KR20070083005A - Current source inverter - Google Patents

Abstract

A current source inverter is provided to minimize the deterioration of efficiency of the inverter caused by iron loss or copper loss of a DC reactor by switching on/off switches respectively in a zero current state. A current source inverter includes a current source(111), a switching unit(112), and a current converting unit(200). The switching unit(112) switches the current supplied from the current source(111) to output the current to a load. The current converting unit(200) bypasses the current flowing to the switching unit(112) from the current source(111) under the control of an inverter control unit, and maintains the bypass state for a predetermined time. The current source(111) is composed of a general DC reactor. The switching unit(112) is composed of a plurality of diodes and IGBTs(Insulated Gate Bipolar Transistor)(SW1-SW4).

Description

Current source inverter {Current source Inverter}

1 is a view showing a general photovoltaic power generation system,

2 shows a typical current source inverter,

3 illustrates a current source inverter according to the present invention;

4A to 4F are views provided to explain the operation of the current source inverter according to the present invention;

5 is a timing diagram of a current source inverter according to the present invention;

Explanation of symbols on the main parts of the drawings

100: solar cell 110: current source inverter

111: current source 112: switching unit

200: current switching unit D1 ~ D4: diode

SW1 to SW4: Switch 201: First IGBT

202: second IGBT 203: first diode

204: second diode 205: capacitor

206: inductor

The present invention relates to a current source inverter designed to minimize the decrease in efficiency of an inverter inevitably caused by iron loss or copper loss of a DC reactor through soft switching of an insulated gate bipolar transistor (IGBT), which is a power switching element. .

In general, a current source inverter is a device that converts DC power into AC power in a photovoltaic power generation system and supplies the load to a load. First, a photovoltaic power generation system using such a current source inverter is briefly described as follows.

Conventional photovoltaic power generation system is a system that converts the light energy of the sun into electrical energy to generate a direct current power, and the generated direct current power is converted into an alternating current power supply to the load.

1 is a diagram illustrating such a general photovoltaic power generation system.

As shown in the drawing, a typical photovoltaic power generation system generally includes a solar cell 100, an inverter 110, a load 120, a current sensor 130, a voltage sensor 140, and a current controller 150.

In the conventional photovoltaic power generation system, when the solar cell 100 receives solar energy to generate DC power, the generated DC power is converted into AC power by the current source inverter 110 through a switching operation to load 120. ), For example, to supply to home appliances and the like.

In such a photovoltaic power generation system, in particular, the current source inverter 110 converts DC power supplied from a solar cell or a fuel cell using solar power, which is a representative alternative energy source, into AC power, and then converts the converted AC power into a load. It is used as a power converter to supply.

As shown in FIG. 2, the current source inverter 110 includes a current source 111 that is a direct current reactor, a plurality of diodes D1 to D4, and an Insulated Gate Bipolar Transistor (IGBT) that is a power switching element.

The current source inverter 110 configured as described above loads the current supplied by the current source 111 in a clockwise and counterclockwise direction while the IGBTs, which are power switching elements, are turned on and off according to a pulse width modulated signal output from an inverter controller (not shown). Alternately input 130 to supply AC power.

The current source inverter 110 is not affected by the inrush current due to a short circuit during an inverter accident, and unlike the voltage source inverter, there is an advantage that the output voltage of the inverter does not need to be set higher than the grid voltage in order to be connected to the grid. .

However, due to iron loss and copper loss of the DC reactor used as the current source 111, the efficiency of the inverter is lowered, and as the capacity of the inverter increases, the degree of the decrease is further increased proportionally.

Therefore, it is necessary to reduce the efficiency deterioration of the inverter inevitably generated through other means.

The present invention was developed to solve such a problem, and can reduce the efficiency of the inverter caused by iron loss or copper loss of the DC reactor through other means, that is, through soft switching of the power switching element IGBT. Its purpose is to

The present invention according to this object

The predetermined current switching unit is installed to be connected to the switching unit including the current source and the IGBT to bypass the current flowing from the current source to the IGBT of the switching unit and maintain the state for a predetermined time.

A specific structure includes a current source, a switching unit for switching a current supplied by the current source and outputting the load to a load, and bypassing a current flowing from the current source to the switching unit by receiving a control signal from, for example, an inverter controller from the outside for a predetermined time. Characterized in that it comprises a current switching unit for maintaining the state.

In this structure, in particular, the current switching unit,

A first IGBT having a collector terminal connected to the current source and a switching unit, a first diode connected to the first IGBT side by side and an anode terminal connected to the current source and the switching unit, and a second collector connected to a cathode terminal of the first diode A capacitor installed between an IGBT, a second diode connected in parallel with the second IGBT, a cathode terminal of the first diode, an emitter terminal of the first IGBT, an anode terminal of the second diode and a collector terminal of the second IGBT, and one side The inductor is connected to the cathode terminal of the second diode and the emitter terminal of the second IGBT, and the other side includes a current source and an inductor connected to the switching unit.

Hereinafter, with reference to the accompanying drawings will be described in more detail the present invention.

The current source inverter shown in FIG. 3 shows a current source inverter according to the present invention as an example.

The current source inverter according to the present invention soft-switches the switches SW1 to SW4 constituting the switching unit 112 using the current switching unit 200, that is, the switches SW1 to SW4 constituting the switching unit 112. This is to minimize the deterioration of the efficiency of the inverter which is inevitably caused by the copper loss or iron loss of the DC reactor by soft switching so that the switch is switched at zero current.

The current source inverter according to the present invention has a structure in which the current switching unit 200 connected to the current source 111 and the switching unit 112 bypasses the current flowing from the current source to the IGBT and maintains the state for a predetermined time.

Specifically, the current source 111, the switching unit 112 for switching the current supplied by the current source 111 to output the load, from the outside, for example, in the current source 111 under the control of an inverter control unit (not shown) The current switching unit 200 bypasses the current flowing through the switching unit 112 and maintains the bypass state for a predetermined time.

Here, the current source 111 is composed of a conventional direct current reactor (reactor).

The switching unit 112 includes a plurality of diodes and an IGBT, for example, a power switching element that is switched under the control of an inverter controller (not shown).

For example, the switching unit 112 for supplying single-phase alternating current to the load may be configured as shown.

That is, four IGBTs (SW1 to SW4) and diodes (D1 to D4) are provided, and the gates of the four IGBTs (SW1 to SW4) are connected one-to-one to an inverter controller (not shown) to provide PWM signals for switching therefrom. Receive input.

Two diodes D1 and D4 of the four diodes D1 to D4 are connected in series to the collectors of adjacent IGBTs SW1 and SW3, and the two diodes D2 and D3 are connected to each adjacent IGBT SW2. , Structured in series with the emitter of SW4).

At this time, the switch of SW1 and the switch of SW2 are turned on or off together, and the switch of SW3 and the switch of SW4 are turned on or off together.

Thus, the switches SW1 and SW2 and the switches SW3 and SW4 are alternately turned on / off under the control of the inverter controller so that the current supplied from the current source 111 is supplied to the load 130 in the clockwise and counterclockwise directions. It is possible to supply AC power.

The current converter 200 is composed of a capacitor, an inductor, a diode, and an IGBT.

For example, when associated with the switching unit for supplying single-phase alternating current to the load, the current source 111 and the switching unit 112 is connected to the collector terminal, the inverter control unit (not shown) is connected to the first gate terminal An IGBT 201, a first diode 203 connected in parallel with the first IGBT 201, a second IGBT 202 connected with a gate terminal, and a second diode connected in parallel with the second IGBT 202. 204, the capacitor 205 interconnecting the first diode 203, the first IGBT 201, the second diode 204, and the second IGBT 202, and the second diode 203 and the first. 2 may be configured as an inductor 206 connecting the IGBT 202 to the current source 111.

The current conversion unit 200 configured as described above bypasses the current flowing from the current source 111 to the switching unit 112 under the control of an inverter controller (not shown), and for example, charge / discharge a predetermined capacitor provided therein for a predetermined time. Maintain that bypass for the time.

For example, during the time interval between the off time of the switches SW1 and SW2 and the on time of the switches SW3 and SW4, the current flowing from the current source 111 to the switching unit 112 is bypassed and provided therein. During the time when a predetermined capacitor is discharged and charged according to the bypassed current, that is, the bypass state, that is, the current supplied from the current source 111 flows to the current converting unit 200 without flowing to the switching unit 112. Keep it.

As a result, the switches SW1 and SW2 and the switches SW3 and SW4 can be turned off and on, respectively in a zero current state, so that the currents flowing in opposite directions simultaneously disappear, thereby causing a current loss. As a result, the inverter's efficiency inevitably caused by iron loss or copper loss of the DC reactor can be compensated to the minimum.

4A to 4F are views provided to explain the operation of the current source inverter according to the present invention.

First, the initial state of the current source inverter according to the present invention is defined as follows.

The current supplied by the current source initially flows through the switch of SW1 and the switch of SW2, and the capacitor 205 is charged to -KVm. The capacitor 205 and the inductor 206 select the difference between the capacitive reactance of the capacitor 205 and the inductive reactance of the inductor 206 to be zero.

Here, K has a value of about 1.3 as the initial charge factor.

In this state, as the switches of SW1 and SW2 are turned on under the control of an inverter controller (not shown), the current supplied by the current source 111 is supplied to the load 130 via the switch of SW1, and the current source through the switch of SW2. Returning to 111, this operation is repeatedly performed for a predetermined time under the control of the inverter controller (Fig. 4A).

When the first IGBT 201 and the second IGBT 202 are turned on in the state where the switches of SW1 and SW2 are turned on, the current supplied from the current source 111 flows to the first IGBT 201, and a predetermined time is As time passes, the switches of SW1 and SW2 are in a zero current state (Fig. 4B).

As described above, the time T1 from the time point at which the switches SW1 and SW2 are turned on to the time point in the zero current state is determined by Equation 1 below.

Here, KVm is the initial voltage across the capacitor, and V _T is the voltage across the AC side.

Next, when the switches of SW1 and SW2 are in the zero current state, the switches of SW1 and SW2 are turned off immediately under the control of the inverter controller, and the current supplied by the current source 111 no longer flows to the switches of SW1 and SW2. , All are bypassed and flow to the current switching unit 200 (FIG. 4C).

Next, the current that is bypassed and flows to the current switching unit 200 is the first IGBT 201, the capacitor 205, the second IGBT 202, and the current source until all the charges charged in the capacitor 205 are discharged. Circulate 111.

The time T2 from a time point when all the current supplied by the current source 111 flows to the current switch unit 200 until the discharge of the capacitor 205 is completed is determined according to Equation 2.

Where Cr is the capacitance of the capacitor, Vc (t ₁ ) is the resonant voltage of the capacitor, and I _dc = Current supplied by the current source 111.

Next, when all the charges charged in the capacitor 205 are discharged and the charge voltage thereof becomes 0 according to the cyclic operation, the current supplied by the current source 111 may cause the first IGBT 201 and the first diode 203 to discharge. And through two paths through the second IGBT 202 and the second diode 204 (FIG. 4D).

In this state, when the first IGBT 201 and the second IGBT 202 are turned off under the control of the inverter controller, the current flows through the second diode Dr2, the capacitor 205, and the first diode Dr1. Only flows through, and therefore capacitor 205 begins to charge (FIG. 4E).

The charging time T ₃ of the capacitor 205 is determined according to equation ( ₃ ).

Where Cr is the capacitance of the capacitor, KVm is the initial voltage across the capacitor, and I _dc : This is the current supplied by the current source 111.

Next, as described above, when the capacitor 205 starts to be charged and its charging voltage is charged to the same value as the initial charging voltage (-KVm), the switch of SW3 and the switch of SW4 are turned on under the control of the inverter controller. do.

As a result, the switches of SW3 and SW4 are turned on in the zero current state (FIG. 4F), and the current supplied by the current source 111 no longer flows to the current switching unit 200 after a predetermined time, and the switching unit SW3 After flowing to the load through the switch of SW4 is returned to the current source 111 through the switch of SW4.

As described above, the time T4 from the time when the switches of SW3 and SW4 are turned on to the time of the zero current state is determined according to Equation 4 below.

Where KVm = initial voltage across the capacitor, V ' _T = Voltage across AC side.

I _dc = Current supplied by the current source 111.

Therefore, the total time at which the current is cut off is the sum of the respective times described in the equations (1) to (4).

As described above, the current converter 200 receives a current flowing from the current source 111 to the switching unit 112 during a time interval between the off time of the switches SW1 and SW2 and the on time of the switches SW3 and SW4. The bypass state, that is, the current supplied from the current source 111 does not flow to the switching unit 112 during the time when the predetermined capacitor 205 provided therein is discharged and charged according to the bypassed current. Soft switching is performed by maintaining the flow to the current conversion unit 200 without.

As a result, in the zero current state, the switches SW1 and SW2 and the switches SW3 and SW4 are turned off and on, respectively, so that the currents flowing in opposite directions at the same time disappear, and the current loss does not occur. The reduction in efficiency of the inverter inevitably caused by the iron loss or copper loss of the reactor can be minimized.

5 is a timing diagram of a current source inverter according to the present invention.

For convenience of explanation, it will be described in connection with FIG. 3.

Here, S1 and S2 are signals applied to the switches of SW1 and SW2, S3 and S4 are signals applied to the switches SW3 and SW4, and Sr1 and Sr2 are signals applied to the first IGBT 201 and the second IGBT 202. to be.

Ir is the inductor 206 current, Vc is the voltage across the capacitor 205, and Idc is the current supplied by the current source.

The signal applied to each switch in the above represents a PWM signal applied from a conventional inverter control unit (not shown).

In the timing diagram of FIG. 5, a portion to be seen is a time interval between when the switches SW1 and SW2 constituting the current source inverter are turned off and when the switches of SW3 and SW4 are turned on, that is, between a time t1 and a time t4. Time interval.

During the time periods t1 to t4 between the two time points, as shown, the current Idc supplied by the current source does not flow to the switching unit, but is bypassed and flows only to the current blocking unit.

As a result, when the switch of SW3, SW4 is turned on and flows to the load in the counterclockwise direction, there is no current flowing to the load in the clockwise direction, so that the current loss is reduced accordingly and thus the inverter's high speed switching operation of the inverter It is possible to reduce the efficiency degradation.

That is, in the present invention, when the signals of Sr1 and Sr2 are applied to the first IGBT and the second IGBT at time t0, the current Idc supplied by the current source is divided into the switching unit and the current switching unit, and then a predetermined time elapses. At the time t1, the flow is no longer flown to the switching section, and the current flows to the current switching section, whereby the current is in the zero current state.

As the current Idc supplied by the current source flows to the switching unit and the current switching unit, the switches of the SW3 and the SW4 are turned on at the time t when the voltage at both ends of the capacitor is discharged and becomes the charging voltage again.

At this time, as described above, since there is no current flowing to the load in the clockwise direction, the current loss is reduced by that amount, thereby reducing the efficiency of the inverter due to iron loss or copper loss by the core of the DC reactor to some extent. .

As described above in detail, the current source inverter according to the present invention minimizes the reduction in efficiency of the inverter due to the high-speed switching operation of the power switching element IGBT through soft switching for the power switching element IGBT. Therefore, it is possible to extend the life of the device, and also to compensate to some extent the efficiency reduction of the inverter due to iron loss or copper loss by the core of the DC reactor used as the current source.

Claims (3)

Current source; A switching unit for switching the current supplied by the current source to output the load; And And a current switching unit configured to receive a control signal from an external source and bypass the current flowing from the current source to the switching unit and maintain the state for a predetermined time to soft switch the switching unit. The method of claim 1, wherein the current switching unit, A first IGBT having a collector terminal connected to the current source and a switching unit; A first diode connected in parallel with the first IGBT and an anode terminal connected to the current source and the switching unit; A second IGBT, the collector terminal of which is connected to the cathode terminal of the first diode; A second diode connected in parallel with the second IGBT; A capacitor provided between the cathode terminal of the first diode, the emitter terminal of the first IGBT, the anode terminal of the second diode and the collector terminal of the second IGBT; And And an inductor connected at one side to the cathode terminal of the second diode and the emitter terminal of the second IGBT, and the other side connected to the current source and the switching unit. The method of claim 2, The capacitor and the inductor current source inverter, characterized in that the difference between the capacitive reactance and the inductive reactance is zero.

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