JPH04275057A - Controller for neutral point clamp type power conversion device - Google Patents

Abstract

PURPOSE:To prevent damage of an element due to application of an entire DC voltage to one element when a PWM control input signal is abruptly varied in a neutral point clamp type power conversion device having four self-arc extinguishing elements connected in series, free-wheeling diodes connected in anti-parallel with the elements, and clamping diodes. CONSTITUTION:A triangular wave generator TRG for generating a triangular wave X varying at one at the sides of zero and positive as a pulse width modulation control carrier signal and a triangular wave Y varying at the other in the same phase as the X at the sides of zero and negative, and means for comparing the waves X and Y with a PWM control input signal to form gate signals g1, g2, are provided. And, a power conversion device is controlled by using the signals g1 and g2.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

[Industrial Application Field] The present invention is applicable to pulse width modulation control (PWM control) converters that convert AC power to DC power, PWM control inverters that convert DC power to AC power, etc. The present invention relates to a control device for a neutral point clamp type power converter that generates three levels of output voltage.

0002

2. Description of the Related Art FIG. 5 shows a main circuit configuration diagram of a neutral point clamp type inverter. The figure shows 1 phase (U phase) and 3
In the case of a phase output inverter, the V, W, and phases are similarly configured.

[0003] In the figure, Vd1 and Vd2 are DC power supplies, S1
-S4 are self-extinguishing elements, D1-D4 are free-wheeling diodes, D5 and D6 are clamp diodes, and LOAD is a load.

The output voltage VU of this inverter is determined by turning on and off the four elements S1 to S4.
It changes as follows. However, the overall DC voltage is Vd
and Vd1,=Vd2=Vd/2. That is, S
1 and S2 are on, VU = +Vd /2S2
When S3 and S3 are on, VU =0. When S3 and S4 are on, VU = -Vd /2. At this time, the elements must be turned on two at a time. If all three of them turn on at the same time, they will short-circuit the DC power supply and destroy the elements due to overcurrent.

For example, when an on signal is applied to the elements S1 to S3, the DC voltage Vd1 is applied to the elements S1 to S3.
A short circuit occurs in diode D6, and an excessive short circuit current flows through the element, destroying the element.

In order to prevent such a DC short circuit, elements S1 and S3 are operated in reverse, and element S2S4 is operated in reverse. That is, when element S1 is on, element S3
is turned off, and when element S3 is on, element S1 is turned off. Similarly, when element S2 is on, element S4 is turned off, and when element S4 is on, element S2 is turned off. FIG. 6 is a time chart for explaining a conventional pulse width modulation control method for a neutral point clamp type inverter.

In the figure, X and Y are carrier wave signals of PWM control, X is a triangular wave that changes between +EMAX and 0, and Y is a
(or a triangular wave whose phase is shifted by 180 degrees in electrical angle). Further, ei is a PWM control input signal. The input signal ei is compared with the triangular waves X and Y, and the element S1
-Create gate signals g1 and g2 of S4. That is, e
When i > X and ei > Y, g1 = 1 and S
Turn on S1 and turn off S3. When ei ≦X or ei ≦Y, g1 = 0, S1 is turned off, S3
Turn on. When ei <X and ei <Y, g2 = 1, turning on S4 and turning off S2. When ei ≧X or ei ≧Y, g2 = 0,
Turn off S4 and turn on S2.

As a result, the output voltage VU becomes as shown in the bottom row of the figure. In this way, the neutral point clamp type inverter
In the output voltage VU, three levels (+Vd/
A voltage of 2,0, -Vd/2) is obtained, resulting in a voltage waveform with few harmonic components. In the case of a motor load, there is an advantage that current pulsation is small and torque ripple is also reduced.

[0009]

However, the conventional neutral point clamp type inverter control device has the following problems. Similar to FIG. 6, FIG. 7 shows a time chart for explaining the conventional PWM control method, and shows the operation when the input signal ei suddenly changes.

[0010] When ei suddenly changes from positive to negative at point a,
The gate signal g1 changes from "1" to "0", and the gate signal g1 changes from "1" to "0".
2 changes from "0" to "1". If the elements S1 to S4 can be turned on and off instantaneously according to this gate signal, the output voltage VU will be as shown in the figure, and no problem will occur.

However, in large-capacity inverters, a GTO (gate turn-off thyristor) or the like is used as a self-extinguishing element, and a snubber circuit is installed to suppress overvoltage during turn-off.

[0012] In order to initialize (discharge) the voltage of the capacitor of this snubber circuit, when the GTO is turned on, it takes a certain period of time (minimum on-time: about 100 microseconds, for example).
Must remain on.

FIG. 8 is an enlarged view of the operation of the gate signal near point a in FIG. 7, and shows the case where the width of the gate signal g1=1 is narrower than the minimum on-time Δt. In order to ensure the minimum on-time Δt of element S1, gate signal g1 is
The period of 1 is expanded as shown in '. As a result, g
1' and g2 overlap for a period δ, and the element S1 is on, S2 is off, S3 is off, and S4 is on.

In the main circuit of FIG. 5, when the output current IU flows in the direction of the arrow in the figure, the diodes D3 and D
4 is conductive and an on signal has come to element S1, so a total DC voltage Vd=Vd1+Vd2 is applied to element S2. Conversely, when the output current IU is flowing in the opposite direction to the arrow in the figure, diodes D1 and D2 are conductive and an on signal is input to S4, so element S3
A full voltage Vd is applied to. In a neutral point clamp type inverter, the withstand voltage of each element (each arm) is DC voltage Vd.
It is designed so that half of the voltage is applied, and if the full voltage is applied, the device will be destroyed due to overvoltage.

FIG. 7 has been explained by taking as an example the case where the input signal ei changes greatly and rapidly. However, if the input signal ei changes even slightly to positive or negative at the point where the triangular waves X and Y intersect (point b), the above problem will occur. occurs.

As described above, the conventional neutral point clamp type inverter PWM control device is vulnerable to sudden changes in the input signal ei, and there is a risk of element destruction, especially near the point where the triangular waves X and Y intersect. You will be exposed.

The present invention has been made in view of the above-mentioned problems.The present invention has been made in view of the above-mentioned problems. An object of the present invention is to provide a control device for a point clamp type power converter. [Structure of the invention]

[0018]

[Means for Solving the Problems] In order to achieve the above object, the present invention comprises four self-extinguishing elements S1,
S2, S3, S4, and free-wheeling diodes D1, D2, connected in antiparallel to each of these elements.
D3, D4 and clamp diodes D5, D6
In a neutral point clamp type power converter consisting of, as carrier waves for pulse width modulation control, one is a triangular wave X that changes between zero and the positive side, and the other is a triangular wave Y that changes between zero and the negative side. The means of generation and these two triangular waves
, Y with the PWM control input signal ei, and when ei > .

[0019]

[Operation] The present invention uses a triangular wave X that changes between 0 and +EMAX as carrier waves for PWM control, and a triangular wave Y that changes between 0 and -EMAX with the same phase as the triangular wave X. , these two triangular waves X, Y and input signal ei
The gate signals for the elements S1, S2, S3, and S4 constituting the neutral point clamp type power converter are generated by comparing the values. That is, when ei >X, element S1
, S2 are turned on (S3, S4 are turned off). When Y≦ei≦X, elements S2, S3 are turned on (S3, S4 are turned off).
When ei <Y, pulse width modulation control is performed so that the elements S3 and S4 are turned on (S1 and S2 are turned off).

[0020] As a result, the triangular waves X and Y are always EMAX
within this voltage difference, the input signal ei
Even if changes, from ei > X to ei < Y,
Alternatively, the mode will no longer change directly from ei <Y to ei > The off mode will no longer occur. Therefore, the full DC voltage is not applied to element S2 or element S3, and the conventional problems can be solved.

[0021]

[Example] Figure 1 shows the neutral point clamp type inverter of the present invention.
1 shows an example of a main circuit configuration diagram and a block diagram of the control device for explaining the control device of the computer.

[0022] In the figure, Vd1 and Vd2 are DC power supplies, S1
, S2, S3, S4 are self-extinguishing elements, D1D2
, D3, D4 are free-wheeling diodes, D5
, D6 is the clamp diode, LOAD is the load,
CTU is a current detector. Also, as a control circuit, comparators CU, C1, C2, and a current control compensation circuit GU
(s), triangular wave generator TRG, Schmitt circuit SH1
, SH2 are provided. Although this figure shows only one phase (U phase), in the case of a three-phase load, the other two phases (V phase, W phase) are configured in the same way.

The U-phase load current IU is detected by the current detector CTU.
and input it to the comparator CU of the current control circuit. The comparator CU compares the current command value IU* and the detected current value IU to obtain the deviation εU=IU*-IU. The deviation εU is converted to the next control compensation circuit GU (s
) is amplified and used as the input signal ei for PWM control.

The triangular wave generator TRG generates two triangular waves X, Y
is generated and input to comparators C1 and C2. Comparator C
1 compares the triangular wave X with the input signal ei and generates a gate signal g1 for the elements S1 and S3 via a Schmitt circuit SH1. Further, the comparator C2 compares the triangular wave Y with the input signal ei, and generates a gate signal g2 for the elements S2 and S4 via the Schmitt circuit SH2. FIG. 2 is a time chart for explaining the operation of the present invention.
This is a diagram.

[0025] PWM control carrier wave X is 0 to +EMAX
It is a triangular wave with a constant frequency that changes between . Further, the carrier wave Y is a triangular wave with a constant frequency varying between 0 and -EMAX, and is in phase with the carrier wave X. That is, X=+EM
When AX, Y=0, and when X=0, Y=-EMAX. Therefore, point b1 (X=0
) to point b2 (Y=-EMAX), there is a voltage difference of EMAX. The PWM control input signal ei is compared with the triangular waves X and Y, and the gate signals g1 and g2 are
make. That is, when ei > X, g1 = 1 and element S1 is turned on (
When ei ≦X, g1 = 0 and element S1 is turned off (
When ei <Y, g2 = 1 and element S4 is turned on (
When ei ≧ Y, g2 = 0 and element S4 is turned off (
Turn on element S2). At this time, the output voltage VU of the inverter changes as follows. However, the entire DC voltage is Vd, and Vd1=Vd2=Vd/2. That is, element S1
When and S2 are on, VU = +Vd /2 element S
2 and S3 are on, VU = 0 elements S3 and S
4 is on, VU = -Vd /2, resulting in three levels of output voltage. The average value VU is a value proportional to the input signal ei.

Now, consider the case where the input signal ei suddenly changes at point a. The width of the gate signal g1 is shorter than the minimum on-time Δt of the element S1, but in order to ensure the minimum on-time Δt, the signal g1' is shown by a broken line. However, if the change in input signal ei is smaller than EMAX, then ei
does not intersect with the triangular wave Y at point a, and the gate signal g2
remains at "0". As a result, g1 ′=1 and g2
The periods of =1 do not overlap, and when the element S1 is on, the element S2 is also always on. Similarly, element S
When element S4 is on, element S3 also always remains on.

In other words, when element S2 is off, element S1 is also off, and the output current I in FIG.
If U flows in the direction of the arrow, diode D3
, D4 conduct, and the total voltage Vd across elements S1 and S2
However, since both are off, a voltage of Vd/2 is applied to each element. Similarly, element S
When S3 is off, element S4 is also off, and no voltage higher than Vd/2 is applied to each element.

That is, according to the conventional PWM control device, when the input signal ei fluctuates around the zero point, the four elements S1
Although there was a risk that the DC full voltage Vd would be applied to either the inner element S2 or S3 among the elements S4 to S4, this risk can be eliminated according to the present invention.

Although the inverter for the U-phase has been described above, the V-phase and W-phase are similarly controlled, and the conventional problems are solved. It goes without saying that the present invention can also be applied to a three-phase, three-wire type load. Although the explanation has been made assuming that the frequencies of the carrier waves X and Y are constant, it goes without saying that the same application can be made even if the frequencies are varied as long as the phases of the carrier waves are the same.

FIG. 3 shows the main circuit configuration of a single-phase full bridge connection neutral point clamp type inverter, and FIG. 4 shows a time chart when the present invention is applied to the inverter. .

[0031] In the figure, Vd1 and vd2 are DC power supplies, S1
-S8 are self-extinguishing elements, D1-D8 are free-wheeling diodes, D9-D12 are clamp diodes, and LOAD is a load. Below, using Figure 4, Figure 3
The PWM control operation of the inverter will be explained.

[0032] PWM control carrier waves X1 and X2 are 0 to
A triangular wave with a constant frequency that changes between +EMAX and
2 is out of phase by 180° with respect to X1. or,
The carrier waves Y1 and Y2 are triangular waves with constant frequencies varying between 0 and -EMAX, and are in phase with X1 and X2, respectively. Gate signal g1 of elements S1 and S3
is obtained by comparing the input signal ei and the triangular wave X1. That is, when ei > X1, g1
When g1 = 1, the element S1 is turned on (the element S3 is turned off). When ei≦X1, when g1 = 0, the element S1 is turned off (the element S3 is turned on). Also, by comparing the input signal ei and the triangular wave Y1, the gate signal g2 of the elements S2 and S4 is determined.
is obtained. When ei < Y1, g2 = 1, turning on the element S4 (turning off the element S2). When ei ≧ Y1, g2 = 0, turning off the element S4 (turning on the element S2). Similarly, input signal ei and triangular waves X2, Y2
By comparing these, gate signals g3 and g4 of the elements S5 to S8 can be obtained. In other words, when ei > When g4 = 1, the element S5 is turned on (the element S7 is turned off). When ei≧Y2, when g4 = 0, the element S5 is turned off (the element S7 is turned on). As a result, the voltage VA at point A and the voltage VB at point B in FIG. 3 become as shown in FIG. 4, and the average value of the voltage VU applied to the load LOAD is a value proportional to the PWM control input signal ei. Become.

Even if the input signal ei suddenly changes, as long as the fluctuation range is smaller than EMAX, the same effect as explained with reference to FIG. 2 can be obtained. Of course, the fluctuation range of the input signal is EM
Even if it becomes larger than AX, no problem will occur as long as it changes slowly.

The control circuit in FIG. 1 is shown as a hardware control block diagram to make the explanation easier to understand.
It goes without saying that the present invention can be carried out by software calculations using a microcomputer or the like.

Although the above description has been made regarding an inverter that converts DC power to AC power, it goes without saying that the present invention can be similarly applied to a converter that converts AC power to DC power.

[0036]

[Effects of the Invention] As explained above, according to the control device for a neutral point clamp type power converter of the present invention, even if the input signal for PWM control suddenly changes, as long as the width of the change is within the allowable value. , it is possible to avoid a mode in which the entire DC voltage is applied to one element, and it is possible to eliminate the risk of element destruction.

[Brief explanation of the drawing]

FIG. 1 is a main circuit configuration diagram and a block diagram of the control device showing an embodiment of the control device for a neutral point clamp type power converter according to the present invention.

FIG. 2 is a time chart diagram for explaining the operation of the present invention.

FIG. 3 is a main circuit configuration diagram showing another embodiment of a neutral point clamp type power converter to which the present invention is applicable.

FIG. 4 is a time chart diagram for explaining the operation when the present invention is applied to the neutral point clamp type power converter shown in FIG. 3;

FIG. 5 is a main circuit configuration diagram of a neutral point clamp type power converter to which the present invention is applied.

FIG. 6 is a time chart diagram for explaining the operation of a control device for a conventional neutral point clamp type power converter.

FIG. 7 is a time chart diagram for explaining the operation when a PWM control input signal is suddenly changed in a conventional control device for a neutral point clamp type power converter.

FIG. 8 is an enlarged view of a part of the time chart of FIG. 7 for explaining the operation of a control device for a conventional neutral point clamp type power converter.

[Explanation of symbols]

Vd1, Vd2...DC power supply, S1 to S4...Self-extinguishing element, D1 to D4...Free wheeling diode,
D5, D6...Clamp diode, LOAD...Load, CTU...Current detector, CU, C1, C2...Comparator, GU(s)...Current control compensation circuit, TRG...Triangular wave generator, SH1, SH2...Schmitt circuit.

Claims (1)

[Claims] [Claim 1] Four self-extinguishing elements S connected in series
1, S2, S3, S4, and free-wheeling diodes D1, D connected in antiparallel to each of these elements.
2, D3, D4 and clamping diode D5
, D6, one is a triangular wave X that changes between zero and the positive side, and the other is a triangular wave that changes between zero and the negative side, as carrier waves for pulse width modulation control. Compare the two triangular waves X and Y with the PWM control input signal ei, and when ei > X, turn on the elements S1 and S2 (turn off S3 and S4). When ei<Y, the elements S2 and S3 are turned on (S1 and S4 are turned off), and when ei <Y, the elements S3 and S4 are turned on (S1 and S2 are turned off). A control device for a neutral point clamp type power converter consisting of: