JPS6115672B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bulk commutation type voltage source inverter or a pulse width modulation type inverter of a type in which a switching element is inserted into the main circuit bus of a DC intermediate circuit, and particularly relates to a pulse width modulation type inverter of a type in which a switching element is inserted into the main circuit bus of a DC intermediate circuit. The present invention aims to provide a new inverter device that can reliably extinguish the arc of the element to be extinguished with very small arc extinguishing energy by not allowing current to flow back into the element to be extinguished. Generally, a switching element is inserted into the main circuit bus of the DC intermediate circuit, and this switching element is turned off during commutation to temporarily cut off the current from the input power supply and perform the specified commutation. Type inverters are well known in the art. The first model showed such a voltage source inverter using the batch commutation method.
In the figure, Ed is a variable DC power supply, and although not shown in the figure, as is well known, this power supply consists of thyristors connected in a Graetz connection and converts input AC power into DC power. , S ₁ to S ₆ are thyristors forming the inverse conversion section, D ₁ to _{D 6} are series diodes, and each commutating capacitor Cu to Cw−Cx
- This is to prevent the charge charge of Cz from being de-charged, D ₇ - _{D 12} are each feedback diodes that are used to circulate the reactive power during commutation, and S ⁷ is the main circuit of the DC intermediate circuit. A thyristor inserted into the bus bar that forcibly extinguishes the thyristor, as shown in the figure, consists of a commutating capacitor C ₁ - a commutating reactor L ₁ - auxiliary thyristors S ₈ and S ₉ - a diode D ₁₃ A circuit is added. M
indicates a load motor such as an induction motor, a permanent magnet type synchronous motor, etc. Since the operation of such a device is well known in the art, only the operation during commutation will be described. For example, when the S ₁ and S ₅ thyristors are conducting, the load current is flowing through the U and V phases, and in this state, the S ₆ thyristor is fired to transfer the load current from the V phase to the W phase. When commutating, first ignite the auxiliary thyristor _S8 of the forced extinguishing circuit, and transfer the charged charge of the commutating capacitor _C1 , which is charged with the polarity shown, to the main thyristor _S7 → auxiliary thyristor S ₈ → commutating reactor. The main thyristor S7 is discharged along the path _L1 →commutated capacitor _C1 , and the main thyristor _S7 is extinguished when the value of the discharge current exceeds the load current flowing through the main thyristor _S7 . After the main thyristor S ₇ is extinguished, a discharge current flows through the diode D _{13 ;}
The main thyristor _S7 is reverse biased by the forward voltage drop of , and the other auxiliary thyristor _S9 is ignited when the commutating capacitor _C1 has a reverse polarity to the illustrated polarity and charging has progressed. In this way the auxiliary thyristor S ₉
When ignites, the charged charge of the commutating capacitor _C1 , which is charged with a polarity opposite to that shown in the figure, is descharged through the path of the auxiliary thyristor _S9 → the feedback diodes _D1 to _D6 of the inverse conversion section → the commutating capacitor _C1 . do. During this series of operations, the inflow current from the power source Ed is cut off by extinguishing the main thyristor _S7 of the DC circuit in the inverse conversion section, but the energy stored in the load motor M is transferred to the motor. V-phase winding → Thyristor _S5 to be extinguished → Feedback diode
D ₁₀ →Recirculates through the U-phase winding path of the motor. At the same time that the load energy circulates in the loop, the thyristor S6 to be fired is fired, and the thyristor _S6 to be fired is extinguished by the charged charge of the commutating capacitor C _Y , which is descharged with the polarity shown. ₅ , but if we focus on thyristor S ₅ that should be extinguished, this thyristor S ₅
As mentioned above, a current that is the sum of the energy of the load motor and the discharge current from each commutating capacitor C ₁ -C _Y flowing in the opposite direction to this load energy flows, and the combined discharge Thyristor _S5 , which should be extinguished, does not extinguish unless the value of the current exceeds the circulating load energy. Therefore, as is clear from the above explanation, the discharge current from one commutating capacitor _C1 is a current that is shunted to the V phase, and if this current value is small, the discharge current from the other commutating capacitor C _Y is Unless the value is increased, thyristor _S5 cannot be turned off reliably. On the contrary, if the discharge current from the commutating capacitor C _Y is small, for example, the thyristor S ₅ cannot be extinguished unless the discharge current from the commutating capacitor C ₁ of the forced extinguishing circuit is increased. In this way, the conventional device shown in FIG. 1 cannot reliably extinguish the thyristor unless the discharge current from the commutating capacitor is extremely large.
Inevitably, it is necessary to increase the capacitance of the commutating capacitor in the forced arc-extinguishing circuit, and further, to increase the capacity of each commutating capacitor in the inverse conversion section to secure a large amount of arc-extinguishing energy. It is clear that if the commutating capacitor has a large capacity as described above, the inverter itself will inevitably become large and very uneconomical in terms of cost.

It should be noted that a so-called "pulse width modulation type inverter" in which a switching element is inserted into a DC intermediate circuit to perform a predetermined chopping operation, like a voltage source inverter of the batch commutation type, is also well known. Although such a pulse width modulation type inverter is not shown, compared to the voltage type inverter shown in FIG.
In terms of configuration, the variable DC power supply is bridge-connected with diodes to make a constant DC power supply, and the switching elements are arranged on the positive and negative busses of the DC intermediate circuit, respectively. However, in terms of operation, the switching element is turned on as appropriate.
It differs from the voltage source inverter in Figure 1 in that by performing OFF control, it performs chopping control at any point on the AC output voltage waveform applied to the load, and changes the pulse width of the output voltage to vary the voltage. . Even in such a conventional pulse width modulation type inverter, during commutation, the energy of the load is circulated through the thyristor and the feedback diode to be extinguished, so that the extinguishing energy can be sufficiently utilized as explained in detail in Fig. 1. As mentioned above, the capacitance of the commutation capacitor must be increased in order to increase the current.

The present invention was invented in view of this point, and will be described in detail below based on a specific example of the pulse width modulation method shown in FIG.

In the embodiment shown in FIG. 2, the same parts as in FIG. It is configured by bridge-connecting and converts the input AC power to DC power, and C ₂ is a smoothing capacitor inserted in the DC intermediate circuit to smooth the DC power supplied to the inverse conversion section. Then, S ₇ −S ₁₀ inserted into the main circuit busbar
are switching elements, the former S ₇ is for controlling the predetermined pulse width, and the latter S ₁₀ is for controlling the predetermined pulse width.
is used to extinguish the arc only during commutation to prevent the load energy from flowing back to the feedback diode group _D7 to _D12 through the switching element _S10 , and the diode _D13 -D connected in anti-parallel to the switching element ₁₄ is for preventing reverse voltage from being applied to each switching element. As is clear from the illustrated configuration, the inverter with the configuration of the present application has a smoothing capacitor C ₂
This inverter is different from conventional inverters in that the circuit with the feedback diode connected in parallel to this capacitor is inserted into the DC input side of switching element _S7 and the DC output side of switching element _S10 . This is a major feature of this application.

Now, the operation of this configuration will be explained in detail with reference to the time chart in FIG. 3. Each thyristor S ₁ to _{S 6} of the inverse conversion section has a conduction width as shown in the time chart in FIG. ON-OFF in specified order at 120°
On the other hand, one switching element S ₇ inserted into the main circuit busbar is appropriately chipped controlled within the conduction period of 120° of the thyristor group, as shown in _FIG. By keeping it constant and adjusting the OFF time width _T2 appropriately,
It performs an operation to control the DC voltage applied to the inverse conversion section. The other switching element _S10 is turned off for a predetermined time every time the thyristor group of the inverse conversion section commutates, as shown in FIG. 3, and this OFF time width _T3 is predefined. During the period corresponding to the OFF time of _T3 , the other switching element _S7 , which performs tipping control in conjunction with switching element _S10 , also
It is specified in advance to turn off.

Now, let us discuss in detail the operation in steady state, especially during commutation, when the above-mentioned operation is carried out.
Switching element at _one point t in the time chart shown in the figure
When S ₇ - S ₁₀ are conductive, the desired DC power is supplied to the inverter, and the thyristor in the inverter
It is assumed that when S ₁ -S ₅ are conductive, a load current is flowing through the U-phase winding and the V-phase winding of the load motor M. While this load current is flowing, the commutating capacitor Cu changes from DC power supply E → switching element S ₇ → thyristor S ₁ → commutating capacitor Cu → diode D ₂ → diode D ₅ → thyristor S ₅ → switching element S ₁₀ . By the current flowing through the path, it is charged to approximately the power supply voltage value with the polarity shown. On the other hand, the other commutating capacitor C _Y is DC power supply E → switching element S ₇ → thyristor S ₁ → diode D ₁ → diode D ₄ → capacitor C _Z → capacitor C _Y → thyristor S ₇ → switching element S ₁₀ By the current flowing through the path, the voltage is charged to approximately the power supply voltage value with the polarity shown. In this state, when one switching element _S7 is extinguished at point _t2 for stepping control, the energy stored in the U-phase winding → V-phase winding of the load motor is transferred from the V-phase winding → the diode. D ₅ -> thyristor S ₅ -> switching element S ₁₀ -> feedback diode D ₁₀ -> Emitted through the path of the U-phase winding. After a predetermined OFF time, the switching element _S5 is fired again to flow the load current between the U-phase winding and the V-phase winding, and then at time _t3 , the load current is commutated from the V-phase to the W-phase. At the same time as igniting the thyristor S ₆ of the inverse conversion section, the switching elements S ₇ to S ₁₀ are forcibly extinguished to cut off the power flowing from the DC power source E. When the incoming power is cut off in this way, the energy stored in the load motor will flow through the thyristor _S5 , which should be extinguished, but since the switching element _S10 on the negative bus side has already extinguished, the energy will not flow. I don't get it. Therefore, the above load energy is V
Phase winding → feedback diode D ₈ → smoothing capacitor
C ₂ → feedback diode D ₁₀ → flows through the path of the U-phase winding, and the smoothing capacitor C ₂ is charged up by the difference between the back electromotive force of the load motor and the power supply voltage of the DC power supply, and at the same time, the thyristor of the Z arm
By igniting _S6 , the charge charged in the commutating capacitor of C _Y with the polarity shown is de-charged through the path of thyristor _S6 → thyristor _S5 → commutating capacitor C _Y , and the arc is extinguished. Since no load energy is flowing through the thyristor _S5 , it is instantly extinguished by the charged charge. Note that the surplus charge of the commutating capacitor C _Y after the thyristor S ₅ is turned off is used as a reverse bias for the thyristor S ₅ in order to restore the forward blocking ability of the thyristor S ₅ that has been turned off. With this operation, the load current is commutated to the thyristor _S6 of the Z arm, and the current flows in the path between the U-phase winding and the W-phase winding of the load motor, and the time chart shown in FIG. 3 follows in the same manner. Commutation is carried out in a predetermined order and at a predetermined period as shown in _FIG .
The voltage pulse width of each half wave of the AC output voltage supplied to the load motor is automatically controlled by appropriately adjusting the OFF time width T ₂ within the load motor. It is clear that the same purpose can be achieved by using a gate turn-off thyristor or a transistor with self-extinguishing ability as the switching element, and furthermore, in this embodiment, the switching element _S10 on the negative side is simply turned Although we have described an example of use in which the switch is turned OFF only when the current is flowing, it is also possible to perform predetermined chopping control to control the pulse width, such as with the switching element on the positive side. In this case, the switching element on the positive side and the negative side Since each performs a predetermined chopping control, the switching frequency can be reduced to 1/2 compared to a single switching element, assuming the inverter output frequency is the same.

As described above, in the present invention, the load energy is prevented from flowing back to the thyristor group side of the inverse conversion section during commutation, whether it is a voltage source inverter using a lump commutation method or a pulse width modulation method inverter. Therefore, various effects can be achieved as shown below.

The arc-extinguishing energy only needs to be applied to sweep out the excess carrier of the thyristor and to apply a predetermined reverse bias voltage for a period corresponding to the turn-off time of the thyristor in order to restore the blocking ability, which is compared to conventional devices. There is an advantage that the thyristor that should be arc-extinguished can be reliably extinguished with very small arc-extinguishing energy.

Based on the advantage of item 1 above, the arc extinguishing energy is small, so according to the experimental results of the present inventors, it is sufficient to reduce the capacity of the commutation capacitor to a few tenths of that of the conventional device. , it has the advantage of being extremely compact and allowing the output frequency of the inverter to be extremely high.

A normal inverter device requires at least six commutating capacitors, so if the capacitance of the commutating capacitors is made small as in the present application, the device itself can be made extremely compact and costs can be significantly reduced.

Since the operation during commutation is very stable, an extremely reliable inverter device can be realized.

[Brief explanation of the drawing]

FIG. 1 is a specific circuit configuration diagram showing a conventional batch commutation type voltage source inverter, FIG. 2 is a specific circuit configuration diagram of a pulse width modulation type inverter showing an embodiment of the present invention, and FIG. The figure is a time chart showing the operation. E is a DC power supply, S ₁ to _{S 6} are thyristors, S ₇ - S ₁₀
is a switching element, _C2 is a smoothing capacitor,
Cu−Cw and Cx−Cz are commutating capacitors, D ₁ to _{D 6}
is a series diode, D ₇ − _{D 12} is a feedback diode,
M is a load motor.

Claims (1)

[Scope of Claims] 1. A forward conversion section that forward converts AC power to DC power, an inverse conversion section that reverse converts DC power to AC power, and a forward conversion section that is connected in parallel to the forward conversion section and smoothes the DC power. a rectifier circuit configured by bridge-connecting a smoothing capacitor and a feedback diode, connected in parallel to the smoothing capacitor, and full-wave rectifying load energy during commutation and storing it in the smoothing capacitor; a first switching element that is inserted into the positive electrode busbar on the DC output side of the converter and performs on-off control and chopping control in synchronization with the commutation of the element group of the inverse converter;
An inverter device comprising: a second switching element that is inserted into the negative bus on the DC output side of the forward converter and performs on-off control in synchronization with the commutation of the element group of the inverse converter. 2. The inverter device according to claim 1, wherein the second switching element performs chopping control.