JPH05191980A - Clamped neutral inverter - Google Patents

Abstract

PURPOSE:To provide a clamped neutral inverter equipped with means for collecting energy from a snubber circuit. CONSTITUTION:First to fourth semiconductor switches 5A-5D for inverting the voltage of a DC power supply 1 into AC voltage is provided, respectively, with a snubber circuit comprising a diode and a capacitor connected in series. A regenerative circuit 12B is connected between a terminal of a snubber capacitor in the second semiconductor switch 5B and a neutral point through a reverse blocking semiconductor switch 11A which operates synchronously with a third semiconductor switch 5C. Furthermore, a regenerative circuit 12C is connected between a terminal of a snubber capacitor in the third semiconductor switch 5C and the neutral point through a reverse blocking semiconductor switch 11B which operates synchronously with the second semiconductor switch 5B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a neutral point clamp type inverter, and more particularly to improvement of a snubber circuit thereof.

[0002]

2. Description of the Related Art Inverters for converting DC power into AC power are widely used in fields such as AC motor drives and uninterruptible power supplies. Among them, the neutral point clamp type inverter, which can reduce the harmonic components of the output AC voltage, is widely used in the fields of power conversion of superconducting magnetic levitation trains and large capacity AC motor drives.

FIG. 9 shows a configuration example of such a neutral point clamp type inverter. Capacitors 2A and 2B are provided between the positive terminal NP and the negative terminal NN of the DC voltage source 1 and the neutral point NS. In the present case, the neutral point NS is the ground potential, the output voltage of the voltage source 1 is 2VS,
Therefore, the potentials of the positive terminal NP and the negative terminal NN are
It is assumed that they are + Vs and -Vs. Between the positive terminal NP and the AC voltage output terminal NO connected to the load 3, a reactor 4
First and second reverse conducting semiconductor switches 5A, 5 via A
B is connected in series, and the third and fourth reverse conducting semiconductor switches 5C, 5D are connected in series via the reactor 4B between the negative side terminal NN and the AC output terminal NO. The reverse conducting semiconductor switches 5A to 5D are, for example, thyristors provided with a reverse conducting diode integrally or externally.

Each of the first to fourth semiconductor switches 5A to 5D is provided with a snubber circuit. The snubber circuits are respectively diodes 8A to 8D and capacitors 7A to
7D and resistors 9A to 9D. A diode 6A is provided between a connection node between the first semiconductor switch 5A and the second semiconductor switch 5B and the neutral point NS, and similarly a connection node between the third semiconductor switch 5C and the fourth semiconductor switch 5D is provided. A diode 6B is provided between the neutral points NS.

The operation of this inverter is as follows.
First, the case where the load current IL is positive will be described. When the first and second semiconductor switches 5A and 5B are on and the third and fourth semiconductor switches 5C and 5D are off, the load current passes through the reactor 4A, and then the first and second semiconductor switches 5A and 5B.
Is supplied via. If the rate of change of the current is sufficiently small and the voltage across the reactor 4A is also small, the potential at the output terminal No becomes + Vs. At this time, the third
Snubber capacitor 7 of fourth semiconductor switch 5C, 5D
C and 7D are charged to the voltage VS.

Next, from this state, the first semiconductor switch 5A is turned off and the third semiconductor switch 5C is turned on.
At this time, if the switches 5A to 5C are turned on at the same time, an overcurrent flows or an overvoltage is applied to the switches. Therefore, it is normally several μs to several meters after the first semiconductor switch 5A is turned off.
The third semiconductor switch 5C is turned on by delaying the time s. When the third semiconductor switch 5C is turned on, a circulating current flows through the snubber capacitor 7C, the semiconductor switch 5C, and the snubber resistor 9C, and the electric charge stored in the snubber capacitor 7C is consumed by the resistor 9C. Further, since the current does not flow in the first semiconductor switch 5A, the current flowing in the reactor 4A is charged in the snubber capacitor 7A via the snubber diode 8A. At this time, the terminal voltage of the first semiconductor switch 5A is
Since it is the same as the terminal voltage of the snubber capacitor 7A, the rate of change in voltage applied to the first semiconductor switch 5A dV / d
t is suppressed by charging the capacitor 7A.

When the terminal voltage of the snubber capacitor 7A becomes sufficiently large, the potential of the connection node N1 between the first semiconductor switch 5A and the second semiconductor switch 5B becomes lower than the potential of the neutral point NS, and a current flows through the diode 6A. . In a steady state, the load current IL is supplied through the diode 6A and the semiconductor switch 5B, and the potential of the output terminal NO becomes 0V, which is the same as the potential of the neutral point NO. Snubber capacitor 7
A is charged to VS.

From this state, next, the second semiconductor switch 5B is turned off and the fourth semiconductor switch 5D is turned on. Also at this time, the timing of turning on the fourth semiconductor switch 5D is slightly delayed from the timing of turning off the second semiconductor switch 5B. Fourth semiconductor switch 5D
Is turned on, a circulating current flows through the snubber capacitor 7D, the semiconductor switch 5D, the snubber resistor 9D, and the electric charge accumulated in the snubber capacitor 7D is consumed by the snubber resistor 9D. Since no current flows through the second semiconductor switch 5B, the load current IL flows through the snubber diode 8B and the snubber capacitor 7B. When the terminal voltage of the snubber capacitor 7B becomes sufficiently large, the potential of the connection node N2 of the third semiconductor switch 5C and the fourth semiconductor switch 5D becomes lower than the potential of the negative side terminal NN of the voltage source 1, and the current flows in the reactor 4B. Flowing. In the steady state, the load current IL is supplied by flowing through the reactor 4B and the semiconductor switches 5D and 5C, and the potential of the output terminal NO becomes -Vs. The snubber capacitor 7B has a voltage VS
Is charged.

From this state, the fourth semiconductor switch 5D
Is turned off and the second semiconductor switch 5B is turned on.
Since the semiconductor switch 5B is turned on, a circulating current flows through the snubber capacitor 7B, the semiconductor switch 5B, and the snubber resistor 9B, and the electric charge accumulated in the snubber capacitor 7B is consumed by the snubber resistor 9B. Since no current flows through the semiconductor switch 5D, the voltage applied to the semiconductor switch 5D charges the capacitor 7D. As a steady state,
The load current IL is the diode 6A and the semiconductor switch 5B.
And the potential of the output terminal No becomes 0V.

From this state, the third semiconductor switch 5C
Is turned off and the first semiconductor switch 5A is turned on.
Since the semiconductor switch 5A is turned on, a circulating current flows through the snubber capacitor 7A, the semiconductor switch 5A, and the snubber resistor 9A, and the electric charge accumulated in the snubber capacitor 7A is consumed by the snubber resistor 9A. Since the current stops flowing through the semiconductor switch 5C, the voltage applied to the semiconductor switch 5C charges the capacitor 7C. As a steady state,
The load current IL is the reactor 4A, the semiconductor switch 5
It is supplied through A and 5B, and the potential of the output terminal No is + V
It becomes S.

The same operation is performed when the load current IL is negative. The state changes of the semiconductor switches 5A to 5D and the potential change of the output terminal NO are summarized in a table as follows.
It becomes like FIG. As is clear from FIG. 10, since the neutral point clamp type inverter can output three values of + VS, 0, -VS depending on the state of the semiconductor switch, the output waveform of the output waveform is different from that of the normal pulse width modulation (PWM) type inverter. The accuracy improves. Further, since the reactors 4A and 4B work when switching the semiconductor switches, the current change rate di / dt applied to the switch element is suppressed to a small level, and the snubber circuit provided in each semiconductor switch reduces the voltage change rate dV.
/ Dt can also be kept small.

However, in such a conventional neutral point clamp type inverter, when the semiconductor switch is turned off,
The electric charge stored in the snubber capacitor is consumed as electric power by the snubber resistor. Therefore, there is a problem that the snubber loss is large, which hinders the improvement of the switching speed, and requires a cooling device to handle the heat loss, which makes the device large and complicated.

On the other hand, a method of regenerating energy to the DC side without consuming power in the snubber circuit has already been proposed in a pulse width modulation (PWM) type inverter (see, for example, USP 4,566,051).

FIG. 11 shows a configuration example of a PWM inverter having such a snubber circuit with a regeneration function. The same reference numerals as those in FIG. 9 are given to the portions corresponding to the configuration of FIG. The snubber circuit provided in the semiconductor switch 5A has no resistance. The energy stored in the snubber capacitor 7A when the semiconductor switch 5A is turned off is temporarily transferred to the capacitor 13 when the semiconductor switch 7A is turned on. Then, it is regenerated to the DC side by the boost chopper circuit composed of the semiconductor switch 14, the inductance 15 and the diode 16.

However, this snubber circuit system of the PWM type inverter cannot be directly applied to the neutral point clamp type inverter. If the regenerative circuit method of FIG. 11 is applied to the second and third semiconductor switches of FIG. 9 as they are, the connection node N1 of the first and second semiconductor switches and the connection node N2 of the third and fourth semiconductor switches. This is because a current path is formed through the regenerative circuit during the period.

[0016]

As described above, in the conventional neutral point clamp type inverter, the power consumption in the snubber circuit prevents the improvement of the switching speed.
Further, there is a problem that the device becomes large due to the necessity of cooling. The present invention has been made in view of the above points, and an object of the present invention is to provide a neutral point clamp type inverter including means for recovering energy in a snubber circuit.

[0017]

A neutral point clamp type inverter according to the present invention includes a DC voltage source and positive and negative terminals of the DC voltage source and a positive terminal provided between the neutral point and the neutral point, respectively. Side capacitor and negative side capacitor, first and second semiconductor switches connected via a reactor between the positive side terminal and the AC output terminal of the DC voltage source, the negative side terminal of the DC voltage source, and A third and a fourth semiconductor switch connected between AC output terminals via a reactor, and a snubber circuit in which a diode and a capacitor are connected in series and are respectively provided in parallel to the first to fourth semiconductor switches. And a reverse blocking circuit that operates in synchronization with the third semiconductor switch between the neutral point and the connection point of the diode and the capacitor in the snubber circuit of the second semiconductor switch. A positive side regenerative circuit is provided via a conductor switch, and operates in synchronization with the second semiconductor switch between a neutral point and a connection point of a diode and a capacitor in a snubber circuit of the third semiconductor switch. The negative-side regenerative circuit is provided via the reverse blocking semiconductor switch.

[0018]

According to the present invention, the regenerative circuits provided in the second and third semiconductor switches are provided with reverse blocking semiconductor switches that are turned on and off in synchronization with the third and second semiconductor switches, respectively. .. Then, when the third semiconductor switch is in the ON state and the second semiconductor switch changes from OFF to ON, the energy of the snubber circuit of the second semiconductor switch is regenerated, and similarly the second semiconductor switch is When the third semiconductor switch is turned on in the on state, the snubber circuit of the third semiconductor switch regenerates energy. In this way, since the regenerative circuit is provided via the reverse blocking semiconductor switch, an unnecessary current path is not formed. And
Since the energy of the snubber circuit can be regenerated without power consumption by a resistor, high-speed switching is possible, and a cooling device or the like is not needed, so that the device is prevented from becoming large and complicated.

[0019]

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

FIG. 1 is a basic configuration of a neutral point clamp type inverter according to an embodiment of the present invention. The parts corresponding to those in the conventional FIG. 9 are denoted by the same reference numerals as those in FIG. 9 and detailed description thereof is omitted. In this embodiment, the snubber circuits provided in the first to fourth semiconductor switches 5A to 5D are respectively composed of capacitors 7A to 7D and diodes 8A to 8D, and consume energy of the capacitors 7A to 7D. There is no resistance.

The snubber circuits of the first to fourth semiconductor switches 5A and 5D are provided with regenerative circuits 12A and 12D via diodes 10A and 10B, respectively. These regenerative circuit systems are similar to those in the conventional PWM inverter shown in FIG. On the other hand, the second
Regarding the snubber circuits of the third semiconductor switches 5B and 5C, a regenerative circuit 12B, a diode with a semiconductor switch, that is, reverse blocking semiconductor switches 11A and 11B, is used.
12C is provided.

FIG. 2 shows the regenerative circuit section of FIG. 1 more specifically. The regenerative circuit 12A of the first semiconductor switch 5A section is composed of a capacitor 13A for temporarily accumulating the electric charge of the snubber capacitor, a switch 14A, a reactor 15A and a diode 16A which constitute a chopper booster circuit. Second semiconductor switch 5
Similarly, the regenerative circuit 12B in the B section includes a capacitor 13B,
It is composed of a switch 14B, a reactor 15B and a diode 16B which form a chopper booster circuit. The regenerative circuit 12C of the third semiconductor switch 5C section is
A capacitor 13C for temporarily storing the electric charge of the snubber capacitor, and a switch 14 forming a chopper booster circuit.
It is composed of a C, a reactor 15C and a diode 16C. The regenerative circuit 12D of the fourth semiconductor switch 5D section is similarly composed of a capacitor 13D, a switch 14D, a reactor 15D and a diode 16D which form a chopper booster circuit.

The basic operation of the neutral point clamp type inverter thus constructed is the same as that of the conventional case of FIG.
Therefore, detailed description of the operation is omitted. In Figure 3,
The relationships among the states of the semiconductor switches 5A to 5D and the load current, the output terminal voltage, and the snubber capacitor voltage are shown together.

In the embodiment shown in FIG. 2, energy regeneration of the snubber circuit is carried out as follows. That is, when the first semiconductor switch 5A is off, the electric charge stored in the snubber capacitor 7A is once transferred to the capacitor 13A via the diode 10A when the first semiconductor switch 5A is turned on, and the electric charge is regenerated by the regenerative circuit 12A. It is regenerated by the capacitor 2A. Similarly, the charge stored in the snubber capacitor 7B when the second semiconductor switch 5B is off is transmitted to the capacitor 13B via the reverse blocking switch 11A when the second semiconductor switch 5B is turned on.
To the capacitor 2B by the regenerative circuit 12B.
Regenerated to. The same applies hereinafter.

However, in the above regenerative operation, the first semiconductor switch 5A and the reverse blocking semiconductor switch 11A are controlled so as not to be turned on at the same time. Similarly, the fourth semiconductor switch 5D and the reverse blocking semiconductor switch 11B
And are controlled so that they are not turned on at the same time. For example, the reverse blocking semiconductor switch 11A in the second semiconductor switch 5B section is controlled to be turned on and off in synchronization with the third semiconductor switch 5C, and the reverse blocking semiconductor switch 11B in the third semiconductor switch 5C section is set to the second blocking switch. Semiconductor switch 5B
ON / OFF control is performed in synchronization with.

Therefore, when the third semiconductor switch 5C is turned on, the reverse blocking semiconductor switch 11A is turned on at the same time, and when the second semiconductor switch 5B is turned on from the off state, the second semiconductor switch 5B is turned on. Semiconductor switch 5
The energy of the snubber capacitor 7B in the B section is regenerated through the reverse blocking semiconductor switch 11A and the regeneration circuit 12B. Similarly, when the second semiconductor switch 5B is turned on, the reverse blocking semiconductor switch 11B is turned on at the same time, and when the third semiconductor switch 5C is turned on from the off state, the third semiconductor switch 5C is turned on. The energy of the snubber capacitor 7C of the switch 5C portion is regenerated via the reverse blocking semiconductor switch 11B and the regeneration circuit 12C.

As described above, according to this embodiment, the energy of the snubber capacitor is recovered without being consumed as electric power by the resistor, and an inverter for performing highly efficient DC / AC conversion can be obtained.

FIG. 4 shows an embodiment in which the present invention is applied to a three-phase inverter. The basic structure is the same as that of the embodiment shown in FIG. 1, and therefore, the portions corresponding to those in FIG. 1 are designated by the same reference numerals. In the case of a multi-phase inverter as shown in the figure, the regenerative circuit of each phase can be shared.

FIG. 5 shows an embodiment in which the number of series elements of each semiconductor switch of the embodiment of FIG. 1 is increased. The basic structure is the same as that of the embodiment shown in FIG.
The same reference numerals as those in FIG. 1 are attached to the portions corresponding to. In the case of the figure, the number of switch elements forming the arm of the main circuit is three. The three semiconductor switches connected in series are turned on and off at the same time, and the energy of three snubber capacitors is recovered in each regenerative circuit. In this configuration, the snubber capacitor is connected to the switch 14 and the regenerative circuit via the diode. Therefore, even if switch 14 is not reverse blocking, current will only flow in one direction. FIG. 6 is an embodiment in which the diode connection of the reverse blocking semiconductor switches 11A and 11B in the embodiment of FIG. 5 is slightly changed.

FIG. 7 shows an embodiment in which the present invention is applied to a four-valued inverter. To configure a four-valued inverter, as shown in the figure, three DC voltage sources 1 connected in series and six reverse conducting semiconductor switches 5A to 5F connected in series are used. The configuration of the snubber circuit provided in each semiconductor switch and the configuration of the regenerative circuit provided therein are basically the same as those of the embodiment of FIG.

With three DC voltage sources, points a, b, and c
The potentials at points d and 3 are 3Vs, 2Vs, Vs and 0, respectively.
Then, the relation among the states of the respective semiconductor switches and the load current and the output terminal voltage is as shown in FIG. The operation of the regenerative circuit is similar to that of the embodiment of FIG.

[0032]

As described above, according to the present invention, in the neutral point clamp type inverter, it is possible to recover the energy of the snubber capacitor and perform high-efficiency DC / AC conversion.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a neutral point clamp type inverter according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration embodying a regenerative circuit section of the embodiment.

FIG. 3 is a diagram showing an operating state of each unit of the embodiment.

FIG. 4 is a diagram showing an embodiment in which the present invention is applied to a three-phase inverter.

5 is a diagram showing an embodiment in which the number of semiconductor switch series elements in FIG. 1 is increased.

FIG. 6 is a view showing an embodiment in which the number of semiconductor switch series elements in FIG. 1 is also increased.

FIG. 7 is a diagram showing an embodiment in which the present invention is applied to a four-value inverter.

FIG. 8 is a diagram showing an operating state of each unit of the embodiment.

FIG. 9 is a diagram showing a configuration of a conventional neutral point clamp type inverter.

FIG. 10 is a diagram showing an operating state of each unit of the conventional example.

FIG. 11 is a diagram showing a configuration example of a PWM inverter having a snubber circuit with a regeneration function.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... DC voltage source, 2 ... Capacitor, 3 ... Load, 4 ... Reactor, 5 ... Reverse conducting semiconductor switch, 6 ... Diode, 7 ... Snubber capacitor, 8 ... Snubber diode, 10 ... Diode, 11 ... Reverse blocking semiconductor switch, 12 ... Regenerative circuit, 13 ... Capacitor, 14 ... Switch, 15 ... Reactor, 16 ... Diode.

Claims (1)

[Claims] 1. A direct current voltage source, a capacitor provided between a positive side terminal and a negative side terminal of the direct current voltage source and a neutral point respectively, and a positive side terminal of the direct current voltage source and an alternating current output terminal. First and second semiconductor switches connected to each other via a reactor, and third and fourth semiconductor switches connected via a reactor between the negative terminal of the DC voltage source and the AC output terminal. A snubber circuit in which a diode and a capacitor are connected in series, the snubber circuit being provided in parallel with each of the first to fourth semiconductor switches; a connection point of the diode and the capacitor in the snubber circuit of the second semiconductor switch; A positive-side regenerative circuit provided between the points via a reverse blocking semiconductor switch that operates in synchronization with the third semiconductor switch, and a snubber circuit of the third semiconductor switch. And a negative side regenerative circuit provided between the connection point of the diode and the capacitor and the neutral point via a reverse blocking semiconductor switch that operates in synchronization with the second semiconductor switch. The neutral point clamp type inverter.