Power conversion system and control method

Abstract

To provide a power conversion system and a control method that can stabilize the behavior of parallel-connected orthogonal power conversion devices.SOLUTION: A power conversion system includes an orthogonal power conversion device whose primary side and secondary side are connected in parallel. Each orthogonal power conversion device includes a DC-DC converter, an inverter, and a control unit. The DC-DC converter is capable of converting first DC power of a first DC on the primary side by first control to generate second DC power of a second DC. The inverter is capable of converting the second DC power by second control to generate AC power. The control unit controls the power conversion of the DC-DC converter by the first control using at least the direction of the first DC.SELECTED DRAWING: Figure 3A

Description

Technical Field

[0001] This invention relates to a power conversion system and a control method.

Background Art

[0002] There is a static orthogonal power converter that includes a DC-DC converter and an inverter, and the DC-DC converter and the inverter are cascade-connected to each other. By connecting the above orthogonal power converters in parallel, the power conversion system can drive an AC load with a capacity exceeding the rated capacity of a single orthogonal power converter. In such a power conversion system, it has been desired to make the behavior of the parallel-connected operating state more stable.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The problem to be solved by the present invention is to provide a power conversion system and a control method capable of making the behavior of parallel-connected orthogonal power converters more stable.

Means for Solving the Problems

[0005] A power conversion system according to an aspect of the embodiment includes an orthogonal power converter in which a primary side and a secondary side are connected in parallel, respectively. Each orthogonal power converter includes a DC-DC converter, an inverter, and a control unit. The DC-DC converter can convert first DC power of a first DC on the primary side by first control to generate second DC power of a second DC. The inverter can convert the second DC power by second control to generate AC power. The control unit controls power conversion of the DC-DC converter by the first control using at least a direction of the first DC.

Brief Description of Drawings

[0006]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0007] Hereinafter, the power conversion system and control method according to the embodiment will be described. In the following description, being electrically connected may be simply referred to as "connected". A minute fixed value in the embodiment may include 0. Note that "based on XX" as used in this specification means "based on at least XX", and includes cases where it is based on another element in addition to XX. Further, "based on XX" is not limited to the case where XX is directly used, and includes cases where it is based on something obtained by performing an operation or processing on XX. "XX" is an arbitrary element (for example, arbitrary information).

[0008] FIG. 1 is a configuration diagram of the power conversion system 1 of the embodiment. FIG. 2 is a schematic configuration diagram of the orthogonal power converters 10A and 10B of the embodiment.

[0009] The power conversion system 1 includes a storage battery B (power source), orthogonal power converters 10A and 10B, and control units 20A and 20B.

[0010] The storage battery B is, for example, a secondary battery, and outputs the stored DC power to the orthogonal power converters 10A and 10B. The positive electrode of the storage battery B is connected to terminals TBSPA and TBSPB, respectively. The negative electrode of the storage battery B is connected to terminals TBSNA and TBSNB, respectively.

[0011] The orthogonal power converters 10A and 10B are each connected in parallel on the primary side and the secondary side. The orthogonal power converters 10A and 10B are an example of a static power converter that generates AC power. When the orthogonal power converters 10A and 10B are described without particular distinction, they may be simply referred to as the orthogonal power converter 10. The orthogonal power converter 10 is an example of a static power converter.

[0012] For example, the orthogonal power converter 10 is configured to be able to mutually convert DC power and AC power. The DC side of the orthogonal power converter 10 is connected to the storage battery B and receives the supply of DC power from the storage battery B. A load that uses, for example, three-phase AC power of the RST phase is connected to the AC side of the orthogonal power converter 10. For example, the connection terminal TB corresponding to the AC output of the orthogonal power converter 10 is connected to the AC power system via a circuit breaker 91 or the like.

[0013] For example, the orthogonal power converter 10A includes a DC-DC converter 12A, an inverter 13A, a transformer 14A, a capacitor 15A, a current sensor 16A, and an instrument transformer 17A. The orthogonal power converter 10B includes a DC-DC converter 12B, an inverter 13B, a transformer 14B, a capacitor 15B, a current sensor 16B, and an instrument transformer 17B. Incidentally, the DCDC converters 12A and 12B, the inverters 13A and 13B, the transformers 14A and 14B, the capacitors 15A and 15B, the current sensors 16A and 16B, and the instrument transformers 17A and 17B may be referred to as the DCDC converter 12, the inverter 13, the transformer 14, the capacitor 15, the current sensor 16, and the instrument transformer 17.

[0014] The DCDC converter 12 boosts the DC power supplied from the storage battery B by functioning as a boost chopper circuit under control and outputs a desired voltage (DC voltage) to the load-side terminal. The positive electrode P (DC bus bar BLP) and the negative electrode N (DC bus bar BLN) of the DC link are connected to the load side of the DCDC converter 12. The DC bus bar 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 this. The voltages of the positive electrode P (DC bus bar BLP) and the negative electrode N (DC bus bar BLN) of the DC link change according to the voltage output by such a DCDC converter 12.

[0015] The DCDC converter 12 includes, for example, a semiconductor switching element for power conversion inside it.

[0016] The capacitors 125 and 126 are provided in parallel with the output of the DCDC converter 12 to 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 a part of the DCDC converter 12, for example, or may be provided outside the DCDC converter 12.

[0017] The DCDC converter 12 further includes a set of a positive electrode terminal TBSP and negative electrode terminals TBSNA and TBSNB as power supply-side terminals, and a set of a positive electrode high-potential terminal T12P, a negative electrode high-potential terminal T12N, and a neutral point T12C as load-side terminals. The neutral point T12C has a midpoint potential.

[0018] The inverter 13 converts the DC power supplied via the DC buses BLP, BLC, and BLN of the DC link described above into three-phase AC power by control and outputs it. The above-described DC-DC converter 12 and inverter 13 each include a semiconductor switching element for power conversion inside.

[0019] Capacitors 135 and 136 are provided in parallel with the input of the inverter 13 to smooth the voltage between 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 a part of the inverter 13, for example, or may be provided outside the inverter 13.

[0020] The inverter 13 generates AC power and supplies the AC power to a load via a connection terminal TB provided on the AC side thereof and a circuit breaker 91 or the like.

[0021] The inverter 13 supplies, for example, the generated three-phase AC power to the AC side. The AC side of the inverter 13 is connected to the primary winding of the transformer 14 via an AC power system 181. The AC power system 181 is composed of three phases of U-phase, V-phase, and W-phase.

[0022] The secondary winding of the transformer 14 is connected to the connection terminal TB via an AC power system 182. The AC power system 182 is composed of three phases of R-phase, S-phase, and T-phase. The connection terminal TB has terminals for each of the R-phase, S-phase, and T-phase.

[0023] The current sensor 16 is provided in the AC power system 182 and 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.

[0024] Capacitor 15 is provided between the phases of the R-phase, S-phase, and T-phase of the AC power system 182 and is connected in a delta configuration. A combination of the transformer 14 and the capacitor 15 forms an LC filter.

[0025] The instrument transformer 17 is connected to the AC power system 182 and detects the line voltage of the AC power system 182.

[0026] For example, the orthogonal power conversion device 10A is controlled by the control unit 20A. The orthogonal power conversion device 10B is controlled by the control unit 20B. When explaining without distinguishing between the control units 20A and 20B, it is simply referred to as the control unit 20.

[0027] The control unit 20 sends a gate pulse GP to the DC-DC converter 12 and controls the power conversion amount by the DC-DC converter 12 based on, for example, a DC voltage reference supplied from a higher-level device. Also, the control unit 20 sends a gate pulse GP to the inverter 13 and controls the power conversion amount by the inverter 13. The control unit 20 has a plurality of control modes including a first control mode used for normal control and a second control mode used for control after an overcurrent is detected. The control unit 20 selects a suitable control mode based on the detected state and controls the orthogonal power conversion device 10. "Normal time" in the embodiment means a situation where no load short-circuit failure or the like has occurred. For example, if it is "normal time", the current value flowing through the orthogonal power conversion device 10 is within a predetermined range. In contrast, a situation where a current of a magnitude exceeding this predetermined range is flowing is included in the "abnormal time" of this 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, "the line voltage feedback values VRS_F and VTS_F in the stationary coordinate system having R-axis, S-axis, and T-axis" are an example of the above voltage feedback value. "The voltage references VD_com and VQ_com in the rotating coordinate system" described later are an example of the above first AC voltage command.

[0029] A configuration example of the inverter 13 will be described. The inverter 13 converts a 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 order of the potential of the high-potential terminal T13P, the potential of the neutral point T13C, the potential of the low-potential terminal N, the potential of the neutral point T13C, the potential of the high-potential terminal T13P, ···.

[0030] The inverter 13 includes switching elements S1U~S4U, S1V~S4V, S1W~S4W. The switching elements S1U~S4U, S1V~S4V, S1W~S4W are switching devices composed of, for example, 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. 2, power MOSFETs may be applied to the switching elements S1U~S2U, S1V~S2V, S1W~S2W, and IGBTs may be applied to the switching elements S3U~S4U, S3V~S4V, S3W~S4W. Alternatively, all the element types of the switching elements S1U~S4U, S1V~S4V, S1W~S4W may be made the same and composed of the same type of self-extinguishing semiconductor elements selected from power MOSFETs, IGBTs, etc.

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

[0032] Figure 2 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 in opposite breakdown 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 in opposite breakdown 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 the connection point T13V of the switching elements S1W and S2W and the neutral point T13C, the switching elements S3W and S4W are connected in series in a direction that can be controlled in opposite breakdown voltage directions.

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

[0034] The potential of the connection point T13U takes one of the potentials of the high-potential terminal T13P, the neutral point T13C, and the high-potential terminal T13N according to 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 takes one of the potentials of the high-potential terminal T13P, the neutral point T13C, and the high-potential terminal T13N according to the states of the switching elements S1V to S4V. The potential of the connection point T13W takes one of the potentials of the high-potential terminal T13P, the neutral point T13C, and the high-potential terminal T13N according to the states of the switching elements S1W to S4W.

[0036] A configuration example of the DCDC converter 12 will be described. The DCDC converter 12 is configured to be capable of performing a boosting operation. The DCDC converter 12 includes, for example, a positive-side converter 12P and a negative-side converter 12N.

[0037] The positive-side converter 12P outputs a positive voltage higher than the potential of the midpoint N (midpoint potential) by a boosting operation. The positive-side converter 12P includes, for example, switching elements 121 and 122, a reactor 12LP, and a capacitor 125.

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

[0039] The 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 - side converter 12N outputs a negative voltage lower than the mid - point potential by a boost operation. The negative - side converter 12N includes switching elements 123, 124, a reactor 12LN, and a capacitor 126.

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

[0042] The connection point between the source of the switching element 123 and the drain of the switching element 124 is connected to terminals TBSNA and TBSNB 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 mid - point potential pole.

[0043] As described above, the positive - side converter 12P and the negative - side converter 12N are connected in series with the mid - point potential pole in between. The DCDC converter 12 configured in this way is an example of a synchronous rectification type. The above - mentioned diodes D1 - D4 may be the body diodes of the MOSFETs.

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

[0045] The DC voltage sensor 18P detects the terminal voltage of the capacitor 125 and outputs a DC positive voltage detection value VDCP_F indicating this voltage. The DC voltage sensor 18N detects the terminal voltage of the capacitor 126 and outputs a DC negative voltage detection value VDCN_F indicating this voltage. Note that the adder 222 (Fig. 3A) adds the magnitudes (absolute values) of the voltage values detected by the DC voltage sensor 18P and the voltage values detected by the DC voltage sensor 18N, and outputs a voltage VDC_F based on the calculation result. The voltage VDC_F may be the sum of the absolute values of the DC positive voltage detection value VDCP_F and the DC negative voltage detection value VDCN_F as described above, may be the average value obtained by dividing this sum by 2, or may simply be referred to as the average value of the above sum.

[0046] The current sensor 11 detects the input current of the DCDC converter 12 and outputs an input current IDC_F indicating this current.

[0047] Referring to FIGS. 2, 3A, and 3B in addition to FIG. 2, the control unit 20 of the embodiment will be described. The control unit 20 adjusts a command value (referred to as a current command value IDC_ref) regarding the output current of the DCDC converter 12 based on the voltages (DC positive voltage detection value VDCP_F, DC negative voltage detection value VDCN_F) output by the DCDC converter 12 and a reference value of the DC voltage output by the DCDC converter 12 (referred to as 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 acquired from the current sensor 11. Note that the control unit 20 can control the power conversion amount of the DCDC converter 12 according to the state of the secondary side of the transformer 14 by adjusting the magnitude of the above current command value IDC_ref based on 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 DCDC converter control unit 22.

[0049] The inverter control unit 21 outputs AC power of the U-phase, V-phase, and W-phase from the connection points 2U, 2V, and 2W by performing PWM (Pulse Width Modulation) control on each of the switching elements S1U to S4U, S1V to S4V, and S1W to S4W. The inverter control unit 21 controls the power conversion of the inverter 13 by means of voltage control, current control, coordinate conversion, PWM control, etc. This control includes enabling both power running and regeneration of the inverter 13. There are no other restrictions, and general methods may be appropriately combined.

[0050] The DCDC converter control unit 22 includes a DC voltage control unit 221, an adder 222, a DC voltage adjustment unit 230, and PWM control circuits 229P and 229N.

[0051] The DC voltage control unit 221 controls the power conversion amount of the DCDC converter 12 based on a second DC current reference IC2_ref based on the estimated value of the DC (first DC) current flowing from the battery B, the 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 the DC voltage detection value VDC_F (second DC voltage detection value) of the second DC.

[0052] 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), a Duty calculator 2216A, a multiplier 2216B, and a compensation amount determination unit 2218. The subtractor 2211 calculates the voltage deviation ΔVDC by calculating the difference between the DC voltage reference VDC_ref and the DC voltage detection value VDC_F. The voltage control unit 2212 calculates a first DC current reference IC1_ref that makes 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. An example of the generation of the second DC current reference IC2_ref by the compensation amount determination unit 2218 will be described later. The subtractor 2214 subtracts the first DC current detection value IDC_F from the current command value IDC_ref to calculate the current deviation ΔIDC. The current control unit 2215 calculates a second DC voltage reference ΔVL_ref such that the current deviation ΔIDC becomes zero. The Duty calculator 2216A divides the second DC voltage reference ΔVL_ref by the DC voltage detection value VDC_F to generate the quotient (1 / VDC_F). The multiplier 2216B multiplies the second DC voltage reference ΔVL_ref by (1 / VDC_F) to derive the modulation rate command (Duty). Such a DC voltage control unit 221 outputs a modulation rate command (Duty) for controlling the power conversion amount of the DCDC converter 12 and the like.

[0053] The DC voltage adjustment unit 230 includes subtractors 231, 235P, 235N, an arithmetic unit 232, a comparator 233, and a multiplier 234.

[0054] The subtractor 231 subtracts the DC negative voltage detection value VDCN_F from the DC positive voltage detection value VDCP_F and outputs the value of the signal VDC_ERR_F.

[0055] The arithmetic unit 232 calculates a compensation amount ERR_CMP_T such that the signal level of the signal VDC_ERR_F output by the subtractor 231 becomes zero. The magnitude of the compensation amount ERR_CMP_T is normalized and may take values, for example, from -1 to +1.

[0056] The comparator 233 determines the magnitude of the first DC current detection value IDC_F with a sign and outputs a three-valued logical value. The comparator 233 determines, for example, according to the following determination criteria.

[0057] When the first DC current detection value IDC_F is equal to or greater than a predetermined threshold value “+A”, the logical value of the signal SGN_CMP is set to “1”. When the first DC current detection value IDC_F is less than or equal to the threshold value “-A”, the logical value of the signal SGN_CMP is set to “-1”. When the first DC current detection value IDC_F is less than the threshold value “+A” and greater than or equal to the threshold value “-A”, set the logical value of the signal SGN_CMP to “0”.

[0058] The multiplier 234 multiplies the logical value of the signal SGN_CMP by the compensation amount ERR_CMP_T to calculate the signal ERR_CMP. That is, according to the above determination conditions, the value of the signal ERR_CMP is as follows. When the first DC current detection value IDC_F is greater than or equal to the predetermined threshold value “+A”, the value of the signal ERR_CMP is the same as the compensation amount ERR_CMP_T. When the first DC current detection value IDC_F is less than or equal to the threshold value “-A”, the value of the signal ERR_CMP has the same absolute value as the compensation amount ERR_CMP_T, and the signs are opposite to each other. When the first DC current detection value IDC_F is less than the threshold value “+A” and greater than or equal to the threshold value “-A”, the value of the signal ERR_CMP is “0”.

[0059] The multiplier 234 multiplies the logical value of the signal SGN_CMP by the compensation amount ERR_CMP_T to calculate the signal ERR_CMP.

[0060] The subtractor 235P subtracts the signal ERR_CMP from the modulation rate command (Duty) output from the DC voltage control unit 221 to calculate the modulation rate command Duty12. The subtractor 235N also subtracts the signal ERR_CMP from the modulation rate command (Duty) to calculate the modulation rate command Duty34. The allowable range for the subsequent stage for the modulation rate commands Duty12 and Duty34 is within the range from -1 to +1. When exceeding the allowable range from -1 to +1 by the above correction, it may be limited to the lower limit value or the upper limit value.

[0061] The PWM control circuit 229P generates gate pulses (G Q1, G Q2) of the switches Q1 and Q2 by PWM control based on the modulation rate command Duty12. The PWM control circuit 229N generates gate pulses (G Q3, G Q4) of the switches Q3 and Q4 by PWM control based on the modulation rate command Duty34.

[0062] As shown in FIG. 3B, the compensation amount determination unit 2218 includes dq conversion units 22182 and 22183, an AC power calculation unit 22184, an AC current estimation calculation unit 22185, an absolute value calculation unit 22186, a comparator 22187, and a compensation amount generation unit 22188.

[0063] The dq conversion units 22182 and 22183 convert the values in the RST-axis coordinates of the three-phase AC into the values in the orthogonal dq-axis coordinates. The dq conversion unit 22182 converts the values of the line-to-line voltages (VRS_F, VTS_F) of the three-phase AC into the AC voltage values (VD_F, VQ_F) in the dq-axis coordinates. The dq conversion unit 22183 converts the values of the line currents (IR_F, IS_F, IT_F) of the three-phase AC into the AC current values (ID_F, IQ_F) in the dq-axis coordinates. Thereby, it can be calculated as a vector in the dq-axis coordinates.

[0064] The AC power calculation unit 22184 calculates the AC power P based on the AC voltage values (VD_F, VQ_F) and the AC current values (ID_F, IQ_F) in the dq-axis coordinates.

[0065] The AC current estimation calculation unit 22185 includes a limiter 221851 and a divider 221852.

[0066] The limiter 221851 limits the DC voltage value (VDC_F) within a predetermined range. If the DC voltage value (VDC_F) is within that range, the limiter 221851 outputs at the level of the input signal. When the DC voltage value (VDC_F) exceeds the upper and lower limits of that range, the limiter 221851 outputs the upper limit value or the lower limit value of that range. For example, it is advisable to define the limiting range so that the output value of this limiter 221851 does not become zero. Note that the above limiter 221851 may be configured as a level conversion unit such that its output value does not become zero instead. The divider 221852 divides the AC power P derived by the AC power calculation unit 22184 by the output value of the limiter 221851, and outputs the quotient, which is the estimated DC current value IC_est, as the calculation result of the AC current estimation calculation unit 22185.

[0067] The absolute value calculation unit 22186 derives the magnitude (Iout) of the alternating current output by the inverter 13 based on the alternating current values (ID_F, IQ_F) output from the dq conversion unit 22183. For example, the absolute value calculation unit 22186 generates the square root of the sum of the squares of the alternating current values (ID_F, IQ_F) and uses the result as the magnitude (Iout) of the alternating current.

[0068] The comparator 22187 discriminates the magnitude (Iout) of the alternating current output by the inverter 13 using a predetermined threshold value (SHT_LVL). For example, if the magnitude exceeds the threshold value (SHT_LVL), it outputs logic "1", and if it does not exceed, it outputs logic "0".

[0069] The compensation amount generation unit 22188 includes a level setting unit 221881, a change rate limiting unit 221882, a subtractor 221883, a limiter 221884, and a multiplier 221885.

[0070] The level setting unit 221881 converts to a predetermined value corresponding to the logic based on the logic of the input signal. For example, the level setting unit 221881 acquires the output signal of the comparator 22187 as the input signal, converts the logic "1" of the input signal to the value "1.0", and converts the logic "0" to the value "0.0".

[0071] The change rate limiting unit 221882 limits the change of the output signal according to the level of the input signal so that it does not exceed a predetermined change rate and follows the change in the level of the input signal (rate control). For example, the output signal level of the level setting unit 221881 changes stepwise from the value "0.0" to the value "1.0". The change rate limiting unit 221882 limits the change in the output signal level of the level setting unit 221881 so that it does not exceed a predetermined change rate and follows the change in that level.

[0072] The subtractor 221883 has the value "1.0" set at the first input and subtracts the output level of the change rate limiting unit 221882 from this value and outputs the result.

[0073] The limiter 221884 limits the output level of the subtractor 221883 within a predetermined range. If it is within that range, it outputs at the level of the input signal, and when exceeding the upper and lower limits of that range, it outputs the upper limit value or the lower limit value of that range.

[0074] The multiplier 221885 multiplies the DC current estimated value IC_est of the operation result of the AC current estimation calculation unit 22185 by the output level (coefficient Pk) of the limiter 221884, and outputs the product as the second current reference IC2_ref.

[0075] The second current reference IC2_ref is generated by the above operation processing by the compensation amount generation unit 22188. The compensation amount generation unit 22188 has a function of adjusting the gain with respect to the DC current estimated value IC_est, and derives the second current reference IC2_ref multiplied by a desired gain. Note that this second current reference IC2_ref changes according to the magnitude of the load current of the inverter 13. The amount flowing out as the load current of the inverter 13 is supplied from the DCDC converter 12 side and compensated thereby.

[0076] For example, in the orthogonal power conversion device 10, there is a load current feed-forward compensation part in the control on the DCDC converter 12 side. Since the current flowing between the DCDC converter 12 and the inverter 13 includes a large ripple current, it is difficult to use the detected value of the DC current for control. Therefore, the average DC current can be calculated by using the load power of the inverter 13 instead of the detected value of the DC current.

[0077] With reference to FIG. 4, the operation of the power conversion system 1 of the present embodiment will be described. FIG. 4 is a diagram for explaining the operation of the power conversion system 1 of the embodiment. FIG. 4(a) shows the flow of the output power of the orthogonal power converters 10A and 10B. FIG. 4(b) shows the flow of the output power when the orthogonal power converter 10A is in the regeneration state. FIG. 4(c) shows the states of the orthogonal power converters 10A and 10B when the circuit breaker 91 responds in the state of FIG. 4(b). FIG. 4(d) shows a comparative example corresponding to FIG. 4(c).

[0078] As shown in FIG. 4(a), the power supplied to the load L during power running becomes the output power of the orthogonal power converters 10A and 10B. As shown in FIG. 4(b), for example, depending on the operating state, the flow of the output power of one of the orthogonal power converters 10A and 10B (orthogonal power converter 10A) may be reversed. In this case, a part of the output power of the other in the power running state (orthogonal power converter 10B) or the power from the load L is supplied to the orthogonal power converter 10A. Even in such a situation, if the regenerated power is consumed by the orthogonal power converter 10A, it does not spread to the primary side.

[0079] However, when the circuit breaker 91 responds and the load L is disconnected in the state of FIG. 4(b), the output power of the orthogonal power converter 10B is supplied to the orthogonal power converter 10A. In the case of the comparative example, when the above event occurs, as shown in FIG. 4(d), power is regenerated up to the primary side of the orthogonal power converter 10A.

[0080] On the other hand, in the power conversion system 1 of the embodiment, if a predetermined condition is satisfied, the orthogonal power converter 10A acts to stop sending power to the primary side, so that a circulating state as shown in FIG. 4(d) above can be prevented.

[0081] As described above, the DCDC converter 12 applied to the orthogonal power converter 10 of the embodiment forms a three-level output chopper circuit (double chopper circuit). In contrast, the DCDC converter control unit 22 performs suppression control so that the balance between the positive voltage (PC side voltage) and the negative voltage (CN side voltage) is not lost. This suppression control by the DCDC converter control unit 22 adjusts the correction of the modulation command according to the direction of the current flowing through the reactor 12L (12LP, 12LN). For example, it is advisable to change the sign of the modulation command.

[0082] As in the above-described embodiment, unipolar elements (for example, MOSFETs) may be used for the switches Q1 - Q4. When using unipolar elements, in order to improve efficiency, it is advisable to avoid conduction to diodes such as body diodes and freewheel diodes. In this case, synchronous rectification may be performed in which the switch on the opposite side of the conducting diode is switched according to the energization timing.

[0083] However, when the orthogonal power converters 10 are connected in parallel, due to the circulating current between the devices, a state may occur in which the current in the reactor 12L (12LP, 12NP) of one side device is always negative despite the boost operation. Such an event is likely to occur especially at no load. If there is a circulating current between the orthogonal power converters 10, in the case of the comparative example, the correction for suppressing the imbalance may instead increase the imbalance.

[0084] Therefore, the power conversion system 1 of this embodiment eliminates this by correcting the compensation value for suppressing the imbalance according to the direction of the current flowing through the reactor 12L.

[0085] According to the above embodiment, the power conversion system 1 includes an orthogonal power conversion device 10 in which the primary side and the secondary side are connected in parallel respectively. Each orthogonal power conversion device 10 includes a DC-DC converter 12, an inverter 13, and a control unit 20. The DC-DC converter 12 can convert the first DC power of the first DC on the primary side by the first control to generate the second DC power of the second DC. The inverter 13 can convert the second DC power by the second control to generate AC power. The control unit 20 controls the power conversion of the DC-DC converter 12 by the first control using at least the direction of the first DC. Thereby, the behavior of the orthogonally connected power conversion devices 10 can be made more stable.

[0086] The above embodiment will be described from another perspective. For example, the control unit 20 corrects the power conversion amount of the DC-DC converter 12 so that the sum of the magnitudes of the positive voltage and the negative voltage of the second DC becomes the voltage reference. The control unit 20 may determine the addition and subtraction of the compensation amount according to the direction of the first DC, and compensate the above power conversion amount using the generated compensation amount so as to equalize the magnitudes of the positive voltage and the negative voltage of the second DC. As described above, the control unit 20 calculates the difference (VDC_ERR_F) between the DC positive electrode voltage detection value VDCP_F and the DC negative electrode voltage detection value VDCN_F, and calculates the compensation amount ERR_CMP_T by PI control so that the value becomes zero. The control unit 20 identifies the polarity of the current (IDC_F) of the reactor 12L for boosting, and determines the positive and negative of the compensation amount according to the result of the identification. The polarity of the above current (IDC_F) and the positive and negative of the compensation amount may be made corresponding.

[0087] Note that the control unit 20 can reduce the fluttering of the switching of the positive and negative of the compensation amount due to current ripple or the like by providing a dead zone in the range including the threshold value (for example, 0.) for identifying the polarity of the current (IDC_F) of the reactor 12L (ERR_CMP). The width of this dead zone may be adjusted, for example, by the values of the threshold +A and the threshold -A in FIG. 3A.

[0088] The control unit 20 calculates the modulation rate command Duty12 for the positive - side converter 12P and the modulation rate command Duty34 for the negative - side converter 12N by adding and subtracting the calculated correction amount to the modulation rate command Duty calculated by voltage control and current control of the chopper circuit of the DCDC converter 12. Note that the PWM control circuit 229P and the PWM control circuit 229N may generate the gate pulse GP (gate command) by comparing the triangular - wave carrier with a 180 - deg phase shift and the modulation rate commands Duty12 and Duty34. With such a configuration, the power conversion system 1 can make the behavior of the orthogonally - connected power conversion devices 10 connected in parallel more stable.

[0089] Next, with reference to FIG. 5, a configuration example of the control unit 20 of the embodiment will be described. FIG. 5 is a diagram for explaining a configuration example of the control unit 20 of the embodiment.

[0090] 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.

[0091] The communication processing unit 812 enables supply of various information acquired by communicating with a higher - level device to the processing unit 811.

[0092] The storage unit 814 is realized by a ROM, a RAM, an HDD, a flash memory, etc. The storage unit 814 is allocated a storage area for storing various setting information, programs, basic programs such as an OS, and application programs for making the control unit 20 function.

[0093] The input / output unit 813 acquires, for example, information on the output state of the orthogonal power conversion device 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 for displaying various information and an operation detection unit. The above display unit and operation detection unit may be configured as a combined touch panel.

[0094] The processing unit 811 sends the gate signal GP to the orthogonal power conversion device 10 via the input / output unit 813 and controls the orthogonal power conversion device 10.

[0095] The processing unit 811 executes a software program including the above functions. By executing the software program, the processing unit 811 forms some 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 (not shown), a portable storage medium, etc., or via a communication line.

[0096] The functions realized by components such as the control unit 20 described in this specification may be implemented in circuitry or processing circuitry. The circuitry or processing circuitry may include a general-purpose processor, an application-specific processor, an integrated circuit, ASICs (Application Specific Integrated Circuits), an FPGA (Field Programmable Gate Array), a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), a conventional circuit, and / or a combination thereof, programmed to realize the described functions. The processor that realizes the above functions includes transistors and other circuits and is regarded as circuitry or processing circuitry. The processor for realizing the above functions may include a programmable processor that executes a program stored in a memory and / or a programmable device reconfigurable by data stored in the memory, or may be such itself. In this specification, circuitry, a unit, or a means is hardware programmed or executed to realize the described functions. The hardware may be any hardware disclosed in this specification or any hardware known as being programmed or executed to realize the described functions. When the hardware is a processor regarded as being of the circuitry type, the circuitry, means, or unit is a combination of hardware and software used to configure the hardware and / or the processor.

[0097] According to at least one embodiment described above, the power conversion system includes an orthogonal power converter in which a primary side and a secondary side are connected in parallel respectively. Each orthogonal power converter includes a DC-DC converter, an inverter, and a control unit. The DC-DC converter can convert the first DC power of the first DC on the primary side by the first control to generate the second DC power of the second DC. The inverter can convert the second DC power by the second control to generate AC power. The control unit controls the power conversion of the DC-DC converter by the first control using at least the direction of the first DC. Thereby, the behavior of the orthogonal power converters connected in parallel can be made more stable.

[0098] As described above, several embodiments of the present invention have been described. However, 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, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and its equivalents. In addition, the above-described embodiments can be implemented in combination with each other.

[0099] For example, the control unit 20 may be configured by dividing it into a plurality of processors, and the processors common to the control unit 20 may perform respective processes.

[0100] <Modification Example> Note that depending on the circuit usage (boost operation and regeneration operation) of the orthogonal power converter 10, the elements mainly switched among the switches Q1-Q4 are different. Therefore, the ways of outputting gate pulses to the switches Q1-Q4 are different. For example, when only one of the power running operation and the regeneration operation is fixedly used, it is not necessary to switch the element on the opposite side of the diode that determines the direction of the current. In addition, in the embodiment, since a MOSFET is exemplified, a case where synchronous control is performed has been described. However, when bipolar elements (for example, IGBTs) are used for switches Q1-Q4, it is not necessary to switch the opposite-side switch for synchronous control.

[0101] (Appendix) The power conversion system 1 and the power conversion control method according to the above embodiment may be configured as follows. (1) The power conversion system 1 is a power conversion system including an orthogonal power conversion device in which a primary side and a secondary side are connected in parallel, respectively, wherein each orthogonal power conversion device includes a DCDC converter capable of converting the first DC power of the first DC on the primary side by first control to generate the second DC power of the second DC, an inverter capable of converting the second DC power by second control to generate AC power, and a control unit for controlling the power conversion of the DCDC converter by the first control using at least the direction of the first DC. It is preferably provided with. (2) In the power conversion system of (1) above, the control unit corrects the power conversion amount of the DCDC converter so that the sum of the magnitudes of the positive voltage and the negative voltage of the second DC becomes a voltage reference, determines the addition or subtraction of the compensation amount according to the direction of the first DC, and compensates the power conversion amount using the compensation amount generated so as to equalize the magnitudes of the positive voltage and the negative voltage of the second DC. (3) In the power conversion system of (2) above, the control unit when the direction of the DC current on the primary side is the same as that during regenerative operation, it is preferable to reverse the sign of the compensation amount by the first control compared to that during regenerative operation. (4) In the power conversion system of (2) or (3) above, the control unit When the direction of the primary-side direct current is the same as that during the regenerative operation and the magnitude of the primary-side direct current exceeds a predetermined threshold value, it is preferable to reverse the sign of the compensation amount by the first control compared to that during the regenerative operation. (5) In the power conversion system according to the above (2) or (3), the control unit When the direction of the primary-side direct current is the same as that during the regenerative operation and the magnitude of the primary-side direct current exceeds a predetermined threshold value, it is preferable to perform the power running operation by the first control. (6) In the power conversion system according to any one of the above (1) to (5), each orthogonal power conversion device is preferably provided with a transformer that transforms the AC power generated by the inverter into AC power to be supplied to the secondary side. (7) In the power conversion system according to any one of the above (1) to (6), the type of the switching element of the DCDC converter is a unipolar element, the control unit is preferably configured to perform the synchronous control of the switching element by the first control using the direction of the first direct current. (8) Each orthogonal power conversion device has its primary side and secondary side connected in parallel, respectively, a DCDC converter capable of converting the first DC power of the first direct current on the primary side into the second DC power of the second direct current by the first control, an inverter capable of converting the second DC power into AC power by the second control, and is provided with the control method of the orthogonal power conversion device includes at least the step of controlling the power conversion amount of the DCDC converter by the first control using the direction of the first direct current and may include.

Explanation of Signs

[0102] 1 Power conversion system 10, 10A, 10B Orthogonal Power Conversion Device 12, 12A, 12B DC-DC Converter 13, 13A, 13B Inverter 14, 14A, 14B Transformer 20, 20A, 20B Control Unit 91 Circuit Breaker (MCCB: Molded Case Circuit Breaker)

Claims

1. A power conversion system including an orthogonal power conversion device in which a primary side and a secondary side are each connected in parallel, wherein each orthogonal power conversion device includes a DCDC converter capable of converting first DC power of a first DC on the primary side by first control to generate second DC power of a second DC, an inverter capable of converting the second DC power by second control to generate AC power, and a control unit that controls power conversion of the DCDC converter by the first control using at least a direction of the first DC; The power conversion system comprising the above components.

2. The control unit corrects a power conversion amount of the DCDC converter so that a sum of magnitudes of a positive voltage and a negative voltage of the second DC becomes a voltage reference, determines addition or subtraction of a compensation amount based on a direction of the first DC, and compensates the power conversion amount using the compensation amount generated to equalize magnitudes of the positive voltage and the negative voltage of the second DC. The power conversion system according to claim 1.

3. The control unit when a direction of a DC current on the primary side is the same as that during a regeneration operation, reverses a sign of the compensation amount by the first control from that during the regeneration operation. The power conversion system according to claim 2.

4. The control unit when a direction of a DC current on the primary side is the same as that during a regeneration operation and a magnitude of the DC current on the primary side exceeds a predetermined threshold value, reverses a sign of the compensation amount by the first control from that during the regeneration operation. The power conversion system according to claim 2 or 3.

5. The control unit when a direction of a DC current on the primary side is the same as that during a regeneration operation and a magnitude of the DC current on the primary side exceeds a predetermined threshold value, performs power running operation by the first control. The power conversion system according to claim 2 or 3.

6. Each orthogonal power conversion device includes a transformer that transforms AC power generated by the inverter and supplies the transformed AC power to the secondary side. The power conversion system according to claim 1.

7. A type of a switching element of the DCDC converter is a unipolar element, and the control unit performs synchronous control of the switching element by the first control using a direction of the first DC. The power conversion system according to claim 1.

8. Each orthogonal power conversion device has a primary side and a secondary side each connected in parallel, and includes a DCDC converter capable of converting first DC power of a first DC on the primary side by first control to generate second DC power of a second DC. An inverter capable of converting the second DC power by second control to generate AC power, is provided, The control method of the orthogonal power conversion device is, a step of controlling a power conversion amount of the DCDC converter by the first control using at least a direction of the first DC A control method including.

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