JPS582552B2 - current source inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current source inverter having a forced commutation circuit suitable for driving an AC motor or the like.

As is well known, there are two types of inverter devices: current type and voltage type, but especially when used as a variable frequency control power source for an AC motor, the thyristor Leonard is used because it is easy to regenerate power to the AC power source during regenerative braking operation. A system that combines a current source inverter is used.

Generally, a voltage source inverter has a feedback diode in antiparallel with the main circuit element, and by turning off the main circuit element a current path is formed through the feedback diode, so only the commutation (turn-off) of the main circuit element is considered. However, current source inverters do not have feedback diodes, and a smoothing reactor connected in series with the main circuit causes a nearly constant current to continue to flow from the power supply, so in addition to commutation of the main circuit elements, The current path and load actance energy handling after the main circuit elements are turned off must be considered.

For this reason, conventional current source inverter devices use commutating capacitors to commutate (turn off) the thyristor, which is the main circuit element, and to process the subsequent current path and reactance energy.

Fig. 1 is a circuit example of a conventional current type Sanwa inverter device based on the above idea, where the input power source is a variable DC power source Vs,
The load is a Sanwa induction motor IM.

This inverter circuit is called a series diode type, and is the most commonly used circuit at present.

To explain the operation during commutation, from the DC power supply Vs to the DC reactor LD, thyristor QUP and diode DUP
, U phase, W phase of load induction motor IM, diode DWN
, a case will be described in which the current flowing in the U phase is commutated to the ■ phase from a state where the current is flowing through the thyristor QWN.

Commutation capacitor CVP is charged with the polarity shown.

When QVP is ignited, QUP is activated by the voltage of the commutating capacitor.
is turned off, and the current from the LD flows through QVP, CVP, and DUP to the U phase, charging CVP to a polarity opposite to that shown in the figure.

When the first charging voltage exceeds the U-V phase voltage of the motor, the DVP begins to conduct, and a resonant circuit is formed by the inductance of the CVP and the motor, and as the U-phase current decreases, the ■-phase current increases, resulting in direct current. When the current becomes equal to the current IDC, the U-phase current becomes zero, and the commutation to the ■ phase is completed.

Although I have explained that only CVP is dynamically fixed as a commutating capacitor, in reality, the series capacitors CWP and CUP are also connected in parallel with CVP, and the capacitor is equivalently 1.5 times that of one commutating capacitor. Operates as a capacity.

The inverted capacitor voltage is further inverted in the process of commutation from ■ to W and from W to U, returning to the initial state.

The first drawback of the above-exemplified current source inverter device is that these commutating capacitors must be charged to a predetermined relationship voltage at startup, and the energy equivalent to the inductance of the motor, which is the load, is Since the commutating capacitor is overcharged, the capacitance of the commutating capacitor must be changed by the load motor in order to operate the inverter optimally, which complicates charge control.The second disadvantage is that the commutating operation After the main circuit thyristor is turned off and the commutating capacitor is charged to the opposite polarity to the load's induced voltage, there is a dead time in which the load current does not change.

This dead time changes depending on the magnitude of the load current and induced voltage, and is a factor in the instability of this type of current source inverter.

Furthermore, when the load current is small, this dead time becomes long and normal operation cannot be performed.

The present invention has been made in view of the above circumstances, and is capable of stably operating and economical equipment that includes a charged capacitor or an auxiliary DC power supply, and allows the load current to start commutation at the same time as commutation operation starts. The purpose is to provide a current source inverter.

Hereinafter, one embodiment of the present invention will be described using a three-phase inverter as an example with reference to FIGS. 2 and 3.

In Fig. 2, ■S is a variable DC power supply, LD is a DC reactor for smoothing, and one terminal of the DC reactor LD is connected to one side of the variable DC power supply ■S (hereinafter simply referred to as DC power supply) through the positive bus P1. Connected to the terminal.

The other terminal of the DC reactor LD is connected to the positive bus P2.

The other terminal of the DC power supply ■S is connected to the negative bus N1.

IN is the induction motor of the load, and the terminals are U, V, and W.

Main thyristor QUP, QVP, QWP, QUN, QVN
, QWN constitute a main three-phase bridge, and as shown in the figure, the anodes of the positive main thyristors QUP, QVP, QWP are connected to the positive bus P2, and the negative main thyristors QUN, QVN, The cathode of QWN is connected to the negative bus N1 mentioned above, the cathode of the main thyristor QUP and the anode of the main thyristor QUN are connected, the connection point is connected to the terminal U of the induction motor IN, and QVP and QVN are similarly connected in series. The connection point is connected to the terminal V, QWP and Hiro are connected in series, and the connection point is connected to the terminal W.

First auxiliary thyristor SUP, SVP, SWP, SUN
, SVN, and SWN constitute an auxiliary three-phase bridge,
The first auxiliary thyristor SUN on the negative side as shown in the figure
, SEN, SWN are connected to the positive bus P3,
The anodes of the first auxiliary thyristors SUP, SVP, and SWP on the positive side are connected to the negative bus N3, the cathode of SUP and the anode of SUN are connected, and the connection point is connected to the terminal U of the induction motor IM, and similarly SVP and SVN are connected in series and their connection point is connected to terminal (2), and SWP and SWN are connected in series and their connection point is connected to terminal W.

Thyristor SP is the second auxiliary thyristor on the positive side,
Its anode is connected to the positive bus P2, and its cathode is connected to the positive bus P3.

Thyristor SN is a second auxiliary thyristor on the negative side,
Its anode is connected to the negative bus N3, and its cathode is connected to the negative bus N1.

CHP is a positive side choppa, CHN is a negative side choppa,
In this embodiment, in order to simplify the explanation, an example will be shown in which GTO (gate turn-off thyristor) is used for these choppers.

The anode of the Chotsuba CHP is connected to the positive bus P3, and the cathode is connected to the positive bus P4.

The anode of the chopper CHN is connected to the positive bus P5, and the cathode is connected to the negative bus N3.

A capacitor Cc or an auxiliary DC power supply (not shown) is connected between the positive bus lines P4 and P5.

Further, DP is a positive side diode, and DN is a negative side diode.

The anode of the diode DP is connected to the positive bus P3, and the cathode is connected to the positive bus P5.

The anode of the diode DN is connected to the positive bus line P4, and the cathode is connected to the negative bus line N3.

In addition, the variable DC power supply ■S often uses DC that is rectified by controlling the phase angle of the Sanwa AC power supply with a three-phase pure bridge, and the Chotupa CHP and CHN are equipped with a commutation device in addition to the GTO. It may also be configured with a silice chopper, a transistor, or the like.

Furthermore, Cc uses a large-capacity electrolytic capacitor or an auxiliary DC power source (such as a storage battery) that can be charged and discharged.

Next, the operation of the present invention configured as above will be explained with reference to FIGS. 2 and 3.

In order to simplify the explanation, Cc will be explained using a capacitor, and it is assumed that the capacitor Cc has a sufficiently large capacity and its voltage does not change even during charging and discharging during the commutation process.

In addition, the inductance of the DC reactor LD is sufficiently large, and the current flowing through this LD during the commutation process is a constant value I
Assume that there is no change in d.

In FIG. 3, IU, IV, and IW represent currents flowing through the windings of the motor, ①CHP to ISWN represent currents flowing to the elements indicated by subscripts, and CHP to SWN represent ignition signals applied to the elements.

Each symbol corresponds to the symbol shown in FIG.

It is assumed that the capacitor Cc is charged with the polarity shown.

For example, before starting the operation of the inverter, this capacitor is connected to the DC power supply
→ Second auxiliary thyristor SP → Diode DP → Capacitor Cc → Diode DN → Second auxiliary thyristor SN
All you have to do is charge it to the desired voltage using the following route.

Now, in Fig. 3, the main thyristors QUP and QWN are turned on at time t0, and the motor IM is connected to the Id
Assume that a current is flowing.

■ DC power supply ■S → DC reactor LD → main thyristor QUP → winding (U-O) → winding (O-W) → main thyristor QWN → DC power supply ■S From such a state, at time t1, the chopper CHP, CHN ,
Second auxiliary thyristor SP and first auxiliary thyristor S
When VP is turned on at the same time, the following closed circuit is formed.

■ Second auxiliary thyristor BP → chopper CHP → capacitor Cc → chopper CHN → first auxiliary thyristor S
VP → winding (V-0) → winding (0-U) → main thyristor QUP → second auxiliary thyristor SP capacitor Cc is discharged through this closed circuit, but as this discharge current increases, finally is the main thyristor QUP → winding (U-0)
The current that was flowing in becomes zero, and in this state, the positive bus P2
The current Id that was flowing through the DC reactor LD all flows through the second auxiliary thyristor SP, the chopper CHP, the capacitor Cc, the chopper CHN, the first auxiliary thyristor SVP, and the winding (V-0).

That is, the current is commutated from the winding (U-0) to the winding (V-0).

This point in time is shown as t2 in FIG.
The time between 1 and t2 is referred to as current overlap time U.

Even after time t2, the choppers CHP and CHN remain on until time t3, and the current is ■ DC power supply ■ S → DC reactor LD → second auxiliary thyristor SP → chopper CHP → capacitor Cc → chopper CHN → first auxiliary Thyristor SVP → winding (V-
0) → winding (0-W) → main thyristor QWN → DC power supply ■S.

The time from time t2 to t3 is selected to be sufficient for the previously conducting main thyristor QUP to recover its forward blocking capability, and this time is designated as the recovery time δ.

That is, the choppers CHP and CHN must remain on for the time TCH that is the sum of the overlap time U and the recovery time δ.

Here, the amount of charge discharged from the capacitor Cc from t1 to t3 is the area D shown by Icc in FIG.

Next, when the choppers CHP and CHN are turned off at time t3, the current flows through the next current path.

■ DC power supply ■ S → DC reactor LD → second auxiliary thyristor SP → diode Dp → capacitor Cc → diode DN → first auxiliary thyristor SVP → winding (V-
0) → Winding (0-W) → Main thyristor QWN → DC power supply VS The current in this current path flows in the direction of charging the capacitor Cc, and the charge weight that flowed out between t1 and t3 described above is The flow is controlled to continue for a sufficient amount of time to recharge an equal amount of charge.

That is, in the diagram of Icc in FIG. 3, area C indicates the amount of recharged charge, and at time t4 when area C and the area D described above become equal, the main thyristor QVP is fired.

The firing time t4 of the main thyristor QVP can be determined by, for example, detecting the voltage of the capacitor Cc and determining the firing timing when this voltage becomes equal to a predetermined value. , it becomes possible to perform stable operation regardless of load fluctuations.

The period from time t3 to time t4 is called a recharge time Tc.

When the main thyristor QVP is turned on at time t4, until now the positive bus P2 second auxiliary thyristor SP → diode DP
→ Capacitor Cc → Diode DN → The current that was flowing into the winding (V-0) through the first auxiliary thyristor SVP now flows through the positive bus P2 → the main thyristor QVP, and at this point it is the first time that the current flows from the main thyristor QUP to the QV
The commutation of current to P is completed.

This switching of the current path occurs almost instantaneously, assuming that there is no inductance in the circuit wiring, for example.

The current path after time t4 is ■ DC power supply ■S → DC reactor LD → main thyristor QVP → winding (V-0) → winding (0-W) → main thyristor QWN → DC power supply ■S, and completes the one-turn process. finish.

The above is an explanation of the commutation operation from U phase to ■ phase, but the third
Commutation operations in other phases will also be easily understood with reference to the figures.

The figure also shows the waveforms of current flowing through each part when operated in this manner.

As another embodiment, an operation mode as shown in FIG. 4 may be adopted.

The operation will be briefly explained with reference to FIGS. 2 and 4.

Current path at time t0 ■ DC power supply ■ S → DC reactor LD → main thyristor QUP → winding (U-0) → winding (0-W) → main thyristor QWN → DC power supply ■ S Chotsupa CHP, C at time t1
At the same time that HN, the second auxiliary thyristor SP, and the first auxiliary thyristor SUP are turned on, the main thyristor QUP is turned off, and the current path becomes as follows.

■ DC power supply VS → DC reactor LD → second auxiliary thyristor SP → chopper CHP → capacitor Cc → chopper CHN → first auxiliary thyristor SUP → winding (U-
0) → winding (0-W) → main thyristor QWN → DC power supply ■S With the current flowing in this path, the capacitor Cc is discharged.

Next, when the choppers CHP and CHN are turned off at time t2, the current flows through the next path.

■ DC power supply ■ S → DC reactor LD → second auxiliary thyristor SP → diode DP → capacitor Cc → diode DN → second auxiliary thyristor SUP → winding (U-
0) → winding (0-W) → main thyristor QWN → DC power supply ■S The capacitor Cc is charged by the current in this path.

Next, when the main thyristor QVP is turned on at time t2, the next closed circuit is created.

■ Positive bus P2 → Main thyristor QVP → Winding (■-0)
→ S line (0-U) → first auxiliary thyristor SUP → diode DN → capacitor Cc → diode DP → second auxiliary thyristor SP → positive bus P2 As the current in this closed circuit increases, finally, Until now, second auxiliary thyristor SP → diode DP → capacitor Cc → diode DN → first auxiliary thyristor SUP
→The current flowing in the winding (U-0) becomes zero, and in this state, the current Id that was flowing into the positive bus P2 through the DC reactor LD all flows through the main thyristor QVP → the winding (V-0) It becomes like this.

That is, the current is commutated from the winding (U-0) to the winding (V-0).

In FIG. 4, this time point is indicated as t4.

The current path after time t4 is: ■ DC current VS → DC reactor → LD → main thyristor QVP → winding (V-0) → winding (0-W) → main thyristor QWN → DC power supply ■S, and one commutation Finish the process.

In the operation mode shown in FIG. 4 as well, time t3 or t2 is controlled so that the areas D and C indicated by the current Ice are made equal.

The above is an explanation of the commutation operation from U phase to ■ phase.
Commutation operations in other phases will also be easily understood with reference to the figures.

FIG. 4 also shows waveforms of current flowing through each part when operating in this manner.

The current source inverter of the present invention can be used by charging an auxiliary DC power source such as a capacitor or storage battery to a predetermined value.
After that, the inverter can be started and stopped at any time, and during operation, the voltage of the capacitor or auxiliary DC power supply is always controlled so that the average voltage is constant, so no special external charging power supply is required. In addition, the dead time of commutation as seen in the series diode type shown in Figure 1 does not exist in principle, and this has a truly remarkable effect on improving stability when, for example, an induction motor is operated as a load. It is something that demonstrates the.

[Brief explanation of the drawing]

Figure 1 is the main circuit diagram of a conventional inverter, Figure 2 is a circuit diagram showing an embodiment of the inverter of the present invention, and Figures 3 and 4 are time frames for explaining the operation of the inverter in Figure 2. It is a chart. ■S: variable DC power supply, LD: DC reactor, QUP-QWN: main thyristor, SUP~SWN: first auxiliary thyristor,
SP, SN...Second positive and negative side auxiliary thyristor, CHP, CHN...Positive and negative side chopper, DP
, DN...Positive, negative side diode, Cc...
...Capacitor or auxiliary DC power supply, ■M...Load induction motor.

Claims (1)

[Claims] 1 Consisting of at least two positive-side main thyristors whose anodes are commonly connected to one of the DC power bus bars obtained via a DC reactor, and at least two negative-side main thyristors whose cathodes are commonly connected to the other of the bus bars. at least two bridge circuits whose cathodes are connected in common.
an auxiliary bridge circuit comprising at least two negative-side first auxiliary thyristors and at least two positive-side first auxiliary thyristors whose anodes are commonly connected, and whose AC terminal is connected to the AC terminal of the bridge circuit; , a second auxiliary thyristor on the positive side inserted between the cathode side of this circuit and one of the busbars and fired in synchronization with the first auxiliary thyristor on the positive side, and an anode side of the auxiliary bridge circuit. and a second auxiliary thyristor on the negative side inserted between the other bus bar and fired in synchronization with the first auxiliary thyristor on the negative side;
The positive side and negative side thyristors are connected in series with a capacitor or an auxiliary DC power supply interposed between the cathode side and the anode side of the auxiliary bridge circuit, and are fired in synchronization with the first auxiliary thyristor on the positive and negative sides. a chopper, a positive side diode connected in parallel to the series circuit section of the positive side chopper and the capacitor or auxiliary DC power supply, and a positive side diode connected in parallel to the series circuit section of the negative side chopper and the capacitor or auxiliary DC power supply. A current source inverter consisting of a negative side diode.