JP2015111962A - Parallel operation power supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly efficient parallel operation power supply system using renewable energy.SOLUTION: The parallel operation power supply system includes: a DC generator 101; a first DC-DC converter 104 for transforming the output of the DC generator 101; an AC generator 102; an AC-DC converter 105 for converting the output of the AC generator 102 into a direct current; an inverter 106 for converting each of the output of the first DC-DC converter 104 and the output of the AC-DC converter 105 into an alternate current; a switch 103 for switching the connection destination of the output of the AC generator 102 to the input of the AC-DC converter 105 or the output of the inverter 106; and a control part 107 for controlling the switching of the switch 103.

Description

  The present invention relates to a power supply system.

  As a power supply system that uses a plurality of power supplies in parallel and can perform parallel power supply from the plurality of power supplies to a load, for example, a technique of Patent Document 1 is known. FIG. 8 is a block diagram showing the configuration of the power supply system of Patent Document 1. As shown in FIG.

  The power supply system of Patent Document 1 includes a converter 2 that converts alternating current from a commercial power system 1 into direct current, a solar cell 9, and a maximum power point tracking control function for always taking out maximum power from the solar cell 9. A power supply device 5 including a DC-DC converter 8, an inverter 3 that converts direct current into alternating current having a predetermined frequency and voltage, a control circuit 4 that performs predetermined control, and a supply source of power supplied to the load 7 A connection switching device 6 for switching is provided.

  In Patent Document 1, the output of the inverter 3 or the commercial power system is switched by switching the connection switching device 6 according to the control signal of the control circuit 4 according to the output power value of the power supply device 5, that is, the power generation state of the solar cell 9. Power is supplied from 1 to the load, and stable power can be supplied to the load without being affected by fluctuations in the power supply amount of the power supply device 5.

JP 2005-328656 A

  However, when the technique of Patent Document 1 is applied to a parallel operation power supply system including a self-supporting generator independent of a commercial power system and a power supply using renewable energy such as a solar battery, the following problems occur. That is, in Patent Document 1, when the power supplied to the load 7 is insufficient with only the output of the power supply device 5, the converter 2 controlled by the control signal from the control circuit 4 operates, and the AC power of the commercial power system 1 is Is converted into DC power, and both the converted DC power and the output of the power supply device 5 are input to the inverter 3, and then necessary AC power is supplied from the inverter 3 to the load 7. That is, when parallel operation is performed in the power supply device 5 and the commercial power system 1, both are connected only at the direct current portion.

  Therefore, when parallel operation is performed by the power supply device 5 and the commercial power system 1, the power supplied from the commercial power system 1 is once converted to direct current, then converted back to alternating current power and supplied to the load. In such conversion, power loss always occurs.

  Further, when the output of the power supply device 5 falls below a preset output value, the connection switching device 6 is switched so that the output of the commercial power system 1 is directly supplied to the load 7. Depending on the case, power is always supplied to the load 7 only by the commercial power system 1, and in this case, the utilization factor of the solar cell 9 of the power supply device 5 is greatly impaired.

  This invention is made | formed in view of such a subject, The objective is to provide the highly efficient parallel operation power supply system using renewable energy.

  The present invention includes a direct current generator, a first DC-DC converter that transforms the output of the direct current generator, an alternating current generator, an AC-DC converter that converts the output of the alternating current generator to direct current, and the first DC. An inverter for converting the output of the DC converter and the output of the AC-DC converter into alternating current, a switch for switching the connection destination of the output of the alternating current generator to the input of the AC-DC converter or the output of the inverter; And a control unit that controls switching of the switch.

  Further, the control unit connects the output of the AC generator to the output of the inverter when the output ratio of the DC generator is less than half of the load power consumption, and the output ratio of the DC generator is a load. When the power consumption is ½ or more, the switch is switched so that the output of the AC generator is connected to the input of the AC-DC converter.

  In addition, the parallel operation power supply system includes a power factor adjustment unit connected in parallel to the output of the AC generator.

  The parallel operation power supply system includes a second DC-DC converter having one end connected to the input of the inverter, and a power storage unit connected to the other end of the second DC-DC converter.

  According to the parallel operation power supply system of the present invention, the usage ratio of renewable energy can be improved.

It is a block diagram which shows Embodiment 1 of this invention. FIG. 6 is a block diagram illustrating a second embodiment. FIG. 6 is a block diagram illustrating a third embodiment. It is a graph which shows the relationship for every time of load power consumption at the time of fine weather, and a DC generator output. It is a graph which shows the relationship for every time of the load power consumption at the time of cloudy weather, and rainy weather, and a DC generator output. It is a graph which shows the relationship for every time of the load power consumption at the time of irregular weather, and a DC generator output. It is a graph explaining the balance of the maximum output of a DC generator and load power consumption. It is a block diagram of the conventional power supply system.

Embodiment 1
A first embodiment of the present invention will be described with reference to FIG. 1 and FIGS. FIG. 1 is a block diagram of a parallel operation power supply system 100 according to the present invention, and FIGS. 4 to 6 are graphs showing the relationship between load power consumption and DC generator output depending on the weather.

  First, the configuration of the parallel operation power supply system 100 will be described with reference to FIG. The parallel operation power supply system 100 includes a DC generator 101 that uses renewable energy, a first DC-DC converter 104 that transforms the output of the DC generator 101, an AC generator 102 that uses fossil fuel, and an AC generator. AC-DC converter 105 that converts the output of 102 into direct current, inverter 106 that converts the outputs of first DC-DC converter 104 and AC-DC converter 105 into alternating current, and the output supply destination of alternating current generator 102 is AC- A switch 103 that switches to the DC converter 105 or the load 109, a control unit 107 that performs system control, and a relay 108 that is interposed between the output of the inverter 106 and the load 109 are provided.

  Next, each block described above will be specifically described. For the DC generator 101, for example, a solar power generation device of about 100 kW can be used. Moreover, not only solar power generation but also a power generation device using other renewable energy can be used.

  The first DC-DC converter 104 is a step-up chopper method, and adjusts the step-up ratio by changing the duty ratio with a built-in microcomputer to perform maximum power point tracking control of the DC generator 101.

  As the AC generator 102, for example, a gas turbine of about 100 kW is used. Further, it is preferable that the speed control can be performed so that the rotor always has a constant speed. For this speed control, a mechanical system using a centrifugal pendulum may be employed, or an electronic system (electronic governor) may be employed. Moreover, you may employ | adopt other rotary generators, such as not only a gas turbine but a diesel generator.

  For example, the AC-DC converter 105 is a combination of a rectifier circuit using a diode bridge and a DC-DC converter for voltage matching. Moreover, the microcomputer is provided inside and the output is adjusted according to the voltage fluctuation | variation of DC system | strain which arises when the 1st DC-DC converter 104 performs maximum power point tracking control.

  The inverter 106 is a transformerless system, and converts the direct current output of the first DC-DC converter 104 or the AC-DC converter 105 into alternating current by PWM (Pulse Width Modulation) control by a built-in microcomputer. Furthermore, an operational amplifier, a current transformer, and an output transformer are built in, and the current value and the voltage value are detected by amplifying the output value with the operational amplifier and performing AD conversion with the microcomputer. Furthermore, a signal is obtained by a sensor that detects a rotor, such as an encoder or resolver (not shown) incorporated in the AC generator, and is synchronized with the AC generator.

  The switch 103 switches the output of the AC generator 102 to connection to the DC bus 114 or connection to the load 109 via the AC-DC converter 105.

  The control unit 107 controls the operations of the first DC-DC converter 104, the AC-DC converter 105, the inverter 106, and the switch 103, for example, using RS485 serial communication.

  The relay 108 is connected to the operating state of the DC generator 101 and the AC generator 102 to connect between the output of the inverter 106 and the load 109.

  Next, the basic operation of the parallel operation power supply system 100 will be described with reference to FIGS. 1 and 4. In the parallel operation power supply system 100 of FIG. 1, the DC generator 101 and the AC generator 102 are operated in parallel according to the following procedure. FIG. 4 is a graph showing the relationship between the load power consumption and the output of the DC generator 101 during parallel operation on a sunny day all the time. Hereinafter, the case where the DC generator 101 is a solar power generation device will be described as an example.

  In addition, with reference to FIG. 4, the relationship between the load power consumption and the output of the DC generator 101 during parallel operation will be described prior to the description of the basic operation. As shown in FIG. 4, the output curve 122 of the DC generator 101 is irregular throughout the day because it uses sunlight, and of course, there is no output at night. Therefore, only the output (not shown) of the AC generator 102 is supplied to the load in the portion where the output curve 122 of the DC generator 101 does not satisfy the value of the load power consumption curve 121 at each time.

Next, an actual basic operation of the parallel operation power supply system 100 will be described with reference to FIG. When only the output of the AC generator 102 is supplied to the load at night as described above, the output of the first DC-DC converter 104 and the inverter 106 is stopped because there is no output of the DC generator 101. However, the first DC-DC converter 104 sequentially monitors the input voltage from the DC generator 101 and transmits it to the control unit 107 every preset time. When the input voltage from the DC generator 101 reaches a preset voltage, the control unit 107 issues an operation instruction to the first DC-DC converter 104 and the inverter 106, and an output operation is started. Note that each of the first DC-DC converter 104, the inverter 106, and the AC-DC converter 105 measures at least the input current in addition to the input voltage and transmits them to the control unit 107. The output procedure from the inverter 106 is as follows.
(1) A reference sine wave having the same frequency as that of the AC generator 102 is created by a microcomputer built in the inverter 106.
(2) The relay 108 is turned off, and the inverter 106 acquires the voltage phase of the AC generator 102 from the detector 117 incorporated in the AC generator 102.
(3) The voltage phase of the reference sine wave is adjusted to match the voltage phase of the AC generator 102.
(4) When the phases in step (3) match, the relay 108 is turned on, and the inverter 106 and the output of the AC generator 102 are connected.
(5) The current value flowing out to the AC generator 102 is detected by the detector 118.
(6) Current feedback control of the inverter 106 is performed so that the value of the current flowing out to the AC generator 102 is maximized and the phase matches the reference sine wave (high power factor).

  Next, details of the control operation of the parallel operation power supply system 100 by the control unit 107 will be described. The control unit 107 controls the inverter 106, and the detector 116 of the inverter 106 detects the output current of the AC generator 102 and the detector 115 detects the voltage of the AC bus 113.

  In addition, control is performed to increase the output current of the inverter 106 so that the current from the DC generator 101 is maximized within the allowable range of the voltage of the AC bus 113. In this operation, even if the output voltage of the inverter 106 is increased, current feedback control is performed with a desired gain until the output current does not increase. That is, control is performed so that the output of the DC generator 101 is maximized in the system.

  On the other hand, when the output current decreases while the output of the inverter 106 is maintained at a constant voltage, it is determined that the output of the DC generator 101 is decreasing due to weather conditions or the like, and the output current decreases. Control is performed to reduce the output voltage of the inverter 106 to a level at which it does not occur.

  Further, switching control of the switch 103 is performed according to the output of the DC generator 101. Specifically, when the output ratio of the DC generator 101 is small, for example, less than ½ of the load power consumption, the switch 103 is switched to the AC bus 113 side according to the instruction of the control unit 107 and the AC− The operation of the DC converter 105 is stopped and the operation based on the basic operation described above is performed.

  When the output ratio of the DC generator 101 is large, for example, when the load power consumption is ½ or more, the switch 103 is switched to the AC-DC converter 105 side according to an instruction from the control unit 107 and the AC-DC converter. 105 starts operation. Here, the switch 103 may be a mechanical type, but a switch using a semiconductor such as a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) or a triac is more preferable.

Further, the control of the inverter 106 is changed to voltage feedback control in order to perform a constant voltage output operation similar to that when a general power conditioner autonomously operates. Below, the procedure of the voltage feedback control of the inverter 106 is demonstrated.
(1) A reference sine wave having the same frequency as that of the AC generator 102 is created by a microcomputer built in the inverter 106.
(2) The voltage phase of the reference sine wave is kept the same as before the switch 103 is switched. (At any time, the voltage phase of the AC generator 102 is detected by the detector 117 and corrected so that synchronization is maintained.)
(3) The voltage value of the AC bus 113 is detected by the detector 115.
(4) Monitor that the voltage of the AC bus 113 is within an allowable range, and perform voltage feedback control so that a constant voltage is maintained.

  The switching operation of the switch 103 and the change of the output control are performed by the control unit 107 instructing the AC generator 102 and the switch 103 by comparing the load power consumption and the output voltage of the DC generator 101. At this time, there is no particular problem in the case of clear weather when the output of the DC generator 101 is small and stable compared to the load power consumption as shown in FIG. 4, or when it is cloudy or rainy as shown in FIG. However, when the weather changes irregularly in units of time, the output curve 122 of the DC generator 101 may increase or decrease frequently as shown by the part surrounded by the circular broken line in FIG.

  In such a case, if the switching of the switch 103 is switched too fast, it becomes difficult to control and synchronize with the inverter 106. Therefore, in the switching control of the switch 103, the state that needs to be switched is longer than a certain time, for example, more than 30 minutes It is preferable to set in advance so as to perform switching when continuing.

  According to the first embodiment, an output in which the output of the DC generator 101 and the output of the AC generator 102 are always supplied to the load 109 so that the output of the DC generator 101 is maximized in the system. Be controlled. Therefore, the use ratio of the renewable energy used for the DC generator 101 can be maximized in the parallel operation power supply system 100.

[Embodiment 2]
Another embodiment of the present invention will be described with reference to FIG. In FIG. 2, the same parts as those of the first embodiment are indicated by the same reference numerals. The present embodiment is different from the first embodiment in that a power factor adjustment unit 110 is added to the AC bus 113.

  The power factor adjustment unit 110 includes a plurality of series circuits of capacitors, reactors, and switches. Moreover, it is more preferable to provide a circuit breaker that prevents excessive phase advance at light load. Then, the power factor adjusting unit 110 performs switching control of the switch by the control unit 107 and adjusts the power factor of the AC bus 113 to a specified power factor by adjusting the capacitor capacity in multiple stages. .

  According to the second embodiment, when the inverter 106 is subjected to voltage feedback control, it is possible to prevent the AC bus 113 from becoming overcurrent depending on the current consumption of the load due to the power factor decreasing.

[Embodiment 3]
Still another embodiment of the present invention will be described with reference to FIGS. In FIG. 3, the same parts as those in the first embodiment or the second embodiment are denoted by the same reference numerals. FIG. 7 is a graph for explaining the balance between the maximum output of the DC generator and the load power consumption.

  The present embodiment is different from the first or second embodiment in that the power storage unit 111 is connected to the DC bus 114 via the second DC-DC converter 112.

  First, the balance between the maximum output of the DC generator and the load power consumption will be described with reference to FIG. In the parallel operation power supply system 100, the maximum use of the output from the DC generator 101 is as described in the above embodiment, and in consideration of this, the maximum output of the DC generator 101 is assumed to be an assumed load. It is preferable to set so as not to exceed the power consumption. However, for example, the maximum output of the DC generator 101 may exceed the load power consumption as shown in FIG. 7 due to the installation conditions of the system including the load. In such a case, the electric power in the portion surrounded by the round broken line exceeding the load power consumption curve 121 is not actually output, and is converted as heat generated by the DC generator 101, so that the utilization efficiency as electric power is reduced. Resulting in. In the present embodiment, as described above, the power storage unit 111 is connected to the DC bus 114 via the second DC-DC converter 112 in order to cope with such a situation.

  Next, a specific configuration and operation of the present embodiment will be described with reference to FIG. As the power storage unit 111, a lead battery, a nickel metal hydride battery, a lithium ion battery, an electric double layer capacitor, a lithium ion capacitor, or the like can be used. The second DC-DC converter 112 is a bidirectional converter that can control the direction of power bidirectionally.

  The second DC-DC converter 112 includes a microcomputer inside, and the first DC-DC converter 104 performs control according to the voltage fluctuation of the DC bus 114 caused by the maximum power point tracking control of the DC generator 101. The step-up / step-down ratio is adjusted by the control of the unit 107, and the output of the DC bus 114 is adjusted. Although illustration is omitted, power storage unit 111 can also be connected to AC bus 113 via a bidirectional inverter.

  According to the third embodiment, the output of the DC bus 114 is backed up by the power storage unit 111 when the output ratio of the DC generator 101 is high or when an output fluctuation occurs due to a sudden change in weather conditions or the like. Thereby, even if the output fluctuation occurs in the DC generator 101, the power quality for the load 109 can be stabilized. Further, even when there is a fluctuation in the output of the DC generator 101, it is possible to suppress frequent switching of the current feedback control and voltage feedback control and the switch switching operation in the inverter 106.

  The embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The parallel operation power supply system according to the present invention can be widely applied to all power supply systems including a system interconnected with a commercial power system.

DESCRIPTION OF SYMBOLS 100 Parallel operation power supply system 101 DC generator 102 AC generator 103 Switch 104 1st DC-DC converter 112 2nd DC-DC converter 105 AC-DC converter 106 Inverter 107 Control part 108 Relay 109 Load 110 Power factor adjustment part 111 Power storage part 113 AC bus 114 DC bus 115, 116, 117, 118 Detector 121 Load power consumption curve 122 Output curve of DC generator 101

Claims (4)

A DC generator,
A first DC-DC converter for transforming the output of the DC generator;
An alternator,
An AC-DC converter for converting the output of the AC generator into a direct current;
An inverter that converts the output of the first DC-DC converter and the output of the AC-DC converter into alternating current;
A switch for switching the connection destination of the output of the AC generator to the input of the AC-DC converter or the output of the inverter;
A parallel operation power supply system comprising: a control unit that controls switching of the switch.   The control unit connects the output of the AC generator to the output of the inverter when the output ratio of the DC generator is less than half of the load power consumption, and the output ratio of the DC generator is the load power consumption. 2. The parallel operation power supply system according to claim 1, wherein the switch is switched so that the output of the AC generator is connected to the input of the AC-DC converter when ½ or more.   The parallel operation power supply system according to claim 1, wherein the parallel operation power supply system includes a power factor adjustment unit connected in parallel to the output of the AC generator.   The parallel operation power supply system includes a second DC-DC converter having one end connected to an input of the inverter, and a power storage unit connected to the other end of the second DC-DC converter. 3. The parallel operation power supply system according to any one of 3 above.