JPH1118435A - High power factor inverter device where resonance of dc link part is suppressed - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an unexpectedly large current from being generated between capacitors by performing setting, so that both of the switching frequency of a PWM converter and that of a PWM inverter become specific values and suppressing the resonance of the switching frequency of a DC link part. SOLUTION: In a high efficiency inverter device, a DC link part 2 for stabilizing a DC voltage consists of two capacitors 11 that are connected to an area close to the DC output side of a PWM converter 21, two capacitors 3 that are connected to an area close to the DC input side of a PWM inverter 23, and a wire 12 for connecting the capacitors 11 and a capacitor 13. Two groups of capacitors 11 and 13 and the inductance of the wire 12 constitute a series LC resonance circuit of. Therefore, the switching frequency of the PWM converter 21 and that of the PWM inverter 23 are set, so that they are smaller than f1/4r2 and larger than 500 Hz, where f1 is the resonance frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to suppressing a resonance phenomenon of a DC link portion of a high power factor inverter device and stably operating the device.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing a conventional high power factor inverter device. In FIG. 6, reference numeral 1 denotes a three-level PWM converter (hereinafter referred to as a PWM converter) for converting AC into DC using a GTO element. And the switching frequency is X1
And 3 is a three-level PWM inverter (hereinafter referred to as a PWM inverter) for converting DC into AC and having a switching frequency of X2. Reference numeral 2 denotes a DC link unit for stabilizing a DC voltage, and two smoothing capacitors 11 (hereinafter, capacitors) connected in close proximity to the DC output side of the PWM converter 1;
It is composed of two smoothing capacitors 13 (hereinafter, capacitors) connected in close proximity to the DC input side of the PWM inverter 3 and a wiring 12 connecting the capacitors 11 and 13 to each other. Reference numeral 5 denotes a power supply having a commercial frequency, and reference numeral 6 denotes an electric motor connected as a load, for example, an induction motor.

The inductances of the two groups of capacitors 11 and 13 and the wiring 12 form an LC series resonance circuit. Here, it is assumed that the resonance frequency is f1.

Next, the operation will be described. The PWM converter 1 converts a power supply voltage of a commercial frequency into a direct current. The DC link unit 2 includes a PWM converter 1 and a PWM inverter 3
Are electrically connected to each other, and a capacitor 11 connected in close proximity to the PWM converter 1 and a capacitor 13 connected in close proximity to the PWM inverter 3 are provided with a converter (PWM converter and PWM).
DC voltage fluctuations associated with the operation of an inverter). The PWM inverter 3 converts a DC voltage into an AC having a variable frequency and supplies power to the electric motor 6.

The switching frequency X1 of the conventional PWM converter and the switching frequency X of the PWM inverter
2 is set to 500 Hz or more because the pulsation on the AC side caused by the switching of the PWM converter and the PWM inverter becomes smaller as the switching frequency is increased (the smaller the pulsation, the better).

The PWM converter 1 is provided with a smoothing capacitor 1 close to the DC output side in order to smooth the fluctuation of the DC output voltage due to the relatively high switching frequency X1.
1 and that the PWM inverter 3 also performs a switching operation at a relatively high frequency (frequency X
Since it is necessary to prevent the fluctuation of the DC voltage accompanying 2), since the smoothing capacitor 13 is required in the immediate vicinity of the DC input side,
The smoothing capacitors 11 and 13 are divided into two as shown in FIG. Moreover, the capacities of these capacitors are set as large as possible to enhance the smoothing effect.

As described above, the DC link unit 2 is a series resonance circuit (resonance frequency f1) made of LC. Also, P
Since both the WM converter 1 and the PWM inverter 3 are excitation sources (excitation frequency X1 or X2) that excite an oscillation current, a resonance phenomenon occurs when either the excitation frequency X1 or X2 approaches f1. As a result, the oscillating current is amplified, and an unexpectedly large current may be generated inside the DC link unit 2. When such a phenomenon occurs, a phenomenon such as heat generation of the smoothing capacitors 11 and 13 or a voltage drop due to the impedance of the wiring 12 becomes excessive and the PWM inverter 3 does not operate normally occurs.

[0008]

Since the conventional high power factor inverter device is configured as described above, an excessive current is generated inside the DC link due to resonance at the switching frequency of the converter or the inverter. There was a problem that there is.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a high-power device capable of obtaining a stable operation without generating an unexpectedly large current between capacitors divided into two groups. It is an object of the present invention to provide a rate inverter device.

[0010]

According to the present invention, a PWM converter and a PWM inverter are connected to a DC output side of the PWM converter, and the smoothing capacitor is connected to the PWM converter.
A capacitor connected to the DC input side of the M inverter;
A high power factor inverter device connected via a DC link unit including a wiring connecting the two capacitors to each other, wherein both the switching frequency of the PWM converter and the switching frequency of the PWM inverter are: Assuming that the primary resonance frequency of the DC link unit is f1, it is set to be smaller than (f1) / √2 and larger than 500 Hz to suppress the resonance due to the switching frequency of the DC link unit.

Further, the present invention provides a PWM converter and a P converter.
The WM inverter is a three-level PWM converter and a three-level PWM inverter, respectively.
Two capacitors of capacitance C1 connected to the DC output side of the M converter, two capacitors of capacitance C2 connected to the DC input side of the PWM inverter, and the converter side capacitor and the inverter side capacitor are connected to each other. And the primary resonance frequency of the DC link portion is f1 = 1 / [2 ・ π ｛(3L) (C1 ・ C2) / (C
1 + C2)｝ ^1/2 ].

Further, the present invention provides two capacitors having a capacitance C1 connected to the DC output side of the PWM converter,
2 of the capacitor C2 connected to the DC input side of the WM inverter
C1 = C2.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of a high power factor inverter device of the present invention. In the figure, reference numeral 21 denotes a three-level PWM converter (hereinafter, PWM converter) configured by using a GTO element for converting alternating current into direct current, the switching frequency of which is regulated as described later. Reference numeral 23 denotes a three-level PWM inverter (hereinafter referred to as a PWM inverter) for converting DC to AC, the switching frequency of which is regulated as described later. Reference numeral 2 denotes a DC link unit for stabilizing a DC voltage, and two capacitors 11 connected in close proximity to the DC output side of the PWM converter 21 and a PWM inverter 2
Two capacitors 13 connected in close proximity to the DC input side
And a wiring 12 for connecting the capacitor 11 and the capacitor 13 to each other. 5 is a commercial frequency power supply, 6
Is an induction motor connected as a load, for example.

The inductances of the two groups of capacitors 11, 13 and the wiring 12 constitute an LC series resonance circuit. Here, it is assumed that the resonance frequency is f1.

Next, the operation will be described. The PWM converter 21 converts a commercial frequency power supply voltage into a direct current. The DC link unit 2 electrically connects the PWM converter 21 and the PWM inverter 23, and the capacitor 11 connected in close proximity to the PWM converter 21 and the capacitor 13 connected in close proximity to the PWM inverter 23 include a converter (PWM converter and PWM). DC voltage fluctuations associated with the operation of an inverter). The PWM inverter 23 converts a DC voltage into an AC having a variable frequency and supplies electric power to the electric motor 6.

FIG. 2 is an explanatory diagram equivalently showing the circuit of FIG. The PWM converter 21 of FIG.
In addition, the PWM inverter 23 of FIG. The smoothing capacitor 11 is called capacitors 11a and 11b as shown in FIG. 2, and the capacitor 13 is called capacitors 13a and 13b. The wiring 12 is called inductances 12a to 12c. This current excitation source 1
The pulsating current due to 21 and 123 is applied to the smoothing capacitor 11a,
11b, 13a, 13b and inductances 12a to 12
It is necessary not to cause resonance during c. The main components of the pulsating current are the switching frequency F1hz of the PWM converter 21 and the switching frequency F2hz of the PWM inverter 23.
1 and F2 are determined to be frequencies that do not promote resonance of the DC link unit 2 at the primary resonance frequency f1hz.

In order to explain in more detail, the primary resonance loop of the DC link unit 2 of the circuit of FIG. 2 is further modified and shown in FIG. In FIG. 3, the smoothing capacitor 11
The capacitance of both a and 11b are C1 farads, the capacitance of the smoothing capacitors 13a and 13b are both C2 farads, and the wiring 1
The inductances 2a to 12c are Lp, Lc, and Ln.

As shown in FIG. 3, the primary resonance circuit of the DC link section 2 has two symmetrical resonance loops (since the inductances Lp and Ln are usually equal). To be deformed. That is, when the inductance Lc shared by the two loops is considered as a parallel circuit having twice the inductance, it becomes easier to study each loop.

FIG. 5 shows one of the loops extracted from FIG.
It is. Since the resonance loop of the DC link unit 2 is shown in FIG. 5, its primary resonance frequency f1 can be expressed by the following equation.

[0020]

(Equation 1)

## EQU1 ## In FIG. 5, reference numeral 110 denotes a frequency F
hz, which corresponds to either the PWM converter 21 or the PWM inverter 23. The current in the circuit shown in FIG. 5 when it is vibrated by the vibration source 110 having the frequency Fhz will be discussed. Assuming that the output current from the excitation source 110 is I, the shunt current to the capacitor 11a is I1, and the shunt current to the capacitor 13a is I2, the shunt rate (I1 / I) and (I2 / I) when C1 = C2. Can be expressed as follows using the primary resonance frequency f1 of the DC link unit 2 and the excitation frequency F of the excitation source 110.

[0022]

(Equation 2)

In order to prevent a problem caused by resonance, the current I1 flowing through the smoothing capacitor 11a or 13a
Alternatively, I2 must not be larger than the excitation current I, that is, 0 <shunt ratio <1.

[0024]

(Equation 3)

From equation (6), the following is obtained: 1 <2-2 (F / f1) ² (F / f1) ² <1/2 F <f1√ (1/2) (7) That is, the frequency F of the excitation source 110 must be lower than 1 / √2 of the primary resonance frequency f1.

When the switching frequency F is lowered, a large pulsating current due to switching appears on the AC side. Therefore, the following consideration is required. F> 500 Hz (8) From formulas (7) and (8), the range of F is 500 Hz <F <f1√ (1/2) (9). That is, the PWM converter or P of the high power factor inverter device
The switching frequency of the WM inverter is lower than 1 / √2 of the primary resonance frequency of the DC link unit, and 500H
By setting it higher than z, it is possible to prevent a resonance current from being generated inside the DC link unit.

Needless to say, the DC link unit 2
Is generally considerably higher than √2 times 500 Hz, so there is no fear that there is no F satisfying the expression (9). When the capacitance (C1C2) / (C1 + C2) = C of the resonance circuit is constant, C1 and C1 are used to enhance the function as a smoothing capacitor that more reliably absorbs voltage fluctuations on the inverter side and the converter side. In order to make C2 as large as possible, it is most efficient to set C1 = C2.

[0028]

As described above, according to the present invention, both the switching frequency of the PWM converter and the switching frequency of the PWM inverter constituting the high power factor inverter device are (1 / √2) of the primary resonance frequency of the DC link section. Lower, 500H
By setting the value to be higher than z, resonance of the DC link unit due to the switching frequency can be suppressed, and heat generation of the capacitor and unstable operation of the converter can be prevented.

Further, since the capacitor capacities on the inverter side and the converter side are made equal, the capacity of the smoothing capacitor can be maximized with respect to the fixed capacitor capacity of the resonance circuit.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a high power factor inverter device according to Embodiment 1 of the present invention.

FIG. 2 is an equivalent circuit diagram illustrating FIG.

FIG. 3 is an explanatory diagram obtained by modifying FIG. 2;

FIG. 4 is an explanatory diagram obtained by modifying FIG. 3;

FIG. 5 is an explanatory view showing a part of FIG. 4;

FIG. 6 is a configuration diagram of a conventional high power factor inverter device.

[Explanation of symbols]

2 DC link section, 11 smoothing capacitor, 12 wiring inductance 13 smoothing capacitor, 21 PWM converter with restricted switching frequency, 23 PWM inverter with restricted switching frequency

Claims (3)

[Claims] 1. A PWM converter and a PWM inverter connect a smoothing capacitor connected to a DC output side of the PWM converter, a capacitor connected to a DC input side of the PWM inverter, and the two capacitors. A high power factor inverter device connected via a DC link unit constituted by wiring and a switching frequency of the PWM converter and the PWM
When any one of the switching frequencies of the M inverter sets the primary resonance frequency of the DC link unit to f1, (f
1) A high power factor inverter device which is set to be lower than / √2 and higher than 500 Hz to suppress resonance due to the switching frequency of the DC link unit. 2. The PWM converter and the PWM inverter are a three-level PWM converter and a three-level PWM inverter, respectively. The DC link unit includes two capacitors having a capacitance C1 connected to a DC output side of the PWM converter, and the PWM inverter. And two wirings of inductance L connecting the capacitor on the converter side and the capacitor on the inverter side to each other. The resonance frequency is f1 = 1 / [2 · π · ｛(3L) (C1 · C2) / (C
1 + C2)｝ ^1/2 ], wherein the high power factor inverter device according to claim 1, wherein resonance of the DC link unit is suppressed. 3. The capacity of two capacitors C1 connected to the DC output side of the PWM converter and two capacitors C2 connected to the DC input side of the PWM inverter is C1 = C2. The high power factor inverter device according to claim 2, characterized in that: