JP2924601B2 - Power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single-phase or multi-phase power converter for converting a single-phase or multi-phase AC voltage into a DC voltage.

[0002]

2. Description of the Related Art FIG. 1 shows a power converter for obtaining a DC voltage from a three-phase AC power supply via a reactor. This device is
It has a function to make the waveform of the current flowing through the reactor sinusoidal, a function to make the device input power factor close to 1, and a function to control the DC voltage to a desired value. The main circuit 33 of this device is configured as follows. The three-phase AC power source 1 is connected to three-phase AC power lines 6u, 6v, and 6w in series.
It is connected to the three-phase bridge circuit 3 via the second and third reactors 2u, 2v, 2w. The three-phase bridge circuit 3 includes first, second, and third reactors 2u, 2v, 2w
And the first to sixth switching elements Q1 to Q6 connected between the output side terminal of the first switching element and the pair of DC output terminals 4 and 5, and the anti-parallel connection to the first to sixth switching elements Q1 to Q6. And first to sixth diodes D1 to D6. The first and second switching elements are connected in series, and the connection point is connected to the output terminal of the first reactor 2u. Similarly, the third and fourth switching elements Q3 and Q4 are connected in series, and the connection point is connected to the output terminal of the second reactor 2v. The fifth and sixth switching elements Q5 and Q6 are connected in series,
The output terminal of the third reactor 2w is connected to the connection point. A smoothing capacitor 7 is connected between the pair of DC output terminals 4 and 5, and AC power supply lines 6u, 6v,
High frequency smoothing capacitors C1, C2 and C3 are connected to 6w.

In the main circuit 33 as described above, as a control means for controlling the waveforms of the currents flowing through the reactors 2u, 2v, 2w in a sine wave shape, making the device input power factor close to 1, and controlling the DC voltage to a desired value. Can be divided into a DC voltage control unit and a current control unit. First, the voltage control unit will be described. The DC voltage control unit controls the reactor 2u to set the voltage between the DC output terminals 4 and 5 to a desired value.
A signal indicating the value of the current to be passed through 2v, 2w is generated.
In order to control the DC voltage Ed, the DC output terminal 4,
5, a DC voltage detector 9 for detecting the DC voltage Ed is provided. The DC voltage command value generator 18 generates a DC voltage command Edr indicating a desired output voltage of the DC output terminals 4 and 5. Output lines of the DC voltage detector 9 and the command value generator 18 are connected to input lines of a voltage controller (AVR) 20. The voltage controller 20 generates a voltage control current command value Id such that an error between the DC voltage Ed input from the input line and the DC voltage command value Edr becomes zero. The voltage controller 20 operating in this manner can be constituted by, for example, a subtractor for obtaining an error signal and a proportional-integral compensator. An output line of the voltage control current command value Id of the voltage controller 20 is connected to multipliers 21 and 22. A voltage detector 34 for detecting at least two of the voltages Vsu, Vsv, and Vsw of the three-phase AC power supply lines 6u, 6v, and 6w is provided to the other input lines of the multipliers 21 and 22.
Output lines are connected. These two voltages Vs
u and Vsw serve as reference sine waves for generating current command values i _ru and i _rw indicating desired values of the u-phase and w-phase reactor currents. The multipliers 21 and 22 multiply the u-phase and w-phase AC voltages Vsu and Vsw by the current control current command value Id, and the result of the multiplication is a u-phase and w-phase reactor current (AC current) _iu. , I _w, the current command value i indicating the desired value
_ru and i _rw .

Next, the current control unit will be described. The current control unit includes a first switching element Q1 and a second switching element Q2 such that the currents i _u and i _w of the reactors 2u and 2w match the current command values i _ru and i _rw generated by the voltage control unit. The connection point voltage Vcu between the reactor 2u, the connection point voltage Vcv between the third switching element Q3, the fourth switching element Q4, and the reactor 2v, and the fifth switching element Q5, the sixth switching element Q6, and the reactor 2w. The power conversion device AC side terminal voltage command values Vru, Vrv, Vrw indicating the desired value of the connection point voltage Vcw are generated. In order to perform such an operation, the reactors 2u, 2v, 2w
Current i _u, i _v, at least two reactors 2u among i _w, a current detector 8u for detecting a current of 2w, 8w are provided for. Output lines of the current detectors 8 u and 8 w and the multipliers 21 and 22 are connected to current controllers (ACR) 14 and 15, respectively. Then, the current controllers 14 and 15 determine the current command values i _ru and i _rw and the detected current i
_{The u-} phase and w-phase power converter AC side terminal voltage command values Vru and Vrw are output so as to make the error between _u and i _w zero. The controllers 14 and 15 operating in this manner can be constituted by, for example, a subtractor for obtaining an error output of two inputs and a proportional-integral compensator. V-phase power converter AC side terminal voltage command value Vrv
Are connected to the input lines of the inverting adder 16 by the current controllers 14, 1
By connecting the 5 output lines, the AC phase terminal voltage command values Vru and Vrw of the u-phase and w-phase power converters are added and the sign is inverted to generate. The control circuit 12 is a DSP
(Digital signal processing device).
Are functionally shown for ease of understanding. Further, the current detectors 8u and 8w and the voltage detector 9 are shown as including an A / D converter. Also, the control circuit 1
2 and clocks necessary for operating the PWM pulse generator 17 are also omitted.

[0005] Finally, the PWM pulse generating means will be described. The PWM pulse generator 17 as a PWM pulse generating means is provided with first to sixth switching elements such that the AC terminal voltages Vcu, Vcv, Vcw become the AC side terminal voltage command values Vru, Vrv, Vrw generated by the current controller. PWM (Pulse Width Modulation) pulse signals Su, Sv, Sw for on / off control of Q1 to Q6 are generated in principle as shown in FIGS. 2B, 2C and 2D. Such a pulse is shown in FIG.
As shown in (A), a high-frequency triangular carrier wave Vt of several kHz to several tens kHz and respective AC-side terminal voltage command values Vru,
It is generated by comparing Vrv and Vrw with a comparator.
The drive circuit 13 that receives these pulses is shown in FIG.
(C) The phase inversion signals of (D) are produced and these 6
Control signals from the first to sixth switching elements Q1 to Q1.
Converts to the signal level required for control of control terminal 6 The first switching element Q1 is driven based on the pulse signal Su, and the second switching element Q2 is driven based on the pulse signal Su.
Driven based on the inverted sign of u. Other elements Q3 to Q
The same applies to 6. In this way, the first to sixth
When the switching elements Q1 to Q6 are driven, the AC terminal voltage Vcu,
Vcv, Vcw and the AC terminal voltage command values Vru, Vrv, Vrw match.

[0006]

By the way, in order to make the input power factor of the device close to 1, a conventional three-phase or single-phase power converter detects a power supply voltage. Therefore, the power conversion device has become expensive and large.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a power converter which can reduce the cost and reduce the size by omitting a power supply voltage detector.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a reactor having an inductance value L connected in series to an AC power supply line for supplying a sine wave AC power supply voltage. A bridge circuit including a plurality of switching elements connected between an output terminal and a pair of DC output terminals, a plurality of diodes connected in anti-parallel to the plurality of switching elements, and a connection between the pair of DC output terminals; A smoothing capacitor, a current detector for detecting an AC current (i) of the AC power supply line,
A DC voltage detector for detecting an output voltage (Ed) of the DC output terminal, a DC voltage command value generator for generating a DC voltage command (Edr) indicating a desired output voltage of the DC output terminal, and the current detector And the DC voltage detector and the DC voltage command value generator, and the DC voltage command value (E
dr) and the DC voltage (Ed) generate a voltage control current command value (Id) such that the error becomes zero, and the estimated value Vs ^* of the AC power supply voltage (Vs) is calculated.

[0009]

(Equation 4)

(Where Ln is a nominal value of the inductance value L, Kan is a nominal value of a half of the output voltage Ed, and K1 and K2 are gains), and the AC voltage is estimated. The value (Vs ^* ) is multiplied by the DC command value for voltage control (Id) to obtain a current command value (ir) indicating a desired value of the AC current (i).
r) and an AC-side terminal voltage command value (Vr) indicating an AC-side terminal voltage (Vc) at an output terminal side of the reactor required to reduce an error between the AC current (i) to zero. A control unit configured to be used for calculating an estimated value (Vs ^* ) of the AC power supply voltage, connected between the control unit and control terminals of the plurality of switching elements, and configured to output the AC-side terminal voltage command value; (Pr) for controlling on / off of the plurality of switching elements in response to (Vr)
The present invention relates to a single-phase or multi-phase power converter including a PWM pulse generating means for generating a WM (pulse width modulation) pulse. As described in claim 2, a reference sine wave is generated, and this phase is changed to an estimated AC power supply voltage Vs.
^The correction may be made based on ^* .

[0011]

According to the invention of each claim of the present application, it is possible to control the input power factor to approach 1 without using the power supply voltage detector. Thereby, cost reduction and size reduction of the power converter can be achieved.

[0012]

First Embodiment Next, a three-phase power converter according to a first embodiment of the present invention will be described with reference to FIGS. However, in FIG. 3, portions common to FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. As is clear from the comparison between FIG. 1 and FIG. 3, the power converter of FIG.
4 is omitted, and a power supply voltage estimator 24 is provided instead. In FIG. 3 and FIG. 6, which will be described later, the control circuit 12 is configured by a DSP, but is shown by an equivalent circuit (functional block) as in FIG. The power supply voltage estimator 24 includes u-phase and w-phase power supply voltage estimators 24u and 24w, and the estimators 24u and 24w are connected to the output lines 10u and 10w of the u-phase and w-phase current detectors 8u and 8w, respectively. And u-phase and w-phase power supply voltage estimated values Vsu based on currents i _u , i _w flowing through reactors 2 u, 2 _w and AC terminal voltage command values Vru, Vrw. ^* And Vsw ^* are sent to multipliers 21 and 22.

U-phase and w-phase power supply voltage estimators 24u, 2
Since 4w is substantially the same, suffixes u, v, and w for distinguishing three phases are omitted, and three-phase alternating currents i _u , _iv ,
i instead of i _{w, and} the three-phase AC terminal voltage command value Vru,
Using Vr instead of Vrv and Vrw, and Vs ^* instead of power supply voltage estimated values Vsu ^* and Vsw ^* , use power supply voltage estimated value Vs ^*.
The above equation (1) can be expressed by the following equation. Accordingly, the voltage estimators 24u and 24w of the u-phase and the w-phase in FIG.
Outputs estimated values Vsu ^* and Vsw ^* according to the calculation of equation (1). These estimated values are input to multipliers 21 and 22 as reference sine waves. This estimator can be configured by deriving a state observer. Hereinafter, the process of deriving the state observer will be described in detail.

In order to guide the state observer, it is necessary to create a state equation of a controlled object. For this purpose, FIG. 4 shows an equivalent block diagram functionally showing one phase of the AC side (current control unit) of the three-phase power converter of FIG. In the figure,
Since each phase can be represented by the same block diagram, each variable has the same value, so the variable symbols are suffixes u, v, w
It is displayed excluding. For example, Vru, Vrv, and Vrw in FIG. 3 are set to Vr in FIG. The transfer function for one phase of the three-phase bridge 3 is represented by the proportional gain Ka = Ed / 2 when considering frequencies other than the frequency near the carrier of the PWM pulse generator, so that the block 40 is obtained. The transfer function of the reactor 2 can be expressed by 1 / L · S when the inductance value is L, so that the block 41 is obtained. The current controller 14 or 15 is represented by a subtractor 42 and a compensator 43. The output line 10 of the current detector 8 coincides with the output of the block 41. The AC power supply voltage Vs is represented by placing a subtraction element 44 between the block 40 and the block 41, subtracting the AC power supply voltage Vs from the AC terminal voltage Vc output from the block 40, and inputting the result to the block 41. The blocks 40, 44, and 41 are called a control target 45.

Assuming that the power supply voltage does not change in a short time, the state equation of the control object in FIG. 4 is as follows: di / dt = (1 / L) (KaVr-Vs) (3) dVs / dt = 0 (4) Become. From the state equations (3) and (4), when the estimated values of i and Vs are i ^* and Vs ^* , the state observer calculates di ^* / dt = (1 / Ln) (KanVr-Vs ^* ) + K1 ( ii ^* ) (5) dVs ^* / dt = K2 (ii ^* ) (6) where Ln and Kan are nominal values of L and Ka, and K1 and K2 are gains. By integrating both sides of Expressions (5) and (6), Expressions (1) and (2) described above are obtained, whereby the estimated value Vs ^* of the power supply voltage is obtained. K1, K2 characteristic equation of the state observer of is arbitrary formula (5) (6) S ² + K1 S
Since + K2 Kan / Ln = 0, the convergence of the estimated value is determined by setting K1 and K2.

FIG. 5 shows the estimated value V based on the equations (1) and (2).
A functional block diagram (equivalent circuit) for obtaining s ^* is shown. The arithmetic circuit 51 of the equation (1) can be represented by three coefficient units (gain amplifiers) 52, 53, and 54, one adder 55, one subtractor 56, and one integrator 57. The arithmetic circuit 58 of the equation (2) can be represented by one coefficient unit (gain amplifier) 59 and one integrator 60.

In the case where the control circuit 12 is configured by software using a microprocessor, when a time at a certain time interval is Ts (sampling period), a sample value of the current i at the time of nTs is i (n), When the value of the nTs time of the AC terminal voltage command Vr is Vr (n) and the equations (3) and (4) are discretized, the following equation is obtained. i (n + 1) = i (n) + (1 / L) ｛KaVr (n) −Vs (n)｝ (7) Vs (n + 1) = Vs (n) (8) Thus, the state observer obtains i ( n), when the estimated values of Vs (n) are i ^* (n) and Vs ^* (n), i ^* (n + 1) = i ^* (n) + (1 / Ln) ｛KanVr (n) −Vs ( n)｝ + KD1 ｛i (n) -i ^* (n)｝ (9) Vs ^※ (n + 1) = Vs ^※ (n) + KD2 ｛i (n) -i ^※ (n)｝ (10) (where Ln , Kan are the nominal values of L and Ka, KD1, KD2:
Gain), and the estimated value Vs ^* of the power supply voltage is obtained. KD1, KD2 is arbitrary equation (9) characteristic equation of the state observer (10) is z ² + (KD1-2 + KD2KanTs
/ L) z-KD1 + 1 = 0, so that the convergence of the estimated value is determined by setting KD1 and KD2.

[0018]

Second Embodiment Next, a power converter according to a second embodiment will be described with reference to FIG. However, in FIG. 6, portions common to FIGS. 1 and 3 are denoted by the same reference numerals, and description thereof is omitted. The power converter of FIG. 6 has a configuration in which the w-phase power supply voltage estimator 24w in the power converter of FIG. 3 is omitted, and a reference sine wave generator 32 and a phase synchronization adjuster 25 are newly added. Other configurations in FIG. 6 are the same as those in FIG.
Note that the phase synchronization adjuster 25 and the reference sine wave generator 32
It has a function as an LL circuit.

In FIG. 6, a reference sine wave generator 32 is provided instead of directly using the estimated value of the power supply voltage estimator 24 as a reference sine wave, and its output is input to multipliers 21 and 22 as a reference sine wave. I have. Then, the estimated power supply voltage Vsu of the estimator 24
A phase synchronization adjuster 25 is provided so that the phase difference between the reference sine wave and the reference sine wave is zero, and the output phase of the reference sine wave generator 32 is corrected. Hereinafter, the phase synchronization adjuster 25 will be described in detail.

The estimated power supply voltage Vsu ^* and the reference sine wave sin ωt
Is used in order to make the phase difference α of the Eq. Vsu ^* = Vmsin (ωt +
α), Vsu ^※ by the formula of Fourier series expansion
Is expanded to the frequency components a1 and b1 of ωt as follows.

[0021]

(Equation 5)

The relationship between the phase difference α and a 1, b 1 is given by equation (11)
Substituting Vsu ^* = Vmsin (ωt + α) into (12) and calculating results in the following equation. a1 = Vmsin α (13) b1 = Vmcos α (14) Here, if the phase difference α is zero, a1 = 0 and b1 = Vm. If the phase difference α is not zero, a110. Therefore, the following equation (15) is calculated in block 28 using cos (ωt + φ), the phase of which is advanced by π / 2 from the reference sine wave sin (ωt + φ).

[0023]

(Equation 6)

By adjusting φ so that a = 0, Vsu
^* And the reference sine wave sin (ωt + φ) are synchronized with a phase difference α = 0. In order to adjust φ so that a = 0, for example, proportional + integral compensation is adopted as shown in a block 29.

The reference sine wave generator 32 includes a data table 23 for a sine wave sin θ, a cosine wave cos θ, and a sine wave sin (θ−120 °), a counter 30 for specifying an address of the data table, and a counter output amount. It comprises an adder 31 for adding the phase correction amount φ generated by the phase adjusting means 25. The address of the data table corresponds to θ, and the counter output outputs a value corresponding to ωt. The data table is created using a ROM, and there is a digital-to-analog converter DAC that converts the output of the ROM into an analog quantity. The outputs of the DAC for converting the data of sin θ and sin (θ−120 °) are connected to multipliers 21 and 22, respectively, and used as reference sine waves. Also cos
The output of the DAC for converting the data of θ is connected to a block 28 for calculating equation (15).

The equation for executing the operation of equation (15) of the second embodiment by software is shown in the following equation (16), similarly to the first embodiment.

[0027]

(Equation 7)

Also in the second embodiment, a detector for the AC power supply voltage is not required, so that the size can be reduced as in the first embodiment.
Cost reduction becomes possible.

[0029]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) The v-phase AC terminal voltage command Vrv is
Is used to calculate from Vru and Vrw, but it can be generated by the current control unit having the same configuration as the u-phase or the w-phase. (2) The present invention can be applied to a single-phase power converter. (3) Instead of configuring the control circuit 12 with a DSP, the control circuit 12 can be configured with an individual digital circuit or analog circuit as shown in FIG. 3 or FIG.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a conventional three-phase power converter.

FIG. 2 is a waveform diagram showing a state of each part in the PWM generator of FIG.

FIG. 3 is a circuit diagram illustrating a three-phase power converter according to a first embodiment.

4 is a diagram showing a functional equivalent block for one phase on the AC side of the three-phase power converter in FIG. 3;

FIG. 5 is a block diagram illustrating a power supply voltage estimator of FIG. 3;

FIG. 6 is a circuit diagram illustrating a three-phase power converter according to a second embodiment.

[Explanation of symbols]

 3 Bridge circuit 8u, 8w Current detector 9 Voltage detector 24 Power supply voltage estimator

Claims (2)

(57) [Claims] 1. An inductance value L connected in series to an AC power supply line for supplying a sinusoidal AC power supply voltage.
A bridge circuit comprising a plurality of switching elements connected between an output terminal of the reactor and a pair of DC output terminals; a plurality of diodes connected in anti-parallel to the plurality of switching elements; and A smoothing capacitor connected between the DC output terminals, a current detector for detecting an AC current (i) of the AC power supply line, and a DC voltage detector for detecting an output voltage (Ed) of the DC output terminal. A DC voltage command value generator for generating a DC voltage command (Edr) indicating a desired output voltage of the DC output terminal; connected to the current detector, the DC voltage detector, and the DC voltage command value generator; , The DC voltage command value (Edr)
A current command value (Id) for voltage control is generated such that the error between the voltage and the DC voltage (Ed) becomes zero, and the estimated value Vs ^* of the AC power supply voltage (Vs) is calculated as follows. (Where Ln is the nominal value of the inductance value L, Kan is the nominal value of half the output voltage Ed, and K
1 and K2 indicate gain. ), And the AC voltage estimated value (Vs ^* ) and the voltage control current command value (I
d) to obtain a current command value (ir) indicating a desired value of the AC current (i), and to obtain an error between the current command value (ir) and the AC current (i) to zero. AC terminal voltage (Vc) at the output terminal side of the reactor
Control means configured to obtain an AC-side terminal voltage command value (Vr) indicating the following, and to use the calculated value for calculating the estimated value (Vs ^* ) of the AC power supply voltage; and controlling the control means and the plurality of switching elements. Terminal voltage command value (Vr)
A PWM pulse generating means for generating a PWM (pulse width modulation) pulse for controlling on / off of the plurality of switching elements in response to a single-phase or multi-phase power conversion. apparatus. 2. An inductance value L connected in series to an AC power supply line for supplying a sine wave AC power supply voltage.
A bridge circuit comprising a plurality of switching elements connected between an output terminal of the reactor and a pair of DC output terminals; a plurality of diodes connected in anti-parallel to the plurality of switching elements; and A smoothing capacitor connected between the DC output terminals, a current detector for detecting an AC current (i) of the AC power supply line, and a DC voltage detector for detecting an output voltage (Ed) of the DC output terminal. A DC voltage command value generator for generating a DC voltage command (Edr) indicating a desired output voltage of the DC output terminal; connected to the current detector, the DC voltage detector, and the DC voltage command value generator; , The DC voltage command value (Edr)
A voltage control current command value (Id) is generated such that the error between the reference voltage and the DC voltage (Ed) becomes zero, and the reference sine is synchronized with the AC power supply voltage (Vs) at a predetermined angular frequency (ωt). A current command value (ir) indicating a desired value of the AC current (i) is obtained by multiplying the reference sine wave by the DC command value for voltage control (Id). An AC-side terminal voltage command value (Vr) indicating an AC-side terminal voltage (Vc) at an output terminal of the reactor required to make an error between a command value (ir) and the AC current (i) zero is obtained. Based on the AC current (i) and the AC terminal voltage command value (Vr), the estimated value Vs ^* of the AC power supply voltage (Vs) is expressed by (Where Ln is the nominal value of the inductance value L, Kan is the nominal value of half the output voltage Ed, and K
1 and K2 indicate gain. ), And calculates an amount a indicating a phase difference between the AC power supply voltage estimated value Vs ^* and the reference sine wave (sin ωt). And control means configured to control the phase of the reference sine wave so that the amount a indicating the phase difference becomes zero, between the control means and the control terminals of the plurality of switching elements. Connected, the AC terminal voltage command value (Vr)
A PWM pulse generating means for generating a PWM (pulse width modulation) pulse for controlling on / off of the plurality of switching elements in response to a single-phase or multi-phase power conversion. apparatus.