JP3494051B2 - Inverter smoothing circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a smoothing circuit for an inverter used in an inverter that obtains AC power from DC power from a battery, and more particularly to a circuit for preventing destruction or characteristic deterioration of a smoothing capacitor.

[0002]

2. Description of the Related Art Heretofore, various inverters have been known which obtain desired AC power from DC power from a battery.
For example, in an electric vehicle, a hybrid vehicle, or the like, the inverter is controlled according to the accelerator opening degree or the like, and thereby the driving of the motor is controlled. Further, during deceleration of the vehicle, regenerative braking is performed using the inverter, and the battery is charged with the generated voltage.

Here, the inverter turns on and off a switching transistor inside the inverter to convert the direct current power from the battery into a desired alternating current and supply it to the motor coil, and the battery voltage fluctuates due to this current supply. There is a risk. Therefore, a smoothing capacitor is arranged in parallel with the inverter to prevent voltage fluctuation.

[0004]

As described above, the smoothing capacitors are used. However, in these smoothing capacitors, if one capacitor is used to obtain a necessary capacitor capacity, the capacitor becomes large in size. There's a problem. Therefore, normally, a plurality of capacitors are used in parallel.

On the other hand, the motor drive current is a large current, and a ripple current flows through the smoothing capacitor based on the change in the motor drive current. Especially, the motor drive current is P
In many cases, WM control is performed, and a ripple current due to switching of a transistor also occurs.

The capacitors generate heat according to the ripple current, but if there is a difference in the amount of ripple current among the capacitors, the amount of heat generation also differs. Therefore, there is a problem in that the degree of deterioration varies among the capacitors, and the deterioration of the capacitors that generate a large amount of heat becomes severe.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a smoothing circuit for an inverter capable of reducing unevenness of heat generation in a smoothing capacitor.

[0008]

SUMMARY OF THE INVENTION The present invention is an inverter smoothing circuit used in an inverter for converting DC power from a battery into AC power, wherein a plurality of inverter smoothing circuits are connected in parallel across the battery and the inverter. And a smoothing capacitor, among the plurality of smoothing capacitors
At least one of the capacitances of other smoothing capacitors
The amount is different from the, and based on the magnitude of the ripple current flowing through the plurality of the capacitance of the smoothing capacitor in each of the smoothing capacitor, a large smoothing co ripple current
For smoothing with large capacitance and small ripple current
It is characterized in that the capacitance of the capacitor is set small . In this case, the smoothing capacitors
Capacitors for smoothing the capacity from the inverter
Based on the magnitude of the impedance of the current path to
The capacitance of the smoothing capacitor with low impedance is
Large smoothing capacitor with large impedance
This means that the capacity of is set small.

The ripple current flowing in and out of the plurality of smoothing capacitors changes according to the impedance of the current path connecting the inverter and each smoothing capacitor. On the other hand, the impedance is proportional to the length of the current path, so that a capacitor closer to the inverter has more ripple current flowing in and out, and thermal stress becomes larger than that of other capacitors. Therefore, the temperature rise of this capacitor causes destruction or deterioration of life.

Therefore, in this embodiment, the capacitance of the capacitor is determined based on the impedance of the ripple current. This makes it possible to balance the thermal stress in the capacitor and prevent destruction or characteristic deterioration due to temperature rise of a specific capacitor.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings.

FIG. 1 is a block diagram of an electric vehicle system including a smoothing circuit of this embodiment. The battery 10 outputs a predetermined driving power, and a secondary battery such as a nickel hydrogen battery is used. Also, in a normal case, a plurality of battery cells are connected in series and have an output voltage of about 200V to 300V.

A smoothing circuit 12 is connected between the positive and negative electrodes of the battery 10. The smoothing circuit 12 is composed of three capacitors C1, C2, and C3, which are connected in parallel.

Further, the smoothing circuit 12 includes an IGBT.
Module 14 is connected. The IGBT module 14 is an IGBT (insulated gate bipolar trans).
istor) and other power transistors are used. For example, six IGBTs are prepared, two of them are connected in series, and three arms are provided. Then, each arm is connected in parallel between the battery electrodes, and the middle point of each arm is connected to the motor 16
Connect to. The smoothing circuit 12 and the IGBT module 14 are collectively called an inverter 18.

In this example, the motor is a three-phase AC motor, the three motor coils of which are connected to the midpoint of each arm. And the upper IGBTs in different arms
By sequentially turning on the lower IGBT and the lower IGBT, three-phase alternating current can be supplied to the motor. Further, the output torque of the motor 16 is controlled by PWM-controlling the IGBT according to the output torque command.

In this embodiment, the capacitors (three in this case) of the smoothing circuit 12 are set to have different capacities.

In FIG. 1, the ripple current flowing in and out of the capacitor C1 is Ic1, the ripple current flowing in and out of the capacitor C2 is Ic2, the ripple current flowing in and out of the capacitor C3 is Ic3, and the impedance of the current path Lc1 of Ic1 is Z (Lc1). , Ic2, the impedance in the current path Lc2 is Z (Lc2), Ic3
Of the impedance in the current path Lc3 of Z (Lc
3).

Since the capacitors C1, C2 and C3 are connected in parallel, the voltages across them are basically the same, and Ic1 × Z (Lc1) = Ic2 × Z (Lc2) = Ic3
× Z (Lc3).

On the other hand, since the impedance Z is proportional to the length of the current path, Ic3>Ic2> Ic in the above example.
It becomes 1. Therefore, if it is left as it is, the ripple current in the capacitor C3 is large, the stress of the capacitor C3 is larger than that of the other capacitors C2 and C1, and the temperature of C3 is destroyed or the life thereof is deteriorated.

Therefore, in this embodiment, the capacities of the three capacitors are set so that C1: C2: C3 = Z (Lc3): Z (Lc2): Z (Lc1) (= Ic1: Ic2: Ic3). .

As a result, the capacitance of the capacitor C3, which has a small impedance Z and a ripple current easily flows, the capacitance of the capacitor C2, which has the second largest ripple current, has the second largest capacitance, and the capacitance of the capacitor C1 which has a large impedance and a ripple current hardly flows. Is set to the smallest. Therefore, it is possible to prevent the thermal stress of each capacitor from being balanced and the generation of heat to be concentrated in a specific capacitor, resulting in destruction or deterioration.

The total required capacitor capacity Call is
It is predetermined and the sum of the three capacitors (C1 + C2
+ C3) is the total required capacitor capacity Call.

FIG. 2 shows a capacitor C in the smoothing circuit.
It is a figure which shows the other example of arrangement | positioning of 1, C2, and C3. In this example, the capacitor C2 is closest to the inverter 16. IG
Capacitor C1 from the + and-terminals of BT module 14
The length of the wiring (bus bar) up to Lc1, capacitor C
When the length of the bus bar up to 2 is Lc2 and the length of the bus bar up to the capacitor C3 is Lc3, Lc1≈Lc3, Lc2 <Lc1 (≈Lc3).

In such a state, if the required capacitor capacity is divided into three equal parts, Ic2 becomes larger than Ic1 and Ic3, and the rise in internal temperature is also biased to the capacitor C2, which causes characteristic deterioration and destruction. Become.

Therefore, the required total capacity of the capacitor is 8000.
In case of about μF, C1 = C3 = 2200 μF, C2 = 3
By setting it to 300 μF, it is possible to suppress the bias of temperature rise due to the imbalance of the ripple current.

[0026]

As described above, according to the present invention,
Since the capacities of the capacitors are determined according to the ripple current, it is possible to balance the thermal stresses in the plurality of capacitors and prevent the generation of heat in a specific capacitor from being biased, resulting in destruction or characteristic deterioration.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of a system.

FIG. 2 is a diagram showing connection of capacitors.

[Explanation of symbols]

10 battery, 12 smoothing circuit, 14 IGBT module, 16 motor, 18 inverter.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuya Shikata 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. (72) Inventor Takahisa Yamakawa 1 Toyota Town, Aichi Prefecture, Toyota Motor Co., Ltd. ( 56) References JP-A-5-292703 (JP, A) JP-A-6-284517 (JP, A) JP-A-9-284995 (JP, A) International Publication 98/053549 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02M 7/48

Claims (2)

(57) [Claims] 1. A smoothing circuit for an inverter used in an inverter for converting DC power from a battery into AC power, comprising: a battery and a plurality of smoothing capacitors connected in parallel between both ends of the inverter. , At least one of the plurality of smoothing capacitors
The capacitance is different from that of other smoothing capacitors.
Ri, and based on the magnitude of the ripple current the smoothing capacitor flows through each of the smoothing capacitor, the lip
The smoothing capacitor with a large
Small smoothing capacitor with small pull current set to small
A smoothing circuit for an inverter, which is characterized in that 2. The DC power from the battery is converted to AC power.
Inverter smoothing used in replacement inverter
A plurality of circuits connected in parallel across the battery and the inverter
Has a smoothing capacitor, a, of at least one of the plurality of the smoothing capacitor
The capacitance is different from that of other smoothing capacitors.
And the capacity of each smoothing capacitor is
The impedance of the current path from each
Based on the size of the impedance
The capacity of the smoothing capacitor is large.
The capacitance of the smoothing capacitor is set to a small value.
Inverter smoothing circuit characterized by the following .