JPH0681512B2 - Current source PWM converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial field of application) The present invention relates to a current type P that is pulse width modulation controlled (PWM controlled).
WM converter

(Prior Art) With the development of self-extinguishing devices such as high-power transistors and gate turn-off thyristors, the performance of power converters has been gradually improved.

One of them is the current type PWM converter, which controls the pulse width modulation (PWM) of the current type power converter composed of self-extinguishing elements.
By performing the control), the output voltage on the AC side can be controlled to a waveform approximate to a sine wave. When the current source PWM converter is used as a sequential converter (converter), the current supplied from the AC power supply can be controlled to a sine wave in phase with the power supply voltage, and the input power factor is always 1 The number of AC / DC power converters can be reduced. When used as an inverse converter (inverter), it can supply a sinusoidal current of variable voltage and variable frequency to a load such as an AC motor,
It becomes possible to operate by reducing the pulsation of the generated torque of the electric motor.

FIG. 5 is a block diagram showing a conventional current source PWM converter.

In the figure, SUP is a three-layer AC power supply, L _S is an AC reactor, CAP
₁ and CAP ₂ are filter capacitors, SS ₁ and SS ₂ are automatic power converters, Ld is a DC reactor, and M is an AC motor.

Further, as the control circuit, the rotation pulse generator PG, the AC detector CTd, the DC current control circuit DCC, the power supply current control circuit ACR ₁ ,
A speed control circuit SPC, a load current control circuit ACR ₂ and pulse width modulation control circuits PWM ₁ and PW ₂ are prepared.

The converter SS ₁ is a so-called PWM converter that directly converts alternating current, and is composed of a self-extinguishing element such as a high power transistor or a gate turn-off thyristor. The converter SS ₁ controls the power collector I _S as DC current Id matches the command value Id ^*. Here, by controlling the power supply current I to be a sine wave in phase with the power supply voltage V _S , the input power factor is always maintained at 1 and the harmonic component of the power supply current is reduced.

Further, the converter SS ₂ is composed of a so-called PWM inverter that converts direct current to alternating current, and also a self-extinguishing element. The converter SS ₂ supplies a sinusoidal current with a variable voltage and a variable frequency to the AC motor M, and supplies a current to the motor M so that the rotation speed ωr of the motor M matches the command value ωr ^*. (Load current) I _L is controlled. As a result, the generated amount of the electric motor M hardly pulsates.

The filter capacitor CAP ₁ smoothes the pulsation of the input current I _{C 1} of the PWM converter SS ₁ and, at the same time, turns off the AC reactor L _S when the self-extinguishing element forming SS ₁ is turned off.
It serves to absorb the surge voltage generated by.
The AC reactor L _S also serves to smooth the power supply current I _S.

Similarly, the filter capacitor CAP ₁ plays a role of smoothing the output current I _{C 2} and absorbing a surge voltage for the PWM inverter SS ₂ . In this case, the AC reactor on the load side is included in the electric motor M.

(Problems to be solved by the invention) The conventional current-type PCM converter utilizes the advantages of the conventional PWM inverter for driving an AC motor or the input power factor = 1.
It is used in the PWM converter, etc., but has the following problems.

That is, it is necessary to provide the filter capacitor CAP ₂ for absorbing the sardine voltage on the AC side of the current source PWM conversion as described above, and the voltage applied thereto largely depends on the PWM control method. In particular, when malfunction occurs due to noise or the like, an overvoltage is generated in the capacitor CAP ₂ and there is a risk of destroying elements and the like.

Further, in the case of the PWM converter SS ₁ , the AC reactor L _S is required between the AC power supply and the filter capacitor CAP ₁ , but the current I _S and the voltage Vcap are generated at the resonance frequency determined by the DC current CAP ₁ and the reactor L _S. The phenomenon of vibration occurs. This phenomenon is the same in the PWM inverter SS ₂ , and the value of the AC reactor L _{S in} that case becomes the value of the leakage inductance of the AC motor M or the like.

When this vibration phenomenon occurs, the output current on the AC side of the converter (the power supply current in the case of the converter and the load current in the case of the inverter) cannot be controlled well, and the output current is
The harmonics of the resonant frequency are superimposed.

Therefore, in the case of the PWM converter SS ₁ , a harmonic current is caused to flow in the power supply system, which has various adverse effects on other electric devices. Further, in the case of the PWM converter SS ₂ , torque pulsation is generated in the AC electric motor M, and when the electric motor M is used in the production line, the quality of the finished product is significantly deteriorated.

The present invention has been made in view of the above problems, and suppresses the resonance phenomenon between the AC reactor L _S and the filter capacitor CAP ₁ , and even when the PWM control malfunctions due to noise or the like, the filter capacitor CAP 1 _The purpose is to provide an electric PWM converter that prevents the voltage applied to _{2 from} becoming an overvoltage.

[Structure of the Invention] (Means for Solving Problems) In order to achieve the above object, the present invention provides a DC current source (DC reactor or the like) and a pulse width modulation control that receives current supply from the DC current source. Self-exciting power converter that outputs the specified DC current, a filter circuit connected to the DC side terminal of the converter, a DC load or an AC power supply connected to the output terminal of the filter circuit, and the AC load Alternatively, means for controlling the current to be supplied to the AC power supply, means for controlling the voltage applied to the filter circuit, and pulse width modulation for the power converter based on the output signals from the current control means and the voltage control means. A current source PWM converter equipped with a control means suppresses the resonance phenomenon of the filter circuit and prevents the application of overvoltage.

(Operation) In other words, a DC current source such as a DC reactor is connected to the DC side terminal of a self-exciting power converter that is composed of a self-extinguishing element (high-power transistor or gate turn-off thyristor, etc.) A filter circuit including a filter capacitor and a filter reactor is connected to the terminal. Further, an AC load or an AC power source is connected via the filter circuit. When the converter is used as an inverter, an AC load (for example, an AC motor) is connected, and when it is used as a converter, an AC power source is connected.

The self-excited power converter converts a direct current of the direct current source into an alternating current with pulse width modulation control. Since the AC power contains a large amount of ripples, it is smoothed by the filter circuit. The PWM converter (self-excited power converter)
Controls the AC current to be supplied to the AC load or AC power source according to a command value. At this time, the voltage of the filter circuit is detected and controlled according to the command value. When a resonance phenomenon is about to occur between the capacitor of the filter circuit and the AC reactor (including the filter reactor), the voltage control circuit of the filter circuit works effectively and suppresses the resonance phenomenon. In addition, due to malfunctions such as noise, PWM
Even if the control is disturbed and the voltage of the filter capacitor is about to become excessive, the voltage control circuit operates to correct the PWM control so as to prevent the overvoltage.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of a current source PWM converter of the present invention.

In the figure, SUP is a three-phase AC power supply, L _S is an AC reactor, CAP
₁ , CAP ₂ and filter capacitors, SS ₁ and SS ₂ self-exciting power converters, Ld DC reactor, M AC motor load, PG rotation pulse generator, CTd DC current detector, PT ₁ , PT ₂ Voltage detector, DCC for DC current control circuit, ACR ₁ for power supply current control circuit, SPC for speed control circuit, ACR ₂ for load current control circuit, A
D ₁ and AD ₂ are adder circuits, AVR ₁ and AVR ₂ are voltage control circuits, PWM ₁ and PW
M ₂ indicates a pulse width modulation control circuit, respectively.

The converter SS ₁ is a PWM converter and the DC current Id is the command value Id ^*
Then, the power supply current I _S is controlled so as to be substantially constant. At this time, PWM control is performed so that the power supply current I _S becomes a sine wave in phase with the power supply voltage V _S, and as a result, the input power factor is always 1 and operation with less harmonic components is performed.

Further, the converter SS ₂ is a PWM inverter, and controls the supply current (load current) to the electric motor M so that the rotation speed ωr of the AC electric motor M matches the command value ωr ^* . At this time, PWM control is performed so that a sinusoidal wave current of variable voltage and variable frequency is supplied to the motor.

First, the operation of the PWA converter SS ₁ will be described. The current Id flowing in the DC reactor Ld is detected by the DC current detector CTd and input to the DC current control circuit DCC. In the direct current control circuit DCC, the direct current detection value Id and its command value Id ^* are compared, and the current I _S (I _SR , I _SS , I _ST to be supplied from the power supply SUP is based on the deviation εd = Id ^* −Id. ) Of the peak value command Ism. For example, the proportional constant Kd is Ism = Kd.εd. A power supply voltage V _S (V _SR , V _SS ,
V _ST ) is multiplied by unit sine waves φ _R , φ _S , and φ _T synchronized with each other, and the command value I _S ^* (I _SR ^* , I _SS ^* , of the power supply current I _S is multiplied.
I _ST ^* ). That, Vsm the peak value of the supply voltage V _S
Then, And as the unit sine wave Is given, the current command values I _SR ^* , I _SS ^* , I _ST ^* are Becomes

The supply current instruction value _{^{I S * (I SR *,}} I SS *, I SR *) The following current control circuit command value of the control current _{I C 1} of the PWM converter SS ₁ is input to the ACR _{¹ I C 1} ^* Is converted to. That is, in the power supply current control circuit ACR ₁ , the current component Icap ₁ ^* flowing into the filter capacitor CAP ₁ is subtracted from the power supply current command value I _S ^* to calculate the control current command value I _{C 1} ^{* of the} PWM converter SS ₁ to calculate the PWM converter SS. command value of ₁ of the control current _{^{I C 1 * (I CR *}} , I CS
^* , I _CT ^* ).

On the other hand, the terminal voltage of the filter capacitor CAP ₁ VcaP ₁ (Vcap
_R , Vcap _S , Vcap _T ) is detected by going up to the voltage detector PT ₁ ,
Input to voltage control circuit AVR ₁ .

The detected value Vcap ₁ is compared with the command value Vcap ₁ ^* (Vcap _R , Vcap _S ^* , Vcap _T ^* ) by the voltage control open circuit AVR ₁ , and the deviation ε _{C 1} = Vcap ₁ ^* -Vcap ₁ is inverted. A correction signal ΔI _{C 1} ^* proportional to the value is obtained. When the constant of proportionality is K _{C 1} , ΔI _{C 1} ^* = − K _{C 1} · ε _{C 1} . This value is applied to the adder AD _1, and the input signal ei ₁ of the PWM control circuit PWM ₁ is created by adding it to the control current command value I _{C 1} ^* . If the PWM converter SS ₁ can be controlled for each phase, the input signals ei _R , ei _S , Si _T of each phase are given as follows.

PWM converter S based on the input signal ei _R , ei _S , Si _T
The pulse width modulation control of S ₁
The control operation will be briefly described.

FIG. 2 shows a specific example of the main circuit configuration of the PWM converter SS ₁ of the apparatus shown in FIG.

In the figure, R, S, T are three-phase terminals of the AC power supply SUP, TrR, TrS, TrT are power transformers, and L _SR , L _SS , L _ST are AC reactors C _SR , C _SS , C
_SS and _ST are filter capacitors, SS-R, SS-S and SS-T are R
Phase, S-phase and T-phase converters, Ld is a DC reactor, L ₀
AD represents load.

The R-phase converter SS-R is composed of self-extinguishing elements S _{11 to} S ₁₄ and controls the R-phase power supply current I _SR .

The S-phase and T-phase converters SS-S and SS-T are similarly configured, and control the S-phase and T-phase power supply currents, respectively.

The R, S, and T-phase converters SS-R, SS-S, and SS-T are connected in series on the DC side, and a common DC current Id flows.

The operation of the PWM control will be described by taking the R-phase converter SS-R as an example.

FIG. 3 is a time chart diagram for explaining the operation of the pulse width modulation control (PWM control) of the R-phase converter.

Triangular waves X and Y are prepared as carrier waves for PWM control. The triangular wave Y is the inverted value of X. This triangular wave X is compared with the aforementioned PWM control input signal ei _R to generate the gate signal g ₁₁ of the elements S ₁₁ and S ₁₂ of FIG. Also, the triangular wave Y and the input signal ei _R are compared to generate the gate signals of the elements S ₁₃ and S ₁₄ . That is, when ei _R X, S ₁₁ : on, S ₁₂ : off When ei _R <X, S ₁₁ : off, S ₁₂ : on ei _{R When} Y, S ₁₃ : on, S ₁₄ : off ei _R <When Y, S ₁₃ : OFF, S ₁₄ : ON.

When the elements S ₁₁ and S ₁₄ are turned on, they become equal to the control current I _CR DC current Id of the R-phase converter. Further, when the elements S ₁₂ and S ₁₃ are on, I _CR = Id. Furthermore, when the elements S ₁₁ and S ₁₃ are on and when the elements S ₁₂ and S ₁₄ are on, the mode is such that the direct current Id is circulated, and I _CR = 0.

As a result, the control current I _CR of the R-phase converter SS-R becomes the third
As shown in the figure, the average value (shown by the broken line) is a value proportional to the input signal ei _R.

Since the gate signals g _{11 of the} elements S ₁₁ and S _{12 and} the gate signals of the elements S ₁₃ and S ₁₄ are 180 ° out of phase with each other, the control frequency of the electric motor I _CR is the carrier frequency, that is, the switching frequency of the elements. Doubles. Therefore, the power supply current I
There is an advantage that the ripple of _SR becomes small.

The S-phase and T-phase converters SS-S and SS-T are similarly controlled.

In this way, the control currents I _CR , I _CS , I _{CT of the} converters of the respective phases are
Are values proportional to the control input signals ei _R , ei _S , and ei _T in FIG. 1, respectively, and as a result, Becomes k is a proportional constant. Thus R-phase supply current I _{SR is, I SR = I CR + Icap} -R = k · I CR * + Icap -R = k · (I ST * -Icap R *) + Icap -R ...... (8) next, k・ If Icap _R ^* = Icap _−R , then I _SR I = k · I _SR ^* (9) Similarly, the S-phase and T-phase power supply currents I _SS and I _ST can be set as follows: I _SS = K · I _SS ^* ... (10) I _ST = I _ST K · ^* (11)

The filter capacitors C _SR , C _SS and C _ST connected to the AC side terminals of each converter are control currents I _CR ,
Since I _CS and I _CT are rectangular currents, they are smoothed and a surge voltage is absorbed to absorb the surge voltage generated on the AC reactor L _S.

Next, the control operation of the voltage applied to the filter capacitors C _SR , C _SS and C _ST will be described.

FIG. 4 shows a voltage and current vector diagram for one phase (R phase) on the power supply side, where V _SR is the power supply voltage, V _LR is the voltage applied to the AC reactor L _SR , and V cad _-R is the capacitor C _SR. Voltage, _SR is power supply current, cap- _R is capacitor current,
_CR represents the vector of the control current of the converter SS-R.
The power supply current I _SR is controlled to be in phase with the power supply voltage V _SR . Therefore, the voltage V _LR applied to the AC reactor L _SR becomes _LR = jω _S · L _SR · _SR (12), and as a result, the capacitor voltage Vcap _−R becomes cap _−R = _{SR −LR} …… (13 ). The capacitor current Icap- _R has a phase 90 ° ahead of the voltage VcaP- _R , and each current satisfies the following equation. _{SR = CR + cap -R ...... (} 14) Thus, (12), once the power source current I _SR to flow from (13), Figure 1 because the voltage Vcap _-R determined to be applied to the capacitor C _SR Voltage control circuit AVR ₁ voltage command value Vc
^{_{ap -R * * (Vcap * -R}} * of the R phase) the ^{_{Vcap -R * = V SR -V LR}} * = V SR * -jω S L SR · SR * ...... given as (15). Here, V _SR ^* is a command value proportional to the power supply voltage V _SR , and I _SR ^* is a power supply voltage command value.

In the voltage control circuit AVR _1, compares the voltage detection value Vcap _-R and the command value of the capacitor C _SR Vcap _-R ^*, the value Δ that inverts and amplifies the deviation ε _CR = Vcap _-R -Vcap _-R
Input I _CR ^* to the adder AD ₁ described above. The ΔI _CR ^* is added to the control current command value I _CR ^* of the converter SS-R,
Input to PWM control circuit PWM ₁ .

When Vcap- _R ^* > Vcap- _R , the deviation ε _CR has a positive value and ΔI _CR ^* has a negative value. Therefore, the PWM control input signal ei _{R is} reduced, and the control current I _CR of the converter SS-R is reduced. Therefore, the current Icap flowing into the capacitor voltage C _CR
-R increases, increasing the capacitor voltage Vcap- _R .

On the contrary, when Vcap- _R ^* <Vcap- _R , ΔI _CR ^* becomes a positive value and e i _R is increased, and as a result, the capacitor current Icap _-R is decreased. Therefore, Vcap- _R decreases and Vcap ≒
Controlled to be Vcap- _R ^* .

The S-phase and T-phase capacitor voltages Vcap- _S and Vcap- _T are similarly controlled.

In this voltage control Vcap ₁ ≒ Vcap ₁ ^* steady state, to no aggressive behavior, nor need thereof.

However, AC reactor L _S and filter capacitor CAP ₁
When a resonance phenomenon is about to occur, the above voltage control works effectively, and the resonance phenomenon is suppressed. Also, if the PWM control is disturbed due to malfunctions such as noise, and as a result, an excessive voltage is about to be applied to the filter capacitor CAP ₁ , the above voltage control operates immediately and the PWM control is performed to prevent overvoltage. It works to correct the movement.

Although the PWM converter SS ₁ has been described above, it goes without saying that the PWM inverter SS ₂ has the same function. In the case of the PWM inverter SS ₂ , if a load such as an AC motor is connected instead of the AC power supply SUP and the AC reactor component is included in the motor, the operating principle of the converter described above is directly applied. Become.

The main circuit configuration of the PWM converter (PWM converter) shown in Fig. 2 is a concrete example in which three single-phase bridges are connected in series on the DC side, but the same applies to a PWM converter with a three-phase grain connection. It goes without saying that it can be applied to.

As described above, according to the current source PWM converter of the present invention,
It suppresses the resonance phenomenon between the filter capacitor and the AC reactor provided at the AC side terminal of the converter, and prevents the voltage applied to the filter capacitor from becoming excessive even if the PWM control is disturbed by noise or other factors. It becomes possible to prevent it. As a result, the output current of the converter (power supply current in the case of converter, load current in the case of inverter) can be controlled faithfully to the desired value, and its performance can be maximized. . In addition, there is no fear of element breakdown due to overvoltage, and reliability can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a current source PWM converter of the present invention, FIG. 2 is a main circuit block diagram showing a concrete example of the PWM converter of FIG. 1, and FIG. 3 is a PWM control operation. FIG. 4 is a diagram showing a time chart for doing so, FIG. 4 is a voltage / current vector diagram for explaining the operation of the device of FIG. 1, and FIG. 5 is a configuration diagram of a conventional current source PWM converter. SUP ... 3-phase AC power supply, L _S ... AC reactor, CAP ₁ ,
CAP ₂ …… Filter capacitor, SS ₁ , SS ₂ …… Self-exciting power converter, M …… AC motor, Ld …… DC reactor, PG
...... Rotation pulse generator, CTd …… AC current detector, PT ₁ , P
T ₂ …… Voltage detector, DCC …… DC current control circuit, ACR ₁ …
… Power supply current control circuit, SPC …… Speed control circuit, ACR ₂ ……
Load current control circuit, AVR ₁ , AVR ₂ ... Voltage control circuit, AD ₁ ,, A
D ₂ …… Adder, DWM ₁ , PWM ₂ …… Pulse width modulation control circuit.

Claims (1)

[Claims] 1. A direct current source, a self-excited power converter that receives a current supply from the direct current source, and outputs a pulse-width-modulated alternating current, and is connected to an AC side terminal of the converter. A filter circuit, an AC load or an AC power source connected to the output terminal of the filter circuit, a means for controlling a current to be supplied to the AC load or the AC power source, and a means for controlling a voltage applied to the filter circuit And a means for controlling pulse width modulation of the self-excited power converter based on output signals from the current control means and the voltage control means.