JP2874212B2 - Input current control method for PWM converter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a PWM converter, and more particularly to an input current control method for a PWM converter.

[Conventional technology]

2 is a block diagram of a PWM converter, FIG. 3 is a block diagram of a conventional example of an input current control circuit for one phase of the three-phase main switching circuit of FIG. 2, and FIG. 4 is input current control. FIG. 4A is a vector diagram at the time of a forward conversion operation, and FIG. 4B is a vector diagram at the time of an inverse conversion operation.

In FIG. 2, a main switching circuit 1 of the PWM converter has U, V, and W phase switching circuits for turning on and off the connection between each phase power supply of a three-phase AC power supply and a load, and input terminals of each phase switching circuit. Are connected to the U, V, and W phase terminals of the AC power supply 2 via the input reactor 3, respectively. Further, a smoothing capacitor 4 is connected to an output terminal of the main switching circuit 1. U, V, W phase switching circuit
Each transistor switching element (hereinafter, referred to as switching elements) S ₁ and S _2, S ₃ and S _4, S ₅ and S ₆ are cascaded, further freewheeling diodes D _1, D _2,
· · ·, D ₆ is connected in parallel to the switching element S ₁ to S _6, respectively.

The on / off control of each phase switching circuit is performed by a power conversion circuit shown in the block diagram of FIG.
In FIG. 3, the deviation between the detected value of the actual output voltage V _DC and the DC voltage command V _COM specifying the output voltage of the PWM converter (hereinafter, referred to as voltage deviation) [Delta] V is inputted to the voltage amplifier 6, effective A current amplitude command ＩI ^* _r is generated. The operation for one U-phase will be described below. Sine table (sine wave generator) 10 inputs a U-phase power supply phase voltage V _m, to produce a unit sine wave sinm. Active current amplitude command ▲ I ^* _r ▼ is multiplied by a unit sinusoid sinm, active current command I _r is generated. Further, for the reason described later, the power supply voltage compensation current amplitude command (hereinafter, referred to as a power supply compensation amplitude command) I ^* _CEMF
▼ is set, and the command ＩI ^* _CEMF ▼ is multiplied by the unit sine wave sinM to generate a power supply voltage compensation current command (hereinafter referred to as a power supply compensation current command) I _CEMF . The effective current command I
_r is vector-subtracted from the power supply compensation current command I _CEMF to generate a current designation I _ref . The subtractor 9 _{outputs the} current command I _ref and PW
An actual current (hereinafter, referred to as a converter input current) I _C input to the M converter is vector-wise compared to generate a current deviation ΔI. The current amplifier 7 receives the current deviation ΔI and receives a converter input voltage command (hereinafter referred to as a voltage command).
Generate V _ref .

Hereinafter, for the neutral point of the AC power supply voltage, it referred to the potential of each phase input terminal of the PWM converter and the converter input voltage V _C. AC power supply, AC power supply phase voltage (hereinafter, referred to as an AC voltage) corresponding to the vector difference between V _m and the converter input voltage V _C V _L (reactor voltage) to the converter input current I _C. When the inductance of the input reactor is L, the transfer function for generating a converter input current I _C from the reactor voltage V _L is 1 / (Ls).

This input current I _C (s) is fed back to the subtractor 9 to generate a voltage command _Vref so as to compensate for the current deviation ΔI.
In the block diagram of FIG. 3, when generating a reactor voltage V _L from the PWM converter input voltage V _C, the AC voltage
V _m acts as a disturbance occurs a difference between the amount corresponding active current command I _r and the converter input current I _C. In order to cancel this disturbance, as described above, the power compensation current command _ICEMF is vector-subtracted from the effective current command. Load current I _L > 0
In the case of (in the direction of the arrow in FIG. 2), the smoothing capacitor 4 discharges, and the output voltage _VDC tends to decrease. As a result, the DC voltage command V _COM > V _DC , and the voltage deviation ΔV = V _COM −V _DC > 0. ▲ I ^* _r ▼> 0. Effective current amplitude command ▲ I
^* _R ▼ becomes active current command I _r is multiplied by a unit sine wave of the AC voltage V _m in phase. Since the converter input current I _C is controlled so as to follow the active current command I _r, the AC voltage
V _m is substantially in phase, and a forward conversion operation is performed. FIG. 4A shows a vector diagram at the time of this forward conversion operation.

When the load current I _L <0, the smoothing capacitor 4 is charged, and the output voltage _{VDC tends} to increase. As a result, the DC voltage command V
_COM <V _{DC and the} voltage deviation ΔV = V _COM− V _DC <0,
As a result, the effective current amplitude command ＩI ^* _r ▼ <0. Active current amplitude command ▲ I ^* _r ▼ is multiplied with a unit sine wave of the AC voltage V _m in phase, the active current command I _r. Converter input current I _C becomes almost reverse phase with the AC voltage V _m to be controlled so as to follow the active current command I _r, the inverse transform operation. FIG. 4B shows a vector diagram at the time of this inverse conversion operation. Thus, the PWM converter can perform forward and reverse power conversion.

In Figure 4, for simplicity of explanation, the case of the forward transform operation (FIG. 4 (a)), but the converter input current I _C and the AC voltage V _m is shown in phase, as shown below To
In general there is a phase difference between V _m and I _C. Similarly, if the inverse transformation operation (FIG. 4 (b)), the phase difference between V _m and I _C is not 180 °. Therefore, the absolute value of the power factor is generally strictly 1
do not become.

 The operation of the input current control circuit of FIG. 3 is as follows.

From the block diagram of Figure 3, when calculating the relationship between the converter input current I _C and the active current command I _r becomes as follows.

Here the transfer function of the current amplifier 7 and -G _I (s), the transfer function (FIG. 3 of the PWM control circuit 8 that generates a converter input voltage V _C from the voltage command V _ref, enter the PWM signal converter The transfer function of each phase switching circuit that generates the input voltage V _C when the power conversion circuit 5 is collectively used)
_Is G _PWM . Here, G _PWM is a scalar quantity. (Although actually difficult to completely converted to a linear voltage command V _ref because of the influence of the upper and lower short-circuit prevention period of the main switching circuit elements of the converter input voltage V _C, using a high-speed switching element, the upper and lower short-circuit prevention period Assuming that the frequency is as short as possible and that the carrier frequency is sufficiently high, it is assumed that the conversion from V _ref to V _C is almost linear and that there is no delay in PWM conversion.) The first term on the right side of the equation (5) Two terms, ie Each active current command I _r and the power supply compensation current command I
_This is a current component corresponding to _CEMF .

Now, assuming that the proportional gain of the current amplifier 7 is g _I and the first-order lag time constant is T, the transfer function G _I (s) is expressed by the following equation.

As described above, the power supply compensation current command I _CEMF is
AC in the case of a signal input to compensate for the AC voltage V _m power factor 1 control (the phase difference between the AC voltage and the converter input current control 0 ° or 180 °) acting as a disturbance since given voltage V _m in phase, is set so it holds the following equation.

V _m (s) = g _I G _PWM I _CEMF (9) Substituting equation (8) into equation (6), and substituting equations (8) and (9) into equation (7), and furthermore, s = jω After all, Normally, G _PWM and g _I are both about several tens, and T is several hundred μsec.
And L is about several mH and ω = 2π · 60, so that TLω ² ≪G _PWM · g _I (12) Therefore, the following equation holds.

Therefore, the gain G ₁ and the phase difference [psi ₁ of I _C1 for I _r is represented by the following equation.

Similarly, gain G ₂ and phase difference I of I _C2 with respect to I _CEMF
2 is represented by the following equation.

Since the parts corresponding to the independent variables of the arctangent function on the right side of the equations (16) and (18) are mutually reciprocal and opposite signs, as is clear from the formula of the trigonometric function, ψ ₁ (ω) and ψ ₂ ( ω) is always 90 ° regardless of ω. Here, in the ideal state ωL≪G _PWM · g _I (19) In the case of T = 0 (19a), G ₁ = 1, ψ ₁ = 0, G ₂ = 0, and the converter input current I _C becomes effective. the phase difference between the current command I _r becomes 0 °.
If the power factor 1 control, active current command I _r is the power running and the AC voltage V _m are in phase. Therefore, in phase from the AC voltage V _m and the converter input current I _C. FIG. 4A is a vector diagram in such a case. In addition, the regeneration time in the case of power factor 1 control, the AC voltage V _m and active current command I _r are opposite phase. Therefore, the converter input current I _C is a phase opposite to the alternating voltage V _m. FIG. 4B is a vector diagram in such a case. However, equations (19) and (19
If the condition represented by a) is not satisfied, the equations (16) and (18) are used between the current components I _C1 and I _C2 of the converter input current I _C and the AC voltage V _m. The phase difference represented by Thus, in the case of the power factor 1 control, the effective current command
Against I _r is the AC voltage V _m, since changes in phase (power running) or reverse phase (during regeneration), so that the vector diagram represented in FIG. 5.

FIG. 5A is a vector diagram during power running, and FIG. 5B is a vector diagram during regeneration. During power running, the converter input current I _C of the phase with respect to the active current command I _r, delay or advances. During regeneration converter input current I _C of the phase to always delayed with respect to the active current command I _r.

[Problems to be solved by the invention]

The input current control method of the above-mentioned conventional PWM converter
Since the phase of the converter input current I _C is shifted relative to the active current command I _r, the phase of the converter input current I _C AC voltage V _m, during power running not in phase, the longer opposite phases at the time of regeneration, There is a problem that the power factor decreases.

Such I _C1 itself delays, and among the phase shift caused by the I _C1 vector I _C2 of the advance 90 °, as the delay [psi ₁ for I _r of I _C1 is apparent from equation (16), the input The inductance L of reactor 3 is large and G
_{As the value of PWM} · g _I is smaller, the magnitude G ₂ of the 90 ° advance vector I _C1 from I _C1 is larger as the first order lag time constant T of the current amplifier 7 is larger, as is apparent from the equation (17). Become.

An object of the present invention is to provide an inductance L and a first-order lag time constant T.
By large, even when the G _PWM · g _I is small, the converter input current I _C is followed without phase difference to active current command I _r, whereby the AC voltage V _m, the phase shift of converter input current I _C An object of the present invention is to provide a PWM converter input current control method that does not cause a reduction in power factor.

[Means for solving the problem]

The input current control method of the PWM converter according to the present invention includes a first current amplitude command corresponding to a voltage deviation of a DC voltage output from the PWM converter with respect to a set voltage, and a first current amplitude command having the same frequency as the AC voltage of the AC power supply. A second current amplitude command set to compensate for the AC voltage acting as a disturbance by generating a first current command by multiplying the sine wave signal and a second current command having the same frequency as the AC voltage A second current command is generated by multiplying a sine wave signal, and the first and second current commands are generated.
PW for the third current command obtained by combining the current commands
To compensate for the current deviation of the input current of the M converter,
A PWM converter that generates an input voltage of a PWM converter that is PWM-controlled in accordance with the current deviation and controls the input current input to the PWM converter via the input reactor from the AC power supply in accordance with the input voltage. An input current control method, wherein a phase of the first current command is compensated for compensating a phase difference between a component corresponding to the first current command and the AC voltage among current components constituting the input current. The phase of the second current command is shifted so that the current component corresponding to the AC voltage input as a disturbance to the current control loop included in the input current control method becomes zero.

[Action]

It advances the phase of the first sine-wave signal so as to compensate for the phase difference between the alternating voltage, a first current command for the leading phase (active current command) ▲ I ^A _r ▼ the original first current command I by using instead of _r, that the advances corresponding to the current command ▲ I ^a _r ▼ phase, to the input current ▲ I ^a _C1 ▼ original first current command I _r and phase the phase of the PWM converter Can be. Thus the input current ▲ I ^A _C1 ▼ The phase of the power running when sometimes the AC voltage V _m in phase, will be power factor 1 control in opposite phase at the time of regeneration.

Also, advances the phase of the second sinusoidal signal, by using in place of the proceeds second current command phase (power compensation current command) ▲ I ^A _CEMF ▼ the original second current command I _CEMF, Take input current ▲ I ^a _C2 ▼ corresponding to the second current command ▲ I ^a _CEMF phase ▼ can be made zero. As a result, the input current I _C of the PWM converter with respect to the AC voltage V _m
Is compensated, and the power factor 1 control is realized.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an input current control circuit for one phase for implementing an input current control method of a PWM converter according to the present invention.

The deviation (voltage deviation) ΔV between the DC voltage command V _COM and the detected value of the actual output voltage V _DC is input to the voltage amplifier 6 to generate an effective current amplitude command (first current amplitude command) ＩI ^* _r生成. Is done. Further, sine table (sine wave generator) 12 inputs the AC voltage V _m output by the AC power source, have the same frequency ω and an AC voltage V _m, and the angle ^{_{α 1 = tan -1 (ωL /}} g _I G
_A unit sine wave (first sine wave signal) sinM1 whose phase is advanced by _PWM ) is generated. Active current amplitude command ▲ I ^* _r ▼ is multiplied by a unit sinusoid SinM1, leading phase active current command (the first current command advanced phase) ▲ I ^A _r ▼ is generated.
Sine table (sine wave generator) 13 inputs the AC voltage V _m, has the same frequency ω and the AC voltage, and the angle α
₂ = tan ^-1 (ωT) unit sine wave advanced in phase (second
Sine wave signal) sinM2 is generated. Unit sine wave sinM2
Is set power compensation amplitude command (second current amplitude command) ▲ I ^* _CEMF ▼ and are multiplied (second current command leading phase) phase lead of the power supply compensation current command ▲ I ^A _CEMF ▼ generation Is done. Active current command ▲ I ^A _r ▼ from the power supply compensation current command ▲
The current command I _{ref is} obtained by subtracting I ^A _CEMF ▼ by vector.
Is generated. Subtractor 9 the input current I _C of the PWM converter to vector subtracted from the current command I _ref, to produce a current deviation [Delta] I. The current amplifier 7 receives the current deviation ΔI and generates a voltage command _Vref . The PWM control circuit 8 oscillates a PWM carrier and compares the carrier with the voltage command _Vref to obtain a PW signal.
Generates the M signal, the main switching circuit 1 of the PWM converter
Output to Main switching circuit 1, the connection between the input and output terminals of the PWM converter is turned on and off, to generate a converter input voltage V _C. As a result, the reactor voltage V _L
Converter input voltage I _C is generated corresponding to. Converter input current I _C is fed back to the subtractor 9.

 Next, the operation of this embodiment will be described.

^{_{First, α 1 = tan -1 (ωL}} / g I G PWM) (20) α 2 = tan -1 ωT (21) Set.

When determining the converter input current I _C from the block diagram of Figure 1 is as follows.

Here, substituting the equation (8) into equation (23), s = j [omega] Distant, and, when TLω ² «g _I G _PWM, The first term and the second term of the equation (24) are respectively expressed as ＩI ^A _C1 ， and そ_れぞ れ
When I ^A _C2 ▼ to, ▲ I ^A _C2 ▼ is expressed by the following equation.

It advances the phase of the active current command ▲ I ^A _r ▼ the corresponding converter input current ▲ I ^A _C1 ▼ will I _r and phase (active current command of the AC voltage V _m in phase) actual active current command.

Further, ▲ I ^A _C2 ▼ is expressed by the following equation.

▲ I ^A _C2 ▼ molecule is modified from equation (21) as follows.

V _m (1 + jωT) − ▲ I ^A _CEMF ▼ g _I G _PWM = {V _m (1 + ω ² T ² ) ^1/2 −I _CEMF g _I G _PWM )} e ^jα2 (26a) Normally at ω ² T ² ≪1 From equation (22) Therefore, I _C becomes I _r in phase, the converter input current I _C is becomes an AC voltage V _m in phase to the power running, since the opposite phase at the time of regeneration, PWM converter of this embodiment is power factor 1
Take control.

〔The invention's effect〕

As described above, the present invention shifts the phases of the first and second current commands by a predetermined amount with respect to the phase of the AC voltage, thereby reducing the inductance of the input reactor,
In addition, the influence of the current follow-up delay caused by the first-order time constant of the current amplifier is completely removed, and power factor 1 control can be achieved. In addition, when the PWM converter is used as a power factor adjuster, it should be adjusted. Even when the power factor is smaller than 1, there is an effect that the converter input current follows the AC voltage at a predetermined phase angle and the power factor can be controlled to a desired value.

[Brief description of the drawings]

FIG. 1 is a block diagram of an input current control circuit for one phase for implementing an input current control method of a PWM converter according to the present invention, FIG. 2 is a block diagram of a PWM converter, and FIG. FIG. 4 is a block diagram of a conventional example of an input current control circuit for one phase of a three-phase main switching circuit, FIG. 4 is a vector diagram of input current control, and FIG. 4
5 (b) is a vector diagram at the time of the inverse conversion operation, FIG. 5 is a vector diagram illustrating the phase relationship between the converter input current and the AC voltage, FIG. 5 (a) is during power running, and FIG. 5 (b) is It is a vector diagram at the time of regeneration. 1 ... main switching circuit, 2 ... AC power supply, 3 ... input reactor, 4 ... smoothing capacitor, 5 ... power conversion circuit, 6 ... voltage amplifier, 7 ... current amplifier, 8 ... PWM control circuit , 9 ... Subtractor, 10,12,13 ... Sine table.

Claims (1)

(57) [Claims] A first current amplitude command corresponding to a voltage deviation of a DC voltage output from a PWM converter with respect to a set voltage is multiplied by a first sine wave signal having the same frequency as an AC voltage of an AC power supply. A second current command is generated, and a second current command is set to compensate for the AC voltage acting as a disturbance.
And a second sine wave signal having the same frequency as the AC voltage to generate a second current command, and a third current command obtained by combining the first and second current commands. In order to compensate for the current deviation of the input current of the PWM converter with respect to the current command, an input voltage of the PWM converter that is PWM-controlled in accordance with the current deviation is generated, and an input voltage is input from the AC power supply in accordance with the input voltage. In an input current control method for a PWM converter that controls the input current input to a PWM converter via a reactor, among the current components constituting the input current, a component corresponding to the first current command, the AC voltage, The phase of the first current command is shifted so as to compensate for the phase difference, and the current component corresponding to the AC voltage input as a disturbance to the current control loop included in the input current control method is set to 0. You The input current control method for a PWM converter as described above, wherein the phase of the second current command is shifted.