JP6884481B2 - Power converter - Google Patents

Description

An embodiment of the present invention relates to a power conversion device.

There are power conversion devices that input AC voltage and convert it to AC voltage of different voltage and frequency, and power conversion devices that input DC voltage and convert it to AC voltage. In such a power converter, when the input voltage is high, a method is used in which a plurality of unit converters are cascaded, multi-leveled, and the unit converter is controlled by one pulse using phase shift control. May be done. Multi-leveling makes it possible to reduce the harmonics of the output waveform and reduce the size of the harmonic filter connected to the output.

In the AC load of the power converter, the power factor may be smaller than 1, and in the unit converter operating under phase shift control, it is supplied to the unit converter as a result of the difference in the active power that can be output. The DC voltage may fluctuate. Also, depending on the power factor and the phase of the unit converter, the unit converter may have to absorb power from the load.

If the unit converter does not have a mechanism for stabilizing the supplied DC voltage, the amplitude of the pulse output by the unit converter may fluctuate and harmonics may not be sufficiently suppressed.

When it becomes necessary to absorb the power from the load when the power conversion device does not support the bidirectional conversion operation, an excessive voltage may be applied to the input side.

Japanese Unexamined Patent Publication No. 2017-85812

The embodiment provides a power conversion device capable of stably supplying power to a load regardless of the power factor of the load.

The power converter according to the embodiment drives a power converter including a first unit converter, a second unit converter cascaded to the first unit converter, and the first unit converter. It includes a control device that generates a first gate drive signal and a second gate drive signal that drives the second unit converter, and controls the power converter in one pulse based on phase shift control. The control device sets the phase of the first gate drive signal to the lead phase of the output voltage of the power converter, sets the phase of the second gate drive signal to the lag phase of the output voltage, and determines. The phase of the first gate drive signal and the phase of the second gate drive signal are exchanged in the cycle of.

In the present embodiment, the first gate drive signal and the second gate drive signal are set to have different phases with respect to the output voltage of the power converter, and the control device switches the phases at a predetermined cycle, so that the power factor of the load is changed. Regardless, it is possible to stably supply power to the load.

It is a block diagram which illustrates the power conversion apparatus which concerns on embodiment. 2 (a) to 2 (c) are schematic vector diagrams for explaining the output voltage, output current, and phase of each unit converter of the power converter. It is a table exemplifying the phase set in each unit converter. This is an example of the operating waveform of the power converter.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the ratio of the sizes between the parts, and the like are not necessarily the same as the actual ones. Further, even when the same parts are represented, the dimensions and ratios may be different from each other depending on the drawings.
In the specification of the present application and each of the drawings, the same elements as those described above with respect to the above-described drawings are designated by the same reference numerals, and detailed description thereof will be omitted as appropriate.

FIG. 1 is a block diagram illustrating an electric power conversion device according to the present embodiment.
As shown in FIG. 1, the power converter 10 includes a power converter 20 and a control device 50. The power conversion device 10 is connected to the AC power supply 1 via the input 12. The AC power supply 1 is, for example, a power system, and outputs a three-phase AC voltage having a frequency of 50 Hz or 60 Hz. The power conversion device 10 is connected to a load (not shown) via outputs 14a and 14b. The load is, for example, an AC load such as an induction motor.

The power converter 20 includes a transformer 22 and unit converters 30a and 30b. The primary side of the transformer 22 is connected to the AC power supply 1 via the input 12. The secondary sides 22a and 22b of the transformer 22 are connected to the unit converters 30a and 30b via the inputs 31a and 31b. The secondary windings of the transformer 22 are isolated from each other and are set to the same number of turns. Therefore, the transformer 22 divides the voltage on the primary side of the AC power supply 1 into the secondary side voltage having the same voltage and supplies the voltage to the unit converters 30a and 30b. The turns ratio between the primary side and the secondary side of the transformer may be adjusted to step down or boost the voltage on the primary side so that the voltage is further divided on the secondary side.

AC voltages having substantially the same voltage value are input to the unit converters 30a and 30b.

The unit converters 30a and 30b are cascade-connected. That is, one output 37a of the unit converter 30a is connected to one output 14a of the power converter 10. The other output 38a of the unit converter 30a is connected to one output 37b of the unit converter 30b. The other output 38b of the unit converter 30b is connected to the other output 14b of the power converter 10.

The unit converter 30a includes a rectifier circuit 32a, a smoothing circuit 34a, and an inverter circuit 36a. The unit converter 30b includes a rectifier circuit 32b, a smoothing circuit 34b, and an inverter circuit 36b. Hereinafter, the configuration of the unit converter 30a will be described. The unit converter 30b has the same configuration as the unit converter 30a, and detailed description thereof will be omitted.

The rectifier circuit 32a inputs an AC voltage from the secondary side 22a of the transformer 22, rectifies it, and outputs it. The rectifier circuit 32a is, for example, a three-phase full-wave rectifier circuit.

The smoothing circuit 34a is connected in parallel to the output of the rectifier circuit 32a. The smoothing circuit 34a is, for example, a capacitor, and together with the rectifying circuit 32a, constitutes a rectifying and smoothing circuit. The smoothing circuit 34a smoothes the rectified voltage output from the rectified circuit 32a and outputs a DC voltage having a pulsating current (hereinafter, also simply referred to as a DC voltage).

The inverter circuit 36a inputs a DC voltage supplied from the smoothing circuit 34a and outputs a square wave AC voltage. The inverter circuit 36a is, for example, a full bridge circuit. The full bridge circuit includes four switching elements ua, va, xa, ya. The switching elements ua and xa are connected in series, and the switching elements va and ya are connected in series. The series circuit of the switching elements ua and xa and the series circuit of the switching elements va and ya are connected in parallel. The connection nodes of the switching elements ua and xa are connected to one output 37a, and the connection nodes of the switching elements va and ya are connected to the other output 38a.

Each of the switching elements ua, va, xa, and ya of the inverter circuit 36a is driven by the gate drive signals VGua, VGva, VGxa, and VGya generated by the control device 50, respectively. Each switching element ub, vb, xb, yb of the inverter circuit 36b is driven by the gate drive signals VGub, VGvb, VGxb, VGyb generated and supplied by the control device 50, respectively.

The control device 50 receives the gate drive signals VGua to VGya, VGub according to the DC voltage input to the unit converters 30a and 30b, the output voltages Va and Vb output by the unit converters 30a and 30b, and the output current Iout. ~ VGyb is generated and supplied to the unit converters 30a and 30b.

As will be described in detail later, the gate drive signal generated by the control device 50 is generated according to the principle of phase shift control, and θ1 and −θ1 (FIG. 2) of the generated gate drive signal are periodically switched.

The power conversion device 10 outputs the voltage Vout via the outputs 14a and 14b. The voltage Vout is a combined voltage of the voltages Va and Vb output by the unit converters 30a and 30b. The output current Iout output by the power converter 20 is equal to the current output by the unit converters 30a and 30b.

The operation of the power conversion device 10 of the present embodiment will be described.
2 (a) to 2 (c) are schematic vector diagrams for explaining the output voltage, output current, and phase of each unit converter of the power converter.
FIG. 2A shows the relationship between the voltage Vout (solid line) and the output current Iout (dashed line) when the power factor cosφ of the load is 1. As shown in FIG. 2A, the phase θa of the voltage Va of the unit converter 30a is set to the lead phase of + θ1 with respect to the voltage Vout. The phase θb of the voltage Vb of the unit converter 30b is set to a lag phase of −θ1 with respect to the voltage Vout.

The active power Pa that can be output by the unit converter 30a is Pa = Va × Iout × cos (θ1). The active power Pb that can be output by the unit converter 30b is Pb = Vb × Iout × cos (−θ1) = Vb × Iout × cos (θ1). If Va = Vb, then Pa = Pb and has a positive value. Therefore, the power converter 20 outputs equal active powers Pa and Pb in the cycle in which the unit converters 30a and 30b output positive or negative voltages. Can be output.

The load of the power conversion device 10 is an AC load, and the power factor cosφ may be smaller than 1. The vector diagram shown in FIG. 2B is a case where the power factor of the load is larger than 0 and smaller than 90 °. In this example, it is shown that the load connected to the power converter 20 has a phase lag of 90 ° from the voltage Va output by the unit converter 30a.

The active power Pa'that can be output by the unit converter 30a is Pa'= Va × Iout × cos 90 ° = 0. That is, the active power cannot be supplied to the load in the cycle in which the unit converter 30a can output a positive or negative voltage.

On the other hand, the phase of the output current Iout described above causes a phase delay of 90 ° -2 × θ1 with respect to the phase of the unit converter 30b. That is, the phase difference between the voltage Vb and the output current Iout is smaller than 90 °.

The active power Pb'that can be output by the unit converter 30b is Pb'= Vb × Iout × cos (90 ° -2 × θ1) and has a positive value.

Therefore, under such load conditions, the unit converter 30a cannot supply active power to the load. On the other hand, the unit converter 30b can supply the load with active power according to the phase difference from the output current Iout.

In the case of a load in which the phase difference between the output current Iout and the output voltage Va of the unit converter 30a is in the range of 0 ° to 90 °, different active powers are applied to the load in each of the unit converters 30a and 30b. It will be supplied.

FIG. 2C shows a vector diagram when the power factor cosφ of the load becomes 0. As shown in FIG. 2C, the phase of the output current Iout is delayed by 90 ° or more from the phase of the unit converter 30a, so that the active power Pa'' to be supplied to the load by the unit converter 30a is negative. Has a value of. Negative active power means that power having an absolute value of the active power is input to the unit converter 30a. On the other hand, in the unit converter 30b, the phase delay of the output current Iout is smaller than 90 ° from the phase of the unit converter 30b. Therefore, the active power Pb ″ output by the unit converter 30b has a positive value.

The unit converters 30a and 30b of this example are supplied with a DC voltage by rectifying and smoothing an AC voltage. Since the DC voltage supplied from the rectifier circuits 32a and 32b and the smoothing circuits 34a and 34b is not stabilized, it changes according to the active power output by the unit converters 30a and 30b. When the DC voltage supplied to the unit converters 30a and 30b fluctuates, the amplitude of the voltage output by the unit converters 30a and 30b fluctuates. Therefore, the voltage waveform output by the power converter 10 is distorted, and the contained harmonics increase.

Further, when the rectifier circuits 32a and 32b are, for example, full-wave rectifier circuits, the unit converters 30a and 30b cannot regenerate electric power to the AC side. Therefore, when the power output by the unit converters 30a and 30b becomes negative, the power from the input load charges the capacitors of the smoothing circuits 34a and 34b. If the capacitor is continuously charged, the voltage across the capacitor rises, resulting in an overvoltage state, which may damage the capacitor.

In the power conversion device 10 of the present embodiment, the phases θ1 and −θ1 set in the unit converters 30a and 30b are switched at a predetermined cycle. The predetermined cycle can be set based on, for example, the cycle of the AC voltage output by the power conversion device 10. This cycle can be n cycles of the output voltage Vout (n is a natural number).

FIG. 3 is a table illustrating the phases set in the best ad-free units 30a and 30b.
As shown in FIG. 3, the phases θa and θb set in the converters 30a and 30b have two patterns. In the first pattern [1], the phase θa = + θ1 of the unit converter 30a is set, and the phase θb = −θ1 of the unit converter 30b is set. In the second pattern [2], the phase θa = −θ1 of the unit converter 30a is set, and the phase θb = + θ1 of the unit converter 30b is set. The first pattern [1] and the second pattern [2] are switched alternately. The switching timing is a predetermined cycle, for example, n cycles of the output voltage Vout.

FIG. 4 is an example of the operating waveform of the power conversion device.
From the top to the bottom of FIG. 4, the gate drive signals VGua, VGva, VGub, VGvb, the output voltages Va and Vb of the unit converters 30a and 30b, the output voltage Vout of the power converter 20, and the output current Iout time. An example of the waveform of the change is shown. The output voltage Vout is a combined voltage of the voltages Va and Vb output by the unit converters 30a and 30b. The output current Iout is equal to the output current of the best ad-free units 30a and 30b.

FIG. 4 shows an example of waveforms for five cycles of the output voltage Vout and the output current Iout. The first pattern [1] and the second pattern [2] are switched every one cycle of the output voltage Vout. The first pattern [1] is set in the cycles of times t0 to t4, t8 to t12, and t16 to t20, and the second pattern [2] is set in the cycles of times t4 to t8 and t12 to t16. Has been done.

In the first pattern [1] of the period of time t0 to t4, t8 to t12, and t16 to t20, the phase setting of the unit converter 30a is + θ1, and the phase setting of the unit converter 30b is −θ1. In the second pattern [2] of the period of time t4 to t8 and t12 to t16, the phase setting of the unit converter 30a is −θ1 and the phase setting of the unit converter 30b is + θ1.

As shown in the figure, the phase set phase is generated in the first pattern [1], for example, the gate drive signal VGua is generated with a lead phase of + θ1 from the time t1. On the other hand, the gate drive signal VGub of the unit converter 30b is generated with a lag phase of −θ1 from time t1.

As shown in FIG. 4, in the first pattern [1], the pulse width of the positive output cycle (for example, time t8 to t10) of the voltage Va output by the unit converter 30a is the voltage output by the unit converter 30b. It is shorter than the pulse width of the positive output cycle of Vb. When switching to the second pattern [2], the pulse width of the positive output cycle of the voltage Va (for example, time t12 to 15) is longer than the pulse width of the positive output cycle of the voltage Vb.

Then, the pulse width of the normal cycle of the voltage Va in the first pattern [1] is substantially equal to the pulse width of the cycle of the normal cycle of the voltage Vb in the adjacent second pattern [2]. .. The pulse width of the normal cycle of the voltage Vb in the first pattern [1] is substantially equal to the pulse width of the cycle of the normal cycle of the voltage Va in the second pattern [2]. The same applies to the cycle of negative cycle. Since the active power output by the unit converters 30a and 30b is substantially proportional to the area of the voltages Va × Iout and Vb × Iout in FIG. 4, the active power output by the unit converters 30a and 30b is substantially proportional. Become equal.

In the power conversion device 10 of the present embodiment, one-pulse control based on phase shift control (hereinafter, also simply referred to as one-pulse control) is used to generate the output voltage and the output current. In the one-pulse control, one cycle of the output voltage Vout in the power conversion device 10 is set as the control cycle. For example, in a cycle in which the voltage Vout is positive, the switching elements ua and ya are turned on and the switching elements va and xa are turned off after advancing the phase by + θ from the voltage Vout. In order to adjust the value of the output voltage Vout, the phase difference between the switching elements ua and ya and the switching elements va and xa is controlled to be narrowed from 180 °. The switching element of the unit converter 30b is also phase-shifted in the same manner after delaying the phase by −θ from the output voltage Vout. By performing the phase shift control in this way, it is possible to adjust, for example, the effective value of the voltage Vout output by the power conversion device 10.

In the example of FIG. 4, it is assumed that the power converter 20 outputs the maximum voltage by setting the phase difference of the gate drive signals VGua and VGva and the phase difference of the gate drive signals VGub and VGvb to 180 °. .. In order to adjust the amplitude of the output voltage of the power converter 20, the phase difference of the gate drive signals VGua and VGva and the phase difference of the gate drive signals VGub and VGvb may be adjusted by phase shift control.

In the above description, an example in which the number of unit converters is two has been described, but there is no limit to the number of unit converters connected in cascade. For example, the number of unit converters may be three or more.

For example, when there are four unit converters, four phase setting patterns are provided. When the phase of each unit converter is set as θa, θb, θc, θd, the first pattern is θa, θb, θc, θd, and the second pattern is θb, θc, θd and θa are used, the third pattern is θc, θd, θa and θb, and the fourth pattern is θd, θa, θb and θc, and each pattern is switched in order.

For example, the control device 50 has a table in which a pattern of phase setting is set. The pattern set in the table is switched by the control device 50 according to the switching cycle of the pattern set separately.

The effect of the power conversion device 10 of the present embodiment will be described.
The power converter 10 of the present embodiment includes a power converter 20 including cascaded unit converters 30a and 30b, and a control device for generating a gate drive signal for operating the unit converters 30a and 30b. The control device sets the phase of the gate drive signal for one-pulse control for the unit converters 30a and 30b, respectively, and switches the phase to be set at predetermined intervals. Therefore, the active power that can be output for each of the unit converters 30a and 30b can be made substantially equal.

The unit converters 30a and 30b operate by supplying an unstabilized DC voltage from the input alternating current by the rectifying and smoothing circuit including the rectifying circuits 32a and 32b and the smoothing circuits 34a and 34b. In the power conversion device 10 of the present embodiment, the active powers output by the unit converters 30a and 30b are substantially the same, so that even if the DC voltage is not stabilized, the fluctuation of the voltage can be reduced. , It is possible to realize an output with less harmonic content at low cost.

Even if the DC voltage supplied to the inverter circuits 36a and 36b is not stabilized, the active power output by each unit converter is substantially equal, so that the fluctuation of the DC voltage can be reduced. Therefore, it is possible to appropriately set the threshold values for overvoltage detection of DC voltage and undervoltage detection.

Even when the power factor cosφ of the load is smaller than 1, and there is a power return from the load to the unit converter, the power converter 10 of the present embodiment uses the unit converter that causes the power return at a predetermined cycle. Since the switching is performed, the voltage of the capacitor of the smoothing circuit does not continue to rise, and an excessive load is not generated on the rectifier circuit and the smoothing circuit.

When a power converter having a cascaded unit converter is controlled by one pulse control, the harmonic component of the output can be substantially canceled by appropriately setting the phase of the unit converter. By performing such a phase setting, the output harmonic filter can be miniaturized or deleted. When such control is performed, if there is a substantial difference in the active power output by the unit converter, the DC voltage fluctuates and the harmonics of the output increase. In the power converter 10 of the present embodiment, since the active power output by each unit converter can be substantially equalized, fluctuations in the DC voltage supplied to the unit converter can be suppressed, which is effective. The harmonic component can be canceled.

According to the embodiment described above, it is possible to realize a power conversion device capable of stably supplying power to the load regardless of the power factor of the load.

Although some embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention and its equivalents described in the claims. Moreover, each of the above-described embodiments can be implemented in combination with each other.

1 AC power supply, 10 power converter, 20 power converter, 22 transformer, 30a, 30b unit converter, 32a, 32b rectifier circuit, 34a, 34b smoothing circuit, 36a, 36b inverter circuit, 50 control device

Claims (4)

A power converter including a first unit converter and a second unit converter cascaded to the first unit converter.
A control device that generates a first gate drive signal for driving the first unit converter and a second gate drive signal for driving the second unit converter, and controls the power converter with one pulse based on phase shift control. When,
With
The control device sets the phase of the first gate drive signal to the lead phase of the output voltage of the power converter, sets the phase of the second gate drive signal to the lag phase of the output voltage, and determines. A power conversion device that exchanges the phase of the first gate drive signal with the phase of the second gate drive signal in the cycle of. The power conversion device according to claim 1, wherein the first unit converter and the second unit converter perform power conversion in one direction. The power conversion device according to claim 2, wherein the first unit converter and the second unit converter include a rectifier circuit that rectifies an AC voltage and a smoothing circuit that smoothes the output of the rectifier circuit, respectively. The power conversion device according to any one of claims 1 to 3, wherein the phase is set based on the order of the harmonics to be offset.

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