JP2567830B2 - Regenerative converter control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a converter capable of regenerating a power source (hereinafter, simply referred to as a regenerative converter). The present invention relates to a control device for a regenerative converter that can be performed.

[Background of the Invention]

A regenerative converter is used to rectify an AC power source and supply DC power to an inverter or a DC motor for driving an AC motor, and when decelerating these motors, the power is fed back from the motor side to the converter. Therefore, the control device of the regenerative converter has a function of controlling the converter so as to return it to the input AC power supply side.

FIG. 1 shows a main circuit configuration diagram of a regenerative converter. A three-phase AC power supply 1 is applied to one ends of switching elements 61 to 66 (for example, transistors) via an AC reactor 2 as shown in FIG. A smoothing capacitor 3 is inserted between the other terminals of ~ 66 and connected to the DC terminals 6 and 7. Diodes 71-76 are normally transistors 61
Although they are diodes built in to 66, if the current capacity is insufficient, rectifying diodes 81 to 86 are separately provided as shown in the figure. These diodes 71 to 76 and 81 to 86 operate as rectifying elements when supplying a direct current from the AC power source 1 to the load, while the transistors 61 to 66 are turned on when power is regenerated from the load to the AC power source 1. The regenerative current to the power supply side. The DC voltage E between the terminals 6 and 7 is detected by the voltage detector 5 and the DC current I is detected by the current detector 4, both of which are used for converter control during regenerative operation. A control signal is applied to the base of.

There are methods to control the power factor to 1 and a method called a 120 ° overcurrent system as the control method of the regenerative converter, but the 120 ° energization method is advantageous for small capacity, small size and low price. The present invention relates to an improvement of this method. FIG. 2 is a block diagram showing the configuration of a conventional control device using the 120 ° overcurrent system. The DC voltage E detected by the voltage detector 5 is in a state in which power is fed back from the load side. Always rises when you hit. Therefore, first, the difference between the DC voltage E and the regeneration start voltage set value E ₁ is input to the voltage error amplifier 14 by the subtracter 13 to obtain the current command value I ₀ . Where the subtractor
As shown in FIG. 3, the input / output characteristics of the voltage error amplifier 14 and the voltage error amplifier 14 are such that when the DC voltage E exceeds the regenerative start voltage set value E ₁ , the current command value I ₀ starts to rise and reaches a certain constant value I ₁ . It has the property of being saturated. Subsequently, the difference between the detected current I of the current detector 4 and the current command value I ₀ is taken by the subtractor 17, and the difference is amplified by the current error amplifier 18. Further, the output of the amplifier 18 is compared with the triangular wave output from the triangular wave generating circuit 20 by a comparator 24 composed of a subtractor 22 and a positive / negative judging device 23, and when the output of the amplifier 18 is larger than the triangular wave, 0 when the output is opposite. Is output from the comparator 24. Therefore, the output of the comparator 24 becomes a pulse train having the same period as the triangular wave, and the pulse width thereof becomes larger as the output of the amplifier 18 becomes larger. On the other hand, the phase detection circuit 25 detects the ON signal 31 to ON as shown in FIG. 4 from the phase of the interphase voltage of the three-phase AC power supply line 1.
36, some of which are input to the power amplifier circuits 51 to 56 through the AND gates 37 to 39, and the other of which are directly input to the power amplifying circuits 51 to 56, and their outputs provide control signals to the transistors 61 to 66. However, the interphase voltage of FIG. 4 is, for example, V _AB = −V _BA = V _A when the voltage of each phase of the power source 1 is V _A , V _B , V _C as shown in FIG.
-V _B, etc., and all the ON signals 31 to 36 have a pulse width of 120 ° with respect to the cycle of the power supply.

According to such a control device, power regeneration is performed as follows. In FIG. 2, when the DC voltage E becomes higher than the regenerative starting voltage E ₁ , the voltage error amplifier 14 produces the regenerative current command value I ₀ according to the characteristic shown in FIG. The deviation between the regenerative current command value I ₀ and the regenerative current detection value I is used as the input of the current error amplifier 18, and this output (equivalently the voltage command value applied to the AC reactor 2 in FIG. 1) and a triangular wave are generated. The magnitude comparison of the triangular waves from the device 20 is performed by the comparator 24, and as described above, the larger the output level of the amplifier 18, the wider the pulse signal is obtained as the output of the comparator 24.

Here, the transistors 62, 64, 66 of the lower arm are the outputs 32, 34, 36 of the 120 ° phase detection circuit 25 and the power amplification circuits 52, 54,
Although it is turned on every 120 ° by the 56, the upper arm transistors 61, 63 and 65 are connected to the output 3 of the 120 ° phase detection circuit 25.
The AND of 1,33,35 and the output of the comparator 24 is obtained by AND gates 37,38,39, respectively, and this output is obtained by the power amplifier circuits 51,5.
Their on-time is controlled by entering 3,55. Therefore, the larger the deviation between the set voltage E ₁ and the detected DC voltage value E, the longer the energization time of the transistors 61, 63 and 65, and the more power is fed back to the power supply side to further reduce the DC voltage E. Therefore, the power supply can be regenerated while keeping the DC voltage E substantially constant.

By the way, a more detailed consideration of such regenerative control is as follows. In the section indicated by 40 in FIG. 4, since the signals 31 and 34 are on, the transistor 64 in FIG. 1 remains on, and the transistor 61 is on only while the output of the comparator 24 and the signal 31 are on. All transistors are off. Moreover, in this section 40, the interphase voltage V _AB = V _A −V
_As shown in Fig. 4, _B is between ± 30 ° around its positive peak value, so the regenerative current from the load side in the direction against this voltage V _AB is transistor 61 → AC reactor 2 → It flows in the route of AC power supply 1 → AC reactor 2 → transistor 64. Assuming that the impedances of the transistors 61 and 64 are sufficiently small, the regenerative current I is t / 2 seconds after the transistor 61 is turned on when the inductance of one phase of the AC reactor 2 is L / 2. That is Determined by. Here, t is very small, and the voltage E, V
If both _AB are considered constant And the current I increases almost linearly. Due to this rise, when the regenerative current I reaches its command value I ₀ , the output of the comparator 24 becomes 0 and the output of the AND gate 37 also becomes 0, and the transistor 61 is turned off. And the current I flowing through the detector 4
Is 0, but the regenerative current that has been flowing is a transistor.
64 → diode 72 → AC reactor 2 → AC power source 1 → AC reactor 2 → Transmits the path of the transistor 64 while attenuating. As a result, the output of the amplifier 18 appears again, and the comparator 24
Becomes the output 1 and the above operation is repeated, so that the current I flowing through the current detector 4 has a peak value I ₀ as shown in FIG.
Saw-tooth wave current with the effective current (average value)
It becomes 1/2 of the peak value I ₀ regardless of the repeating cycle.
However, since the AC power receiving voltage often fluctuates by about ± 10%, it is necessary to set the regeneration start voltage E ₁ shown in FIG. 3 to a high value on the assumption that the power receiving voltage is increasing. When the received voltage is high, the DC voltage E when supplying power to the load is also high. Therefore, the regeneration start voltage E ₁ must be set higher than this, and the regenerative operation will occur even if it is not in the regenerative state. Because it will start. However, when E ₁ is set in this way, when the received voltage drops, V _AB
Since E-V _{AB in} equation (1) increases because the rise of DC regenerative current I shown in FIG. 5 becomes steep and the regenerative current command value I ₀ is reached in a short time. The period T of the sawtooth wave in FIG. 5 is also reduced, and accordingly the number of sawtooth waves in the period 40 in FIG. 4 is also increased. Since this is exactly the same for the other transistors, the on / off frequency of the transistors 61 to 66 is increased when the power receiving voltage is decreased, and the regenerative current command value I ₀ is increased due to the increase in switching loss and the control delay of the control circuit. Further, the regenerative current I causes a problem such as overshoot.

[Object of the Invention]

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to keep the rate of change of the regenerative current substantially constant even when the AC power receiving voltage fluctuates, and therefore, the regenerative control with good control efficiency and stable regenerative control is possible. It is to provide a control device for a converter.

[Outline of Invention]

The above-mentioned object is a peak value detecting means for detecting the inter-phase voltage peak value of the input AC power supply of the regenerative converter, and a regenerative voltage setting means for setting a value obtained by adding a constant value to the inter-phase voltage peak value as the regenerative start voltage value, Current command value setting means for outputting a current command value according to the difference when the DC voltage at the output end of the regenerative converter exceeds the regenerative start voltage value, and the regenerative current flowing from the output end to the regenerative converter is the current When the command value is lowered, an ON signal having a pulse width proportional to the difference is generated, and the ON signal is given to the switching element for causing the regenerative current to flow to the AC power supply side through the reactor, and the effective regenerative current is supplied. It is achieved by including a control means for controlling the value.

Since the regenerative start voltage value is a value obtained by adding a constant value to the interphase voltage peak value, the regenerative start voltage value fluctuates according to the fluctuation of the AC power receiving voltage, and the rate of change of the regenerative current becomes substantially constant. Moreover, the DC voltage never becomes larger than the AC power receiving voltage, and the switching loss is small and the efficiency is high.

Example of Invention

An embodiment of the present invention will be described below with reference to FIG. In the figure, the interphase voltage V _AB of the AC received voltage (same for other interphase voltages)
Detecting a peak value, this providing a voltage setting circuit 26 for outputting a regeneration starting voltage E ₀ plus a predetermined value, except that so as to enter its output E ₀ to the subtracter 13, the second The configuration is exactly the same as the conventional example shown in the figure. Just set the voltage as above
Since E ₁ is E ₀ , the input / output characteristics of the subtracter 13 and the amplifier 14 are also shown in FIG. 7 in which E ₁ in FIG. 3 is changed to E ₀ , and this E ₀ is not a fixed value like E _1. It changes depending on the received voltage. However, the constant value is added to the peak value of the interphase voltage in consideration of an error in the detection of the peak value, and the size of the constant value may be considered to be sufficiently small. Therefore, when the motor as a load is unloaded or in the power running state, the DC voltage E does not exceed the peak value of the AC power receiving voltage (phase-to-phase voltage). Therefore, the input / output characteristics of the voltage error amplifier 14 in FIG. The command value I ₀ becomes 0 and no regenerative current flows. When the motor decelerates and the rotational energy of the motor is returned to the DC power supply as electrical energy, the DC voltage E exceeds the peak value of the AC power reception voltage and becomes voltage E ₀ or higher, and the regenerative current command determined by the characteristics in Fig. 7 The value I ₀ is generated and the regenerative current flows as in the conventional case. Further, since the regenerative current command I ₀ increases as the DC voltage E increases, the DC voltage E rises and becomes steady until the regenerative current command value I _{0 in} which the feedback power from the motor and the regenerative power to the AC power supply are balanced. It becomes a state. When the value of the DC voltage E in this case is E ₂ , the control system is designed so that E ₂ −E ₀ is almost constant with respect to the set value E ₀ and the characteristic of FIG. Therefore, the DC voltage E ₂ becomes a value slightly higher than the set value E ₀ , and accordingly the AC power receiving voltage peak value. Moreover, even if the received voltage fluctuates in this steady state, the set value E ₀ changes by the same amount as the fluctuation, and accordingly the voltage E ₂ also changes by the same amount. On the other hand, since the change in the interphase voltage V _{AB in} the equation (1) is the change in the received voltage itself, the rate of change in the regenerative current defined by the equation (1) hardly changes. For this reason, the transistor switching frequency hardly increases as the power receiving voltage rises, and the DC voltage E ₂ during regeneration is not fixed to a value higher than the maximum value of the expected AC power receiving voltage fluctuation range. Since it is set according to the magnitude of the AC received voltage at that time,
The switching loss of the transistor can be made smaller than that of the conventional control method. Furthermore, since the current change rate of the regenerative current does not change even when the received voltage drops, the amount of overcurrent of the regenerative current due to the control delay of the control circuit can be reduced, the current limiting operation becomes stable, and the control performance improves. . Further, as described above, the DC voltage E ₂ is not fixed to an unnecessarily high value as in the conventional case, so that when the inverter is used as a load in the regenerative converter, the switching loss of the inverter can be reduced. Moreover, when the DC motor is used as a load, the increase in the motor terminal voltage during regeneration does not become unnecessarily high, so that the chance of rectification limitation and flashover due to the terminal voltage increase can be greatly reduced.

〔The invention's effect〕

As apparent from the above examples, according to the present invention,
Even if the received voltage changes, the rate of change of the regenerative current can be kept almost constant, and the DC voltage can be kept to the necessary minimum.
There is an effect that the regenerative converter can be operated with high efficiency and in a good control state.

[Brief description of drawings]

1 is a diagram showing a main circuit of a regenerative converter, FIG. 2 is a diagram showing a conventional control device of a regenerative converter, FIG. 3 is a characteristic diagram of a conventional regenerative current command value, and FIG. 4 is a 120 ° phase detection. A time chart showing the operation of the circuit, FIG. 5 is a diagram showing a waveform of a DC regenerative current, and FIG. 6 is a diagram showing an embodiment of the present invention.
FIG. 7 is a characteristic diagram of the regenerative current command value in the embodiment of FIG. 1 ... AC power supply, 3 ... AC reactor, 4 ... Current detector, 5 ... DC voltage detector, 61-66 ... Transistor, 13,17,22 ... Subtractor, 14 ... Voltage error amplifier , 20 ...
… Triangle wave generator, 24 …… Comparator, 25 …… Phase detection circuit,
31-36 …… ON signal, 37-39 …… AND gate, E ……
DC voltage, I ... regenerative current, I ₀ ... current command value, E ₀ ...
Regeneration start voltage.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Juichi Ninomiya 7-1-1 Higashi Narashino, Narashino-shi Narashino Factory, Hitachi Ltd. (72) Inventor Sumio Kobayashi 7-1-1 Higashi Narashino, Narashino City Hitachi, Ltd. Narashino Factory (56) Reference JP-A-58-179180 (JP, A) JP-A-58-108972 (JP, A)

Claims (1)

(57) [Claims] 1. A peak value detecting means for detecting a peak value of an interphase voltage of an input AC power supply of a regenerative converter, and a regenerative voltage setting means for setting a value obtained by adding a constant value to the peak value of the interphase voltage as a regenerative start voltage value. A current command value setting means for outputting a current command value corresponding to the difference when the DC voltage at the output end of the regenerative converter exceeds the regenerative start voltage value, and the regenerative current flowing from the output end to the regenerative converter is When the current command value is lowered, an ON signal having a pulse width proportional to the difference is generated, and the ON signal is given to the switching element for flowing the regenerative current to the AC power source side through the reactor to supply the ON signal. A control device for a regenerative converter, comprising: a control means for controlling an effective value.