JPH10285943A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the power loss in a zero voltage circuit, by controlling the initial current to a reactor for resonance according to the output current detected by a detecting means. SOLUTION: A power converter 10 is composed of an inverter circuit 3 for converting DC power into AC power synchronous with a system power supply, a zero voltage circuit 2 for turning the input voltage to zero voltage at the time of switching, a controller 11 for controlling the zero voltage circuit 2 and the inverter circuit 3 through a first and a second drivers 7, 8, and a current sensor 12 for detecting the output current of the inverter circuit 3. Here, the initial current IL0 to a reactor L for resonance when resonance of the zero voltage circuit 2 starts is controlled so as to satisfy a following expression, IL0 =k.Is+I0 (k is a factor, about 1.5), where Is is the output current of the inverter circuit and I0 is the initial current required for exciting the reactor for resonance at no-load. By this method, noise and loss due to a switching can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for converting DC power into DC power and AC power having different voltages by on / off control of a switching element, and more particularly, to reducing switching noise and switching loss. In addition, the present invention relates to a power converter that performs switching in a state where an input voltage is set to zero voltage.

[0002]

2. Description of the Related Art In recent years, a distributed power source and a commercial power source using photovoltaic power have been interconnected, and when the power cannot be provided by the distributed power source alone, the power is supplied from the grid side. A photovoltaic power generation system has been developed which allows reverse power flow to commercial power when the amount of power generated by photovoltaic power generation is excessive.

In such a photovoltaic power generation system, a pulse width is changed as a power conversion circuit for converting DC power from a solar cell disposed on a roof of a house or the like into AC power synchronized with a commercial power supply. For example, a switching inverter (radiation noise) is generated in this PWM inverter because switching is performed at a high frequency such as 20 kHz, and this causes a failure in another device. There is a fear.

[0004] As a method of reducing such switching noise and switching loss, a power converter based on so-called zero-voltage switching, in which a PWM inverter is switched while an input voltage is kept at zero volt, is being studied.

FIG. 8 is a configuration diagram of a photovoltaic power generation system including such a power conversion device using zero voltage switching.

In FIG. 1, reference numeral 1 denotes a DC power source composed of a solar cell having an output voltage Vs, and 2 denotes a parallel resonant DC link (Parare).
ll Resonant DC Link) circuit consisting of zero voltage circuit, 3
The inverter circuit of a PWM-controlled to convert the DC power to the synchronized AC power and system power supply 4, 5 _0, 6 zero voltage circuit 2 and the inverter circuit 3, the first, second driver 7 and 8 The first and second control circuits 9 that are controlled via the respective switches are loads.

As shown in FIG. 9, for example, the zero voltage circuit 2 includes a resonance reactor L, a resonance capacitor C ₁ ,
C ₂ , diodes D _{1 to} D _4, and semiconductor switches S _{1 to} S ₃ as switching elements, for temporarily reducing the input voltage of the inverter circuit 3 to zero volt by resonance operation. ,
Input voltage of the inverter circuit 3 is the semiconductor switch S ₁ to S ₃ to be zero voltage is controlled by the first control circuit 5 _0.

As shown in FIG. 10, for example, an inverter circuit 3 includes four semiconductor switches Q _{1 to} Q ₄ and diodes D ₅ to D ₅ connected in parallel to each of the semiconductor switches Q _{1 to} Q _4.
And a D _8, the semiconductor switches Q ₁ to Q ₄ and the second
The on / off control is performed by the control circuit 6 of FIG.

[0009] Each control circuit 5 _0, 6, for example, a CPU and a logic circuit, the first control circuit 5 _0, the second control circuit to form a PWM pulse and a sinusoidal wave and a reference triangular wave 6 and outputs a switching pulse based on the PWM pulse to the zero voltage circuit 2 via the first driver 7, while the second control circuit 6 outputs a delayed PWM pulse obtained by delaying the PWM pulse by a certain time. Is output to the inverter circuit 3 via the second driver 8 so that the input voltage of the inverter circuit 3 is reduced to zero volt by the resonance operation of the zero voltage circuit 2 when the inverter circuit 3 is switched. Switching (soft switching) is performed.

[0010]

In order to perform such zero voltage switching, it is necessary to apply an initial current for excitation to the resonance reactor L of the zero voltage circuit 2; Since the initial current changes according to the output current (load current) of the inverter circuit 3,
A method of setting an initial current required when the output current is the maximum is adopted.

However, according to the method of setting the initial current required when the output current is assumed to be the maximum, an extra initial current is supplied to the zero voltage circuit during the period when the output current is not the maximum. There is a drawback that power loss occurs when supplied, and power consumption increases.

The present invention has been made in view of the above points, and has as its object to reduce power loss in a zero voltage circuit as much as possible.

[0013]

In order to achieve the above-mentioned object, the present invention is configured as follows.

That is, the present invention provides a power conversion circuit for converting DC power by ON / OFF control of a switching element, and a zero voltage circuit for making an input voltage of the power conversion circuit zero voltage by resonance operation when the switching element is switched. A power conversion device comprising: a detection unit for detecting an output current of the power conversion circuit, and an initial current to a resonance reactor of the zero voltage circuit according to the output current detected by the detection unit. And control means for controlling.

The power conversion circuit is an inverter circuit,
It is preferable that the zero voltage circuit is a resonance DC link circuit including the resonance reactor, a resonance capacitor, and a switching element.

Preferably, the control means controls the initial current by controlling a timing of a switching operation of the switching element for exciting the resonance reactor.

The control means may determine that the initial current value to the resonance reactor at the start of the resonance operation is a current value obtained by multiplying the output current value detected by the detection means by a coefficient and the resonance current value at no load. It is preferable to perform control so as to be an added value obtained by adding a current value necessary for exciting the reactor.

The detecting means may be a current sensor, and the control means may include an amplifier circuit for amplifying an output of the current sensor, and an output required for exciting the resonance reactor when no load is applied to the output of the amplifier circuit. An addition circuit for adding a reference voltage corresponding to the current value may be provided.

According to the power converter of the present invention, the output current of a power conversion circuit such as an inverter circuit is detected, and a zero voltage circuit such as a resonant DC link circuit is connected to a resonance reactor in accordance with the output current. Since the initial current is controlled, the initial current to the resonance reactor can be suppressed as compared to the conventional example in which the output current is set to the maximum when the output current is the maximum, and the power loss in the zero voltage circuit is reduced. It can be reduced.

Further, by controlling the timing of the switching operation of the switching element for exciting the resonance reactor, the initial current can be easily controlled.

[0021] Further, the control means may determine that the initial current value to the resonance reactor at the start of the resonance operation is:
Since the control is performed so that the current value obtained by multiplying the output current value detected by the detection means by a coefficient and the current value required to excite the resonance reactor at no load is added, the control is performed so that the initial value is obtained. The current is suppressed to a necessary minimum and the power loss is reduced.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a configuration diagram of a main part of a photovoltaic power generation system provided with a power conversion device according to one embodiment of the present invention, and portions corresponding to FIG. Assign a sign.

The photovoltaic power generation system of this embodiment
A DC power supply 1 composed of a solar cell having an output voltage Vs and a power converter 10 according to the present invention are provided. The power converter 10 converts DC power into AC power synchronized with the system power supply 4. Inverter circuit 3 as power conversion circuit
And a zero voltage circuit 2 for setting the input voltage of the inverter circuit 3 to zero voltage when the inverter circuit 3 is switched.
And a control means 11 for controlling the zero voltage circuit 2 and the inverter circuit 3 via the first and second drivers 7 and 8, and a detecting means for detecting the output current (load current) of the inverter circuit 3 Current sensor 12 is provided. In addition, 9 is a load.

The zero voltage circuit 2 has, for example, the configuration shown in FIG. 9 described above, and includes a resonance reactor L, resonance capacitors C ₁ and C ₂ , diodes D _{1 to} D _4, and semiconductor switches S _{1 to} S _3. And the input voltage of the inverter circuit 3 is temporarily reduced to zero volt by the resonance operation. The inverter circuit 3 has, for example, the configuration shown in FIG. 10 described above, and has four semiconductor switches Q ₁ to Q ₁ . and Q _4, a diode D ₅ connected in parallel to the semiconductor switches Q ₁ to Q ₄
And a ~D _8.

In this embodiment, in order to suppress the initial current for exciting the resonance reactor L of the zero voltage circuit 2 and reduce the power loss in the zero voltage circuit 2, the control means 11 includes a current sensor 12 The initial current to the resonance reactor L of the zero voltage circuit 2 is controlled according to the output current of the inverter circuit 3 detected by the above.

That is, in the above-mentioned conventional example, the initial current to the resonance reactor L of the zero voltage circuit 2 is fixed to the initial current required when the output current of the inverter circuit 3 is the maximum. On the other hand, in this embodiment, the output current Is of the inverter circuit 3 is detected by the current sensor 12, and the initial current of the zero voltage circuit 2 is controlled in accordance with the detected output current. In this embodiment, the resonance reactor L at the start of the resonance operation
Is controlled as follows.

In this embodiment, the initial current value to the resonance reactor L at the start of the resonance operation of the zero voltage circuit 2 is I _L0 , the detected output current of the inverter circuit 3 is Is, The control is performed such that I _L0 = k · Is + I _{0 assuming} an initial current I ₀ required for exciting the reactor L.

Here, k is a coefficient, which is determined by experiments or the like, and is, for example, about 1.5.

As described above, in order to control the value I _L0 of the initial current to the resonance reactor L at the start of the resonance operation so as to be a value represented by the above equation, the control means 11
Is an amplification circuit 13 that amplifies the output of the current sensor 12 that detects the output current Is of the inverter circuit 3 by a factor k.
An addition circuit 14 for adding a voltage corresponding to an initial current I ₀ required to excite the resonance reactor L at no load to the output of the amplification circuit 13, and an output voltage of the addition circuit 14 voltage and the like integrating circuit for converting - the time conversion circuit 15, the voltage - on the basis of the output on-time conversion circuit 15, by controlling the semiconductor switch S ₂ of the zero voltage circuit 2, excitation start of resonant reactor L To control the excitation period from the start of the resonance operation to the start of the resonance operation, whereby the value I _L0 of the initial current to the resonance reactor L at the start of the resonance operation is controlled to be a value according to the above equation. And the PWM from the first control circuit 5.
Based on the pulse, and a second control circuit 6 which controls the semiconductor switches Q ₁ to Q ₄ of the inverter circuit 3 as in the conventional example described above. The first control circuit 5 forms a PWM pulse from a sine wave and a reference triangular wave as in the above-described conventional example.

FIG. 2 is a timing chart for explaining the control timing of the zero voltage circuit 2 shown in FIG. 9, and FIGS. 2A to 2C show the semiconductor switches S _{1 to} S _3.
(D) shows the current waveform of the resonance reactor L, and (e) shows the output voltage of the zero voltage circuit 2.

Conventionally, the initial current for exciting the resonance reactor L is fixed to the initial current required when the output current of the inverter circuit 3 is maximized, that is, in FIG. The excitation period Ts from when the initial current starts to flow through the resonance reactor L to start excitation until the resonance operation starts is controlled to be constant, and the initial current value I _L0 at the start of the resonance operation is set to be constant. On the other hand, in this embodiment, the output current Is of the inverter circuit 3 is detected, and
The semiconductor switch S ₂ of the zero voltage circuit 2 shown in FIG.
Is controlled, and as shown in the current waveform of the resonance reactor L in FIG. 3, the excitation period Ts of the resonance reactor L is varied, for example, to Ts ₁ , Ts ₂ , and the resonance is performed. Initial current value I at the start of operation
_L0 is a value represented by the above equation, that is, a current value k · Is obtained by multiplying the output current value Is of the inverter circuit 3 by a coefficient k.
And a current value I ₀ required to excite the resonance reactor L under no load is controlled so as to be an added value (k · Is + I ₀ ).

The following relationship is established between the excitation period Ts and the initial current value I _L0 at the start of resonance.

Ts = (L / Vs) · I _{L0 When} the excitation period Ts is varied to control the initial current value I _L0 of the resonance reactor L at the start of resonance, the zero voltage period changes. The timing at the center thereof is substantially constant, and the control timing of the inverter circuit 3 may be the same as that of the related art.

FIG. 4 shows the output current Is of the inverter circuit 3.
FIG. 7 is a diagram illustrating a temporal change of an initial current I _L0 to the resonance reactor L at the start of the resonance operation. As shown in FIG. 4, according to the output current Is of the inverter circuit 3, the value of the initial current I _L0 to the resonance reactor L at the start of the resonance operation is controlled as shown in the above equation. The value of the initial current I _L0 to the resonance reactor L at the start of the resonance operation is determined by the output current I _L of the inverter circuit 3.
Compared to the conventional example shown by the imaginary line which is fixed to the initial current required when s is the maximum, the initial current is suppressed as shown by the oblique line, and thereby the zero current is suppressed. Power loss in the voltage circuit 2 can be reduced.

In the above embodiment, the timing of the semiconductor switch S ₂ of the zero voltage circuit 2 is controlled.
As another embodiment of the present invention, semiconductor switches S ₁ ,
S ₃ or may be controlled in combination.

Further, the zero voltage circuit 2 of the present invention is not limited to the above-described embodiment, but may be, for example, the semiconductor switches Ss, Sr, the diodes Ds, Dr, the resonance reactor L, and the resonance reactor L shown in FIG. As shown in FIG. 5 (B), the circuit is applied to a zero voltage circuit composed of
By controlling the semiconductor switches Ss and Sr to control the excitation period Ts of the resonance reactor L, the initial current value I at the start of resonance is controlled.
May control _L0, or semiconductor switches S ₁ to S ₄ shown in FIG. 6 (A), the diode D ₁ to D _4, resonant reactor L and zero voltage with a resonance capacitor C _1, C ₂ Applying to the circuit, as shown in FIG.
Resonant reactor L by controlling semiconductor switches S ₁ and S ₃
To control the initial period I _L0 at the start of resonance.
Or a zero-voltage circuit including semiconductor switches T _{1 to} T ₃ , diodes D _{1 to} D ₅ , a resonance reactor L, and resonance capacitors C ₁ and C _{2 shown} in FIG. As shown in FIG. 7B, the semiconductor switches T _{1 to} T ₃ are controlled to control the excitation period Ts of the resonance reactor L to control the initial current value I _L0 at the start of resonance. And may be applied to other zero voltage circuits.

In the above-described embodiment, the excitation period Ts of the resonance reactor L is controlled in accordance with the detected output current of the inverter circuit 3. However, in another embodiment of the present invention, the resonance The excitation period of reactor L is
A plurality may be set in advance and switched to one of the excitation periods according to the detected output current of the inverter circuit 3.

In the above-described embodiment, the present invention is applied to the inverter circuit 3 as a power conversion circuit. However, the present invention is not limited to the inverter circuit 3, but is applied to, for example, a DC-DC converter and other power conversion circuits that perform switching. May be.

Although the above embodiment has been described with reference to the photovoltaic power generation system, the present invention is not limited to the photovoltaic power generation system.

In the above embodiment, the DC power supply 1
Although a solar cell was used as a battery, a DC power supply such as a battery power supply other than the solar cell may be used.

[0042]

As described above, according to the present invention, the output current of the power conversion circuit is detected, and the initial current to the resonance reactor of the zero voltage circuit is controlled according to the output current. Can be suppressed as compared with the conventional example in which the initial current is set to the maximum when the maximum value is set, and the power loss in the zero voltage circuit can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a photovoltaic power generation system including a power conversion device according to one embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation;

FIG. 3 is a current waveform diagram of a resonance reactor.

FIG. 4 is a diagram showing a time change of an output current and an initial current at the start of a resonance operation.

FIG. 5 is a circuit diagram and a timing chart of another embodiment of the present invention.

FIG. 6 is a circuit diagram and a timing chart of still another embodiment of the present invention.

FIG. 7 is a circuit diagram and a timing chart of still another embodiment of the present invention.

FIG. 8 is a configuration diagram of a conventional example.

FIG. 9 is a configuration diagram of a zero voltage circuit.

FIG. 10 is a configuration diagram of an inverter circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 2 Zero voltage circuit 3 Inverter circuit 11 Control means 12 Current sensor 13 Amplification circuit 14 Addition circuit

Claims (5)

[Claims] 1. A power conversion circuit comprising: a power conversion circuit for converting DC power by on / off control of a switching element; and a zero voltage circuit for reducing an input voltage of the power conversion circuit to zero voltage by resonance operation when the switching element is switched. An apparatus, comprising: detecting means for detecting an output current of the power conversion circuit; and control means for controlling an initial current to a resonance reactor of the zero voltage circuit in accordance with the output current detected by the detecting means. A power converter characterized by comprising: 2. The power conversion circuit is an inverter circuit for converting DC power into AC power, and the zero voltage circuit is a resonance DC link circuit including the resonance reactor, a resonance capacitor, and a switching element. The power converter according to claim 1. 3. The power converter according to claim 1, wherein the control unit controls the initial current by controlling a timing of a switching operation of the switching element for exciting the resonance reactor. 4. The controller according to claim 1, wherein the initial current value to the resonance reactor at the start of the resonance operation is a current value obtained by multiplying an output current value detected by the detection means by a coefficient, and the current value at no load. 2. The control system according to claim 1, wherein the control is performed such that an added value is obtained by adding a current value necessary for exciting the resonance reactor.
4. The power converter according to any one of claims 3 to 3. 5. The detection means is a current sensor, and the control means amplifies an output of the current sensor, and energizes the output of the amplification circuit with the no-load resonance reactor. The power conversion device according to claim 4, further comprising: an addition circuit that adds a reference voltage corresponding to a current value necessary for the power conversion.