JPH0767272B2 - Neutral point clamp type power converter controller - Google Patents

Description

Detailed Description of the Invention

 [Object of the Invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse width modulation control (PWM control) converter for converting AC power into DC power, and a PWM control inverter for converting DC power into AC power.
The present invention relates to a control device for a neutral-point clamp type power converter that generates a three-level output voltage applied to a power converter or the like.

[0002]

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

In the figure, V _d1 and V _d2 are DC power supplies, and S _{1 to} S ₄
The self-turn-off device, D ₁ to D ₄ is flip - wheeling diode - de, D _5, D ₆ are clamping diodes - a de, LOAD if load.

The output voltage V _U of this inverter changes as follows by turning on and off the _four elements S _{1 to} S ₄ . However, the total DC voltage is V _d, and V _d1 , = V _d2 = V _d / 2. That is, when S ₁ and S ₂ are on, V _U = + V _d / 2 When S ₂ and S ₃ are on, V _U = 0 When S ₃ and S ₄ are on, V _U = −V _d / It becomes 2. At this time, two devices must be turned on each. If all three are turned on at the same time, the DC power supply is short-circuited and the device is destroyed due to overcurrent.

For example, when an ON signal is input to the elements S _{1 to} S ₃ , the DC voltage V _d1 is short-circuited by the element S ₁ -S ₂ -S ₃ -diode D ₆ and an excessive short-circuit current flows to the elements. , The element is destroyed.

In order to prevent such a DC short circuit, the elements S ₁ and S ₃ are operated in reverse and the elements S ₂ S ₄ are operated in reverse. That is, when the element S ₁ is on, the element S ₃ is turned off, and when the element S ₃ is on, the element S ₁ is turned off. Similarly, when the element S ₂ is on, the element S ₄ is turned off, and when the element S ₄ is on, the element S ₂ 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 PWM control carrier signals, and X is + E _MAX to -E _MAX. A triangular wave that changes between
Is an inverted value of X (or a triangular wave whose phase is shifted by 180 electrical degrees). Further, e _i is a PWM control input signal. The input signal e _i is compared with the triangular waves X and Y, and the element S ₁
The gate signals g ₁ and g ₂ of S ₄ are generated. That is, e _i > X
And when e _i > Y, g ₁ = 1 and S ₁ is turned on, S
Turn off ₃ . When e _i ≤X or e _i ≤Y, g
_{When 1} = 0, S ₁ is turned off and S ₃ is turned on. e _i <X
, And e _i <Y, g ₂ = 1 and S ₄ is turned on, S
Turn off ₂ . When e _i ≧ X or e _i ≧ Y, g
₂ = 0, the S ₄ off, turn on the S _2.

As a result, the output voltage V _U becomes as shown at the bottom of the figure. As described above, in the neutral point clamp type inverter, the output voltage V _U is set at three levels (+ V _d / 2,
0, the voltage of -V _d / 2) is obtained, and less voltage waveform of the harmonic component. In the case of a motor load, there are advantages that the pulsation of current is reduced and the torque ripple is also reduced.

[0009]

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

When e _i suddenly changes from positive to negative at point a, the gate signal g ₁ changes from "1" to "0" and the gate signal g ₂ changes from "0" to "1". . If the elements S _{1 to} S ₄ can be turned on and off instantly according to this gate signal, the output voltage V _U becomes as shown in the figure, and no problem occurs.

However, in a large-capacity inverter, 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 at turn-off.

In order to initialize (discharge) the voltage of the capacitor of this snubber circuit, when the GTO is turned on, a fixed 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 in the vicinity of point a in FIG. 7, showing a case where the width of the gate signal g ₁ = 1 becomes narrower than the minimum on-time Δt. The minimum on-time Δt of the element S ₁ is indispensable for protecting the element itself.
Yes, and finally by the circuit that creates the gate pulse to the device
And the element has a minimum on-time Δt.
A gate signal g'is provided . As a result, g ₁ ′ and g ₂ overlap each other for a period δ, and the element S ₁ is on, S ₂ is off, and S
₃ turns off and S ₄ turns on.

In the main circuit of FIG. 5, when the output current I _U is flowing in the direction of the arrow in the figure, the diodes D ₃ and D ₄ are conducting and the ON signal is coming to the element S ₁ . , The total DC voltage V _d = V _d1 + V _d2 is applied to the element S ₂ . On the contrary, when the output current I _U is flowing in the direction opposite to the arrow in the figure, the diodes D ₁ and D ₂ are conducting, and the ON signal is input to S ₄ , so that the total voltage is applied to the element S _3. V _d is applied. In the neutral point clamp type inverter, each element (each
Is designed so that half of the DC voltage V _d is applied, and when the full voltage is applied, the element is destroyed due to overvoltage.

FIG. 7 has been described by taking as an example the case where the input signal e _i changes abruptly and sharply. However, if the input signal e _i changes positively or negatively at the point (point b) where the triangular waves X and Y intersect, the above-mentioned case occurs. Problems occur.

As described above, the conventional neutral point clamp type inverter PWM control device is weak against a sudden change of the input signal e _i , and frequently has a risk of element destruction especially near the intersection of the triangular waves X and Y. Will be exposed to.

The present invention has been made in view of the above-mentioned problems. In the present invention, the total DC voltage is not applied to one element even if the input signal e _i of the PWM control changes abruptly. An object of the present invention is to provide a controller for a sex point clamp type power converter. [Constitution of Invention]

[0018]

In order to achieve the above-mentioned object, the present invention comprises a neutral point output terminal connected between DC terminals.
And the four self-extinguishing elements S ₁ , S ₂ , S ₃ , S ₄ connected in series between the DC terminals with the same polarity ,
Freewheeling diodes D ₁ , D ₂ , D ₃ and D ₄ connected in anti-parallel to each of these elements and connected in series
Antiparallel to the two self-turn-off devices S _2, S ₃ being
Series circuit of connected clamp diodes D ₅ and D ₆
And the self-extinguishing elements S ₁ and S ₃ and S ₂ and S _{4 are} reversed.
Gate with minimum on / off time ensured to operate
A gate control means for on / off control by a signal is provided, and
The series connection point of the lamp diodes D ₅ and D ₆ and the neutrality
The point output terminal is connected to the four self-extinguishing elements S ₁ ,
AC terminal at the intermediate connection point of the series circuit of S ₂ , S ₃ , S ₄
In the provided neutral point clamp type power converter, as a carrier for controlling pulse width modulation, one is a triangular wave X changing between zero and + Emax , and the other is a triangular wave X and a frequency and a phase.
Means for generating a triangular wave Y that coincides and changes between zero and -Emax , and a PWM control input satisfying -Emax ≤ e _i ≤ + Emax
Comparing means for generating a signal e _i, the two triangular wave X, and Y and the PWM control input signal e _i, when e _i> X,
The element S _1, S ₂ was turned element S _3, S ₄ off of
The gate signal is generated which, when Y ≦ e _i ≦ X, gate to turn off the element S _1, S ₄ are turned on the element S _2, S ₃
Of the elements S ₃ and S when e _i <Y
A gate signal that turns on element ₄ and turns off elements S ₁ and S ₂
It is characterized in that a means for controlling pulse width modulation so as to generate is provided.

[0019]

According to the present invention, as a carrier wave for PWM control, one is a triangular wave X changing between 0 and + E _MAX , and the other is a triangular wave Y changing in phase with the triangular wave X and between 0 and −E _MAX. By comparing the two triangular waves X and Y with the input signal e _i , the element S ₁ constituting the neutral point clamp type power converter,
The gate signals of S ₂ , S ₃ and S ₄ are produced. That is, when e _i > X, the elements S ₁ and S ₂ are turned on (S ₃ , S 2
₄ is turned off) When Y ≦ e _i ≦ X, the elements S ₂ and S ₃ are turned on (S ₁ , S
₄ is off) When e _i <Y, elements S ₃ and S ₄ are turned on (S ₁ , S
Pulse width modulation control is performed so that ₂ is turned off).

As a result, the triangular waves X and Y always have a voltage difference of E _MAX , and even if the input signal e _i changes within this voltage difference, the state of e _i > X changes to e _i <Y. Or e
The mode does not change directly to the state of _i <Y to e _i > X, and even if the minimum on-time of the element is taken into consideration, the element S
₁ ON to turn off element S ₂ or element S ₄ to turn ON element S
_The mode in which ₃ is turned off does not occur. Therefore, the total DC voltage is not applied to the element S ₂ or the element S ₃ , and the conventional problems can be solved.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a neutral point clamp type inverter of the present invention.
1 is a block diagram of a main circuit configuration diagram and a control device for explaining a control device for a computer.

In the figure, V _d1 and V _d2 are DC power supplies, S ₁ and
S _2, S _3, S ₄ are self-turn-off _{device, D 1 D 2, D 3} , D
₄ flip - wheeling diode - de, D _5, D ₆ are clamping diodes - de, LOAD is the load, CT _U is a current detector. Further, as control circuits, comparators C _U , C ₁ ,
C ₂ , current control compensation circuit G _U (s), triangular wave generator TR
G and Schmitt circuits SH ₁ and SH ₂ are provided.
This figure shows only one phase (U phase), but in the case of a three phase load, the other two phases (V phase, W phase) are similarly configured.

[0023] The load current I _U of the U-phase detected by the current detector CT _U, is input to a comparator C _U of the current control circuit. The comparator C _U compares the current command value I _U ^* and the current detection value I _U, a deviation εU = I _U ^* -I _U. The deviation ε _U is amplified by the next control compensation circuit G _U (s) and used as the input signal e _{i for} PWM control.

The triangular wave generator TRG has two triangular waves X and Y.
Is generated and input to the comparators C ₁ and C ₂ . The comparator C ₁ compares the triangular wave X with the input signal e _i , and the Schmitt circuit S
A gate signal g ₁ of the device elements S ₁ and S ₃ is produced via H ₁ . Further, the comparator C ₂ compares the triangular wave Y with the input signal e _i , and the device elements S ₂ and S ₂ are connected via the Schmitt circuit SH _2.
Generate a gate signal g ₂ of ₄ . FIG. 2 is a time chart for explaining the operation of the present invention.

The carrier wave X for PWM control is a triangular wave having a constant frequency which varies between 0 and + E _MAX . Further, the carrier wave Y is a triangular wave having a constant frequency that varies between 0 and -E _MAX , and is in phase with the carrier wave X. That is, when X = + E _MAX , Y = 0, and when X = 0, Y = −E _MAX
Becomes Therefore, from b ₁ point (X = 0) to b ₂ point (Y = -E
There is a difference of E _MAX as a voltage difference up to _MAX ). The PWM control input signal e _i is compared with the triangular waves X and Y to generate gate signals g ₁ and g ₂ . That is, when e _i > X, g ₁ = 1 and the element S ₁ is turned on (element S _1
3 is turned off) When e _i ≤X, g ₁ = 0 and the element S ₁ is turned off (element S
₃ is turned on) When e _i <Y, g ₂ = 1 and element S ₄ is turned on (element S
₂ is turned off) When e _i ≧ Y, g ₂ = 0 and the element S ₄ is turned off (element S
₂ is turned on). At this time, the output voltage V _U of the inverter changes as follows. However, the total DC voltage is V _d, and V
Let _d1 = _Vd2 = _Vd / 2. That is, when the elements S ₁ and S ₂ are on, V _U = + V _d / 2 When the elements S ₂ and S ₃ are on, V _U = 0 When the elements S ₃ and S ₄ are on, V _U = − The output voltage becomes V _d / 2 and the output voltage becomes three levels. The average value V _U becomes a value proportional to the input signal e _i .

Now, consider the case where the input signal e _i changes abruptly at point a. Although the width of the gate signal g ₁ becomes shorter than the minimum on-time Δt of the element S ₁ , it becomes the signal g ₁ ′ shown by the broken line in order to secure the minimum on-time Δt. However, the input signal e _i
When the change of is smaller than E _MAX , e _i does not intersect the triangular wave Y at the point a, and the gate signal g ₂ maintains the state of “0”. As a result, the periods of g ₁ ′ = 1 and g ₂ = 1 do not overlap, and when the element S ₁ is on, the element S ₂ is always on. Similarly, when the element S ₄ is on, the element S
₃ is always on.

In other words, when the element S ₂ is off, the element S ₁ is also off, and when the output current I _{U of} FIG. 1 flows in the direction of the arrow, the diodes D ₃ , D ₄ becomes conductive and the total voltage V _d is applied to the series circuit of the elements S ₁ and S ₂ , but both are off, so a voltage of V _d / 2 is applied to each element. Similarly, when the element S ₃ is off, the element S ₄ is also off, and each element also has V _d / 2.
The above voltage is not applied.

That is, according to the conventional PWM control device, when the input signal e _i fluctuates in the vicinity of the zero point, the four elements S ₁ ...
There is a risk that the DC total voltage V _d is applied to either the inner element S ₂ or S ₃ of S ₄ , but according to the present invention, the risk can be eliminated.

Although the inverter for the U phase has been described above, the V phase and W phase are controlled in the same manner, and the conventional problems can be solved. Needless to say, the present invention can also be applied to a three-phase, three-wire type load. Although the frequencies of the carrier waves X and Y have been described as constant, it is needless to say that the same can be applied even if the frequencies are varied as long as the phases of the carrier waves match.

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

In the figure, V _d1 and v _d2 are DC power supplies, and S _{1 to} S ₈
The self-turn-off device, D ₁ to D ₈ are flip - wheeling diode - de, D ₉ to D ₁₂ are clamping diodes - a de, LOAD is the load. The P of the inverter shown in FIG. 3 will be described below with reference to FIG.
The WM control operation will be described.

Carrier waves X ₁ and X _{2 for} PWM control are 0 to + E
A constant frequency triangular wave that changes between _MAX , where X ₂ is X ₁
The phase is 180 ° out of phase with. Also, the carrier wave Y ₁ ,
Y ₂ is a triangular wave with a constant frequency that varies between 0 and −E _MAX , and is in phase with X ₁ and X ₂ , respectively. Element S ₁
And the gate signal g ₁ of S ₃ are obtained by comparing the input signal e _i with the triangular wave X ₁ . That is, when e _i > X ₁ , g ₁ = 1 and the element S ₁ is turned on (element S ₃ is turned off). When e _i ≦ X ₁ , g ₁ = 0 and the element S ₁ is turned off (element S _{1 3} turns on). Further, by comparing the input signal e _i with the triangular wave Y ₁ , the gate signal g ₂ of the elements S ₂ and S ₄ can be obtained. When e _i <Y ₁ , g ₂ = 1 and the element S ₄ is turned on (element S ₂ is turned off). When e _i ≧ Y ₁ , g ₂ = 0 and the element S ₄ is turned off (element S ₂ is turned on). ON). Similarly, by comparing the input signal e _i with the triangular waves X ₂ and Y ₂ , the gate signals g ₃ of the elements S _{5 to} S ₈
g ₄ is obtained. That is, when e _i > X ₂ , g ₃ = 1 and element S 8 is turned on (element S ₆ is off). When e _i ≦ X ₂ , g ₃ = 0 and element S 8 is turned off (element S ₆ is turned on). On) When e _i <Y ₂ , g ₄ = 1 and element S 5 is turned on (element S ₇ is turned off) When e _i ≧ Y ₂ , g ₄ = 0 and element S 5 is turned off (element S ₇ is turned on) ON). As a result, the voltage V _{A at the} point _A and the voltage V B at the point _B in FIG. 3 become as shown in FIG. 4, and the average value of the voltage V _U applied to the load LOAD is the PWM control input signal e.
_The value is proportional to _i .

Even if the input signal e _i changes abruptly, the fluctuation range is E
If it is smaller than _MAX, the same effect as that described with reference to FIG. 2 is obtained. Of course, even if the fluctuation range of the input signal becomes larger than E _MAX , no problem will occur as long as it changes gently.

The control circuit of FIG. 1 is shown as a hardware control block diagram for easy understanding.
It is needless to say that the present invention can be carried out by software using a microcomputer or the like.

Although the inverter for converting the DC power into the AC power has been described above, it goes without saying that the same can be applied to the converter for converting the AC power into the DC power.

[0036]

As described above, according to the control device of the neutral point clamp type power converter of the present invention, even if the input signal of the PWM control suddenly changes, if the width of the change is within the allowable value. It is possible to avoid a mode in which the total DC voltage is applied to one element, and it is possible to eliminate the risk of element destruction.

[Brief description of drawings]

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

FIG. 2 is a time chart 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 can be applied.

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

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 for explaining the operation of a conventional neutral point clamp type power converter control device.

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

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

[Explanation of symbols]

V _d1 , V _d2 ... DC power supply, S _{1 to} S ₄ ... Self-extinguishing element, D
₁ ~ D ₄ ... Freewheeling diode, D ₅ , D ₆ ...
Clamping diodes - de, LOAD ... load, CT _U ... current _{detector, C U, C 1, C} 2 ... comparator, G _U (s) ... current control compensation circuit, TRG ... triangular wave generator, SH _1, SH ₂ ...
Schmidt circuit.

Claims (1)

[Claims] 1. A neutral point output terminal connected between DC terminals
A DC power source having the four self arc-extinguishing elements connected in series with the same polarity between the DC terminals _{S 1, S 2, S 3} , S 4
And a free circuit connected in anti-parallel to each of these elements.
Wheeling diode D ₁ , D ₂ , D ₃ , D ₄ and series
Reversed to the _two self-extinguishing elements S ₂ , S _{3 connected}
Series of clamp diodes D ₅ and D ₆ connected in parallel
A circuit, and the self-turn-off elements S ₁ and S ₃ and S ₂ and S ₄
The minimum on / off time is secured so that the
Equipped with gate control means for on / off control with a
The series connection point of diodes D ₅ and D ₆ for clamping and the above
The four self-extinguishing elements S are connected to the neutral point output terminal.
AC terminal at the intermediate connection point of the series circuit of ₁ , S ₂ , S ₃ and S _4.
In the neutral point clamp type power converter provided with a child, as the carrier for pulse width modulation control, one is zero and + Emax
The triangular wave X that changes between the two, and the other is the triangular wave X and the frequency
Means for generating a triangular wave Y whose phase coincides with that of zero and changes between −Emax , and a PWM satisfying −Emax ≦ e _i ≦ + Emax
Means for generating a control input signal e _i, the two triangular wave X, compared with the Y and the PWM control input signal e _i, e _i> time of X, the element S _1, element turns the S ₂ S
_3, S ₄ generates a gate signal for turning off the, when Y ≦ e _i ≦ X, containing turning on the element S _2, S ₃
A gate signal for turning off the children S ₁ and S ₄ is generated, and when e _i <Y, the elements S ₃ and S ₄ are turned on and the element S is turned on.
_1, the control unit of the neutral point clamped power converter comprising comprising means for controlling the pulse width modulation to generate a gate signal for turning off the S _2.