JPH08140356A - Pwm converter for air conditioner - Google Patents

Abstract

PURPOSE: To provide a PWM converter of an air conditioner, which needs no excessive increase in cost even if cooling fins are compact. CONSTITUTION: A diode module element 6 where a current dividing diode 5 is subjected to three-phase bridge connection is connected in parallel to a module power element 3 where a rectifier diode 2 whose both terminals are short- circuited or opened by a switching element 1. A three-phase power supply is inputted to the module power element 3 and the switching element 1 is subjected to PWM control for converting to DC.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PWM converter for an air conditioner mounted on an outdoor unit of an inverter air conditioner.

[0002]

2. Description of the Related Art Conventionally, a device using a rectifying circuit and a large capacity smoothing capacitor has been used as a power source for an outdoor unit of an inverter air conditioner. However, such a capacitor-input type power supply device has a problem that the input current of the circuit contains a very large harmonic component and adversely affects the power supply side.

Therefore, a PWM converter was adopted to solve this problem, and FIG. 2 shows an example in which the PWM converter is applied to a three-phase power source (for example, Japanese Patent Laid-Open No. 61-61, 1985). -244273). In the figure, reference numeral 10 is a load, and in the case of an inverter, for example, it is an induction motor via a switching element or the like for converting direct current into alternating current. The load voltage (V
C) is detected by the voltage detection circuit 8 and input to the PWM control circuit 11. And this PWM control circuit 11
Then, the built-in reference voltage is compared with the input, and the load voltage (VC) is turned on so as to be in accordance with the reference voltage.
The switching element 1 is controlled by the / OFF command to open and close both ends of the rectifying diode 2. Also, the switching element 1 is controlled by creating a sine wave signal from the input voltage and the input current. Due to this switching operation and the reactor 9 inserted on the input side, the input current of the PWM converter has less low-order harmonics and is close to a sine wave with a power factor of 1. In the figure, 7 is a smoothing capacitor.

[0004]

By the way, in a small / medium-capacity air conditioner equivalent to an inverter air conditioner for consumer use, the rectifier diode 2 and the switching element 1 are integrally formed in the PWM converter in order to make the electric components compact. The formed module power element 3 is normally used. For some of this module power element 3,
Table 1 shows characteristic examples.

[0005]

[Table 1]

The module power element 3 generates heat during operation mainly due to its steady loss and switching loss. However, in an air conditioner such as the inverter air conditioner as described above, it is necessary to make the cooling fins of the module power element 3 as small as possible in order to make the electrical components compact, and the cooling fan for the fins is not used. , It is naturally cooled. Since the temperature rise of the module power element 3 with respect to a certain loss increases as the cooling fin becomes smaller, the module power element 3 which has a large capacity and is expensive is required in order to make the electrical components compact. In particular, when the loss of only a specific element of the switching element 1 and the rectifying diode 2 included in the module power element 3 becomes larger than the allowable value, it is more than necessary as a whole for that specific element. In addition, the module power element 3 having a large capacity must be used, so that there is a problem that the cost becomes higher than necessary.

The present invention has been made in order to solve the above-mentioned conventional drawbacks, and an object thereof is to provide an air conditioner which is compact and which can avoid unnecessary increase in cost and can be reduced in cost. It is to provide a PWM converter.

However, in order to judge what kind of means should be used to achieve the above object, the operation of the module power element 3 is analyzed and the module power element 3 is analyzed.
It becomes possible only by accurately grasping the loss of each element included in and the allowable value thereof. Therefore, the operation analysis performed for that purpose will be described below.

First, taking a PWM converter used for a three-phase power source as an example, switching elements 1a and 1b and a rectifying diode 2 connected to, for example, the R phase among the three phases.
The currents flowing through a and 2b are shown in FIGS. 3 and 4, respectively.
In each case, the horizontal axis represents time and the vertical axis represents current value. As can be seen from both figures, the current is the switching element 1
a and 1b and the rectifying diodes 2a and 2b alternately flow in the upper arm and the lower arm, so that a current flows in each of the switching elements 1a and 1b and the rectifying diodes 2a and 2b for a half cycle.

Next, the currents flowing through the rectifying diode 2 and the switching element 1 will be compared in FIG. As shown at point B in the figure, it can be seen that almost no current flows through the switching element 1 and most of it flows through the rectifying diode 2.

Here, the losses of the switching element 1 and the rectifying diode 2 which are operating as described above will be calculated. First, the steady loss WON is the average input current value I = 12 [A] at the maximum power of the air conditioner, the ON voltage VO of both the rectifying diode 2 and the switching element 1.
When N = 1.5 [V], current flows through each element for only half a period as shown in FIGS. 3 and 4, and thus WON = I × VON × 1/2 = 9 [W]. As shown in FIG. 5, most of the current flows through the rectifying diode 2, so that the steady loss is mostly rectifying diode loss.

Next, the switching loss is obtained. Normally, the switching loss of the rectifying diode 2 is negligible as compared with the switching loss of the switching element 1, and therefore only the switching element 1 will be calculated here. For this switching element 1, turn-on time tr = 200 [nS] and turn-off time tf = 3
Assuming 50 [nS], the turn-on loss Esw (ON) and the turn-off loss Esw per switching operation are set.
(OFF) when the DC voltage VDC = 660 [V], Esw (ON) = VDC / 2 × I / 2 × tr = 0.4
[MJ] Esw (OFF) = VDC / 2 × I / 2 × tf = 0.7
[MJ]. From this, the switching frequency fsw = 20 [k
Hz], the switching loss per element Wsw
Wsw = [Esw (ON) + Esw (OFF)] × fs
w × 1/2 = 11 [W].

From the above, it can be seen that the rectifying diode loss per element is about 9 [W] and the switching element loss is about 11 [W]. Since the module power element 3 shown in FIG. 2 has six rectifying diodes 2 and six switching elements 1 each, the loss per element of the module power element 3 is about 54 [W] for the rectifying diode loss. Element loss is about 66
[W].

If the cooling fins of the module power element 3 are small in size and are naturally cooled in order to meet the demand for compact electrical components as described above, the temperature rise is large, usually about 90 to 100 ° C. . On the other hand, the permissible temperature of the switching element 1 and the rectifying diode 2 is 150 ° C. in the standard, and normally derating is carried out to about 125 ° C. Therefore, the allowable temperature rise T is T = 125− (90 to 100) = 35 to 25 [° C.]. Then, the allowable loss WAL at this time can be obtained as WAL = T / θ [W] when the thermal resistance of the element is θ [° C / W]. Therefore, the above formula was applied to each element example listed in Table 1 and compared with the previously obtained switching element loss (about 66 [W]) and rectifying diode loss (about 54 [W]) of the module power element 3. The results are shown in Table 2.

[0015]

[Table 2]

As is clear from Table 2, the switching element loss is within the permissible range for the elements A and B, but the diode loss is outside the permissible range.
This PWM converter requires a module power element whose allowable direct current is larger than 50 [A]. Therefore, the above object of the present invention can be achieved by reducing the loss of the rectifying diode to be within the allowable range.

[0017]

In view of the above, a PWM converter for an air conditioner according to a first aspect of the present invention is a module power system in which a plurality of first diodes 2 whose both ends are short-circuited / open-controlled by a switching element 1 are bridge-connected to be integrally formed. Element 3
In the PWM converter of the air conditioner for converting the AC 4 into the DC by inputting the AC 4 into the module and PWM-controlling the switching element 1, all the first diodes 2 included in the module power element 3 are The second diode 5 is connected in parallel with the direction.

A PWM converter for an air conditioner according to a second aspect is characterized in that a plurality of the second diodes 5 are provided, and a diode module element 6 integrally formed by bridge-connecting the second diodes 5 is used.

Further, the PWM converter for an air conditioner according to claim 3 is characterized in that the alternating current (4) is a three-phase power supply.

[0020]

In the PWM converter for an air conditioner according to claim 1, the second diodes 5 are arranged in the same direction and in parallel with all the first diodes 2 included in the module power element 3.
Are connected. Therefore, a part of the current that has conventionally flowed in the first diode 2 can be shunted to the second diode 5, and therefore the first diode loss can be made smaller than in the conventional case and can be kept within the allowable range.

In the PWM converter for an air conditioner according to a second aspect, the diode module element 6 in which the plurality of second diodes 5 are bridge-connected to be integrally formed is used. Therefore, since only one part is added, the assembling process is simplified, and it is possible to meet the demand for compactness.

Further, in the PWM converter for an air conditioner according to claim 3, a three-phase power source is applied as the alternating current 4. Therefore, it can be easily implemented as a PWM converter of an air conditioner.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of a PWM converter for an air conditioner according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing the main part of this embodiment. The function of converting the input AC into DC by performing PWM control of the switching element 1 has the conventional PW.
Since it is the same as the M converter, detailed description thereof is omitted here.

In FIG. 1, 3 is a module power element. The module power element 3 will be described for one phase of the three-phase power supply. First, the switching element 1a is connected in parallel to the opposite ends of the rectifier diode 2a in the opposite direction to the upper arm 12a. Form. Further, a lower arm 12b is formed by a similar configuration, and the upper arm 12a and the lower arm 12b are connected in series to form one arm 12 so that the rectifier diodes 2a and 2b are connected in series in the same direction. To do. Both ends of the arm 12 are used as output terminals 14a and 14b, and an intermediate portion of the arm 12 to which the upper arm 12a and the lower arm 12b are connected is used as an input terminal 16a. Since the three-phase power source 4 is used as an input here, the arms 12 are used for three phases, and the respective rectifying diodes 2 ...
b and 16c, and both ends of the output terminal 14
They are integrally formed by three-phase bridge connections a and 14b.

Here, the bridge connection means that the two diodes 2a and 2b are connected in series in the same direction with one input terminal sandwiched therebetween to form the arm 12, and an input terminal required for an alternating current to be input. The above-described arms 12 are connected in parallel in the same direction, and both ends of the connected arms 12 are used as output terminals. Therefore, in the above three-phase bridge connection for inputting three-phase power,
Three diodes 12 ... Form three arms 12 ... And have three input terminals and two output terminals.

Further, reference numeral 6 in FIG. 1 denotes a diode module element in which the shunt diode 5 is integrally formed by three-phase bridge connection. This diode module element 6
Forms a shunt arm 13 by serially connecting the upper shunt diode 5a and the lower shunt diode 5b in the same direction, the middle portion of which is an input terminal 17a, and both ends thereof are output terminals 15a.
One phase is formed as 15b. Then, the shunt arm 13 is used only for three phases, and each shunt diode 5 ...
Are connected in parallel so as to be in the same direction to obtain input terminals 17a, 17b, 17c for the three-phase power supply, and both ends thereof are used as output terminals 15a, 15b. The input terminals 17a, 17b, 17c and the output terminals 15a, 15b of the diode module element 6 are connected to the module power element 3 described above.
Input terminals 16a, 16b, 16c and output terminal 14a of
14b, so that the shunt diode 5 is connected in the same direction and in parallel with all the rectifying diodes 2 in the module power element 3.

As in the conventional example shown in FIG. 2, 7 is a smoothing capacitor and 9 is a reactor in the figure.

Here, as the diode module element 6, a general component (for example, 6R130G or the like) having a thermal resistance θ = 0.8 [° C./W] can be used. Then, when the allowable temperature rise is 35 to 25 [° C.], the allowable loss WAL ′ is WAL ′ = 35 to 25 [° C.] / 0.8 [° C./W]≈44 to 31 [W].

Therefore, the module power element 3 is shown in Table 1.
The allowable loss WAL of the diode when the diode module element 6 is connected in parallel as shown in FIG. 1 by using the element A (CM50) in the above, using the values in Table 2, WAL = (50 + 44)-( 36 + 31) = 94 to 67 [W]. In the above operation analysis, the total required allowable loss of the rectifier diode 2 at the maximum power of the air conditioner is 5
Since it was 4 [W], the element A (CM50: 50 [A] product) which could not be used due to insufficient capacity in the past is a general diode module element 6 (6R130G: 30).
It can be used by adding [A] product).

Normally, the module power element 3 is expensive, but if a large capacity is required for this, the parts will be specialized and the cost will increase dramatically. On the other hand, in this embodiment, by adding the diode module element 6 which is usually less than 1/10 the price of the module power element 3, it is possible to avoid an unnecessary increase in cost of the module power element 3. .

Further, as for the parts to be added, since there is only one general diode module element which is three-phase bridge-connected to the three-phase power supply of the air conditioner, the assembly process is not complicated and the cost is not increased. Also, it is possible to save space.

The specific embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the present invention. For example, although the diode module element 6 is used in the above embodiment, a plurality of shunt diodes 5 may be individually connected to the module power element 3, or the diode module element 6 and the individual shunt diode 5 may be mixed. You may Further, although the present invention is applied to the three-phase power source, the present invention is not limited to this as long as the module power element 3, the diode module element 6, the PWM control circuit 11 and the like are applicable, and may be applied to, for example, a single-phase power source.

[0034]

In the PWM converter for an air conditioner according to claim 1, all the first converters included in the module power element are included.
The second diode is connected in parallel to the diode in the same direction. Therefore, a part of the current flowing through the first diode in the related art can be shunted to the second diode, so that the loss of the first diode can be made smaller than that in the related art. Then, according to the above-mentioned operation analysis, it is possible to reduce the capacitance required for the module power element, and thus it is possible to avoid an unnecessary increase in cost and reduce the cost.

According to a second aspect of the PWM converter for an air conditioner, a diode module element in which the plurality of second diodes are bridge-connected to be integrally formed is used. Therefore, since only one part is added, the assembling process can be simplified, the cost can be further reduced, and the demand for compactness can be met.

Furthermore, in the PWM converter for an air conditioner according to claim 3, a three-phase power source is applied as the alternating current 1. Therefore, it can be easily implemented as a PWM converter of an air conditioner.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a main part in an embodiment of the present invention.

FIG. 2 is a block diagram showing a PWM converter of an air conditioner in a conventional example.

FIG. 3 is an operation analysis diagram of a module power element in a conventional example.

FIG. 4 is an operation analysis diagram of a module power element in a conventional example.

FIG. 5 is an operation analysis diagram of a module power element in a conventional example.

[Explanation of symbols]

 1 switching element 2 rectifier diode 3 module power element 4 three-phase power supply 5 shunt diode 6 diode module element

Claims (3)

[Claims] 1. A module power element 3 in which a plurality of first diodes (2) whose both ends are short-circuited / open-controlled by a switching element (1) are integrally connected by bridge connection.
In the PWM converter of the air conditioner for converting the alternating current (4) into the direct current by inputting the alternating current (4) into the DC and PWM controlling the switching element (1), all of the module power elements (3) included A PWM converter for an air conditioner, wherein a second diode (5) is connected in parallel to the first diode (2) in the same direction. 2. The air conditioner according to claim 1, wherein a plurality of the second diodes (5) are provided, and a diode module element (6) integrally formed by connecting them in a bridge connection is used. PWM converter. 3. The PWM converter for an air conditioner according to claim 1, wherein the alternating current (4) is a three-phase power source.