JP2672907B2 - DC voltage controller for inverter input circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC voltage control device for an inverter input circuit for controlling the voltage of a DC side circuit of an inverter device.

[0002]

2. Description of the Related Art Recently, variable speed control of AC motors such as induction motors, synchronous motors, and linear synchronous motors using a voltage-type PWM inverter has been frequently performed. Application to large-capacity AC motors and magnetic levitation high-speed railways is also under consideration, and high performance and high reliability are being demanded. In order to make the variable speed control by the inverter highly reliable, it is an essential prerequisite that the DC voltage input to the inverter is controlled with high accuracy and high stability.

FIG. 4 is a block diagram showing a method of controlling the input DC voltage of the inverter with high performance, which was announced at the National Conference of Industrial Application Division of the Institute of Electrical Engineers of Japan (lecture number 2) in 1990. In FIG. 4, 1 is a transformer for a converter, 31
Is a controllable converter that converts AC power to DC power,
In this example, a thyristor converter is assumed. 3
Is an inverter that reversely converts DC power into AC power, which is a voltage-type PWM inverter in this example. Reference numeral 4 is an AC electric motor (including a linear synchronous motor) connected to the inverter 3, 5 is a DC chopper device installed in a DC circuit that links the converter 31 and the inverter 3, and 6 is a resistor connected in series with the chopper device 5. Vessel, 7 is a DC circuit P
-N is a DC smoothing capacitor that operates to keep the voltage between N constant, 32 is a DC reactor that mainly suppresses the current ripple caused by the voltage ripple generated by the controllable converter 31, and 10 is the voltage between DC circuits P-N. Detecting voltage detector, 11 is a current detector for detecting inverter input direct current, 33 is a current detector for detecting converter output direct current, and detection signals from the voltage detector 10, current detectors 11 and 33, respectively. Is a feedback signal to the DC voltage controller.

Further, 34 and 35 are current detectors 33 and 11.
Is a filter coefficient unit for smoothing the detected current value from each of them and converting the magnitude into a value commensurate with the DC voltage control device side, and finally the output of the filter coefficient unit 34 becomes the output current detected value of the converter 31. , Filter coefficient unit 3
The output of 5 becomes the input current detection value of the inverter 3. Further, 36 is a filter coefficient unit that smoothes the voltage detection signal from the DC voltage detector 10 and converts the magnitude into a voltage value suitable for the DC voltage control device side. Finally, the output of the filter coefficient unit 36 is It becomes the DC voltage detection value. Reference numeral 37 is a subtractor that takes the difference between the inverter input current detection value that is the output of the filter coefficient unit 35 and the converter output current detection value that is the output of the filter coefficient unit 34, and 38 is the current difference value that is the output of the subtractor 37. Is a proportional amplifier that amplifies with a designated amplification factor, and 39 is an integrator that integrates the current difference value with a designated time constant.

On the other hand, 40 is a subtracter for taking the difference between the DC voltage command value output from the DC voltage command means 50 and the DC voltage detection value which is the output of the filter coefficient unit 36, and 41 is the output of the subtractor 40. A proportional amplifier that amplifies the voltage difference value with a designated amplification factor, 42 is an integrator that integrates the voltage difference value with a designated time constant, 43 is a multiplier that takes the product of the voltage difference value and the DC voltage detection value, Reference numeral 44 denotes a proportional inverting amplifier that amplifies the multiplication output value of the multiplier 43 at a designated amplification factor, and further inverts the polarity of the amplification result and outputs the amplified result. 45 designates the voltage difference value from the subtractor 40 as a designated time constant. It is an inverting integrator that integrates with and further inverts and outputs the polarity of the integration result.

Reference numeral 46 is an adder for adding the outputs of the proportional amplifiers 38, 41 and the integrators 39, 42, and outputs the addition result to the converter gate signal controller 48 as the output voltage command value of the controllable converter 31. The converter gate signal controller 48 outputs a gate signal to the controllable converter 31 according to the output voltage command value. On the other hand, 47 is an adder for adding the output of the proportional inverting amplifier 44 and the output of the inverting integrator 45, and outputs the addition result to the chopper gate signal controller 49 as the conduction ratio command value of the chopper device 5, and the chopper gate. The signal controller 49 outputs a gate signal to the chopper device 5 in accordance with the flow rate command value. Also,
The element parts are put together, 34, 35 and 37 are current difference output means, 36 and 40 are voltage difference output means, 43, 44 and 4
5, 47 are chopper flow rate control means, 38, 39, 4
1, 42 are called converter voltage control means.

Next, the operation will be described. First, the control principle will be described. FIG. 5 shows a model of the inverter DC side circuit. Considering the converter as a variable voltage source and the chopper as a variable resistance R _V, and letting the resistance value when the conduction ratio is 1 (that is, the resistance value of the resistor 6 in FIG. 4) R _O , the conduction ratio δ and the variable resistance The relationship with R _V is δ = R _O / R _V (1) On the other hand, the inverter controls the current connected to the load connected to the AC side of the inverter, so that the circuit on the DC side of the inverter is regarded as a constant current source. Therefore, in the DC voltage control of the inverter DC side circuit, the converter output voltage E _C and the chopper conduction ratio δ are adjusted to control the DC voltage V _C regardless of the value of the inverter input current I _{2 which} cannot be controlled by the DC side circuit. The target is to control so that it becomes equal to the given DC voltage command value V _C ^* . Therefore, assuming that the converter output current is I ₁ , the state equation of the circuit diagram shown in FIG. 5 is expressed by the following equation.

[0008]

(Equation 1)

The system represented by the equations (2) and (3) is
The state variable is (I ₁ , V _C ), the operation input is (E _C , δ), and there is a product term of the state variable V _C and the operation input δ. Therefore, the system of equations (2) and (3) can be considered as a bilinear multivariable system. Considering the control targets of this system as V _C = V _C ^* and I ₁ = I ₂ , the variable conversion of the following equation is performed.

[0010]

(Equation 2)

By converting the equation (4), the equations (2) and (3) are as follows.

[0012]

(Equation 3)

Consider the following control law for the system of equation (7). u _i = k _i (x ^T (B _i + B _i ^T ) x + 2C _i ^T x) + F _i ^T (8) where K _i <0, F _i is an appropriate column vector, and the subscript “T” is The transposed matrix is shown.

Now, it will be investigated that stable control is possible by the control law of the equation (8). Therefore, the Lyapunov function V
Consider the following equation as (x). V (x) = x ^T x (9) When the time derivative of the equation (9) is taken along the solution trajectory in which the control law of the equation (8) is substituted into the equation (7), the following is obtained.

[0015]

(Equation 4)

According to Lyapunov's stability theorem, x ≠ 0
Then, if the time derivative of V (x) becomes a negative value, the global stability is guaranteed. Looking at the equation (10), the first term on the right side can always be a negative value by an appropriate F if the linear system (A, C) is stable (conclusion from the linear system theory).
The third term on the right side always takes a negative value as long as k _i <0. The second term on the right-hand side can be a positive value or a negative value depending on the value of x, but considering the case of equation (7), B ₁ =
Although it is 0, when i = 1, it becomes equal to zero regardless of the value of F _i , and when i = 2, if F ₂ = 0, then
This also becomes zero, and after all, the second term on the right side is F ₂ =
When it is set to 0, it becomes equal to 0 and can be erased from the equation (10). After that, by deciding F ₁ appropriately, the first on the right side
If the term has a negative value, the whole equation (10) (that is, V
Stability is guaranteed because the (time derivative of (x)) becomes a negative value. More specifically, the control law of the equation (8) is written down as follows.

[0017]

(Equation 5)

When the conditions of f ₁ , f ₂ and k ₂ are obtained so that the time derivative of V (x) in the equation (10) is negative, the result is as follows. f ₁ <R, f ₂ <1, k ₂ <0 (13) As long as the conditions of equation (13) are satisfied and the control is performed by equations (11) and (12), the system of equation (7) is always stable. Controlled by. When the above result is converted into E _C and δ using the equation (4), the following equation is obtained.

[0019]

(Equation 6)

When G ₁ > 0, G ₂ > 0, and G ₃ > 0 are included in the condition of the equation (13), the control gain G
_{If 1} , G ₂ and G ₃ are positive, stable control can be ensured. In addition to the above-mentioned principle, an integrator having an appropriate time constant is added in order to compensate for the offset generated by ΔE _{C in} equation (14) and fluctuations in disturbance and main circuit constants. If the integration time constant is not made too fast, stability is maintained even if an integrator is added. Expression (14), (15)
FIG. 4 shows an embodiment of a control device in which an integrator is added to the equation. The amplification factor of the proportional amplifier 38 corresponds to G ₁ in the equation (14), and the amplification factor of the proportional amplifier 41 corresponds to G ₂ in the equation (14). In multiplier 43, the inverting amplification factor of ^{_{V C · (V C * -V}} C) inverting amplifier 44 together is computed is (1
It corresponds to -G ₃ in the formula 5). Integrators 39 and 42 and an inverting integrator 45 are added for offset compensation.

From the above description, it is understood that the DC voltage can be stably controlled even if both the converter and the chopper are operated at the same time. Brake control is particularly important when a voltage-type PWM inverter is used for transportation such as a magnetic levitation railway. Even when the power supply voltage drops and the regenerative operation by the converter becomes impossible, as long as the converter and chopper are operating at all times, the chopper will automatically function without switching in sequence. The brake control is not hindered, and therefore a highly reliable one can be obtained. Further, if the converter and the chopper are operating at the same time, the voltage control itself will be fast and highly accurate.

[0022]

Since the conventional DC voltage control device for the inverter input circuit is constructed as described above, if the converter 31 is a thyristor converter, a high speed, high accuracy and high reliability is required. Obtained, but PWM
There is a problem in that it is not applicable to a converter that does not directly operate the voltage and current on the DC circuit side like a converter, but operates the voltage and current on the power supply system side.

The present invention has been made in order to solve the above problems, and can be applied to a PWM converter, and for an inverter input circuit capable of controlling an inverter input DC voltage with high speed and stability by emphasizing a chopper. An object is to provide a DC voltage control device.

[0024]

A DC voltage control device for an inverter input circuit according to the present invention has a PWM converter and a chopper each having means for DC voltage control.
Means for setting the amplification factors of the respective proportional amplification elements in the DC voltage control means in association with each other so as to satisfy the cooperative condition.

[0025]

The DC voltage control device for an inverter input circuit according to the present invention can control the DC voltage at the same time without interference between the PWM converter and the chopper by the setting of the amplification factor satisfying the above-mentioned cooperation, so that the control accuracy is high. improves. Further, even if one of them fails, the other one is immediately controlled, so that the reliability is improved.

[0026]

[Embodiment 1] Embodiment 1 of the present invention will be described below with reference to the drawings. 1, 1, 3 to 7, 1
0 and 11 are the same as those in the conventional example of FIG. 2 is different from the controllable converter 31 shown in FIG.
A PWM converter for converting AC power into DC power, 8 is a rectifier for initial charging of the DC smoothing capacitor 7, 9 is a transformer for the rectifier 8 for initial charging, and 12, 13 and 14 detect AC current on the power system side. The current detector 15 is a coefficient unit for converting the detection signal from the voltage detector 10 into a value suitable for the DC voltage control system, and the output of the coefficient unit 15 finally becomes the DC voltage detection value. 16 is a DC voltage command means, 1
Reference numeral 7 is a subtractor for taking the difference between the DC voltage command value from the DC voltage command means 16 and the DC voltage detection value from the coefficient unit 15, 18
Is a proportional amplifier for amplifying the voltage difference value from the subtractor 17 with a designated amplification factor, 19 is a coefficient unit for converting the magnitude of the detection signal from the current detector 11 into a value suitable for the DC voltage control system, 20 Is an adder that adds the output of the proportional amplifier 18 and the output of the coefficient multiplier 19.

Further, 27 is a current detector 12, 13, 14
The three-phase / two-phase coordinate converter for converting the detected AC three-phase current value from the three-phase to the two phases of the dq axis, 21 is the output of the adder 20 and the output of the three-phase / 2-phase coordinate converter 27. A subtractor for subtracting a certain d-axis current detection value, 22 is a subtractor for subtracting the q-axis current detection value which is the output of the 3-phase / 2-phase coordinate converter 27 from zero, 2
3 is an amplifier that amplifies the d-axis current difference value that is the output of the subtractor 21, 24 is an amplifier that amplifies the q-axis current difference value that is the output of the subtractor 22, 25 is a two-phase / amplifier from the outputs of the amplifiers 23 and 24 It is a two-phase / three-phase coordinate converter that performs three-phase conversion and converts into an AC three-phase voltage command. Reference numeral 26 is a PWM controller that converts a three-phase voltage command of the two-phase / 3-phase coordinate converter 25 into an actual gate pulse of the PWM converter 2, and the PWM pulse is used to control the PWM converter 2.

Further, 30 is a DC voltage command value which is the output of the DC voltage command means 16, the amplification factor of the proportional amplifier 18, the resistance value R _O of the resistor 6, and the rated voltage value V _d of the power supply system side.
Is given to calculate the amplification factor of the proportional amplifier 28, 28 is a proportional amplifier that multiplies the voltage difference value that is the output of the subtractor 17 and the amplification factor that is the output of the amplification factor calculator 30, and 29 is proportional Based on the output of the amplifier 28, the chopper 5
Is a chopper gate control device that outputs the gate pulse of the. In addition, the above-mentioned components 19, 20, 21, 22, 2
3, 24, 25, 27 by d of the PWM converter 2
A q-axis current control system is configured. Also, the component 1
5, 16, 17, and 18 form a DC voltage control system for the PWM converter 2.

Next, the operation will be described. FIG. 2 shows a model of the main circuit configuration shown in FIG. The operating principle will be described with reference to FIG. The PWM converter 2 includes the components 19, 20, 21, 22, 23, 24, 2 shown in FIG.
The dq axis current control system composed of Nos. 5 and 27 performs high-speed current control with a power factor 1 on the power supply side. That is,
Current in the same phase as the power system voltage (d-axis current) flows, 90 °
The phase-shifted reactive current (q-axis current) is zero. For the study of DC voltage control, the transient characteristics of the dq axis current control system can be ignored.

Therefore, in FIG. 2, the input to the system by the PWM converter 2 is regarded as the power supply side d-axis current I _d . Furthermore, assuming that the PWM converter 2 is performing constant power conversion, it is assumed that I _d V _d = I _C V _C holds. On the other hand, the chopper 5 is considered to have the function of a controllable resistor when combined with the resistor 6. In this case, the resistance R
Is considered to be R = R _O / δ as the chopper conduction ratio δ.
From the above, the equation of state for the DC voltage V _C is (1
6)

[0031]

(Equation 7)

Here, X = V _C −V _CO (V _CO is a DC voltage command value = the output of the DC voltage command means 16 in FIG. 1)
When approximated in the vicinity of V _CO , equation (16) becomes equation (17).

[0033]

(Equation 8)

The DC voltage control of the PWM converter and the chopper are both proportional controllers, and their proportional gains are K
₁ and K ₂ . At this time, the control side for I _d and δ is (1
Expressions 8) and (19) are obtained. I _d ^* = K ₁ X + (V _CO / V _d ) _IL (K ₁ <0) (18) δ = K ₂ X (K ₂ > 0) (19) For I _d ^* , (V _{CO IL} ) / V _d feedforward is added. As a result, the PWM converter normally operates preferentially. Further, this feedforward also improves the DC voltage control performance and has the effect of reducing the capacity of the DC smoothing capacitor. If it is difficult to directly detect I _L , there is also a method of calculating instantaneous power in the inverter current control system and performing feedforward based on this.

Now, (18), (19) and the equation (17)
Substituting it into the equation and rearranging it yields equation (20).

[0036]

(Equation 9)

K is set so that the value in () of the expression (22) becomes negative.
_It can be seen that if ₁ is selected, it is always stable, the transient characteristics are good, and even if the PWM converter 2 and the chopper 5 are simultaneously operated, the DC voltage can be controlled without interference. The embodiment shown in FIG. 1 is one implementation of the method described above. That is, in FIG. 1, the amplification factor calculator 30
Is the DC voltage command value V which is the output of the DC voltage command means 16.
The proportional gain K ₁ of the proportional amplifier 18, which is a DC voltage controller of the PWM converter 2, is input to _CO, and the rated value V _{d of the} power supply voltage and the resistance value R _O of the chopper resistor 6 are input ((21)). The proportional gain K ₂ for controlling the DC voltage of the chopper 5 is calculated by the formula shown in the formula. The coefficient value which is this output is multiplied by the voltage difference value which is the output of the calculator 17 by the proportional amplifier 28, and the DC voltage control by the chopper 5 is achieved.

As described above, according to the above embodiment, the PW
Even if the M converter 2 and the chopper 5 are simultaneously operated, the DC voltage control is carried out in a coordinated manner. Therefore, even if one of the PWM converter 2 and the chopper 5 becomes uncontrollable, the other one is switched in sequence. It works automatically without, so you get a reliable one.

Embodiment 2 FIG. Next, FIG. 3 shows another embodiment of the present invention. The same reference numerals as those in FIG. 1 are the same as those in FIG. As a new configuration, 52 is provided with a DC voltage command value V _CO from the DC voltage command means 16, a resistance value R _O of the resistor 6, a power system voltage rated value V _d and a DC voltage control convergence degree K _V. a coefficient calculator for calculating a DC voltage control proportional gain K ₂ DC of the PWM converter 2 voltage control proportional gain K ₁ and the chopper 5. Here, the DC voltage control convergence degree K _V is a parameter representing the speed of response of the DC voltage control, and is within () of the equation (22), that is,

[0040]

(Equation 10)

Is given by Conversely, given the value of K _V ,
The coefficient calculator 52 derives K ₁ from the equation (23) and further calculates K ₂ from the equation (21). The values of K ₁ and K ₂ from the coefficient calculator 52 are multiplied by the voltage difference values by the multipliers 51 and 28 to achieve the DC voltage control. When the desired DC voltage response speed is input, the method of FIG. 3 automatically sets the PWM converter and the chopper to operate cooperatively while satisfying the input.

[0042]

As described above, according to the present invention, the PWM
Since the converter and chopper are operated at the same time so that the DC voltage can be controlled in a coordinated manner, even if the PWM converter cannot be regenerated due to a decrease in the power system voltage, for example, the chopper will immediately function without switching. It is possible to process regenerative energy from the load side and obtain highly reliable conversion equipment, and when both are operating at the same time, a DC voltage control device with highly accurate control performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a circuit model diagram of a PWM converter, a chopper, and an inverter.

FIG. 3 is a configuration diagram showing another embodiment of the present invention.

FIG. 4 is a configuration diagram of a DC voltage control device in a conventional thyristor converter, a chopper, and an inverter system.

FIG. 5 is a circuit model diagram of a conventional thyristor converter, a chopper, and an inverter.

[Explanation of symbols]

 1 Transformer for Transformer 2 PWM Converter 3 Inverter 4 AC Motor 5 Chopper 6 Resistor 7 Capacitor 8 Rectifier 9 Rectifier Transformer 10 Voltage Detector 11 Current Detector 12 Current Detector 13 Current Detector 14 Current Detector 15 Coefficient Device 16 DC voltage command means 17 Subtractor 18, 28 Proportional amplifier 19 Coefficient device 20 Adder 21 Subtractor 22 Subtractor 23 Amplifier 24 Amplifier 25 Two-phase three-phase coordinate converter 26 PWM controller 27 Three-phase two-phase coordinate converter 29 Chopper gate controller 30 Amplification factor calculator

Claims (1)

(57) [Claims] 1. A PWM converter capable of controlling an input current, a chopper device provided in a DC circuit of the PWM converter and capable of controlling a conduction ratio, and an inverter for converting DC power of the DC circuit into AC power. , A means for detecting the input current of the PWM converter and a detection axis of the input current are synchronized with the voltage phase of the input side AC circuit of the PWM converter to have the same phase as the d-axis current and a 90 ° phase delay q Inverter input circuit DC voltage control device having means for converting into a shaft current, means for controlling the d-axis current according to an arbitrarily given d-axis current command value, and means for controlling the q-axis current to zero In, a current detector and a voltage detector for detecting the input current and the input voltage of the inverter, and a DC voltage command hand for giving a command value of the input side DC voltage of the inverter. And first and second amplifiers for amplifying the difference between the DC voltage command from the DC voltage command means and the inverter input DC voltage detection value from the voltage detector, the output of the first amplifier and the current A means for adding a signal proportional to the output of the detector and giving the addition result as the d-axis current command value, and a chopper flow for determining the flow rate of the chopper device according to the output of the second amplifier. A DC voltage control apparatus for an inverter input circuit, comprising: rate control means; and means for determining the amplification factor of the second amplifier according to the amplification factor of the first amplifier.