Power conversion system and control method

Abstract

To provide a power conversion system and a control method capable of making behavior more stable when a load short circuit occurs.SOLUTION: A power conversion system includes a DC-DC converter, an inverter, and a control unit. The DC-DC converter is capable of converting a first DC power of a first DC to generate a second DC power of a second DC. The inverter is capable of converting the second DC power by control to generate AC power. The control unit controls the amount of power conversion of the DC-DC converter on the basis of a second DC current reference based on a current estimation value of the first DC, a first DC current detection value of the first DC, a second DC voltage reference of the second DC, and a second DC voltage detection value of the second DC. The control unit corrects the current estimation value on the basis of a result of identifying the magnitude of the AC current detection value related to the AC power, and generates the second DC current reference on the basis of the result of the correction.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a power conversion system and a control method. [Background technology]

[0002] There is a power conversion system that has a DC-DC converter and an inverter, which are cascaded together. It is desirable to make such a static power conversion device not only stable in normal operation, but also stable in the event of a load short circuit and when the load short circuit is removed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 60-084922 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a power conversion system and a control method capable of making the behavior more stable when a load short circuit occurs. [Means for solving the problem]

[0005] A power conversion system according to an embodiment includes a DC-DC converter, an inverter, and a control unit. The DC-DC converter is capable of converting a first DC power of a first DC to generate a second DC power of a second DC. The inverter is capable of converting the second DC power by control to generate AC power. The control unit controls the amount of power conversion of the DC-DC converter based on a second DC current reference based on a current estimation value of the first DC, a first DC current detection value of the first DC, a second DC voltage reference of the second DC, and a second DC voltage detection value of the second DC. The control unit corrects the current estimation value based on a result of identifying the magnitude of the AC current detection value related to the AC power, and generates the second DC current reference based on the result of the correction. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a configuration diagram of a power conversion system according to an embodiment. [Diagram 2] FIG. 2 is a schematic configuration diagram of a control unit according to the embodiment. [Diagram 3] FIG. 4 is a diagram showing interruption characteristics of the circuit breaker according to the embodiment. [Figure 4] 3A and 3B are diagrams for explaining the operation of the power conversion system according to the embodiment. [Diagram 5] FIG. 2 is a diagram for explaining an example of the configuration of a control unit according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The power conversion system and control method of the embodiment will be described below. In the following description, being electrically connected may simply be referred to as being "connected". The small fixed value in the embodiment may include 0. In this specification, "based on XX" means "based on at least XX" and includes the case where it is based on another element in addition to XX. Furthermore, "based on XX" is not limited to the case where XX is directly used, but also includes the case where it is based on XX that has been calculated or processed. "XX" is any element (for example, any information).

[0008] FIG. 1 is a configuration diagram of a power conversion system 1 according to an embodiment.

[0009] The power conversion system 1 includes a storage battery B (power source), a static power converter 10, and a control unit 20.

[0010] The storage battery B is, for example, a secondary battery, and outputs stored DC power to the static power converter 10. The positive electrode of the storage battery B is connected to the terminal TBSP. The negative electrode of the storage battery B is connected to the terminal TBSN.

[0011] The static power converter 10 is an example of a power converter that generates AC power. For example, the static power converter 10 is configured to be capable of converting between DC power and AC power. The DC side of the static power converter 10 is connected to a storage battery B, and receives DC power from the storage battery B. A load that uses three-phase AC power of, for example, the RST phase, is connected to the AC side of the static power converter 10. For example, a connection terminal TB corresponding to the AC output of the static power converter 10 is connected to an AC power system via a main circuit breaker 91.

[0012] For example, the static power converter 10 includes a DC-DC converter 12, an inverter 13, a transformer 14, a capacitor 15, a current sensor 16, and a potential transformer 17.

[0013] The DCDC converter 12 boosts the DC power supplied from the storage battery B under control and outputs a desired voltage (DC voltage) to a terminal on the load side. The positive pole P (DC bus BLP) and negative pole N (DC bus BLN) of the DC link are connected to the load side of the DCDC converter 12. The DC bus BLC is connected to the neutral point T12C, and the neutral point T12C is connected to the midpoint of the input of the inverter 13 via the DC bus BLC. The voltage output by the DCDC converter 12 changes the voltages of the positive pole P (DC bus BLP) and negative pole N (DC bus BLN) of the DC link.

[0014] The DC-DC converter 12 includes, for example, a semiconductor switching element for power conversion therein.

[0015] The capacitors 125 and 126 are arranged in parallel with the output of the DC-DC converter 12 and smooth the voltages of the positive electrode (high potential terminal T12P) and the negative electrode (low potential terminal T12N) with respect to the potential of the midpoint 12C. The capacitors 125 and 126 may be configured as part of the DC-DC converter 12 or may be arranged outside the DC-DC converter 12, for example.

[0016] The DC-DC converter 12 further includes a pair of a positive terminal TBSP and a negative terminal TBSN as terminals on the power supply side, and a pair of a positive high potential terminal T12P, a negative high potential terminal T12N, and a neutral point T12C as terminals on the load side. The neutral point T12C is at a midpoint potential.

[0017] The inverter 13 converts the DC power supplied via the DC buses BLP, BLC, and BLN of the DC link into three-phase AC power through control and outputs the power. The DC-DC converter 12 and the inverter 13 each include a semiconductor switching element for power conversion therein.

[0018] The capacitors 135 and 136 are provided in parallel with the input of the inverter 13, and smooth the voltages of the positive electrode (high potential terminal T13P) and the negative electrode (low potential terminal T13N) with respect to the potential of the midpoint 13C. The capacitors 135 and 136 may be configured as part of the inverter 13, or may be provided outside the inverter 13, for example.

[0019] The inverter 13 generates AC power and supplies the AC power to a load via a connection terminal TB provided on the AC side, a main breaker 91, a breaker 92, and the like.

[0020] The inverter 13 supplies, for example, the generated three-phase AC power to its AC side. The AC side of the inverter 13 is connected to the primary side (primary winding) of the transformer 14 via an AC power system 181. The AC power system 181 is configured with three phases: U-phase, V-phase, and W-phase.

[0021] The secondary side (secondary winding) of the transformer 14 is connected to a connection terminal TB via an AC power system 182. The AC power system 182 is configured with three phases: R-phase, S-phase, and T-phase. The connection terminal TB has terminals for each of the R-phase, S-phase, and T-phase.

[0022] The current sensor 16 is provided in the AC power system 182, detects the current flowing in each of the R-phase, S-phase, and T-phase, and outputs the detection results IR_F, IS_F, and IT_F.

[0023] The capacitors 15 are provided between the R-phase, S-phase and T-phase of the AC power system 182, and are connected in a Δ configuration. The combination of the transformer 14 and the capacitors 15 forms an LC filter.

[0024] The potential transformer 17 is connected to the AC power system 182 and detects the line voltage of the AC power system 182 .

[0025] The static power converter 10 is controlled by a control unit 20 which will be described later.

[0026] The control unit 20 of the embodiment will be described with reference to FIG. FIG. 2 is a schematic configuration diagram of the control unit 20 according to the embodiment.

[0027] The control unit 20 sends a gate pulse GP to the DCDC converter 12 based on a DC voltage reference supplied from a higher-level device, for example, to control the amount of power conversion by the DCDC converter 12. The control unit 20 also sends a gate pulse GP to the inverter 13 to control the amount of power conversion by the inverter 13. The control unit 20 has a plurality of control modes including a first control mode used for control during normal operation and a second control mode used for control after an overcurrent is detected. The control unit 20 selects an appropriate control mode based on the detected state to control the static power converter 10. In the embodiment, "normal operation" refers to a situation in which no load short circuit fault or the like occurs. For example, in "normal operation," the current value flowing from the static power converter 10 is within a predetermined range. In contrast, a situation in which a current exceeding this predetermined range flows is included in "abnormal operation" in the present embodiment.

[0028] When the control unit 20 selects the first control mode, it performs AC voltage control based on the voltage feedback value and the first AC voltage command, and current control using the result of the AC voltage control and the current feedback value to generate a first AC voltage reference. For example, "line voltage feedback values ​​VRS_F, VTS_F in a stationary coordinate system having an R-axis, an S-axis, and a T-axis" is an example of the above-mentioned voltage feedback value. "Voltage references VD_com and VQ_com in a rotating coordinate system" described later is an example of the above-mentioned first AC voltage command.

[0029] An example of the configuration of the inverter 13 will be described. The inverter 13 converts the three-level DC voltage into a three-phase (U-phase, V-phase, W-phase) AC voltage and supplies the three-phase AC voltage to the transformer 14. Each of the three-phase AC voltages generated by the inverter 13 is a three-level AC voltage that changes in the following order: potential of the high potential terminal T13P, potential of the neutral point T13C, potential of the low potential terminal N, potential of the neutral point T13C, potential of the high potential terminal T13P, . . .

[0030] The inverter 13 includes switching elements S1U to S4U, S1V to S4V, and S1W to S4W. The switching elements S1U to S4U, S1V to S4V, and S1W to S4W are, for example, switching devices formed of self-extinguishing semiconductor elements that can be turned on and off by a gate signal and anti-parallel connected diodes. For example, as shown in Fig. 1, power MOSFETs may be applied to the switching elements S1U-S2U, S1V-S2V, and S1W-S2W, and IGBTs may be applied to the switching elements S3U-S4U, S3V-S4V, and S3W-S4W. Alternatively, all of the switching elements S1U-S4U, S1V-S4V, and S1W-S4W may be the same type of self-extinguishing semiconductor element selected from power MOSFETs, IGBTs, and the like.

[0031] The switching elements S1U to S4U constitute a three-level inverter that converts a DC voltage into a U-phase AC voltage. The switching elements S1V to S4V constitute a three-level inverter that converts a DC voltage into a V-phase AC voltage. The switching elements S1W to S4W constitute a three-level inverter that converts a DC voltage into a W-phase AC voltage.

[0032] FIG. 1 shows a three-level inverter according to the T-type NPC (Advanced T-type Neutral-Point-Clamped) method. That is, the switching elements S1U and S2U are connected in series between the high potential terminal T13P and the high potential terminal T13N. Between the connection point T13U of the switching elements S1U and S2U and the neutral point T13C, the switching elements S3U and S4U are connected in series in a direction that can be controlled to have opposite withstand voltage directions. Similarly, the switching elements S1V and S2V are connected in series between the high potential terminal T13P and the high potential terminal T13N. Between the connection point T13V of the switching elements S1V and S2V and the neutral point T13C, the switching elements S3V and S4V are connected in series in a direction that can be controlled to have opposite withstand voltage directions. The switching elements S1W and S2W are connected in series between the high potential terminal T13P and the high potential terminal T13N. Between a connection point T13V of the switching elements S1W, S2W and a neutral point T13C, the switching elements S3W, S4W are connected in series in a direction that allows them to be controlled to have opposite withstand voltage directions.

[0033] U-phase, V-phase, and W-phase AC power are output to the transformer 14 from connection points T13U, T13V, and T13W, respectively.

[0034] The potential of the connection point T13U is the potential of the high potential terminal T13P, the potential of the neutral point T13C, or the potential of the high potential terminal T13N, depending on the states of the switching elements S1U to S4U. For example, when the switching elements S1U and S4U are on and the switching elements S2U and S3U are off, the potential of the connection point T13U becomes the potential of the high potential terminal T13P. When the switching elements S1U and S4U are off and the switching elements S2U and S3U are on, the potential of the connection point T13U becomes the potential of the high potential terminal T13N. When the switching elements S1U and S2U are off and the switching elements S3U and S4U are on, the potential of the connection point T13U becomes the potential of the neutral point T13C.

[0035] Similarly, the potential of the connection point T13V is either the potential of the high potential terminal T13P, the potential of the neutral point T13C, or the potential of the high potential terminal T13N depending on the states of the switching elements S1V to S4V. The potential of the connection point T13W is either the potential of the high potential terminal T13P, the potential of the neutral point T13C, or the potential of the high potential terminal T13N depending on the states of the switching elements S1W to S4W.

[0036] An example of the configuration of the DC-DC converter 12 will be described. The DC-DC converter 12 is configured to be capable of boosting the voltage. The DC-DC converter 12 includes, for example, a positive converter 12P and a negative converter 12N.

[0037] The positive converter 12P performs a boost operation to output a positive voltage higher than the potential (midpoint potential) of the midpoint N. The positive converter 12P includes switching elements 121 and 122, a reactor 12LP, and a capacitor 125, for example.

[0038] For example, switching element 121 includes a MOSFET (called switch Q1) and a diode D1 (not shown) connected in anti-parallel to the MOSFET. Switching element 122 includes a MOSFET (called switch Q2) and a diode D2 (not shown) connected in anti-parallel to the MOSFET. Switching element 121 and switching element 122 are connected in series, with switching element 121 on the high side and switching element 122 on the low side.

[0039] A connection point between the source of the switching element 121 and the drain of the switching element 122 is connected to the terminal TBSP via the reactor 12LP and the power line 12PLP. The drain of the switching element 121 is connected to the high potential terminal T12P. The source of the switching element 122 is connected to the neutral point T12C. A capacitor 125 is connected in parallel to the high potential terminal T12P and the neutral point T12C. The capacitor 125 is an example of a positive side capacitor connected to the output of the positive side converter 12P and the pole of the midpoint potential.

[0040] The negative converter 12N outputs a negative voltage lower than the midpoint potential by a boost operation. The negative converter 12N includes switching elements 123 and 124, a reactor 12LN, and a capacitor 126.

[0041] For example, switching element 123 includes a MOSFET (called switch Q3) and a diode D3 (not shown) connected in anti-parallel to switching element 124. Switching element 124 includes a MOSFET (called switch Q4) and a diode D4 (not shown) connected in anti-parallel to switching element 124. Switching element 123 and switching element 124 are connected in series, with switching element 124 serving as the negative high side and switching element 123 serving as the negative low side.

[0042] A connection point between the source of the switching element 123 and the drain of the switching element 124 is connected to the terminal TBSN via the reactor 12LN and the power line 12PLN. The source of the switching element 124 is connected to the high potential terminal T12N. The drain of the switching element 123 is connected to the neutral point T12C. A capacitor 126 is connected in parallel to the high potential terminal T12N and the neutral point T12C. The capacitor 126 is an example of a negative side capacitor connected to the output of the negative side converter 12N and the pole of the midpoint potential.

[0043] As described above, the positive converter 12P and the negative converter 12N are connected in series across the pole of the midpoint potential. The DC-DC converter 12 configured in this manner is an example of a synchronous rectification type.

[0044] The power conversion system 1 further includes DC voltage sensors 18P and 18N, a current sensor 11, and an adder 18A.

[0045] DC voltage sensor 18 includes, for example, DC voltage sensors 18P, 18N and adder 18A (not shown). DC voltage sensor 18P detects the terminal voltage of capacitor 125 and outputs a voltage VDCP_F indicating this. DC voltage sensor 18N detects the terminal voltage of capacitor 126 and outputs a voltage VDCN_F indicating this. Adder 18A adds the magnitude (absolute value) of the voltage value detected by DC voltage sensor 18P and the magnitude (absolute value) of the voltage value detected by DC voltage sensor 18N, and outputs a voltage VDC_F based on the calculation result. Voltage VDC_F may be the sum of the absolute values ​​of voltage VDCP_F and voltage VDCN_F as described above, or may be the average value obtained by dividing this by 2, or the above sum may simply be referred to as the average value.

[0046] The current sensor 11 detects the input current of the DC-DC converter 12, and outputs an input current IDC_F indicative of this.

[0047] The control unit 20 of the embodiment will be described with reference to FIG. FIG. 2 is a configuration diagram of the control unit 20 according to the embodiment. The control unit 20 adjusts a command value (called a current command value IDC_ref) regarding the output current of the DCDC converter 12 based on the voltage (voltage VDC_F) output by the DCDC converter 12 and a reference value of the DC voltage output by the DCDC converter 12 (called a DC voltage reference VDC_ref), and performs current control regarding the output current of the DCDC converter 12 based on the adjusted command value (current command value IDC_ref) and the input current IDC_F obtained from the current sensor 11. In addition, the control unit 20 adjusts the magnitude of the above-mentioned current command value IDC_ref based on the state of the secondary side of the transformer 14, thereby becoming able to control the amount of power conversion of the DCDC converter 12 in accordance with the state of the secondary side of the transformer 14.

[0048] For example, the control unit 20 includes an inverter control unit 21 and a DC-DC converter control unit 22.

[0049] Inverter control unit 21 controls switching elements S1U to S4U, S1V to S4V, and S1W to S4W by PWM (Pulse Width Modulation) to output U-phase, V-phase, and W-phase AC power from connection points 2U, 2V, and 2W. As shown in FIG. 2, the inverter control unit 21 includes a voltage control unit 211, a current control unit 212, an inverse dq transformation unit 213, and a PWM control circuit 214.

[0050] The voltage control unit 211 generates AC current references (ID_ref, IQ_ref) so that the AC voltages (VD_F, VQ_F) approach AC voltage references (VD_com, VQ_com) designated by a higher-level device or the like. The current control unit 212 generates an output voltage command (VD_ref, VQ_ref) so that the AC current (ID_F, IQ_F) approaches the AC current reference (ID_ref, IQ_ref). In addition, the current control unit 212 of the embodiment may switch the AC current references (ID_ref, IQ_ref) to a predetermined value by control. This switching is performed when an overcurrent due to a short circuit state is detected, for example. The inverse dq transformation unit 213 transforms the output voltage commands (VD_ref, VQ_ref) in the Cartesian coordinate system into output voltage commands (Vu, Vv, Vw) in the three-phase coordinate system using the reference phase θ0.

[0051] The PWM control circuit 214 controls the switching elements S1U-S4U, S1V-S4V, and S1W-S4W in response to the output voltage commands (Vu, Vv, Vw). Specifically, the PWM control circuit 214 compares the corrected output voltage commands (Vu, Vv, Vw) with a carrier signal to generate gate signals for PWM-controlling the on / off of the switching elements S1U-S4U, S1V-S4V, and S1W-S4W of the inverter 13.

[0052] The DC-DC converter control unit 22 includes a DC voltage control unit 221 , dq conversion units 222 and 223 , an AC power calculation unit 224 , an AC current estimation calculation unit 225 , an absolute value calculation unit 226 , a comparator 227 , and a compensation amount generation unit 228 .

[0053] The DC voltage control unit 221 controls the amount of power conversion of the DCDC converter 12 based on a second DC current reference IC2_ref based on a current estimate value of the DC (first DC) flowing from the battery B, a first DC current detection value IDC_F of the first DC, a DC voltage reference VDC_ref (second DC voltage reference) of the DC (second DC) applied to the DC bus, and a DC voltage detection value VDC_F (second DC voltage detection value) of the second DC.

[0054] For example, the DC voltage control unit 221 includes subtractors 2211 and 2214, a voltage control unit 2212 (AVR), an adder 2213, a current control unit 2215 (ACR), and a duty calculator 2216. A subtractor 2211 calculates the difference between the above-mentioned DC voltage reference VDC_ref and the DC voltage detection value VDC_F to calculate a voltage deviation ΔVDC. A voltage control section 2212 calculates a first DC current reference IC1_ref so as to make the voltage deviation ΔVDC zero. The adder 2213 adds the first DC current reference IC1_ref and the second DC current reference IC2_ref to calculate a current command value IDC_ref. This current command value IDC_ref is an example of a correction signal. A subtractor 2214 calculates a current deviation ΔIDC by subtracting the first DC current detection value IDC_F from the current command value IDC_ref. A current control unit 2215 calculates a second DC voltage reference ΔVL_ref such that the current deviation ΔIDC becomes zero. The duty calculator 2216 divides the second DC voltage reference ΔVL_ref by the detected DC voltage value VDC_F, and generates a duty based on the quotient.

[0055] The dq converters 222 and 223 convert the RST-axis coordinate values ​​of the three-phase AC into orthogonal dq-axis coordinate values. The dq converter 222 converts the line voltage values ​​(VRS_F, VTS_F) of the three-phase AC into AC voltage values ​​(VD_F, VQ_F) in the dq-axis coordinates. The dq converter 223 converts the line current values ​​(IR_F, IS_F, IT_F) of the three-phase AC into AC current values ​​(ID_F, IQ_F) in the dq-axis coordinates. This allows calculation as a vector in the dq-axis coordinates.

[0056] The AC power calculation unit 224 calculates AC power P based on the AC voltage values ​​(VD_F, VQ_F) and AC current values ​​(ID_F, IQ_F) of the dq axis coordinates.

[0057] The AC current estimation calculation unit 225 includes a limiter 2251 and a divider 2252 .

[0058] The limiter 2251 limits the DC voltage value (VDC_F) within a predetermined range. If the DC voltage value (VDC_F) is within the range, the limiter 2251 outputs it at the level of the input signal. If the DC voltage value (VDC_F) exceeds the upper or lower limit of the range, the limiter 2251 outputs the upper or lower limit of the range. For example, it is preferable to define the limiting range so that the output value of the limiter 2251 does not become 0. Note that the above-mentioned limiter 2251 may instead be configured as a level conversion unit whose output value does not become 0. The divider 2252 divides the AC power P derived by the AC power calculation section 224 by the output value of the limiter 2251, and outputs the quotient, that is, the DC current estimated value IC_est, as the calculation result of the AC current estimation calculation section 225.

[0059] The absolute value calculation unit 226 derives the magnitude (Iout) of the AC current output by the inverter 13, based on the AC current values ​​(ID_F, IQ_F) output from the dq conversion unit 223. For example, the absolute value calculation unit 226 generates a root of the sum of squares of the AC current values ​​(ID_F, IQ_F) and sets the result as the magnitude (Iout) of the AC current.

[0060] The comparator 227 uses a predetermined threshold (SHT_LVL) to identify the magnitude (Iout) of the AC current output by the inverter 13. For example, if the magnitude exceeds the threshold (SHT_LVL), the comparator 227 outputs a logic "1" and if not, the comparator 227 outputs a logic "0."

[0061] The compensation amount generation unit 228 includes a level setting unit 2281 , a change rate limiting unit 2282 , a subtractor 2283 , a limiter 2284 , and a multiplier 2285 .

[0062] The level setting unit 2281 converts the logic of an input signal into a predetermined value corresponding to the logic. For example, the level setting unit 2281 receives the output signal of the comparator 227 as an input signal, and converts the logic "1" of the input signal into a value "1.0" and the logic "0" into a value "0.0."

[0063] The change rate limiting unit 2282 limits the change in the output signal according to the level of the input signal so as not to exceed a predetermined rate of change, thereby following the change in the level of the input signal (rate control). For example, the output signal level of the level setting unit 2281 changes in a stepwise manner from a value of "0.0" to a value of "1.0". The change rate limiting unit 2282 limits the change in the output signal level of the level setting unit 2281 so as not to exceed a predetermined rate of change, thereby following the change in the level.

[0064] The value "1.0" is set to a first input of the subtractor 2283, which subtracts the output level of the change rate limiter 2282 from this value and outputs the result.

[0065] Limiter 2284 limits the output level of subtractor 2283 to a predetermined range. If it is within that range, it outputs the level of the input signal, and if it exceeds the upper or lower limit of that range, it outputs the upper or lower limit of that range.

[0066] A multiplier 2285 multiplies the DC current estimate value IC_est, which is the calculation result of the AC current estimation calculation section 225, by the output level (coefficient Pk) of the limiter 2284, and outputs the product as the second current reference IC2_ref.

[0067] Through the above-mentioned calculation process by the compensation amount generating unit 228, the second current reference IC2_ref is generated. The compensation amount generating unit 228 has a function of adjusting the gain for the DC current estimate value IC_est, and derives the second current reference IC2_ref multiplied by a desired gain. The second current reference IC2_ref changes according to the magnitude of the load current of the inverter 13. The current flowing out as the load current of the inverter 13 is supplied from the DC-DC converter 12 side and is thereby compensated.

[0068] For example, in the static power converter 10, the control on the DC-DC converter 12 side includes a feedforward compensation part for the load current. The current flowing between the DC-DC converter 12 and the inverter 13 includes a large ripple current, so it is difficult to use the detected value of the DC current for control. Therefore, the load power of the inverter 13 can be used instead of the detected value of the DC current to calculate the average DC current.

[0069] An example of the characteristics of a typical main circuit breaker 91 and a circuit breaker 92 is shown in FIG. 3 is a diagram showing interruption characteristics of a circuit breaker 92 according to an embodiment. The interruption characteristics of the circuit breaker 92 are defined by an operating characteristic curve drawn on a coordinate plane having a current value (horizontal axis) and an operating time (vertical axis) as axes.

[0070] When a short circuit occurs on the load side of the static power converter 10 and when the short circuit is eliminated and the normal state is restored, the calculated power value related to the load power of the inverter 13 may be disturbed. In such a case, the short circuit state may be naturally eliminated in a shorter time than the time it takes for the circuit breaker 92 to respond.

[0071] The operation of the power conversion system 1 of this embodiment will be described with reference to FIG. Fig. 4 is a diagram for explaining the operation of the power conversion system 1 of the embodiment. In the timing chart shown in Fig. 4, Fig. 4(a) shows the change in the output current of the power conversion system 1, Fig. 4(b) shows the overcurrent detection signal SSD, Fig. 4(c) shows the operation mode of the power conversion system 1, Fig. 4(d) shows the AC power P derived by the AC power calculation unit 224, that is, the estimated value of the power conversion amount of the DCDC converter 12 using feedforward control, Fig. 4(e) shows the coefficient Pk used to calculate the compensation amount of the power conversion of the DCDC converter 12, and Fig. 4(f) shows the compensation amount of the power conversion of the DCDC converter 12 (second current reference IC2_ref).

[0072] The state before time t0 shown in Fig. 4 indicates a situation where no load short circuit has occurred. In a situation where no load short circuit has occurred, as shown in Fig. 4(a), the output current of the power conversion system 1, i.e., the AC current from the inverter 13, is less than the threshold value ITH1. At this time, the power conversion system 1 functions under control in the normal control mode as shown in Fig. 4(d). As described above, the threshold value ITH1 is a threshold value specified for overcurrent detection. As shown in Fig. 4(b), the overcurrent detection signal SSD is at an L level indicating that a load short circuit has not been detected.

[0073] Assume that a short circuit (load short circuit) occurs on the load side of the transformer 14 at time t0. The output current increases due to the load short circuit. Until the magnitude of the output current becomes equal to or greater than the threshold ITH1, the power conversion system 1 does not detect the occurrence of the load short circuit, and therefore performs control in the normal control mode until time t1. In the normal control mode, the power conversion system 1 sets the current command value of the inverter 13 to a desired value and adjusts the output voltage of the inverter 13 to a desired value (rated AC voltage) by CVCF control, thereby performing so-called constant current control with a minor current loop.

[0074] 4(b), an overcurrent state is detected as a result of detection by the current sensor 16, and the overcurrent detection signal SSD goes to H level. This time is referred to as time t1.

[0075] 4(a), in response to detection of an overcurrent after time t1, the current control unit 212 switches the AC current references (ID_ref, IQ_ref) to predetermined values ​​so that the amplitude of the output current becomes I0. The inverse dq transformation unit 213 and the PWM control circuit 214 in the subsequent stages continue control in response to the output level of the current control unit 212. As a result, the amplitude of the output current of the inverter 13 is controlled to become I0 by the control of the current control unit 212.

[0076] When a load short circuit occurs, the phase-to-phase voltages of the transformer 14, i.e., the AC voltages (VD_F, VQ_F) instantly become 0 or close to 0. This affects the results of calculations based on the information on the AC voltages (VD_F, VQ_F), but it is desirable to reduce the effect on the control of the power conversion amount of the DC-DC converter 12 during the period when the AC voltages (VD_F, VQ_F) are 0 or close to 0.

[0077] As described above, voltage control section 211 of inverter control section 21 cannot distinguish this from a state in which the output voltage of inverter 13 is insufficient, and acts to increase the output current of inverter 13. On the other hand, because of the short circuit state, the magnitude of the AC currents (ID_F, IQ_F) detected by the current sensor 16 also increases. These tend to cancel each other out, but the output of the current control section 212 may become unstable. Therefore, the current control unit 212 of the embodiment may switch the AC current references (ID_ref, IQ_ref) to a predetermined value by control. This switching is performed when an overcurrent due to a short circuit state is detected, for example.

[0078] Now, assume that the short circuit condition is resolved at time t2. In a situation where the amplitude of the output current of the inverter 13 is controlled to be I0, the load short circuit is eliminated, and the magnitude of the output current of the inverter 13 decreases. As the magnitude of the output current of the inverter 13 returns to the value up to time t0, the magnitude of the output current of the inverter 13 becomes less than the threshold value ITH1, and the overcurrent detection signal SSD is inverted (time t3).

[0079] Note that the phase-to-phase voltage of transformer 14 recovers from 0 or near 0 to a normal level. This also recovers the magnitude of power P that was calculated using the magnitude of AC voltages (VD_F, VQ_F). At this stage, the output current of the inverter 13 is already flowing, and the interphase voltage of the transformer 14 is not 0. In this situation, if the control state is suddenly switched, it becomes difficult to ensure the stability of the control of the DC-DC converter 12 and the inverter 13.

[0080] Therefore, in the embodiment, the amount of compensation for the power conversion of the DCDC converter 12 may be adjusted to adjust the amount of conversion of the power supplied from the battery B to the static power converter 10. This adjustment is multiplied by the gain of the compensation for the power conversion of the DCDC converter 12 to adjust its magnitude. For example, the change in the gain of the compensation amount can be made gentle by making the change in the gain of the compensation amount a ramp function set in the change rate limiting unit 2282. As shown in the figure, the gain of the signal amplitude can be changed in a trapezoidal shape. As a result, the compensation amount of the power conversion of the DCDC converter 12 can be changed as shown in FIG. 4(e). According to this example, the compensation amount of the power conversion of the DCDC converter 12 gradually increases after time t3. This allows the magnitude of the current reference for the inverter 13 to be reduced.

[0081] According to the above embodiment, the power conversion system 1 includes a DCDC converter 12, an inverter 13, and a control unit 20. The DCDC converter 12 can convert a first DC power of a first DC to generate a second DC power of a second DC. The inverter 13 can convert the second DC power by control to generate AC power. The control unit 20 controls the amount of power conversion of the DCDC converter based on a second DC current reference based on a current estimation value of the first DC, a first DC current detection value of the first DC, a second DC voltage reference of the second DC, and a second DC voltage detection value of the second DC. The control unit 20 corrects the current estimation value based on a result of identifying the magnitude of the AC current detection value related to the AC power, and generates the second DC current reference based on the result of the correction. This makes it possible to make the behavior more stable when a load short circuit occurs.

[0082] The above embodiment will be described from a different perspective. For example, if a load current (overcurrent) outside the normal operating range occurs, it is determined that a load short circuit has occurred due to this detection, and a gain is applied to the DC current feedforward compensation amount to reduce the compensation amount. This detection does not suddenly lower the gain, but rather limits the amount of change by rate processing to slowly lower it, thereby reducing the effect on the calculation results of the current control unit 2215 (PI controller). It is preferable to detect an overcurrent based on the magnitude of the current vector on the dq coordinate axes.

[0083] For example, when the circuit breaker 92 responds by cutting off the overcurrent and then returns to the normal current range, the gain applied to the DC current feedforward compensation amount is returned. At this time, the gain is not dropped all at once, but is returned slowly by rate processing, thereby reducing the impact on the PI controller.

[0084] Next, a configuration example of the control unit 20 according to the embodiment will be described with reference to FIG. FIG. 5 is a diagram for explaining an example of the configuration of the control unit 20 according to the embodiment.

[0085] The control unit 20 includes, for example, a processing unit 811, a communication processing unit 812, an input / output unit 813, and a storage unit 814 (STRAGE). For example, the processing unit 811, the communication processing unit 812, the input / output unit 813, and the storage unit 814 are connected via a bus BUS or the like.

[0086] The communication processing unit 812 enables various information acquired through communication with a higher-level device to be supplied to the processing unit 811 .

[0087] The storage unit 814 is realized by a ROM, a RAM, a HDD, a flash memory, etc. The storage unit 814 is allocated a storage area for storing various setting information and programs for operating the control unit 20, basic programs such as an OS, application programs, and the like.

[0088] The input / output unit 813 acquires, for example, information on the output state of the static power converter 10 as input information, and outputs a gate signal GP. The input / output unit 813 may include, for example, a display unit such as a liquid crystal display that displays various information, and an operation detection unit. The display unit and the operation detection unit may be configured as a touch panel in which they are combined.

[0089] The processing unit 811 sends a gate signal GP to the static power converter 10 via the input / output unit 813 to control the static power converter 10 .

[0090] The processing unit 811 executes a software program including the above functions. The processing unit 811 executes a software program to form a part or all of its functions. The software program for realizing the functions of the processing unit 811 may be stored in advance in the storage unit 814, or may be downloaded to the storage unit 814 from an external device or a portable storage medium (not shown), or via a communication line.

[0091] The functions described herein and realized by the components such as the control unit 20 may be implemented in a circuit or processing circuitry. The circuit or processing circuitry may include general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), FPGAs (Field Programmable Gate Arrays), CPUs (Central Processing Units), GPUs (Graphics Processing Units), conventional circuits, and / or combinations thereof, programmed to realize the described functions. The processor that realizes the above functions includes transistors and other circuits and is considered to be a circuit or processing circuitry. The processor for realizing the above functions may include or may be a programmable processor that executes a program stored in a memory, and / or a programmable device that can be reconfigured by data stored in a memory. In this specification, a circuit, unit, or means is hardware that is programmed to realize or executes the described functions, which may be any hardware disclosed in this specification or any hardware known to be programmed to realize or execute the described functions. If the hardware is a processor considered to be a type of circuitry, the circuitry, means, or unit is a combination of the hardware and software used to configure the hardware and / or processor.

[0092] According to at least one embodiment described above, the power conversion system includes a DC-DC converter, an inverter, and a control unit. The DC-DC converter is capable of converting a first DC power of a first DC to generate a second DC power of a second DC. The inverter is capable of converting the second DC power by control to generate AC power. The control unit controls the amount of power conversion of the DC-DC converter based on a second DC current reference based on a current estimation value of the first DC, a first DC current detection value of the first DC, a second DC voltage reference of the second DC, and a second DC voltage detection value of the second DC. The control unit corrects the current estimation value based on a result of identifying the magnitude of the AC current detection value related to the AC power, and generates the second DC current reference based on the result of the correction. This makes it possible to make the behavior when a load short circuit occurs more stable.

[0093] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. In addition, the above-mentioned embodiments can be implemented in combination with each other.

[0094] For example, the control device 31 and the state identification unit 32 may be configured with separate processors, or a processor common to the control device 31 and the state identification unit 32 may execute the respective processes.

[0095] As shown in Fig. 3, the interruption characteristics of the circuit breaker 92 are defined by an operating characteristic curve drawn on a coordinate plane with the current value (horizontal axis) and the operating time (vertical axis) as axes. Elements of the interruption characteristics include the rated current, rated short-time withstand current value, time-delay tripping range, instantaneous tripping range, and maximum total breaking time. For example, the time-delay tripping range and the instantaneous tripping range are defined by an operating characteristic curve that divides these ranges. The current value IS1 related to the instantaneous tripping range is the lower limit of the current that instantly breaks the circuit due to a relatively excessive overcurrent such as a short circuit current. When the current exceeds a current value IS2 that is larger than the current value IS1, the circuit breaker 92 responds in a time TB that is shorter than the maximum total breaking time under the current conditions.

[0096] For example, when a current Ie that exceeds the above current value IS2 but does not exceed the allowable current of the inverter 13 continues to flow through the circuit breaker 92 for a time TB, the circuit breaker 92 opens the electrical connection between the input side circuit and the output side circuit of the circuit breaker 92, electrically disconnecting the power conversion system 1 from the location where the load short circuit has occurred. This allows the circuit breaker 92 to instantaneously interrupt the short circuit current.

[0097] In this way, even if the circuit breaker 92 is able to detect an overcurrent and cut off the short-circuit current caused by a load short circuit, if the short circuit is resolved before the circuit breaker 92 cuts off the overcurrent, the circuit breaker 92 will not respond.

[0098] (Additional Note) The power conversion system 1 according to the above embodiment may be configured as follows. (1) The power conversion system 1 includes a DC-DC converter capable of converting a first DC power having a first direct current to generate a second DC power having a second direct current; an inverter capable of converting the second DC power to generate AC power under control; a control unit that controls an amount of power conversion of the DC-DC converter based on a second DC current reference based on a current estimation value of the first DC, a first DC current detection value of the first DC, a second DC voltage reference of the second DC, and a second DC voltage detection value of the second DC; Equipped with. The control unit may correct the current estimation value based on a result of identifying a magnitude of an AC current detection value related to the AC power, and generate the second DC current reference based on a result of the correction. (2) In the power conversion system 1 according to (1) above, the control unit It is preferable to use a DC current reference based on the magnitude of the AC power and the magnitude of the second DC voltage detection value, and the second DC current reference obtained by correcting the current estimate value based on the magnitude of the AC current detection value related to the AC power, for controlling the power conversion amount of the DCDC converter. (3) In the power conversion system 1 according to (1) or (2) above, the control unit It is preferable to generate a DC current reference based on the magnitude of the AC power and the magnitude of the second DC voltage detection value, generate the second DC current reference by correcting the current estimate value based on the magnitude of the AC current detection value related to the AC power, and generate a first DC current reference based on the DC current reference and the second DC current reference. (4) In the power conversion system 1 according to any one of (1) to (3) above, the control unit The magnitude of the second DC current estimate value may be determined based on the magnitude of the second DC voltage detection value with a limited amount of change and the magnitude of the AC power. (5) In the power conversion system 1 according to any one of (1) to (4) above, the control unit It is preferable to generate an overcurrent detection signal based on the result of identifying the magnitude of the AC current detection value, generate a correction signal in which the amount of change in the overcurrent detection signal is limited, and generate the second DC current reference by correcting the magnitude of the second DC current estimation value using the correction signal. (6) In the power conversion system 1 according to any one of (1) to (5) above, The AC outputs of the inverters are each connected to a primary winding of a transformer. the control unit derives a magnitude of the AC current detection value based on a detection result of a current flowing through a secondary winding of the transformer; The magnitude of the AC power may be derived based on the detection result of the current and the AC voltage on the secondary side of the transformer. (7) The power conversion system 1 according to any one of (1) to (6) above, The power supply may further include an inverter control unit that controls an amount of power conversion of the inverter based on a magnitude of an AC current detection value related to the AC power. [Explanation of symbols]

[0099] 1. Power Conversion System 10. Static power converter 12 DC-DC Converter 13 Inverter 14 Transformers 20 Control section 91 Main circuit breaker 92 Molded Case Circuit Breaker (MCCB)

Claims

1. A DC-DC converter capable of converting a first DC power having a first DC current to generate a second DC power having a second DC current; an inverter capable of converting the second DC power to generate AC power under control; a control unit that controls an amount of power conversion of the DC-DC converter based on a second DC current reference based on the first DC current estimation value, a first DC current detection value of the first DC, a second DC voltage reference of the second DC, and a second DC voltage detection value of the second DC; Equipped with The control unit is correcting the current estimation value based on a result of identifying a magnitude of the AC current detection value related to the AC power, and generating the second DC current reference based on a result of the correction. Power conversion systems.

2. The control unit is A DC current reference based on the magnitude of the AC power and the magnitude of the second DC voltage detection value, and the second DC current reference obtained by correcting the current estimation value based on the magnitude of the AC current detection value related to the AC power are used to control the power conversion amount of the DC-DC converter. The power conversion system of claim 1 .

3. The control unit is generating a DC current reference based on the magnitude of the AC power and the magnitude of the second DC voltage detection value, generating the second DC current reference by correcting the current estimation value based on the magnitude of the AC current detection value related to the AC power, and generating a first DC current reference based on the DC current reference and the second DC current reference. The power conversion system of claim 2 .

4. The control unit is determining a magnitude of the second DC current estimation value based on a magnitude of the second DC voltage detection value with a limited amount of change and a magnitude of the AC power; The power conversion system of claim 1 .

5. The control unit is generating an overcurrent detection signal based on a result of identifying the magnitude of the AC current detection value, generating a correction signal in which a change amount of the overcurrent detection signal is limited, and generating the second DC current reference by correcting the magnitude of the second DC current estimation value using the correction signal; The power conversion system of claim 1 .

6. A primary winding of a transformer is connected to each of the AC outputs of the inverter, The control unit is deriving a magnitude of the AC current detection value based on a detection result of a current flowing through a secondary winding of the transformer; deriving a magnitude of the AC power based on a result of the current detection and an AC voltage on a secondary side of the transformer; The power conversion system of claim 1 .

7. an inverter control unit that controls the amount of power conversion of the inverter based on the magnitude of the AC current detection value related to the AC power; The power conversion system according to claim 1 , further comprising:

8. A DC-DC converter capable of converting a first DC power having a first DC current to generate a second DC power having a second DC current; an inverter capable of converting the second DC power to generate AC power under control; A control method for a power conversion system comprising: Controlling a power conversion amount of the DC-DC converter based on a second DC current reference based on the first DC current estimated value, a first DC current detection value of the first DC, a second DC voltage reference of the second DC, and a second DC voltage detection value of the second DC; correcting the current estimation value based on a result of identifying a magnitude of an AC current detection value related to the AC power, and generating the second DC current reference based on a result of the correction; A control method comprising:

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