JP3256814B2 - Control device for polyphase power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a polyphase power converter for supplying AC power to a load via a transformer.
In particular, the present invention relates to a power converter control device that is suitable in the field of using a power converter that requires a large capacity.

[0002]

2. Description of the Related Art As a method of controlling demagnetization of a transformer used in a multiphase power converter such as an inverter, there is a method of correcting a DC component of a voltage command value according to an average value of one cycle of an exciting current. Normally, the integration result of one cycle of the excitation current is zero, but when a magnetic bias occurs, the amount of the magnetic bias current is superimposed and does not become zero. The DC component of the voltage command value is adjusted in a direction to reduce the bias current according to the polarity of the integration result. An example of this is disclosed in
There is an apparatus as disclosed in Japanese Patent Publication No. 5365.

Further, there is a method in which the positive / negative current maximum value near the maximum of the transformer magnetic flux density is sampled and held, and the amount of magnetization is detected from the difference between the two. An example of this is disclosed in
There is an apparatus as shown in JP-A-93475.

[0004]

SUMMARY OF THE INVENTION Japanese Patent Application Laid-Open No. Sho 64-5365
In the conventional device described in Japanese Patent Application Laid-Open Publication No. H11-107, the detection of the amount of demagnetization is detected by integration of one cycle of the current, so that the integration is performed over one cycle including the offset of the detector. The current detector detects a current including a load current and an exciting current. Normally, the ratio of the exciting current to the load current is very small, about several percent to about 10%. Therefore, there is a problem in that the offset component cannot be ignored with respect to the exciting current component to be detected, so that the accuracy of the demagnetization detection decreases.

In the conventional device described in Japanese Patent Application Laid-Open No. 3-93475, since the maximum value of each of the positive and negative values of the exciting current is sampled and held, if the instantaneous current value is erroneously detected due to noise, etc. It is assumed that magnetism has occurred. In this case, an erroneous detection signal is input to the demagnetization suppression control circuit, and the normal demagnetization suppression operation is not performed.

The present invention has been made in view of the above circumstances, and can reduce the influence of an offset of a current detector for detecting an exciting current of a transformer and prevent erroneous detection due to noise . It is an object of the present invention to provide a control device for a multi-phase power converter that can improve the accuracy of the magnetic bias control .

[0007]

A control device for a polyphase power converter according to the present invention comprises a PW converter for converting a direct current to an alternating current.
M, and the output AC of the power converter is
In a control device for a polyphase power converter for supplying a load, an exciting current detection for detecting an exciting current of each phase of the transformer from a difference between a primary current and a secondary current of each phase of the transformer. Means and said excitation
Average value of exciting current of each phase detected by current detecting means
The average value is subtracted from the excitation current of each phase to calculate
An excitation current compensating means for obtaining an exciting current of the exciting current complement
More phases of excitation currents determined in amortization means for each cycle
A polarization compensating means for integrating and correcting the pulse width of the PWM control based on the integrated value .

[0008]

In the control device for a multi-phase power converter having the above configuration, the primary current of each phase of the transformer is detected by the exciting current detecting means.
The exciting current of each phase of the transformer is detected from the difference between the current and the secondary current , and based on this, the exciting current compensating means detects the exciting current.
Subtract the average value of the exciting current of each phase from the exciting current of each phase.
Thus, the offset component included in the detected exciting current and the component due to the unbalance of the power supply of each phase are removed . Soshi
The demagnetization compensator means that the compensated excitation current of each phase
Integrate every period to obtain the integral value corresponding to the amount of magnetic declination.
The pulse width of PWM control to reduce the amount of magnetism
I do. As a result, the magnetic bias of the transformer can be reduced.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of an embodiment of a control device for a polyphase power converter according to the present invention. In FIG. 1, AC power output from an AC power supply 1 is converted into DC power by a converter 2, returned to AC power by a power converter 21, and then supplied to a load 5 via a transformer 4. The control device according to the present invention includes a demagnetization suppression control circuit 10, a control circuit 31, a reference pulse generation circuit 32, and a gate pulse generation circuit 33.

By the way, the capacitor 3 is connected between the load 5 and
Since the DC voltage, which is the voltage across the capacitor 3, fluctuates by charging and discharging through the power converter 21 and the transformer 4, the output voltage is adjusted by the converter 2 and the DC voltage is adjusted by the control circuit 31. There is a need. Therefore, the control circuit 31 takes in the voltage between the terminals of the capacitor 3 directly, takes in the input voltage of the load 5 from the instrumentation transformer 8, takes in the current supplied to the load from the instrumentation current transformer 7, and Control the value.

The control circuit 31 outputs a voltage V * applied to the load and a phase difference command φ * based on the detected values. The reference pulse generation circuit 32 supplies an on / off pulse for obtaining a desired output voltage from V * and φ * to the power converter.

The control device for a polyphase power converter according to the present invention has a demagnetization suppression control circuit 10 for suppressing the demagnetization of a transformer provided on the output side of a power converter (inverter) 21. I have. i1 and i2 are a load side current and a converter side current, respectively. Here, the load side is defined as primary, and the converter side is defined as secondary. The current on the converter side is detected by the current transformer 6 for the instrument. Switching angle information θP in addition to the gate pulse of polarized磁抑system control circuit 10 in the current i1, i2, as input .theta.N, and an input of each phase of the reference signal Sy.

At the time of occurrence of magnetic declination, pulse width corrected switching angle information θP ′ and θN ′ are output. The gate pulse generation circuit 33 generates a gate pulse to be supplied to the power converter 21 based on the pulse width corrected switching angle information θP ′ and θN ′ from the demagnetization suppression control circuit 10.

Next, FIG. 3 shows a specific configuration of the demagnetization suppression control circuit 10. As shown in FIG. Referring to FIG. 1, an excitation current detection circuit 101 includes circuit configurations 1011, 1012, and 1013 for three phases, and detects the excitation current of each phase. Excitation current detector 101
In step 1, the exciting current i0U is output from the ampere-turn difference between the U-phase primary current i1U and the secondary current i2U of the transformer for one bridge. If the secondary conversion current of i1U is i1U ', then i2U
The excitation current i0U can be obtained by subtracting i1U 'from. Similarly, i0v and i0w are obtained for the V phase and the W phase. The detector unbalance compensation circuit 201 compensates for imbalance between three phases and offset of an operational amplifier or the like at the time of current detection. The exciting currents i0U, i0v, i0w of each phase are added to an adder 201.
The result obtained by averaging three phases by the averaging circuit 2012 is given to the subtractors 2013, 2014, and 2015 to obtain excitation currents i0U ', i0v', and i0w 'from which noise on the circuit has been removed.

Next, in the demagnetization compensation circuit 301, the demagnetization compensation circuit 301 of each phase is provided for each phase for one cycle of the exciting current.
At 1, 3012, and 3013, demagnetization compensation is performed and pulse width correction is performed.

Next, the operation of the demagnetization suppression control will be described. FIG.
3 shows a specific configuration of the demagnetization compensation circuit in FIG. 3, and FIG. 2 shows operation waveforms of the respective circuits in FIGS. 1, 3, and 4. With reference to these drawings, the operation will be described focusing on the U phase. For example, assuming that a voltage waveform v as shown in FIG. 2A is output from the reference pulse generating circuit 32 and applied to the winding of the transformer, the magnetic flux density B is integrated and the waveform as shown in FIG. Becomes When the magnetism is not generated in the iron core, the exciting current waveform i0 has a waveform substantially similar to that of FIG. When the magnetic bias occurs, the exciting current becomes excessive in the first part where the magnetic flux density B takes a peak value,
The current waveform is as shown in FIG. The portion indicated by a circle in this figure shows a case where the magnetic field is deflected to the positive side. In the voltage waveform, a magnetizing current is likely to occur near the last portion θP of the continuing positive voltage pulse and near the last portion θN of the continuing negative voltage pulse.

Therefore, the detection of magnetic flux demagnetization of the transformer can be achieved by measuring the positive / negative imbalance for one period of the exciting current i0 of each phase since the magnetic flux is almost proportional to the exciting current. That is, one cycle of the exciting current i0 of each phase is integrated. By controlling the pulse width in a direction that cancels the polarity of the value of the integration result, it is possible to suppress the magnetization. The operation will be specifically described.

FIG. 2D shows a U-phase reference signal Syu. The phase detector 3021 of the U-phase demagnetization compensation circuit 3011 detects the phase based on the U-phase reference signal Syu, and the reset signal generator 3022 outputs a U-phase integration reset signal (FIG. 2).
(E)) is obtained. The generation phase of the U-phase integration reset signal is generated at each midpoint of two positive pulses of the reference pulse having the voltage waveform of FIG.

A sample and hold signal generator 3023
Obtains a U-phase sample signal (FIG. 2 (g)). The generation phase of the U-phase sample signal is generated at the falling point of the pulse before the two positive-side pulses of the reference pulse having the voltage waveform of FIG.

A P multiplication reference generator 3024 obtains a P multiplication signal (FIG. 2 (k)). This P-multiplied signal has a limited time width tw centered on the falling point of the pulse after the two positive pulses of the reference pulse of the voltage waveform (FIG. 2A) and has a value of "1". It is a pulse.

The N multiplication reference generator 3025 obtains an N multiplication signal (FIG. 2 (l)). The N-multiplied signal has a limited time width tw centered on the falling point of the pulse after the two negative pulses of the reference pulse of the voltage waveform (FIG. 2A) and has a value of "1". It is a pulse.

The integrator 3026 integrates the exciting current i0U 'signal from the U-phase reset signal to the next U-phase reset signal. FIG. 2F shows the result of integration. FIG.
When the magnetic field is polarized as in (c), the result of one-period integration is not zero, and the integrated value remains for h. The remaining integral value h is stored in the sample and hold unit 3027 as a sample signal generated by the sample and hold signal generator 3023.

The integral correction SH (FIG. 2 (h)) which is the output signal of the sample hold unit 3027 is held until the sample signal output at the next timing.

Next, in the gain elements 3028 and 3029, pulse correction widths Δθ Pu and Δθ Nu are obtained from the integral correction amount SH. The gain characteristics are reversed left and right at 3028 and 3029 because the pulse width correction direction for suppressing the demagnetizing current has the opposite relationship between the positive side pulse and the negative side pulse. Since SH> 0, the phase compensation amount Δθ PU becomes Δθ PU <0 due to the gain elements 3028 and 3029 (FIG. 2).
(I)), the phase compensation amount ΔθNU becomes ΔθNU> 0 (FIG. 2)
(J)).

The multiplier 3030 multiplies the phase compensation amount ΔθPU by the P multiplication signal , and calculates the switching angle θPU of the reference pulse voltage output from the reference pulse generating circuit 32 in the cycle immediately after the cycle in which the magnetic field is demagnetized. At the timing synchronized with the P multiplication signal, correction is made by Δθ PU and the switching angle θ
To reduce the P.

The multiplier 3031 multiplies the phase compensation amount ΔθNU by the N multiplication signal , and calculates the switching angle θNU of the reference pulse voltage output from the reference pulse generating circuit 32 in the cycle immediately after the cycle in which the magnetization has occurred. , corrected by ΔθNU at a timing synchronized with the N multiplied signal, to increase the switching angle ShitaNU. That is, the adder 3032
And ΔθPU to obtain θPU ′. The adder 303
3 adds θNU and ΔθNU to obtain θNU ′.

In the example shown in FIG. 2 (m), the demagnetization current indicated by a circle is in the positive direction, so that after detecting the demagnetization, the width of the positive side pulse is narrowed and the width of the negative side pulse is widened. Period θP,
Reflected in θN, the bias current can be suppressed.

Similarly, the timing of the V-phase demagnetization control is
The phase reset signal (FIG. 2 (n)) and the V-phase sample signal (FIG. 2 (p)) are used. The timing of the W-phase demagnetization control is based on the W-phase reset signal (FIG. 2 (o)) and the W-phase This is performed by the sample signal (FIG. 2 (q)).

In the present invention, since the detection accuracy of the amount of magnetization can be increased, the present invention is sufficiently applicable to applications where the DC voltage is high.

The above embodiment can be realized by software processing using a microcomputer. In this case, hardware for demagnetization suppression control is not required, and the circuit configuration can be implemented only by adding a part of software of a control device of a normal power converter.

[0031]

According to the present invention as described above,
Inverter of each phase of the current detector that detects the exciting current of the transformer
False detection due to lance, drift, offset, noise, etc.
Can be prevented, the accuracy of the control for suppressing the magnetizing of the transformer can be improved, and the power converter can be operated in a stable state.

Further, since the magnetic bias of the transformer can be suppressed with high accuracy, the magnetic flux density of the iron core can be designed to be higher and the size and weight can be reduced.

Further, since the overcurrent due to the magnetic polarization can be suppressed, the overcurrent can be prevented from being destroyed due to the magnetic polarization of the semiconductor switch used in the power conversion circuit. Further, it becomes easy to increase the capacity of the self-excited converter by transformer multiplexing.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a control device for a polyphase power converter according to the present invention.

FIG. 2 is a waveform diagram showing an operation state of each unit of the control device of the multiphase power converter shown in FIG.

FIG. 3 is a block diagram showing a specific configuration of a demagnetization suppression control circuit in FIG. 1;

FIG. 4 is a block diagram showing a specific configuration of a magnetic bias compensation circuit in FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply 2 Converter 3 Capacitor 4 Transformer 5 Load 6 Current detector 7 Current detector 8 Instrument transformer 10 Depolarization suppression control circuit 21 Power converter 31 Control circuit 32 Reference pulse generation circuit 33 Gate pulse generation circuit 101 Excitation Current detection circuit 201 Detector unbalance compensation circuit 301 Demagnetization compensation circuit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-93475 (JP, A) JP-A-4-1933063 (JP, A) JP-A-4-207797 (JP, A) JP-A-4-199 207974 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H02M 7/537

Claims (1)

(57) [Claims] 1. A power converter for converting DC to AC is a PW converter.
M, and the output AC of the power converter is
A control device for a polyphase power converter for supplying a load , wherein the transformer is determined based on a difference between a primary current and a secondary current of each phase of the transformer.
Exciting current detecting means for detecting the exciting current of each phase of the device, and the exciting current of each phase detected by the exciting current detecting means .
Obtain the average value and subtract the average value from the excitation current of each phase.
An excitation current compensating means for determining respective phases of the exciting current Te, the exciting current of each phase determined by the excitation current compensating means
Integrates every cycle, and based on the integrated value, the PWM system
A control device for a polyphase power converter, comprising: a polarization compensating means for correcting a control pulse width.