangular wave generating circuit by a comparator array consisting of a subtracter η and a sign/minus judger O, and when the output of the amplifier 18 is larger than the triangular wave, 1. The opposite signal O is output from the comparator. Therefore, the comparison output is a pulse train having the same period as the triangular wave, and the pulse width becomes larger as the output of the amplifier 18 becomes larger. On the other hand, the phase detection circuit 5 generates ON signals 31 to 36 as shown in FIG. - Inputs are input to the power amplifier circuits 51 to 56, and control signals are given to the transistors 61 to 66 by their outputs. However, the phase-to-phase voltages in FIG. 4 are set, and the voltages of each phase of the power supply 1 are VA and Va as shown in FIG.

When Vc is 1, e.g. VA] 3 = -VBA = VA
-Vs, etc., and also on signals 31 to 36r.
Both ri have a pulse width of 120° with respect to the period of the power supply.

According to such a control device, power regeneration is performed in the following manner. In FIG. 2, when the DC voltage E becomes higher than the regeneration start voltage El, the voltage error amplifier 14 generates a regenerative current command value IO according to the characteristics shown in FIG. This regenerative current command value 1. The deviation of the detected regenerative current value I is input to the current error amplifier 18, and this output (which equivalently becomes the voltage command value applied to the AC reactor 2 in FIG. 1) is compared in magnitude with the triangular wave from the triangular wave generator Masuda. is performed by the comparator U, and as described above, the larger the output voltage of the amplifier 18, the larger the width of the signal is obtained from the output of the comparator U.

Here, lower arm transistors 62, 64, 66
are the outputs of the 120° phase detection circuit 5 32 , 34 , 36
and 120' by the power amplifier circuits 52, 54, and 56.
The transistor 61 in the upper arm
, 63 and 65 are 1200 phase detection circuits.
], 33, 35 and the output of the comparator U are taken by AND gates 37, 38, 39, respectively, and the outputs are sent to power amplification circuits 51, 53.

5, their on-times are controlled. Therefore, the larger the deviation between the set voltage E1 and the detected DC voltage value E, the longer the energization time of the transistors 61, 63, and 65 becomes, and more power is fed back to the power source, thereby lowering the DC voltage E to a greater extent. Therefore, power regeneration can be performed while keeping the DC voltage E substantially constant.

By the way, if we consider this type of regeneration control in more detail, it will be as follows. In the section indicated by 40 in FIG. 4, the signals 31 and 34 are on, so the transistor 6 in FIG. , all other transistors are off. Moreover, this section is 40
As shown in Figure 4, the correlated voltage VAB = VA - VB is between ±30' around its positive peak value, so the regenerative current from the load side flows through the transistor in the direction against this voltage VAB. 61 - AC reactor 2 -> AC power supply 1 - AC reactor 2 - transistor tank. Assuming that the impedance of the transistors 61 and 64 is sufficiently high, this regenerative current I is set to L/2, which is the inductance of one phase of the AC reactor 2, and t seconds after the transistor 61 is turned on, I E-VAB:L- It is determined by t. Here, t is very small, and during this time the voltage E,
When both VAB and VAB are considered constant, the current (2) increases linearly. When the regenerative current reaches its command value 0 due to this increase, the output of the comparator U becomes 0. Therefore, the output of the AND gate 37 also becomes O, and the transistor 61 is turned off.

Then, the current I flowing through the detector 4 becomes 0, but the regenerative current that has been flowing until now is attenuated while circulating through the path of transistor 6 -> diode 72 - AC reactor 2 - AC power supply 1 - AC reactor 2 -> transistor. As a result, the output of the amplifier 18 appears again, the comparator U becomes output 1, and the above operation is repeated, so the current I flowing through the current detector 4
This results in a sawtooth wave current having a peak value Io'l as shown in FIG. 5, and this effective current (average value) has a peak value of 1. It becomes 1/2 of that. However, in AC power reception, the voltage often fluctuates by about ±10%, so the regeneration start voltage E + ij shown in Figure 3.

It is necessary to set it to a high value in case the voltage is rising. This is because when the receiving voltage is high, the DC voltage E when supplying power to the load also becomes high, so the regeneration start voltage El
This is because unless it is set to a higher value, regeneration operation will start even though it is not in a regeneration state. But like this, EI'Ii! : When set, if the receiving voltage decreases, VAB decreases, so E −V in equation (1)
AB increases, the rise of the fc DC regenerative current I shown in Fig. 5 becomes steep, and the regenerative current command value 0 is reached in a short time, so the period T of the sawtooth wave in Fig. 5 also increases. The smaller the number of waves, the more the number of sawtooth waves within period 40 in FIG. 4 increases.

This is exactly the same for other transistors, so when the receiving voltage drops, the on/off frequency of transistors 61 to 66 increases, resulting in an increase in switching loss and control delay in the control circuit. When the regenerative current is 0, the regenerative current causes problems such as overshooting.

[Purpose of the invention]

An object of the present invention is to eliminate the drawbacks of the prior art described above, and to provide a regenerative converter that can maintain a substantially constant rate of change in regenerative current even if the AC power receiving voltage fluctuates, and that can therefore perform highly efficient and stable regenerative control. A control device 7 is provided.

[Summary of the invention]

The present invention provides a means for detecting the peak value of the correlation voltage of an AC power source, and variably sets a voltage obtained by adding a fixed value to the peak value as a regeneration start setting voltage, so that the DC voltage and the regeneration start setting voltage are variably set. The present invention is characterized in that the rate of change of the regenerative current is kept almost constant even when the AC power receiving voltage fluctuates by using the difference between the two as the regenerative current command.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

In the figure, a voltage setting circuit 26 is provided that detects the peak value of the phase-to-phase voltage VAB of the AC power receiving voltage (the same applies to other phase-to-phase voltages), and outputs a regeneration start voltage Eo by adding a certain value to the peak value, and outputs the output Eo. The configuration is completely the same as the conventional example shown in FIG. 2, except that the input signal is input to the subtracter 13. However, since the set voltage El is set to EO as mentioned above, the input/output characteristics of the subtracter 13 and the amplifier 14 are also as shown in Figure 7, where El in Figure 3 is changed to E, and this Eo is changed like El. It is not a fixed value but changes depending on the receiving voltage. However, the reason for adding a constant value to the peak value of the phase-to-phase voltage here is to take into account errors in peak value detection, etc., and it can be considered that the magnitude of the constant value is sufficiently small. Therefore, when the electric motor as a load is under no load or in a power running state, the DC voltage E never exceeds the peak value of the AC receiving voltage (phase-to-phase voltage), so the regenerative current is Command value Io
becomes O, and no regenerative current flows. When the motor is in a deceleration state and the rotational energy of the motor is fed back to the DC power supply as electrical energy, the DC voltage E exceeds the peak value of the AC receiving voltage and becomes higher than the voltage EO, with the characteristics shown in Figure 7. The determined regenerative current command value IO is generated and the regenerative current flows as in the conventional case. Furthermore, since the regenerative current command If increases with the rise of the DC voltage E, the DC voltage Et/'i increases until the regenerative current command value IoY, which balances the feedback power from the motor and the regenerative power to the AC power source, is generated, and the steady state is reached. becomes. If the value of DC voltage E in this case is E2, then
This is because the control system is designed so that E2 - Eo is almost constant with respect to the set value EO and falls on the sloped part of the characteristics shown in Figure 7, so this DC voltage E2 is equal to the set value Eel, and therefore the AC receiving voltage The value is slightly higher than the peak value. Furthermore, even if the received power voltage fluctuates in this steady state, the set value Eo changes by the same amount as the fluctuation, and therefore the voltage E2 also changes by the same amount. On the other hand, since the change in the phase-to-phase voltage VAB in equation (1) is the change in the received voltage itself, the rate of change in the regenerative current determined by equation (1) hardly changes. Therefore, the transistor switching frequency hardly increases due to an increase in the receiving voltage, and the DC voltage E2 during regeneration is
is not fixed to a value larger than the expected maximum value of the AC power receiving voltage fluctuation range, but is set according to the magnitude of the AC power receiving voltage at that time, making the switching loss of the transistor smaller than in the conventional control method. be able to. Furthermore, since the current rate of change of the regenerative current does not change even when the receiving voltage drops, the amount of overshoot of the regenerative current due to control delay in the control circuit can be reduced, stabilizing the current limiting operation and improving control performance. Become. In addition, as mentioned above, the DC voltage E2 is not fixed at an unnecessarily high value as in the conventional case, so when an inverter is used as a load in this regenerative converter, the switching loss of the inverter can be reduced. Furthermore, when the DC motor is used as a load, the rise in motor terminal voltage during regeneration does not become unnecessarily high, so it is possible to significantly reduce the chances of rectification restriction and flashover occurring due to a rise in terminal voltage.

〔Effect of the invention〕

As is clear from the above embodiments, according to the present invention, even when the receiving voltage changes, the rate of change of the regenerative current can be kept almost constant, and the DC voltage can also be maintained at the minimum necessary level, so the regenerative converter can be This has the effect of being able to operate efficiently and under good control.

[Brief explanation of drawings]

Figure 1 shows the main circuit of the regenerative converter, Figure 2 shows the conventional control device for the regenerative converter, Figure 3 shows the characteristics of the conventional regenerative current command value, and Figure 4 shows 120° phase detection. A time chart showing the operation of the circuit, Fig. 5 is a diagram showing the waveform of the DC regenerative current, Fig. 6 is a diagram showing one embodiment of the present invention, and Fig. 7 is a diagram showing the regenerative current in the embodiment of Fig. 6. It is a characteristic diagram of a command value. 1... AC power supply, 3... AC reactor, 4...
Current detector, 5... DC voltage detector, 61 to 66...
・Transistor, 13.17.22...Subtractor, 14
...voltage error amplifier, addition...triangle wave generator, Sae...
・Comparator, 5... Phase detection circuit, 31 to 36 river ON signal, 37 to 39... And dirt, E... DC voltage, ■... Regenerative current, 0... Current command value , B...
・Regeneration start voltage. Representative Patent Attorney Tadashi Akimoto Figure 1 Figure 2 Figure 4 Figure 4 Figure 5 Figure 6 Figure 4

Claims (1)

[Claims] A peak value detection means for detecting a phase-to-phase voltage peak value of the input AC power supply of the regenerative converter, a regeneration voltage setting means for setting a regeneration start voltage which is a predetermined value added to the peak value, and a regeneration voltage setting means for setting the regeneration start voltage by adding a certain value to the peak value; A current command value setting means that outputs a current command value corresponding to the difference when the regeneration start voltage is exceeded, and a current command value setting means that outputs a current command value according to the difference when the regeneration start voltage is exceeded, and a current command value setting means that outputs a current command value according to the difference when the regeneration start voltage control means for generating an on signal with a proportional nosolus width and applying the on signal to a switching element for causing the regenerative current to flow to the AC power source side via the reactor to control the effective value of the regenerative current. A regenerative converter control device characterized by: