JPH0340793A - Current control circuit for inverter - Google Patents

Abstract

PURPOSE:To eliminate regulation mainly at each stage by adding a feedback input of offset correction of a proportional integration amplifier during stopping to a correction value immediately after start of held operation. CONSTITUTION:An offset signal is detected from the output side of a proportional integration amplifier A1 during stopping. An offset signal is fed back to the input side of a proportional integration amplifier A1 through a correcting circuit 10 with a sample holding means (SH). Thus, it is so controlled that the offset signal becomes zero. Simultaneously, the output signal value of the circuit 10 immediately before the start of operation is held by the means SH at the time of start of operation. This is added to the input side of the amplifier A1 to be offset corrected. Thus, each time the operation is stopped, a current sine wave command and the offset value of the current detection are generally corrected. A torque ripple can be improved without regulating each stage, a signal source, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a current control circuit for a current control type voltage source inverter used for controlling an induction motor, etc. Regarding control circuits.

B0 Summary of the Invention The present invention provides a current control circuit for a current control type voltage source inverter used to control an induction motor, etc., by detecting an offset signal from the output side of the proportional-integral amplifier during operation stop; The offset signal is fed back to the input side of the proportional-integral amplifier through the correction circuit with sample and hold means, and the offset signal is controlled to be zero, and at the start of operation, the hold means outputs the output of the correction circuit just before the start of operation. holding the signal value and adding it to the input signal of the proportional-integral amplifier to perform offset correction;
The current sine wave command and current detection offset value can be comprehensively corrected each time the operation is stopped, eliminating the need for adjustments at each stage or signal source, achieving close to ideal control, and reducing torque ripple. The purpose of this project is to provide technology that significantly improves

C1 Conventional technology Vector control of induction motors is divided into excitation current and torque current, and the torque current vector and magnetic flux are always orthogonal, thereby achieving variable speed performance equivalent to or better than that of a DC motor. I am trying to do.

FIG. 3 is a block diagram showing an example of a vector control device, in which numeral 31 is an induction motor and 32 is its speed detector. A speed calculation unit 33 is connected to the speed detector 32, which calculates the speed from the detected value, compares it with the speed command N, and inputs it to the torque calculation unit 34, and calculates the torque current command value by proportional integration (Pl). A primary current calculation unit 35 calculates a primary current value from this torque current and excitation current setting value. On the other hand, the phase calculation section 36 calculates the phase angle between the torque current and the excitation current, and the slip frequency calculation section 37 calculates the slip frequency from the torque current, the excitation current, and the second-order time constant of the motor. Adding this slip frequency to the detected speed value yields the primary angular frequency.

The above-mentioned - blow mold flow value 1 phase angle and - next color frequency are input to the three-phase current calculation section 38 to calculate the primary current of the motor,
By using this current as a current command for the inverter 39, the inverter 39 supplies the primary current to the motor.

When driving an elevator, etc. with a current-controlled voltage source inverter, the inverter output current generally needs to be controlled from the DC level to the target frequency, so the current detection means is a current detector using a Hall element (Hall CT ) is used.

FIG. 4 is a configuration diagram showing a conventional current control circuit.
41 is a current detector (Hall CT), 42 is a sine wave circuit,
43 is a carrier wave circuit, 44 is a comparator, ISU is a sine wave command, and IDtl is IM! Current detection signal of current, AI and A are amplifiers, RI and R1 are butt resistors, R3 and c
l is a resistor and capacitor for PI control, and Swl is a control cutoff switch.

The current detection signal IDU detected by the Hall CT 41 and the power sine wave command ISO from the sine wave circuit 42 are matched via matching resistors R1 and R2, and then the phase difference is calculated by Pl in the matching amplifier A1, and the output is The signal is put on a carrier wave by the comparator 44 and sent to the gate circuit.

The switch Swl is turned off during operation to enable PI control by the resistor Ro and capacitor C2, but is turned on during stoppage to cut off the control. If the control is cut off,
Since the operation is stopped, theoretically, a zero value is sent to the comparator 44 when comparing the current detection signal ICU and the power supply sine wave command ISO, and the control is initialized.

D1 Problems to be Solved by the Invention However, in the conventional current control circuit described above, the offset value actually remains and is detected by the comparator 44. If there is an offset in the current command and current detection, this will cause the DC component to be superimposed on the output current.
Causes torque ripple in the induction motor.

Further, the temperature drift of the Hall CT is generally quite large, and even if zero adjustment is performed at a certain temperature, the temperature drift will be at an unacceptable level in view of the torque ripple of the induction motor due to temperature changes. Additionally, there are offsets in the current command circuit and the amplifier circuits of each stage, and these values are too large to ignore in terms of torque ripple, so conventionally an offset adjustment circuit using a variable resistor was provided. .

However, with conventional offset correction circuits, it is not possible to comprehensively correct the current sine wave command and current detection offset values every time the operation is stopped, and it is necessary to perform zero adjustment at each stage or signal source. , the control was far from ideal.

The present invention was created in view of these problems, and
The current sine wave command and current detection offset value can be comprehensively corrected each time the operation is stopped, eliminating the need for adjustments at each stage or signal source, achieving close to ideal control and reducing torque ripple. The object of the present invention is to provide an automatic offset correction circuit for a current-controlled voltage source inverter that is significantly improved.

08 Means for Solving the Problems Means for solving the above problems in the present invention is current control of an inverter equipped with a proportional-integral amplifier that matches a current sine wave command and a current detection signal and outputs a command current to a gate circuit. In the circuit, an offset signal is detected from the output side of the proportional-integral amplifier while the operation is stopped, and the offset signal is returned to the input side of the proportional-integral amplifier via a correction circuit with sample and hold means, so that the offset signal becomes zero. At the start of operation, the output signal value of the correction circuit immediately before the start of operation is held by the holding means, and this is added to the input signal of the proportional-integral amplifier to perform offset correction.

11 Effects The present invention comprehensively detects the current sine wave command and the offset value of current detection every time the operation is stopped, and adds the value as a correction amount to the input of the matching amplifier to perform operation.

In the present invention, the proportional-integral amplifier that matches the current sine wave command and the current detection signal is provided with a correction circuit having an output extraction means and an integrating means, and the extraction means generates an offset signal from the output of the proportional-integral amplifier during operation stop. is detected, and the integrating means holds a correction value based on the output of the extracting means at the start of operation.

This correction value is constantly fed back to the input of the proportional-integral amplifier through a closed loop while the motor is stopped, so that the output of the amplifier becomes zero. Then, at the start of operation, the optimal correction value held in the integrating means immediately before the start of operation is automatically used, and the offset of the entire current control circuit is corrected to a zero value.

The automatic offset correction circuit of the present invention can be implemented in analog or digital format. In the case of analog, for example, an inverting amplifier can be used as the extraction means and an integrating amplifier can be used as the integrating means. In that case, a switch etc. can be used as the sample and hold means. In the digital case, for example, if you use a counter as an extraction means and connect an integrating amplifier to the ladder resistor corresponding to each stage, it becomes an integrating means. In this case, a gate circuit may be provided in front of the counter as a sample and hold means.

G. Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of an automatic offset correction circuit of the present invention. In the figure, 1 is a current detector (
Hall CT), 2 is a sine wave circuit, 3 is a carrier wave circuit, 4 is a comparator, 5 and 6 are output points, ISU is a power supply sine wave command, IDU is an induction motor line current detection signal, A+, '
A1. As, A4 are amplifiers, R+, nt are butt resistors, R3 and CI are resistors and capacitors for PI control,
R,,It,,n.

Rq, Re, Re, and Rho are circuit resistances, R11 is an offset correction input resistor, C6 is an integrating capacitor, and SW and S w t are turned off when the motor is in operation and turned on when the motor is stopped. When the switch SW+ is turned on when the operation is stopped, the control of the amplifier A is cut off, and the switch Swt is turned off when the operation is started, forming sampling and holding means for holding the sample at that time. lO is a correction circuit that is affected by each of the above elements.

Here, the power supply sine wave command l5tl and the current detection signal IDU at the time of operation stop are ideally zero, but
Actually, a value corresponding to the offset remains, and its total value is detected at output point 5 of amplifier A.

However, at this time, the switch Sw+ is on. This total value is inverted by amplifier A and input to integrating amplifier A4. The output of amplifier A4 is detected at output point 6 and is input to the input side of amplifier A via offset correction input resistor R8. At this time, the value of the output point 6 is controlled so that the value of the output point 5 becomes zero when the operation is stopped, and when the value is zero, an equilibrium state is reached. That is, the value at output point 6 at this time becomes the total offset correction value.

At the start of operation, switches Sw and Sw are turned off. By turning off the switch Swt, the offset immediately before the start of operation is held, and this held correction value is added to the input of the amplifier A to perform offset correction.

In addition, in this circuit, the value of output point 6 may cause a time drift due to the input bias of amplifier A4 during operation.
For elevators, which have a maximum operating time of about 30 to 60 seconds, this value is small and does not pose a problem.

This embodiment has the following effects.

(+) The offset value of the iJ flow sine wave command current detection is comprehensively corrected every time the operation is stopped.

(2) Offset correction enables near-ideal control and greatly improves motor torque ripple.

As a result of actual driving, compared to the case without comprehensive correction value,
/2 to 1/3.

(3) There is no need to make adjustments at each stage or signal source, and the overall offset is automatically corrected.

(4) The offset correction method is simple and inexpensive.

FIG. 2 is a block diagram showing another embodiment of the automatic offset correction circuit 10 of the present invention. In the figure, 1 is a current detector (Hall CT), 2 is a sine wave circuit, 3 is a carrier wave circuit, 4 and 8 are comparators, 5.6 and 7 are output points,
9 is an up/down counter, O is an oscillation circuit, IsU is a power supply sine wave command, IDU is an induction motor line current detection signal,
CLK is a clock, A1. A*, A3 is the amplifier, R1
, Rt are butt resistors, R3 and C1 are resistors and capacitors for pt control, R4, Rs, Re, Rt, Re, R
e and Rlo are circuit resistances, R1 is offset correction input resistance, R1, , R, , R, and R+5 are ladder resistances,
Sw.

is a switch that cuts off control.

Here, the power supply sine wave command l5tl and the current detection signal IDIJ at the time of operation stop should ideally be zero, but in reality, an offset value remains, and the total value is determined by the amplifier A1. Output to output point ■5. However, at this time, the switch Sw is on. The polarity of this output point O is determined by the second comparator 8, and the gate circuit (
The signal is input to the counter 9 via the sample and hold means SH consisting of a logic IC. An oscillation circuit 10 is connected to the input side of the counter 9, and its clock CL'
In this case, when the polarity of the detection point 5 is positive, the counter 9 is DOWN.
When the polarity of point 5 is negative, t of counter 9
It is input to the JP terminal. On the output side of the counter 9 is a ladder resistor RI corresponding to each stage (A, B, C, D) of the count value.
~R+s are connected, and the output of any of the ladder resistors is detected at point 6 by amplifier A3 and added to the input of amplifier A1 via offset correction input resistor R0.

The ladder resistors RIP to RI5 and the amplifier A constitute D/A conversion. In addition, the signal value at output point 6 is controlled so that the value at output point 5 becomes zero, and an equilibrium state is reached at the zero value, and the value at output point 6 at this time is the total offset correction value. .

AND gate G I-+ and G1 of the logic IC
-2 is configured to receive an "H" or "Lo" signal indicating the operating state, and during operation, the output point 7 is "L".
”, the clock CLK is not input and the total offset correction value is held. Therefore, each time the operation is stopped, the offset at that time is comprehensively corrected, making ideal current control possible. Furthermore, since the sample and hold value is held by the count value of the counter 9, there is no time drift in the value at the output point 6.

In addition, in the figure, the OR gates G, -4 and G of the logic IC
t-1 and the backflow prevention elements G, -1 and G, -2 are provided to prevent the counter 9 from overflowing. Furthermore, although the counter 9 is shown as having 4 bits, in order to perform offset adjustment precisely, the desired precision can be obtained by increasing the number of bits of the counter and the number of digits of the ladder resistance.

This embodiment has the following effects.

(1) The current sine wave command and the offset value of current detection are comprehensively corrected every time the operation is stopped.

(2) Offset correction enables near-ideal control and greatly improves motor torque ripple.

(3) There is no need to make adjustments at each stage or signal source, and the overall offset can be rejected without any adjustment.

(4) The offset correction method is simple and inexpensive.

(5) There is no integration circuit in the extraction means, hold is performed digitally, there is no problem of time drift in offset correction, and it can be used with confidence even in applications with long operating times.

H. Effects of the Invention As explained above, according to the present invention, the current sine wave command and the current detection offset value can be comprehensively corrected each time the operation is stopped, easily and inexpensively, and each stage and signal source It is possible to provide an automatic offset correction circuit for a current control type voltage source inverter that does not require any adjustment, enables ideal control, and significantly improves torque ripple.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a block diagram of another embodiment of the present invention, Fig. 3 is a block diagram of a motor vector control circuit, and Fig. 4 is a block diagram of a conventional example. FIG. l... Current detector, 2... Sine wave circuit, 3... Carrier wave circuit, 4, 8... Comparator, 5, 6.7...
・Output point, 9...Counter, lO...Correction circuit, S
H...sample hold means, 0...oscillation circuit, l
5tl...Power supply sine wave command, IDtl...Current detection signal, CLK...Clock, At, At, As,
A4...Amplifier, R1, Rt'...Butt resistance, R8...PI control resistance, R4-R3゜...Circuit resistance, R8,...Offset correction input resistance, R1゜~
R81...Ladder resistance, CI, CI...Capacitor,
Sw□, Swl...Control cutoff switch.

Claims (1)

[Claims] (1) Match the current sine wave command and the current detection signal,
In a current control circuit of an inverter equipped with a proportional-integral amplifier that outputs a command signal to a gate circuit, an offset signal is detected from the output side of the proportional-integral amplifier while the operation is stopped, and a correction circuit with a sample-hold means is used to detect the offset signal. is fed back to the input side of the proportional-integral amplifier and controlled so that the offset signal becomes zero, and at the start of operation, the hold means holds the output signal value of the correction circuit immediately before the start of operation and uses it as the proportional-integral amplifier. An inverter current control circuit characterized by performing offset correction by adding it to an input signal of an integrating amplifier.