WO2023221203A1

WO2023221203A1 - Three-phase imbalance output control method and system therefor

Info

Publication number: WO2023221203A1
Application number: PCT/CN2022/097822
Authority: WO
Inventors: 刘超厚; 安天宏
Original assignee: 浙江艾罗网络能源技术股份有限公司
Priority date: 2022-05-17
Filing date: 2022-06-09
Publication date: 2023-11-23
Also published as: CN114844065A

Abstract

A three-phase imbalance output control method and a system therefor. The method comprises: by using the sum Pac of output powers of three phases, the sum Pexport of grid-connected port powers of the three phases, and a limit value PexprotLimit of the grid-connected port powers of the three phases, and adjusting the output powers, enabling the sum Pexport of the grid-connected port powers of the three phases to be 3 × PexprotLimit, and limiting the grid-connected port powers of two of the three phases to be PexprotLimit, so as to realize three-phase imbalance output. The system therefor comprises several photovoltaic modules, wherein an output side of each photovoltaic module is correspondingly connected to a DC/DC converter and a DC/AC converter; and the DC/AC converter is connected to a three-phase line terminal and a neutral wire terminal of a three-phase mains supply by means of four relays.

Description

Three-phase unbalanced output control method and system

Technical field

The invention relates to an output control method, in particular to a three-phase unbalanced output control method and its system.

Background technique

With the development of society and the progress of science and technology, people's demand for energy is also increasing. Facing the shortage of traditional energy, the development of new energy technology is supported by national policies, and solar energy is an inexhaustible source of energy. Clean energy and photovoltaic power generation technology have developed rapidly, and the installed capacity of photovoltaic power generation systems has also increased year by year. However, photovoltaic power generation is greatly affected by the environment. Its power generation changes with changes in lighting conditions. It is an unstable energy source. When a large number of photovoltaic systems are connected to the traditional power grid system, it will have an impact on the stability of the power grid system. ; Therefore, power companies in some countries and regions have put forward requirements for users of photovoltaic grid-connected power generation systems to use them spontaneously and do not allow grid-fed power.

Currently, the existing three-phase photovoltaic grid-connected power generation systems are three-phase balanced output systems, which can achieve zero grid-connected power control of the sum of the three-phase grid-connected power. However, when the user load has three-phase unbalance, each phase cannot be achieved. In the case of zero grid-connected power control of the grid-connected port power, there will be situations where some phases have grid-fed power and some phases need to draw power from the mains. Therefore, the current three-phase grid-connected power generation system cannot simultaneously meet the requirements of being friendly to the traditional power grid system, realizing self-use and improving photovoltaic energy utilization.

Contents of the invention

The object of the present invention is to provide a three-phase unbalanced output control method and its system. The invention can simultaneously meet the requirements of being friendly to the traditional power grid system, realizing spontaneous self-use and improving photovoltaic energy utilization.

Technical solution of the present invention: a three-phase unbalanced output control method, including the following steps:

S1. According to the collected three-phase mains voltage U _R , U _S , _UT and three-phase output current I _R , _IS , _IT , the output powers _PR and _PS of the three-phase photovoltaic grid-connected inverter are obtained respectively. and P _T ;

According to the collected three-phase mains voltage U _R , U _S , U _T and the three-phase grid-connected port currents I _{export_R} , I _{export_S} , and I _{export_T} , the three-phase grid-connected port powers P _{export_R} , P _{export_S} , and P _{export_T} are obtained respectively;

S2. According to the three-phase output powers P _R , P _S and _PT , the sum of the three-phase output powers Pac is obtained;

According to the three-phase grid-connected port powers P _{export_R} , P _{export_S} and P _{export_T} , the sum of the three-phase grid-connected port powers P _export is obtained;

S3. According to the three-phase grid-connected port power limit set by _the user as P _exprotLimit for each phase, as well as the sum of the three-phase output powers Pac and the sum of the three-phase grid-connected port powers P _export , the three-phase photovoltaic grid-connected inverter is obtained The output power limit _PacLimit ;

S4. Compare the sizes of P _acLimit and P _ac , adjust the output power accordingly, and obtain the voltage target value output by the photovoltaic module, so that the sum of the three-phase grid-connected port powers P _export is 3×P _exprotLimit ;

S5. Limit the power of the R-phase and S-phase grid-connected ports, and adjust the three-phase output currents I _{peak_ref[R]} , I _{peak_ref[S]} and I _{peak_ref[T]} to achieve three-phase unbalanced output.

In the aforementioned three-phase unbalanced output control method, the difference between the bus voltage control loop reference value Bus _{Ac_ref} and the bus voltage value U _bus is used as an error signal to output the AC current peak reference value I _peak through the PI controller;

The difference between the AC grid-connected port power limit P _exprotLimit and the R-phase grid-connected port power P _{export_R} is used as the error signal. After being controlled by the PI controller, the smaller value of the current output value and I _peak is taken as the peak value of the R-phase current. Reference value I _{peak_ref[R]} ;

The difference between the AC grid-connected port power limit P _exprotLimit and the S-phase grid-connected port power P _{export_s} is used as an error signal and controlled by the PI controller. The smaller value of the current output value and I _peak is taken as the peak reference of the S-phase current. valueI _{peak_ref[S]} ;

Take I _peak as the current peak reference value I _{peak_ref[T]} of the T phase.

In the aforementioned three-phase unbalanced output control method, the calculation formula of the three-phase output power and the three-phase grid-connected port power is:

Among them, T represents the mains cycle time, u(t) represents the instantaneous value of the mains voltage, and i(t) represents the instantaneous value of the current.

In the aforementioned three-phase unbalanced output control method, the sum of the three-phase output powers _Pac = P _R + P _S + P _T ; the sum of the three-phase grid-connected port powers P _export = P _{export_R} + P _{export_S} + P _{export_T} .

In the aforementioned three-phase unbalanced output control method, the output power limit value _PacLimit =P _ac +K×(3×P _exprotLimit -P _export ), where K is an internal control parameter.

In the aforementioned three-phase unbalanced output control method, step S4 is specifically: compare the sizes of _PacLimit and _Pac . If _PacLimit ﹤P _ac , the power limit flag is set. If _PacLimit ﹥(P _ac + hysteresis return threshold), the power limit flag is cleared; if the power limit flag is set, the power limit control loop is executed, and the voltage output value of the power limit control loop is used as the voltage target value output by the photovoltaic module; if the power limit flag is If the bit is not set, the maximum power tracking algorithm is used to obtain the voltage target value output by the photovoltaic module.

In the aforementioned three-phase unbalanced output control method, the power limit control loop uses _PacLimit as the reference value, _Pac as the feedback value, and outputs the voltage target value U _pvref of the photovoltaic module through the PI controller.

A system for realizing the above-mentioned three-phase unbalanced output control method, including a plurality of photovoltaic components, the output side of each photovoltaic component is connected to a DC/DC converter, and the output end of each DC/DC converter is The DC bus is connected to the input end of the DC/AC converter, the output end of the DC/AC converter is connected to the three-phase line ends of the three-phase mains through three-phase relays, and the midpoint of the DC bus is connected to the three-phase line through the neutral relay. The neutral terminal of the mains is connected.

In the aforementioned system, the three-phase relay and the DC/AC converter are each connected in series with an output current sensor for measuring the output current of the three-phase photovoltaic grid-connected inverter; the three-phase relay and the three-phase mains are connected in series. The corresponding grid-connected port current sensor for measuring the three-phase grid-connected port current is connected in series. The user-side three-phase load and Voltage sensor for measuring three-phase mains voltage.

Compared with the prior art, the beneficial effects of the present invention are:

By designing a control algorithm for a three-phase four-wire output mode, the present invention realizes unbalanced output of three-phase power, thereby reducing the impact of the photovoltaic system on the traditional power grid system, and achieving control of the optimal output power of the photovoltaic module, thereby improving The utilization rate of photovoltaic energy can not only meet the requirements of users for self-use, but also enable users to minimize the use of electricity from the grid system and reduce electricity bills.

The present invention also designs a three-phase photovoltaic grid-connected inverter that is compatible with two output modes: three-phase three-wire output and three-phase four-wire output. Users can independently choose three-phase output power balance control or three-phase output power balance control. Balance control, and controls the output mode of the three-phase four-wire system to realize the unbalanced output function of the three-phase four-wire system.

Description of the drawings

Figure 1 is a schematic diagram of the power limit control loop of the sum of three-phase grid-connected port power in the present invention;

Figure 2 is a schematic diagram of the limit control loop of the power of each phase grid-connected port in the present invention;

Figure 3 is a schematic diagram of the grid-connected inverter circuit structure of a three-phase unbalanced system.

Detailed ways

The present invention will be further described below with reference to the examples, but they are not used as a basis for limiting the present invention.

Example:

A three-phase unbalanced output control method includes the following steps:

S1. Select the three-phase four-wire output of the three-phase photovoltaic grid-connected inverter. According to the collected three-phase mains voltage U _R , U _S , _UT and three-phase output current I _R , I _S , I _T , we get respectively Three-phase output power P _R , _PS and _PT of the three-phase photovoltaic grid-connected inverter;

According to the collected three-phase mains voltage U _R , U _S , and U _T and the three-phase grid-connected port currents I _{export_R} , I _{export_S} , and I _{export_T} , the three-phase grid-connected port powers P _{export_R} , P _{export_S} , and P _{export_T} are obtained respectively;

The calculation formula of the three-phase output power and the three-phase grid-connected port power is:

S2. According to the three-phase output power P _R , _PS and _PT , obtain the sum of the three-phase output power _Pac of the three-phase photovoltaic grid-connected inverter, _Pac = P _R + P _S + P _T ;

According to the three-phase grid-connected port powers P _{export_R} , P _{export_S} and P _{export_T} , the sum of the three-phase grid-connected port powers P _export is obtained, P _export =P _{export_R} +P _{export_S} +P _{export_T} ;

S3. According to the three-phase grid-connected port power limit set by _the user as P _exprotLimit for each phase, as well as the sum of the three-phase output powers Pac and the sum of the three-phase grid-connected port powers P _export , the three-phase photovoltaic grid-connected inverter is obtained The output power limit _PacLimit ; _PacLimit = _Pac +K × (3 × P _exprotLimit -P _export ), where K is an internal control parameter, and K is 0.1 in this embodiment.

S4. Compare the sizes of _PacLimit and _Pac . If _PacLimit ﹤P _ac , the power limit flag is set and the power limit flag is assigned a value of 1; if _PacLimit ﹥ (P _ac + hysteresis threshold), the power limit flag is set. The flag is cleared and the power limit flag is assigned a value of 0; the hysteresis threshold is an internal control parameter to avoid frequent setting and clearing of the power limit flag. In this embodiment, the hysteresis threshold is 200w; and then it is determined whether the power limit flag is set. bit, if the power limit flag is set, the power limit control loop is executed, and the voltage output value of the power limit control loop is used as the voltage target value output by the photovoltaic module; if the power limit flag is not set, the maximum power tracking is used The algorithm obtains the voltage corresponding to the maximum power as the voltage target value output by the photovoltaic module. In this way, the sum of the three-phase grid-connected port powers P _export is 3×P _exprotLimit .

Among them, the power limit control loop uses _PacLimit as the reference value and _Pac as the feedback value to adjust the output power of the photovoltaic module, and output the voltage target value U _pvref of the photovoltaic module through the PI controller, as shown in Figure 1.

S5. Limit the power of the R-phase and S-phase grid-connected ports, control the power of the R-phase and S-phase grid-connected ports to P _exprotLimit , and adjust the peak reference value of the three-phase output current. As shown in Figure 2, the bus voltage The difference between the control loop reference value Bus _{Ac_ref} and the bus voltage value U _bus is used as an error signal through the PI controller to output the AC current peak reference value I _peak ;

When the three phases are unbalanced, I _{peak_ref[R]} , I _{peak_ref[S]} , and I _{peak_ref[T]} are different current values, thereby achieving three-phase unbalanced output. When the grid-connected port power limit value P _exprotLimit is 0, Then the zero output power of each phase grid-connected port is achieved.

A system for implementing the above three-phase unbalanced output control method, as shown in Figure 3, includes several photovoltaic modules. The output side of each photovoltaic module is connected to a DC/DC converter, and each DC/DC The output terminals of the converter are connected to the input terminal of the DC/AC converter through the DC bus. The output terminals of the DC/AC converter are connected to the R terminal of the three-phase mains through three-phase relays S _R , S _S , and S _T respectively. , S line end and T line end are connected correspondingly. The midpoint of the DC bus is connected to the N line end of the three-phase mains through the neutral relay S _N. The three-phase relays S _R , S _S and S _T are connected to the DC/AC converter. There are output current sensors used to measure the three-phase photovoltaic grid-connected inverter output currents I _R , I _S and _IT in series corresponding to each other; the three-phase relays S _R , S _S , S _T and the R line terminals of the three-phase mains The grid-connected port current sensors for measuring the three-phase grid-connected port currents I _{export_R} , I _{export_S} , and I _{export_T} are connected in series between the S line terminal and the T line terminal. Between the R line and the N line, and between the S line and the N line The user-side three-phase loads Z _R , Z _S , and Z _T and the voltage sensors used to measure the three-phase mains voltages U _R , U _S , and _UT are respectively connected between them, and between the T line and the N line.

When selecting the three-phase three-wire output of the three-phase photovoltaic grid-connected inverter, disconnect the relay S _N of the N line to achieve balanced control of the three-phase output power.

When selecting the three-phase four-wire output of the three-phase photovoltaic grid-connected inverter, close the relay S _N of the N line to achieve unbalanced control of the three-phase output power.

The three-phase output power can be calculated by the DSP controller through the collected three-phase output current and three-phase grid voltage of the three-phase photovoltaic grid-connected inverter. Alternatively, a three-phase electricity meter can be used to calculate the mains port power of the three-phase photovoltaic grid-connected inverter. Then use the above three-phase power unbalanced output control method to achieve zero output or unbalanced output of grid-connected port power.

Claims

A three-phase unbalanced output control method is characterized by: including the following steps:

S1. According to the collected three-phase mains voltage U R , U S , UT and three-phase output current I R , IS , IT , the output powers PR and PS of the three-phase photovoltaic grid-connected inverter are obtained respectively. and P T ;

According to the collected three-phase mains voltage U R , U S , U T and the three-phase grid-connected port currents I export_R , I export_S , and I export_T , the three-phase grid-connected port powers P export_R , P export_S , and P export_T are obtained respectively;

S2. According to the three-phase output powers P R , P S and PT , the sum of the three-phase output powers Pac is obtained;

According to the three-phase grid-connected port powers P export_R , P export_S and P export_T , the sum of the three-phase grid-connected port powers P export is obtained;

S3. According to the three-phase grid-connected port power limit set by the user as P exprotLimit for each phase, as well as the sum of the three-phase output powers Pac and the sum of the three-phase grid-connected port powers P export , the three-phase photovoltaic grid-connected inverter is obtained The output power limit PacLimit ;

S4. Compare the sizes of P acLimit and P ac , adjust the output power accordingly, and obtain the voltage target value output by the photovoltaic module, so that the sum of the three-phase grid-connected port powers P export is 3×P exprotLimit ;

S5. Limit the power of the R-phase and S-phase grid-connected ports, and adjust the three-phase output currents I peak_ref[R] , I peak_ref[S] and I peak_ref[T] to achieve three-phase unbalanced output.
A three-phase unbalanced output control method according to claim 1, characterized in that: S5 specifically includes: using the difference between the bus voltage control loop reference value Bus Ac_ref and the bus voltage value U bus as an error signal through the PI controller Output AC current peak reference value I peak ;

The difference between the AC grid-connected port power limit P exprotLimit and the R-phase grid-connected port power P export_R is used as the error signal. After being controlled by the PI controller, the smaller value of the current output value and I peak is taken as the peak value of the R-phase current. Reference value I peak_ref[R] ;

The difference between the AC grid-connected port power limit P exprotLimit and the S-phase grid-connected port power P export_s is used as an error signal and controlled by the PI controller. The smaller value of the current output value and I peak is taken as the peak reference of the S-phase current. valueI peak_ref[S] ;

Take I peak as the current peak reference value I peak_ref[T] of the T phase.
A three-phase unbalanced output control method according to claim 1, characterized in that: the calculation formula of the three-phase output power and the three-phase grid-connected port power is:
Among them, T represents the mains cycle time, u(t) represents the instantaneous value of the mains voltage, and i(t) represents the instantaneous value of the current.
A three-phase unbalanced output control method according to claim 1, characterized in that: the sum of the three-phase output powers Pac = P R + P S + P T ; the sum of the three-phase grid-connected port powers P export =P export_R +P export_S +P export_T .
A three-phase unbalanced output control method according to claim 1, characterized in that: the output power limit PacLimit = Pac +K×(3×P exprotLimit -P export ), where K is internal control parameter.
A three-phase unbalanced output control method according to claim 1, characterized in that: step S4 is specifically: comparing the size of PacLimit and Pac , if PacLimit ﹤ Pac , the power limit flag is set, if PacLimit ﹥( Pac +hysteresis threshold), then the power limit flag is cleared;

If the power limit flag is set, the power limit control loop is executed, and the voltage output value of the power limit control loop is used as the voltage target value output by the photovoltaic module; if the power limit flag is not set, the maximum power tracking algorithm is used to obtain The voltage target value output by the photovoltaic module.
A three-phase unbalanced output control method according to claim 6, characterized in that: the power limit control loop uses PacLimit as a reference value, Pac as a feedback value, and outputs photovoltaic modules through a PI controller. The voltage target value U pvref .
A system for implementing the three-phase unbalanced output control method according to any one of claims 1 to 7, characterized in that it includes a plurality of photovoltaic modules, and the output side of each photovoltaic module is correspondingly connected to a DC/DC converter. converter, the output end of each DC/DC converter is connected to the input end of the DC/AC converter via the DC bus, and the output end of the DC/AC converter is respectively connected to the three-phase line end of the three-phase mains through a three-phase relay. connection, the midpoint of the DC bus is connected to the neutral end of the three-phase mains through the neutral relay.
A system according to claim 8, characterized in that: an output current sensor for measuring the output current of a three-phase photovoltaic grid-connected inverter is connected in series between the three-phase relay and the DC/AC converter; The phase relays and the three-phase mains are connected in series with the grid port current sensors used to measure the three-phase grid port currents, between the R line and the N line, between the S line and the N line, and between the T line and the N line. The user-side three-phase loads and voltage sensors used to measure the three-phase mains voltage are respectively connected between them.