JPH0332303B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for controlling a power conversion device that includes a DC voltage source that receives power from an AC power source and its load device.

[Technical Background of the Invention] Load devices using a DC voltage source as a power source include a pulse width modulation control (PWM) inverter + induction motor, or a DC chopper + DC motor. There are not many problems when using a battery as this DC voltage source, but when obtaining DC voltage from a commercial power supply via an AC/DC power converter, reactive power and harmonics generated on the commercial power supply side have recently become a problem. It's getting old.

In order to solve this problem, a method was proposed in which a pulse width modulation control (PWM) converter is inserted between the commercial power supply and the DC voltage source (capacitor) as an AC/DC power converter (Japanese Patent Application No. 171886, etc.). has been done.

FIG. 1 shows a configuration diagram of a conventional power conversion device using a PWM converter as an AC/DC power converter.

In the figure, SUP is a single-phase AC power supply, Ls is an AC reactor, CONV is an AC/DC power converter,
Cd is a DC smoothing capacitor, and LAD is a load device. The converter CONV is an element with self-extinguishing capability (e.g. gate turn-off thyristor) S ₁
~ _S4 , wheeling diodes _D1 ~ _D4 , and DC reactors _L1 , _L2, and the above elements _S1 ~ _S4
In order to control the value of the AC side voltage Vc, well-known pulse width modulation control is performed. In other words, the converter CONV is a DC voltage source (capacitor) Cd
When viewed from above, it becomes a pulse width modulation control (PWM) inverter, and in that case, the AC power supply SUP side can be seen as a type of load.

This conventional power conversion device uses the above DC voltage source Cd
It controls the current Is supplied from the AC power supply so that the voltage Vd of
Capable of quadrant operation.

The above input current Is is always controlled to be in phase with the power supply voltage Vs, and the input power factor is 1.

Also, since the input current Is is controlled sinusoidally, harmonics are extremely small.

is a feature.

The control operation of this device will be briefly explained below.

The following control circuits are available. CTc is an AC current detector, R ₁ and R ₂ are voltage dividing resistors for detecting DC voltage, ISO is an isolation amplifier,
VR is a DC voltage setting device, C ₁ to C ₃ are comparators, G _v (S)
is a voltage control compensation circuit, ML is a multiplier, OA is an inverting operational amplifier, G _I (S) is a current control compensation circuit, TRG
is a carrier wave (triangular wave) generator, and GC is a gate control circuit.

First, the DC voltage Vd detected via the isolation amplifier ISO and the voltage command value Vd ^* from the voltage setting device VR are input to the comparator _C1 , and the deviation ε _v =Vd ^* −Vd is determined.
The deviation ε _v is input to the control compensation circuit G _v (S), where it is integrally amplified or proportionally amplified, and the input current is
The peak value command Im of Is becomes.

The peak value command Im is input to the multiplier ML and multiplied by the other input sinωt. The input signal sinωt is a unit sine wave synchronized with the power supply voltage Vs=Vm·sinωt, and is obtained by detecting the power supply voltage Vs and multiplying it by a constant (1/Vm).

The output signal Is ^* of the multiplier ML gives a command value of the current to be supplied from the power supply, and is expressed by the following equation.

Is ^* = Im·sinωt (1) The input current command value Is ^* is inverted by the inverting amplifier OA, and becomes the command value Ic ^* of the alternating current Ic supplied from the converter CONV to the power supply SUP. Hereinafter, Ic ^* will be referred to as converter output current command value.

Converter output current Ic is detected by alternating current detector CTc and input to comparator _C2 . comparator
The above command value Ic ^* and detected value Ic are compared by C ₂ ,
The deviation ε _I = Ic ^* − Ic is found. The deviation ε _I is input to the next control compensation circuit G _I (S), where it is proportionally amplified and becomes a control input signal e _i for pulse width modulation control.

Pulse width modulation control is a known method, and is performed by a carrier wave generator TRG, a comparator _C3 , and a gate control circuit GC.

In other words, the carrier wave generator TRG generates a triangular wave e _T with a frequency of about 1 kHz, and the comparator C ₃ compares the triangular wave e _T with the input signal e _i and controls the gate according to the deviation ε _T = e _i −e _T. The control circuit GC provides on/off signals to the gate turn-off thyristors S ₁ to _{S 4} .

When e _i >e _T , that is, when the deviation ε _T is positive, thyristors S ₁ and S ₄ are turned on (at this time, S ₂ and S ₃ are turned off), and the AC output voltage Vc of the converter becomes +Vd.

Also, when e _i <e _T , that is, when the deviation ε _T is negative,
Thyristors S ₂ and S ₃ are turned on (at this time, S ₁ , S ₄
is off), Vc = -Vd.

Furthermore, if e _i is a large positive value, the on periods of S ₁ and S ₄ become longer, the on periods of S ₂ and S ₃ become shorter, and the average value of Vc becomes proportional to the input signal e _i . It becomes a positive value in voltage. Conversely, when e _i is a negative value, the on periods of S ₂ and S ₃ are longer than the on periods of S ₁ and S ₄ , and the average value of the converter output voltage Vc is proportional to the input signal e _i. becomes a negative value.

That is, the output voltage Vc of the converter is controlled to a value proportional to the input signal e _i .

The output current Ic of the converter (the inverted value of the input current Is supplied from the power supply) is controlled by adjusting the output voltage Vc of the converter.

The AC reactor Ls has a voltage difference between the power supply voltage Vs and the output voltage Vc of the above converter, V _L = Vs − Vc.
is applied.

When Vs>Vc, the power supply current Is increases in the direction of the arrow in the figure. In other words, the converter output current Ic
acts to decrease in the direction of the arrow in the figure. vice versa
When Vs<Vc, converter output current Ic tends to increase in the direction of the arrow in the figure.

When the actual current Ic has a relationship of Ic ^* > Ic with respect to the converter output current command value Ic ^* , the deviation ε _I = Ic ^* −
Ic becomes a positive value and increases the PWM control input signal e _i via the control compensation circuit G _I (S). Therefore, the converter output voltage Vc also increases in proportion to the input signal e _i , and Vc>Vs, causing the converter output current Ic to increase in the direction of the arrow in the figure. Conversely, when Ic ^* <Ic, the deviation ε _I becomes a negative value and reduces e _i , that is, Vc. Therefore, the output current Ic of the converter is controlled to match the command value Ic ^* . If the command value Ic ^* is changed in a sinusoidal manner, the actual current Ic is also controlled in a sinusoidal manner following it.

The converter output current Ic is the input current from the power supply
This is the inverted value of Is, and the command value Ic ^* of the converter output current is the inverted value of the command value Is ^* of the input current from the power supply. Therefore, the input current Is is its command value Is ^*
It will be controlled according to the following.

Next, the control operation of the voltage Vd of the DC capacitor Cd will be explained.

Comparator _C1 compares the detected DC voltage value Vd and its command value Vd ^* . When Vd ^* > Vd, the deviation ε _V
becomes a positive value, and increases the input current peak value Im via the control compensation circuit G _V (S). The input current command value Is ^* is given by a sine wave that is in phase with the power supply voltage, as shown in equation (1). Therefore, if the actual input current Is is controlled to Is=Is ^* as described above,
When the above peak value Im is a positive value, the active power Ps shown by the following equation is from the single-phase power supply SUP to the converter C
It is supplied to the DC capacitor Cd via NV.

Ps=Vs×Is =Vm・Im・(sinεt) ² =Vm・Im・(1−cos2εt)/2 …(2) Therefore, the energy Ps・t is the DC capacitor
It is accumulated in Cd as 1/2CdVd ² , and as a result, the DC voltage Vd increases.

Conversely, when Vd ^* <Vd, the deviation ε _V becomes a negative value, and the peak value Im is reduced through the control compensation circuit G _v (S), until Im<0. Therefore,
The active power Ps also becomes a negative value, and this time, the energy Pst is regenerated from the DC capacitor Cd to the power supply. As a result, the DC voltage Vd decreases and eventually
Controlled by Vd=Vd ^* .

The load device LAD is, for example, a known PWM inverter-driven induction motor, and exchanges power with a DC capacitor Cd, which is a DC voltage source. When the load device LAD consumes power, the DC voltage Vd decreases, but by the above control, the active power Ps is supplied from the power supply and is always controlled to be Vd≈Vd ^* . Conversely, when power regeneration is performed from the load device LAD (when the induction motor is operated regeneratively),
Although Vd increases once, by regenerating active power Ps to the power supply SUP by that amount, Vd≈Vd ^* . That is, the power Ps supplied from the power source SUP is automatically adjusted according to the power consumption or power regeneration of the load device LAD.

At this time, the input current Is is controlled to be a sine wave in phase or in phase with the power supply voltage (during regeneration), so naturally the input power factor is 1 and the harmonic components are extremely small.

[Problems with Prior Art] Such conventional power converters have the following problems.

In other words, it is desirable that the voltage of the DC capacitor, which is the DC voltage source of the load device, be maintained at a constant voltage value regardless of the magnitude of the load current or regenerative power running. Since the feedback control method was adopted, there was a delay in the control response, and the above-mentioned DC voltage fluctuated greatly in response to sudden load changes.

In particular, an integral element is often used in the next voltage control compensation circuit in order to eliminate the steady-state component of the deviation ε _V = Vd ^* −Vd between the DC voltage command value Vd ^* and the actual voltage detection value Vd, and the response is not very fast. I couldn't have expected it.

If the DC voltage fluctuates significantly due to the control delay, the device must be designed to have a higher withstand voltage by the amount of the fluctuation, resulting in an uneconomical system. Further, the DC voltage fluctuation affects the control operation of the pulse width modulation control converter, making accurate current control impossible and causing waveform distortion of the input current. Furthermore, when viewed from the load side, the DC voltage source is considered to be a power source with a large output impedance, and has a particularly low transient load capacity.

[Object of the Invention] The present invention has been made in view of the above problems, and provides a power conversion device that improves the response of the DC voltage control system and eliminates fluctuations in DC voltage due to sudden changes in load current. The purpose is to provide a control method for

[Summary of the Invention] The present invention provides an AC power supply, a pulse width modulation control converter connected to the AC power supply via an AC reactor, a smoothing capacitor connected to the DC side of the pulse width modulation control converter, and a smoothing capacitor connected to the DC side of the pulse width modulation control converter. In a power conversion device comprising a load device using a capacitor as a voltage source, a current supplied to the load device is detected, a command value of the current to be supplied from the AC power supply is calculated based on the detected value, and the pulse width is This is a control method for a power conversion device that aims to improve the response of a DC voltage control system by controlling the current supplied from the AC power supply using a modulation control converter.

[Embodiment of the Invention] FIG. 2 is a configuration diagram showing an embodiment of the power conversion device of the present invention.

In the figure, SUP is a single-phase AC power supply, Ls is an AC reactor, CNV is a pulse width modulation control converter,
Cd is a DC smoothing capacitor, and LAD is a load device. Converter CNV is an element with self-extinguishing capability (e.g. gate turn-off thyristor) S ₁ ~
_S4 , wheeling diodes _D1 to _D4 , and DC reactors _L1 and _L2 .

Also, as a control circuit, a current transformer for current detection is used.
CTc, CTo, DC voltage detection voltage dividing resistor R ₁ , R ₂ ,
Isolation amplifier ISO, DC voltage setting device VR, comparator C ₁ ,
C ₂ , C ₃ , voltage control compensation circuit G _v (S), adder AD,
Multipliers MLo, MLs, operational amplifier Km, inverting operational amplifier OA, current control compensation circuit G _I (S), carrier wave generator TRG, and gate control circuit GC are provided.

The voltage Vd of the DC smoothing capacitor Cd is the voltage dividing resistor.
Detected via R ₁ , R ₂ and isolation amplifier ISO,
One is input to comparator _C1 and the other one is input to multiplier
Entered into MLo.

The comparator _C1 compares the voltage command value Vd ^* from the DC voltage setting device VR with the DC voltage detection value Vd, and calculates the deviation ε _V =Vd ^* −Vd. The deviation ε _V is input to the next voltage control compensation circuit G _V (S). G _V (S) usually uses an integral element and is slowly controlled so that the steady-state component of the deviation ε _V becomes zero. The output d of G _V (S) is input to the adder AD,
It is added to the output Im of the operational amplifier Km, which will be described later, to become the peak value command of the input current Is.

The current detector CTo detects the current Io supplied from the DC voltage source (smoothing capacitor Cd) to the load device LAD.
The detected value Io is the multiplier MLo
is input.

The above load current detection value Io is determined by the multiplier MLo.
The product of the DC voltage detection value Vd and the DC voltage detection value Vd is calculated to obtain the DC power Po=Vd·Io to be supplied to the load. This DC power Po is input to the operational amplifier Km, multiplied by a constant (2/Vm), and then the peak value command mentioned above is generated.
Im. Here, Vm is the peak value of the power supply voltage.

The output signal Im+d of adder AD is sent to another multiplier MLs
A unit sine wave input to and synchronized with the power supply voltage Vs
Can be multiplied by sinεt. Multiplier MLs output Is ^*
= (Im+d)・sinεt is the command value of the input current Is supplied from the power supply SUP, and its inverted value Io ^*
=-Is ^* is the AC output current Ic of converter CNV
(=-Is) command value. Note that the inverting operational amplifier OA is an inverter with a magnification of 1.

The converter output current Ic detected by the current detector CTc and the command value Ic ^* are input to the comparator _C2 , and the deviation ε _I =Ic ^* -Ic is determined.
The deviation ε _I is input to the next current control compensation circuit G _I (S), where it is proportionally amplified and becomes a control input signal e _i for pulse width modulation control.

Pulse width modulation control is a known method, and is performed by a carrier wave generator TRG, a comparator _C3 , and a gate control circuit GC.

That is, the carrier wave generator TRG generates a triangular wave e _T with a frequency of about 1 kHz, and the comparator _C3 generates the triangular wave e _T
and the input signal e _i , and the deviation ε _T = e _i −e _T
The gate control circuit GC gives on/off signals to the gate turn-off thyristors S ₁ to _{S 4} in accordance with the above.

When e _i > e _T , that is, when the deviation ε _T is positive, thyristors S ₁ and S ₄ are turned on (at this time, S ₂ and S ₃ are turned off), and the AC side output voltage Vc of converter CONV is +
becomes Vd. Also, when e _i <e _T , that is, the deviation ε _T
When is negative, thyristors S ₂ and S ₃ are turned on (at this time S ₁ and S ₄ are off), and Vc = -Vd. Furthermore, if e _i is a large positive value, the on periods of S ₁ and S ₄ become longer, the on periods of S ₂ and S ₃ become shorter, and the average value of Vc becomes equal to the value of input signal e _i . It becomes a proportional positive voltage value. Conversely, when e _i is a negative value, S ₁ and S ₄
The on-periods of S ₂ and S 3 are longer than the on-periods of S 2 and S ₃ , and the average value of the output voltage Vc of the converter becomes a negative value proportional to the input signal e _i .

That is, the output voltage Vc of the converter is controlled to a value proportional to the input signal e _i .

The output current Ic of the converter (the inverted value of the input current Is supplied from the power supply) is controlled by adjusting the output voltage Vc of the converter.

The AC reactor Ls has a voltage difference between the power supply voltage Vs and the output voltage Vc of the above converter, V _L = Vs − Vc.
is applied.

When Vs>Vc, the power supply current Is increases in the direction of the arrow in the figure. In other words, the converter output current Ic
acts to decrease in the direction of the arrow in the figure. vice versa
When Vs<Vc, converter output current Ic tends to increase in the direction of the arrow in the figure.

When the actual current Ic has a relationship of Ic ^* > Ic with respect to the converter output current command value Ic ^* , the deviation ε _T = Ic ^* −
Ic becomes a positive value and increases the PWM control input signal e _i via the control compensation circuit G _I (S). Therefore,
The converter output voltage Vc also increases in proportion to the input signal e _i , and when Vc > Vs, the converter output current increases.
Increase Ic in the direction of the arrow in the figure. Conversely, Ic ^* < Ic
In this case, the deviation ε _I becomes a negative value, and e _i , that is,
Vc is decreased so that Vc<Vs, and the output current Ic is decreased. As a result, the output current Ic of the converter is controlled to match the command value Ic ^* . If the command value Ic _* is changed in a sinusoidal manner, the actual current Ic is also controlled in a sinusoidal manner following it.

The converter output current Ic is the input current from the power supply
It is the inverted value of Is, and the command value Ic ^* of the output current of the converter is the inverted value of the command value Is ^* of the input current from the power supply. Therefore, the input current Is is controlled to follow the command value Is ^* .

Next, the voltage Vd of the DC capacitor Cd of the device of the present invention
The control operation will be explained below.

First, the multiplier MLo multiplies the DC voltage Vd and the DC current Io supplied to the load LAD to obtain Po=Vd·Io (3). This is the active power supplied to the load LAD.

This active power Po is input to the next operational amplifier Km, and the peak value command Im of the input current Is supplied from the power supply SUP is determined.

Im=(2/Vm)·Po (4) A correction amount d is added to the actual peak value command I′m=Im+d, but the explanation will be given first assuming that this correction amount d is zero.

The above wave height command Im is obtained by the following multiplier MLs,
Unit sine wave synchronized with power supply voltage Vs = Vm・sinεt
Multiply by sinεt to obtain the input current command value Is ^* as Is ^* = Im・sinωt (5). The actual input current Is follows this command value Is ^* and is controlled to be a sine wave in phase with the power supply voltage Vs.

Therefore, the active power supplied from the AC power supply SUP
Ps is expressed as follows.

Ps=Vs・Is =Vm・Im・(sinωt) ² =Vm・Im・(1−cos2ωt)/2 …(6) This active power Ps is the angular frequency ω of the AC power supply SUP
It changes at an angular frequency twice that of , and its average value is
Ps becomes =Vm・Im/2=Po...(7). In other words, assuming that there is no circuit loss, the active power Po supplied to the load LAD is equal to the power supply
It is equal to the average value of the active power Ps supplied from the SUP, and it can be considered that there is almost no input or output of energy to the DC smoothing capacitor Cd. However, in the case of a single-phase power supply, since the active power Ps fluctuates at a frequency twice the power supply frequency as described above, it is assumed that a DC capacitor Cd with a capacity capable of smoothing the fluctuation is prepared.

Therefore, the active power Po required for the load LAD is immediately supplied as AC power Ps from the AC power supply SUP, and even with sudden load fluctuations, the voltage Vd of the DC capacitor Cd hardly changes and remains at a nearly constant value. Retained.

However, in actual circuits, circuit loss always exists, and some kind of active power correction becomes necessary.

The correction amount d input to the adder AD is for performing the above-mentioned active power correction, and is obtained by performing DC voltage control using conventional feedback control. That is, the comparator C ₁ compares the DC voltage command value Vd ^* and the DC voltage detection value Vd, and the deviation ε _V = Vd ^* − Vd
The correction amount d is determined via the control compensation circuit G _V (S).

The control compensation circuit G _V (S) is composed of an integral element and the like, and is designed to exhibit a slow control response.

When there is a circuit loss, the energy of the DC capacitor Cd gradually decreases due to the loss, and the DC voltage Vd decreases. When Vd ^* >Vd, the deviation ε _V =Vd ^* -Vd becomes a positive value, and the correction amount d is increased via the control compensation circuit G _V (S).
Therefore, the peak value Im' = Im + d of the input current command value Is ^* = (Im + d) · sinεt (8) increases, increasing the average value of the active power supplied from the AC power supply SUP, and Vd
= Vd ^* .

Conversely, when Vd ^* < Vd, the deviation ε _V becomes a negative value and decreases the correction amount d, reducing the average value of the active power supplied from the AC power supply SUP, so that Vd = Vd ^* . controlled as follows.

This voltage control is performed very slowly and does not respond to sudden changes in load.

That is, in the power converter of the present invention, in response to a sudden change in load, the peak value command Im of the input current to be immediately supplied from the power supply is calculated from the load current value, the input current Is is controlled, and the circuit DC voltage errors due to losses and the like are corrected by constructing a relaxed voltage control system.

Although the embodiment shown in FIG. 2 has been explained using a single-phase AC power source as an example, it goes without saying that the present invention can be similarly applied to a three-phase or polyphase AC power source.

Further, as the load device LAD, a DC chopper device + DC motor, or a pulse width modulation control inverter + induction motor, etc. can be considered.

Furthermore, in the embodiment shown in Fig. 2, when determining the active power Po supplied to the load, it was determined from the product of the measured DC voltage value Vd and the DC current Io, but the DC voltage Vd was almost equal to the command value Vd ^* . On the premise that they match, it may be obtained as Po=Vd ^*・Io.

Further, when the load device LAD is a pulse width modulation control inverter + AC motor, etc., the active power Po supplied to the AC load may be determined, and the peak value command Im of the input current may be determined from that value.

[Effects of the Invention] As described above, according to the power converter control method of the present invention, the peak value command of the input current Is to be supplied from the power source is immediately given in response to a sudden load change,
It has become possible to extremely reduce fluctuations in DC voltage Vd due to control delays, which was a problem in the past. As a result, various adverse effects caused by DC voltage fluctuations (problems such as an increase in converter capacity, input current waveform distortion, or a decrease in transient load capacity) are eliminated, resulting in extremely economical and highly reliable power conversion. equipment can be provided.

It goes without saying that it has the characteristics of an input power factor of 1 and a low harmonic content of the input current.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional power converter, and FIG. 2 is a block diagram showing an embodiment of the power converter of the present invention. SUP...AC power supply, Ls...AC reactor,
CONV…Pulse width modulation control converter, Cd…DC smoothing capacitor, LOAD…Load device, S ₁ to _{S 4}
…Gate turn-off thyristor, D ₁ to _{D 4} … Wheeling diode, L ₁ , L ₂ … DC reactor,
R ₁ , R ₂ ...Voltage dividing resistor, ISO...Isolation amplifier, CTc,
CTo...Current detector, VR...DC voltage setting device, C ₁ ~
C ₈ ... Comparator, AD... Adder, ALo, Mls... Multiplier,
G _V (S), G _I (S)...control compensation circuit, Km...operational amplifier, OA...inverting operational amplifier, TRG...carrier wave generator, GC...gate control circuit.

Claims (1)

[Claims] 1 A converter that is connected to an AC power source via a reactor and capable of regenerative operation that controls the AC input current by pulse width modulation control and outputs a desired DC voltage; a capacitor for smoothing voltage; a first calculating means for multiplying the DC voltage by the current supplied from the DC voltage to a load to obtain a first current reference; and a correction unit for comparing the DC voltage and the reference voltage. A voltage control means for obtaining a signal and a second calculation means for obtaining a second current reference according to the sum of the first current reference and the correction signal are provided, and the second current reference and the input current are A power conversion device characterized by performing pulse width modulation control by comparison.