JP2540877B2 - How to start the inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an inverter starting method for starting a PAM control type inverter.

B. Summary of the Invention The present invention is a method of starting an inverter driven by PAM control, which comprises a forward converter, a chopper circuit for voltage control, and an inverse converter, and an electric power stored in a smoothing capacitor on the inverse converter side. When the energy is larger than a predetermined set electric quantity, the electric energy is regenerated to the smoothing capacitor on the forward converter side by the control of the chopper circuit, and the electric energy is reduced to a predetermined set electric quantity or less and then the reverse conversion is performed. Drive control of the converter eliminates the need for a discharge resistor for discharging and consuming the energy stored in the smoothing capacitor on the inverse converter side, a magnet switch used as a condition for stopping the operation of the inverter, etc. In addition to downsizing, the inverter prevents overcurrent stop due to V / F control deviation at the start.

C. Conventional Technology Conventionally, an inverter driven by PAM (Pulse Amplitude Modulation) control has been constructed, for example, as shown in FIG. In FIG. 3, reference numeral 1 is a forward converter for converting 3-phase AC power into DC power, which is configured by connecting diodes in a 3-phase bridge. The positive output terminal of the forward converter _{1 is connected to} the collector of the first transistor TR ₁ forming the chopper circuit 2 via a parallel circuit composed of the inrush current control resistor R ₁ and the contact Mg ₁ of the short-circuit electromagnetic contactor. It is connected to the. A diode D ₁ having the illustrated polarity is connected between the collector and emitter of the transistor TR ₁ . The emitter of the transistor TR ₁ is connected to the positive terminal of the inverse converter 3 for converting DC power into AC power via the current detector (Hall CT) HCT ₁ and the ripple smoothing inductance L. Inverter 3 is 6
It is configured by connecting three transistors in a three-phase bridge. The negative terminal of the reverse converter 3 and the negative output terminal of the forward converter 1 are commonly connected via a DC negative bus N. A ripple smoothing capacitor C ₁ is connected between the common connection point 4 of the resistor R ₁ and the transistor TR ₁ and the DC negative bus N. Between the common connection point 5 of the transistor TR ₁ and the current detector HCT ₁ and the DC negative bus bar N, the second transistor TR ₂ constituting the chopper circuit 2 and the diode D of the polarity shown in the figure are provided.
₂ are connected in parallel. Between the ripple smoothing inductance L and the common connection point 6 of the inverse converter 3 and the DC negative bus N, a ripple smoothing capacitor C ₂ and a series circuit composed of a contact Mg ₂ and a resistance R _{2 of the} electromagnetic contactor are provided. It is connected in parallel. The DC output voltage of the forward converter 1 is voltage-controlled by the chopper circuit 2 and applied to the ripple smoothing capacitor C ₂ . The inverse converter 3 converts the direct current energy stored in the capacitor C ₂ into alternating current and supplies it to a load (not shown).

D. Problems to be Solved by the Invention In the starting method of the inverter configured as described above, the contact Mg ₂ of the electromagnetic contactor is closed on condition that the operation of the inverter is stopped, and the transistor TR ₁ Leakage from the capacitor and the electric charge of the capacitor C ₂ accumulated at the time of a fault trip are discharged and consumed by the resistor R ₂ , and then the inverter is started. As described above, according to the starting method of FIG. 3, an electromagnetic contactor and a discharge resistor are required to discharge and consume the stored energy of the capacitor C ₂ when the inverter is stopped, and the number of parts in the main circuit increases. The size of the entire device becomes large and the cost becomes high. Further, there is a problem in that the temperature inside the device rises due to heat generation due to the power consumption of the discharge resistance, and the charging power of the capacitor C ₂ cannot be effectively used.

Also, when starting without using the discharge resistance,
V / F control for controlling the ratio between the voltage V and the frequency F is largely shifted by the electric charge accumulated in the capacitor C ₂ , and the inverter may not start normally due to overcurrent.

The present invention has been made in view of the above points, and an object thereof is V / V without using a discharge resistor or a magnet switch.
An object of the present invention is to provide a starting method of an inverter that can start the inverter without causing an F shift.

E. Means for Solving the Problems In the present invention, a positive side output end of a forward converter for direct current exchange of alternating current power is connected to a direct current through a first transistor for a chopper circuit and a smoothing inductance in series. It is connected to a positive side input terminal of an inverse converter for converting electric power into AC, a first smoothing capacitor is connected between the positive and negative output terminals of the forward converter, and a second smoothing capacitor is connected between the positive and negative input terminals of the inverse converter. And a diode for a chopper circuit is connected in parallel to the first transistor such that the cathode is on the forward converter side and the anode is on the inverse converter side.
A second chopper circuit is provided between the common connection point of the first transistor and the smoothing inductance and the DC negative bus.
In the starting method of the inverter for starting the PAM control type inverter configured by connecting the transistors, the electric energy stored in the second smoothing capacitor at the time of starting the inverter is larger than a predetermined set amount of electricity. When the first transistor of the chopper circuit is turned off, the second transistor is chopper controlled to regenerate the electric energy stored in the second smoothing capacitor to the first smoothing capacitor. If the electric energy stored in the second smoothing capacitor is less than or equal to a predetermined set amount of electricity, the first transistor of the chopper circuit is turned on and then the inverse converter is driven and controlled. It is characterized by that.

F. Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In FIGS. 1A and 1B, the same parts as those in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted. FIG. 1 (a) shows the main circuit configuration of the inverter when the embodiment of the present invention is applied. The difference from FIG. 3 is that the contact Mg _{2 of the} electromagnetic contactor and the resistance R ₂ for discharging are At the same time, the regenerative discharge circuit 7 including the resistor R ₃ and the transistor TR ₃ is connected between the common connection point 4 of the resistor R ₁ and the transistor TR ₁ and the DC negative bus N, and the common connection point 6 is provided.
Current detector (Hall CT) HCT ₂
Is inserted, and the other parts are configured the same as in FIG. The regenerative discharge circuit 7 is a circuit for regenerating energy when, for example, dynamic braking is performed during operation of the inverter. FIG. 1 (b) is a control circuit for executing the starting method of the present invention, and CP is a comparator having a hysteresis effect and an overcurrent limiting function.
The detection output of the current detector HCT ₁ is input to the inverting input terminal of the comparator CP via the resistor R ₄ . Comparator CP
A reference voltage obtained by dividing the control power supply voltage +15 V by resistors R ₅ and R ₆ is applied to the non-inverting input terminal of the. A resistor R ₇ is connected between the non-inverting input terminal and the output terminal of the comparator CP. The output of the comparator CP (the deviation between the detection output of the current detector HCT ₁ and the reference voltage) is supplied to one input terminal of the AND circuit 8. An inverter operation command (gate ON signal) is supplied to the other input terminal of the AND circuit 8 from a microcomputer (not shown). The output signal of the AND circuit 8 is supplied to the chopper gate 9 of the control circuit of the chopper circuit 2 as an ON / OFF control signal. The output signal of the chopper gate 9 is supplied to the bases of the transistors TR ₁ and TR ₂ of the chopper circuit 2 via the drivers 10a and 10b.

Next, the operation of starting the inverter using the circuit configured as described above will be described with reference to the time chart of FIG. Now, it is assumed that the operation of the inverter is stopped and a predetermined amount of electric charge is accumulated in the ripple smoothing capacitor C ₂ . First, at time t ₁ , a motion command signal (“H” level signal) for starting the inverter is supplied from the microcomputer (not shown) to the other input end of the AND circuit 8. If the detection output of the current detector HCT ₁ (electrical signal proportional to the amount of energy stored in the capacitor C ₂ ) is larger than the reference voltage applied to the non-inverting input terminal of the comparator CP, the deviation output of the comparator CP becomes It is at the “L” level. Therefore, the output of the AND circuit 8 becomes an "L" level signal, and the driver 10a controls the transistor TR ₁ of the chopper circuit 2 to be off based on the output of the chopper gate 9. After turning off the transistor TR _{1 in} this way, the transistor TR ₂ is chopper-controlled to control the capacitor C ₂
The stored energy of the inductance L, current detector HCT ₁
And it is regenerated to the ripple smoothing capacitor C ₁ on the side of the forward converter ₁ via the diode D ₁ . This regenerative operation is performed, for example, by alternately turning on and off the transistor TR ₂ . That is, when the transistor TR ₂ is turned on, the charge of the capacitor C ₂ is discharged through the inductance L, the current detector HCT ₁ and the transistor TR ₂ , and energy is stored in the inductance L at that time. Next, when the transistor TR ₂ is turned off, the energy stored in the capacitor C ₂ and the inductance L is supplied to the capacitor C ₁ via the current detector HCT ₁ and the diode D ₁ . In this way, when the energy stored in the ripple smoothing capacitor C ₂ on the inverse converter 3 side is regenerated to the ripple smoothing capacitor C ₁ on the forward converter 1 side, the terminal voltage of the capacitor C ₂ drops and the current detector The detection output of HCT ₁ becomes smaller than the reference voltage applied to the non-inverting input terminal of comparator CP. Therefore, the deviation output of comparator CP is "H".
The output level of the AND circuit 8 is also inverted to "H" level. Then at time t _2, the with the driver 10a is turned on control transistor TR ₁ of the chopper circuit 2 based on the output of the chopper gate 9, the control circuit of the inverter 3 (not shown) is a transistor gate of the inverter 3 ON control. This starts the inverter.
The reference voltage applied to the non-inverting input terminal of the comparator CP is the inverse converter 3 when the inverse converter 3 is ON-controlled.
Is set to a value that will not stop the operation due to overcurrent. With this setting, the stored energy (voltage across both ends) of the ripple smoothing capacitor C ₂ on the inverse converter 3 side can be set to a normal value during the period T from the time t ₁ to the time t _2, and a smooth value can be obtained. The inverter can be started. Although the detection output of the current detector HCT ₁ is used in the above embodiment, the present invention is not limited to this, the voltage across the ripple smoothing capacitor C ₂ is detected, and the detected voltage is introduced to the inverting input terminal of the comparator CP. It may be configured to do so.

Since the signal for controlling the chopper circuit 2 is created based on the output of the comparator CP having a hysteresis effect, even if the comparator input changes significantly,
Saturation and oscillation of the inductance L can be suppressed.

G. Effects of the Invention As described above, according to the present invention, the following effects can be obtained. That is, (1) the discharge resistor for discharging and consuming the stored energy of the smoothing capacitor on the inverse converter side and the magnet switch used as a condition for stopping the operation of the inverter are unnecessary, improving reliability and reducing the device size. The cost can be reduced.

(2) Unlike the conventional starting method, the discharge resistor does not consume power, and the energy stored in the smoothing capacitor on the reverse converter side is regenerated to the smoothing capacitor on the forward converter side. It does not rise, and power can be used effectively.

(3) Since the energy stored in the smoothing capacitor on the inverse converter side can be suppressed to a normal value when the inverter is started,
The inverter will not stop due to overcurrent due to V / F control deviation.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a), (b) and FIG. 2 all show an embodiment of the present invention, and FIG. 1 (a) is a main circuit diagram of an inverter,
1 (b) is a control circuit diagram of the inverter, FIG. 2 is a time chart of the operation mode, and FIG. 3 is a main circuit diagram of the inverter for explaining a conventional starting method. 1 ... Forward converter, 2 ... Chapper circuit, 3 ... Inverse converter, 8 ... AND circuit, 9 ... Chopper gate, 10a, 10
b …… Driver, C ₁ , C ₂ …… Ripple smoothing capacitor, D ₁ , D ₂ …… Diode, HCT ₁ …… Current detector, L…
… Ripple smoothing inductance, R _{1 to} R ₇ … Resistance, TR
₁ , TR ₂ , TR ₃ …… Transistor, CP …… Comparator.

Claims (1)

(57) [Claims] 1. A reverse converter for converting DC power to AC through a positive side output end of a forward converter for converting AC power to DC through a first transistor for a chopper circuit and a smoothing inductance in series in order. The first smoothing capacitor is connected between the positive and negative output terminals of the forward converter and the second smoothing capacitor is connected between the positive and negative input terminals of the reverse converter, and the chopper is connected to the positive side input terminal. A circuit diode is connected in parallel to the first transistor such that the cathode is on the forward converter side and the anode is on the inverse converter side,
A second chopper circuit is provided between the common connection point of the first transistor and the smoothing inductance and the DC negative bus.
In the starting method of the inverter for starting the PAM control type inverter configured by connecting the transistors, the electric energy stored in the second smoothing capacitor at the time of starting the inverter is larger than a predetermined set amount of electricity. When the first transistor of the chopper circuit is turned off, the second transistor is chopper controlled to regenerate the electric energy stored in the second smoothing capacitor to the first smoothing capacitor. If the electric energy stored in the second smoothing capacitor is less than or equal to a predetermined set amount of electricity, the first transistor of the chopper circuit is ON-controlled and then the inverse converter is drive-controlled. A method for starting an inverter, which is characterized in that