TWI691138B - Energy-storing power converter switching between low-voltage-ride-through mode and island mode and control method thereof - Google Patents

Abstract

An energy-storing power converter is provided. The power converter switches between a low-voltage-ride-through (LVRT) mode and an island mode. A control strategy can be employed to the power converter for utilities of energy storage, solar energy, wind energy, etc. to be applied in a micro-grid system having renewable energy. The power converter is operated in a real/reactive power quality (PQ) mode or a voltage/frequency (VF) mode. When an abnormal voltage (e.g., voltage dips) at a connecting point to the mains is detected, the power converter needs to be able to control output current for LVRT. If the low-voltage duration exceeds the limit of IEEE 1547A (decentralized parallel power connection) specification, the power converter triggers and switches the connecting point to turn the micro-grid into an island mode. At the same time, the energy-storing system is operated in the VF mode to establish a reference voltage source for a micro-grid system or a virtual plant. Thus, local loads and utilities of decentralized power and renewable energy are maintained in stable operations; the use time of renewable energy is increased; and, the operation stability of the micro-grid system is improved.

Description

Energy storage power conversion device with low voltage ride-through and island mode switching and control method

The present invention relates to an energy storage power conversion device and control method with low voltage ride-through and island mode switching, in particular to a power converter that can be used for energy storage systems, solar energy, wind energy, etc. Applied to microgrid systems containing renewable energy.

In response to the government's energy-saving and carbon-reduction policies, renewable energy power generation must account for at least 20% of the total power generation in Taiwan by 2025. Currently, the government is actively promoting the construction of renewable energy power generation. Because intermittent renewable energy can cause voltage fluctuations in the distribution system, in order to stabilize the disturbance of renewable energy and stabilize the voltage of the distribution system, when the microgrid is connected in parallel with the mains terminal, it can be operated in the voltage/frequency (VF) mode through the energy storage system In order to achieve the effect of quickly stabilizing the voltage of the parallel connection point between the microgrid and the mains terminal, so as to increase the grid connection capacity of renewable energy.

According to the above, when the amount of renewable energy connected to the grid is gradually increasing, in order to stabilize the voltage of the distribution system, the energy storage system will operate in the VF mode. However, if an abnormal situation such as a sudden voltage drop at the mains side occurs, the current energy storage system on the market Operating in VF mode in the grid mode and failing to control and recover the fault current in real time, causing the energy storage system to trip without the low voltage ride through (LVRT) function, which prevents the energy storage system from being abnormal when the power system is abnormal , Continue to connect to the grid, resulting in increased speed of power system collapse. In addition, according to IEEE The 1547A (Decentralized Power Supply Parallel) specification requires that the distributed power supply must be tripped, causing the microgrid system to be completely black, making the load in the microgrid system unusable and reducing the utilization rate of renewable energy.

Therefore, how can a microgrid system including decentralized power sources such as renewable energy sources operate in real power/virtual power (PQ) mode or VF mode in an energy storage system, with functions such as LVRT, current control, and island mode switching, This ensures that the microgrid can continue to operate during periods of low voltage on the mains side. And to achieve the stable operation of renewable energy and users in the micro-grid system, increase the use time of distributed power sources such as renewable energy, and improve the operational stability of the micro-grid system, such technologies are still lacking.

In view of the shortcomings of the conventional standard of paralleling with the distributed power supply during the low voltage period of the city power terminal, and in order to maintain the grid connection of the microgrid system during system abnormalities, it is important to increase the load utilization rate and renewable energy utilization rate in the microgrid system. The inventor of the present case is anxious to invent a "storage power conversion device and control method with low voltage ride-through and island mode switching" to ensure that the microgrid can continue to operate during the low voltage period of the mains side; and make the microgrid system Renewable energy and users maintain stable operation, increase the use time of distributed power sources such as renewable energy, and improve the operational stability of microgrid systems.

The main purpose of the present invention is to overcome the above-mentioned problems encountered in the conventional arts, and to provide an energy storage power conversion device and control method with low voltage ride-through and island mode switching. The adopted control strategy can be used in energy storage systems Power converters for solar, solar, or wind power equipment are used in microgrid systems containing renewable energy. When the power converter is operating in PQ mode or VF mode, if the voltage of the parallel junction of the commercial power is detected to be abnormal (For example, voltage sag), the power converter needs to control the output fault current for low voltage ride-through. If the low voltage duration exceeds the limit of IEEE 1547A (distributed power supply parallel) specification, Then the power converter triggers and the contact switch trips, turning the microgrid system into island operation, while the energy storage system is operating in VF mode, establishing a reference voltage source for the microgrid system or virtual power plant to disperse the load and spread within the range Power supply, renewable energy and other equipment can maintain stable operation. When the voltage of the parallel connection between the microgrid system and the mains terminal returns to normal, synchronous parallel connection through phase-lock loop (PLL) control and other methods to restore to the mains Run in parallel.

To achieve the above purpose, the energy storage power conversion device provided by the present invention with low voltage ride-through and island mode switching is applied in a microgrid system to provide an energy storage system, a renewable energy source, a load and other distributed power sources The three-phase power line is connected to a mains terminal through a parallel contact switch. The energy storage power conversion device is provided in the energy storage system. It includes: a power converter connected to the three-phase power line; the DC side, the system It is connected to the power converter; and a control strategy unit is connected to the parallel contact switch and the power converter. When the energy storage system runs in parallel with the mains terminal, the state of the power converter is measured first The initial value, and then determine whether the power converter is operating in PQ mode or VF mode, and then detect whether the voltage of the parallel contact switch is within the operating range, adjust the output current of the power converter, so that the mains terminal can be abnormal Low voltage ride-through, and when the abnormal duration of the mains voltage exceeds the IEEE 1547A (distributed power supply parallel) specification, the power converter is commanded to trigger the parallel contact switch to trip, so that the microgrid system is converted to an island mode of operation After the mains terminal restores normal voltage, it will resume parallel operation with the mains terminal, so that the load, decentralized power supply and renewable energy in the microgrid system can be continuously used.

In the above embodiments of the present invention, the energy storage power conversion device may also be installed in the renewable energy source.

In the above embodiment of the present invention, the control strategy unit can stably control the output current of the power converter in any mode when the voltage of the commercial power terminal suddenly drops, and perform low voltage Through, the micro-grid system is continuously connected in parallel with the mains terminal.

In the above embodiment of the present invention, the control strategy unit instructs the power converter to trigger the parallel contact switch to trip, so that the microgrid system is converted to the island operation mode, and at the same time the power converter is operated in the VF mode to establish The reference voltage source of the micro-grid system enables the load, decentralized power and renewable energy in the micro-grid system to maintain stable operation. After the voltage of the parallel contact between the micro-grid system and the municipal power terminal returns to normal, the phase-locking The loop regulates the parallel contact switch to perform synchronous parallel connection and resumes parallel operation with the mains terminal.

In the above embodiment of the present invention, the operating range is between 0.88 p.u. and 1.1 p.u.

In order for your reviewing committee to have a further understanding and understanding of the features, purposes and functions of the present invention, the detailed structure and design rationale of the present invention are explained by the following embodiments so that the reviewing committee can understand the present invention Features.

1: Microgrid system

11: Energy storage system

111: Power converter

112: DC side

113: Control strategy unit

12: Renewable energy

13: load

14: Other distributed power supplies

15: Parallel contact switch

16: Power line

2: Mains terminal

s11~s20: steps

Figure 1 is a schematic diagram of the microgrid architecture of the present invention.

Figure 2 is a flow chart of the control method of the energy storage power conversion device with low voltage ride through and island mode switching according to the present invention.

Figure 3 is a schematic diagram of the voltage and frequency Droop slope of the present invention.

Figure 4 is a schematic diagram of the output current cross-axis components of the energy storage system of the present invention during a low voltage period.

Please refer to "Figure 1 ~ Figure 4", which are respectively the schematic diagram of the microgrid architecture of the present invention, the flowchart of the control method of the energy storage power conversion device with low voltage ride-through and island mode switching of the present invention, the invention A schematic diagram of the voltage and frequency drop (Droop) slope, and a schematic diagram of the output current cross-axis components of the energy storage system of the present invention during a low voltage period. As shown Shown: The present invention is an energy storage power conversion device and control method with low voltage ride-through and island mode switching. It is a control strategy for power converters used in energy storage systems, solar energy, or wind energy equipment. It can be applied to In the micro-grid system of renewable energy, by controlling the output current of the power converter, the function of low voltage ride through (LVRT) can be achieved when the mains terminal is abnormal, and the duration of the abnormal mains terminal voltage reaches IEEE 1547A ( When the distributed power supply is connected in parallel), the micro-grid system is ordered to switch to the island operation mode. After the mains terminal is restored, it will resume parallel operation with the mains terminal. The microgrid system 1 architecture of FIG. 1 of this embodiment at least includes an energy storage system 11, a renewable energy source 12, a load 13, and other distributed power sources 14 through a parallel contact switch 15 to a three-phase power line 16 and a mains terminal 2 connection, the energy storage power conversion device is installed in the energy storage system 11, which includes a power converter 111 connected to the three-phase power line 16, a DC side 112 connected to the power converter 111, and a The control strategy unit 113 connected to the parallel contact switch 15 and the power converter 111. The control strategy of the present invention is to detect and contact the voltage of the switch 15 near the mains terminal 2, and control the output current of the power converter 111 of the energy storage system 11 through the adopted control strategy. When the mains terminal 2 has a sudden voltage drop, it can be Stably control the output current of power converter 111 in any mode, perform LVRT, and continuously connect microgrid system 1 and mains terminal 2 in parallel, but if it exceeds the IEEE 1547A (distributed power supply parallel) specification, the power converter 111 is commanded to trigger The parallel contact switch 15 trips to turn the microgrid system into an island operation mode. After the mains power returns to normal voltage, it will resume parallel operation with the mains terminal 2. Through this control strategy, the load in the microgrid system 1 can be enabled 13. The decentralized power supply 14 and renewable energy 12 are continuously used.

The control strategy flow adopted by the energy storage power conversion device provided by the present invention with low voltage ride-through and island mode switching is shown in Figure 2. After the control strategy is started, the process proceeds to step s11 when the energy storage system and the commercial power terminal are operated in parallel , The initial value of the state of the energy storage system (V/F/P/Q) is measured first, and then at step s12 it is determined that the power converter of the energy storage system is operating in the PQ mode or the VF mode. First, if the power converter of the energy storage system is operating in the VF mode, proceed to step s13, according to the voltage and frequency Droop slope set by the user in the energy storage system (V droop and f droop, as shown in Figure 3), The reference values of voltage and frequency (V_reference command and f_reference command), the energy storage system will control the output real power and virtual power according to the actual voltage and frequency in the microgrid system, and then in step s14 will determine the microgrid system and the mains Whether the terminal parallel contact voltage (Vpcc) is within the operating range, that is, between 0.88pu and 1.1pu, if it is within the normal range, then return to step s13, the energy storage system needs to automatically output the actual value according to the voltage and frequency Droop slope Power and virtual power; if it is less than 0.88pu, then enter LVRT during step s15. At this time, the energy storage system needs to control the output current of the power converter. The output current can be divided into a straight axis component (Id) and a cross axis component ( Iq), where Id is fixed to the current direct axis component (Id ₀ ) when the Vpcc voltage is 0.88pu; and the initial value of Iq is the current cross axis component (Iq ₀ ) when the Vpcc voltage is 0.88pu, but if the Vpcc voltage is low At 0.88pu, you need to increase the output current cross-axis component (as shown in Figure 4), and the maximum output current cross-axis component (Iq _m ) is limited by formula (1) to not exceed the energy storage system The principle is twice the rated current (I _rated ). Next, at step s16, it is determined whether the LVRT time exceeds the limits of the IEEE 1547A (Distributed Power Parallel) specification (as shown in Table 1), and whether the microgrid transition signal is received. If the grid transition signal is returned to step s14, it is determined whether the Vpcc voltage has recovered to between 0.88pu and 1.1pu. If the voltage returns to normal, then according to step s13, the Droop slope and voltage according to the voltage and frequency set by the user in the energy storage system With the reference value of frequency, the energy storage system controls the output real power and virtual power according to the actual voltage and frequency in the microgrid system; if the Vpcc voltage is still lower than 0.88pu, then continue to control the energy storage system output as step s15 The straight axis component (Id) and the cross axis component (Iq) of the current. However, if the clearing time is reached, the specification requires that the decentralized equipment must be tripped, then go to step s17 and the energy storage system sends a trip signal to the parallel contact switch to trip the switch to isolate the microgrid system from the mains terminal, After the power grid transition signal, as in step s18, the energy storage system is switched to the island operation mode, and the voltage is set to 220V and the frequency is 60Hz, which is used as the reference power source of the microgrid system. Then, in step s19, continue to detect whether the Vpcc voltage returns to normal. If the Vpcc voltage is still lower than 0.88pu, then return to step s18 to maintain the island operating mode; but if the Vpcc voltage returns to between 0.88pu and 1.1pu Then, entering step s20 can restore the parallel connection of the microgrid system and the commercial power terminal through the phase-locked loop.

Secondly, if the power converter of the energy storage system is operating in the PQ mode, step s21 is entered, and the output real power and virtual power (P command and Q command) set by the user in the energy storage system are controlled to control the output real power and The virtual power, then in step s22, it will be determined whether the microgrid system Vpcc is within the operating range, that is, between 0.88pu and 1.1pu, if it is within the normal range, then return to step 21, the energy storage system needs to output the actual value according to the set value Power and virtual power; if it is lower than 0.88pu, then enter LVRT during step s23. At this time, the energy storage system needs to control the output current of the power converter. The output current can be divided into a straight axis component (Id) and a cross axis component ( Iq), where Id is fixed to the current direct axis component (Id ₀ ) when the Vpcc voltage is 0.88pu; and the initial value of Iq is the current cross axis component (Iq ₀ ) when the Vpcc voltage is 0.88pu, but if the Vpcc voltage is low At 0.88pu, you need to increase the output current cross-axis component (as shown in Figure 4), and the maximum output current cross-axis component (Iq _m ) is limited by formula (1) to not exceed the energy storage system Two times the rated current is the principle. Next, at step s24, it is determined whether the LVRT time exceeds the limits of the IEEE 1547A (Distributed Power Parallel) specification (as shown in Table 1), and whether the microgrid transition signal is received. If the grid transition signal is returned to step s22, it is determined whether the Vpcc voltage is restored to between 0.88pu and 1.1pu. If the voltage returns to normal, then step s21 is based on the real power and virtual power set by the user in the energy storage system. Control the real power and virtual power of the output; if the Vpcc voltage is still lower than 0.88pu, then continue to control the direct axis component (Id) and the cross axis component (Iq) of the energy storage system output current as in step s23. However, if the clearing time is reached, the specification requires that the decentralized equipment must be tripped, then go to step s17 and the energy storage system sends a trip signal to the parallel contact switch to trip the switch to isolate the microgrid system from the mains terminal, After the power grid transition signal, as in step s18, the energy storage system is switched to the island operation mode, and the set voltage is 220V and the frequency is 60Hz, which is used as the reference power source of the microgrid system. Then, in step s19, continue to detect whether the Vpcc voltage returns to normal. If the Vpcc voltage is still lower than 0.88pu, then return to step s18 to maintain the island operating mode; but if the Vpcc voltage returns to between 0.88pu and 1.1pu Then, entering step s20 can restore the parallel connection of the microgrid system and the commercial power terminal through the phase-locked loop.

Accordingly, the technical features of the present invention are described as follows:

1. An energy storage power conversion device and control method with low voltage ride-through and island mode switching provided by the present invention can be used for electricity in energy storage systems, solar energy, or wind energy equipment Force converters are used in microgrid systems containing renewable energy.

2. The invention enables the energy storage power conversion device to operate in the PQ mode or VF mode under the parallel connection of the commercial power. When the voltage of the commercial power terminal is abnormal, it can maintain the parallel operation without tripping immediately.

3. The present invention enables the energy storage power conversion device not to shut down the microgrid system when the abnormal duration of the mains voltage reaches the IEEE 1547A (distributed parallel power supply) specification, but to change the microgrid system to the islanding mode of operation. The load, decentralized power supply, renewable energy and other equipment in the power grid system can maintain stable operation, increase the use time of decentralized power supply such as renewable energy, and improve the operation stability of the microgrid system.

In summary, the present invention is an energy storage power conversion device and control method with low voltage ride-through and island mode switching, which can effectively improve the various shortcomings of the conventional. The control strategy adopted by the energy storage power conversion device can make the micro The grid system is still connected to the mains terminal during the low voltage period to avoid aggravating the voltage breakdown of the mains terminal. However, when the time required to trip is required by the IEEE 1547A (distributed power supply parallel) specification, it is switched to an island operation to make the microgrid The load and decentralized power supply can still continue to operate, increase the use time of decentralized power supply such as renewable energy, and improve the operation stability of the microgrid system, so that the production of the present invention can be more advanced, more practical, and more in line with users What is necessary has indeed met the requirements for the application for an invention patent, and the patent application has been filed in accordance with the law.

However, the above are only preferred embodiments of the present invention, which should not be used to limit the scope of implementation of the present invention; therefore, simple equivalent changes and modifications made according to the scope of the patent application of the present invention and the content of the invention description , Should still fall within the scope of this invention patent.

1: Microgrid system

11: Energy storage system

111: Power converter

112: DC side

113: Control strategy unit

12: Renewable energy

13: load

14: Other distributed power supplies

15: Parallel contact switch

16: Power line

2: Mains terminal

Claims (8)

An energy storage power conversion device with low-voltage ride-through and island mode switching is used in a micro-grid system for supplying an energy storage system, a renewable energy source, a load, and other distributed power sources through a parallel contact switch to three-phase The power line is connected to a commercial power terminal, and the energy storage power conversion device is provided in the energy storage system, which includes: a power converter connected to the three-phase power line; the DC side is connected to the power converter; and A control strategy unit is connected to the parallel contact switch and the power converter. When the energy storage system runs in parallel with the mains terminal, the initial value of the state of the power converter is measured first, and then the power conversion is judged The device operates in real power/virtual power (PQ) mode or voltage/frequency (VF) mode, and then detects whether the voltage of the parallel contact switch is within the operating range, and regulates the output current of the power converter to make the mains terminal Low voltage ride through (LVRT) can be performed when abnormal, and when the abnormal duration of the mains voltage exceeds the IEEE 1547A (decentralized power supply parallel) specification, the power converter is ordered to trigger the parallel contact switch to jump Off, turning the microgrid system into an island operation mode, and after the mains terminal restores normal voltage, it can resume parallel operation with the mains terminal, thereby continuously using the load, decentralized power and renewable energy in the microgrid system . The energy storage power conversion device with low voltage ride-through and island mode switching as described in item 1 of the patent scope, wherein the energy storage power conversion device can also be installed in the renewable energy source. The energy storage power conversion device with low voltage ride-through and island mode switching as described in item 1 of the patent scope, wherein the control strategy unit is capable of stable control in any mode when a sudden voltage drop occurs at the mains terminal The power converter output current, into Perform LVRT to continuously parallel the micro-grid system with the mains terminal. The energy storage power conversion device with low voltage ride-through and island mode switching as described in item 1 of the patent scope, wherein the control strategy unit commands the power converter to trigger the parallel contact switch to trip, so that the microgrid The system is switched to the island operation mode, and the power converter is operated in the VF mode, and the reference voltage source of the microgrid system is established, so that the load, decentralized power supply and renewable energy in the microgrid system can maintain stable operation. After the voltage of the micro-grid system and the parallel contact of the mains terminal returns to normal, the parallel contact switch is controlled and synchronized in parallel through a phase-lock loop (PLL) to resume parallel operation with the mains terminal. The energy storage power conversion device with low voltage ride-through and island mode switching as described in item 1 of the patent scope, wherein, when the power converter operates in the VF mode, it is based on the voltage set by the user in the energy storage system The reference values of the slope, voltage and frequency of the droop frequency, the power converter will control the output real power and virtual power according to the actual voltage and frequency in the microgrid system, and the control strategy unit will judge the Whether the voltage of the parallel contact switch between the microgrid system and the mains terminal is within the operating range of 0.88pu to 1.1pu, if it is within the normal range, the power converter needs to output automatically according to the voltage and frequency Droop slope Real power and virtual power; if it is less than 0.88pu, then enter the LVRT period, at this time need to control the output current of the power converter, the output current can be divided into straight axis component (Id) and cross axis component (Iq), where Id is fixed to the current direct axis component (Id ₀ ) when the Vpcc voltage is 0.88pu; and the initial value of Iq is the current cross axis component (Iq ₀ ) when the Vpcc voltage is 0.88pu, but if the Vpcc voltage is lower than 0.88pu , The cross-axis component of the output current needs to be increased, and the maximum cross-axis component of the output current (Iq _m ) is limited by the formula (I), with the principle of not exceeding twice the rated current (I _rated ) of the energy storage system, The formula (1) is as follows:

An energy storage power conversion device with low voltage ride through and island mode switching as described in item 5 of the patent scope, wherein, when the control strategy unit determines that the LVRT time exceeds the limit of the IEEE 1547A (distributed power parallel connection) specification, Then the power converter is commanded to send a trip signal to the parallel contact switch, so that the switch trip isolates the micro-grid system from the mains terminal, so that the micro-grid system is switched to an island operation mode, and continuously detects the parallel connection Whether the voltage of the point switch returns to normal. If the voltage of the parallel point switch returns to between 0.88pu and 1.1pu, the micro-grid system can be restored in parallel with the mains terminal through a phase-locked loop. The energy storage power conversion device with low voltage ride through and island mode switching as described in item 1 of the patent scope, wherein, when the power converter operates in the PQ mode, it is based on the actual setting of the user in the energy storage system Power and virtual power to control the output real power and virtual power, and the control strategy unit will determine whether the voltage of the parallel contact switch between the microgrid system and the mains terminal is within the operating range of 0.88pu to 1.1pu In the normal range, the power converter needs to output real power and virtual power according to the set value; if it is less than 0.88pu, it enters the LVRT period, at this time it is necessary to control the output current of the power converter, the output current It can be divided into a straight axis component (Id) and a cross axis component (Iq), where Id is fixed to the current straight axis component (Id ₀ ) when the Vpcc voltage is 0.88pu; and the initial value of Iq is when the Vpcc voltage is 0.88pu The current cross-axis component (Iq ₀ ), but if the Vpcc voltage is lower than 0.88pu, the output current cross-axis component needs to be increased, and the maximum output current cross-axis component (Iq _m ) is limited by formula (1), Taking the principle of not exceeding twice the rated current (I _rated ) of the energy storage system, the formula (1) is as follows:

The energy storage power conversion device with low voltage ride-through and island mode switching as described in item 7 of the patent scope, wherein, when the control strategy unit determines that the LVRT time exceeds the limit of the IEEE 1547A (distributed power parallel connection) specification, Then the power converter is commanded to send a trip signal to the parallel contact switch, so that the switch trip isolates the micro-grid system from the mains terminal, so that the micro-grid system is switched to an island operation mode, and continuously detects the parallel connection Whether the voltage of the point switch returns to normal. If the voltage of the parallel point switch returns to between 0.88pu and 1.1pu, the micro-grid system can be restored in parallel with the mains terminal through a phase-locked loop.

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