JP6978899B2 - Inverter device, power conversion device - Google Patents

Description

The present invention relates to an inverter device.

Power conversion devices such as inverters and converters are used in industrial machinery, industrial vehicles, factories, electric vehicles, power generation systems, and the like. FIG. 1 is a circuit diagram showing an example of a power conversion device.

The power conversion device 100R includes a rectifier 102, a DC link 104, a smoothing capacitor 106, and an inverter 108. The rectifier 102 receives a three-phase AC voltage AC and generates a rectified voltage between the two DC links 104p and n of the P pole and the N pole. The smoothing capacitor 106 is connected between two DC links 104p and n and smoothes the voltage between the DC links 104p and n (referred to as _{DC link voltage VDC).} The inverter 108 receives a DC link voltage _VDC , converts it into an AC voltage, and supplies it to a load 200 such as a motor.

For example, the three-phase inverter 108 has U, V, W phase legs, and each leg has a high side arm and a low side arm. The high side arm and the low side arm switch complementarily and alternately. When the duty ratio of switching is d, the output voltage V _{U to W} ) of each phase is ideally given by the equation (1).
V _{U ~ W} = _VDC × d… (1)

In practice, a dead time is inserted in which the high side arm and the low side arm are turned off at the same time in order to prevent the high side arm and the low side arm from turning on at the same time and flowing a through current. Due to the influence of this dead time, the output voltages V _{U to W} deviate from the ideal value of the equation (1).

Conventionally, the duty ratio d has been compensated in order to correct the error of _{the output voltages VU to W} due to the dead time. The compensation amount at this time was calculated assuming that _{the DC link voltage VDC was constant.}

Japanese Unexamined Patent Publication No. 8-223930

As the DC link capacitor, a large-capacity electrolytic capacitor having a short life is often used. For applications where periodic replacement is difficult, a DC link capacitor-less inverter with a reduced capacity or omitted DC link capacitor is used. In the DC link condenserless inverter, the DC link voltage _VDC is not a direct current but a three-phase full-wave rectified waveform, which fluctuates with time. Therefore, in the conventional compensation method on the premise that the DC link voltage V _DC is constant, the error of the _{output voltages V U to W becomes large.}

The present invention has been made in view of the above problems, and one of the exemplary purposes of the embodiment is to provide a DC link capacitorless inverter with improved output voltage accuracy.

One aspect of the present invention relates to a DC link capacitorless inverter device. The inverter device controls the inverter with a pair of DC links, an inverter that converts the DC link voltage generated in the DC links into alternating current and supplies it to the load, and a duty ratio corrected according to the fluctuation amount of the DC link voltage. It is equipped with an inverter controller.

Another aspect of the invention relates to a power converter. The power conversion device may include a rectifier that generates a voltage obtained by full-wave rectifying a three-phase AC voltage between a pair of DC links, and an inverter device.

It should be noted that any combination of the above components or components or expressions of the present invention that are mutually replaced between methods, devices, systems, etc. are also effective as aspects of the present invention.

According to the present invention, the accuracy of the output voltage can be improved.

It is a circuit diagram which shows an example of a power conversion device. It is a circuit diagram of the power conversion apparatus which concerns on embodiment. It is a block diagram of an inverter controller. It is a figure explaining an example of compensation by a correction amount generation part. It is a figure which shows the conveyor lane.

Hereinafter, the present invention will be described with reference to the drawings based on the preferred embodiments. The same or equivalent components, members, and processes shown in the drawings shall be designated by the same reference numerals, and duplicate description thereof will be omitted as appropriate. Further, the embodiment is not limited to the invention, but is an example, and all the features and combinations thereof described in the embodiment are not necessarily essential to the invention.

In the present specification, the "state in which the member A is connected to the member B" means that the member A and the member B are physically directly connected, and the member A and the member B are electrically connected to each other. It also includes cases of being indirectly connected via other members that do not substantially affect the connection state or impair the functions and effects performed by the combination thereof.

Similarly, "a state in which the member C is provided between the member A and the member B" means that the member A and the member C, or the member B and the member C are directly connected, and their electricity. It also includes cases of being indirectly connected via other members that do not substantially affect the connection state or impair the functions and effects performed by the combination thereof.

FIG. 2 is a circuit diagram of the power conversion device 100 according to the embodiment. The power conversion device 100 includes a rectifier 102 and a DC link capacitorless inverter device 300. The inverter device 300 includes a pair of DC links 302P and 302N, an inverter 310, an inverter controller 320, a gate driver 330, and an upper controller 340.

_{The host controller 340 is a voltage VU} to W to be supplied to the load 200 so that the state (rotation speed, speed, position, torque, etc.) of the load (for example, motor) 200 approaches the target value, in other words, the duty ratio of switching. Generates a control command value PWM # that indicates. The host controller 340 may be a feedback controller or an open loop controller.

Inverter 310 converts the AC DC link voltage _{V DC} generated between the DC link and supplies to the load 200. The inverter controller 320 generates _{a pulse signal S PWM} having a duty ratio corresponding to the control command value PWM # from the host controller 340. The gate driver 330 _{generates a gate drive signal in response to the pulse signal S PWM} , and PWM drives the switching element of the inverter 310.

In the inverter controller 320, a dead time for preventing a through current is inserted. Further, the duty ratio is corrected in order to compensate for the error of _{the output voltages VU to W} caused by this dead time.

Further, the inverter controller 320 _{monitors the DC link voltage VDC} , corrects the duty ratio PWM # according to the fluctuation amount ΔV _DC , and controls the inverter 310 with the corrected duty ratio PWM'.
PWM'= PWM # + PWMc'… (2)
PWMc'represents the correction amount of the duty ratio.

FIG. 3 is a block diagram of the inverter controller 320. The inverter controller 320 includes a sampling circuit 322, a correction amount generation unit 324, an adder 326, and a pulse width modulator 328. The inverter controller 320 can be configured with software-controllable hardware such as a CPU and a microcomputer. In that case, the correction amount generator 324, the adder 326, and the pulse width modulator 328 are realized by the CPU, the microcomputer, and the like. Indicates the function to be performed. Alternatively, the inverter controller 320 may be configured by a digital circuit, in which case the correction amount generation unit 324, the adder 326, and the pulse width modulator 328 are each configured by a digital circuit.

Sampling circuit 322 at a predetermined sampling period, sampling the DC link voltage _{V DC.} The sampling cycle may match the update cycle of the control command value PWM #.

The correction amount generation unit 324 receives the signal i # a (where # is U to V) _{indicating the detected value (or the direction thereof) of the output currents IU to W and the sampled voltage value VDC} [0]. The correction value PWMc is generated according to them. The sign of the correction value PWMc changes according to the direction of the output current.
For example, in a certain phase, when the output current flows in the direction of flowing into the load 200, the output current is positive, the correction value PWMc at this time is negative, and the duty ratio is compensated in the direction of decreasing.

On the contrary, when the current flows from the load 200 to the inverter 310, the output current is negative, and the correction value PWMc at this time is positive, and the duty ratio is compensated in the increasing direction.

The adder 326 adds the control command value PWM # and the correction value PWMc to generate the corrected duty command value PWM'.

The pulse width modulator 328 generates _{a pulse signal S PWM} having a duty ratio corresponding to the duty command value PWM'. Although the pulse signal S _PWM is shown here by one signal line, in reality, two signal lines of the high side arm and the low side arm of the inverter may exist for three phases.

FIG. 4 is a diagram illustrating an example of compensation by the correction amount generation unit 324. The detection value _{VDC [0] of the current DC link voltage VDC} is input to the correction amount generation unit 324 at a predetermined sampling rate. The correction amount generation unit 324 has a fluctuation amount ΔV _DC = (V _DC [-1] −V _DC [0]) _{which is the difference between the previous voltage value V DC} [-1] and the current voltage value V _{DC [0].} A correction value PWMc is generated for the duty ratio according to the above. Since the sampling period is constant, it can be said that this fluctuation amount ΔV _DC represents the gradient of the DC link voltage _VDC , and the duty ratio correction amount PWMc'is the first proportional to the gradient of the _{DC link voltage VDC.} It can be said that the component ΔPWMc and the second component PWMc that does not depend on the fluctuation amount of the DC link voltage _{VDC are included.}
PWMc'= PWMc + ΔPWMc ... (3)

The second component PWMc corresponds to a compensation amount defined on the assumption that _{the DC link voltage VDC is constant.}

On the other hand, the first component ΔPWMc is proportional to the fluctuation amount of the _{DC link voltage VDC.}
ΔPWMc = PWMc × k × ΔV _DC / V _DC [-1]
_{= PWMc × k × (V DC} [0] -V DC [-1]) / V DC [-1] ... (4)

ΔV _DC / V _DC [-1] is a volatility based on the previous voltage value. For example, k = 0.5 can be set.

Summarizing the equations (3) and (4), the correction amount is expressed by the equation (5).
PWMc'= PWMc × (1 + k · ΔV _DC / _VDC [-1])… (5)

According to the inverter device 300 according to the embodiment, it is possible to correct the duty ratio in consideration of the fluctuation of the _{DC link voltage V DC , reduce the error of the output voltage V OUT} , and improve the accuracy.

Subsequently, the use of the inverter device 300 will be described. FIG. 5 is a diagram showing a conveyor lane. The conveyor lane 400 is installed in factories, airports, and the like to carry products and luggage. The conveyor lane 400 is configured by connecting a plurality of units 402. Each unit 402 is provided with a motor 404 for driving the belt, and as a result, the plurality of motors 404 are spatially dispersed.

If a plurality of inverters 406 for driving a plurality of motors 404 are centrally arranged at one place (control panel 405) as shown by a broken line, the wiring length of the power line 408 between the inverter 406 and the motor 404 becomes long. The loss will increase. In addition, changing the layout involves re-laying the power line, which makes it difficult to change the layout once it has been decided.

Therefore, in the conveyor lane 400 of FIG. 5, a power conversion device 410 including an inverter and a rectifier is provided on the unit 402 side, and AC power is individually supplied to the power conversion device 410.

When the power conversion device including the inverter 406 is centrally arranged on the control panel 405 as shown by the alternate long and short dash line, the number of parts of the power conversion device may not be a problem because there are few size restrictions. In addition, in the centralized layout, maintenance labor is relatively small, so even if parts with a short life are used, measures such as regular replacement can be taken. However, the centralized layout also has the disadvantage of requiring a dedicated space for installing the control panel 405.

On the other hand, as shown by the solid line in FIG. 5, when the power conversion device 410 is built in the unit 402 and distributed, the power conversion device 410 is required to be miniaturized, and therefore the number of parts is required to be reduced. Further, if a plurality of power conversion devices 410 are distributed and arranged, maintenance labor is relatively increased, and therefore, the adoption of parts having a short life should be avoided.

In the centralized arrangement, there is room to select a relatively good environment as the installation location of the control panel, but in the distributed arrangement, each unit 402 may have to be installed in a bad environment, and the unit 402 has a sealed structure. May be required. In this case, the temperature inside the housing of the unit 402 tends to rise, so that the component life (particularly the capacitor) tends to be shortened.

The power conversion device 100 according to the embodiment can be suitably used as a power conversion device 410 in a system adopting a distributed layout. Specifically, since the power conversion device 100 does not require a DC link capacitor for smoothing (or can be reduced in capacity), the size can be reduced and the unit 402 can be easily provided.

In addition, although an electrolytic capacitor having a short life is used as the DC link capacitor, the power conversion device 100 according to the embodiment does not require an electrolytic capacitor, so that periodic replacement work is not required and maintenance labor is required. Can be reduced.

The present invention has been described above based on examples. It will be understood by those skilled in the art that the present invention is not limited to the above embodiment, various design changes are possible, various modifications are possible, and such modifications are also within the scope of the present invention. By the way. Hereinafter, such a modification will be described.

(First modification)
The inverter controller 320 may _{detect the output voltages V U to} V _W and adjust the duty ratio by feedback so as to match the voltage command value. Even in this case, the error of the output voltage can be reduced by correcting the duty ratio based on _{the DC link voltage VDC.}

(Second modification)
The DC link capacitor does not have to be completely zero, and the present invention can be applied to an inverter provided with a DC link capacitor having a small capacity. Therefore, DC link capacitorless can include not only the case where the DC link capacitor is zero, but also an inverter provided with a small DC link capacitor.

The present invention has been described using specific terms and phrases based on the embodiments, but the embodiments merely indicate the principles and applications of the present invention, and the embodiments are defined in the claims. Many modifications and arrangement changes are permitted within the scope of the above-mentioned idea of the present invention.

100 Power converter 102 Rectifier 104 DC link bus 106 Smoothing capacitor 108 Inverter 200 Load 300 Inverter device 302 DC link 310 Inverter 320 Inverter controller 322 Sampling circuit 324 Correction amount generator 326 Adder 328 Pulse width modulator 330 Gate driver 340 Upper controller

Claims (7)

It is a DC link capacitorless inverter device.
A pair of DC links and
An inverter that converts the DC link voltage generated in the DC link into alternating current and supplies it to the load.
An inverter controller that samples the DC link voltage and controls the inverter with a duty ratio corrected according to the fluctuation amount of the DC link voltage obtained from the difference between the previous voltage value and the current voltage value.
An inverter device characterized by being equipped with. Previous _V DC [-1] the voltage value, when the current voltage value _{V DC} [0], the compensation amount of the duty _{ratio, (V DC [0] -V} DC [-1]) / V The inverter device according to claim 1 , wherein the inverter device includes a first component proportional to _DC [-1]. When the compensation amount specified on the assumption that the DC link voltage is constant is PWMc, the previous voltage value is _VDC [-1], the current voltage value is _VDC [0], and the predetermined coefficient is k. , The compensation amount of the duty ratio is
_{ΔPWMc = PWMc × k × (V} DC [0] -V DC [-1]) / V DC [-1]
The inverter device according to claim 1 , wherein the inverter device includes the first component represented by. It is a DC link capacitorless inverter device.
A pair of DC links and
An inverter that converts the DC link voltage generated in the DC link into alternating current and supplies it to the load.
An inverter controller that controls the inverter with a duty ratio corrected according to the slope of the DC link voltage.
An inverter device characterized by being equipped with. The inverter device according to claim 4, wherein the compensation amount of the duty ratio includes a first component proportional to the slope of the DC link voltage. The inverter device according to any one of claims 1 to 5, wherein the DC link voltage is sampled at a duty ratio update cycle. A rectifier that generates a voltage obtained by full-wave rectifying a three-phase AC voltage between the pair of DC links.
The inverter device according to any one of claims 1 to 6 and the inverter device.
A power conversion device characterized by being equipped with.

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