JPH0417038B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a motor control device using a voltage source inverter.

[Background of the invention]

Most motor control devices using voltage source inverters are constructed as shown in FIG.

1 is a three-phase AC power supply, 2 is a forward converter that receives power from the power supply 1 and rectifies it, 3 is a capacitor that smoothes the output of the forward converter 2, and 4 is a converter that receives the DC power smoothed by the capacitor 3, and this 6 is a switching control circuit that constitutes a part of the inverter, and 7 is a current that detects the magnitude of the input current of the inverter. This is a shunt resistor as a detection means.

The main circuit 4 of the inverter is composed of transistors Q ₁ -Q ₆ as main switching elements, and flywheel elements D ₁ -D ₆ connected in antiparallel to the respective main switching elements.

Transistors Q ₁ and Q ₂ , Q ₃ and Q ₄ , and Q ₅ and Q ₆ are connected in series, and both ends thereof are connected to both terminals of capacitor 3. Also, the series connection point P ₁ ,
One terminal of the electric motor is connected to P ₂ and P ₃ , respectively.

The switching control circuit 6 has a built-in speed command means, and is configured to control each main switching element so that the output voltage and output frequency of the inverter become values corresponding to the output of the speed command means. There is. Further, the switching control circuit 6 is configured to make each of the main switching elements Q ₁ to Q ₆ non-conductive when the current detection means 7 detects a current of a certain value or more.

Now, this current detection means 7 is provided for the purpose of protecting the main switching elements Q ₁ to _{Q 6} and the motor 5 from overcurrent, but during regeneration control, in addition to the current flowing through the current detection means 7, for example, the electric motor 5 , the diode D ₁ , and the main switching element Q ₅ to reach the motor 5. It is found that if only the current detection means 7 is provided on the input side of the inverter 4, the main switching elements Q ₁ to _{Q 6} It was found that the motor 5 and motor 5 could not be protected from overcurrent. Circulating current can also be detected by providing a current detection means on the output side of the inverter 4, but in this case it is not a special measure because it is necessary to separately detect the currents flowing in at least two phases.

It should be noted that a device in which a current detection means is provided on the input side of the inverter is known from Japanese Patent Application Laid-open No. 78372/1983.

[Purpose of the invention]

The present invention has been made in view of the above points, and its object is to construct a motor control device that can protect a main switching element and a motor from circulating current.

[Summary of the invention]

That is, in the present invention, an OFF control means is provided for temporarily turning OFF the main switching elements that were in the conductive state at the same time, thereby preventing the growth of circulating current.

First, a first embodiment of the present invention will be described with reference to FIGS. 1 to 3. The main circuit configuration is the same as that shown in FIG. This embodiment has a feature in the switching control circuit 6, which will be explained below.

In this embodiment, mode detection means 10 is provided to detect the regeneration mode, and when the mode detection means 10 detects the regeneration mode, the off control means 11 is operated to temporarily turn off all the main switching elements Q ₁ to _{Q 6} at the same time. It is configured to be in the state.

101 is a speed command means for commanding the speed of the electric motor 5, and 102 is a slow acceleration/deceleration command output means for softening sudden changes in the output of the speed command means.

Reference numeral 103 denotes voltage command means 1 for commanding a voltage of a magnitude matching the output of the slow acceleration/deceleration command output means 102;
04 is a frequency command means for commanding a frequency that matches the output of the slow acceleration/deceleration command output means 102.

105 is a sine wave generating means for generating a sine wave with a voltage matching the output of the voltage commanding means 103 and a frequency matching the output of the frequency commanding means 104; 106 is a carrier wave generating means.

A pulse width modulation circuit 107 compares the output of the sine wave generation means 105 and the output of the carrier wave generation means 106 to modulate the pulse width.

A logic circuit 108 performs a logical operation on the output of the pulse width modulation circuit 107 and the output of the off control means 11, and this output becomes the base signal of the main switching element _Q1 .

109 is an inversion circuit that inverts the output of the pulse width modulation circuit 107; 110 is a logic circuit that performs a logical operation on the output of the inversion circuit 109 and the output of the off control means 11; this output is the base signal of the main switching element _Q2 ; becomes. The main switching element _Q3
~The circuit that creates the base signal to _Q6 is not shown in this diagram. These are provided with sine wave generating means that receive the output of the voltage command means 103 and the output of the frequency command means 104, and have a phase difference of 120 degrees and 240 degrees in electrical angle from the output of the sine wave generation means 105, respectively. Consider that there are two more sets of circuits that have the same configuration except for one thing. In this case, the carrier wave generating means 106
and off control means 11 are used commonly for all phases.

Now, the mode detection means 10 is the speed command generation 10.
1. In addition to the gradual acceleration/deceleration command output means 102, the output of the speed command means 101 and the gentle deceleration command output means 102
The comparator 111 compares the output of the
This comparator 111 is connected to the slow acceleration/deceleration command output means 102.
It is determined that the regeneration mode is in effect when the output of the speed command means 101 is smaller than the output of the speed command means 101.

The off control means 11 compares the signals of the sawtooth wave generation circuit 112 and the binary level signal generation circuit 113, and determines whether the output of the sawtooth wave generation circuit 112 is higher than the output of the binary level signal generation circuit 113. The comparator 114 generates a signal only when the signal is large. The binary level signal generation circuit 113 always outputs a signal larger than the output of the sawtooth wave generation circuit 112 and outputs a signal indicating the regeneration mode when the mode detection means 10 is not outputting a signal indicating the regeneration mode. Sometimes, it is configured to output a signal between the output of the sawtooth wave generating circuit 112 and the maximum and minimum values.

In addition, 115 is a change stop command circuit that temporarily stops the output change of the slow acceleration command output means when the output of the current detection means 7 is above a certain value, and the configuration of this circuit is detailed in Japanese Patent Publication No. 59-20274. It is written.

Now, in the configuration as described above, the mode detection means 10 does not send any signal to the off control means in the forward mode. Therefore, as shown in FIG. 2, the output a of the binary level signal generation circuit 113
is always larger than the output b of the sawtooth wave generating circuit 112, so the output of the comparator 114 is always "L" as shown in c. Therefore, the logic circuit 108 outputs the output of the pulse width modulation circuit 107 as it is as the base signal of the main switching element _Q1 .
Reference numeral 10 outputs the output of the inversion circuit 109 as it is as a base signal of the main switching element _Q2 .
d is a current flowing through the current detection means 7.

When in the regeneration mode, the mode detection means 10 outputs a signal to the off control means indicating that it is in this mode. Therefore, the binary level signal generation circuit 1
The output of 13 becomes a value smaller than the maximum value of the output b of the sawtooth wave generating circuit 112, as shown by a', and the comparator 114 comes to output a pulse-like signal shown as c'. Therefore, the logic circuit 10
8, 110, regardless of the output of the pulse width modulation circuit 107 or the inverting circuit 109, the comparator 114
When outputting an H'' signal, the base signals of Q ₁ and Q ₂ are cut off.The output of this off control means 11 is output to the other main switching element Q ₃ as described above.
Since it also acts in common on the circuit that generates the base signal of ~ _Q6 , all the main switching elements _Q1 ~ _Q6 are temporarily turned off at the same time.

Since the electric motor 5 includes reactance, the circulating current tends to grow with a certain time constant as time passes. However, in the present invention, since the circulating current is temporarily interrupted, it decreases when the interruption occurs and increases again when the interruption is removed. Therefore, an increase in vertical ring current can be suppressed. Since the main switching elements Q ₁ to _{Q 6} are all temporarily cut off, the circulating current changes its flow path as shown by d ₁ , d ₂ , and d ₃ in FIG. 3 and flows into the current detection means 7.

FIG. 4 shows a different embodiment of the invention. The difference from the embodiment shown in FIG. 1 is that in the embodiment shown in FIG. 1, all switching elements _Q1 to _Q6 are cut off when in regeneration mode, whereas What is shown in the figure is that all the switching elements Q ₁ to _{Q 6} are cut off when the current detection means 7 detects a current value of a certain value or more.
For this purpose, a comparator 111' is provided to compare the output of the current detection means 7 with a set value, and this comparator 111' outputs a signal "L" when the output of the current detection means 7 is smaller than the set value, and outputs a signal "L" when the output is larger than the set value. It is configured to output "H". In addition, the binary level signal generation circuit 113 outputs the output of the comparator 111' as "L".
When , it is configured to output a constant value larger than the maximum value of the sawtooth wave generation circuit 112, and when it is "H", a signal between the maximum value and the minimum value of the sawtooth wave generation circuit 112 is output. be. Although the case where a transistor is used as the main switching element has been described above, the present invention can also be implemented when a thyristor is used.

〔Effect of the invention〕

As is clear from the above description, the present invention has the effect of suppressing the growth of circulating current since it is provided with an off control means that temporarily turns off the main switching elements that are in a conductive state at the same time.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the control device of the present invention, FIG. 2, FIG. 3 is a time chart used to explain the operation of the embodiment shown in FIG. 1, and FIG. 4 is a control device of the present invention. FIG. 5 is a circuit diagram showing a conventional control device. 2 is a forward converter, 3 is a capacitor, 4 is an inverse converter, 7 is a current detection means, 10 is a mode detection means,
11 is an off control means.

Claims (1)

[Scope of Claims] 1. A DC power source, and an inverter that receives power from the DC power source, converts the power to AC, and supplies the power to an electric motor, and the inverter includes a plurality of main switching elements and the A motor control device comprising a plurality of flywheel elements connected in antiparallel to each of the main switching elements, and a switching control circuit that controls on/off the plurality of main switching elements. an off control means that simultaneously turns off all of the motors; a mode detection means that detects that the electric motor is in a regenerative operation mode; and an output signal of the off control means and the switching control based on the mode detection means detecting the regeneration mode. A motor control device comprising a signal switching means for alternately switching output signals of a circuit. 2. It has a DC power supply, an inverter that receives the power of the DC power supply, converts the power to AC, and supplies it to the electric motor, and a current detection means that detects the magnitude of the input current of the inverter, The inverse converter includes a plurality of main switching elements, a plurality of flywheel elements connected in antiparallel to each of the main switching elements, and a plurality of main switching elements that turn on the plurality of main switching elements;
A motor control device comprising a switching control circuit that performs OFF control, including OFF control means that simultaneously turns off all of the plurality of main switching elements, and an OFF control circuit that controls the motor to be in a regenerative operation mode and the input current of the inverter is a predetermined value. mode detecting means for detecting that the switching control circuit has exceeded the switching control circuit; and signal switching means for alternately switching between the output signal of the off control means and the output signal of the switching control circuit based on the detection output of the mode detecting means. Electric motor control device.