JP4466830B2 - AC / AC direct conversion device - Google Patents

Description

  The present invention relates to an AC / AC direct conversion device that converts a polyphase AC voltage to a polyphase AC voltage having an arbitrary magnitude and frequency by using a semiconductor switching element, and particularly in a power conversion device that does not have a large energy buffer. It is characterized by a commutation method for preventing short circuit of the power source and opening of the load end.

Hereinafter, a three-phase input / three-phase output matrix converter will be described as an example of this type of multiphase AC / AC direct converter.
FIG. 8 shows a circuit for one phase of the output of the matrix converter. In FIG. 8, V _max is the input terminal of the maximum voltage phase (for example, the R phase of the three-phase AC power supply), V _mid is the input terminal of the intermediate voltage phase (the same S phase), and V _min is the minimum voltage phase (the same T phase). , U is a U-phase output terminal, S ₁ , S ₂ , S ₃ are AC switches, S _1a , S _1b , S _{2a / b} , S _{2b / a} , S _3a , S _3b constitute each AC switch It is a unidirectional switch such as an IGBT.

The subscripts “1”, “2”, “3” of the AC switches S ₁ , S ₂ , S ₃ are used to indicate that they are connected to the maximum voltage phase, the intermediate voltage phase, and the minimum voltage phase, For example AC switch S ₁ is R phase AC switch, the S ₂ are S-phase AC switch, the S ₃ can be a T-phase AC switch. Here, the unidirectional switch constituting the R-phase AC switch is S _ru , S _ur , the unidirectional switch constituting the S-phase AC switch is S _su , S _us , and the unidirectional switch constituting the T-phase AC switch is S _tu. , S _ut , for example, the unidirectional switches S _1a , S _1b constituting the AC switch S ₁ in FIG. 8 correspond to the unidirectional switches S _ru , S _ur of the R-phase AC switch (for other phases). Is easy to infer, so the explanation is omitted).

Further, in FIG. 8, a switch with a suffix “a” indicates a switch that operates in the IGBT mode, and a switch with a suffix “b” indicates a switch that operates in the freewheeling diode mode.
The IGBT mode refers to an operation mode in which a forward voltage is applied between the collector and the emitter (the collector voltage is higher than the emitter voltage), and is an operation mode in which a current flows at the same time as the gate is turned on. The freewheeling diode mode is an operation mode in which a reverse voltage is applied between the collector and the emitter (the collector voltage is lower than the emitter voltage). In this case, the forward voltage is applied and the gate is not turned on. Since no current flows and the operation is almost the same as that of a freewheeling diode in an inverter, it is called a freewheeling diode mode.

Furthermore, the unidirectional switches _S 2a / _b constituting the AC switch _{S 2,} and the case for _{S 2b / a,} the AC switch _{S 2} is operating as an upper arm and when operating as a lower arm, IGBT mode, freewheeling diode Since the unidirectional switches to be switched are switched, a / b and b / a are added to the subscripts of the reference symbols.
For example, the AC switch _{S 1} is the upper arm, when the _{S 2} is switched with the lower arm, the switch _{S 2a / b} is IGBT mode, the _{S 2b / a} is operated at the diode mode, the AC switch _{S 2} the upper arm, when the _{S 3} is switched under arm, switch _{S 2b / a} is IGBT mode, the _{S 2a / b} is operated at a diode mode.

In general, an AC / AC direct conversion device such as a matrix converter is constituted by an AC switch. In order to prevent a short circuit of a power source and an opening of a load end, an AC switch is constituted by two unidirectional switches as shown in FIG. The on / off timing of each unidirectional switch is controlled.
That is, when the power supply is short-circuited, an excessive short-circuit current is generated and the switch is damaged.When the load is an inductive load, the return path of energy stored in the inductive load disappears by opening the load end. It is applied to the switch as an excessive surge voltage, destroying the switch.
For this reason, the commutation operation for appropriately controlling the on / off timing of each unidirectional switch is important.

FIG. 9 shows a commutation pattern when the magnitude relationship between the power supply voltages of the respective phases is V _r > V _s > V _t .
FIG. 9A shows the switching between the AC switches S ₁ and S ₂ , FIG. 9B shows the switching between the AC switches S ₁ and S _3, and FIG. 9C shows the switching between the AC switches S ₂ and S _3. It is a flow pattern and represents command pulses for the AC switches S ₁ , S ₂ , S ₃ and the unidirectional switches S _1a , S _1b , S _2a , S _2b , S _3a , S _3b , respectively.

As is clear from these figures, at the time of commutation between two AC switches, the magnitude relationship of the power supply voltage is detected, and first, the unidirectional switch to which the reverse bias of the opposite arm (commutation destination) is applied is turned on. After the commutation period has elapsed, the switch to which the forward bias of the opposite arm is applied is turned on.
For example, at the time of commutation between the AC switch S ₁ and S ₂ of FIG. 9 (a), first, on the unidirectional switch S _2b, and turns on the unidirectional switch S _2a after the elapse of the commutation period.
This commutation operation will be described by dividing it into a commutation source and a commutation destination.

a. Commutation destination: unidirectional switch-on in freewheeling diode mode b. Commutation source: IGBT mode unidirectional switch-off c. Commutation destination: IGBT mode unidirectional switch-on d. Commutation source: Unidirectional switch-off in freewheeling diode mode

  A specific method of this commutation is disclosed in, for example, Patent Document 1 below, and instead of determining the magnitude relationship between the power supply voltages, the voltage at both ends of each AC switch is detected and the same output phase is detected. The forward bias and the reverse bias are discriminated using another gate pulse for driving the unidirectional switch, and the on / off order of the unidirectional switch is switched to generate a commutation pattern.

JP 2001-61276 A (Claim 1, [0042] to [0044], FIG. 5 etc.)

The conventional commutation method disclosed in Patent Document 1 and the like has the following problems.
a. The commutation period corresponds to a so-called dead time in the conventional inverter, and causes a decrease in voltage utilization rate and an output voltage error. As a result, the desired performance cannot be obtained when the load is an electric motor.

b. Since the commutation operation requires four steps as described above, the circuit for generating the gate pulse from the voltage command becomes complicated, and if the voltage command changes within the commutation period, only the voltage error increases. In the worst case, a power supply short circuit or load end opening occurs, which destroys the semiconductor switching element. Moreover, a complicated commutation circuit causes an increase in cost of the AC / AC direct conversion device.

c. FIG. 10 shows an output voltage waveform based on the minimum voltage at the time of commutation between the maximum voltage phase and the minimum voltage phase of the power supply (for example, between the R phase and the T phase in the above example). Yes.
In the case of commutation from the maximum voltage phase to the minimum voltage phase, the output voltage changes in amplitude by an amount corresponding to the maximum line voltage (v _max −v _min ) of the power supply as shown in the figure. Such a large change in the output voltage causes noise and adversely affects other devices such as malfunction.
Further, when the load is an electric motor, a surge voltage is generated at the terminal of the electric motor with a sudden change in the output voltage, and in the worst case, the insulation of the electric motor may be deteriorated by the surge voltage and burnout may occur.
Furthermore, in order to prevent the propagation of these surge voltages and noises, it is conceivable to provide a filter circuit on the input side or output side of the converter, but this filter circuit causes an increase in size and cost of the converter. It will be.

  Accordingly, the present invention provides a simple sequence commutation circuit, reduces surge voltage and noise generated at the load terminal, and makes it possible to achieve desired control performance, cost reduction, and downsizing of the apparatus. An AC direct conversion device is to be provided.

In order to solve the above problems, the invention described in claim 1 is configured such that an AC switch is constituted by at least two unidirectional switches capable of controlling a unidirectional current, and the AC switch is connected between input and output phase terminals. In the AC / AC direct conversion device for converting the multi-phase AC voltage on the power source side to the multi-phase AC voltage having an arbitrary magnitude and frequency by connecting to
Means for determining the magnitude relationship between the power supply voltages for each phase;
Means for generating a pulse that always turns on the unidirectional switch to which the reverse voltage is applied, based on the voltage command pulse of each phase AC switch generated according to the magnitude relationship determined by this means. It is.

  When the commutation is performed between the maximum voltage phase of the power source and the minimum voltage phase of the power source, the unidirectional switch connected to the intermediate voltage phase of the power source is turned on and off during the commutation period. It has a means to make it.

The invention described in claim 3 is the AC / AC direct conversion device according to claim 1,
Depending on the polarity of the load current detected by this means and the polarity of the load current detected by this means, one of the unidirectional switches constituting the AC switch of the commutation destination or commutation source phase is always on. Means for turning on and off only one unidirectional switch excluding the directional switch according to the voltage command pulse.

According to the present invention, an AC / AC direct conversion device such as a matrix converter has the following effects.
According to the first aspect of the present invention, the unidirectional switch to which the reverse voltage is applied, that is, the unidirectional switch of the freewheeling diode mode is always turned on, so that the pulse of the unidirectional switch of the IGBT mode is the same as that of the conventional inverter. The commutation is possible only by providing a dead time in the.
According to the invention of claim 2, the change in the amplitude of the output voltage is reduced by passing through the intermediate voltage phase when commutating between the maximum voltage phase and the minimum voltage phase.
According to the invention of claim 3, by fixing the IGBT mode element that switches according to the polarity of the load current, commutation can be naturally performed without providing a dead time.

  As a result, the desired control performance can be obtained without lowering the voltage error and voltage utilization rate that occur during commutation, and noise and surge voltage can be suppressed. A direct conversion device can be constructed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, Table 1 shows a first embodiment of the present invention corresponding to claim 1, and the constraint condition for each output voltage of the unidirectional switch for each output phase (respective output voltages V _r , V _s , shows the the oN or oFF state) required to generate the V _t. Here, the magnitude relationship between the power supply voltages of the respective phases is assumed to be V _r > V _s > V _t .

In Table 1, “1” represents on, “0” represents off, and “*” represents either on or off. For example, in order to output the R-phase voltage _Vr as the output voltage, the unidirectional switches S _1a and S _1b must be turned on, and S _{2a / b} and S _3a are turned off to prevent a power supply short circuit. It must be. In addition, S _{2b / a} and S _3b other than these may be on or off. This is because _a reverse voltage (reverse bias) is applied to the unidirectional switches S _{2b / a} and S _3b due to the magnitude relationship of the power supply voltage described above, so that no current actually flows even when the gate is turned on. This is because it is in the state (reflux diode mode).
Similarly, the constraint conditions when it is desired to output the S-phase voltage V _s may be S _{2a / b} and S _{2b / a} being on, S _1a and S _3a being off, and S _1b and S _3b being on or off. constraints to output a T-phase voltage _{V t is, S 3a,} S _3b is turned _on, S _1a, the _{S 2b / a off, S 1b,} S _{2a / b} will be or off in on.

FIG. 1 is a control block diagram according to the present embodiment. The present embodiment unidirectional switches _S ru output phase one phase (U-phase) _{component, S ur, S su, S} us, S tu, is a construction for obtaining a pulse for _{S ut,} other output The same applies to the phase.

In Figure 1, first, the magnitude relationship of each phase power supply voltage determined by the voltage level decision means 4, to obtain the logical value, the voltage command pulse _S ^RUR AC switch _*, ^S sus _*, pulse sequence and _{S tut} ^* Rearrangement is performed by the replacement means 1. That, R-phase from the U-phase output phase, S phase, the original voltage command pulse for outputting the voltage of the T-phase ^{_{S rur *, S sus *,}} S tut * considers the magnitude of phase voltage since not, connect in accordance with the magnitude relation, the pulse _{^S rur *, S} sus _*, the voltage command pulse _S ^{1 *} for AC switch _{S 1} which is connected to the maximum voltage phase _{S tut} ^*, the intermediate voltage phase The voltage command pulse S ₂ ^* for the alternating current switch S ₂ is rearranged into the voltage command pulse S ₃ ^* for the alternating current switch S ₃ connected to the minimum voltage phase. These voltage command pulses correspond to S ₁ , S ₂ , and S ₃ in FIG. 8 described above.

After that, the gate pulses of the unidirectional switches S _1a , S _{2a / b} or S _{2b / a} , S _3a operating in the IGBT mode are generated. At this time, dead time is generated to prevent a power supply short circuit. Generated by means 2 and added to the gate pulse.

Unidirectional switches S _{2a / b} of the AC switch S ₂ is connected to the intermediate voltage _{phase, S} 2b / _a, the unidirectional reverse bias is applied depending on whether the AC switch S ₂ is or lower arm becomes the upper arm The switch is different. Therefore, the reverse bias determination unit 3, _* voltage command pulse S ^{_1, S} 2 ^_*, S ₃ ^* AC switch S ₂ detects whether or become lower arm becomes the upper arm based on the by unidirectional switches S _{It is determined which of 2a / b} and _{S2b / a} is applied with a reverse bias, and the changeover switch 6 is driven to switch the gate pulse for the IGBT mode unidirectional switch and the freewheeling diode mode unidirectional switch.

According to previous Table 1, phase separate V _r of the output _voltage, V _s, irrespective of the V _t, unidirectional switch S _1b of the reflux diode mode a reverse voltage is _applied, because S _3b good at always on, A gate-on command “1” is constantly applied to the unidirectional switches S _1b and S _3b . Further, when outputting V _s and V _t , a gate-on command “1” is applied to the unidirectional switch S _{2a / b,} and when outputting V _r and V _s , a gate-on command “1” is applied to the unidirectional switch S 2. _The changeover switch 6 is operated so as to add _{2b / a} .

As a result, pulses S _1a , S _1b , S _{2a / b} , S _{2b / a} , S _3a , S _3b for all unidirectional switches are generated and input to the pulse distribution means 5. In this pulse distribution means 5, the pulses S _1a , S _1b , S _{2a / b} , S _{2b / a} , S _3a , S _3b are converted into the output phase U phase of the matrix converter based on the magnitude relation of the phase power supply voltages. decodes allocate in any unidirectional switch connected, pulses _{S ru, S ur, S su} , in _{which S us,} S _tu, supplied by distributed as _{S ut} each unidirectional switch.

FIG. 2 shows a commutation pattern in the present embodiment. When commutation is performed between the AC switches S ₁ and S ₂ as shown in (a), the unidirectional switches S _1b , S _{2b / a} , S _3b is always on, and when commutating between the AC switches S ₁ and S ₃ as shown in (b), the unidirectional switches S _1b and S _3b are always on and shown in (c). Thus, when commutating between the AC switches S ₂ and S ₃ , the unidirectional switches S _1b , S _{2a / b} , and S _3b are always turned on, and the IGBT mode unidirectional switch (for example, FIG. A commutation pattern can be generated simply by adding dead time to S _1a , S _{2a / b,} etc.).

  As described above, in this embodiment, the commutation sequence is performed by always turning on the freewheeling diode mode unidirectional switch (unidirectional switch to which a reverse voltage is applied) that may be turned on or off during commutation. This simplifies the configuration of the commutation circuit.

As a result, in the past,
a. Commutation destination: unidirectional switch-on in freewheeling diode mode b. Commutation source: IGBT mode unidirectional switch-off c. Commutation destination: IGBT mode unidirectional switch-on d. Commutation source: a and d in the commutation sequence that required four steps of unidirectional switch-off in the reflux diode mode can be omitted.

Next, FIG. 3 is a control block diagram of a second embodiment of the present invention corresponding to claim 2.
This embodiment is characterized by a commutation pattern when commutating from the maximum voltage phase to the minimum voltage phase, or from the minimum voltage phase to the maximum voltage phase.

In FIG. 3, the switching determination means 11 is added to the output side of the pulse rearrangement means 1 in FIG. The determination means 11 detects a commutation from the maximum voltage phase to the minimum voltage phase or from the minimum voltage phase to the maximum voltage phase based on the voltage command pulses S ₁ ^* , S ₂ ^* , S ₃ ^* , In these cases, the voltage command pulse for the intermediate voltage phase is output as S ₂ ^* = 1. Note that S ₁ ^* and S ₃ ^* input to the determination unit 11 are output as they are.
As a result, even when commutation between AC switch S _1, S _3, thereby performing switching via an intermediate voltage.

FIG. 4 shows a commutation pattern in the present embodiment, and is a case where commutation occurs between the AC switches S ₁ and S ₃ .
As described above, when the commutation is performed between the maximum voltage phase and the minimum voltage phase, the intermediate voltage is set by turning on the unidirectional switches S _{2a / b} and S _{2b / a} in the intermediate voltage phase during the commutation period. Via. In this case, the commutation operation includes the following steps.

a. Turn off the IGBT mode unidirectional switch of the commutation source b. Turn on unidirectional switch in IGBT mode of intermediate voltage phase (becomes freewheeling diode mode after commutation) c. Turn off unidirectional switch in free-wheeling diode mode of intermediate voltage phase (becomes IGBT mode after commutation) d. Turn on the IGBT mode unidirectional switch at the commutation destination

That is, in FIG. 4, when commutation is performed from the AC switch S ₁ to the AC switch S ₃ , the following occurs.
a. Turn off unidirectional switch _S1a b. Turn on unidirectional switch _{S2a / b} c. Turn off unidirectional switch _{S2b / a} d. The unidirectional switch S _3a is turned on. Note that the unidirectional switches S _1b and S _3b are always turned on as in the first embodiment.

FIG. 5 is a waveform diagram of an output voltage based on the minimum voltage at the time of commutation between the maximum voltage phase and the minimum voltage phase in this embodiment. In FIG. 10 relating to the prior art, the amplitude of the voltage change is the maximum line voltage (v _max −v _min ) of the power supply, which causes noise generation, but in the example of FIG. The amplitude in a single voltage change is reduced, and the generation of noise can be suppressed.

  FIG. 6 is a control block diagram showing a third embodiment of the present invention corresponding to the third aspect. In this embodiment, the first embodiment is further simplified, and commutation is performed without dead time by determining the polarity of the load current.

In FIG. 6, the difference from FIG. 1 will be described. An IGBT mode element selection unit 22 is provided instead of the dead time generation unit 2 of FIG. 1, and the selection unit 22 includes the phase (U the output from the current polarity discriminating means 21 for discriminating the polarity of the load current i _u phase) is added.
In this embodiment, based on the load current polarity determined by the determination means 21 and the voltage command pulses S ₁ ^* , S ₂ ^* , S ₃ ^* , the IGBT mode element selection means 22 sets the IGBT mode unidirectional switch to be turned on / off. In addition to the determination, the gate pulse is determined and output as shown in Table 2 below, together with the other unidirectional switches in the freewheeling diode mode.

As shown in Table 2, for example, when the polarity of the current i _u is positive and commutation is performed between the AC switches S ₁ and S ₃ , the voltage command pulse S for the AC switch S _{1 is} applied to the unidirectional switch S _1a . _The same pulse as ₁ ^* is output, the unidirectional switches S _1b and S _3b are turned on, and the unidirectional switches S _{2a / b} , S _{2b / a} and S _3a are turned off.
In the following, the principle of commutation without dead time in this embodiment will be described.

  When an IGBT mode unidirectional switch is turned off, in the case of an inductive load, if the unidirectional switch of the return diode mode of the commutation destination is turned on in order to secure a return path, the anti-direction switch will naturally Conducts (natural commutation). At this time, current does not flow through the IGBT mode unidirectional switch that is the commutation destination. Therefore, the current does not need to be turned on and may be turned off.

With reference to FIG. 7, as an example a case in which natural commutation from the AC switch S ₁ to S _3, the operation of this embodiment will be described.
In FIG. 7, the unidirectional switch that has been turned off is deleted, and the unidirectional switch in the freewheeling diode mode is represented using a diode symbol. In this example, the unidirectional switches S _{2a / b} and S _{2b / a} connected to the intermediate voltage phase V _mid are turned off, and S _1b and S _3b (the unidirectional switches in the free-wheeling diode mode for switching operation) are turned on. Keep it.

When turning off the unidirectional switch S _1a of the IGBT mode of AC switches S _1, if the direction of polarity is illustrated current i _u, the unidirectional switch S _3a, represented by broken lines without ON ON state S It commutates naturally to _3b , and the minimum voltage V _min appears in the output voltage.
That is, the dead time is provided in order to prevent a power supply short circuit due to simultaneous turn-on of the unidirectional switches S _1a and S _3a , but dead because the unidirectional switch S _3a need not be turned on by the natural commutation described above. There is no need to add dead time by means of time generation, and if the unidirectional switch S _1a is turned on / off according to the voltage command pulse S ₁ ^* , the output voltage is maximized by the unidirectional switches S _1a and S _3b without dead time. It can be switched between voltage and minimum voltage.

Similarly, when the polarity of the current i _u is negative at the time of commutation between the AC switches S ₁ and S ₃ , the unidirectional switches S _1b and S _3b are turned on as shown in Table 2, and the unidirectional without turning on the switch S _1a just off the S _3a according to a voltage command pulse S ₃ ^*, unidirectional switch S _1b, the output voltage by S _3a can be switched between a minimum voltage and the maximum voltage.
Hereinafter, also in the case of commutation with the intermediate voltage phase, based on the polarity of the load current, the free-wheeling diode mode unidirectional switch that naturally commutates is turned on and connected to the output phase (for example, U phase) By simply turning on and off one IGBT mode unidirectional switch according to the voltage command pulse, it is possible to commutate without adding dead time.

  That is, in this embodiment, the unidirectional switch in the free-wheeling diode mode that is always turned on among the unidirectional switches constituting the AC switch of the commutation destination or commutation source phase according to the detected polarity of the load current. Only one unidirectional switch in the IGBT mode, excluding, may be turned on / off according to the voltage command pulse.

It is a control block diagram concerning a 1st embodiment of the present invention. It is a figure which shows the commutation pattern in 1st Embodiment. It is a control block diagram concerning a 2nd embodiment of the present invention. It is a figure which shows the commutation pattern in 2nd Embodiment. In 2nd Embodiment, it is a wave form diagram of the output voltage on the basis of the minimum voltage at the time of commutation between the maximum voltage phase and the minimum voltage phase. It is a control block diagram concerning a 3rd embodiment of the present invention. It is explanatory drawing of the commutation method in 3rd Embodiment. It is a circuit diagram for one phase of the output phase of the matrix converter. It is a figure which shows the commutation pattern in the prior art of FIG. FIG. 9 is a waveform diagram of an output voltage based on the minimum voltage at the time of commutation between the maximum voltage phase and the minimum voltage phase in the prior art of FIG. 8.

Explanation of symbols

1: Pulse rearrangement unit 2: Dead time generation unit 3: Reverse bias determination unit 4: Voltage magnitude determination unit 5: Pulse distribution unit 6: Changeover switch 11: Switching determination unit 21: Current polarity determination unit 22: IGBT mode element selection Means S ₁ , S ₂ , S ₃ : AC switch S _1a , S _1b , S _{2a / b} , S _{2b / a} , S _3a , S _3b : Unidirectional switch

Claims (3)

An AC switch is composed of at least two unidirectional switches capable of controlling a unidirectional current, and this AC switch is connected between each phase terminal on the input and output sides to increase the multiphase AC voltage on the power source side to an arbitrary magnitude. In the AC / AC direct conversion device for converting to a polyphase AC voltage having a thickness and frequency,
Means for determining the magnitude relationship between the power supply voltages for each phase;
Means for generating a pulse that always turns on the unidirectional switch to which the reverse voltage is applied, based on the voltage command pulse of each phase AC switch generated according to the magnitude relationship determined by this means;
An AC / AC direct conversion device characterized by comprising: In the AC / AC direct conversion device according to claim 1,
When commutating between the maximum voltage phase of the power source and the minimum voltage phase of the power source, the unidirectional switch connected to the intermediate voltage phase of the power source is turned on and off during the commutation period. AC to AC direct conversion device. In the AC / AC direct conversion device according to claim 1,
Means for detecting the polarity of the load current;
One unidirectional switch excluding the unidirectional switch that is always turned on among the unidirectional switches constituting the AC switch of the commutation destination or commutation source phase according to the polarity of the load current detected by this means Only on / off according to the voltage command pulse,
An AC / AC direct conversion device characterized by comprising:

Images