Power conversion system and inverter device

Abstract

To suppress a cross current of an AC current and a DC current generated between inverter devices in parallel operation of the inverter device.SOLUTION: A power conversion system PS includes a plurality of inverter devices 1 provided in parallel with respect to a load. Each of the inverter devices 1 includes: a power conversion unit 2 that converts a DC input into an AC and outputs it; a filter circuit 3; a current detection unit 6 that detects a reactor current Ia; a voltage detection unit 7 that detects an output voltage Vo; a control unit 5 that generates a PWM control signal and outputs it to the power conversion unit 2; and a DC current extraction unit 8 that extracts a DC component of the reactor current Ia. The control unit 5 has a function of adjusting a reference voltage based on a DC component of the reactor current Ia.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a power conversion system including an inverter device configured to be capable of autonomous operation and an inverter device configured to be capable of autonomous operation.

Background Art

[0002] In a parallel operation in which an inverter device configured to be capable of autonomous operation is connected in parallel to a load (hereinafter, simply referred to as PQ droop control is known.

[0003] Patent Document 1 discloses a power conversion device having a droop control unit. Further, Patent Document 1 discloses a technique of generating a voltage compensation value for compensating for a voltage drop due to wiring impedance based on the output current of the power conversion device and a preset wiring impedance from the output terminal of the power conversion device to the connection point, and correcting an AC voltage command value with the voltage compensation value.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the case of the technique of Patent Document 1, it is necessary to grasp in advance the wiring impedance from the output terminal of the power conversion device to the connection point. However, the wiring of the power conversion device may be changed according to the installation situation or the like, and every time the wiring is changed, it is necessary to obtain the wiring impedance of the new wiring and generate a new voltage compensation value again, which is troublesome. In other words, there is a problem that the degree of freedom in changing the wiring is low after the wiring impedance is once determined.

[0006] Also, if only PQ droop control is performed, a cross current (offset current) of direct current may occur between inverter devices due to, for example, detection errors of individual inverter devices. At the product shipment stage, it is conceivable to adjust so that the above detection error becomes small, but it is difficult to completely eliminate the offset current at the product shipment stage.

[0007] In view of the above problems, an object of the present invention is to suppress cross currents of alternating current and direct current generated between inverter devices in parallel operation of inverter devices configured to be capable of independent operation.

Means for Solving the Problems

[0008] A power conversion system according to a first aspect of the present invention includes a plurality of inverter devices provided in parallel to supply AC power to a common load. Each of the inverter devices includes a power conversion unit that converts a DC input input from an input terminal into AC and outputs it, a filter circuit provided between the power conversion unit and an output terminal and having a reactor and a capacitor, a current detection unit that detects a reactor current flowing through the reactor, a voltage detection unit that detects an output voltage output from the output terminal, a control unit that outputs a PWM control signal corresponding to a reference voltage generated based on the active power and the reactive power calculated from the reactor current and the output voltage to the power conversion unit, and a DC current extraction unit that extracts a DC component of the reactor current. The control unit is configured to have a function of adjusting the reference voltage based on the DC component of the reactor current.

[0009] According to this aspect, in a power conversion system configured such that so-called PQ droop control based on active power and reactive power is executed by inverter devices operating in parallel, it is configured to have a function of adjusting the reference voltage used for PQ droop control based on the DC component of the reactor current extracted by the DC current extraction unit. Thereby, it is possible to suppress cross currents of alternating current and direct current generated between the inverter devices connected in parallel.

Effects of the Invention

[0010] In the parallel operation of an inverter device configured to be capable of independent operation, it is possible to suppress the cross currents of the alternating current and direct current generated between the inverter devices.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely illustrative in nature and is not intended to limit the present invention, its scope of application, or its uses.

[0013] FIG. 1 is a block diagram showing an example of the configuration of a power conversion system.

[0014] The power conversion system PS has a configuration in which a plurality of inverter devices 1 are connected in parallel to a load Z. In other words, the output terminals of the plurality of inverter devices 1 are connected to the load Z via a common wiring W.

[0015] Note that the number and uses of the inverter devices 1 connected to the load Z are not particularly limited. Also, (1) each inverter device 1 may be mounted on a substrate, and a plurality of the mounted substrates may be collectively stored in a common housing, or (2) the plurality of inverter devices 1 may be stored in separate housings and installed in separate locations. In other words, the inverter devices 1 constituting the power conversion system PS may be installed together in one place, or may be installed at separate positions and connected to the load via the wiring W to perform parallel operation.

[0016] - Inverter Device - The inverter device 1 includes a power conversion unit 2, a filter circuit 3, a control unit 5, a current detection unit 6, a voltage detection unit 7, and a DC current extraction unit 8.

[0017] The inverter device 1 converts the DC power input via the input terminal IN into AC power and outputs it from the output terminal OUT. When a rechargeable battery B is connected to the input terminal IN, the inverter device 1 may be a bidirectional type. In this embodiment, a two - wire type inverter device is illustrated. Note that the technology of the present disclosure is not limited to the two - wire type, and a three - wire type inverter device may also be used, and the same effect can be obtained.

[0018] 〔Power Conversion Unit〕 The power conversion unit 2 includes a bridge circuit (for example, an H - type bridge circuit) in which a plurality of semiconductor switches (not shown) are bridge - connected. Each semiconductor switch performs a switching operation based on a PWM control signal output from a PWM generation unit described later, and the input - output power of the power conversion unit 2 is adjusted. In other words, the power conversion unit 2 is PWM - controlled based on the PWM control signal output from the control unit 5.

[0019] 〔Filter Circuit〕 The filter circuit 3 is provided between the power conversion unit 2 and a pair of output terminals OUT, and has a reactor 31 and a capacitor 32. The filter circuit 3 has a function of attenuating the harmonic components of the AC power output from the power conversion unit 2.

[0020] The reactor 31 is composed of a plurality of reactor elements (not shown). The reactor elements are provided, for example, on a wiring L1 connected to one output terminal OUT and a wiring L2 connected to the other output terminal OUT, respectively.

[0021] The capacitor 32 is composed of one or more capacitive elements and is provided, for example, between the wiring L1 and the wiring L2. The configurations of the reactor element and the capacitive element are not particularly limited, and conventionally known elements can be used.

[0022] 〔Current detection unit〕 The current detection unit 6 detects the reactor current Ia (corresponding to an alternating current) of the reactor 31 and outputs it to the control unit 5. FIG. 1 shows an example in which the current detection unit 6 detects the reactor current Ia flowing through the wiring L1. The current detection unit 6 only needs to be configured to be able to detect an alternating current, and the specific configuration and measurement method are not particularly limited. For example, various conventionally known current sensors and the like can be used.

[0023] 〔Voltage detection unit〕 The voltage detection unit 7 detects the output voltage output from the inverter device 1 and outputs it to the control unit 5. FIG. 1 shows an example in which the voltage detection unit 7 detects the voltage between the wiring L1 and the wiring L2 between the filter circuit 3 and the output terminal OUT. The voltage detection unit 7 only needs to be configured to be able to detect a voltage, and the specific configuration and measurement method are not particularly limited. For example, various conventionally known voltage sensors and the like can be used.

[0024] 〔DC current extraction unit〕 The DC current extraction unit 8 extracts the DC component (DC current component) of the alternating current detected by the current detection unit 6 and outputs it to the control unit 5. The DC current extraction unit 8 only needs to be configured to be able to detect the DC component from the alternating current, and the specific configuration and extraction method are not particularly limited. For example, a conventionally known low-pass filter (described as LPF in the drawing) and the like can be used.

[0025] 〔Control unit〕 The control unit 5 calculates the active power P and the reactive power Q from the alternating current detected by the current detection unit 6 and the output voltage detected by the voltage detection unit 7. Further, the control unit 5 generates a reference voltage based on the calculated active power P and reactive power Q, and transmits a PWM control signal corresponding to the generated reference voltage to the power conversion unit 2. As described above, the power conversion unit 2 is PWM-controlled based on the PWM control signal output from the control unit 5.

[0026] The control unit 5 is realized by, for example, a so-called computer. Although not shown, the computer as the control unit 5 is composed of, for example, hardware such as a processor, a memory, and an interface, and software such as a control program and data implemented in the memory. More specifically, each function of the control unit 5 described later is realized by a processor such as a CPU executing a program stored in the memory. Note that the control unit 5 may be realized by hardware (such as a sequence circuit) such as an ASIC or an FPGA having a function equivalent to that of a processor executing a program, or may be realized by the cooperation of software and hardware.

[0027] FIG. 2 shows a block diagram illustrating an example of the control unit 5 and its peripheral configuration.

[0028] The control unit 5 includes, as a functional block configuration, a power calculation unit 51, a P-loop control unit 52, a Q-loop control unit 53, a PI controller 54, a CVCF control unit 55, and a PWM generation unit 56.

[0029] The power calculation unit 51 calculates the active power P and the reactive power Q from the alternating current detected by the current detection unit 6 and the output voltage detected by the voltage detection unit 7. The power calculation unit 51 outputs the calculated active power P to the P-loop control unit 52 and the calculated reactive power Q to the Q-loop control unit 53.

[0030] The P-loop control unit 52 generates a phase adjustment value θ based on the active power P calculated by the power calculation unit 51 and outputs it to the CVCF control unit 55.

[0031] Based on the reactive power Q calculated by the power calculation unit 51, the Q loop control unit 53 generates an effective value voltage adjustment value Vr and outputs it to the CVCF control unit 55.

[0032] Based on the DC component of the reactor current extracted by the DC current extraction unit 8, the PI controller 54 generates a DC voltage adjustment value Vd and outputs it to the CVCF control unit 55.

[0033] Regarding the DC voltage adjustment value Vd generated by the PI controller 54, a predetermined limit value may be provided. Basically, since the adjustment of the output current for each inverter device 1 is performed at the time of shipment, the cross-flow current is assumed to be weak. Therefore, since the DC voltage adjustment value Vd is assumed to fall within a predetermined range, it is possible to provide a predetermined limit value. By providing such a predetermined limit value, for example, it becomes possible to handle a load Z that uses a half-wave voltage. Also, it becomes possible to avoid the load being damaged or malfunctioning due to an adjustment value of an unexpected magnitude being set as the DC voltage adjustment value Vd. The predetermined limit value is not particularly limited, but is set to a value such as ±0.1% of the effective value of the output voltage, for example.

[0034] The CVCF (Constant Voltage Constant Frequency) control unit 55 has a function of generating a control signal Dy for bringing the output voltage and output frequency of the inverter device 1 to a predetermined steady state based on the voltage information input from the voltage detection unit 7 and the current information input from the current detection unit 6, and outputting it to the PWM generation unit 56. Furthermore, the CVCF control unit 55 has a function of adjusting the phase, effective value voltage, and DC voltage offset of the sine wave voltage output from the inverter device 1 based on the results of PQ loop control and DC suppression control. In other words, it has a function of adjusting the reference voltage based on the DC component of the alternating current extracted by the DC current extraction unit 8.

[0035] FIG. 3 shows a block diagram illustrating an example of the CVCF control unit 55 and its peripheral configuration. The CVCF control unit 55 includes a reference voltage generation unit 551, a voltage control unit 552, a load current estimation unit 553, and a current control unit 554. In the example of FIG. 3, the DC component of the reactor current Ia extracted by the DC current extraction unit 8 in FIG. 2 is input to the reference voltage generation unit 551, and an example is shown in which the reference voltage generation unit 551 is provided with a function of adjusting the reference voltage (hereinafter, also simply referred to as the "adjustment function"). However, the block provided with the above adjustment function is not limited to this, and may be provided in a block subsequent to the reference voltage generation unit 551.

[0036] Specifically, the reference voltage generation unit 551 generates a voltage command value Vx based on the phase adjustment value θ generated by the P-loop control unit 52, the effective value voltage adjustment value Vr generated by the Q-loop control unit 53, and the DC component of the reactor current Ia extracted by the DC current extraction unit 8. The voltage command value Vx is a target waveform that the inverter wants to output, and is, for example, a sine wave.

[0037] The voltage control unit 552 generates a voltage error value Vg based on the voltage command value Vx generated by the reference voltage generation unit 551 and the output voltage Vo detected by the voltage detection unit 7. The voltage error value Vg is, for example, an error signal that is the difference between a reference sine wave and the sine wave output by the inverter. The error signal is, for example, a small signal containing harmonic components because, in the steady state, there is almost no difference between the reference sine wave and the sine wave output by the inverter.

[0038] The load current estimation unit 553 estimates the load current flowing through the load Z based on the voltage error value Vg generated by the voltage control unit 552, the reactor current Ia detected by the current detection unit 6, and the output voltage Vo detected by the voltage detection unit 7.

[0039] The current control unit 554 generates a control signal Dy for setting the output voltage and output frequency of the inverter device to a predetermined steady state based on the estimation result of the load current by the load current estimation unit 553, and outputs it to the PWM generation unit 56.

[0040] Based on the control signal Dy generated by the current control unit 554, the PWM generation unit 56 generates a PWM control signal for driving the semiconductor switches of the power conversion unit 2 and outputs it to the power conversion unit 2. In other words, the PWM generation unit 56 outputs a PWM control signal corresponding to the reference voltage generated based on the active power P and the reactive power Q calculated from the alternating current detected by the current detection unit 6 and the output voltage detected by the voltage detection unit 7 to the power conversion unit 2.

[0041] As described above, in the power conversion system PS configured such that the PQ loop control is executed by the inverter devices 1 operating in parallel, based on the DC component of the reactor current Ia extracted by the DC current extraction unit 8, it is configured to adjust the reference voltage used for the PQ loop control. Thereby, it is possible to suppress the cross currents of the alternating current and the direct current generated between the inverter devices connected in parallel.

Industrial Applicability

[0042] According to the present invention, it is possible to suppress the cross currents of the alternating current and the direct current generated between the inverter devices in the parallel operation of the inverter devices configured to be capable of independent operation, which is extremely useful.

Explanation of Signs

[0043] PS Power conversion system 1 Inverter device 2 Power conversion unit 3 Filter circuit 5 Control unit 6 Current detection unit 7 Voltage detection unit 8 DC current extraction unit

Claims

1. A power conversion system in which a plurality of inverter devices are provided in parallel to supply AC power to a common load, wherein each of the inverter devices includes: a power conversion unit that converts a DC input input from an input terminal into AC and outputs it; a filter circuit provided between the power conversion unit and an output terminal and having a reactor and a capacitor; a current detection unit that detects the reactor current of the reactor; a voltage detection unit that detects the output voltage output from the output terminal; a control unit that outputs a PWM control signal corresponding to a reference voltage generated based on the active power and reactive power calculated from the reactor current and the output voltage to the power conversion unit; a DC current extraction unit that extracts a DC component of the reactor current; the control unit has a function of adjusting the reference voltage based on the DC component of the reactor current; A power conversion system characterized by the above.

2. In the power conversion system according to claim 1, a predetermined limit value is set for the adjustment amount of the reference voltage, the control unit adjusts the reference voltage based on the DC component of the reactor current within a range not exceeding the predetermined limit value; A power conversion system characterized by the above.

3. An inverter device that supplies AC power to a common load together with other inverter devices provided in parallel, a power conversion unit that converts a DC input into AC and outputs it; a filter circuit provided between the power conversion unit and an output terminal and having a reactor and a capacitor; a current detection unit that detects the reactor current of the reactor; a voltage detection unit that detects the output voltage output from the output terminal; a control unit that outputs a PWM control signal corresponding to a reference voltage generated based on the active power and reactive power calculated from the reactor current and the output voltage to the power conversion unit; a DC current extraction unit that extracts a DC component of the reactor current; the control unit has a function of adjusting the reference voltage based on the DC component of the reactor current; An inverter device characterized by the above.

4. In the inverter device according to claim 3, an upper limit is set for the adjustment amount of the reference voltage, the control unit adjusts the reference voltage based on the DC component of the reactor current within a range not exceeding the upper limit of the adjustment amount; An inverter device characterized by the above.

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