JP4775101B2 - AC-AC direct conversion device - Google Patents

Description

  The present invention relates to an AC-AC direct conversion device (matrix converter) that converts a voltage or frequency input from a single-phase or multi-phase AC power source into an arbitrary voltage or frequency and outputs the voltage or frequency. The present invention relates to reactive power control when driving.

  This type of AC-AC direct conversion device that has existed in the past switches a bidirectional switch using a self-extinguishing semiconductor element at high speed, and converts a single-phase or multi-phase AC input to power of an arbitrary voltage or frequency. FIG. 5 shows a basic configuration of a conversion device for conversion. An input filter (InputFilter) 2 and an AC-AC direct conversion circuit 3 having bidirectional switches S1 to S9 are inserted in the R, S, and T phases of the three-phase AC power source 1, and both are controlled by a controller (controller) 4. By performing PWM control of the direction switch at a frequency sufficiently higher than the power supply frequency, an AC output of U, V, W controlled to an arbitrary voltage or frequency is obtained while directly applying an input voltage to a load Load such as a motor.

  The switching pattern of the bidirectional switch in the AC-AC direct conversion device includes, for example, a PWM converter pattern that is a signal synchronized with the input voltage and a PWM inverter pattern that is created according to the output frequency and voltage in the case of a modulation method using carrier amplitude. And the AND condition. As a result, the input current of the AC-AC direct conversion device is limited by the PWM converter pattern, the output voltage and frequency are controlled by the PWM inverter pattern, and the input current is converted to a sine wave and output while keeping the input power factor “1”. Realizes waveform sine wave and frequency conversion at the same time. The bidirectional switch may be configured by using a plurality of unidirectional switches as shown in the figure.

In the AC-AC direct conversion device as described above, the input power factor is generally controlled to “1”, but the input power factor may be controlled, that is, reactive power may be actively controlled. The reactive power is controlled by controlling the phase difference Δθ between the input current vector and the input voltage vector of the converter according to the reactive power command value. In addition, a method for estimating the phase difference Δθ on the power supply side without using an input current detector and a voltage detector for power factor control of the PWM cycloconverter has been proposed (see, for example, Patent Document 1).
JP 2001-69759 A

The AC-AC direct conversion device converts the current, voltage, and frequency arbitrarily by directly connecting the AC power supply and the load. Therefore, the input current is reduced in the low load state, and there is no reactive power control device in parallel with the power supply. When the load is driven alone, the amount of reactive power that can be generated on the AC power supply side is also limited.
In addition, in a device configuration in which a DC circuit is inserted by a combination of a PWM converter and a PWM inverter, reactive power control can be performed independently of the load state using an input AC reactor and converter (however, the load Care must be taken when the device rated capacity exceeds the required active energy and the reactive energy controlled by the input), and when an AC-AC direct conversion device without a DC circuit is used alone, it is controlled independently. I can't. Further, when controlling the output voltage of the AC-AC direct conversion device, there is a problem that if the reactive energy corresponding to the load current at that time is randomly controlled, the voltage according to the output voltage command is not faithfully output.

  An object of the present invention is to provide an AC-AC direct conversion device capable of controlling the amount of reactive power independently of the load state and capable of performing stable reactive power control without causing waveform distortion.

  The present invention for solving the above-described problems is characterized by the following configuration.

(1) Reactive power is supplied to each phase of a single-phase or multi-phase AC power source by a control device that is connected to a load via an AC-AC direct conversion circuit having a bidirectional switch configuration and performs PWM control of each bidirectional switch. In the AC-AC direct conversion device to be controlled,
The magnitude | Is | of the input current Is of the AC-AC direct conversion circuit is estimated from the matching condition between the input active power including the power conversion efficiency η of the AC-AC direct conversion circuit and the active power required by the load. The phase difference Δθ of the input current Is with respect to the power supply phase voltage Vs is estimated from the magnitude of the input current | Is |, the magnitude of the power supply phase voltage Vs | Vs |, and the reactive power command value Qref, and the magnitude of the input current Is | Is |, arithmetic means for estimating the input current Is required for reactive power control from the power supply phase voltage Vs and the phase difference Δθ,
The control device adjusts the phase difference Δθ in accordance with the input current Is estimated by the calculation means, the power supply phase voltage Vs, the output current I ₀ , and the output phase voltage command value Vrefp, whereby AC-AC direct The reactive power of the conversion circuit is controlled.

(2) The calculation means is configured to perform an estimation calculation of the estimated input current Is and an estimation calculation of the phase difference Δθ in parallel.
(3) The computing means limits the magnitude | Is | of the estimated input current Is so as to be a value obtained by multiplying the magnitude | I ₀ | of the output current I ₀ by a preset coefficient value. It is provided with.

  (4) The calculation means includes means for limiting the maximum value of the phase difference Δθ to a preset value.

  As described above, according to the present invention, the amount of reactive power can be controlled independently of the load state, and further, stable reactive power control can be performed without causing waveform distortion.

  Specifically, by deriving the magnitude of the input current and the phase difference between the input current vector and the input voltage vector from the matching condition between the output voltage command and the active power, the desired reactive energy can be obtained even if the load fluctuates. The input current phase can be controlled so as to be obtained on the power supply side.

  In addition, the calculation of the input current command value | Is | and the input current voltage phase difference Δθ necessary for a control device having a reactive power control function is simplified in advance, and the feedback loop is eliminated in the control, thereby speeding up the calculation. Can be expected.

In addition, the input current command value is limited to a preset value in consideration of the maximum current / voltage utilization ratio of 0.866, which is a fundamental constraint for controlling the input / output current voltage waveform without distortion. Thus, distortion can be prevented. In addition, since the input current command value based on the output current detection value I ₀ is limited, the limit value can be changed at any time according to the state of the load, and load fluctuations can be dealt with.

  In addition, when a reactive power command is given at a low load, by limiting the maximum value of the phase difference Δθ to a preset value, it is possible to always avoid a condition that easily causes unstable operation.

(Embodiment 1)
FIG. 1 is a configuration diagram of an AC-AC direct conversion device showing an embodiment of the present invention, and shows a calculation block configuration of reactive power control added to the control device 4.

  First, reactive power control according to the present embodiment will be described in principle. In the configuration of a general AC-AC direct conversion device as shown in FIG. 5, when a reactive power control device or the like is not connected in parallel to the AC power source 1 and the load is driven by the device alone, the load is low Since the input current for controlling the reactive power is also small, the amount of reactive power that can be controlled depends on the active power required by the load.

  Now, assuming that the exchange of active power coincides with the input and output of the AC-AC direct conversion device, the power conversion efficiency of the AC-AC direct conversion circuit can be defined as shown in equation (1).

Where η is the power conversion efficiency, Vs is the power source side input phase voltage, Is is the input current, cos θ is the input power factor, Vrefp is the output phase voltage command value, I ₀ is the output current, and cos φ is the output power factor.

Considering the case where the power supply phase voltage Vs and the output current I ₀ are detected from the coincidence condition of the equation (1), and the output according to the output phase voltage command Vrefp is generated to perform the AC-AC direct conversion, the output power factor is considered. cos φ can be obtained from the phase relationship between the output phase voltage command Vrefp and the output current I ₀ . Therefore, the unknown amount is the magnitude of the input current Is and the input power factor cos θ.

  Here, when the relationship between the input current Is, the input power factor cos θ, and the reactive power command value Qref is defined as in the equation (2), the magnitude of the input current Is is calculated from the simultaneous equations of the equations (1) and (2). In addition, the necessary phase difference Δθ between the input current Is with respect to the power supply phase voltage Vs can be obtained.

From the above, in this embodiment, the calculation blocks 11 to 17 shown in FIG. 1 estimate the input current (magnitude and phase) necessary for reactive power control according to the reactive power command value Qref, and the reactive power by the control device. Allows control.
The calculation block 11 calculates the absolute value (magnitude) | Vs | of the power supply phase voltage Vs, the calculation block 12 calculates the magnitude | I ₀ | of the output current I ₀ , and the calculation block 13 calculates the magnitude of the output voltage command Vref. | Vref | is obtained. The calculation block 14 obtains the output power factor cos φ from the phase of the output current I ₀ and the output voltage command Vref.
The calculation block 15 receives the power supply phase voltage Vs, the output current I ₀ , the output phase voltage command Vrefp, and the output power factor cos φ from the calculation blocks 11 to 14, and further converts the conversion efficiency η and the level of the conversion circuit. The above equation (1) is calculated from the phase difference (estimated value) Δθ to obtain the estimated magnitude | Is | of the input current Is.
The calculation block 16 performs the calculation of the above equation (2) from the magnitude of the input current | Is |, the magnitude of the power supply phase voltage | Vs |, and the reactive power command value Qref, and calculates the estimated input current Is with respect to the power supply phase voltage Vs. A phase difference Δθ is obtained. The calculation block 17 obtains a vector (phase and magnitude) of the estimated input current Is from the magnitude | Is | of the estimated input current, the power supply phase voltage Vs, and the phase difference Δθ.
More arithmetic blocks 11 to 17 by the vector of the estimated input current Is (phase and magnitude) is determined, the control unit 4 and the estimated input current Is, the detection value of the power supply phase voltage Vs output current I _0, and the output The input power factor cos θ is controlled from the phase voltage command value Vrefp with the active power corresponding to the output current I ₀ , that is, the input of the AC-AC direct conversion circuit 3 so as to obtain the reactive power amount according to the reactive power command value Qref. The current phase θ is controlled.
According to the present embodiment, the magnitude and phase of the input current Is at that time are estimated from the matching condition between the input active power of the AC-AC direct conversion circuit and the active power required by the load, and the level of the power supply phase voltage Vs is estimated. Since the phase difference Δθ is adjusted, arbitrary reactive power control can be performed as instructed even when the load condition (active power) changes.

(Embodiment 2)
Solving the simultaneous equations of the above equations (1) and (2) yields equations (3) and (4).

In the present embodiment, as shown in the operation block configuration in FIG. 2, calculations are performed according to equations (3) and (4) to control reactive power. The calculation blocks 11 to 14 and 17 are the same as those in FIG. 1, and the calculation block 21 calculates the magnitude of the estimated input current Is by calculating according to the expression (3) from the calculation output, the efficiency η, and the reactive power command Qref. Is | is calculated | required and the calculation block 22 calculates | requires phase difference (DELTA) (theta) by the calculation according to (4) Formula.
According to the present embodiment, in addition to being able to control reactive power according to the load state as in the first embodiment, since there is no feedback loop of the estimated phase difference Δθ, high speed control can be expected by these parallel operations. .

(Embodiment 3)
In the first and second embodiments, the input current of the actual AC-AC direct conversion circuit 3 is compared with the input current control according to the magnitude of the input current Is obtained by the calculation of the expression (3) according to the reactive power command value. When the value also flows as it is, a desired reactive power amount is obtained.
On the other hand, in the case of an AC-AC direct conversion circuit, the output voltage waveform can be output in the reverse phase, so the envelope of the output voltage waveform is composed of 6-phase AC including the reverse phase. For this reason, the maximum value of the voltage / current utilization rate at which the AC-AC direct conversion device can control the input / output waveform without distortion is 0.866. Beyond that, a sinusoidal current-voltage waveform cannot be obtained, but the estimated input current command value obtained by equation (3) is a calculation derived from the input current value required for the reactive power command. For this reason, there are cases in which 0.866 times the magnitude of the load current is exceeded, ignoring the constraints in principle. If it is given as it is as a command value, the actual input current will not be as large as the estimated input current command value, but errors and distortion will be produced, and only the input current Is in equation (3) will be increased.
Therefore, in this embodiment, in addition to the first embodiment, the estimated input current magnitude | Is | and the output current detection value magnitude | I ₀ | are always compared, and | Is |> 0.866 × | I _0. When |, the reactive power command value Qref is limited, that is, the magnitude | Is | of the input current Is in Expression (3) is limited.
FIG. 3 is a control block diagram of the present embodiment, and operation blocks equivalent to those in FIGS. 1 and 2 are denoted by the same reference numerals. The calculation block 16 calculates the input phase difference Δθ by calculation according to the equation (2), and the calculation block 21 calculates the magnitude | Is | of the input current by calculation according to the equation (3). Here, in the present embodiment, an arithmetic block 31 is inserted that limits | Is |, which is an input of the arithmetic block 16, by 0.866 × | I ₀ |.
By the insertion of the calculation block 31, the phase difference Δθ in the equation (4) is also limited, and no distortion occurs. However, at this time, the reactive power amount according to the reactive power command value cannot be obtained, and it is limited by an arbitrary value depending on the load current. However, the reactive power control that gives priority to the prevention of waveform distortion is obtained. Can do.
According to this embodiment, when the reactive power command value exceeds the theoretical constraint, it is saturated, so that an estimated input current command value error and waveform distortion can be prevented.

The limit value is not limited to the above 0.866 × | I ₀ | but can be determined based on the state of the load current I ₀ and can be limited while changing in real time according to the load condition.

(Embodiment 4)
As is clear from the above equation (4), when the reactive power command is largely given at low load when the active current (output current I ₀ × cos φ) is small, a state in which the phase difference Δθ between the input current and the voltage increases frequently occurs. . The phase difference of ± 90 degrees is the maximum value, but under the condition with a large phase difference, the numerator in the equations (2) and (4) is larger than the denominator, and θ is extremely variable and constant. Exceeding the ratio may cause instability in a real machine with many disturbances.
Therefore, in the present embodiment, as shown in FIG. 4, in addition to the restriction of the input current magnitude | Is | in the third embodiment, a calculation block 41 that restricts the unstable phase difference Δθ predicted at the time of low load is provided. Provide. The limit of the phase difference Δθ is set in advance with a maximum fluctuation range. The determination of the fluctuation range is arbitrary, but here, as an example, if ± 60 degrees is set as the θ maximum value, if a phase difference Δθ exceeding ± 60 degrees is input, it is forcibly saturated at the limit value If the phase difference Δθ within ± 60 degrees is given, the limit value of the input current | Is | in the calculation block 31 in the third embodiment is maximized.
According to this embodiment, it is possible to prevent abnormal control of the phase difference Δθ that becomes variable when a reactive power command value is given at low load, and to avoid unstable operation. When restricted, the reactive power amount does not coincide with the command value, but reactive power control giving priority to avoiding unstable operation can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS The block diagram of the alternating current-alternating-current direct conversion apparatus which shows Embodiment 1 of this invention. The reactive power control circuit diagram which shows Embodiment 2 of this invention. The reactive power control circuit diagram which shows Embodiment 3 of this invention. The reactive power control circuit diagram which shows Embodiment 4 of this invention. The basic block diagram of an alternating current-alternating current direct conversion apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 AC power source 2 Input LC filter 3 AC-AC direct conversion circuit 4 Control device 11-17 Calculation block 21, 22 Calculation block 31 Calculation block 41 Calculation block

Claims (4)

AC that controls reactive power by a control device that performs PWM control of each bidirectional switch by connecting to each phase of a single-phase or multiphase AC power source via a direct-current AC / AC conversion circuit having a bidirectional switch configuration. -In an AC direct conversion device,
The magnitude | Is | of the input current Is of the AC-AC direct conversion circuit is estimated from the matching condition between the input active power including the power conversion efficiency η of the AC-AC direct conversion circuit and the active power required by the load. The phase difference Δθ of the input current Is with respect to the power supply phase voltage Vs is estimated from the magnitude of the input current | Is |, the magnitude of the power supply phase voltage Vs | Vs |, and the reactive power command value Qref, and the magnitude of the input current Is | Is |, arithmetic means for estimating the input current Is required for reactive power control from the power supply phase voltage Vs and the phase difference Δθ,
The control device adjusts the phase difference Δθ in accordance with the input current Is estimated by the calculation means, the power supply phase voltage Vs, the output current I ₀ , and the output phase voltage command value Vrefp, whereby AC-AC direct An AC-AC direct conversion device characterized by controlling reactive power of a conversion circuit.   2. The AC-AC direct conversion device according to claim 1, wherein the calculation unit is configured to perform an estimation calculation of the estimated input current Is and an estimation calculation of the phase difference Δθ in parallel. The computing means includes means for limiting the magnitude | Is | of the estimated input current Is so as to be a value obtained by multiplying the magnitude | I ₀ | of the output current I ₀ by a preset coefficient value. The AC / AC direct conversion device according to claim 1, wherein the AC / AC direct conversion device is provided. The AC-AC direct conversion device according to any one of claims 1 to 3, wherein the arithmetic means includes means for limiting a maximum value of the phase difference Δθ to a preset value.

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