JP2000060196A - Controller for power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of phase shift, the drop in torque and excess current by limiting the AC voltage commands of all phases with the same rate and changing the output value of an AC voltage limitter, when the phase voltage of one of AC voltage commands exceeds a prescribed value that is previously set. SOLUTION: An AC voltage command computing element 1 reads the rotation speed command and the rotation speed of an induction motor 8 and the value of current flowing in an induction motor 8, operates AC voltage commands Vu0, Vv0 and Vw0 based on the values and outputs them to a zero-phase adder 2. The zero-phase adder 2 outputs voltage commands Vu1, Vv1 and Vw1, to which zero-phases are added, to an AC voltage limitter 3. The AC voltage limitter 3 limits all the voltage commands Vu1, Vv1 and Vw1 with the same rate, when the phase voltage of one of voltage commands Vu1, Vv1 and Vw1 exceeds prescribed value and cauges the output values of Vu2, Vv2 and Vw2 to be changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC motor drive system for driving a three-phase AC motor using a power converter such as an inverter, and a forward converter for converting AC power to DC. It relates to expansion of voltage utilization rate by improvement of limiter and stabilization of control system during transient.

[0002]

2. Description of the Related Art When an AC motor is driven using an inverter, vector control has been widely used in recent years.
In the vector control, the magnitude and phase of the current flowing through the AC motor are controlled, and the generated torque of the motor with respect to the command torque is linearized. Vector control can be realized by separating an alternating current into a magnetic flux component and a torque component, and controlling each component. As a result of these current controls, the voltage of the inverter is output with a predetermined phase. With this technology, AC motors can achieve the same or better performance than DC motors.

[0003] In a converter (forward converter), similarly to the AC motor, the magnitude and phase of the current input to the converter are controlled. This is a technique equivalent to the vector control of an AC motor, and a power supply power factor of 1 can be realized simultaneously with the control of the DC voltage. Inverter (converter)
There is a limit to the output (input) voltage of, and it is usually used in a region where the voltage is not saturated. The voltage limit is determined by the DC voltage of the converter and the characteristics of the switching elements that make up the converter. Since a minimum pulse width (ON width, OFF width) needs to be ensured for the switching element, a voltage margin must be ensured for the minimum pulse width. Also,
In order to prevent a short circuit due to a delay in switching operation, it is necessary to provide an arm short circuit prevention period. Since the arm short-circuit prevention period causes current distortion, a compensation voltage is usually applied. It is necessary to secure this compensation voltage as a voltage margin. To secure these voltage margins, the limit value of the voltage used for control itself is
It is several percent lower than the DC voltage.

Therefore, in order not to exceed the above limit value,
A voltage limiter is inserted on the AC side or on the rotation coordinate axis (dq coordinate axis).

[0005]

In the control of an AC motor, a voltage command may be increased during acceleration or when a load disturbance occurs. For this reason, the voltage value of the inverter output in the steady state is set low so as not to apply the limiter. In order to increase the inverter capacity in a steady state, the voltage value in a steady state may be increased, but the voltage limiter is easily applied in a transient state.

As described above, in vector control which is widely used at present, it is necessary to control the magnitude and phase of a current to predetermined values. When a voltage is applied to a limiter, these relationships are broken, and the transient response is deteriorated. Or torque loss may occur. In particular, the phase shift causes a difference between the magnetic flux axis for control and the actual magnetic flux axis of the electric motor, and the principle of vector control itself is broken.

[0007] The phase shift occurs because the voltage limiter is inserted independently for each phase. For example, when only one phase exceeds the limit value and the other phase is output as it is, the balance of the three phases changes and the phase relationship is broken. The same applies to the case where the limiter processing is performed on the dq coordinate axes.

As an example of these countermeasures, reference 1 (Japanese Unexamined Patent Application Publication No.
No. 149699). This is a method in which voltage commands on the dq coordinate axes are vector-combined, and the voltage commands of each axis are corrected so that only the magnitude is limited without changing the phase of the vector. However, since the limit value of the voltage vector is fixed, the range of the output voltage of the inverter viewed on the dq axis is a circle having the limit value as a radius.

The output voltage range of a normal power converter is dq
It is hexagonal on the axis. In the method of Document 1, a circle inscribed in the hexagon is the output voltage range of the inverter, and an unused portion remains. Since the portion between the hexagon and the circle is not used, if the voltage command actually reaches the limit value, the transient response may be delayed.

[0010] In addition to the above problems, the forward conversion device has the following problems. The voltage-type converter has a diode connected in anti-parallel to each switching element, and functions as a diode rectifier by turning off all the switching elements. Therefore, the converter operation and the diode rectifier operation can be switched and used depending on the voltage required by the load, and the efficiency of the forward conversion system can be improved. However, the DC voltage value when operating as a diode rectifier is lower than the DC voltage value (minimum value) during converter operation, and it is difficult to switch these smoothly. This occurs because the above-described voltage limit value is several percent lower than the DC voltage value. Therefore, when the converter operation and the diode rectifier operation are simply switched, an excessive current is generated due to the switching shock, and the switching element may be destroyed.

[0011]

In a control device for a power converter according to the present invention, when an AC voltage command is limited, when at least one phase exceeds a limit value, a voltage command for all other phases is set. At the same time. If the limiting ratio is equal for each phase, only the amplitude is suppressed without changing the phase of the voltage. Thereby, the phase shift is suppressed, and the occurrence of torque loss and excessive current can be suppressed. Furthermore, the output voltage range extends to the maximum of the converter.

The final limit value of the AC voltage command is:
Since the formalization is performed based on the phase of the voltage command, the same effect can be obtained even if the AC voltage command is limited (limit processing) using these formulated tables (or arithmetic expressions).

Further, when limiting the voltage command values on the dq coordinate axes, these voltage commands are once converted into AC voltage commands and compared with a predetermined limit value, and at least one phase exceeds the limit value. In this case, the two voltage commands on the dq coordinate axes may be limited at an equal ratio.

Further, since the final limit value of the voltage command on the dq coordinate is formulated by the phase of the voltage command, using these formulated tables (or arithmetic expressions), What is necessary is just to limit a voltage command.

[0015]

FIG. 1 shows a first embodiment of the present invention.

FIG. 1 shows an induction motor driving device for driving a three-phase induction motor by a PWM inverter.

In FIG. 1, 1 is an AC voltage command calculator for calculating a voltage command applied to the induction motor, 2 is a zero-phase voltage for improving the maximum output voltage of the inverter, A zero-phase adder for adding all three, an AC voltage limiter for limiting the magnitude of the three-phase AC voltage command according to a limit value (a maximum value and a minimum value), and a voltage limiter for calculating the limit value of three The value calculator 5 generates a PWM (pulse width modulation) signal based on an AC voltage command.
A WM controller, 6 is an inverter driven by a PWM signal, 7 is a current detector for detecting a current flowing through the induction motor, 8 is an induction motor driven by the inverter,
9 is a speed detector for detecting the rotation speed of the induction motor, 11
Is a speed controller that calculates the current commands Idr and Iqr of the induction motor and the primary angular frequency ω1 based on the rotation speed ωm of the induction motor and the rotation speed command ωr.
An integrator that integrates ω1 to calculate a phase angle φ, 13
A dq coordinate converter that converts a current detection value of the induction motor into a dq coordinate axis based on the phase angle φ, and a dq coordinate axis based on the current detection values Id and Iq on the dq coordinate axis and the Idr and Iqr. This is a current controller that calculates the above voltage commands Vd0 and Vq0.

FIG. 2 shows the configuration of the AC voltage limiter and the voltage limit value calculator in FIG. Part number 31
Is a multiplier that multiplies the AC voltage commands Vu1, Vv1, Vw1 by a coefficient Klim output from the voltage limit value calculator,
32 is a switch for switching between two input signals,
When the control signal Sw is "1", it is switched to 1 side, and when it is "0", it is switched to 0 side. 41 is an absolute value calculator for calculating the absolute values of Vu1, Vv1, and Vw1;
Select the largest input signal from the two input signals,
A maximum value selector for output, 43 is a maximum voltage setter for setting the maximum value Vmax that can be output by one phase of the inverter; 44 is a divider for dividing Vmax by the output of 42;
A comparator 45 compares two input signals and outputs “1” when the value on the “+” side is larger than the value on the “−” side, and outputs “0” when the value is opposite.

The operation of FIG. 1 will be briefly described as follows. The AC voltage command calculator 1 is a controller for performing vector control of the induction motor 8. A rotation speed command and a rotation speed of the induction motor, and a current value flowing through the induction motor are read, and an AC voltage command (Vu0, Vv0, Vw0) required by the induction motor is calculated and output based on these values. The inverter is controlled based on these AC voltage commands, and applies a voltage according to the commands to the induction motor,
Vector control is realized. In order to realize the vector control with high accuracy, it is important to perform the calculation in the AC voltage command calculator 1, but it is also important to minimize the error from the AC voltage command to the actual applied voltage.

The amplitude value of the AC voltage command calculated by the AC voltage command calculator 1 increases substantially in proportion to the speed in a steady state, but when the speed command of the induction motor changes suddenly or when the load of the induction motor is changed. In a transient state such as when abruptly changes, the amplitude value rapidly increases or decreases. At this time, the output voltage range of the inverter may be exceeded, which is a problem.

The zero-phase adder 2 is a voltage command corrector for improving the output voltage of the inverter, and is one of techniques for reducing the above problem. In recent years, it has been commonly used (details will be described later). 3, 4
5 is a voltage limiter which is a feature of the present invention. Even when the voltage suddenly changes and exceeds the allowable value of the inverter, voltage value limit processing is performed so that vector control is achieved as much as possible.

Next, the operation of FIG. 1 will be described in detail.

In FIG. 1, the AC currents Iu, Iv, Iw detected by the current detector 7 are converted by the dq converter into the current I on the dq coordinate axis according to the following equations (1) and (2).
d, Iq.

[0024]

(Equation 1)

[0025]

(Equation 2)

On the other hand, the detected speed value ωm detected by the speed detector is converted into a speed command value ωr
And a torque current command required for the electric motor is calculated based on the value. Also, the magnetic flux current command of the motor is
It may be changed according to the speed. Usually, the torque current command is output to the current controller as Iqr, and the excitation current command as Idr. At the same time, based on Iqr and Idr,
The primary angular frequency ω1 of the motor is calculated.

[0027]

(Equation 3)

In the above equation, r2 and L2 are constants of the motor.

In the current controller, a voltage command Vd on the dq coordinate axis is obtained based on Idr, Iqr and the detected values Id, Iq.
0 and Vq0 are calculated. In the calculation of Vd0 and Vq0,
Normally, PI control (proportional-integral compensation) is used. Recently, in order to improve the current response, non-interference compensation is often added. However, in this embodiment, any control method can be applied. Vd0 and Vq0 are converted by the dq inverse converter 15 into the three-phase AC voltage commands Vu0 and Vu according to Equations 4 and 5.
It is converted to v0, Vw0.

[0030]

(Equation 4)

[0031]

(Equation 5)

Vu0, Vv0, Vw0 in the above equation are:
In a steady state, it becomes a sine wave without distortion. Although the induction motor can be driven by this AC voltage command value, in recent years, a zero-phase adder 2 is added to add a common signal (zero-phase voltage) to all phases, and the output voltage of the inverter is maximized. It is almost common sense to improve the value (Reference 2: Transactions of the Institute of Electrical Engineers of Japan, Vol. 109, No. 11, P. 809-
816, 1989). Details of the zero-phase addition will be described later.

Voltage commands Vu1, Vv to which zero phase is added
1, Vw1 are limited in the maximum value and the minimum value in the AC voltage limiter, and finally Vu2, Vv2, V
Output as w2. The limit value of each phase is calculated by the voltage limit value calculator 4.

In the PWM controller 5, Vu2, Vv2, V
According to the value of w2, a PWM signal is generated by a triangular wave comparison method or the like to drive the switching element of the inverter. The inverter outputs a voltage corresponding to Vu2 to Vw2, and drives the induction motor. Next, the voltage limit value calculator 4
Will be described with reference to FIG.

In the maximum voltage setting unit 43 shown in FIG. 2, a maximum value Vmax which can be output from the inverter is set. Vmax
Is

[0036]

(Equation 6)

The relationship is as follows. In the above equation, Vdc is the DC voltage of the inverter, and Mmax is the maximum modulation rate of the inverter (Mmax is 0 ≦ Mmax ≦ 1). Mmax depends on the switching device used for the inverter.
It is set to about 9 to 1.0.

FIG. 3 shows the relationship between the AC voltage command and Vmax. The value of 1/2 of the DC voltage Vdc of the inverter ideally becomes the maximum voltage. However, in order to secure the minimum off time of the switching element and to reduce the voltage drop due to the influence of the arm short circuit prevention period (dead time). Is set several percent lower than Vdc / 2.
The absolute value calculator 41 calculates the absolute value of each of Vu1, Vv1, and Vw1, selects the one having the largest value from the calculated values (this is referred to as Vuvwmax), and calculates the coefficient Klim shown in the following equation. I do.

[0039]

(Equation 7)

Klim is at least one of Vu1 to Vw1.
If the phase exceeds Vmax, it will be less than one. Therefore, the value of Klim and 1 are compared by the comparator 45, and Klim <
In the case of 1, the Sw signal is set to 1 (when Klim> 1, S
w = 0).

In the AC voltage limiter, the Sw signal is "1".
In this case, the switch 32 is switched to the "1" side to control (limit) the voltage command at a fixed ratio with respect to the input. In that case, the voltage commands for all three phases are limited to Klim times. Klim is the ratio of the largest value of the three phases to Vmax. Therefore, by multiplying the voltage command of all phases by Klim, all three phases must be limited to the range of ± Vmax. become. Further, since the three phases are limited by the common ratio, no phase shift occurs in the voltage command.

Next, the operation principle of the present invention will be described in comparison with the conventional system. 3A of FIG. 4A is a configuration diagram of a generally used conventional voltage limiter. 32, 43, and 45 in the figure are the same as those in FIG. When Vu1 exceeds the value of Vmax, the output is limited to Vmax, and when Vu1 falls below -Vmax,-
Vmax. The input voltage Vu of this voltage limiter
The relationship between 1 and the output voltage Vu2 is as shown in FIG.
Suppose a case where one-phase AC voltage command out of three phases exceeds a limit value as shown in FIG. In the figure, V
During the period when u1 exceeds Vmax, Vu2 is Vma as shown in the figure.
Limited to x. However, during this time, Vv1 and Vw1 are not limited, and pass through the voltage limiter as it is. Looking at this relationship on the αβ axis, it is as shown in FIG. αβ transformation is

[0043]

(Equation 8)

Defined by Vu1 in FIG.
Since Vv1 and Vw1 do not change during the period in which is applied to the limiter, Vβ does not change from Expression 8. Therefore, when a voltage command is viewed as a vector as shown in FIG. 5A, a phase shift occurs (Δθ in the figure).

On the other hand, in the voltage limiter system according to the present invention, since the voltage commands for all three phases are limited at the same ratio, both Vα and Vβ are simultaneously limited at the same ratio. As a result, no phase shift occurs as shown in FIG.
Therefore, there is no excess or deficiency of the motor torque due to the phase shift, and stable motor control with high response can be realized.

Next, the principle of zero-phase addition and the operation of this embodiment when zero-phase addition is performed will be described.

FIG. 6 shows the configuration of the zero-phase adder 2 in FIG. 21 is a three-phase AC voltage command Vu0, Vv0, Vw
A zero-phase generator that calculates and outputs a zero-phase voltage V0 based on a value of zero. Since V0 is a value common to the three phases, there is no effect on the line voltage in principle regardless of the waveform. Although there are many possible V0s, a representative example will be described.

FIG. 7A shows an AC voltage command before the zero-phase addition is performed. This waveform is represented by the following equation.

[0049]

(Equation 9)

Next, FIG. 7 shows a waveform when half of the phase having the middle magnitude among the three-phase voltage commands is the zero-phase voltage.
(B). In FIG. 7A, in the section of θ1,
The W phase has an intermediate size. The zero-phase voltage V01 at this time
Is

[0051]

(Equation 10)

Is as follows. In the next section from 90 ° to 120 °, the V phase becomes the intermediate phase. Thus, the function of the zero-sequence voltage changes every 60 °. When V01 is added, each voltage command becomes as shown in FIG. 7 (b), and becomes a waveform in which the vicinity of the peak of the sine wave is lowered. By this zero-phase addition, the maximum output voltage of the inverter is about 1.15 times (2 / √3
(Reference 2: IEICE Transactions D, 10)
9 vol. 11, p. 809-816, 1989). Note that the value of “1.15 times” indicates that the peak value of the voltage command is V
It is the ratio at the time when it matches max (the ratio of the maximum value of the output voltage under the condition that the waveform is not distorted).

FIG. 7C shows the three-phase voltage commands having the largest absolute value and Vdc / 2 or -Vd.
The difference from c / 2 is taken and the value is added to each phase as a zero-phase voltage. In the period of θ2 in FIG.

[0054]

[Equation 11]

Becomes zero-phase voltage. As can be seen from FIG. 7C, when this zero-phase addition is performed, a period occurs in which the maximum value and the minimum value of the AC voltage command exceed ± Vmax and are continuously stuck to the value of ± Vdc / 2. . Voltage command is ± Vdc
The period of / 2 means that the switching operation of that phase is not performed. Therefore, when the zero-phase addition of Equation 11 is performed, the number of switching times is reduced by ３. Also in this method, the output voltage of the inverter increases about 1.15 times (2/２3 times) as compared with the sine wave of FIG. 7A (Reference 2: IEEJ Transactions D, 109 volume 11,
P. 809-816, 1989). As shown in FIG. 7C, a method in which only two of the three phases are switched is called “two-phase switching”. The methods of zero-phase addition can be broadly classified into three-phase switching as shown in FIG. 7B and two-phase switching as shown in FIG. 7C.

The voltage limiter system shown in FIG.
The method can be applied to the zero-phase addition method (three-phase switching method) shown in FIG. Among the three-phase voltage commands, two phases simultaneously exceed Vmax and -Vmax, but there is no problem.

In the case of the two-phase switching system as shown in FIG.

FIG. 8 shows an embodiment in which the two-phase switching system is considered. Compared to FIG. 1, the processes of the zero-phase adder 2 and the AC voltage limiter 3 are interchanged. In the voltage limit value calculator 4B, Vmax is multiplied by K0.

Vu0 to Vw0 are pure sine waves.
Therefore, if the limiter processing is performed before the zero-phase addition, the effect of improving the output voltage by the zero-phase addition cannot be obtained. Therefore, considering the zero-phase addition, increase the value of Vmax.
(K0 times). K0,

[0060]

(Equation 12)

In this case, it is possible to realize a limiter that eliminates a phase shift by utilizing the effect of zero-phase addition. The method shown in FIG. 8 can be applied to the zero-phase addition shown in FIG. 7B.

Next, a method of limiting the AC voltage command using the line voltage will be described. In the embodiments described above, the absolute value of each phase voltage is calculated, the largest one is selected, and the coefficient Klim is calculated. However, the same effect can be obtained by using the line voltage. FIG. 9 shows the configuration of the voltage limit value calculator 4C. 42 to 46 in the figure are the same as those of the same number in FIG. A minimum value selector 47 selects the smallest voltage from the three inputs and outputs the selected voltage.
By taking the difference between this output and the output of the maximum value selector 42, the maximum value VLmax of the line voltage is obtained. Since the condition that the line voltage matches the DC voltage of the inverter is the maximum value of the inverter output voltage, VLmax is halved,
By calculating the ratio to Vmax, Klim can be obtained.

The coefficient K0 is K when performing zero-phase addition.
0 = 1 is set, and when not performed, K0 = √3 / 2 is set. Thus, similarly to FIGS. 1 and 8, the voltage command can be limited without changing the phase.

Next, an embodiment for limiting the AC voltage command using only the phase information of the AC voltage command will be described. FIG.
FIG.

In FIG. 10, 10 is Vd0, Vq0
And a phase calculator 4D for calculating the phase θ of the AC voltage command from the phase φ of the dq coordinate axis, and a voltage for calculating the maximum output value and the minimum value of each phase determined depending only on the value of θ. The limit value calculator 3D is an AC voltage limiter that limits the voltage command based on the maximum value and the minimum value of each phase. The other reference numerals are the same as those of the same reference numerals in the invention of FIG. Next, the operation principle of the embodiment of FIG. 10 will be described with reference to FIG. In FIG.
In the voltage phase calculator 10, using the values of Vd0 and Vq0,

[0066]

(Equation 13)

Is calculated, and

[0068]

The voltage phase θ is calculated as θ = φ + δdq (Equation 14). Voltage limit value calculator 4D
Then, the upper limit value (Vumax to Vwmax) and the lower limit value (Vumin to Vwmin) of each phase determined by θ are output. The AC voltage limiter compares these limit values with the voltage command for each phase, and switches to the upper limit value when the command value exceeds the upper limit value and switches to the lower limit value when the command value falls below the lower limit value. In the present embodiment, as in the embodiment of FIG.
The process of limiting the value to lim times is not performed, which corresponds to changing the value of Vmax (−Vmax) in the conventional example of FIG. 4A according to the value of the phase θ.

Next, the relationship between these limit values and θ will be described.

FIG. 12A is a waveform after the limiter processing when the AC voltage command becomes excessive in some sections in the embodiment of FIG. 1 or FIG. At this time, the zero-phase addition uses the one of Expression 10 (FIG. 7B). If the amplitude of the AC voltage command is further increased, the result finally becomes as shown in FIG. Even if the amplitude is further increased, the waveform after the limit remains as shown in FIG.

In the case of three-phase AC, once the phase θ is determined, the ratio of the instantaneous values of the three-phase voltages is uniquely determined. Therefore, even if the voltage command value is limited by the AC voltage limiter, the final waveform after the limitation is uniquely determined as long as all the phases are limited at the same ratio. If this relationship is formulated, the limit value is obtained from the phase. In the section of θ1 in the waveform of FIG. 12, the upper limit of the U phase is V
max and the lower limit of the V phase are −Vmax, and only the intermediate W phase is a complicated function.

The limit value of the W phase is as follows.

In the section θ1 (30 ° ≦ θ ≦ 90 °), the command value Vw1 becomes

[0074]

(Equation 15)

Is obtained. Also, the U phase

[0076]

(Equation 16)

Is as follows. In this period, the U phase and the W phase simultaneously reach Vmax and -Vmax. As one representative, when the coefficient Klim is calculated in the U phase,

[0078]

[Equation 17]

Is obtained. This is multiplied by Equation 15 to get W
This is the phase limit. The upper limit value Vwmax is

[0080]

(Equation 18)

The lower limit value Vwmin is

[0082]

[Equation 19]

Is obtained. Therefore, it is understood that the function is a function of only θ without depending on Vp (amplitude) at all.

Here, Equation 18 (Equation 19) is generalized,

[0085]

(Equation 20)

FIG. 13 shows the calculation of the limit value of each phase in each phase section. As can be seen from FIG. 13, when the voltage phase is determined, only one of Vmax and Vmin is defined for each phase, but the remaining limit values are not defined (no definition is required).

The relationship shown in FIG.
D may be stored as a table, and each limit value may be output for a given θ.

In this embodiment, since all phases are always limited at the same time, the comparator 45 in FIG. 11 can be provided for only one phase and the output can be common to each phase. .

As described above, as an embodiment of the present invention, a method of performing a limit process on an AC voltage command has been described. As described above, when the amplitude of the voltage command is increased using the embodiment of FIGS.
The waveform shown in FIG. Therefore, the embodiment of FIGS. 1 and 8 has the same effect as that of FIG.

When the induction motor is driven in the state of the waveform shown in FIG. 12B, the waveform distortion increases, but the maximum output voltage of the inverter increases on average. No phase shift occurs at this time. Therefore, the present invention is extremely effective when a large voltage is required temporarily, such as during a transition.

As the amplitude of the voltage command is increased in the conventional method (FIG. 4), the value of the intermediate phase (corresponding to the W phase in the section θ1 in FIG. 12) continues to change with the increase of the amplitude.
Eventually, the value of the intermediate phase also sticks to Vmax or -Vmax. Also in this case, although the maximum value of the output voltage of the inverter becomes large, the phase shift reaches ± 30 ° at the maximum. Therefore, an axis shift occurs, and the transient response deteriorates.

Next, another embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG.

In FIG. 14, 1E is a voltage command calculator for calculating a voltage command applied to the induction motor, and 3E is
The DC voltage limiters 4E for limiting the magnitudes of the voltage commands Vd0, Vq0 provide Vd0, Vq based on the voltage phase θ.
A voltage limit value calculator that calculates a limit value of 0, 15E is d
The dq-αβ coordinate converter 5E that converts the voltage command on the q coordinate axis into a voltage command on the αβ axis is a PWM controller that generates a PWM signal based on the voltage command on the αβ axis. The other reference numerals are the same as those of the embodiment of FIGS. 1 and 10.

The present embodiment is characterized in that the voltage command is not coordinate-converted into three-phase alternating current. Instead, a voltage command limiter process is performed on the voltage command on the dq axes. At this time, the voltage limit value is changed according to the voltage phase θ. In the PWM controller 5E, a PWM signal is directly generated based on a voltage command of the αβ axis. Such PWM control is called a space vector method, and expresses the output voltage of the inverter in a biaxial space and calculates the pulse output time. Details will be described later.

FIG. 15 shows a configuration of the DC voltage limiter 3E and the voltage limit value calculator 4E. 43E in FIG.
A setter for a voltage limit value on the dq axes, 48 is a route calculator, and 49 is a function generator for generating a predetermined function for θ. The other components are the same as those of the previous embodiment with the same reference numerals.

Next, the operation principle of the present invention will be described. The value Vdqlimit of the voltage limit value setting device 43E is

[0097]

(Equation 21)

Are set as follows. This value is obtained by setting the maximum value of the line voltage as Vdc · Mmax (that is, in Expression 9,
Vp = Vdc · Mmax / √3) This is equivalent to the magnitude of a vector on dq coordinates when the voltage is dq-converted. That is, it matches the maximum value for outputting a sine wave.

The voltage limit value Vlimit is obtained by multiplying Vdqlimit by Kv. Kv is a function of the voltage phase θ, and the function is shown in FIG. The value of Kv changes in a 60 ° cycle.

On the other hand, Vd0 and Vq0 are added after being squared, respectively, and the magnitude of vector (| V |) is output by the route calculator 48. Voltage limiting factor K
lim is obtained from the ratio between | V | and Vlimit.

The processing of the DC voltage limiter 3E is similar to that of the AC voltage limiter, in that the voltage commands of the respective dqs are converted to Klim
Is smaller than 1, it is limited by Klim times.

Next, the principle of operation of this embodiment will be described. First, the expression of the output voltage of the inverter on two axes will be described.

FIG. 17 is a configuration diagram of a three-phase full-bridge voltage source inverter. In the drawing, only one of the upper and lower switching elements of each of the U to W phases is on. Assuming that the upper side (Sup) of the U phase is on and the lower sides (Svn and Swn) of the V and W phases are on, the phase voltages Vui to Vwi are as follows:

[0104]

(Equation 22)

The following is obtained. When this is converted to a voltage on the αβ axis according to Equation 8,

[0106]

(Equation 23)

Is obtained. Equation 23 is defined as a vector V1, and α
FIG. 18 shows a diagram in the β space. Similarly,

[0108]

(Equation 24)

Then,

[0110]

(Equation 25)

Is obtained. When the space vector is calculated in this manner, the voltages that can be output from the inverter are eight vectors (of which two are zero vectors) shown in FIG.

In order to generate a PWM signal, a voltage command is also represented by a space vector. As shown in FIG. 18, it is assumed that the voltage command vector Vr is inside a triangular space surrounded by V0 (zero vector), V1, and V2. In this case, the vector V0, V1, V2
Are output for times t0, t1, and t2, respectively, and Vr is approximately output. The relationship between the voltage command and the output time of each vector is

[0113]

Vr = t1 · V1 + t2 · V2 + t0 · V0 (Formula 26)

[0114]

T = t1 + t2 + t0 (Formula 27)
From these two equations, t0 to t2 are obtained. That is, when performing the PWM control with the space vector,
The voltage command is expressed by a space vector, an inverter vector for approximating the voltage command is selected, the output time of each is calculated, and finally converted to a PWM pulse.

Next, the output voltage range when the inverter is controlled by the space vector will be considered. When the voltage command is a sine wave, Vr rotates at a constant speed (angular frequency speed) in a circle. Therefore, if the output voltage of the inverter is limited to a sine wave, the output voltage range of the inverter is inside the circle shown in FIG. If the voltage vector is limited within this circle, the system of the prior art (JP-A-9-149699) is used. Also in the present embodiment, if the output Kv of the function generator 49 in FIG.
Is equivalent to

In this embodiment, Kv is set to θ in order to maximize the use of the output voltage of the inverter and achieve a high response.
Is changed to one or more. Unless the output voltage is limited to a sine wave, the output voltage range of the inverter is as shown in FIG.
Inside the hexagon shown in That is, it is possible to output a voltage in a wider range than the output range when the sine wave is limited. In order to use all the hexagonal regions, the value of Kv is made variable according to θ.

Next, the relationship between θ and Kv will be described with reference to FIG. In the figure, the maximum vector size that can be output is x. From the relationship in FIG.

[0118]

Y = x cos (30 ° −θ) (Equation 28) Therefore,

[0119]

(Equation 29)

Is obtained. Here, since y matches the maximum value of the sine wave output range, y = Vdqlimit. Therefore,

[0121]

[Equation 30]

Is obtained. However, the above equation is 0 ≦ θ ≦ 60 °
Holds in the range of The value of Kv can be similarly obtained in other sections of θ. The result is the function shown in FIG. As described above, according to the embodiment of FIG. 14, on the dq coordinate axes, it is possible to use the inverter output voltage to the maximum and limit the command value without changing the vector phase.

Next, another embodiment for limiting the voltage command on the dq coordinate axes will be described.

The voltage limit value calculator 4F in FIG.
This is a feature of the present embodiment. This voltage limit value calculator 4F is
Applying in place of the voltage limit value calculator 4E in FIG.
Further, the voltage phase calculator of FIG. 14 is eliminated and used. Others are the same as FIG.

Next, the operation principle of this embodiment will be described. In FIG. 20, a voltage limit value calculator 4F receives voltage commands Vd0 and Vq0, and performs a coordinate conversion to a three-phase AC voltage once on a dq coordinate axis phase φ. Thereafter, as in the embodiment of FIG. 9, the maximum value of the line voltage is calculated, and the coefficient Klim is calculated from 1/2 of the value and the value of Vmax. As previously mentioned,
Since the maximum output range of the inverter is obtained when the line voltage and the DC voltage of the inverter match (corresponding to the hexagon in FIG. 18), the output voltage range is utilized to the maximum by this calculation, and the voltage phase Will not change. Although the present invention is equivalent to the invention of FIG. 14, the route calculation is not required, so that the calculation time can be shortened.

Next, an embodiment of the forward conversion apparatus according to the present invention will be described with reference to FIG.

In FIG. 21, 1G is a converter 6G.
(Forward conversion device) A voltage command calculator for calculating an input voltage command, 8G is a three-phase AC power supply, 9G is a phase detector for detecting the power phase of the three-phase AC power supply, and 50 is a converter 6G
Is a voltage detector for detecting the voltage of the output voltage Vdc of the converter 6G, 52 is a load device connected to the converter, 17
Is a converter output voltage command Vdcr and a detection value Vdc
Is a voltage controller that calculates the input current command of the converter from the value of. The other components are the same as the components in the previous embodiments.

In the control of the converter, the phase φ of the AC power supply is detected, and a current component having the same phase as the power supply voltage is expressed by Iq,
The input current is controlled with the component shifted by 90 ° in phase as Id. At this time, by controlling so that Id = 0, a power supply power factor of 1 can always be achieved. Also, the DC voltage Vd
The control of c is performed using Iq. In some cases, the current required by the load device 52 is fed forward to Iqr. Also in the present embodiment, the addition of the voltage limit value calculator 4 and the AC voltage limiter 3 makes it possible to make maximum use of the input voltage of the converter. Each embodiment related to the control of the inverter described so far can be applied as it is.

FIG. 22 shows the structure of a converter widely used at present. If the output of the PWM controller is P
It is assumed that all the WM pulses are turned off and the gate signals of all the switching elements forming the converter are turned off. Then, the input current flows through the freewheel diode connected in anti-parallel to each switching element, and operates as a diode rectifier.

A diode rectifier is very efficient because it does not involve a switching operation unlike a converter. When the power consumption of the load device increases, the distortion of the input current waveform increases and the power factor also deteriorates. However, there is no problem in a light load state.

Therefore, by switching between the diode rectifier and the converter operation according to the power consumption of the load device,
An overall efficient forward conversion system can be realized.

However, when the operation is actually switched from the diode rectifier operation to the converter operation, the conventional converter generates an inrush current as shown in FIG. This is problematic in that the output voltage of the diode rectifier is lower than the minimum value of the output voltage of the converter, and there is a difference of ΔV as shown in the figure. Since the converter having the configuration shown in FIG. 22 is a step-up converter, the relationship between the converter input voltage and the output DC voltage is inversely proportional. That is, in order to minimize the DC voltage, it is necessary to maximize the converter input voltage. However, in the conventional converter, since the input voltage range was within the circle of FIG. 18, considering the voltage margin,
It was difficult to get the maximum voltage.

However, in the forward conversion device according to the present invention, the input voltage range of the converter can be expanded to the hexagon in FIG. 18, so that the average value of the input voltage can be increased, and FIG. ), Vdc can be started up smoothly. Therefore, the rush current accompanying the switching is reduced.

Although the inverters and converters in the above-described embodiments are of a three-phase full bridge type, they can be similarly applied to a three-level converter and other multiplex converters.

Although the example of the induction motor has been described as the motor drive system, the invention can be applied to all other AC motors such as a synchronous motor.

[0136]

According to the present invention, it is possible to utilize the output voltage of the inverter to the maximum and control the error of the voltage phase to zero.

When the present invention is applied to a converter (forward conversion device), the output voltage range of the converter is expanded, and the efficiency of the device can be improved as a forward conversion system.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an AC motor driving device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of an AC voltage limiter and a voltage limit value calculator.

FIG. 3 is a diagram showing a relationship between an AC voltage command and a voltage limit value.

FIG. 4 is a configuration diagram of a conventional voltage limiter.

FIG. 5 is a diagram showing the effects of the conventional system and the system according to the present invention.

FIG. 6 is a configuration diagram of a zero-phase adder.

FIG. 7 is a diagram showing the principle of zero-phase addition.

FIG. 8 is a configuration diagram of an AC motor driving device according to an embodiment of the present invention.

FIG. 9 is a configuration diagram of a voltage limit value calculator.

FIG. 10 is a configuration diagram of an AC motor driving device according to an embodiment of the present invention.

FIG. 11 is a configuration diagram of a voltage phase calculator, a voltage limit value calculator, and an AC voltage limiter.

FIG. 12 is a view for explaining the operation principle of the embodiment in FIG. 10;

FIG. 13 is a view showing a voltage limit value with respect to a phase θ.

FIG. 14 is a configuration diagram of an AC motor driving device according to an embodiment of the present invention.

FIG. 15 is a configuration diagram of a voltage limit value calculator and a DC voltage limiter.

FIG. 16 is a diagram showing functions used in the embodiment of FIG. 14;

FIG. 17 is a main circuit configuration diagram of a three-phase full-bridge voltage source inverter.

FIG. 18 is a diagram showing an output voltage of an inverter and a space vector display of a voltage command.

FIG. 19 is a diagram showing the principle of the embodiment in FIG. 14;

FIG. 20 is a configuration diagram of a DC voltage limiter and a voltage limit value calculator.

FIG. 21 is a configuration diagram of a forward conversion device according to an embodiment of the present invention.

FIG. 22 is a main circuit configuration diagram of a three-phase full-bridge voltage source converter.

FIG. 23 is a diagram showing the operation of the converter according to the conventional method and the converter according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... AC voltage command calculator, 2 ... Zero phase adder, 3 ... AC voltage limiter, 4 ... Voltage limit value calculator, 5 ... PWM controller, 6 ... Inverter, 7 ... Current detector, 8 ... Induction motor, 9: speed detector, 11: speed controller, 12: integrator, 13: dq coordinate converter, 14: current controller.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor ▲ Taka ▼ Junichi Hashimi 5-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Omika Plant, Hitachi, Ltd. (72) Yoshinori Akita Omika, Hitachi City, Ibaraki Prefecture 7-1-1, Machi F-term in Hitachi Research Laboratory, Hitachi, Ltd. F term (reference) 5H576 BB02 BB10 CC01 CC05 DD02 DD04 DD05 EE01 EE11 EE16 GG02 GG04 HB02 JJ05 JJ22 JJ24 JJ28 LL01 LL22 LL24 LL30 LL39

Claims (10)

[Claims] An AC voltage command generator for generating a voltage command on the AC side of the power converter, an AC voltage limiter for limiting the AC voltage command value, and an output of the AC voltage limiter. A PWM controller that generates a PWM pulse and controls the power converter on the basis of at least one phase voltage of the AC voltage command or a line voltage exceeds a predetermined value set in advance. A control device for a power converter, wherein the AC voltage commands of all phases are restricted at the same ratio to change the output value of the AC voltage limiter. 2. The apparatus according to claim 1, further comprising means for calculating or detecting a voltage phase of the AC voltage command, wherein at least one phase voltage or line voltage of the AC voltage command is a predetermined value set in advance. A control device for a power converter, wherein the output value of the AC voltage limiter is changed based on a function defined by the voltage phase when the voltage value exceeds the voltage phase. 3. A power converter, a dq voltage command generator for generating a voltage command on the AC side of the power converter on a rotating coordinate axis (dq coordinates) rotating in synchronization with three-phase AC,
A dq voltage limiter for limiting a value of a voltage command on the dq coordinate axis, and a PW based on an output of the dq voltage limiter.
A PWM controller that generates M pulses and controls the power converter. The voltage command is coordinate-converted into an AC voltage command (dq inverse conversion), and at least one phase voltage of the AC voltage command is Or, when the line voltage exceeds a predetermined value set in advance,
By limiting the values of the two voltage commands on the dq axes at the same ratio,
A control device for a power converter, wherein an output value of the dq voltage limiter is changed. 4. The dq-axis voltage command vector according to claim 3, further comprising means for calculating or detecting an AC-side voltage phase based on the voltage command on the dq coordinate axis and the phase of the dq coordinate axis. Calculating a sum, and, when the sum exceeds a predetermined value, changing an output value of the dq voltage limiter based on a function defined by the voltage phase. Vessel control device. 5. The voltage limiter according to claim 4, wherein the function of the voltage limiter is a voltage phase θ = 0 to 6.
A function defined by the following equation for an interval of 0 °,
The other section is a function that repeats the following equation every 60 °, wherein the controller is for a power converter. (Equation 31) 6. A power converter for converting direct current to three-phase alternating current,
AC motor driven by the power converter, and means for detecting or estimating the rotational speed of the AC motor,
A speed command, an AC voltage command generator that generates a three-phase AC voltage command for the AC motor based on the detected value or estimated value of the speed, an AC voltage limiter that limits the value of the AC voltage command, A PWM controller that generates a PWM pulse based on the voltage command limited by the AC voltage limiter and controls the power converter, wherein at least one phase voltage or line voltage of the AC voltage command is An AC motor system, wherein, when a predetermined value is exceeded, AC voltage commands of all phases are limited at the same ratio to change an output value of the AC voltage limiter. 7. A power converter for converting DC to three-phase AC,
AC motor driven by the power converter, and means for detecting or estimating the rotational speed of the AC motor,
A dq voltage command generator for generating a voltage command on the AC side of the AC motor based on the speed command and the detected or estimated value of the speed on a rotating coordinate axis (dq coordinate axis); and a value of the voltage command. And a PWM controller that generates a PWM pulse based on the voltage command limited by the dq voltage limiter and controls the power converter, and converts the voltage command into an AC voltage command. Coordinate conversion (dq inverse conversion), and when at least one phase voltage or line voltage of the AC voltage command exceeds a predetermined value set in advance,
By limiting the values of the two voltage commands on the dq axes at the same ratio,
An AC motor system, wherein an output value of the voltage limiter is changed. 8. A power converter for converting three-phase alternating current to direct current;
A voltage detector for detecting a DC voltage of the power converter, a DC voltage command, and a voltage command calculator for calculating a three-phase AC voltage command based on the DC voltage; and limiting a value of the AC voltage command. An AC voltage limiter, and a PWM controller that generates a PWM pulse based on the voltage command limited by the AC voltage limiter and controls the power converter, at least one phase voltage of the AC voltage command, Alternatively, when the line voltage exceeds a predetermined value set in advance, the AC voltage commands of all phases are limited at the same ratio, and the output value of the AC voltage limiter is changed. . 9. A power converter for converting three-phase alternating current to direct current;
A voltage detector for detecting a DC voltage of the power converter, a DC voltage command on a rotating coordinate axis (dq coordinate axis),
A voltage command generator that generates a voltage command on the AC side of the power converter based on the DC voltage, a dq voltage limiter that limits the value of the voltage command, and a voltage command that is limited by the dq voltage limiter. And a PWM controller that generates a PWM pulse based on the voltage command and controls the power converter. The voltage command is coordinate-converted into an AC voltage command (dq inverse conversion), and at least one phase of the AC voltage command is converted. When the voltage or line voltage exceeds a predetermined value set in advance,
By limiting the values of the two voltage commands on the dq axes at the same ratio,
A forward converter, wherein an output value of the dq voltage limiter is changed. 10. The method according to claim 8, wherein when the power consumption of the load device is less than a predetermined value, or when the input voltage required by the load device is less than a predetermined value,
A forward converter, wherein a PWM pulse output from a WM controller is turned off, and the power converter is driven as a diode rectifier.