JP4191625B2 - Distributed power system - Google Patents

Description

  The present invention relates to a distributed power supply system having a plurality of distributed power supply units.

In the conventional distributed power supply system, in order for each unit to detect only the DC bus voltage and autonomously operate, each unit determines an operation mode based on the DC voltage as shown in FIG. 2 (see, for example, Patent Document 1). .
Japanese Unexamined Patent Publication No. 2003-339118 (page 4-8, FIG. 1-18)

  By the way, in the distributed power supply control method described above, there is a problem that when there are a plurality of interconnection units and power storage units, it cannot be flexibly handled. There is a problem of constructing a procedure for adjusting an operation mode for a DC voltage so that each unit operates in cooperation with each addition. There is also a problem of clarifying a method for connecting units of different capacities.

  The present invention is for solving the above-described problems, and its purpose is to allow a plurality of distributed power supply units to autonomously perform cooperative operation and to easily add units without depending on the device capacity. It is to provide a system that makes it possible.

  A DC bus that is allowed to vary in voltage within a predetermined range, and is connected to the DC bus, and power is exchanged with the DC bus, and the amount of power exchange is determined based on the DC bus voltage. In a distributed power supply system with multiple power supply units determined autonomously, in order to autonomously determine the amount of power exchange, the function to change the DC voltage command value according to the power or current input / output from the unit to the DC bus or By providing the unit with a function of changing the controllability of the DC voltage, it becomes possible to easily add the unit.

  The function of changing the command value is realized by a function of subtracting a value obtained by multiplying a DC current gain from the DC voltage command value in order to change the DC voltage command value, and a function of changing the gain according to the DC voltage. The

  According to the present invention, a DC bus that is allowed to vary in voltage within a predetermined range, and the DC bus are connected to and receive power from the DC bus, and based on the DC bus voltage. In a distributed power supply system with multiple power supply units that autonomously determine the amount of power exchange, multiple distributed power supply units operate autonomously and add units easily without depending on the device capacity It is possible to provide a system that makes it possible.

  Therefore, the expandability and maintainability of the system can be improved and it can contribute to the spread of the distributed power supply system.

  In the distributed power supply system configuration of FIG. 1, an embodiment will be described below.

1. Control Method of Interconnection / Power Storage Unit In the power storage unit, the DC voltage controller generates a current command value Ibt ^* such that the DC voltage Vdc becomes the command value Vdc ^* . The current controller PWM-operates the chopper so that the battery current Ibt becomes Ibt ^* . The battery charger / discharger sets Ibt ^* to zero when the battery is fully charged or discharged. On the other hand, in the interconnection unit, the DC voltage controller generates a current command value Iac ^* such that the DC voltage Vdc becomes the command value Vdc ^* . The current controller performs PWM operation of the converter so that the system current Iac becomes Iac ^* .

  The power storage unit and the interconnection unit constitute a DC voltage control system as described above. The direct current output of the unit becomes a voltage source, and if there is an error in voltage control between the units, cross current occurs. In order to suppress this easily, it is sufficient to insert an impedance into the output, but this is not realistic because loss occurs and costs increase. Refer to FIG.

Therefore, as shown in FIG. 3B, in the DC voltage control system, a path for detecting the DC current Idc of the unit and multiplying by the gain K is subtracted from the DC voltage command value Vdc ^* .
When the DC voltage Vdc follows Vdc ^* ,
Vdc = Vdc0−K · Idc
K · Idc represents a voltage drop, and K is an equivalent impedance. Therefore, even if no impedance is actually inserted, the cross current can be suppressed by adding the K · Idc path.

Consider the design of K. Since the equivalent impedance is only a resistance component, K is a constant.
When the DC system voltage is 345 V ± 8 V and the unit rating is 10 kW, K is determined by the following equation.

K = ΔVdc · Vdcmin / Pu = 0.27 (Ω) (1)
However, ΔVdc: voltage fluctuation amount 8V, Vdcmin: DC voltage lower limit value 337V, Pu: rated power 10 kW.

  The relationship between the output voltage Vdc and the output current Idc is as shown in FIG. The slope is the equivalent resistance, and the area surrounded by the two-dotted line is the rated power.

When connecting units of different capacities, the equivalent resistance K may be a value calculated by the equation \ ref {eq_k}. For a unit rated at 5 kW, K = 0.54.
In FIG. 4, the broken line indicates the relationship between the output voltage Vdc and the output current Idc of the 5 kW unit. When a unit of 5 kW and a unit of 10 kW are connected and Vdc = 340V, the current flowing out from each unit is Idc10k = (345-340) / (0.27) = 18.5A (point B in FIG. 4)
Idc5k = (345-340) / (0.54) = 9.25A (point A on FIG. 4)
However, the current flows out from the unit of Idc10k: 10kW, and the current flows out of the unit of Idc5k: 5kW, so that a current proportional to the unit capacity can be passed.

2. Control of Power Generation Unit In the solar power generation unit, the MPPT controller generates a current command Ipv ^* that maximizes the generated power. The current controller performs PWM operation on the step-up chopper so that the current of the solar panel follows this command value. The power generation suppressor limits Ipv ^* to an appropriate value when the DC voltage increases. In the wind power generation unit, the MPPT controller generates a rotational speed command value ω ^* that maximizes the generated power. The speed controller generates a torque current command value Iwgq ^* such that the rotational speed ω of the windmill becomes ω ^* . The current controller performs PWM operation on the inverter so that Iwgq ^* becomes Iwgq. Like the solar power generation unit, the power generation suppressor limits Iwgq ^* to an appropriate value when the DC voltage increases.

  A power generation unit such as a solar or wind power generation unit is controlled so that it can be seen as a current source when viewed from the DC system as shown in FIG. That is, current control is performed so as to output a current of a command value given from the MPPT controller. DC voltage is not controlled. Since it is connected to the DC system as a current source, no cross current flows between the power generation unit and other units. The DC system voltage is determined by the unit that controls the DC voltage.

  For example, consider the DC system voltage when only one power generation unit and one interconnection unit are connected to the DC system. FIG. 5A shows an equivalent circuit. When a current of 10 A is output from the power generation unit, the DC system voltage Vdc is Vdc = 345 + 0.27 × 10 = 347.7 $ V if the equivalent resistance of the interconnection unit is 0.27Ω.

3. Autonomous coordinated control of interconnection unit and power storage unit In the case of a distributed power source with a power storage unit, if the generated power is surplus with respect to the load power, that power is stored in the storage unit, and if the generated power is insufficient, it is released from the storage unit Want to.
It is better not to exchange power from the AC system via the interconnection unit as much as possible. But,
1. In the control method described in the section, the interconnection unit and the power storage unit share the power equally.

  Therefore, as shown in FIG. 6, the equivalent resistance characteristics of the interconnection unit and the power storage unit are made variable according to the value of the DC voltage. In this figure, in the range of 345V ± 6V, the equivalent resistance of the power storage unit is much smaller than the equivalent resistance of the interconnection unit, and when it exceeds ± 6V, the equivalent resistance of the power storage unit becomes larger than the equivalent resistance of the interconnection unit. For example, when the generated power is 16A and the DC system voltage is 349V, the power storage unit 15A (point a1) and the interconnection inverter 1A (point a2) share, and power storage is preferentially performed. When the generated power is 48 A and the DC system voltage is 352.5 V (when the rating of the power storage unit is exceeded), the power storage unit 27A (point b1) and the interconnection inverter 21A (point b2) are shared.

  The equivalent resistance of the interconnection unit is reduced, and power that cannot be absorbed by the power storage unit is absorbed by the interconnection unit and regenerated to the AC system.

It is a figure which shows the distributed power supply system connected to the direct current bus. It is a figure which shows control operation mode switching by the direct current voltage of a conventional system. It is a figure which shows the DC voltage control system of a connection / power storage unit. It is a figure which shows the relationship between DC voltage-DC output current. It is a figure which shows the direct current | flow output control method of an electric power generation unit. It is a figure which shows the electric power sharing of a connection unit and an electric power storage unit.

Claims (1)

A DC bus that is allowed to vary in voltage within a predetermined range; and
A plurality of power supply units connected to the DC bus, wherein power is exchanged with the DC bus, and the amount of power exchange autonomously determined based on the DC bus voltage;
In a distributed power system comprising:
The power supply unit operates as a voltage source connected to a power source that inputs and outputs current, and a DC voltage controller that sets a current command value so that a voltage at a connection end of the DC bus becomes a voltage command value. And a current controller for controlling the current input / output to / from the power source to be the current command value,
The DC voltage controller detects a current input / output to / from the DC bus, and subtracts a value obtained by multiplying the detected current value by a predetermined gain from the voltage command value. Make corrections
The plurality of power supply units include first and second power supply units, and the gain corresponding to the first power supply unit when the voltage of the DC bus is included in a predetermined range. When the voltage of the DC bus is higher or lower than the predetermined range, the gain corresponding to the first power supply unit is smaller than the gain corresponding to the second power supply unit. Is set to a value larger than the gain corresponding to the second power supply unit ,
The first power supply unit is a power storage unit to which a battery is connected as the power supply,
The second power supply unit is distributed power supply system, characterized in interconnection unit der Rukoto the AC system is connected as the power source.

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