JP6964731B1 - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device capable of stably continuing power conversion even when an overcurrent or an overvoltage occurs. A control unit 50 of a power converter 100 determines a detected current based on a deviation between a command value of a current in an AC / DC converter unit 10 and the current detected by the detection units 15 and 16. The control amount is derived using the set control gain ω to control the AC / DC converter unit 10 so as to follow the command value, and at least one of the detected current and voltage is set correspondingly. When the first threshold is less than Is and Vth, the first gain ω1 is used as the control gain ω, and when at least one of the detected current and voltage is equal to or higher than the first threshold Is and Vth, the control gain ω is larger than the first gain ω1. A large second gain ω2 is used. [Selection diagram] Fig. 1

Description

The present application relates to a power converter.

Conventionally, in a power converter equipped with a power converter that converts alternating current to direct current or direct current to alternating current, when an overcurrent occurs due to superimposition of harmonics on the alternating current system, etc., power is generated. There is a problem that the conversion operation becomes unstable and the operation cannot be continued in some cases. In order to solve such a problem, for example, a power conversion device having the following configuration is disclosed.

That is, the conventional power conversion device is provided with a leg circuit in which a plurality of converter cells composed of a semiconductor switch element and a DC capacitor are connected in series in each phase of AC, and power conversion is performed between AC and DC. It includes a device and a control device that controls this power converter. The control device includes an overcurrent detection unit that detects the presence or absence of an overcurrent flowing through each arm. When an overcurrent is detected by the overcurrent detector, the control device adjusts the control gain such as PI control to raise the control response. Phase voltage balance control, the direction in which the voltage of the DC capacitor balances the control gain that controls the circulating current. Control to adjust to. Even if an overcurrent occurs due to a malfunction of the AC system, by adjusting the control gain in this way, the voltage of the DC capacitor in the converter cell is stabilized, the generation of chained overcurrent is suppressed, and the occurrence of chained overcurrent is continuously suppressed. Power is supplied (see, for example, Patent Document 1).

Japanese Patent No. 6274447

However, with the above-mentioned countermeasure method, there is a problem that the followability of the overcurrent current to the target current value may be deteriorated, and the power conversion device may not be able to continue the operation stably. ..
The present application discloses a technique for solving the above-mentioned problems, and an object of the present application is to provide a power conversion device capable of stably continuing a power conversion operation even when an overcurrent occurs.

The power converter disclosed in the present application is
An AC / DC converter unit that has a semiconductor switching element and an inductance component and performs power conversion between alternating current and direct current.
A detection unit that detects at least one of a current and a voltage in the AC / DC converter unit and a control unit that controls the AC / DC converter unit are provided.
The control unit
Based on the deviation between the command value of the current and the current detected by the detection unit, the control amount is derived using the control gain set so that the detected current follows the command value. Then, the semiconductor switching element of the AC / DC converter unit is controlled.
When at least one of the detected current and voltage is less than the first threshold value set correspondingly, the first gain is used as the control gain, and at least one of the detected current and voltage is the first threshold value. In the above, the second gain larger than the first gain is used as the control gain.
It is a thing.

According to the power conversion device disclosed in the present application, power conversion can be stably continued even when an overcurrent occurs.

It is a block diagram which shows the schematic structure of the power conversion apparatus according to Embodiment 1. It is a block diagram which shows the schematic structure of the control part of the power conversion apparatus by Embodiment 1. FIG. It is a block diagram which shows the schematic structure of the gain setting part of the control part of the power conversion apparatus according to Embodiment 1. FIG. It is a block diagram which shows the gain characteristic of the gain setting part of the control part of the power conversion apparatus according to Embodiment 1. FIG. It is a figure which shows the frequency characteristic of the transfer function of the feedback control system of the power conversion apparatus according to Embodiment 1. FIG. It is a figure which shows the frequency characteristic of the transfer function of the feedback control system of the power conversion apparatus according to Embodiment 1. FIG. It is a figure explaining the threshold value determination method for determining an overcurrent in the power conversion apparatus according to Embodiment 1. FIG. It is a figure which shows an example of the hardware composition of the control part of the power conversion apparatus according to Embodiment 1. FIG.

Embodiment 1.
FIG. 1 is a block diagram showing a schematic configuration of the power conversion device 100 according to the first embodiment.
The power conversion device 100 includes an AC / DC converter unit 10 that converts alternating current into direct current, and a control unit 50 that controls the AC / DC converter unit 10, and performs power conversion between alternating current and direct current. The AC side of the power converter 100 is connected to an AC power supply 1 such as a commercial AC system, and the DC side is connected to a load 2 such as a battery.

The AC / DC converter unit 10 includes a diode bridge 11 as a rectifier circuit, a reactor 12 as a current limiting circuit, a semiconductor switching element 13, and a rectifier diode 14.
In the present embodiment, the semiconductor switching element 13 uses a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) in which a diode is built in between the source and the drain.

The diode bridge 11 is composed of a diode element and rectifies alternating current from the alternating current power supply 1 to direct current. The output of the diode bridge 11 is connected to the first end of the reactor 12. The drain terminal of the semiconductor switching element 13 and the anode terminal of the rectifier diode 14 are connected to the second end of the reactor 12. The cathode terminal of the rectifying diode 14 is connected to the first end of the load 2 in the output stage. Further, the source terminal of the semiconductor switching element 13 is connected to the second end of the load 2.

Further, the power conversion device 100 is connected to the input side of the diode bridge 11 in series with the AC power supply 1 and has an input current detection circuit (SI1) 16 as a detection unit for detecting the input current Iin from the AC power supply 1 and an AC. It includes an input voltage detection circuit (SV1) 15 as a detection unit that is connected in parallel to the power supply 1 and detects an input voltage Vin. Further, the power conversion device 100 is connected in parallel with the load 2 and includes a DC voltage detection circuit (SV2) 17 as a detection unit for detecting the DC voltage Vdc which is the output voltage of the AC / DC converter unit 10.
The detection values Iin, Vin, and Vdc detected by the input current detection circuit 16, the input voltage detection circuit 15, and the DC voltage detection circuit 17 provided at these setting points are input to the control unit 50, respectively.

The AC / DC converter unit 10 performs PWM (Pulse Voltage Modulation) control in which the control unit 50 controls the semiconductor switching element 13 on and off at a set cycle using the detected detection values Iin, Vin, and Vdc. This is a boosted high power factor converter that boosts the voltage and converts it into DC power while controlling the current flowing through the current limiting reactor 12 to a high power factor so as to have a waveform synchronized with the AC voltage.

Next, the configuration of the control unit 50 will be described.
FIG. 2 is a block diagram showing a schematic configuration of a control unit 50 of the power conversion device 100 according to the first embodiment.
A microcomputer is used for the control unit 50. The control unit 50 includes a current determination unit 20, a voltage determination unit 21, an OR circuit 22, a gain setting unit 30, a PI controller 23, and a gate signal generator 24.

The current determination unit 20 determines whether the absolute value of the input current Iin is equal to or higher than the first threshold value Is for current determination, and outputs the signal 20A which is the determination result. The voltage determination unit 21 determines whether the absolute value of the input voltage Vin is equal to or higher than the first threshold value Vth for voltage determination, and outputs the signal 21A which is the determination result. The current determination unit 20 and the voltage determination unit 21 output Hi as signals 20A and 21A when the input current Iin and the input voltage Vin are equal to or higher than the first threshold values Is and Vth, respectively, and are less than the first threshold values Is and Vth. In the case, Lo is output.

The OR circuit 22 outputs the logical sum of the signal 20A from the current determination unit 20 and the signal 21A from the voltage determination unit 21 as the determination signal 22A.
The determination signal 22A becomes Hi when at least one of the absolute value of the input current Iin and the absolute value of the input voltage Vin is equal to or higher than the corresponding first threshold values Is and Vth, respectively. Further, the determination signal 22A becomes Lo when both the absolute value of the input current Iin and the absolute value of the input voltage Vin are less than the corresponding first threshold values Is and Vth, respectively.

The gain setting unit 30 uses the determination signal 22A from the OR circuit 22, the absolute value | Iin | of the input current Iin, and the absolute value | Vin | of the input voltage Vin as inputs to be used in the subsequent PI controller 23. Outputs the gain ω as the gain.
The PI controller 23 takes as inputs the deviation ΔIin between the detected value of the input current Iin and the current command value Iin * of the input current Iin, and the gain ω from the gain setting unit 30, and proportionally integrates (proportionally integrates) based on these inputs. Proportional-Integral) control is performed. The PI controller 23 outputs the target voltage VLin of the applied voltage of the reactor 12 based on the control amount of the PI control.
The gate signal generator 24 drives the semiconductor switching element 13 based on the target voltage VLin of the voltage applied to the reactor 12 from the PI controller 23, the detected input voltage Vin, and the detected DC voltage Vdc. A gate signal G is generated and output.

Next, a method of generating the gain ω used in the PI control of the PI controller 23 and generated by the gain setting unit 30 will be described with reference to FIGS. 3 and 4 together with the configuration of the gain setting unit 30.
FIG. 3 is a block diagram showing a schematic configuration of a gain setting unit 30 of the control unit 50 shown in FIG.
FIG. 4 is a diagram showing the characteristics of the gain ω used in the PI control of the PI controller 23 shown in FIG.
In FIG. 4, the horizontal axis represents the absolute value | Iin | of the input current Iin, and the vertical axis represents the gain ω. Since the characteristics of the gain ω are the same even when the horizontal axis is the input voltage Vin, the illustration of the characteristics of the gain ω with respect to the input voltage Vin is omitted.

As shown in FIG. 3, the gain setting unit 30 includes a control amount setting unit 31 and an adder 32.
The control amount setting unit 31 adjusts the gain ω by inputting the determination signal 22A from the OR circuit, the absolute value | Iin | of the input current Iin, and the absolute value | Vin | of the input voltage Vin. Generate the quantity Δω. The generated adjustment amount Δω is added by the adder 32 to the first gain ω1 having a constant value set in advance, and a gain ω having a value of the second gain ω2 is generated.

Assuming that the equation obtained by linearly approximating the second gain ω2 shown by the solid line in FIG. 4 is ω2 = A × | Iin | + B (A and B are arbitrary coefficients), Δω = from ω2 = ω1 + Δω as described above. ω2-ω1 = A × | Iin | + B-ω1. That is, the adjustment amount Δω indicating the difference between the second gain ω2 and the first gain ω1 is set to a value that gradually increases as the absolute value | Iin | of the input current Iin increases.

The control amount setting unit 31 shown in FIG. 3 has an input current Iin, when the determination signal 22A from the OR circuit is Hi, that is, when at least one of the input current Iin and the input voltage Vin is in an overvoltage or overcurrent state. The adjustment amount Δω of the value that gradually increases as the absolute value of the input voltage Vin increases is output. In this way, when at least one of the input current Iin and the input voltage Vin is in the overvoltage and overcurrent states, the gain setting unit 30 increases the absolute values of the input current Iin and the input voltage Vin as shown in FIG. A gain ω having a value of the second gain ω2 that gradually increases with it is generated and output.

On the other hand, the control amount setting unit 31 sets the adjustment amount Δω to 0 when the determination signal 22A from the OR circuit is Lo, that is, when the input current Iin and the input voltage Vin are not in the overvoltage or overcurrent state. Therefore, when the input current Iin and the input voltage Vin are not in the overvoltage or overcurrent state, the gain setting unit 30 outputs the gain ω having the value of the first gain ω1 which is a preset constant value.
The gain ω set to the value of the first gain ω1 or the second gain ω2 in this way is input to the PI controller 23 shown in FIG. 2 and used in the PI control.

Next, the operation of the control unit 50 when the harmonic voltage is superimposed on the AC power supply 1, that is, when the input current Iin becomes an overcurrent will be described.
As described with reference to FIG. 2, the control unit 50 performs proportional integration (PI) control by the PI controller 23 using the deviation ΔIin between the current command value Iin * of the input current Iin and the input current Iin as the feedback amount. A target voltage VLin, which is a target value of the applied voltage of the reactor 12, is generated. After that, the control unit 50 generates the gate signal G by the gate signal generator 24 using the target voltage VLin.

Here, when the semiconductor switching element 13 operates at an arbitrary duty ratio D1, the DC voltage Vdc, the input voltage Vin, and the target voltage of the output of the AC / DC converter unit 10 are provided for one cycle of the switching cycle of the semiconductor switching element 13. The relationship of VLin is expressed by the following (Equation 1).
Vin = VLin + Vdc (1-D1) ... (Equation 1)

The gate signal generator 24 calculates the duty ratio D1 according to the following (Equation 2) based on the above (Equation 1), generates a gate signal G that PWM-controls the semiconductor switching element 13 according to the duty ratio D1, and generates the semiconductor switching element. Output to 13.
D1 = 1- (Vin-VLin) / Vdc ... (Equation 2)

When the input current Iin is within the steady-state range that is not an overcurrent less than the first threshold value Is, the control unit 50 performs PI control using the first gain ω1 as the gain ω as described above.
When the harmonic voltage is superimposed on the AC power supply 1 and the absolute value of the input current Iin rises to be equal to or higher than the first threshold value Is, the current determination unit 20 outputs Hi. As a result, the determination signal 22A output by the OR circuit 22 changes from Lo to Hi. Upon receiving this determination signal 22A, the gain setting unit 30 outputs a gain ω having a value of the second gain ω2 corresponding to the magnitude of the absolute value of the input current Iin to the PI controller 23. In this way, the gain ω used in the PI controller 23 is set from the first gain ω1 to the second gain ω2.

By performing PI control using the second gain ω2 having a value larger than the first gain ω1 by the PI controller 23, the deviation between the input current Iin and the current command value Iin * becomes small, and the current command value Iin becomes small. The followability of the input current Iin to * is improved. In this way, even for a sudden change in the input current such as when harmonics are superimposed on the AC power supply 1, the input current Iin is quickly made to follow the current command value Iin * to suppress the increase, and an overcurrent is generated. Can be suppressed.

Next, a method of setting the value of the second gain ω2 will be described.
Assuming that the inductance value of the inductance component of the reactor 12 controlled by the control unit 50 is L1 and the series resistance value is R1, the transfer function of the reactor 12 is expressed by the following (Equation 3).

From the transfer function of the reactor 12, the break point frequency of the gain diagram in the Bode diagram of the reactor 12 is R1 / L1 [rad / sec], and the phase diagram starts from 0 degrees with R1 / L1 [rad / sec] as the boundary. The graph turns in phase at −90 degrees.
Let L11 be the inductance value when a current of the magnitude of I11 flows through the reactor 12. Further, the inductance value when a current having a value larger than I11 and having a magnitude of I12 flows through the reactor 12 is defined as L12. In this case, since the reactor 12 has a characteristic that the inductance value becomes smaller when a larger current flows than the DC superimposition characteristic, L11> L12 when I11 <I12. Therefore, the break point frequency and the frequency at which the phase turns are higher when the current I12, which is larger than the current I11, flows than R1 / L11 <R1 / L12.

A board showing the frequency characteristics of the transfer function when the inductance of the reactor 12 is L11 in the open loop characteristics of the Bode diagram created based on the PI control that performs proportional integration control in the feedback control system and the transfer function of the reactor 12. The diagram is shown in FIG. 5, and the Bode diagram showing the frequency characteristics of the transfer function when the inductance is L12 is shown in FIG.
FIG. 5 is a Bode diagram of the open loop characteristic when the inductance of the reactor 12 according to the first embodiment is L11.
FIG. 6 is a Bode diagram of the open loop characteristic when the inductance of the reactor 12 according to the first embodiment is L12.

Here, the phase margin is the amount of difference in phase between the phase and −180 degrees at the gain intersection frequency at which the gain is 0 dB, and the phase margin required for ensuring the operational stability of the AC / DC converter unit 10 is Pn. .. The gain margin is the difference between the gain and the gain at 0 dB at the phase crossing frequency at which the phase is −180 degrees, and the gain margin required for ensuring the operational stability of the AC / DC converter unit 10 is Gn.
Based on the above, in FIG. 5, the gain margin is G1 and the phase margin is P1 when the inductance value is L11. Further, in FIG. 6, when the inductance value is L12, the gain margin is G2 and the phase margin is P2. In this case, as described above, when a current having a value of I12 larger than I11 flows, the breaking point frequency and the frequency at which the phase rotates are higher, so that P1 <P2 and G1 <G2.

At the time of control design, the inductance of the reactor 12 is large (the input current Iin is small), which is a stricter condition with a small phase margin and gain margin so that the operational stability of the AC / DC converter can be ensured under any conditions. That is, the gain under the condition at the maximum inductance value is set to the first gain ω1 in consideration of the DC superimposition characteristic of the reactor 12. Therefore, the first gain ω1 is set to a value at which P1 = Pn and G1 ≧ Gn (or P1 ≧ Pn and G1 = Gn) can be secured.

In this case, when the current flowing through the reactor 12 is large I12, P2> Pn and G2> Gn, and a phase margin larger than the required phase margin and gain margin and a gain margin can be secured. Therefore, the second gain ω2 is the first. It can be set to a value larger than the gain ω1. That is, as shown in FIG. 4, a gain ω having a second ω2 value that gradually increases as the absolute value | Iin | of the input current Iin increases can be set.

Here, the value of the second gain ω2 is an upper limit value at which P2 = Pn and G2 ≧ Gn (or P2 ≧ Pn and G2 = Gn) can be secured. That is, the second gain ω2 is set to a value larger than the first gain ω1, and the value is the gain margin and the gain margin at the phase crossing frequency of the frequency characteristic when the input current Iin is equal to or higher than the first threshold Isth. Set so that the upper limit value at which the phase margin at the gain tolerance frequency is secured is not exceeded.

Further, from the following (Equation 4), which is a relational expression of the voltage and current of the reactor 12, the larger the input voltage Vin, the larger the input current Iin.
V = L × di / dt (V: voltage applied to the reactor 12, i: current flowing through the reactor 12, L: inductance of the reactor 12) ... (Equation 4)
Therefore, the method of setting the second gain ω2 with respect to the input voltage Vin is the same as the method of setting the value of the second gain ω2 with respect to the input current Iin described above.

As described above, the AC / DC converter unit 10 of the present embodiment uses the gain ω having a value gradually increasing as the absolute value of the input current Iin or the absolute value of the input voltage Vin increases in the PI control. The input current Iin can be quickly made to follow the command value to suppress the overcurrent, and the set gain ω value can be set to a value that can secure the necessary phase margin and gain margin. Stable operation Continuous operation becomes possible.

Further, if the value of the first gain ω1 is set so that "gain margin G1" = "gain margin Gn which is the stability limit value" and "phase margin P1" = "phase margin Pn which is the stability limit value". , A high gain is the default gain ω used in PI control. In this case, since the first gain ω1 having a high gain value is used from the time when the input current Iin rises to the first threshold value Is or more and the time when the second gain ω2 is set to the gain ω. , The peak of the input current Iin can be further suppressed. Further, in the power factor control of the input current Iin, the followability to the sine wave synchronized with the AC voltage Vac becomes higher, so that the power factor can be controlled with a high power factor. As a result, more stable continuous operation of the power conversion device becomes possible.
Of the gain margin G1 and the phase margin P1, the one set to the stability limit value may be the one in which the margin is more restricted.

Further, as the minimum value of the current I11 at which the reactor 12 has the maximum inductance value, for example, when the power conversion device 100 is connected to a general commercial AC system, the rated current (effective value 15A) of the AC system 100V is used. ), Which is equal to or less than the peak value of 20A or less (0A to 20A). In this way, by setting the value of the minimum current I11, which is the condition where the reactor 12 becomes the maximum inductance value and the operation stability is the lowest, according to the application conditions of the power conversion device 100, what kind of method can be used. The operational stability of the power converter 100 can be ensured even under the input conditions.

Next, an example of a method of setting the first threshold value Is in the current determination unit 20 for determining whether the input current Iin is an overcurrent will be described with reference to FIG. 7.
FIG. 7 shows that in the control unit 50 of the present embodiment, the maximum value of the harmonics to be allowed is superimposed on the voltage of the AC power supply 1 when the value of the gain ω is not adjusted by the gain setting unit 30. It is a figure which shows the waveform of the input current Iin at that time.

From FIG. 7, the timing at which the input current Iin exceeds the rated operating range of the AC / DC converter unit 10 and becomes the overcurrent value Ioc is defined as t1 as the first time point. In this case, the first threshold value Is (indicated as Is_1 in FIG. 7) needs to be set to the minimum current value between the time t1 and the time t2 which is traced back by the set period Δt.
Then, the control unit 50 records the minimum voltage value within the set period Δt in advance when the gain setting unit 30 has not adjusted the value of the gain ω by an experiment or the like, and records the recording. The voltage value is set as the first threshold value Is.

Here, the setting period Δt is taken for the input current detection circuit (SI1) 16 and the input voltage detection circuit (SV1) 15 to detect the values of the input current Iin and the input voltage Vin and transmit the signal to the control unit 50. Includes control delay time.
Further, in the setting period Δt, the control unit 50 processes the input current Iin and the input voltage Vin in absolute values, and the current determination unit 20 and the voltage determination unit 21 determine the threshold value to change the determination signal 22A. Including time.
Further, in the setting period Δt, the control delay time until the value of the gain ω is changed to the second gain ω2 by the gain setting unit 30 based on the determination signal 22A and the second gain ω2 is reflected in the gate signal G is set. include.
Further, the setting period Δt includes a transient delay time from when the second gain ω2 is reflected in the gate signal G until the increase in the input current Iin is actually suppressed.
Further, the setting period Δt includes a value obtained by totaling the margin times including the detection error due to the component variation of the input current detection circuit (SI1) 16.

In order to prevent the occurrence of overcurrent, it is necessary to change the gain after the current / voltage reaches the threshold value or more to suppress the increase in current. When the setting period required for the threshold value determination is short and the threshold value is high, even if the threshold value is determined and the gain is changed, a gain reflection delay occurs due to each of the delay times and the like, and the current cannot be suppressed and an overcurrent occurs. Further, if the setting period required for the threshold value determination is too long, the gain reflection delay occurs. Therefore, the setting period Δt is set to the minimum necessary period including the above-mentioned control delay time and the like. The threshold value is, for example, when an overcurrent is applied when a harmonic voltage (harmonic voltage to be allowed) is applied in consideration of the standard test, market environment, etc. defined in IEC61000-4-13 of IEC (International Electrotechnical Commission). It is set to a threshold value that can be prevented (the minimum current value between the time t1 and the time t2 that goes back by the set period Δt).

As a result, when a harmonic less than the allowable harmonic voltage is superimposed on the power supply voltage, it is possible to prevent the operation from being impossible to continue in each phase, and stable power conversion becomes possible.
The first threshold value Is is set to a value larger than the peak value (peak value) of the rated input current Iin of the power converter 100.

The method of determining the first threshold value Vth in the voltage determination unit 21 is also the same as the method of determining the first threshold value Is because an overcurrent is generated by superimposing a harmonic voltage on the AC power supply 1.
That is, the first threshold value Vth is set to the minimum voltage value between the time t1 which is the timing at which the overcurrent value Ioc is reached and the time t2'going back by the set period Δt'. The set period Δt'and time t2' correspond to the set period Δt and time t2 in the above-mentioned explanation of how to determine the first threshold value Is.
Then, the control unit 50 records the minimum voltage value within the set period Δt in advance when the gain setting unit 30 has not adjusted the value of the gain ω by an experiment or the like, and records the recording. The voltage value is set as the first threshold value Vth.
The first threshold value Vth is set to a value larger than the peak value (peak value) of the rated input voltage of the power converter 100.

Next, a method of setting the value of the gain ω used in the PI controller 23 to the second gain ω2 and then setting it to the value of the first gain ω1 again will be described.
The current determination unit 20 has an absolute value of the input current Iin equal to or more than the first threshold value Is and outputs Hi, and then the absolute value of the input current Iin is less than the first threshold value Is (hereinafter referred to as the first threshold value Is_1). When the value is equal to or less than the second threshold value Is'(hereinafter referred to as the second threshold value Is_2), Lo is output. As a result, the determination signal 22A changes from Hi to Lo, and the gain setting unit 30 changes the gain ω used in the PI controller 23 from the value of the second gain ω2 to the first gain ω1.

The second threshold value Is_2 is set to a value smaller than the first threshold value Is_1 with reference to the first threshold value Is_1 in consideration of the detection value fluctuation due to noise or the like of the input current detection circuit (SI1) 16.

FIG. 4 illustrates the relationship between the first threshold value Is_1 and the second threshold value Is_1 and the first gain ω1 and the second gain ω2 in the gain setting unit 30.
As described above, the larger the current, the smaller the inductance value of the reactor 12, so that the larger the input current Iin, the larger the value of the second gain ω2 can be set.

When the input current Iin is small, the first gain ω1 is set for the gain ω in the PI controller 23, and when the absolute value of the input current Iin becomes equal to or higher than the first threshold Is_1, the second gain ω2 is set as the value of the gain ω. Set.
After the input current Iin becomes the first threshold value Is_1 or more, the first gain ω1 is set again when the input current Iin becomes the second threshold value Is_1 or less.

In this way, the hysteresis width is set between the first threshold value Is_1 used when switching the setting from the first gain ω1 to the second gain ω2 and the second threshold value Is_2 used when switching the setting from the second gain ω2 to the first gain ω1. Is provided, and "second threshold value Is_2" <"first threshold value Is_1". As a result, it is possible to prevent the gain ω from being frequently switched and the operation from becoming unstable when the input current Iin fluctuates near the threshold value, and the control can be stabilized.

The relationship between the first threshold value Vth_1 and the first threshold value Vth_2 in the voltage determination unit 21 and the first gain ω1 and the second gain ω2 in the gain setting unit 30 is the same as described above.

Further, in the present embodiment, the value of the second gain ω2 is set to a value obtained by adding the adjustment amount Δω to the first gain ω1, but the value is not limited to this. The value of the second gain ω2 may be set to a value that increases according to the value of the input current Iin or the input voltage Vin, and can be expressed by, for example, the following (Equation 5) to (Equation 8).

For example, the second gain ω2 may be set to be a value obtained by multiplying the adjustment amount Δω by the first gain ω1 as shown in the following (Equation 5).
ω2 = ω1 × Δω ・ ・ ・ (Equation 5)

Further, for example, the adjustment amount Δω may be a value that increases according to the value of the input current Iin or the input voltage Vin, and as shown in the following (Equation 6) and (Equation 7), the absolute value of the input current Iin | Iin | The values Δωi and Δωv may be set according to the difference between the first threshold value Is_1 and the absolute value | Vin | of the input voltage Vin | and the difference between the first threshold value Vth_1.
Δωi = C × (| Iin | -Itth_1) + D-ω1 ... (Equation 6)
However, C and D are arbitrary coefficients Δωv = C'× (| Vin | -Vth_1) + D'-ω1 ... (Equation 7)
However, C'and D'are arbitrary coefficients.

Further, the second gain ω2 is a value obtained by multiplying the first gain ω1 by the adjustment amounts Δωi and Δωv shown in the above (Equation 6) and (Equation 7) as shown in the following (Equation 8) and (Equation 9). It may be set to be.
ω2 = ω1 × Δωi ・ ・ ・ (Equation 8)
ω2 = ω1 × Δωv ・ ・ ・ (Equation 9)

Further, in the above embodiment, as shown in FIG. 4, the second gain ω2 shows that the adjustment amount Δω increases linearly as the input current Iin and the input voltage Vin increase. However, the second gain ω2 may be set so as to monotonically increase as the input current Iin and the input voltage Vin increase. Therefore, the adjustment amount Δω may be set to increase non-linearly with respect to the absolute value of the input current Iin or the input voltage Vin.

When the second gain ω2 is indicated by a monotonous increase function that gradually increases as the input current Iin and the input voltage Vin increase, the rate of increase (gradient) of the second gain ω2 in this monotonous increase function is the input current Iin and the input voltage. The gain difference (adjustment range of the value of gain ω) obtained from the gain margin in the frequency characteristics when at least one of the Vins is less than the first threshold value and the gain margin in the frequency characteristics when at least one of the Vins is equal to or more than the first threshold value. It may be set based on.

Further, the above-mentioned control of reflecting the value controlled by proportional integration (PI) with the ΔIin of the current command value Iin * and the input current Iin as the feedback amount to the gate signal G is performed every set cycle, but the input is performed. When the current Iin or the input voltage Vin becomes an overcurrent or an overvoltage, the feedback value may be immediately reflected in the gate signal G without waiting for the setting cycle as described below.
For example, within the above set cycle, the input current Iin and the input voltage Vin are detected, and the AD conversion of the detected value is performed at any time. Therefore, when the determination signal 22A indicating the overcurrent or the overvoltage changes from Lo to Hi, The gain setting unit 30 receives the determination signal 22A and immediately outputs the second gain ω2 to the PI controller 23.

Specifically, immediately before the first period of performing PI control within the above setting cycle, the control unit 50 confirms whether the gain ω set in the PI controller 23 is the first gain ω1 or the second gain ω2. I decided to. Then, when the gain ω set in the PI controller 23 is different from the gain ω output from the gain setting unit 30, the control unit 50 immediately outputs the gain in the PI controller 23 from the gain setting unit 30. Change to the gain ω.
As a result, the control unit 50 immediately reflects the gain ω corresponding to the input current Iin or the input voltage Vin detected at any time in the gate signal G and reflects it as the duty of the semiconductor switching element 13.

As a result, the input current responds to an increase in the input current Iin or the input voltage Vin earlier than in the case where the gain ω is determined in advance before the setting cycle or before the first period in which the PI control is performed. It is possible to suppress an increase in Iin and prevent overcurrent. This enables stable continuous operation of the power converter 100.

In the above embodiment, as a condition for setting the gain of PI control to the second gain ω2, the absolute value of the input current Iin is equal to or higher than the first threshold value Is, or the absolute value of the input voltage Vin is the first threshold value. It was determined in the control unit 50 that it was Vth or higher. However, this determination is not limited to the case where the determination is made within the control unit 50. For example, a current threshold value determination circuit for determining whether the value of the input current Iin is equal to or higher than the first threshold value Is is configured outside the control unit 50 with a shunt resistor, an operational amplifier, a comparator, and the like. Then, the result of this current threshold value determination circuit may be input to the control unit 50. This also applies to the method of determining whether the absolute value of the input voltage Vin is equal to or higher than the first threshold value Vth.

As a result, the input current Iin and the input voltage Vin can be determined faster than the determination of the input current Iin and the input voltage Vin in the control unit 50 composed of the microcomputer. Therefore, the second gain ω2 is reflected in the gate signal G earlier, and the overcurrent can be suppressed at an early stage. This is more effective when the short-circuit tolerance of the semiconductor switching element 13 is small and the overcurrent value is small.

The material of the semiconductor switching element 13 constituting the AC / DC converter unit 10 is a gallium nitride based material (GaN: Gallium Nitride) or silicon carbide (SiC: Silicon Carbide), which is a wide bandgap semiconductor capable of high-speed operation. , Diamond-based materials may be used. Since a semiconductor switching element using a wide bandgap semiconductor has a small short-circuit withstand capability, it has a small withstand voltage against overcurrent, and therefore, overcurrent must be suppressed. According to the control unit 50 of the power conversion device 100 of the present embodiment, the gain ω is changed to the second gain ω2 even in the AC / DC converter circuit composed of the semiconductor switching element made of a material that easily stops operation. As a result, fluctuations in current can be suppressed at an early stage, enabling stable continuous operation.

Further, in the above, as the AC / DC converter unit 10, a high power factor converter having a diode bridge 11 which is a rectifier circuit on the input side is shown, but the configuration of the AC / DC converter unit 10 is not limited to this. No. The AC / DC converter unit 10 may have an inductance component and perform power conversion between alternating current and direct current. For example, a plurality of converter cells including a semiconductor switch element and a direct current capacitor are connected in series. An MMC (Modular Multilevel. Converter) in which a leg circuit is provided for each phase of alternating current may be used.

Even in such an MMC type power conversion device, the gain ω can be adjusted in the same manner as described above based on the transfer function of the reactor or parasitic inductance provided in series with each leg circuit and the resistance component. Therefore, when an overcurrent occurs in a leg circuit of a certain phase, the switching element constituting the leg circuit of the phase in which the overcurrent has occurred is turned off, and the semiconductor constituting the leg circuit of the phase in which the overcurrent has not occurred is turned off. Gain control that increases the control gain of the switch element and suppresses the output decrease of the power converter becomes unnecessary. Therefore, in order to cope with the current flowing in the leg circuit of the phase in which the overcurrent is generated flows in the leg circuit of the phase in which the overcurrent is not generated, the switching element constituting the leg circuit of each phase is correspondingly increased. It is no longer necessary to use an element that can carry a large current. Therefore, the cost of the MMC type power conversion device can be reduced.

In addition, since the input current of each phase fluctuates greatly and it is possible to prevent an overcurrent from occurring in the leg circuit of each phase, all the semiconductor switching elements of the leg circuit of each phase are used to suppress the overcurrent. There is no need to turn it off and stop operation. This enables stable continuous operation even in the MMC type power conversion device.

When the MMC type AC / DC converter unit 10 is used, the overvoltage and overcurrent may be determined by using the input current and the input voltage on the AC side as the determination target, or a defect on the DC terminal side. The direct current flowing through the leg circuit of each phase due to the above may be the determination target.

Hereinafter, the hardware configuration of the control unit 50 will be described.
FIG. 8 is a diagram showing an example of the hardware configuration of the control unit 50 according to the first embodiment.
The control unit 50 includes a processor 40 and a storage device 41 as shown in FIG. 8 as an example of the hardware configuration. Although the storage device is not shown, it includes a volatile storage device such as a random access memory and a non-volatile auxiliary storage device such as a flash memory.
Further, an auxiliary storage device of a hard disk may be provided instead of the flash memory. The processor 40 executes the program input from the storage device 41. In this case, the program is input to the processor 40 from the auxiliary storage measure via the volatile storage device. Further, the processor 40 may output data such as a calculation result to the volatile storage device of the storage device 41, or may store the data in the auxiliary storage device via the volatile storage device.

The power conversion device of the present embodiment configured as described above is
An AC / DC converter unit that has a semiconductor switching element and an inductance component and performs power conversion between alternating current and direct current.
A detection unit that detects at least one of a current and a voltage in the AC / DC converter unit and a control unit that controls the AC / DC converter unit are provided.
The control unit
Based on the deviation between the command value of the current and the current detected by the detection unit, the control amount is derived using the control gain set so that the detected current follows the command value. Then, the semiconductor switching element of the AC / DC converter unit is controlled.
When at least one of the detected current and voltage is less than the first threshold value set correspondingly, the first gain is used as the control gain, and at least one of the detected current and voltage is the first threshold value. In the above, the second gain larger than the first gain is used as the control gain.
It is a thing.

As described above, the power converter sets the gain used in PI control from the first gain used in the steady state in the state of overcurrent or overvoltage in which at least one of the detected current and voltage is equal to or higher than the first threshold value. It is used by setting it to the second gain, which is larger than the first gain. As a result, the deviation between the input current and the current command value is made smaller, the followability of the input current to the current command value is improved, and the current is quickly followed by the target value even when the current changes suddenly. The rise can be suppressed and the overcurrent can be suppressed. As a result, the power conversion operation can be continued stably.

Further, the power conversion device of the present embodiment configured as described above is
The second gain is set to a value that gradually increases as the current or the voltage increases.

In this way, even when an overcurrent or overvoltage occurs in which at least one of the detected currents and voltages greatly exceeds the first threshold value, the second gain corresponding to the magnitude of the currents and voltages is used, so that the second gain can be quickly obtained. It is possible to suppress the overcurrent by making the current follow the target value and suppressing the increase.

Further, the power conversion device of the present embodiment configured as described above is
In the open-loop transfer function of the feedback control system including the inductance component of the AC / DC converter unit,
The first gain is the gain margin at the phase crossing frequency and the phase at the gain tolerance frequency of the frequency characteristics of the transfer function when at least one of the current and the voltage in the AC / DC converter unit is less than the first threshold value. It is set to a value that ensures a margin,
The second gain is a value larger than the first gain, and the frequency characteristic of the transmission function when at least one of the current and the voltage in the AC / DC converter unit is equal to or higher than the first threshold value. Is set to a value at which the gain margin at the phase crossing frequency and the phase margin at the gain tolerance frequency are secured.
It is a thing.

In this way, the gain ω is set so as to secure the operation stability by using the open-loop transfer function of the feedback control system including the inductance component of the AC / DC converter unit. That is, the first gain is set to a value at which the gain margin and the phase margin are secured when the current in the AC / DC converter unit is less than the first threshold value and the operation stability is the condition that is the lowest.
By setting the first gain in this way, the operational stability of the power converter can be ensured under any current conditions.
Further, by setting the second gain to a value larger than the first gain, the current followability to the target current is improved as described above, and the upper limit of the set second gain value is set to the gain margin and the phase margin. Set to a value that can be secured. As a result, the value of the second gain is not set to a value that deviates from the range in which the operation stability can be ensured, so that the operation stability of the power conversion device can be ensured.

Further, the power conversion device of the present embodiment configured as described above is
The first gain is at the gain margin or gain tolerance frequency at the phase crossing frequency of the frequency characteristic of the transfer function when at least one of the current and the voltage in the AC / DC converter unit is less than the first threshold value. At least one of the phase margins is set to a value that becomes a predetermined stability limit value.
It is a thing.

In this way, the value of the first gain ω1 is set so that “gain margin G1” = “gain margin Gn” or “phase margin P1” = “phase margin Gn” in the first gain ω1. As a result, the first gain having a high gain value is used from the time when the current or voltage becomes overcurrent or overvoltage until the second gain is set in the gain ω, so that the peak of the input current is used. Can be suppressed more. Further, when the AC / DC converter unit that controls the high power factor is used, the followability of the input current to the sine wave becomes higher, so that the power factor can be controlled with a higher power factor. In the case of a power conversion device having a control and circuit configuration in which both the gain margin G1 and the phase margin P1 can be set to the stable limit value, the first gain ω1 is set so that both the gain margin G1 and the phase margin P1 are the stable limit values. You may set the value.

Further, the power conversion device of the present embodiment configured as described above is
The second gain is indicated by a monotonically increasing function that gradually increases as the current or voltage increases, and the rate of increase of the monotonically increasing function is
The current in the AC / DC converter unit, the gain margin when at least one of the voltages is less than the first threshold value, and the gain margin.
The difference between the current in the AC / DC converter unit and the gain margin when at least one of the voltages is equal to or greater than the first threshold value, or the current in the AC / DC converter unit and at least one of the voltages With the phase margin when it is less than the first threshold value,
The difference between the current in the AC / DC converter unit and the phase margin when at least one of the voltages is equal to or higher than the first threshold value.
Set according to the difference of at least one of
It is a thing.

In this way, the rate of increase of the second gain that gradually increases as the current or voltage increases, the gain margin in the frequency characteristics when a small current less than the first threshold flows, and the case where a large current greater than or equal to the first threshold flows. It is set based on the gain margin in the frequency characteristic of and the gain difference (adjustment range of the second gain ω2). Alternatively, the rate of increase of the second gain is the phase margin difference between the phase margin in the frequency characteristic when a small current less than the first threshold flows and the phase margin in the frequency characteristic when a current larger than the first threshold flows. It is set based on (adjustment range of the second gain ω2). Thereby, the increase rate of the second gain according to the actual gain characteristic and the phase characteristic of the AC / DC converter unit can be determined. As a result, the operational stability of the power converter can be ensured with high accuracy.

Further, the power conversion device of the present embodiment configured as described above is
The control unit
At least one of the minimum value of the current and the minimum value of the voltage within the set period before the first time point in which at least one of the current and the voltage exceeds the rated operating range of the AC / DC converter unit is recorded.
The recorded minimum value is set as the first threshold value.
It is a thing.

As a result, when a harmonic less than the allowable harmonic voltage is superimposed on the power supply voltage, it is possible to prevent the operation from being impossible to continue in each phase, and stable power conversion becomes possible.

Further, the power conversion device of the present embodiment configured as described above is
The set period is
The control delay in the control unit from the detection of the current or the voltage exceeding the first threshold value by the detection unit to the setting of the control gain to the second gain by the control unit.
The control gain is set to a period including at least one delay after the control gain is set to the second gain by the control unit until the current or the voltage becomes less than the first threshold value.
It is a thing.

As a result, the threshold value including the delay time of the actual power conversion device can be set, so that the operation stability of the power conversion device can be ensured with high accuracy.

Further, the power conversion device of the present embodiment configured as described above is
The AC / DC converter unit is an AC / DC converter that includes a reactor having the inductance component and controls the power factor of electric power from the alternating current.
The current is an input current from the AC side to the AC / DC converter unit.
The voltage is an input voltage from the AC side to the AC / DC converter unit.
The second gain is set to an absolute value of the input current or a value that gradually increases as the absolute value of the input voltage increases.
The control unit controls the semiconductor switching element so that the input current from the alternating current side follows the command value.
It is a thing.

As a result, for example, when harmonics are superimposed on the power supply voltage on the AC side due to external factors, the fluctuation of the input current becomes large, and even if an overcurrent occurs, high power factor control while suppressing the overcurrent. Is possible. As a result, the power conversion operation can be stably continued, and a power conversion device having a high power factor can be provided.

Further, the power conversion device of the present embodiment configured as described above is
The second gain is set to a value obtained by adding the adjustment amount gradually increasing as the current or the voltage increases to the first gain, or a value obtained by multiplying the first gain.
It is a thing.
Further, the power conversion device of the present embodiment configured as described above is
The second gain is a value obtained by adding an adjustment amount that gradually increases as the deviation between the absolute value of the input current or the absolute value of the input voltage and each of the first thresholds increases to the first gain. Or, it is set to a value obtained by multiplying the first gain.
It is a thing.

In this way, the value of the second gain that gradually increases as the voltage and current in the AC / DC converter unit increases can be derived by each calculation method. As a result, the degree of freedom in the method of setting the second gain in the control unit can be secured, and the control diversity can be ensured.

Further, the power conversion device of the present embodiment configured as described above is
The control unit
After the control gain is set to the second gain, when the current and the voltage become equal to or less than the second threshold set to a value less than the first threshold value, the control gain is changed from the second gain. Set to the first gain,
It is a thing.

As a result, by using the first gain smaller than the second gain as the gain used when the current is small, overshoot in PI control can be prevented, and the operation stability of the power conversion device can be ensured.

Although exemplary embodiments are described in the present application, the various features, aspects, and functions described in the embodiments are not limited to the application of a particular embodiment, either alone or. It can be applied to embodiments in various combinations.
Therefore, innumerable variations not illustrated are envisioned within the scope of the techniques disclosed in the present application. For example, it is assumed that at least one component is modified, added or omitted.

1 AC power supply (AC), 13 semiconductor switching element,
12 Reactor (inductance component), 10 AC / DC converter,
15 Input voltage detection circuit (detection unit), 16 Input current detection circuit (detection unit),
50 control unit, 100 power converter.

Claims (12)

An AC / DC converter unit that has a semiconductor switching element and an inductance component and performs power conversion between alternating current and direct current.
A detection unit that detects at least one of a current and a voltage in the AC / DC converter unit and a control unit that controls the AC / DC converter unit are provided.
The control unit
Based on the deviation between the command value of the current and the current detected by the detection unit, the control amount is derived using the control gain set so that the detected current follows the command value. Then, the semiconductor switching element of the AC / DC converter unit is controlled.
When at least one of the detected current and voltage is less than the first threshold value set correspondingly, the first gain is used as the control gain, and at least one of the detected current and voltage is the first threshold value. In the above, the second gain larger than the first gain is used as the control gain.
Power converter. The second gain is set to a value that gradually increases as the current or voltage increases.
The power conversion device according to claim 1. In the open-loop transfer function of the feedback control system including the inductance component of the AC / DC converter section,
The first gain is the gain margin at the phase crossing frequency and the phase at the gain tolerance frequency of the frequency characteristics of the transfer function when at least one of the current and the voltage in the AC / DC converter unit is less than the first threshold value. It is set to a value that ensures a margin,
The second gain is a value larger than the first gain, and the frequency characteristic of the transmission function when at least one of the current and the voltage in the AC / DC converter unit is equal to or higher than the first threshold value. Is set to a value at which the gain margin at the phase crossing frequency and the phase margin at the gain tolerance frequency are secured.
The power conversion device according to claim 1 or 2. The first gain is at the gain margin or gain tolerance frequency at the phase crossing frequency of the frequency characteristic of the transfer function when at least one of the current and the voltage in the AC / DC converter unit is less than the first threshold value. At least one of the phase margins is set to a value that becomes a predetermined stability limit value.
The power conversion device according to claim 3. The second gain is indicated by a monotonically increasing function that gradually increases as the current or voltage increases, and the rate of increase of the monotonically increasing function is
The current in the AC / DC converter unit, the gain margin when at least one of the voltages is less than the first threshold value, and the gain margin.
The difference between the current in the AC / DC converter unit and the gain margin when at least one of the voltages is equal to or greater than the first threshold value, or the current in the AC / DC converter unit and at least one of the voltages With the phase margin when it is less than the first threshold value,
The difference between the current in the AC / DC converter unit and the phase margin when at least one of the voltages is equal to or higher than the first threshold value.
Set according to the difference of at least one of
The power conversion device according to claim 3 or 4. The control unit
At least one of the minimum value of the current and the minimum value of the voltage within the set period before the first time point in which at least one of the current and the voltage exceeds the rated operating range of the AC / DC converter unit is recorded.
The recorded minimum value is set as the first threshold value.
The power conversion device according to any one of claims 1 to 5. The set period is
The control delay in the control unit from the detection of the current or the voltage exceeding the first threshold value by the detection unit to the setting of the control gain to the second gain by the control unit.
The control gain is set to a period including at least one delay after the control gain is set to the second gain by the control unit until the current or the voltage becomes less than the first threshold value.
The power conversion device according to claim 6. The AC / DC converter unit is an AC / DC converter that includes a reactor having the inductance component and controls the power factor of electric power from the alternating current.
The current is an input current from the AC side to the AC / DC converter unit.
The voltage is an input voltage from the AC side to the AC / DC converter unit.
The second gain is set to an absolute value of the input current or a value that gradually increases as the absolute value of the input voltage increases.
The control unit controls the semiconductor switching element so that the input current from the alternating current side follows the command value.
The power conversion device according to any one of claims 1 to 7. The second gain is set to a value obtained by adding the adjustment amount gradually increasing as the current or the voltage increases to the first gain, or a value obtained by multiplying the first gain.
The power conversion device according to any one of claims 1 to 8. The second gain is a value obtained by adding an adjustment amount that gradually increases as the deviation between the absolute value of the input current or the absolute value of the input voltage and each of the first thresholds increases to the first gain. Or, it is set to a value obtained by multiplying the first gain.
The power conversion device according to claim 8. The control unit
After the control gain is set to the second gain, when the current and the voltage become equal to or less than the second threshold set to a value less than the first threshold value, the control gain is changed from the second gain. Set to the first gain,
The power conversion device according to any one of claims 1 to 10. A wide bandgap semiconductor made of silicon carbide, gallium nitride-based material, or diamond is used as the semiconductor switching element.
The power conversion device according to any one of claims 1 to 11.

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