JP2003029857A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power converter capable of measuring the DC side voltage and currents of a power converter by making it unnecessary to input a positive disturbance signal for measurement. SOLUTION: A power is converted from AC into DC or vice versa, and a ripple signal corresponding to an AC side frequency is produced at the DC side due to a circuit structure, and equipment is connected to the DC side in this power converting device. At least either the voltage or current components of the ripple signal produced at the DC side of the power converting device are measured by a measuring part, and prescribed signal processing is carried out based on the obtained measured result, and the characteristics of the power converter and/or the characteristics of equipment connected to the DC side of the power converter are controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power conversion device for converting power from direct current to alternating current or vice versa, and is particularly useful for high-speed measurement that does not require special disturbance and that the response of the power converter is not limited. The present invention relates to a power conversion device that enables the conversion.

[0002]

2. Description of the Related Art In an inverter device as a power converter for converting direct current into alternating current, voltage / current characteristics of a direct current power source (solar cell, etc.) connected to an input side, that is, output impedance is measured. The input impedance of the inverter on the power receiving side is optimally controlled based on the output impedance obtained by the measurement.

FIG. 2 shows an example of a circuit diagram of this type of inverter. For example, the DC power source 1 such as a solar cell is
It is connected to the input of the inverter 4, and the AC output power is obtained from the output of the inverter 4. DC power source 1
Is internally composed of an electromotive force 3 and an output impedance 2.

The inverter 4 is controlled by the control unit 10, and the power setting value 5 obtained by the adder 13 is controlled by the control unit 10.
And the addition signal of the disturbance signal for measurement 11 by the adder 13 is input as a power command value that defines the output voltage of the inverter. The current measurement value signal and the voltage measurement value signal are input to the signal processing unit 9, the output impedance is obtained as described later, and the output impedance is output to the control unit 10. The measurement disturbance signal 11 is applied to one input of the adder 13 via the switch 12 only when measuring the DC-side voltage / current characteristic of the inverter 4. When the disturbance signal for measurement 11 is applied, the change signal corresponding to this applied signal is generated by the inverter 4
Of course, it appears not only in the AC power output, but also in the DC side which is the input side, so the change appearing on this DC side is detected.

The change signal appearing on the DC side is the amplifier 6
Amplified by 8 and 8 and input to the signal processing unit 9 as a voltage measurement signal and a current measurement signal. That is, the DC power source 1
The voltage across both ends of is the voltage measurement value amplified by the amplifier 6, the output current of the DC power source 1 is detected by the current sensor 7, and then amplified by the amplifier 8 to become the current measurement value,
Each is input to the signal processing unit 9. The signal processing unit 9 uses these measured values to determine the value of the output impedance 2 of the DC power source 1 as described later.

By the way, the conditions for sending the power of the DC power source 1 to the inverter 4 on the power receiving side with maximum efficiency are as follows:
That is, the output impedance 2 of the DC power source 1 and the input impedance of the inverter 4 are equal.

Therefore, in the circuit shown in FIG. 2, the input impedance of the inverter 4 is the same as the output impedance 2 of the DC power source 1 based on the value of the output impedance 2 of the DC power source 1 obtained by the signal processing unit 9. The control unit 10 controls so that

The output impedance of the DC power source 1 is the voltage / current of the input terminal (DC side) of the inverter 4 corresponding to ON / OFF of the disturbance signal for measurement 11 applied to the control unit 10. It can be determined by measuring the change.

A specific method for obtaining the output impedance of the DC power source 1 is as follows. Here, considering a battery as a typical DC power source, its output impedance can be obtained by measuring the voltage / current characteristics through the following steps.

(1) First, the switch 12 is turned off, and the voltage V1 across the DC power source 1 and the current I1 flowing into the inverter 4 are obtained. These measured values are amplifier 6 and amplifier 8.
Respectively as the output of.

(2) Next, the switch 12 is turned on to apply the disturbance signal 11 for measurement to the inverter 4, and the voltage V2 across the DC power source 1 and the current I2 flowing into the inverter 4 at that time are obtained. These measured values are respectively obtained as the outputs of the amplifier 6 and the amplifier 8 as in the case of (1).

(3) Since the impedance is the ratio of voltage and current (voltage / current), the output impedance R of the DC power source 1 is calculated according to the following equation from the voltage and current values obtained in (1) and (2). The calculation is performed by the processing unit 9. R = (V2-V1) / (I2-I1)

In the above description, an example of an inverter is shown. However, in a converter for converting AC power into DC power, the DC output of the converter is adjusted according to the state of the load impedance connected to the DC output terminal. The control is performed and the command value such as the current value of the converter is controlled according to the load impedance calculated by the same method as the above (1) to (3).

Further, in order to convert the input DC power into the AC power with the maximum efficiency as in the maximum power point tracking method of the solar power generation system composed of the solar cell and the power converter (inverter), It is necessary to make the input impedance of the inverter equal to the internal impedance of the solar cell, which is the DC power source. In such a case, the voltage / current of the inverter input described above is detected, and the inverter It controls the input current.

[0015]

However, the conventional power conversion apparatus having the voltage / current characteristic measuring function has the following problems.

That is, as described above, in the conventional technique, in order to measure the voltage-current characteristics on the DC side of the power converter, the original control amount that determines the output of the power converter, that is, FIG. It is necessary to always apply a small amount of disturbance (measurement disturbance signal 11 in FIG. 2) in addition to the power set value 5 of.
Therefore, a circuit for applying this disturbance is required, and more inconveniently, although it is used with a small amount of unnecessary disturbance added, this disturbance is a normal power signal. From the perspective, it becomes unnecessary noise.

Further, in order to accurately control this kind of power conversion device, it is necessary to accurately inject the "disturbance" signal. In this case, in order to accurately measure the influence of the disturbance generated on the DC side, a considerable waiting time is required until the system stabilizes after the control because of the control time constant inside the power converter. Therefore, a problem that the measurement time becomes long occurs, and as a result, it is difficult to operate the control loop at high speed. Furthermore, as will be described later, ripples exist on the DC side of the power converter. And
Since this ripple is superimposed on the disturbance signal for measurement, it is necessary to integrate the ripple for a sufficient time to remove this effect, resulting in a problem that the measurement time becomes long.

Therefore, an object of the present invention is to provide a power conversion device capable of measuring the voltage / current on the DC side of the power conversion device without requiring the above-mentioned conventional problem, that is, a positive disturbance signal for measurement. To do.

[0019]

In order to solve the above problems, the power converter according to the present invention employs the following characteristic configuration.

(1) Converting power from AC to DC or vice versa, a ripple signal corresponding to the frequency on the AC side is generated on the DC side due to the circuit structure, and a device is connected to the DC side. In the power conversion device, a measurement unit that measures at least one of a voltage component and a current component of the ripple signal generated on the direct-current side of the power conversion device, and signal processing that performs a predetermined calculation using the output of the measurement unit as an input. And a control unit that receives the output of the signal processing unit and controls the electrical characteristics of both or one of the power conversion device and a device connected to the DC side of the power conversion device. Converter.

(2) A power converter having a converter function for converting power from AC to DC, in which a ripple signal corresponding to a frequency on the AC side is generated on the DC side due to a circuit structure. A load unit connected to the DC output of the converter device, a measuring unit that measures at least one of the voltage and current components of the ripple signal generated in the DC output of the power converter, and an output of the measuring unit. A signal processing unit that calculates the characteristics of the load unit as an input, a control unit that receives the output of the signal processing unit and controls the DC output power of the converter device and / or the characteristics of the load unit. A power conversion device comprising.

(3) A power converter having an inverter function for converting electric power from direct current to alternating current, in which a ripple signal corresponding to the frequency on the alternating current side is generated on the direct current side. A DC power source connected to the DC side, a voltage of the ripple signal generated on the DC side of the power converter, a measuring unit that measures at least one of current components, and an output of the measuring unit as an input. A signal processing unit for calculating the characteristics of the DC power source,
A power converter comprising: a controller that receives the output of the signal processor and controls the DC input power of the power converter and / or the characteristics of the DC power source.

(4) A DC power source, an inverter for converting DC of the DC power source into AC power, and a ripple signal corresponding to an AC frequency generated on the DC power source side due to the circuit structure of the inverter. Measuring unit for measuring the voltage and current components, a signal processing unit for obtaining the output impedance of the DC power source based on the voltage and current components of the ripple signal from the measuring unit, and the output impedance from the signal processing unit A power converter comprising: a controller that controls both or one of the inverter and the DC power source to obtain an AC output of maximum efficiency.

(5) The power converter according to any one of the above (1) to (4), wherein the signal processing section uses a plurality of voltage and current component values of the ripple signal and averages them. .

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of a power converter according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a configuration block diagram of an embodiment of a power conversion device according to the present invention, which relates to an embodiment example in which a solar cell and an inverter (DC → AC) are combined to form a solar power generation device. is there.

In FIG. 1, by measuring the output impedance of the DC power supply (solar cell) 1 connected to the input side of the inverter 4, the power generated by the DC power supply (solar cell) 1 is converted into the inverter 4 with maximum efficiency. Control to take in.

The solar cell 1 as a DC power source is composed of an electromotive force 3 and an output impedance 2 as shown in an equivalent circuit. The DC power source (solar cell) 1 is connected to the input of the inverter 4, and AC power is obtained from the output of the inverter 4.

The inverter 4 is usually composed of a switching element such as a bridge-connected transistor, and the input DC power is converted into AC power by this switching element. In the case of such an inverter, a component (ripple), which is an integral multiple of the AC output, leaks to the input side in the actual inverter due to factors such as the performance of the smoothing circuit.

In the present invention, attention is paid to the ripple generated on the DC side (power receiving side) due to the circuit structure of such an inverter, and a new additional circuit is not required for measurement, and this ripple is measured. For example, the output impedance of the solar cell is measured. That is, in the present invention, the leakage ripple is measured, for example, the voltage / current characteristic of the solar cell connected to the DC side of the inverter is measured, and the output impedance of the solar cell is measured from the measurement result.

The measurement of the output impedance of the solar cell according to this embodiment will be specifically described below.

First, the input side of the inverter 4, that is, the voltage across the DC power source 1 is amplified by the amplifier 6 and output to the signal processing circuit 9 as a voltage measurement value signal. On the other hand, the output current of the DC power supply 1 is detected by the current sensor 7 and then amplified by the amplifier 8 and output to the signal processing unit 9 as a current measurement value signal.

In the signal processing unit 9, from the input voltage measurement value signal and current measurement value signal, the voltage variation (that is, voltage ripple component: ΔV) and the current variation (that is, current ripple component: ΔI). Is calculated, and the value of the output impedance R is calculated as R = (ΔV
/ ΔI).

The control unit 10 of the inverter controls the characteristics of the inverter 4 based on the output impedance value obtained by the signal processing unit 9. A power setting value (voltage source) 5 for setting the AC power output of the inverter 4 is connected to the control unit 10 of the inverter.

Next, in the present embodiment, the inverter 4
The operation following the maximum output power of the solar cell (DC generator 1) will be described. Considering a case where the graph of the output voltage / current characteristic (not shown) of the solar cell is overlapped with the graph of the input voltage / current characteristic (that is, the input impedance characteristic) of the inverter 4, the intersection (P) of these two characteristics is considered.
Is the operating point of the solar cell. The output power of the solar cell (in other words, the input power of the inverter 4) is
It is represented by the product of the voltage and the current determined at the intersection point P. This indicates that the power from the solar cell can be controlled by changing the input impedance of the inverter 4.

The solar cell maximum output power tracking method of the present embodiment uses this principle, and the output voltage and output current of the DC power source (that is, the solar cell) 1 is appropriately monitored to make the DC power source 1 The control circuit 10 controls the input impedance of the inverter 4 so that the product of the output voltage and the output current becomes maximum.

When calculating the input impedance, the current measurement value and the voltage measurement value are measured as described above. Originally, this measurement signal is a ripple signal superimposed on the DC voltage on the DC side of the inverter 4, Was used as noise in inverter applications. Therefore, the voltage and current values of the ripple signal are slightly smaller than the originally used DC voltage value. Therefore, it is possible to improve the SN ratio by performing the measurement a plurality of times and integrating (averaging) the measurement results. In the case of the present invention, since the ripple signal is used, its cycle is faster than that in the prior art in which a positive disturbance due to the supply of the measurement disturbance signal is used, so that the integration can be effectively performed. . Also, since the ripple cycle is known (an integral multiple of the frequency of the AC output), the SN ratio can be improved by phase-detecting the instantaneous voltage / current measurement values.

The present invention is not limited to the above-described embodiments, but various modifications and variations can be made as follows. For example, in the above-described embodiment, the present invention is applied to the inverter device that extracts AC from DC, but it goes without saying that the present invention may be applied to a converter device that extracts DC from AC. In this case, when it is necessary to measure the voltage / current characteristics on the load (DC side) side in the converter device, according to the present invention, the measurement can be performed without adding a new circuit.

Further, in the above-described embodiment, the control unit 10
The output of the inverter 10 is controlled, but it is also possible to control the inverter 4 and / or the DC generator 1 or both of them. That is, it is generally possible to control the characteristics of the power converter and / or the characteristics of the device connected to the DC side of the power converter.

In the above-described embodiment, the voltage and current measuring section is added to measure the voltage and current on the DC side of the power converter (see the alternate long and short dash line in FIG. 1). In some cases, the voltage / current status on the DC side is detected. In such a case, the voltage / current measuring function incorporated in the power converter itself can be used.

Further, in the above embodiment, it is assumed that a single-phase alternating current is used on the alternating current side of the power converter, but any structure can be used as long as the power converter can generate ripples on the direct current side. It can correspond to the number of AC phases.

Further, even in the AC three-phase system in which the ripple is not normally generated, the ripple is generated if the phase balance is broken to such an extent that there is no practical problem, so that the present invention can be applied.

In the above embodiment, the power converter is controlled based on the measured data of both the voltage and the current. However, this measures either the voltage or the current and uses the result to measure the power converter. Of course, you may control.

[0044]

As described above, in the power converter according to the present invention, for example, the ripple signal leaking from the AC side to the DC side, which is caused by the structure of the semiconductor power converter, is used, and the electrical characteristics of the DC side are used. The output power can be controlled by measuring That is, the voltage / current characteristics of the DC side of the power converter can be measured by using the AC signal leakage (ripple) from the AC side to the DC side that the power converter itself has due to its circuit structure. As in the prior art, it is possible to eliminate a wasteful time of giving a special disturbance and then measuring it after it becomes stable, and it is possible to perform high-speed measurement without being limited by the response of the power converter.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of a power conversion device according to the present invention.

FIG. 2 is a configuration block diagram of a conventional power conversion device.

[Explanation of symbols]

1 DC power source 2 Output impedance 3 electromotive force 4 inverter 5 power setting 6 amplifier 7 Current detector 8 amplifier 9 Signal processing unit 10 Control unit 11 Disturbance signal for measurement 12 switches 13 adder

Claims (5)

[Claims] 1. A power for converting power from alternating current to direct current or vice versa, a ripple signal corresponding to the frequency on the alternating current side is generated on the direct current side due to a circuit structure, and power is connected to equipment on the direct current side. In the conversion device, a measurement unit that measures at least one of the voltage and current components of the ripple signal that is generated on the DC side of the power conversion device, and a signal processing unit that performs a predetermined calculation using the output of the measurement unit as an input. And a control unit that receives the output of the signal processing unit and controls the electrical characteristics of both or one of the power conversion device and the device connected to the DC side of the power conversion device. A characteristic power conversion device. 2. A power converter having a converter function for converting power from AC to DC, wherein a ripple signal corresponding to a frequency on the AC side is generated on the DC side due to a circuit structure, A load unit connected to the DC output of the converter device, a measuring unit that measures at least one of the voltage and the current component of the ripple signal generated in the DC output of the power converter, and the output of the measuring unit is input. As a signal processing unit that calculates the characteristics of the load unit, and a control unit that receives the output of the signal processing unit and controls the DC output power of the converter device and / or the characteristics of the load unit. A power conversion device comprising: 3. A power converter having an inverter function for converting power from direct current to alternating current, wherein a ripple signal corresponding to the frequency on the alternating current side is generated on the direct current side. A direct current power source connected to the direct current side, a voltage of the ripple signal generated on the direct current side of the power converter, a measuring unit that measures at least one of current components, and an output of the measuring unit as an input A signal processing unit that calculates the characteristics of the DC power source, a control unit that receives the output of the signal processing unit and controls both or one of the characteristics of the DC input power of the power conversion device and the DC power source, A power conversion device comprising: 4. A direct current power source, an inverter for converting direct current of the direct current power source into alternating current, and a ripple signal corresponding to an alternating current side frequency generated on the direct current power source side due to a circuit structure of the inverter. A measuring unit that measures voltage and current components, a signal processing unit that obtains the output impedance of the DC power source based on the voltage and current components of the ripple signal from the measuring unit, and an output impedance from the signal processing unit. A control unit that controls both or one of the inverter and the DC power source to obtain an AC output of maximum efficiency based on
A power conversion device comprising: 5. The signal processing unit according to claim 1, wherein a plurality of voltage and current component values of the ripple signal are used, and the signal processing unit averages and outputs the values. Power converter.