JPH044756A - Controller of pwm inverter - Google Patents

Abstract

PURPOSE:To eliminate a pilot reactor and to correct the shifted magnetization of an instantaneous output transformer by providing a pulse width modulation control circuit giving the gate signal of a power converter on the basis of the sum of respective output signals from a primary current control means and a load current control means. CONSTITUTION:A current detector CTL detects a load current IL and inputs the current to a comparator C1. The comparator C1 compares a current detection value IL and a load current command value I1* and amplifies the deviation by a current control compensating circuit GL (S) into a PWM control input signal ei via adders A1, A2. Also, a current detector CT1 detects the primary current I1 of a transformer TR and compares the detected value with a primary current command value I1* by a comparator C2. The deviation is amplified by a current control compensating circuit G1 (S) and inputted to a pulse width modulation control circuit PWM. Thus, the load current IL and the primary current I1 of the output transformer are always controlled to appropriate values so that the biased magnetization of the transformer can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a control device for a voltage source PWM inverter that supplies variable voltage variable frequency power to an AC load via an output transformer.

(Prior Art) In recent years, large-capacity self-extinguishing elements (eg, gate turn-off thyristors, etc.) have been actively developed and are being used in power conversion devices such as inverters. especially,
Pulse width modulation control (PWM control) inverters are capable of converting direct current into alternating current with variable voltage and variable frequency, and have come to be widely used as driving power sources for induction motors, synchronous motors, and the like.

This PWM inverter requires a high voltage and large current as the capacity of the load side of AC motors etc. increases, so the AC side of the converter is isolated by an output transformer and multiple converters are operated in parallel. things are being done.

FIG. 4 shows the configuration of a conventional PWM control inverter device, which supplies power to an AC load via an output transformer.

In the figure, Vd is a DC power supply, INV is a PWM control inverter, PL is a pilot reactor, TR is an output transformer,
LOAD is an AC load. Inverter INV includes self-extinguishing elements $1 to S4 and freewheeling diode D
, ~D4.

In addition, as a control circuit, a current detector CT P L vC
TL, comparators C1, C,, adder A1. A2, control compensation circuit GL (S), Gp+- (S), rectifier. , r
DO2, sample and hold circuits SH1 and SH2, and pulse width modulation control circuit P are prepared.

The inverter INV converts the DC voltage Vdtr into AC power of variable voltage and variable frequency through PWM control, and supplies power to the AC load LOAD via the output transformer TR.

Load current IL is controlled as follows.

In other words, the load current is measured by the current detector CTL.

is detected and input to comparator Cj. The comparator C4 compares the current command value L* and the detected current value ■L, and calculates the deviation εL"IL' IL. The deviation ε.

is amplified by the following current control compensation circuit, and adder A1
．． It is input to the PWM control circuit PWH via A2. The PWM control circuit PldM performs pulse width modulation control on the inverter INV so as to generate a voltage V proportional to the input signal ei.

When ■♂>IL, the deviation εL takes a positive value, increases the output voltage ■1 of the inverter INV, increases the load current IL, and is controlled so that IL≠IL*. Conversely, if I L*< I L, the deviation ε.

becomes a negative value, which reduces the output voltage of the inverter INV and reduces the load current IL. Therefore, ■L≠1 after all
- and calm down. If the current command value is changed in a sinusoidal manner, the actual current will also follow it and be controlled in a sinusoidal manner.

Another signal input to adder A, which is load LO
This is to compensate for the back electromotive force of the AD, etc., and is added to improve the response of the load current control.

The output transformer TR connects the DC power supply Vcl and the AC load LOA.
V1 is placed for the purpose of insulating D or when multiple inverters are operated in parallel. Usually, the excitation current of this transformer flows so as to generate a voltage on the secondary side that is proportional to the output voltage of the inverter INV. In a load where the output frequency and voltage are proportional to each other, or a load with a constant voltage and constant frequency, the excitation current of this transformer is approximately a constant value.

However, in reality, a slight DC bias may be applied to the output transformer from the inverter side due to drift in the control circuit or imbalance in the switching characteristics of the elements. When a DC voltage bias is applied to the transformer, the transformer TR will gradually become biased, and eventually the iron core will become saturated and an excessive excitation current will flow through the transformer TR.
Not only will the transformer TR burn out, but the inverter INV
There is even a risk that the elements constituting the device may be destroyed by overcurrent.

Therefore, a pilot reactor P is connected in parallel with the output transformer.
L is connected, the biased magnetization of this pilot reactor PL is monitored, and the output voltage of the inverter INν is corrected according to the amount of biased magnetism to prevent the biased magnetization of the transformer TR.

That is, first, the current IPL flowing into the pilot reactor PL is detected by the current detector CTPL. This current detection value IPL is converted into a rectifier circuit. , and input into Do2, the positive side current I PL'+ゝ and the negative side current I PL'
Separate into Next sample and hold circuits SH0 and S
By H2, the peak value IPL of the above positive side current IP%+1
Peak value IPL'' of PE noise and load current IPL'-ゝ
PE^ is held every half cycle of the output frequency. Furthermore, the comparator C7 calculates the positive side current peak value P♂+' PEAK and the load side current peak value I PL''P.
Compare EAK and its deviation E PEAKI PL”PE
Find AK-I PL”PEAK/The relevant deviation f PE
AK is inverted and integrated by the next control compensation circuit GPL (S), and a DC bias voltage △ is used to correct the biased magnetization of the transformer.
vDc is input to the PWM control circuit PνH via the adder A2.

For example, if a positive DC bias △■B engineering ^S is applied to the output voltage due to variations in the elements that make up the inverter INV, both the transformer TR and the pilot reactor PL will gradually become biased toward the positive side. . As a result, the output I PL"'PIEA of the sample hold circuit SH1
K becomes larger than the output IPL"PI!AK of SH, and the deviation εPEAK becomes a positive value, and the control compensation circuit GPL
(S) is inverted and integrated, making the compensation voltage Δ■Dc a negative value. Therefore, this compensation voltage ΔVoc acts to cancel the DC bias voltage ΔVBIAS, and can prevent biased magnetization of the transformer TR and pilot reactor PL.

The above-mentioned conventional PWM inverter device can increase the capacity by increasing the number of inverters with output transformers, and by controlling the inverters with multiplexed pulse width modulation, a sine wave output with less high disturbance waves can be obtained. It has the characteristic of being

(Problems to be Solved by the Invention) However, this conventional power conversion device has the following problems.

That is, a pilot reactor PL is used to detect biased magnetization of the output transformer TR, but when biased magnetization occurs, the current IPL flowing into the pilot reactor PL and the excitation current 0 of the output transformer TR are completely They are not proportional and one of them may become biased first. For this reason, the compensation voltage ΔVoc may be applied even though the transformer TR is not yet biased, or conversely, the compensation voltage △■Dc may not be applied even though the transformer TR is biased. A contradiction occurs. As described above, it is difficult to match the saturation characteristics of the iron core of the pilot reactor PL and the saturation characteristics of the iron core of the output transformer TR, and there is a drawback that proper anti-bias control cannot be performed. Also, the capacity of this pilot reactor PL is 1 of the output transformer TR.
It has a capacity of about 10%, and occupies a large proportion of the entire device.
It was also a cause of increased costs.

Furthermore, in the conventional bias prevention control described above, the peak value of the current is sampled and held every half cycle of the output frequency, so when the output frequency becomes low, the time delay for detection becomes longer, and during that time, the peak value of the current is sampled and held. This may cause the transformer to burn out, or the elements that make up the inverter to be destroyed due to overcurrent.

The present invention was made in view of the above problems, and it is possible to omit the pilot reactor used in conventional devices, and to correct the biased magnetization of the instantaneous output transformer regardless of the high or low output frequency of the inverter. It is an object of the present invention to provide a control device for a PWM inverter.

[Structure of the invention]

(Means for Solving Problem 111) In order to achieve the above objects, the device of the present invention includes an AC load and a pulse width modulation control system that supplies variable voltage and variable frequency power to the load via an output transformer. PWM) inverter, and means for controlling the current flowing through the AC load;
The power converter includes means for controlling a primary current of the output transformer, and a pulse width modulation control circuit that provides a gate signal for the power converter based on the sum of each output signal from the primary current control and the load current control means. ing.

(Operation) A PWM inverter converts DC power into variable voltage variable frequency (
VVVF) AC power. An output transformer is installed between the inverter and the AC load.

First, a load current flowing into the AC load is detected, and the load current is controlled according to a command value. This is the original role of the P'WM inverter. On the other hand, the primary current of the output transformer is detected, and the sum of the excitation current command value that generates the necessary voltage from the transformer and the load current command value is given as the primary current command value. The primary current detection value is instantaneously compared and controlled to an appropriate value.

In this way, in the device of the present invention, the load current and the primary current of the output transformer are always controlled to appropriate values, so even if
Even if a DC bias voltage is applied to the output transformer due to element imbalance, etc., correction control is immediately performed, and biased magnetization of the transformer can be prevented.

Note that since the load current control signal and the primary current control signal are applied to the inverter in parallel, there is a concern that both control systems may interfere with each other. By making it smaller, interference can be eliminated. Especially since the output transformer's biased magnetism does not progress rapidly.

It is more realistic to lower the gain of the transformer's primary current control system.

In this way, the device of the present invention can prevent biased magnetization of the output transformer without using a pilot reactor, and can control the primary current of the transformer to an appropriate value regardless of the high or low output frequency of the inverter. This makes it possible to provide a highly reliable PWM control inverter device.

(Embodiment) FIG. 1 is a configuration diagram showing an embodiment of a PWM inverter device of the present invention.

In the figure, Vd is a DC voltage source, INV is a PWM control inverter, TR is an output transformer, and LOAD is an AC load.

The inverter INV is composed of self-extinguishing elements (for example, gate turn-off thyristors: GT○) 81 to s4 and freewheeling diodes D to D4.

In addition, as a control circuit, a current detector CT1, comparators C, C2, current control compensation circuits G□(S), GL(S
), adder A1. A, and pulse width modulation control circuit P
WM is available.

To simplify the explanation below, the primary/
The description will be made assuming that the secondary turns ratio is 1.

First, the PWM control operation of this multiplex inverter INV will be explained.

FIG. 2 shows a time chart for explaining the PWM control operation of the inverter INV of FIG. 1.

PWM control carrier signals (triangular waves) x, y (inverted value of x) are compared with control input signal ei, and gate signal gi+g
Make z. That is, when ei≧X, g1=1, element S: on, S2:
Off e (When <X, g
On When el<Y, gz=0, element S3: on,
S4: Turns off.

The output voltage (1) of the inverter INV is determined as follows by turning on and off the elements 81 to S4.

When Sl and 84 are on, ■□=10Vd When 52 and S are on, V1=-Vd and other modes, ■□20 is obtained, and the waveform at the bottom of FIG. 2 is obtained. The average value V 1 (indicated by a broken line) is a value proportional to the aforementioned control input signal e1.

In this way, the output voltage ■1 of the inverter INV is PW
Control will be performed at a frequency twice the carrier wave frequency of M control.

As long as the transformer TR is not saturated, the voltage V2 applied to the load LOAD is equal to the voltage v1.

Next, the operation of load current control will be explained.

The current detector CTL detects the current (load current) IL flowing into the load LOAD and inputs it to the comparator C1. The comparator C□ compares the current detection value ■L and the load current command value ♂ to find the deviation εL"IL' IL. The deviation εL is amplified by the next current control compensation circuit at, (S). , adder A, , PWM control input signal ei via A2
It is said that

When I I-” > I L, the deviation εL becomes a positive value, increasing the output voltage of the inverter INV,
The load current is increased, and IL4IL* is controlled.

Conversely, when IL'<IL, the deviation IL becomes a negative value, reducing the output voltage 1 of the inverter INV and reducing the load current IL. Therefore, IL ≠ 1 self and calm down. If the current command value 1 is changed in a sinusoidal manner,
The actual current ■ also follows it and is controlled to be a sine wave.

Another signal input to adder A, which is load LO
This is to compensate for AD's back electromotive force, etc. in a positive manner.

Added to improve the response of the load current control described above.

Next, the operation of primary current control of the transformer TR will be explained.

The primary current 11 of the transformer TR is detected by the current detector CT1, and compared with the primary current command value IL* by the comparator C2. The deviation ε1==E,*+1 is amplified by the next current control compensation circuit G□(S) and inputted to the pulse width modulation control circuit PWM via the adder A2.

When I 1''> I, the deviation E1 becomes a positive value and increases the input signal ei of the PWM control circuit PW)I. Therefore, the output voltage (■) of the inverter INV increases and the voltage of the transformer TR increases. The primary current 11 of is increased.

Conversely, when I,'<I, the deviation E1 becomes a negative value and decreases the input signal ei of the PWM control circuit PWM. Therefore, the output voltage V□ of the inverter INV decreases, and the primary current 11 of the transformer TR decreases.

Therefore, it is controlled so that ■=1-.

Here, the above-mentioned primary current command value 1□ town, load current command value ■♂ and transformer excitation current command value ■. given by the sum of bundles. Command value of the excitation current. Town, so that the voltage vL required on the load side is generated from the transformer TR,
It is given as follows. However, M is the mutual inductance of the transformer TR, and ω is the output angular frequency.

I O'= VL"/ jωM...
(1) Therefore, the primary current command value ■1* is given as shown in the following equation.

■, *=■, East+IO East=I L*+VL”/ j
ωM ・= (21 In this way, in the device of the present invention, the load current L and the primary current 11 of the output transformer are always controlled to appropriate values. Even if a voltage is applied, correction control is performed immediately and biased magnetization of the transformer can be prevented.

Note that since the load current control signal and the primary current control signal are applied to the inverter in parallel, there is a concern that both control systems may interfere with each other. By making it smaller, interference can be eliminated. In particular, since the biased magnetization of the output transformer does not progress rapidly, it is more realistic to lower the gain of the primary current control system.

FIG. 3 is a configuration diagram showing another embodiment of the PWM control inverter device of the present invention.

In the figure, Vd is a DC voltage source, INV-1, INV-2 are first and second PWM control inverters, TR1, TR2
is the output transformer and LOAD is the load. Inverter I
NV-1 and INV-2 are constructed in the same manner as in FIG.

In addition, the load LOAD has a resistance R, an inductance LL, and a back electromotive force ■. It consists of In addition, as a control circuit, current detectors CTL, CT1, CT, and comparators C0 to C
3. Current control compensation circuit G, (S), G, (S).

Gt, (S), adders A1-A2 and pulse width modulation control circuit PldM1. PWM2 is available.

This device uses two inverters INV-1 and INV-
2 are operated multiplexed via transformers TR1 and TR2. That is, the carrier wave signals X, Y, (inverted value of X) given to the first PWM control circuit PIIIM1 and the second Pw
Carrier wave signal X2. to be applied to M control circuit PtIIM2. Y2
PWM by shifting the phase of (inverted value of X2) by 90"
is in control. Here, the primary/
Assuming that the secondary turns ratio is 1:1, the transformer TR1
The secondary voltage ■1□ is the output voltage V of inverter INV-1
Matches 11. Similarly, the output voltage v2□ of the transformer TR2 also matches v21.

The sum of secondary voltages ■1□ and ■2□ of the transformers TR, TR2 is applied to the load LOAD. The load voltage ■L-
The equivalent carrier frequency of (1), 2+(2), and 2 can be obtained to be four times the PWM control carrier frequency due to the effect of the multiplex operation. Therefore, the pulsation of the current supplied to the load LOAD has an extremely small value.

The load current is controlled by two inverters INV-1 and INV-.
The control is performed by simultaneously adjusting the two output voltages.

That is, the current detector CT detects the load current IL,
The comparator C3 determines the load current command value■ Deviation from self εt=I
c* Find IL. The deviation EL is amplified by the current control compensation circuit GL(S), and is used as the input signal e□ of the PWM via the adder A1, and as the input signal e,2 of the PIIM2 via the adder A2.

When IL*>IL, the deviation εL becomes a positive value,
Increase the input signal eiite, load voltage ■L=■□
Increase 2+v22. Therefore, the load current IL increases, and 1. : I am controlled by myself. On the contrary, 工♂〈工. In this case, the deviation ε becomes a negative value, and the input signal e11. e1
2 and decrease the load voltage vL=v1□+■2□. Therefore, the load current decreases, and as expected, ■L≠IL
*Controlled by *. Here, the signal vLN applied to the adder A3 is used to improve the response of the load current control described above, and positively compensates the voltage on the load side. This VL
” is given as follows.

VL"= (VC*+ j (11L L "I L
K + Rt, ・I L *) / 2- (3) Now, the third
In the device shown in the figure, inverters INV1 and INV-2
Due to variations in the switching characteristics of the elements constituting the transformers, a slight DC bias is applied to the transformers TR1 and TR2, which may cause DC biased magnetization. Therefore, in the device shown in FIG. 3, the primary currents of the two transformers are detected and the primary currents are controlled by each inverter.

First, the primary current of the transformer TR1 is detected by the current detector CT1 and input to the comparator C. Comparator C1
Then, the primary current command value * is compared with the detected value above to find the deviation εx"L'Ix.The second deviation ε1 is increased by the next current control compensation circuit aX(S), and the adder input to PwM via A1.

1,'>1. In this case, the deviation E becomes a positive value and increases the input signal ei□ of the PWM control circuit PWM. Therefore, the output voltage V 11 of inverter INV-1
increases, causing the primary current of the transformer TR1 to increase by 12.

Conversely, when I x''< r, the deviation ε1 becomes a negative value, and the input signal ei of the PWM control circuit PvM-1
.

decrease. Therefore, the output voltage V1□ of the inverter INV-1 decreases, and the primary current of the transformer TR1 decreases. Therefore, ■, 41. ' is controlled so that

The primary current 12 of transformer TR7 is similarly controlled.

Similarly, even in multiple operation of three or more inverters, the load current can be controlled while controlling the primary current of each output transformer.

Although the inverter with a single-phase output has been described above, it goes without saying that the present invention can be similarly implemented with a PWM inverter with two or more phases.

〔Effect of the invention〕

As described above, according to the PWM inverter control device of the present invention, biased magnetization of the output transformer can be prevented without using a pilot reactor, and the device can be made smaller, lighter, and lower in cost. Further, it is possible to appropriately control the load current and the primary current of the transformer regardless of the high or low output frequency of the inverter, and a highly reliable PWM control inverter device can be provided.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the PWM control inverter device of the present invention, FIG. 2 is a time chart diagram for explaining the PWM control operation of the device of FIG. 1, and FIG. 3 is a diagram of the PWM control inverter device of the present invention. A block diagram showing another embodiment, FIG. 4 is a block diagram of a conventional PWM control inverter device. Vd...DC voltage source INV...PWM control inverter TR...Transformer LOAD...AC load S1
~S4...Self-extinguishing elements D1-D,...Freewheeling diode CTL
, CT1...Current detector C1, C2...Comparator A1. A2...Adder G1(s)...Primary current control circuit GL(S)...Load current control compensation circuit PWM...Pulse width modulation control circuit

Claims (2)

[Claims] (1) Pulse width modulation control that supplies variable voltage and variable frequency power to an AC load and the load via an output transformer (
PWM) in an inverter, means for controlling the current flowing through the AC load, means for controlling the primary current of the output transformer, and based on the sum of each output signal from the primary current control means and the load current control means. A control device for a PWM inverter, comprising a pulse width modulation control circuit that provides a gate signal for the power converter. (2) The control device for a PWM inverter according to claim 1, wherein the control gain of the load current control means is higher than the control gain of the primary current control means.