JP2019058021A - Three-level chopper and control circuit of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a three-level chopper capable of suppressing overheating of a switching element to continue operation and suppressing a ripple current while equalizing the voltages of two series capacitors, and a control circuit thereof. SOLUTION: In a three-level chopper provided with switching elements S1, S2, capacitors C1, C2 and the like, a balance command value generation for generating a balance command value for equalizing these voltages according to the voltages of the capacitors C1 and C2 is generated. The unit 102, the PWM circuits 105 and 106 that generate drive signals for turning on / off the switching elements S1 and S2 based on the balance command value, the input voltage and output voltage of the chopper, and the current flowing through the chopper during the step-down operation of the chopper. A balance command value adjusting unit 200A that adjusts the balance command value according to the input / output voltage ratio that maximizes the ripple rate is provided. [Selection diagram] FIG. 5

Description

  The present invention relates to a technique for equalizing the voltages of two capacitors that share the output voltage of a three-level chopper.

FIG. 13 is a main circuit configuration diagram of the DC power supply system described in Patent Document 1.
This DC power supply system boosts a DC power supply voltage and converts it into a DC voltage having a neutral point by operation of a semiconductor switching element (hereinafter simply referred to as a switching element), and is constituted by a so-called three-level chopper. Yes.

The three-level chopper includes a DC power source BAT, a series circuit of switching elements S ₁ and S ₂ connected between the positive and negative electrodes via reactors L ₁ and L ₂ , and a switching element S _{3 at} both ends of the series circuit. , S ₄ and capacitors C ₁ and C ₂ connected in series, respectively, and a load LD is connected to both ends of the series circuit of the capacitors C ₁ and C ₂ .
D _{1 to} D ₄ are free-wheeling diodes connected in reverse parallel to the switching elements S _{1 to} S ₄ , P is a positive terminal, N is a negative terminal, and M is the switching elements S ₁ and S ₂ . This is a series connection point (neutral point) of the capacitors C ₁ and C ₂ connected to the series connection point.

The operation of this circuit will be briefly described below.
First, when both switching elements S ₁ and S ₂ are turned on, energy is accumulated in reactors L ₁ and L ₂ . Next, to turn off the switching element S ₂ remains turned on the switching element S _1, the capacitor C ₂ is charged via a switching element S ₁ and the freewheeling diode D ₄ by stored energy of the reactor L _1, L ₂ . Then, when turning on the switching element _{S 2} turns off the switching element _{S 1,} the capacitor _{C 1} is charged through the stored energy of the reactor _L 1, _{L 2} and wheel diode _{D 3} and the switching element _{S 2.}

By repeating the above operation, the output voltage V _pn between the terminals P and N is boosted to a voltage higher than the DC power supply voltage V _bat . Here, since the output voltage V _pn can take three levels (V _dcp , V _dcn , and V _dcp + V _dcn ), it is called a three-level chopper.

In this type of three-level chopper, if the voltages V _dcp and V _dcn of the output-side capacitors C ₁ and C ₂ are biased due to a failure of the switching element or a variation in circuit constants, the switching element or the capacitor May be destroyed by overvoltage.
For this reason, in Patent Document 1, control is performed to equalize the voltages V _dcp and V _dcn using the control circuit of FIG.

FIG. 14 shows a control circuit for driving the switching elements S _{1 to} S ₄ .
In FIG. 14, the voltage regulators AVR ₁ and AVR ₂ are set so that the voltages V _dcp and V _dcn of the capacitors C ₁ and C ₂ are respectively equal to ½ of the DC voltage command value (output voltage command value) V _pn ^*. In operation, these outputs are applied to PWM circuits PWM _A and PWM _B having the same configuration via changeover switches SW ₁ and SW ₂ .

The PWM circuits PWM _A and PWM _{B each} include a comparator Cmp, timers TM ₁ and TM ₂ , logic circuits 11 to 15, falling detection circuits 16 and 17, and a DQ flip-flop 18. The switching signals 1 and ₂ for the input side switches SW ₁ and SW _{2 are} provided.
The pulse output determination circuit PJ uses the output signals S ₁ ′ to S ₄ ′ of the PWM circuits PWM _A and PWM _B as drive signals for the switching elements S _{1 to} S ₄ according to the magnitude relationship between the voltage detection values V _dcp and V _dcn. Select (gate signal) and output.

In the control circuit, as shown in FIGS. _15A and _15B , the ON times of the switching elements S ₁ and S ₂ are adjusted according to the magnitude relationship between the voltage detection values V _dcp and V _dcn . Specifically, in order to increase the charge amount of the capacitor having the lower voltage, the on-time of the switching element connected in series to the capacitor is increased to increase or decrease the current I _{ch in} FIG. 13, and the voltage V _dcp , Control to equalize V _dcn is performed.
The switching elements S ₃ and S ₄ function to regenerate the energy of the capacitors C ₁ and C ₂ to the DC power supply side and maintain the voltages V _dcp and V _dcn at predetermined values.

JP 2013-5649 A (paragraphs [0015] to [0023], FIGS. 1 and 3 to 5)

In the technique described in Patent Document 1, if the ON time of the switching element S ₁ or S ₂ becomes too long in order to equalize the voltage, the temperature of the element becomes higher than the design value, and as a result, the switching element There is a case where the protection operation for preventing the destruction works to stop the operation of the apparatus.
On the other hand, when the voltages of the capacitors C ₁ and C ₂ are not equal, a large amount of ripple current is included in the current flowing through the chopper, and the power system connected to the chopper via the inverter circuit and its connected load There was a problem such as adversely affecting.

  Therefore, the problem to be solved by the present invention is to provide a three-level chopper that can equalize the voltage of the series capacitor on the output side, prevent overheating of the switching element and continue the operation stably, and suppress the ripple current. It is to provide the control circuit.

In order to solve the above-described problem, a three-level chopper according to claim 1 is configured such that first and second switching elements are connected in series between positive and negative electrodes of a DC power source via a reactor. First and second capacitors are connected in series to both ends of a series circuit of switching elements via first and second diodes, respectively, and a series connection point of the first and second switching elements and the A three-level chopper connected to a series connection point of the first and second capacitors, and a load connected to both ends of the series circuit of the first and second capacitors,
A PWM command generator for generating a PWM command value for making the voltage across the series circuit of the first and second capacitors coincide with the command value;
A balance command value generator for generating a balance command value for equalizing the voltages of the first and second capacitors in accordance with the voltages of the first and second capacitors;
The balance command value is adjusted according to the input voltage and output voltage of the three-level chopper and the input / output voltage ratio that maximizes the ripple rate of the current flowing through the chopper during the step-down operation of the three-level chopper. A balance command value adjustment unit for generating a balance command adjustment value;
Means for generating a drive signal for turning on and off the first and second switching elements based on the PWM command value and the balance command adjustment value;
It is provided with.

In the three-level chopper according to claim 2, the first and second switching elements are connected in series between the positive and negative electrodes of the DC power source via a reactor, and both ends of the series circuit of the first and second switching elements. The first and second capacitors are connected in series via the first and second diodes, respectively, and the series connection point of the first and second switching elements and the first and second capacitors are connected to each other. A three-level chopper in which a load is connected to both ends of the series circuit of the first and second capacitors,
A PWM command generator for generating a PWM command value for making the voltage across the series circuit of the first and second capacitors coincide with the command value;
A balance command value generator for generating a balance command value for equalizing the voltages of the first and second capacitors in accordance with the voltages of the first and second capacitors;
For adjusting the balance command value according to the input voltage and output voltage of the three-level chopper and the input / output voltage ratio that maximizes the ripple rate of the current flowing through the chopper during the boost operation of the three-level chopper A balance command value adjustment unit for generating a balance command adjustment value;
Means for generating a drive signal for turning on and off the first and second switching elements based on the PWM command value and the balance command adjustment value;
It is provided with.

In the three-level chopper according to claim 3, the first and second switching elements are connected in series between the positive and negative electrodes of the DC power source via a reactor, and both ends of the series circuit of the first and second switching elements. The first and second capacitors are connected in series via the first and second diodes, respectively, and the series connection point of the first and second switching elements and the first and second capacitors are connected to each other. A three-level chopper in which a load is connected to both ends of the series circuit of the first and second capacitors,
A PWM command generator for generating a PWM command value for making the voltage across the series circuit of the first and second capacitors coincide with the command value;
A balance command value generator for generating a balance command value for equalizing the voltages of the first and second capacitors in accordance with the voltages of the first and second capacitors;
The balance command value is adjusted according to the input voltage and output voltage of the three-level chopper and the input / output voltage ratio at which the ripple rate of the current flowing through the chopper at the time of step-up / step-down operation of the three-level chopper is maximized. A balance command value adjustment unit for generating a balance command adjustment value for
Means for generating a drive signal for turning on and off the first and second switching elements based on the PWM command value and the balance command adjustment value;
It is provided with.

The three-level chopper according to claim 4 is the three-level chopper according to any one of claims 1 to 3,
The balance command value adjustment unit obtains a deviation between the product of the output voltage and the input / output voltage ratio and the input voltage, and adjusts the balance command value based on a product of the deviation and a predetermined gain. It is characterized by.

The three-level chopper according to claim 5 is the three-level chopper according to any one of claims 1 to 4,
A third switching element is connected in antiparallel to the first diode, and a fourth switching element is connected in antiparallel to the second diode.

The three-level chopper according to claim 6 is the three-level chopper according to claim 5,
The third and fourth switching elements are turned on to regenerate the energy of the first and second capacitors to the DC power supply.

The control circuit of the three-level chopper according to claim 7 is configured such that the first and second switching elements are connected in series via a reactor between the positive and negative electrodes of the DC power source, and the first and second switching elements are connected in series. A first capacitor and a second capacitor are connected in series to both ends of the circuit via first and second diodes, respectively, and a series connection point of the first and second switching elements is connected to the first and second capacitors. A control circuit for a three-level chopper in which a load is connected to both ends of the series circuit of the first and second capacitors.
A PWM command generator for generating a PWM command value for making the voltage across the series circuit of the first and second capacitors coincide with the command value;
A balance command value generator for generating a balance command value for equalizing the voltages of the first and second capacitors in accordance with the voltages of the first and second capacitors;
The balance command value is adjusted according to the input voltage and output voltage of the three-level chopper and the input / output voltage ratio that maximizes the ripple rate of the current flowing through the chopper during the step-down operation of the three-level chopper. A balance command value adjustment unit for generating a balance command adjustment value;
Means for generating a drive signal for turning on and off the first and second switching elements based on the PWM command value and the balance command adjustment value;
It is provided with.

In the control circuit for a three-level chopper according to claim 8, the first and second switching elements are connected in series via a reactor between the positive and negative electrodes of the DC power supply, and the first and second switching elements are connected in series. A first capacitor and a second capacitor are connected in series to both ends of the circuit via first and second diodes, respectively, and a series connection point of the first and second switching elements is connected to the first and second capacitors. A control circuit for a three-level chopper in which a load is connected to both ends of the series circuit of the first and second capacitors.
A PWM command generator for generating a PWM command value for making the voltage across the series circuit of the first and second capacitors coincide with the command value;
A balance command value generator for generating a balance command value for equalizing the voltages of the first and second capacitors in accordance with the voltages of the first and second capacitors;
For adjusting the balance command value according to the input voltage and output voltage of the three-level chopper and the input / output voltage ratio that maximizes the ripple rate of the current flowing through the chopper during the boost operation of the three-level chopper A balance command value adjustment unit for generating a balance command adjustment value;
Means for generating a drive signal for turning on and off the first and second switching elements based on the PWM command value and the balance command adjustment value;
It is provided with.

In the control circuit for a three-level chopper according to claim 9, the first and second switching elements are connected in series via a reactor between the positive and negative electrodes of the DC power supply, and the first and second switching elements are connected in series. A first capacitor and a second capacitor are connected in series to both ends of the circuit via first and second diodes, respectively, and a series connection point of the first and second switching elements is connected to the first and second capacitors. A control circuit for a three-level chopper in which a load is connected to both ends of the series circuit of the first and second capacitors.
A PWM command generator for generating a PWM command value for making the voltage across the series circuit of the first and second capacitors coincide with the command value;
A balance command value generator for generating a balance command value for equalizing the voltages of the first and second capacitors in accordance with the voltages of the first and second capacitors;
The balance command value is adjusted according to the input voltage and output voltage of the three-level chopper and the input / output voltage ratio at which the ripple rate of the current flowing through the chopper at the time of step-up / step-down operation of the three-level chopper is maximized. A balance command value adjustment unit for generating a balance command adjustment value for
Means for generating a drive signal for turning on and off the first and second switching elements based on the PWM command value and the balance command adjustment value;
It is provided with.

A control circuit for a three-level chopper according to claim 10 is:
In the control circuit of the three-level chopper according to any one of claims 7 to 9,
The balance command value adjustment unit obtains a deviation between the product of the output voltage and the input / output voltage ratio and the input voltage, and adjusts the balance command value based on a product of the deviation and a predetermined gain. It is characterized by.

According to the present invention, in each of the step-down mode region and the step-up mode region of the three-level chopper, it is not necessary to unnecessarily increase the ON time of the switching element in order to equalize the voltage of the output side series capacitor. For this reason, it is possible to prevent overheating of the switching element, and it is possible to continue the stable operation of the apparatus without performing the protective operation.
Moreover, the ripple component of the electric current which flows into a chopper can be suppressed, and the bad influence given to an electric power grid | system and its connection load can be prevented.

It is a figure which shows the relationship between the input voltage of a chopper, and a current ripple rate. It is a figure explaining the operation | movement of the current path in the step-down mode of a chopper, and a switching element. It is a figure explaining the operation | movement of the electric current path in the step-up mode of a chopper, and a switching element. It is a figure which shows the ripple current when the voltage of the output side capacitor | condenser of a chopper is equal, and when it is non-uniform | heterogenous. It is a block diagram of the control circuit which concerns on 1st Embodiment of this invention. It is a figure which shows the relationship between the input voltage of a chopper and each signal of FIG. 5 in 1st Embodiment. It is a figure which shows the relationship between the input voltage in 1st Embodiment, a current ripple rate, and a balance command rate. It is a block diagram of the control circuit which concerns on 2nd Embodiment of this invention. It is a figure which shows the relationship between the input voltage of a chopper and each signal of FIG. 8 in 2nd Embodiment. It is a figure which shows the relationship between the input voltage in 2nd Embodiment, a current ripple rate, and a balance command rate. It is a block diagram of the control circuit which concerns on 3rd Embodiment of this invention. It is a figure which shows the relationship between the input voltage and current ripple rate in 3rd Embodiment. 2 is a main circuit configuration diagram of a DC power supply system described in Patent Document 1. FIG. 2 is a configuration diagram of a control circuit described in Patent Document 1. FIG. It is a wave form diagram which shows the operation | movement of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the principle of the present invention will be described. The present invention focuses on the fact that the ripple rate of the DC input current of a three-level chopper (hereinafter also simply referred to as “chopper”) changes according to the voltage imbalance of the capacitors C ₁ and C ₂ on the output side. That is, for each of the step-down operation and step-up operation of the chopper, the balance command value (balance command rate) for equalizing the voltages of the capacitors C ₁ and C ₂ is adjusted according to the relationship between the input and output voltages of the chopper. Thus, the ripple current is suppressed and the voltages of the capacitors C ₁ and C ₂ are equalized.

First, FIG. 1 shows the relationship between the input voltage and the current ripple rate (ΔI / I _dc ) in the step-down mode region and the step-up mode region of the chopper. Here, the DC input current _{I dc} chopper is the same as the _{I ch} in FIG 13, the output voltage _{V o} is the same as the _{V pn} in FIG.
The step-down mode of the chopper refers to a mode where the input voltage V _in > (output voltage V _o / 2), and the step-up mode of the chopper refers to a mode where the input voltage V _in <(output voltage V _o / 2). say.
In the step-down mode region and the step-up mode region of FIG. 1, the relationship between the input and output voltages when the current ripple ratio becomes maximum can be obtained as follows (in conclusion, in the chopper step-down mode, the input voltage V when _in is (√3 + 3) / 6 times the output voltage _{V o,} in boost mode chopper, when the input voltage _{V in} is 1/3 times the output voltage _{V o,} each current ripple factor becomes maximum ).

FIG. 2 is a diagram for explaining the relationship between input and output voltages when the current ripple rate becomes maximum in the step-down mode of the chopper. 2A shows the path of the input current I _dc when the switching element S ₁ is turned on and the switching element S ₂ is turned off. FIG. 2B shows the path of the input current I _dc when the switching elements S ₁ and S ₂ are turned off. Arrow). C _in is a smoothing capacitor, and V _in is an input voltage of the chopper.

また、電流リップル率（ΔＩ／Ｉ_ｄｃ）は数式２となる。この数式２において、ＬはリアクトルＬ_１，Ｌ_２のインダクタンス、Ｐは入力電力である。

As shown in FIG. 2C, when the switching elements S ₁ and S ₂ are alternately switched at a cycle T = 1 / f _sw (f _sw : switching frequency), the on-time of the switching element S ₁ is expressed by Equation 1. Represented by

Further, the current ripple rate (ΔI / I _dc ) is expressed by Equation 2. In Equation 2, L is the inductance of reactors L ₁ and L ₂ , and P is input power.

Input voltage V _in when the current ripple ratio (ΔI / I _dc) is maximum is the value when the value obtained by differentiating Equation 2 by V _in becomes zero, can be represented by Equation 3.

FIG. 3 is a diagram for explaining the relationship between the input and output voltages when the current ripple ratio becomes maximum in the step-up mode of the chopper. FIG. 3A shows the switching elements S ₁ and S ₂ turned on. 3B shows a path (arrow) of the input current I _dc when the switching element S ₂ is turned off while the switching element S ₁ is turned on. In FIG. 3C, t _onS12 is a time for turning on both of the switching elements S ₁ and S ₂ .

また、電流リップル率（ΔＩ／Ｉ_ｄｃ）は数式５となる。

Here, the on-time switching element S ₁ is represented by Equation 4.

Further, the current ripple rate (ΔI / I _dc ) is expressed by Equation 5.

Input voltage V _in when the current ripple ratio (ΔI / I _dc) is maximum is the value when the value obtained by differentiating the equation 5 by V _in becomes zero, can be represented by Equation 6.

4A shows the ripple current ΔI included in the input current I _dc when the voltages of the capacitors C ₁ and C ₂ are equal, and FIG. 4B shows the voltage of the capacitors C ₁ and C ₂ . The ripple current ΔI when it is not equal is shown. 4 (a) and 4 (b), it can be seen that when the voltages of the capacitors C ₁ and C ₂ are unbalanced, the ripple current ΔI and the current ripple rate (ΔI / I _dc ) increase.

Next, FIG. 5 is a block diagram of the control circuit according to the first embodiment of the present invention.
In the first embodiment, when the chopper is operated in the step-down mode region (see FIG. 1), the drive signals for the switching elements S _{1 to} S ₄ are generated in order to equalize the voltages of the capacitors C ₁ and C _2. Is.

The outline of the operation of the first embodiment is as follows.
That is, in the step-down mode, when V _in = V _o , the balance command value (balance command rate) is set to 0, thereby preventing the bias of the switching element and continuing the operation of the apparatus.
Further, the balance command value is gradually increased from the state of V _in = V _o according to the decrease of V _in , and the time point at which V _in = {(√3 + 3) / 6} V _{o at which} the current ripple rate becomes maximum is reached. By maximizing the balance command value (balance command rate is 100%), the ripple current is reduced and the connected devices of the power system are protected.
Further, the balance command value is gradually decreased from the time point of V _in = {(√3 + 3) / 6} V _o according to the decrease of V _in , and the balance command value is reduced to 0 (at the time of V _in = V _o / 2. By setting the balance command rate to 0%, the bias of the switching element is prevented and the operation of the apparatus is continued.

In the control circuit of FIG. 5 according to the first embodiment, the PWM command generation unit 101 uses the above-described Vc based on the DC voltage command value V _o ^{*, the} DC voltage detection value V _o, and the DC current detection value I _dc of the chopper. A PWM command (voltage command) for controlling _o to V _o ^* is generated.
This PWM command is added / subtracted to / from a balance command value output from an upper / lower limit limiter 211 of a balance command value adjusting unit 200A described later by adders / subtractors 103, 104, and input to PWM circuits 105, 106 (PWM1, PWM2). The The PWM circuits 105 and 106 compare the input command value with the carriers 1 and 2, respectively, thereby driving signals for the switching elements S ₁ and S ₃ and the switching elements S ₂ and S ₄ in FIG. 13. Is generated.

Balance command value generating unit 102, a DC voltage above the detection value (voltage detection value of the capacitor C ₁ in FIG. 13) V _C1 and the DC voltage lower detection value (voltage detection value of the capacitor C ₂₎ Balance command value V _C2 Metropolitan The balance command value is input to the balance command value adjustment unit 200A.

Next, the configuration of the balance command value adjustment unit 200A will be described.
First, the input voltage _{V in} of the chopper is input to the adder-subtracter 204 via the low-pass filter 201. Further, the output voltage V _o of the chopper is input to a multiplier 203 through a low-pass filter 202, the multiplication result of a constant {(√3 + 3) / 6 } is input to the adder-subtracter 204.
The output a of the adder / subtracter 204 is input to a comparator 205 for determining the sign, and a comparison result with “0000 hex (hex is a hexadecimal number)” is added to the changeover switch 206.

The output a of the adder / subtracter 204 is input to the input terminals T and F of the changeover switch 206 via the gains 1 and 2, respectively. Here, the gain 1 is a coefficient that becomes “1000 hex” when V _in = V _o / 2, and the gain 2 is a coefficient that becomes “1000 hex” when V _in = V _o . Note that the input terminal T of the changeover switch 206 indicates “True”, and F indicates “False”.
The comparator 205 outputs a signal for selecting the input terminal T side of the changeover switch 206 when the input a is negative.

The output of the changeover switch 206 is input to the adder / subtracter 208 as an absolute value signal b by the absolute value calculation circuit 207. The adder / subtracter 208 detects a deviation c between “1000 hex” and the absolute value signal b, and the deviation c is input to the multipliers 209 and 210.
The multipliers 209 and 210 multiply the deviation c by the upper limit value and the lower limit value, respectively, and output the multiplication results as the upper limit value and the lower limit value of the upper / lower limiter 211. The upper / lower limiter 211 performs upper / lower limit processing on the balance command value input from the balance command value generation unit 102 and outputs the output signal d to the adders / subtractors 103 and 104.

Figure 6 is a diagram showing the relationship between each signal a~d in the input voltage V _in and 5 of the chopper. The balance command value d finally output from the balance command value adjustment unit 200A by the operation of the control circuit in FIG. 5 becomes 0 when V _in = V _o / 2, V _in = V _o , and V _in = { When (√3 + 3) / 6} V _o , the maximum value (balance command rate is 100%).

Next, FIG. 7 is a diagram illustrating a relationship between the input voltage, the current ripple rate, and the balance command rate in the design example based on the first embodiment. Here, the maximum value of the current ripple rate 20 [%], the output voltage _{V o} of the chopper and 1100 [V]. For this reason, the input voltage V _in when the current ripple ratio becomes maximum is V _in = {(√3 + 3) / 6} V _o ≈868 [V].

As is clear from the outline of the operation described above, the ripple current due to the voltage non-uniformity of the capacitors C ₁ and C ₂ is hardly a problem because the current ripple rate is small at the time points (1) and (3) in FIG. . Therefore, the balance command value output from the balance command value adjusting unit 200A in FIG. 5 is set to 0 (balance command rate is 0%) so that the ON times of the switching elements S ₁ and S ₂ are not biased, and the thermal balance of the elements Keep.
Since the current ripple rate is large at the point (2) in FIG. 7, the ripple current due to the voltage non-uniformity of the capacitors C ₁ and C ₂ is large. For this reason, the balance command value output from the balance command value adjustment unit 200A is set to the maximum value (balance command rate is 100%), the ripple current is suppressed, and the connected devices of the power system are protected.

As described above, by gradually changing the balance command value in the range of (1) to (2) to (3) in FIG. 7 in accordance with the current ripple rate, the switching elements S ₁ and S in the step-down mode of the chopper. ₂ overheat protection and ripple current suppression.

Next, FIG. 8 is a block diagram of a control circuit according to the second embodiment of the present invention.
In the second embodiment, when the chopper is operated in the boost mode region (see FIG. 1), the drive signals of the switching elements S _{1 to} S ₄ are generated in order to equalize the voltages of the capacitors C ₁ and C _2. Is.

The outline of the operation of the second embodiment is as follows.
That is, in the boost mode, when V _in = V _o / 2, the balance command value (balance command rate) is set to 0, so that the bias of the switching element is prevented and the operation of the device is continued.
Further, the balance command value is gradually increased from the state of V _in = V _o / 2 according to the decrease of V _in , and the balance command value is reached at the time of V _in = V _o / 3 when the current ripple rate becomes maximum. Is maximized (balance command rate is 100%) to reduce ripple current and protect connected devices in the power system.
Further, the balance command value is gradually decreased as V _in decreases from the time point of V _in = V _o / 3, and the balance command value is set to 0 (the balance command rate is 0%) when V _in = 0. Thus, the operation of the apparatus is continued while preventing the bias of the heat of the switching element.

In either step-down mode or step-up mode, when _one of the voltages of the capacitors C ₁ and C ₂ is an overvoltage and the other is an undervoltage, the balance command value is maximized regardless of the magnitude of the input voltage. The operation of the device can be continued.

The control circuit of FIG. 8 according to the second embodiment is different from that of FIG. 5 in that the constant input to the multiplier 203 in the balance command value adjustment unit 200B is 1 / in place of (√3 + 3) / 6 in FIG. 3 and the gain on the input side of the changeover switch 206 is gain 3 and 4. Here, the gain 3 is a coefficient that becomes “1000 hex” when V _in = 0, and the gain 4 is a coefficient that becomes “1000 hex” when V _in = V _o / 2.

Figure 9 is a diagram showing the relationship between each signal a~d in the input voltage V _in and 8 of the chopper. The balance command value d finally output from the balance command value adjustment unit 200B by the operation of the control circuit in FIG. 8 becomes 0 when V _in = 0 and V _in = V _o / 2, and V _in = V _o The maximum value (balance command rate is 100%) at / 3.

Next, FIG. 10 is a diagram illustrating a relationship between an input voltage, a current ripple rate, and a balance command rate in a design example based on the second embodiment. Like the first embodiment, the maximum value of the current ripple rate 20 [%], the output voltage _{V o} of the chopper and 1100 [V]. For this reason, the input voltage V _in when the current ripple ratio becomes maximum is V _in = V _o / 3≈367 [V].

As is clear from the outline of the operation described above, the ripple current due to the voltage non-uniformity of the capacitors C ₁ and C ₂ is hardly a problem because the current ripple ratio is small at the points (4) and (6) in FIG. . Accordingly, the balance command value output from the balance command value adjusting unit 200B of FIG. 8 is set to 0 (balance command rate is 0%) so that the ON times of the switching elements S ₁ and S ₂ are not biased, and the thermal balance of the elements Keep.
Since the current ripple rate is large at the time point (5) in FIG. 10, the ripple current due to the voltage nonuniformity of the capacitors C ₁ and C ₂ is large. For this reason, the balance command value output from the balance command value adjustment unit 200B is set to the maximum value (balance command rate is 100%), the ripple current is suppressed, and the connected devices of the power system are protected.

As described above, by gradually changing the balance command value in the range of (4) to (5) to (6) in FIG. 10 according to the current ripple rate, the switching elements S ₁ and S in the step-up mode of the chopper. ₂ overheat protection and ripple current suppression.

FIG. 11 is a block diagram of a control circuit according to the third embodiment of the present invention.
In the third embodiment, when the chopper is operated as a step-up / step-down chopper (when the step-down mode region and the step-up mode region in FIG. 1 are used separately), the switching elements are used to equalize the voltages of the capacitors C ₁ and C _2. The drive signals S _{1 to} S ₄ are generated.

11, parts other than the balance command value adjusting unit 200C are the same as those in FIGS. 5 and 8, and this balance command value adjusting unit 200C includes the main part of the balance command value adjusting unit 200A in FIG. 5 and the balance in FIG. This corresponds to a combination of the main part of the command value adjustment unit 200B.
In the balance command value adjustment unit 200C, the comparator 230 compares V _in and V _o / 2 to determine the step-down mode and the step-up mode. If the step-down mode (V _in > V _o / 2), the changeover switch 229 is set. If the boost mode (V _in <V _o / 2) is set on the terminal T side, the changeover switch 229 is switched to the terminal F side.

  On the boost mode side in the balance command value adjustment unit 200C, 221 and 222 are low-pass filters, 223 are multipliers, 224 and 228 are adders / subtracters, 225 is a comparator, 226 is a changeover switch, and 227 is an absolute value calculator. is there. The gain 5 is an appropriate coefficient for correcting the balance command value to match the current ripple rate.

FIG. 12 is a diagram illustrating the relationship between the input voltage and the current ripple in the design example based on the third embodiment. Since the relationship between the input voltage and the balance command rate is the same as in FIGS. 7 and 10, the illustration is omitted.
First, as in the second embodiment, the maximum value of the current ripple rate 20 [%], and the output voltage V _o of the chopper and 1100 [V], the input voltage V _in when the current ripple ratio becomes maximum In the step-down mode, V _in ≈868 [V], and in the step-up mode, V _in ≈367 [V].

At the time of (1), (3), (4), and (6) in FIG. 12, since the current ripple rate is small, the ripple current due to the voltage nonuniformity of the capacitors C ₁ and C ₂ hardly poses a problem. Therefore, the balance command value output from the balance command value adjusting unit 200C of FIG. 11 is set to 0 (balance command rate is 0%) so that the ON time of the switching elements S ₁ and S ₂ is not biased, and the thermal balance of the elements Keep.
Since the current ripple rate is large at the point (2) in the step-down mode region of FIG. 12, the ripple current due to the voltage nonuniformity of the capacitors C ₁ and C ₂ is large. For this reason, the balance command value output from the balance command value adjusting unit 200C is set to the maximum value (balance command rate is 100%), the ripple current is suppressed, and the connected devices of the power system are protected.
Further, the time point (5) in the boost mode region may be a balance command value corresponding to the current ripple rate.

As described above, for each of the step-down mode region and the step-up mode region, the range of (1) to (2) to (3) or (4) to (5) to (6) in FIG. 12 according to the current ripple rate. By gradually changing the balance command value, the overheating protection of the switching elements S ₁ and S ₂ and the ripple current can be suppressed.

Note that if the switching elements S ₃ and S ₄ in FIG. 13 are turned on, the energy of the capacitors C ₁ and C ₂ can be regenerated to the DC power source BAT. However, the present invention is based on the switching elements S ₃ and S _4. It can also be applied to a three-level chopper that does not have

  The three-level chopper according to the present invention can be used for, for example, an uninterruptible power supply device, a photovoltaic power generation system, or a vehicle power conversion device such as a railway vehicle or an electric vehicle whose input voltage greatly varies.

BAT: DC power supply S _{1 to} S ₄ : switching elements D _{1 to} D ₄ : freewheeling diodes L ₁ and L ₂ : reactors C ₁ and C ₂ : capacitor C _in : smoothing capacitor LD: load P: positive terminal N: negative Side terminal M: Neutral point 101: PWM command generation unit 102: Balance command value generation unit 103, 104, 204, 208, 224, 228: Adder / subtractor 105, 106: PWM circuits 200A, 200B, 200C: Balance command value adjustment Units 201, 202, 221, 222: Low-pass filters 203, 209, 210, 223: Multipliers 205, 225, 230: Comparators 206, 226, 229: Changeover switches 207, 227: Absolute value calculator 211: Upper / lower limiter

Claims (10)

The first and second switching elements are connected in series between the positive and negative electrodes of the DC power supply via a reactor, and the first and second diodes are connected to both ends of the series circuit of the first and second switching elements. The first and second capacitors are connected in series via each, and the series connection point of the first and second switching elements and the series connection point of the first and second capacitors are connected, A three-level chopper in which a load is connected to both ends of a series circuit of first and second capacitors,
A PWM command generator for generating a PWM command value for making the voltage across the series circuit of the first and second capacitors coincide with the command value;
A balance command value generator for generating a balance command value for equalizing the voltages of the first and second capacitors in accordance with the voltages of the first and second capacitors;
The balance command value is adjusted according to the input voltage and output voltage of the three-level chopper and the input / output voltage ratio that maximizes the ripple rate of the current flowing through the chopper during the step-down operation of the three-level chopper. A balance command value adjustment unit for generating a balance command adjustment value;
Means for generating a drive signal for turning on and off the first and second switching elements based on the PWM command value and the balance command adjustment value;
A three-level chopper characterized by comprising The first and second switching elements are connected in series between the positive and negative electrodes of the DC power supply via a reactor, and the first and second diodes are connected to both ends of the series circuit of the first and second switching elements. The first and second capacitors are connected in series via each, and the series connection point of the first and second switching elements and the series connection point of the first and second capacitors are connected, A three-level chopper in which a load is connected to both ends of a series circuit of first and second capacitors,
A PWM command generator for generating a PWM command value for making the voltage across the series circuit of the first and second capacitors coincide with the command value;
A balance command value generator for generating a balance command value for equalizing the voltages of the first and second capacitors in accordance with the voltages of the first and second capacitors;
For adjusting the balance command value according to the input voltage and output voltage of the three-level chopper and the input / output voltage ratio that maximizes the ripple rate of the current flowing through the chopper during the boost operation of the three-level chopper A balance command value adjustment unit for generating a balance command adjustment value;
Means for generating a drive signal for turning on and off the first and second switching elements based on the PWM command value and the balance command adjustment value;
A three-level chopper characterized by comprising The first and second switching elements are connected in series between the positive and negative electrodes of the DC power supply via a reactor, and the first and second diodes are connected to both ends of the series circuit of the first and second switching elements. The first and second capacitors are connected in series via each, and the series connection point of the first and second switching elements and the series connection point of the first and second capacitors are connected, A three-level chopper in which a load is connected to both ends of a series circuit of first and second capacitors,
A PWM command generator for generating a PWM command value for making the voltage across the series circuit of the first and second capacitors coincide with the command value;
A balance command value generator for generating a balance command value for equalizing the voltages of the first and second capacitors in accordance with the voltages of the first and second capacitors;
The balance command value is adjusted according to the input voltage and output voltage of the three-level chopper and the input / output voltage ratio at which the ripple rate of the current flowing through the chopper at the time of step-up / step-down operation of the three-level chopper is maximized. A balance command value adjustment unit for generating a balance command adjustment value for
Means for generating a drive signal for turning on and off the first and second switching elements based on the PWM command value and the balance command adjustment value;
A three-level chopper characterized by comprising In the three-level chopper according to any one of claims 1 to 3,
The balance command value adjustment unit
A three-level chopper characterized by obtaining a deviation between the product of the output voltage and the input / output voltage ratio and the input voltage and adjusting the balance command value based on a product of the deviation and a predetermined gain. In the 3 level chopper described in any one of Claims 1-4,
3. A three-level chopper, wherein a third switching element is connected in antiparallel to the first diode, and a fourth switching element is connected in antiparallel to the second diode. The three-level chopper according to claim 5,
A three-level chopper, wherein the third and fourth switching elements are turned on to regenerate the energy of the first and second capacitors to the DC power source. The first and second switching elements are connected in series between the positive and negative electrodes of the DC power supply via a reactor, and the first and second diodes are connected to both ends of the series circuit of the first and second switching elements. The first and second capacitors are connected in series via each, and the series connection point of the first and second switching elements and the series connection point of the first and second capacitors are connected to each other. A control circuit of a three-level chopper in which a load is connected to both ends of a series circuit of first and second capacitors,
A PWM command generator for generating a PWM command value for making the voltage across the series circuit of the first and second capacitors coincide with the command value;
A balance command value generator for generating a balance command value for equalizing the voltages of the first and second capacitors in accordance with the voltages of the first and second capacitors;
The balance command value is adjusted according to the input voltage and output voltage of the three-level chopper and the input / output voltage ratio that maximizes the ripple rate of the current flowing through the chopper during the step-down operation of the three-level chopper. A balance command value adjustment unit for generating a balance command adjustment value;
Means for generating a drive signal for turning on and off the first and second switching elements based on the PWM command value and the balance command adjustment value;
A control circuit for a three-level chopper, comprising: The first and second switching elements are connected in series between the positive and negative electrodes of the DC power supply via a reactor, and the first and second diodes are connected to both ends of the series circuit of the first and second switching elements. The first and second capacitors are connected in series via each, and the series connection point of the first and second switching elements and the series connection point of the first and second capacitors are connected to each other. A control circuit of a three-level chopper in which a load is connected to both ends of a series circuit of first and second capacitors,
A PWM command generator for generating a PWM command value for making the voltage across the series circuit of the first and second capacitors coincide with the command value;
A balance command value generator for generating a balance command value for equalizing the voltages of the first and second capacitors in accordance with the voltages of the first and second capacitors;
For adjusting the balance command value according to the input voltage and output voltage of the three-level chopper and the input / output voltage ratio that maximizes the ripple rate of the current flowing through the chopper during the boost operation of the three-level chopper A balance command value adjustment unit for generating a balance command adjustment value;
Means for generating a drive signal for turning on and off the first and second switching elements based on the PWM command value and the balance command adjustment value;
A control circuit for a three-level chopper, comprising: The first and second switching elements are connected in series between the positive and negative electrodes of the DC power supply via a reactor, and the first and second diodes are connected to both ends of the series circuit of the first and second switching elements. The first and second capacitors are connected in series via each, and the series connection point of the first and second switching elements and the series connection point of the first and second capacitors are connected to each other. A control circuit of a three-level chopper in which a load is connected to both ends of a series circuit of first and second capacitors,
A PWM command generator for generating a PWM command value for making the voltage across the series circuit of the first and second capacitors coincide with the command value;
A balance command value generator for generating a balance command value for equalizing the voltages of the first and second capacitors in accordance with the voltages of the first and second capacitors;
The balance command value is adjusted according to the input voltage and output voltage of the three-level chopper and the input / output voltage ratio at which the ripple rate of the current flowing through the chopper at the time of step-up / step-down operation of the three-level chopper is maximized. A balance command value adjustment unit for generating a balance command adjustment value for
Means for generating a drive signal for turning on and off the first and second switching elements based on the PWM command value and the balance command adjustment value;
A control circuit for a three-level chopper, comprising: In the control circuit of the three-level chopper according to any one of claims 7 to 9,
The balance command value adjustment unit
A deviation between the product of the output voltage and the input / output voltage ratio and the input voltage is obtained, and the balance command value is adjusted based on a product of the deviation and a predetermined gain. Control circuit.

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