CN109950969A - An emergency power supply for substation DC system based on photovoltaic backup - Google Patents

Abstract

The invention discloses a kind of transformer station direct current system emergency power supply spare based on photovoltaic, the power supply includes the double power supply converting switch connecting with substation two sections of ac bus, DC-AC inverter, photovoltaic DC-DC current transformer and two are connected to the isolated form DC-DC current transformer of transforming plant DC bus.Emergency power supply of the present invention is in station AC system maintenance or power loss, or station, with charger damage or when overhauling, roof of transformer substation photovoltaic realizes redundant power supply, while passing through the seamless incision of isolation DC-DC current transformer realization, the risk of only storage battery power supply is reduced, system redundancy and reliability are improved；When normal operation, photovoltaic electricity can be uploaded to ac bus by double power supply converting switch, reduce operating cost；It can also act as battery automatic discharging circuit, reduce operation operating procedure, improve safety coefficient；It is very suitable for transforming plant DC bus emergency guarantee field.

Description

An emergency power supply for substation DC system based on photovoltaic backup

technical field

The invention relates to an emergency power supply for a direct current system of a substation based on photovoltaic backup, and belongs to the technical field of power electronics.

Background technique

In recent years, with the advancement of technology and the reduction of cost, photovoltaic power generation has been widely used. Photovoltaic power generation is a renewable energy source, which can not only effectively reduce pollution, but also effectively control the flow of power through the inverter. At the same time, with the development of the economy, the number and scale of substations are getting larger and larger, but the requirements for power supply reliability are also increasing, so the design requirements of substations are also getting higher and higher. Although the multi-segment DC bus is powered by multiple chargers and battery packs, the report shows that the DC bus of the substation still has certain potential safety hazards. The normal operation of electric power enterprises has caused certain economic losses and social impacts.

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the present invention provides an emergency power supply for the DC system of the substation based on photovoltaic backup. When the station AC system is overhauled or lost, or the station charger is damaged or overhauled, the rooftop photovoltaic of the substation realizes redundant power supply. At the same time, seamless switching is achieved by isolating the DC-DC converter, reducing the risk of only battery power supply, and improving system redundancy and reliability; during normal operation, the photovoltaic power can be uploaded to the AC bus through the dual power switch, reducing operating costs. ; It can also act as an automatic discharge circuit of the battery, reducing the operation steps and improving the safety factor; it is very suitable for the field of emergency protection of the DC bus of the substation.

The present invention adopts following technical scheme to realize:

An emergency power supply for a DC system of a substation based on photovoltaic backup, comprising a dual power switch, a DC-AC inverter, a photovoltaic DC-DC converter connected to the two sections of the AC bus of the substation, and two connected to the two sections of the substation respectively. Isolated DC-DC converter for DC bus;

The two sections of AC bus are respectively set as No. 1 AC bus and No. 2 AC bus;

The first power port of the dual power switch is connected to the station with the No. 1 AC bus, the second power port is connected to the station with the No. 2 AC bus, and the output port is connected to the AC side of the DC-AC inverter;

The DC-AC inverter adopts a PWM converter, the AC side of the DC-AC inverter is connected to the output port of the dual power switch through an inductor, and the DC side of the DC-AC inverter is connected to the emergency power supply DC common bus, and is connected with DC filter capacitors in parallel;

The photovoltaic DC-DC converter is a non-isolated BOOST circuit, its input is connected to the busbar output of the photovoltaic array, and the output is connected to the emergency power supply DC public bus;

The two isolated DC-DC converters are respectively a first isolated DC-DC converter and a second isolated DC-DC converter, the first isolated DC-DC converter and the second isolated DC converter -The DC converter is two double half bridge converters (DHB), the middle is isolated by a high-frequency transformer, and the power can flow in both directions. 2 paragraphs.

The dual power switch is a commercially available Chint NZ7-125 intelligent switch.

When the station AC bus is in normal operation, the electric energy provided by the photovoltaic array flows into the emergency power DC common bus through the BOOST circuit, and then is output through the DC-AC inverter, and then enters the AC bus through the dual power switch to supply power to the substation AC load. When the station AC bus is out of service, the electric energy provided by the photovoltaic array flows into the emergency power DC common bus through the BOOST circuit, and then outputs through two isolated DC-DC converters to supply power to the substation DC load, reducing the power consumption when only the battery is powered. probability of failure.

When the station chargers are damaged, the electric energy provided by the photovoltaic array flows into the emergency power DC common bus through the BOOST circuit, and then outputs through two isolated DC-DC converters to supply power to the DC load of the substation; if the photovoltaic array cannot supply power, the DC - The AC inverter rectifies and absorbs power from the AC bus, stabilizes the DC common bus of the emergency power supply, and then outputs through two isolated DC-DC converters to supply power to the DC load of the substation, reducing the probability of failure when only the battery is powered.

When the battery needs to be discharged, there is no need to perform the discharge load wiring process. It only needs to send a command to the emergency power supply. The converter feeds back power to the emergency power DC common bus, then passes through the DC-AC inverter output, and finally enters the AC bus through the dual power switch to supply power to the AC load of the substation, and the battery can be discharged after a certain period of time. experiment.

The emergency power supply immediately detects the voltage of the DC bus of the substation. When the voltage of a certain section of the DC bus is lower than a certain threshold, it will automatically trigger the operation of the isolated DC-DC converter to ensure the stability of the DC voltage.

Beneficial effects achieved by the present invention:

1. Make full use of the substation roof for photovoltaic power generation and reduce the operating cost of the substation;

2. By means of photovoltaic power supplying DC bus, the reliability of DC bus power supply can be effectively improved when the AC bus fails;

3. Through the automatic control of the isolated DC-DC converter, the DC bus voltage can be stabilized and a short-term voltage drop can be prevented;

4. It can automatically act as a battery discharge device to detect the performance of the battery, and the power is fed back to the AC bus with low loss;

5. All control logic is automatically completed, and there is no obvious DC power-off process.

Description of drawings

1 is a schematic diagram of an emergency power supply of the present invention;

2 is a schematic diagram of a DC-AC inverter of the present invention;

3 is a schematic diagram of the photovoltaic array BOOST circuit of the present invention;

4 is a schematic diagram of an isolated DC-DC converter of the present invention;

Fig. 5 is the energy flow diagram a of the present invention;

Fig. 6 is the energy flow diagram b of the present invention;

Fig. 7 is the energy flow diagram c of the present invention;

Fig. 8 is the energy flow diagram d of the present invention;

Fig. 9 is the energy flow diagram e of the present invention;

Fig. 10 is the energy flow diagram f of the present invention;

Fig. 11 is the control flow chart of the present invention;

12 is a schematic diagram of the battery discharge principle of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings. The following examples are only used to illustrate the technical solutions of the present invention more clearly, and cannot be used to limit the protection scope of the present invention.

As shown in Figure 1, an emergency power supply for the DC system of a substation based on photovoltaic backup, the power supply includes a dual power switch connected to two AC busbars in the substation, a DC-AC inverter, and a photovoltaic DC-DC converter. converter, and two isolated DC-DC converters respectively connected to two DC busbars of the substation.

The first power port of the dual power switch is connected to the station's No. 1 AC bus, the second power port is connected to the station's No. 2 AC bus, and the output port of the dual power switch is connected to the AC side of the DC-AC inverter. .

As shown in Figure 2, the DC-AC inverter uses a PWM converter, which includes 3 phase inductors, 6 IGBTs and a DC filter capacitor. The 6 IGBTs form a three-phase bridge. The side is connected to the output port of the dual power switch, and the DC side of the DC-AC inverter is connected to the DC common bus of the emergency power supply;

As shown in Figure 3, the photovoltaic DC-DC converter is a non-isolated BOOST circuit, its input is connected to the busbar output of the photovoltaic array, and the output is connected to the emergency power DC common bus; the non-isolated BOOST circuit contains an IGBT ( S _pv ), a diode D _pv and an inductor L _pv , one end of the inductor L _pv is connected to the positive output terminal of the bus bar of the photovoltaic array, the other end of the inductor L _pv is connected to the node _Opv , and _Opv is connected to the diode D _pv The anode and the collector of the IGBT (S _pv ), the emitter of the IGBT (S _pv ) is connected to the negative output terminal of the bus bar of the photovoltaic array and the negative electrode of the common DC bus of the emergency power supply, and the cathode of the diode D _pv is connected to the common DC bus of the emergency power supply. positive electrode.

The isolated DC-DC converter adopts a dual half bridge (DHB); the first isolated DC-DC converter and the second isolated DC-DC converter are isolated by high-frequency transformers respectively. , the power can flow in both directions, its input is the emergency power supply DC common bus, and the output is connected to the first and second sections of the DC bus.

As shown in Figure 4, the dual half-bridge converter consists of 4 MOSFETs (S _D1 - S _D4 ), 4 capacitors (C _D1 - C _D4 ), an inductor L _D and a high frequency transformer T _D . The MOSFETs on the DC common bus side of the emergency power supply are S _D1 and S _D2 , the D pole of S _D1 is connected to the positive pole of the common bus, and the S pole of S _D1 is connected to the D pole of S _D2 , forming a neutral point O _D1 , S _D1 of S D1 The pole is connected to the negative pole of the common bus; one end of C _D1 is connected to the positive pole of the common bus, the other end of C _D1 is connected to one end of C _D2 , forming a neutral point O _D2 , and the other end of C _D2 is connected to the negative pole of the common bus; O _D1 is connected to one end of the inductor _LD , the other end of _LD is connected to one end of the primary side of the high-frequency transformer _TD , and the other end of the primary side of _{TD is connected to O D2 .} The MOSFETs on the 1st or 2nd stage of the DC bus are S _D3 and S _D4 . The D pole of S _D3 is connected to the positive pole of the 1st or 2nd stage of the DC bus, and the S pole of S _D3 is connected to the D pole of S _D4 , forming a neutral point O _D3 , and the S pole of S _D4 is connected to the 1st or 2nd stage of the DC bus The negative pole of the segment; one end of C _D3 is connected to the positive pole of the 1st or 2nd segment of the DC bus, the other end of C _D3 is connected to one end of C _D4 , forming a neutral point O _D4 , and the other end of C _D4 is connected to the 1st segment of the DC bus Or the negative pole of 2 segments; O _D3 is connected to one end of the secondary side of the high-frequency transformer _TD , and the other end of the secondary side of _{TD is connected to O D4 .} The driving pulses of S _D1 and S _D2 are square waves and complementary. The driving pulses of S _D3 and S _D4 are also square waves and complementary. There is a certain phase shift angle between the pulses of S _D1 and S _D3 , which is used to control the transmission. power.

As shown in FIG. 5 to FIG. 10 , the emergency power supply of the present invention mainly has five energy flow modes.

Figure 5 provides power for photovoltaics. First, the power is transmitted to the emergency power DC common bus through the BOOST circuit, and then the power is inverted and fed back to the AC bus through the DC-AC inverter for the AC load of the substation.

Figure 6 also provides power for photovoltaics. First, the power is transmitted to the DC common bus of the emergency power supply through the BOOST circuit, and then the power is supplied to the DC bus through the isolated DC-DC converter for use by the DC load of the substation.

Figure 7 provides power for the AC bus. First, it is rectified into the emergency power DC common bus power through the DC-AC inverter, and then the power is supplied to the DC bus through the isolated DC-DC converter for use by the DC load of the substation.

Figure 8 shows that the AC bus and photovoltaic jointly provide power. First, the power is transmitted to the emergency power DC common bus through the DC-AC inverter rectification and photovoltaic boost circuit, and then the power is supplied to the DC bus through the isolated DC-DC converter. For substation DC load use.

Figures 9 and 10 are battery discharge. First, through circuit switching, the isolated DC-DC converter transfers the battery power to the emergency power DC common bus in reverse, and then the DC-AC inverter is used to invert the power and feed it back to the AC bus. , for the AC load of the substation.

In order to achieve the above functions, the dual power switch control unit directly measures the voltages Vac1 and Vac2 of the two AC busbars, and selects the AC busbar segment to be put in according to the voltage conditions. Then switch on the live AC bus section. If the two AC bus sections are out of power, an alarm signal will be sent immediately and the photovoltaic power supply mode will be activated, as shown in Figure 6.

As shown in Figure 11, the control of the emergency power supply includes initialization, protection and control of each module, and its core control process includes the following steps:

1) Collect the voltage and current information of each channel, and complete the preliminary signal filtering and overvoltage and overcurrent protection judgment;

2) The photovoltaic module realizes MPPT adjustment according to the voltage Vpv, current Ipv of the photovoltaic array and the DC common bus voltage Vdc of the emergency power supply, controls the BOOST PWM pulse, and integrates the photovoltaic array into the DC link according to the maximum power tracking power generation;

3) The two isolated DC-DC converters adopt the output voltage closed-loop control mode, and calculate the PWM pulses of the power devices according to the voltage values measured by the respective DC bus sections, so as to maintain the stability of the two DC bus voltages Vdc1 and Vdc2;

4) The DC-AC inverter, the core unit of the emergency power supply, adopts the double closed-loop mode of the DC voltage outer loop and the current inner loop to control and balance the energy of the DC common bus of the emergency power supply, and to maintain the stability of the voltage Vdc of the DC common bus of the emergency power supply. Automatically realize multi-directional transmission of energy.

If the battery needs to be discharged, first start the interrupt program, and switch the position of the output circuit breaker according to the discharge battery command, and then control the reverse discharge power of the corresponding isolated DC-DC converter according to the battery discharge curve requirements, until the verification of the battery pack is completed. . In order to facilitate the discharge of the battery, as shown in Figure 12, the isolated DC-DC converter is also attached with an additional battery discharge branch, and through the switching of the DC circuit breakers K1 and K2, the DC bus can be powered by the charger and the battery can be supplied. Through the reverse discharge of the emergency device of the present invention, as shown in FIG. 9 and FIG. 10 , the energy is finally merged into the AC bus of the substation.

The above-mentioned emergency power source makes full use of the idle substation roof for photovoltaic power generation, which can prolong the maintenance time of the battery when the AC bus of the substation is out of power, reduce the overall risk of power loss of the substation, and effectively control the operating cost; it can also realize the battery automatic discharge experiment, And discharge energy feedback AC bus, low loss, very suitable for substation DC emergency protection field.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the technical principle of the present invention, several improvements and modifications can also be made. These improvements and modifications It should also be regarded as the protection scope of the present invention.

Claims (7)

1. An emergency power supply for the direct current system of a substation based on photovoltaic backup is characterized in that: comprising a dual power switch connected with two AC bus bars of the substation, a DC-AC inverter, a photovoltaic DC-DC converter, and two Isolated DC-DC converters respectively connected to two DC busbars in substations; The two sections of AC bus are respectively set as No. 1 AC bus and No. 2 AC bus; The first power port of the dual power switch is connected to the station with the No. 1 AC bus, the second power port is connected to the station with the No. 2 AC bus, and the output port of the dual power switch is connected to the AC side of the DC-AC inverter. 2 . The emergency power supply for the DC system of a substation based on photovoltaic backup according to claim 1 , wherein the DC-AC inverter adopts a PWM converter, and the AC side of the DC-AC inverter is connected to a dual power supply switch. 3 . The output port of the switch, the DC side of the DC-AC inverter is connected to the DC common bus of the emergency power supply. 3. The emergency power supply for a substation DC system based on photovoltaic backup according to claim 1, wherein the photovoltaic DC-DC converter is a non-isolated BOOST circuit, the input of which is connected to the busbar output of the photovoltaic array, The output terminal is connected to the emergency power supply DC common bus. 4 . The emergency power supply of the substation DC system based on photovoltaic backup according to claim 1 , wherein the two isolated DC-DC converters are a first isolated DC-DC converter and a second isolated DC-DC converter, respectively. 5 . DC-DC converter, the first isolated DC-DC converter and the second isolated DC-DC converter are two bidirectional double half-bridge converters, which are isolated by high-frequency transformers in the middle, and the power can be Two-way flow, its input is the emergency power DC common bus, and the output is connected to the first and second sections of the DC bus. 5. The control mode of the emergency power supply of the substation DC system based on photovoltaic backup according to claim 1, characterized in that, it specifically comprises: 1) When the station AC bus is in normal operation, the electric energy provided by the photovoltaic array flows into the emergency power DC common bus through the BOOST circuit, and then is output through the DC-AC inverter, and then enters the AC bus through the dual power switch, and supplies AC to the substation. load power supply; 2) When the station AC bus is out of service, the electric energy provided by the photovoltaic array flows into the emergency power DC common bus through the BOOST circuit, and then is output through two isolated DC-DC converters to supply power to the substation DC load, reducing only the storage battery. The probability of failure when supplying power; 3) When the station chargers are damaged, the electric energy provided by the photovoltaic array flows into the emergency power supply DC common bus through the BOOST circuit, and then outputs through two isolated DC-DC converters to supply power to the substation DC load; if the photovoltaic array cannot Power supply, DC-AC inverter rectifies and absorbs power from the AC bus, stabilizes the DC common bus of the emergency power supply, and then outputs through two isolated DC-DC converters to supply power to the DC load of the substation, reducing the probability of failure when only the battery is powered ; 4) When the battery needs to be discharged, there is no need to perform the discharge load wiring process, but only need to send an instruction to the emergency power supply. - The DC converter feeds back to the DC common bus of the emergency power supply, and then outputs through the DC-AC inverter, and finally enters the AC bus through the dual power switch to supply power to the AC load of the substation, which can be realized after a certain period of time. Battery discharge experiment. 6 . The control mode of the emergency power supply of the substation DC system based on photovoltaic backup according to claim 5 , wherein, in the control mode, the emergency power supply detects the voltage of the DC bus of the substation immediately, and when a certain section of the DC bus When the voltage is lower than a certain threshold, the isolated DC-DC converter is automatically triggered to operate to ensure the stability of the DC voltage. 7. A method for controlling emergency power supply of substation DC system based on photovoltaic backup according to claim 1, characterized in that, comprising the following steps: 1) Collect the voltage and current information of each channel, and complete the preliminary signal filtering and overvoltage and overcurrent protection judgment; 2) The photovoltaic module realizes MPPT adjustment according to the voltage Vpv, current Ipv of the photovoltaic array and the DC common bus voltage Vdc of the emergency power supply, controls the BOOST PWM pulse, and integrates the photovoltaic array into the DC link according to the maximum power tracking power generation; 3) The two isolated DC-DC converters adopt the output voltage closed-loop control mode, and calculate the PWM pulses of the power devices according to the voltage values measured by the respective DC bus sections, so as to maintain the stability of the two DC bus voltages Vdc1 and Vdc2; 4) The AC-DC inverter, the core unit of the emergency power supply, adopts the double closed-loop mode of the DC voltage outer loop and the current inner loop to control and balance the energy of the DC common bus of the emergency power supply, and maintain the stability of the voltage Vdc of the emergency power supply DC common bus. Automatically realize multi-directional transmission of energy.