JPH0783636B2 - PWM inverter device - Google Patents

Description

The present invention relates to a PWM inverter device for variable speed control of an AC motor, and more particularly to a means for detecting an estimated value of its output voltage.

[Conventional technology]

PWM for variable speed control of AC motors such as conventional induction motors
The inverter device has a voltage detector for detecting the inverter output voltage applied to the electric motor, and the voltage value detected by the voltage detector is fed back to the control unit of the PWM inverter device for variable speed control.

Examples of the voltage detector of the inverter output voltage include, for example, Proc.
As shown in 48), an instrument transformer (hereinafter referred to as PT) was used for direct detection.

However, in the method using the above PT, there is a problem of amplitude and phase error due to magnetic flux saturation of PT in the low frequency region, and the output voltage of the inverter cannot be accurately detected. It was necessary to increase the size of the PT iron core, which resulted in a large storage space and cost reduction.

FIG. 5A shows the relationship between the modulated wave (a) which is the voltage command signal output from the inverter control unit and the triangular wave carrier (b) which is the carrier, and FIG. 5B compares the modulated wave (a) with the carrier. And the pulse width modulation signal (c) as the output voltage of the PWM inverter device obtained by
The relationship of the fundamental wave component (d) included in is shown.

The inverter control unit needs to detect the output voltage of the inverter device and feed back the fundamental wave component (d). The output voltage waveform of the PWM inverter device is shown by the solid line in FIG. 5B. Since it is the rectangular wave (c) shown, the output of the conventional output voltage detector has a similar waveform. From such a PWM voltage wave (c), FIG.
In order to detect the fundamental wave component (d) indicated by the broken line in Fig. 4 in an analog manner, filter processing is required, so a delay occurs in the detection signal, and the output voltage of the PWM inverter device cannot be accurately detected. Further, when attempting to perform sampling digital control by the microprocessor, the PWM output voltage waveform (c) shown by the solid line in FIG. In order to detect the fundamental wave component shown by the broken line, the pulse width must be detected accurately, so control must be performed with a very short sampling time, which is not possible with the processing capacity of a normal microprocessor. It was possible. In addition, ringing due to LC resonance during switching occurs due to the winding inductance of the PT and the stray capacitance between windings, which impairs the detection accuracy.

[Problems to be Solved by the Invention]

Since the conventional PWM inverter device uses a voltage detector such as PT to detect the output voltage, errors occur in the amplitude and phase of the detected value due to magnetic flux saturation in the low frequency region, and the above output The voltage cannot be detected accurately, and when obtaining the fundamental wave component from the PWM voltage waveform consisting of the rectangular wave detected by the above voltage detector, there is a time delay because it requires filter processing for analog detection. However, in the case of sampling digital control, there is a problem that it cannot be processed by a normal microprocessor because it requires control in a very short sampling time.

The present invention has been made to solve the above problems, and provides a PWM inverter device equipped with a means for outputting an accurate estimated value without actually detecting the output voltage of the PWM inverter device. The purpose is to get.

[Means for Solving the Problems]

An output voltage estimated value generation means for estimating the output voltage of the PWM inverter is provided, and this output voltage estimated value generation means is used to output one phase of the AC voltage command signal as V _U ^* and the crest value of the carrier wave as V _U ^* .
_C , when the voltage of the DC voltage source of the PWM inverter detected by the voltage detector is V _DC , the peak value of V _U ^* is V _C
If it is larger, the peak value of V _U ^* is set to V _U ′, which is limited to the level below V _C , and then (V _DC / 2) × (1 / V _C ) ×
V _U ′ is calculated, and the peak value of V _U ^* is V _C
If it is smaller, the output voltage of the PWM inverter is estimated by calculating (V _DC / 2) × (1 / V _C ) × V _U ^* .

[Operation] The output voltage estimated value generating means in the present invention is the DC voltage source of the PWM inverter detected by the voltage detector, wherein V _U ^* is one phase of the AC voltage command signal, V _{C is} the peak value of the carrier wave. If the peak value of V _U ^* is larger than the above V _C when the voltage is V _DC , then the peak value of the above V _U ^* is set to V _U ′ which is limited to the level below the above V _C , and then (V _DC / 2) × (1 / V _C ) × V _U ^* and when the peak value of V _U ^* is smaller than V _C above, (V _DC / 2) × (1 / V _C ) × V _U ^* is calculated to estimate the output voltage of the PWM inverter.

〔Example〕

An embodiment of the present invention will be described with reference to FIG. Fig. 1 shows a PWM using a vector control method without a speed detector for an induction motor.
It is a block diagram which shows an inverter apparatus.

In the figure, (1) the speed setting circuit for outputting a rotational speed command value omega _r ^* of the induction motor (18), (2) is a speed control circuit (2), described later with the rotational speed command value omega _r ^* Of the rotation speed of the electric motor (18) output by the speed estimation circuit (3) To output the current command values i _des ^* , i _qes ^* of the motor (18). (3) is a speed estimation circuit, which will be described later in three phases 2
Orthogonal biaxial current values output by the phase coordinate conversion circuit (9)
i _des , i _qes and the orthogonal two-axis voltage values v _des , v _qes output from the three-phase two-phase coordinate converter (8) are input, and the above estimated values are obtained. Is output. (4) is the above estimated value And a slip frequency ω _s output by a slip frequency calculation circuit (5) described later are added to output the output frequency ω of the inverter device.
, (5) is the orthogonal biaxial current i _des , i
_This is a slip frequency calculation circuit that inputs _qes and calculates and outputs the slip frequency ω _s of the electric motor (18). (6) is an integrator that integrates the inverter output frequency ω and outputs the phase angle θ of the dq coordinate axes, and (7d) and (7q) are the current command values i _des ^* , i _des ^* and the two orthogonal axes. current value i _des of, and the i _QES type respectively, the i _des is i _des ^*, the voltage command value as i _QES to follow each _i qes ^* v _des ^*, v current control circuit for outputting a _QES ^* Is. (8) and (9) are three-phase / two-phase coordinate conversion circuits, in which the three-phase AC components of u, v, w are converted into the d-axis component on the dq coordinate of the two orthogonal axes rotating at the inverter output frequency ω and the q-component. Convert to the axis component. (10) is a two-phase / three-phase coordinate conversion circuit that converts the d, q-axis components on the dq coordinates into the three-phase AC components of u, v, w. (11) inputs the three-phase AC voltage command values V _u ^* , V _v ^* , V _w ^* output from the two-phase three-phase coordinate conversion circuit (10), and based on this voltage command value, the inverter (15) Estimated output voltage
It is an inverter output voltage estimated value generation circuit as an inverter output voltage estimated value generation means for outputting V _u , V _v , V _w . For the configuration and operation of (11), refer to FIG. 2 to FIG. See below. (12u) to (12w) are comparators that input the voltage command values V _u ^* , V _v ^* , V _w ^* and the triangular wave carrier output from the triangular wave carrier generation circuit (13) and output a three-phase PWM signal. (14u) to (14W) are base amplifiers for amplifying the above three-phase PWM signal and supplying the base current of the power transistor which constitutes the inverter (15) in the subsequent stage, (16)
Is a DC voltage source of the inverter (15), (17) is a DC voltage detector for detecting the voltage V _DC of the DC voltage source (16), (17u) ~
(17w) is an inverter (1) supplied to the induction motor (18)
This is a current detector that detects the three-phase output currents i _u , i _v , and i _w in 5). In addition, the speed control circuit (2) to the inverter output voltage estimated value generation circuit (11) are used to control the inverter control unit (23).
Is configured.

Next, the operation of the block diagram shown in FIG. 1 will be described. Inverter detected by DC voltage detector (17) (1
5) The voltage V _DC of the DC voltage source (16) and the three-phase AC voltage command values V _u ^* , V _v ^* , V _w output from the two-phase / three-phase coordinate conversion circuit (10)
^* And the peak value V _C of the output of the triangular wave carrier generation circuit (13), the fundamental wave component V _u , V _v , of the output voltage of the inverter (15) is calculated by the inverter output voltage estimated value generation circuit (11). Detect V _w .

These V _u , V _v , V _w are dq in the three-phase two-phase coordinate conversion circuit (8).
Converted to coordinate voltage components v _des and v _des . The three-phase alternating currents i _u , i _v , i _w detected by the current detector (17) are the current components i _des , i on the dq coordinates in the three-phase two-phase coordinate conversion circuit (9).
_Converted to _qes . The speed estimation circuit calculates the rotation speed of the electric motor (18) based on the voltage and current components v _des , v _qes , i _des , i _qes on the dq coordinates, the inverter output frequency ω, and the motor constant input in advance. Estimate of Is output. The slip frequency calculation circuit (5) is composed of i _des and i
_The slip frequency ω _s to be given to the electric motor (18) is _calculated from _qes and output. ω _s Is added by the adder (4) to become the inverter output frequency ω, and ω is integrated by the integrator (6), and d−
It becomes the phase angle θ of the q coordinate. The speed control circuit (2) _Outputs current command values i _des ^* , i _qes ^* to be supplied to the electric motor (18) so as to follow the speed command value ω _r ^* . Current control circuit (7d), (7q) is, i _des ^*, i _QES ^* to i _des, as i _QES to follow, ^* voltage command value v _des, v _QES ^*, and outputs a. These voltage command values v _des ^* , v _qes ^* are converted into three-phase AC voltage command values V _u ^* , V _v ^* , V _w ^* by the two-phase three-phase coordinate conversion circuit (10). V _u ^* , V _v ^* , V _w ^* are comparators (12u) to (12
In w), it is compared with the triangular wave carrier and becomes a three-phase PWM signal, which is further amplified by the base amplifier circuit (14) and becomes the drive signal for the inverter (15). The inverter (15) controls the induction motor (18) at a variable speed.

Next, details of the inverter output voltage estimated value generation circuit (11) for outputting the estimated value of the output voltage of the PWM inverter, which is the point of the present invention, will be described with reference to FIGS. 2 and 3. FIG. 2 is a block diagram showing the inverter output voltage estimated value generation circuit (11). In the figure, (19
u), (19v), and (19w) are clamp circuits that limit the input voltage to a preset clamp voltage level V _C or less and output it. (20u), (20v), and (20w) are 1 / Magnifier that increases the output by V _C times and outputs, (21) is an amplifier that outputs 1/2 times the input voltage, (22u), (22v), (22w) is an amplifier (20u) , (20v), (20w) and amplifier (21)
Of the clamp circuits (19u) to (19w), the amplifiers (20u) to (20w), (2
1) The multipliers (22u) to (22w) make up the inverter output voltage estimated value generation circuit.

FIG. 3 is an explanatory diagram of the operation of the block circuit shown in FIG. 2, and the operation of the circuit of FIG. 2 will be described below with reference to this figure. It should be noted that although FIG. 3 is an explanatory diagram for the u phase, v
The phases of the phases w and w are different from each other by 2π / 3, which is the same as the case of the above u phase.

The three-phase AC voltage command V _u ^* , V _v ^* , V _w ^* as shown by V _u ^* in FIG. 3A input to the clamp circuit (19) is a clamp circuit (19 which simulates the saturation of the output voltage of the inverter. ),
Signals V _u ′, V _v ′, V _w ′ as shown in FIG. 3B are limited to a level equal to or lower than the preset peak value V _C of the triangular wave carrier.
become. V _u ′, V _v ′, V _w ′ are respectively multiplied by 1 / V _C by the amplifier (20), and the signal V _u ″, as shown in FIG. 3C,
V _v ″, V _w ″, and V _u ″, V _v ″, V _w ″ are respectively V _DC / 2 by an amplifier (21) and a multiplier (22) in order to compensate the fluctuation of the DC voltage source of the inverter. The signals are multiplied and become signals V _u , V _v , and V _w indicating the estimated value of the inverter output voltage having the peak value V _DC / 2 as shown in FIG. 3D.

Fig. 3 shows an example in which the crest value of the three-phase AC voltage command V _u ^* is larger than the crest value V _{C of the} triangular carrier wave, and the estimated output voltage of the inverter is clamped at V _DC / 2. However, if the peak value of the voltage command V _u ^* is below V _C , the peak value of the inverter output voltage is Indicated by. In the multipliers (22u) to (22w), multiplying the input voltage V _u ″ to V _w ″ by half the voltage V _DC of the DC power supply (16) of the inverter (15) is the output AC This is because the voltage reference is found to be 1/2 of the DC voltage V _DC , and the voltage is oscillated in positive and negative symmetry. The estimated value of the inverter output voltage obtained by the above is very similar to the actual inverter output voltage with no phase delay, and this value is the same as the three-phase to two-phase coordinate conversion circuit () of the inverter controller (23). As a result of being input to 8), an inverter device having extremely good variable speed control characteristics can be obtained.

In the above embodiment, the inverter control section (23) in FIG. 1 (inside the broken line) and the inverter output voltage estimated value generation circuit (11) in FIG. It can be realized by any of the software processing by the sensor.

FIG. 4 is a flow chart in the case of software processing of the inverter output voltage estimated value generation circuit (11) shown in FIG. 2, and the operation during this software processing will be described.
At step (100), this software (program) process is started at the same time when the inverter device is powered on. Three-phase AC voltage command value V _{u at} steps (101) and (102)
Check the magnitude relationship between the absolute value of the crest value of ^* and the absolute value of the crest value of the triangular wave carrier V _C. | V _u ^* | ≦ | V _C | If the inverter output voltage is determined in step (103) Calculates the ends the step (101) calculating step of said V _u consisting of - step (105) (106), the next step (1
Move to V _v calculation in 07). If │V _u ^* │> │V _C │, then if _Vu ^* is positive, go to step (104). If negative, step (105) And proceed to step (107). Step ((107),
Step (108), the inverter output voltage V _v, the estimated value of V _w is calculated as in the case of V _u in the step (106), and ends at step (109).

In the case of software processing, the operation of the block circuit shown in FIG. 2 can obtain the estimated value of the inverter output voltage by a simple process of judgment of magnitude and multiplication, as shown in the flow chart of FIG. Therefore, it is very advantageous in that the load on the microprocessor is not increased and the cost is not increased. Although a voltage detection circuit (17) for the DC voltage source (16) is required as shown in Fig. 1, generally in a PWM inverter, in order to protect main circuit elements such as transistors from overvoltage, a DC voltage source ( The voltage detection circuit (17) in 16) is indispensable, and it is not necessary to newly install it to detect the output voltage of the inverter.

Further, in the above-mentioned embodiment, the case of the PWM inverter device of the vector control system without the speed detector of the induction motor has been described, but it may be the device of the control system of the AC motor which requires the detection of the output voltage of the inverter device. The same effect as that of the above embodiment is obtained.

〔The invention's effect〕

As described above, according to the present invention, the estimated value generating means for the output voltage of the PWM inverter estimates the inverter output voltage by correcting the AC voltage command signal, which is a modulation wave, with the triangular wave carrier and the DC voltage of the inverter. Since it is configured to output the output voltage, the PT
This has the effect of eliminating the need for a voltage detector such as the one described above, and moreover, being one that is not affected by the saturation of the inverter output voltage and the fluctuation of the DC voltage.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a PWM inverter device according to an embodiment of the present invention, FIG. 2 is a block diagram showing the detailed configuration of the inverter output voltage estimated value generating circuit in FIG. 1, and FIG. Waveform diagram for explaining the operation of FIG.
FIG. 5 is a flow chart when the effect of the present invention is realized by a microprocessor, and FIG. 5 is an explanation of operation waveforms of the PWM inverter. In the figure, (1) is a speed setting circuit, (2) is a speed control circuit, (3) is a speed estimation circuit, (4) is an adder, and (5).
Is a slip frequency calculation circuit, (6) is an integration circuit, (7d),
(7q) is a current control circuit, (8) and (9) are three-phase to two-phase coordinate conversion circuits, (10) is a two-phase to three-phase coordinate conversion circuit, (11) inverter output voltage estimated value generation circuit, (12u). ~ (12w) comparator, (13) triangular wave carrier wave generation circuit, (14u)
~ (14w) is a base amplifier, (15) is an inverter, (1
6) DC voltage source, (17) DC voltage detector, (17u) ~
(17w) is a current detector, (18) is an induction motor, (19u) ~
(19w) is a clamp circuit, (20u) to (20w) and (2
1) is a widening device, (22u) to (22w) are multipliers, and (23) is an inverter controller. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A PW for speed control of an AC motor, which is controlled by a pulse width modulation signal obtained by comparing an AC voltage command signal with a modulating wave and a carrier wave input separately from the modulating wave.
In the M inverter device, an output voltage estimated value generation means for estimating the output voltage of the PWM inverter is provided, and the output voltage estimated value generation means is configured to generate one phase of the AC voltage command signal by V _U ^* , and a wave of the carrier wave. When the high value is V _C and the voltage of the DC voltage source of the PWM inverter detected by the voltage detector is V _DC , when the peak value of V _U ^* is larger than V _{C, the} above V _C
'After _{a, (V DC / 2) ×} (1 / V C) × V U' V U of the peak value of _U ^* is limited to the level below the V _C performs calculation, the V _U ^* of If the peak value is smaller than the above V _C , (V _DC /
2) A PWM inverter device characterized in that the output voltage of the PWM inverter is estimated by performing the operation of × (1 × V _C ) × V _U ^* .