CN115313861A - Control method based on two-stage bidirectional inverter parallel system - Google Patents
Control method based on two-stage bidirectional inverter parallel system Download PDFInfo
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- 238000007600 charging Methods 0.000 claims abstract description 88
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- 239000003990 capacitor Substances 0.000 claims description 32
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/0068—Battery or charger load switching, e.g. concurrent charging and load supply
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/007—Regulation of charging or discharging current or voltage
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/007—Regulation of charging or discharging current or voltage
- H02J7/00712—Regulation of charging or discharging current or voltage the cycle being controlled or terminated in response to electric parameters
- H02J7/007182—Regulation of charging or discharging current or voltage the cycle being controlled or terminated in response to electric parameters in response to battery voltage
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/02—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries for charging batteries from ac mains by converters
- H02J7/04—Regulation of charging current or voltage
- H02J7/06—Regulation of charging current or voltage using discharge tubes or semiconductor devices
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/32—Means for protecting converters other than automatic disconnection
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
- H02M7/68—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters
- H02M7/72—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/79—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/797—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/70—Energy storage systems for electromobility, e.g. batteries
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Abstract
The invention belongs to the technical field of energy exchange, and discloses a control method based on a two-stage bidirectional inverter parallel system, which is used for collecting voltage and current data of a two-stage bidirectional inverter and battery charge state data in real time; when the power grid voltage exists at the charging port, the parallel system enters a charging mode, and the direct current-direct current converter of each two-stage bidirectional inverter carries out bus voltage building; when the voltage of the bus reaches a rated value, the voltage build-up of the bus is finished, the corresponding charging relay is closed at the zero point of the voltage of the power grid, and the charging relay formally enters a charging mode to start charging the battery; when the power grid voltage does not exist at the charging port, the parallel system enters a discharging mode, whether the charge state of the battery is larger than a charge threshold value or not is judged, and if not, the two-stage bidirectional inverter is in a standby state; and if so, carrying out parallel operation on each two-stage bidirectional inverter according to a parallel operation control strategy, and then carrying out output power distribution based on the respective battery charge state.
Description
Technical Field
The invention belongs to the technical field of energy exchange, and particularly relates to a control method based on a two-stage bidirectional inverter parallel system.
Background
The bidirectional inverter integrates charging and discharging, and can meet the power consumption requirements of most people when being used with a vehicle-mounted power battery of the new energy automobile, so that the bidirectional inverter has an important promotion effect on the development of the new energy automobile. With the increasing quantity and capacity of electric equipment, a single inverter is not enough to provide enough power supply power, and scholars propose an inverter parallel technology to solve the problem of insufficient power supply power. At present, the research on the inverter parallel technology mainly focuses on power sharing and circulation suppression, but research on the output power distribution of each submodule in the inverter parallel system based on the state of charge of the battery to achieve maximum utilization of the energy of the battery is receiving more and more attention.
However, the operation of the two-stage inverter is still affected by a large inrush current generated in the starting process of the two-stage inverter, and the system efficiency is reduced by generally adopting a buffer circuit to suppress the starting inrush current, so that a new control method is urgently needed to suppress the starting inrush current to the maximum extent in the starting process of the two-stage inverter.
Disclosure of Invention
The invention provides a control method based on a two-stage bidirectional inverter parallel system, which can inhibit starting impact current without adopting a buffer circuit, improves the system efficiency and realizes the maximum utilization of battery energy.
The invention can be realized by the following technical scheme:
a control method based on a two-stage bidirectional inverter parallel system is used for a single-phase power grid system,
acquiring voltage and current data and battery charge state data of a two-stage bidirectional inverter in real time;
when the power grid voltage exists at the charging port, the parallel system enters a charging mode, and the direct current-direct current converter of each two-stage bidirectional inverter builds the bus voltage;
when the voltage of the bus reaches a rated value, the voltage build-up of the bus is finished, the corresponding charging relay is closed at the zero point of the voltage of the power grid, and the charging relay formally enters a charging mode to start charging the battery;
when the power grid voltage does not exist at the charging port, the parallel system enters a discharging mode, whether the charge state of the battery is larger than a charge threshold value or not is judged, and if not, the two-stage bidirectional inverter is in a standby state;
and if so, each two-stage bidirectional inverter is parallel-connected according to a parallel-connection control strategy, and then output power distribution is carried out based on the respective battery charge state.
Further, the method for carrying out bus voltage building by the direct current-direct current converter comprises the following steps:
s1: setting a virtual voltage reference value to linearly rise from the working voltage of the battery;
s2: generating a power switch control signal of the DC-DC converter by a difference value obtained by subtracting the measured value of the bus voltage from the current voltage reference value so as to boost the bus;
s3: the bus voltage starts to rise linearly from the battery voltage, whether the bus voltage reaches a rated value or not is judged, if yes, S4 is executed, and if not, S2 is executed;
s4: the dc-dc converter stops operating.
Further, the instantaneous value u of the network voltage of the charging port is obtained according to the detection ac Determining the instantaneous value u ac And if the voltage is within-5V to +5V of the zero point, delaying the power frequency period of one grid voltage by each charging relay and closing the charging relay again by the difference value of the self closing delay time.
Further, when the battery is charged, whether the battery voltage is lower than the upper limit threshold of the battery voltage is judged, and if yes, a current loop is adopted for constant current charging; otherwise, the charging is finished by adopting a voltage current loop.
Further, the method for ending the charging by adopting the voltage current loop comprises the following steps:
s1: setting a virtual voltage reference value, subtracting the measured value of the battery voltage from the voltage reference value, and limiting the amplitude of the battery voltage through a compensator to obtain an amplitude limiting signal, wherein the amplitude limiting range is-b-c;
s2: a difference signal of the amplitude limiting signal plus the current reference value minus the charging current measured value is processed by a compensator to obtain a modulation signal, and the current reference value is set as a charging current set value;
s3: the modulation signal is subjected to pulse width modulation to obtain a power switch tube control signal of the direct current-direct current converter;
s4: and controlling the direct current-direct current converter to finish charging according to the control signal of the power switch tube.
Further, the charge threshold is set as a lower threshold of the battery working state of charge;
and the output power distribution of each two-stage bidirectional inverter based on the charge state of the battery is set to be distributed according to the specific proportion between the charges of the battery or according to the equal distribution of the total output power of the parallel system.
Further, the two-stage bidirectional inverter parallel system comprises a plurality of two-stage bidirectional inverters connected in parallel, each two-stage bidirectional inverter is composed of a direct current-direct current converter and a direct current-alternating current converter, and the input end of the direct current-direct current converter and the battery end capacitor C are connected in parallel inn And a battery U inn Are respectively connected in parallel, the output end of the DC-DC converter is connected with the bus capacitor C busn In parallel, the bus capacitor C busn And is also connected in parallel with the DC side of the DC-AC converter, which is connected with the filter inductor L in series n And a filter capacitor C n In parallel, the filter inductance L n And a filter capacitor C n The common terminal of the relay S is connected in series to discharge n1 The electric equipment R is connected to the filter capacitor C n The other end of (1), the filter inductance L n And a filter capacitor C n The common terminal and the charging relay S n2 One end is connected with the charging relay S n2 Another end of (d) and the grid u ac Is connected to the grid u ac Another terminal of (1) and a filter capacitor C n And the other end of the two are connected.
The beneficial technical effects of the invention are as follows:
1. the control method of the parallel system of the two-stage bidirectional inverter provided by the invention realizes the output power distribution of each two-stage bidirectional inverter in the parallel system based on the charge state of the battery, ensures that the charge state of the battery is above the lower limit threshold of the charge state of the battery, and prolongs the service life of the battery.
2. The control method of the two-stage bidirectional inverter parallel system provided by the invention can inhibit the impact current generated by the two-stage bidirectional inverter in the starting process without adding a buffer circuit, and ensures the safe operation of the two-stage bidirectional inverter.
Drawings
Fig. 1 is a control flow chart of a two-stage bidirectional inverter parallel system provided by the invention;
fig. 2 is a topology diagram of a two-stage bidirectional inverter parallel system provided by the present invention;
FIG. 3 is a two-stage bi-directional inverter topology according to an embodiment of the present invention;
FIG. 4 is a diagram of a voltage loop control according to an embodiment of the present invention;
FIG. 5 is a charging control diagram according to an embodiment of the present invention;
FIG. 6 is a voltage feedforward effective value feedback control diagram of a host according to an embodiment of the present invention;
FIG. 7 is an initial duty cycle plus current loop control diagram for a slave according to an embodiment of the present invention;
FIG. 8 is a diagram of a battery state of charge based power distribution according to an embodiment of the present invention.
Detailed Description
The following detailed description of the preferred embodiments will be made with reference to the accompanying drawings.
As shown in fig. 1, the invention provides a control method based on a two-stage bidirectional inverter parallel system, which collects voltage and current data of a two-stage bidirectional inverter and battery state of charge data in real time; when the power grid voltage exists at the charging port, the parallel system enters a charging mode, and the direct current-direct current converter of each two-stage bidirectional inverter builds the bus voltage; when the voltage of the bus reaches a rated value, the voltage build-up of the bus is finished, the corresponding charging relay is closed at the zero point of the voltage of the power grid, and the charging relay formally enters a charging mode to start charging the battery; when the power grid voltage does not exist at the charging port, the parallel system enters a discharging mode, whether the charge state of the battery is larger than a charge threshold value or not is judged, and if not, the two-stage bidirectional inverter is in a standby state; and if so, carrying out parallel operation on each two-stage bidirectional inverter according to a parallel operation control strategy, and then carrying out output power distribution based on the respective battery charge state. The method comprises the following specific steps:
as shown in fig. 2, the two-stage bidirectional inverter parallel system of the present invention includes a plurality of two-stage bidirectional inverters connected in parallel, each of the two-stage bidirectional inverters is composed of a dc-dc converter and a dc-ac converter, and an input terminal of the dc-dc converter and a battery terminal capacitor C are connected in parallel inn And a battery U inn Are respectively connected in parallel, the output end is connected with the bus capacitor C busn In parallel, the bus capacitor C busn And is also connected in parallel with the DC side of the DC-AC converter, which is connected in series with the filter inductor L n And a filter capacitor C n In parallel, the filter inductance L n And a filter capacitor C n The common terminal of the relay S is connected in series to discharge n1 The electric equipment R is connected to the filter capacitor C n The other end of the filter inductor L n And a filter capacitor C n The common terminal and the charging relay S n2 One end is connected with the charging relay S n2 Another end of (d) and the grid u ac Is connected to one end of the grid u ac Another terminal of (1) and a filter capacitor C n And the other end of the two are connected.
In the discharging mode, the input end of each two-stage bidirectional inverter is connected with a battery U inn The output ends of the two-stage bidirectional inverters are connected with an electric device R together, and the discharge relay S of each two-stage bidirectional inverter n1 Closed and the charging relay S n2 Disconnecting; in the charging mode, the input ends of the two-stage bidirectional inverters are connected with an alternating current grid u ac The output end of the battery is connected with a battery U inn At this time, the discharging relay S of each two-stage bidirectional inverter n1 Open and charge the relay S n2 And (5) closing.
Specifically, as shown in fig. 3, the dc-dc converter adopts a two-phase interleaved parallel circuit, the dc-ac converter adopts a single-phase full-bridge inverter circuit, and the battery adopts a lithium battery.
Charging mode of parallel system:
step one, generating voltage for bus
Real-time acquisition of output alternating voltage u of each two-stage bidirectional inverter ac Voltage of battery U in Bus voltage U bus Load voltage u o And battery state of charge;
s1: setting a virtual voltage reference U ref The working voltage of the battery is increased linearly, generally, the working voltage of the battery is 40-60V, and any value can be selected as the initial value of the voltage reference value, such as 60V;
s2: subtracting the measured value u of the bus voltage from the current voltage reference value bus Generating a power switch control signal of the DC-DC converter by the obtained difference value so as to carry out boosting treatment on the bus;
due to the voltage reference value U ref The voltage difference is not synchronous with the rise of the battery voltage, so a certain difference always exists between the two, the difference obtains a modulation signal through a compensator, and then the modulation signal is processed to obtain a power switch tube S in the DC-DC converter 1 ～S 4 The control signal of (2) so as to control the dc-dc converter to perform the voltage boosting process on the bus, wherein the compensator can be a proportional-integral compensator, a proportional-resonant compensator, a lead-lag compensator, etc.
S3: the bus voltage starts to rise linearly from the battery voltage, whether the bus voltage reaches a rated value such as 325V is judged, if yes, S4 is executed, and if not, S2 is executed;
s4: the dc-dc converter stops operating.
Because the two-stage bidirectional inverter is started and charges the filter capacitor instantly, a large starting impact current can be generated, and overcurrent protection can be triggered, even the equipment is damaged. Therefore, it is necessary to suppress the start-up rush current during the start-up of the power electronic device. As shown in FIG. 3, the lithium battery supply capacitor C p1 And C p2 A starting rush current is generated during charging. From the equations (1) and (2), the capacitor charging current i c Is in positive correlation with the switching duty cycle D. Therefore, when the boosting duty ratio D is instantaneously raised from 0 to the rated value, a large starting rush current is generated.
Similarly, the charging process shown in fig. 1 shows that: network voltage u ac When the capacitor C is butted with the DC-AC converter p3 The impulse current is generated when the power grid is charged; the DC-AC converter feeds the capacitor C by rectification p1 And C p2 A rush current is generated during charging.
Therefore, when the bus voltage is built up, the mode of slowly increasing the duty ratio D from zero to the rated value is selected to inhibit the starting impact current when the bus voltage is boosted, namely, when the bus voltage of the DC-DC converter is built up, the virtual voltage reference value U in the voltage ring control is set ref The duty ratio D is slowly increased from zero to a rated value by a mode of linear increase of the working voltage of the battery, so that starting impact current generated by voltage build-up of a bus during charging is restrained.
Step two, the charging relay is closed at the zero point of the grid voltage
Obtaining the instantaneous value u of the network voltage of the charging port according to the detection ac Determining the instantaneous value u ac Whether the voltage is within-5V- +5V of the zero point or not, of course, other limited ranges are also available, the range of +/-5 is not exceeded as much as possible, if so, each charging relay can be controlled to be closed, but in consideration of the fact that the relay needs to be closed for a certain working time, in order to improve the accuracy of the matching of the closing time and the zero point of the grid voltage, the closing time of each charging relay needs to be delayed by one power frequency cycle of the grid voltage and the self closing delayThereby reducing the magnitude of the surge current generated by charging the filter capacitor when the grid is connected to the DC-AC converter, i.e. reducing the inductor current i L3 The rush current of (2).
The charging port of the invention has alternating voltage with 230V (220V-230V) effective value and 50Hz frequency, so that the power frequency cycle of the grid voltage is 20ms, and the charging relay S n2 Is about 7.6ms, i.e. the charging relay S n2 It may be delayed by 20ms minus 7.6ms before closing.
Specifically, as shown in fig. 3, the following steps are known: in the charging mode, firstly the DC-DC converter supplies a bus voltage U via the voltage loop bus Boosting the pressure; when the bus voltage U bus After 325V is reached, the DC-DC converter is in standby; then the network voltage u is sampled by the controller ac Considering the charging port relay S 10 After a closing delay time of (about 7.6 ms), the grid voltage u is applied ac When the voltage is 0V, the direct current-alternating current converter is in butt joint; at this time, the grid voltage u ac Starting to supply filter capacitor C at 0V p3 Charging to achieve the effect of inhibiting starting impact current; the DC-AC converter adopts uncontrolled rectification to the capacitor C p1 And C p2 Charging to make the bus voltage U bus Maintaining the voltage at 325V can suppress the rush current caused by the sharp fluctuation of the bus voltage.
Step three, the parallel system enters a charging mode to start charging the battery
Real-time acquisition of inductive current i of each two-stage bidirectional inverter L1 Inductor current i L2 Voltage of battery U in (ii) a Judging whether the battery voltage is lower than the upper limit threshold of the battery voltage, if so, performing constant current charging by adopting a current loop; otherwise, the charging is finished by adopting a voltage current loop.
As shown in fig. 5, assuming that the upper threshold of the battery voltage is 60V, when the battery voltage is less than 60V, the constant current charging is performed as follows:
s1: current reference value I L1 Subtracting the preceding inductor current-i L1 The difference signal of (1) is processed by a proportional-integral compensator to obtain a compensation signal 1;
s2: current reference value I L2 Subtracting the preceding inductor current-i L2 The difference signal of (2) is processed by a proportional-integral compensator to obtain a compensation signal 2;
s3: after adding the compensation signal 2 to the compensation signal 1, limiting the amplitude of the compensation signal by an amplitude limiter to 0-0.96 to obtain a modulation signal;
s4: the modulation signal is subjected to pulse width modulation to obtain a control signal S of the power switch tube 1 ～S 4 ；
S5: control signal S of power switch tube 1 ～S 4 And controlling the DC-DC converter to charge the battery at a constant current of 10A.
When the voltage of the battery is more than 60V, the execution steps of ending the charging by adopting a voltage current loop are as follows:
s1: reference value of voltage U in Subtracting the instantaneous value u of the battery voltage in Then limiting the amplitude of the signal by a proportional-integral compensator to obtain an amplitude limiting signal, wherein the amplitude limiting range is-5-0;
reference value of voltage U in Setting the maximum working voltage value of the battery to be 60V; when the battery voltage is higher than 60V, the voltage reference value U in Subtracting the measured value u of the cell voltage in The difference signal of (2) is a negative value, and the negative value of the compensation signal after passing through the proportional-integral compensator is continuously reduced; as the charging current is set to be 10A, the charging current of two phases is forced to be reduced to be 0A, and the amplitude limit of the compensation signal is-5-0.
S2: a difference signal of the amplitude limiting signal, the current reference value and the charging current measured value is subtracted to obtain a modulation signal through a compensator, wherein the current reference value is set as a charging current set value;
because the DC-DC converter of the embodiment is a two-phase interleaved parallel circuit, the signals after amplitude limiting are divided into two paths, which are marked as an amplitude limiting signal 1 and an amplitude limiting signal 2; the limited signal 1 is added with a current reference value I L1 Subtracting a preceding stage inductor current i L1 The difference signal of (1) is processed by a proportional-integral compensator to obtain a compensation signal 1; the limited signal 2 plus a current reference value I L2 Subtracting a preceding stage inductor current i L2 The difference signal is compensated by a proportional-integral compensatorSignal 2;
the current reference is a charging current set value which is set to be 10A, namely the two-phase current reference values are both 5A; the preceding stage inductor current is the actual charging current.
S3: the modulation signal is subjected to pulse width modulation to obtain a power switch tube control signal of the direct current-direct current converter; adding the compensation signal 1 to the compensation signal 2, limiting the amplitude of the signals by an amplitude limiter to 0-0.96 to obtain a modulation signal, and modulating the modulation signal by pulse width to obtain a control signal S to the power switch tube 1 ～S 4 ；
S4: control signal S of power switch tube 1 ～S 4 And controlling the DC-DC converter to reduce the charging current to 0A to finish charging.
As shown in fig. 5, the voltage outer loop adopts a proportional-integral compensator: the integral link of the proportional-integral compensator can enable the signal value passing through the proportional-integral compensator to be accumulated continuously, and the proportional link of the proportional-integral compensator can proportionally amplify or reduce the signal value passing through the proportional-integral compensator, so that the numerical value of a compensation signal passing through the proportional-integral compensator is slowly reduced from 0 to-5 by setting a smaller integral parameter and a smaller proportional parameter, the direct current-direct current converter is controlled to gradually reduce the charging current to 0A to finish charging, and the charging stability of the two-stage bidirectional inverter is improved.
Discharge mode of parallel system:
the two-stage bidirectional inverter parallel system adopts a master-slave control idea to set each two-stage bidirectional inverter as a master machine and a slave machine; the direct current-direct current converters of the host and the slave adopt a bus voltage building control method in a charging mode of a parallel system; the direct current-alternating current converter of the host machine adopts voltage feedforward effective value feedback to control the voltage amplitude of the stable bus; and the DC-AC converter of the slave computer adopts the initial duty ratio and current loop control to regulate the output power.
As shown in fig. 6, the steps of stabilizing the bus voltage amplitude by the voltage feedforward and effective value feedback control of the dc-ac converter of the host are as follows:
s1: calculating the effective value of the output alternating voltage of the host;
s2: the difference is made between the voltage reference value and the calculated effective value of the alternating voltage, and the difference signal is subjected to amplitude limiting of-0.1 by a proportional-integral compensator to output a compensation signal d 1 ；
S3: dividing the theoretical amplitude 325V of the output alternating voltage by the theoretical value 360V of the bus voltage to obtain a fixed duty ratio D;
s4: compensating signal d 1 Adding the sum with a fixed duty ratio D, and multiplying the sum by a unit power frequency periodic signal sin100 pi t to obtain a modulation signal;
s5: and the modulation signal is subjected to sine pulse width modulation to obtain a control signal of a power switch tube of the DC-AC converter.
The fixed duty ratio D provided by the voltage feedforward is used for stably outputting the amplitude of the alternating voltage; control compensation signal d for effective voltage value 1 Ensuring the amplitude precision of the output alternating voltage; thus, the compensation signal d 1 The amplitude of the output alternating voltage is ensured to be stable when the duty ratio is far smaller than the fixed duty ratio D; meanwhile, the effect of adjusting the amplitude of the output alternating voltage is realized; therefore, the compensation signal d 1 The amplitude limit is-0.1.
Specifically, the step of calculating the effective value of the output ac voltage of the main unit includes:
s1: sampling the amplitude of the output alternating voltage of a power frequency period for 400 times, and squaring the amplitude;
s2: then, the average value of the square sum of the data is obtained;
s3: obtaining an effective value of the output alternating voltage according to a proportional relation between an average value of the sum of squares of the data and the effective value of the output alternating voltage;
assuming that the amplitude of the output ac voltage is 1, the proportional relationship between the average of the sum of squares of the data and the effective value of the output ac voltage is:
wherein, U avg Is the mean of the sum of squares of the data, U rms For the purpose of outputting AC voltageThe value is obtained.
As shown in fig. 7, the steps of adjusting the output power of the dc-ac converter of the slave by the initial duty ratio and the current loop control are as follows:
s1: the slave receives the output power signal sent by the host and calculates a current reference value I L3 ；
S2: current reference value I L3 And the inductor current i L3 Making difference, the difference signal is amplitude limited by proportional-integral compensator to-0.1 to obtain compensation signal d 2 ；
S3: the slave machine obtains the output alternating voltage phase sin100 pi t of the master machine through a phase-locked loop, the theoretical amplitude 325V of the output alternating voltage is divided by the theoretical value 360V of the bus voltage to obtain the fixed duty ratio D, and therefore the two quantities are multiplied to obtain the initial duty ratio Dsin100 pi t;
s4: initial duty ratio signal Dsin100 π t and compensation signal d 2 Adding to obtain a modulation signal;
s5: and the modulation signal is subjected to sine pulse width modulation to obtain a control signal of a power switch tube of the DC-AC converter.
The initial duty ratio signal Dsin100 pi t is used for ensuring the amplitude and the phase of the host and the slave to be consistent, and ensuring that the host and the slave can realize parallel operation; amplitude consistency of master and slave requires compensation signal d of current loop 2 Much less than the fixed duty cycle D; simultaneously realize the regulation of the inductive current i L3 The function of (2); thus, the compensation signal d 2 The amplitude limit is-0.1.
Judging whether the charge state of the battery is larger than a charge threshold value or not, and if not, waiting for the two-stage bidirectional inverter; and if so, carrying out parallel operation on each two-stage bidirectional inverter according to a parallel operation control strategy, and then carrying out output power distribution based on the respective battery charge state. Wherein the charge threshold is set to a lower threshold, such as 20%, of the battery operating state of charge.
The output power distribution of each two-stage bidirectional inverter based on the state of charge of the battery is set to be distributed according to the total output power of the parallel system, as shown in fig. 8, specifically as follows:
s1: each two-stage bidirectional inverter outputs the detected AC powerPress u o And the inductor current i L3 Multiplying, and obtaining the output power of each single two-stage bidirectional inverter through a digital filter;
s2: the master machine calculates the output power of each slave machine according to the received output power of each single two-stage bidirectional inverter and sends a power signal to the slave machine;
s3: judging whether the charge state of the host is less than 25%, if so, turning to S4, otherwise, turning to S8;
s4: judging whether the charge state of the slave is less than 20%, if so, turning to S15, otherwise, turning to S5;
s5: judging whether the load power is less than 1500W, if so, turning to S6, otherwise, turning to S14;
s6: judging whether the charge state of the host is less than 20%, if so, turning to S14, otherwise, turning to S7;
s7: regulating output voltage u by host o The slave machine provides load power;
s8: judging whether the charge state of the slave is less than 20%, if so, turning to S15, otherwise, turning to S11;
s9: judging whether the charge state of the host is less than 20%, if so, turning to S14, otherwise, turning to S10;
s10: the master machine provides load power, and the slave machine is shut down;
s11: judging whether the load power is less than 500W, if so, turning to S7, otherwise, turning to S12;
s12: judging whether the load power is less than 3000W, if so, turning to S13, otherwise, turning to S14;
s13: the power of the host and the slave is divided equally;
s14: the host machine and the slave machine are shut down;
s15: and judging whether the load power is less than 1500W, if so, turning to S9, and otherwise, turning to S14.
According to the steps, the charge state of the battery of each two-stage bidirectional inverter is above 20%, and the problem that the working performance of the battery is poor and the service life of the battery is influenced due to the insufficient power of the battery is avoided.
Although specific embodiments of the present invention have been described above, it will be appreciated by those skilled in the art that these are merely examples and that many variations or modifications may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is therefore defined by the appended claims.
Claims (7)
1. A control method based on a two-stage bidirectional inverter parallel system is used for a single-phase power grid system and is characterized in that:
acquiring voltage and current data and battery charge state data of a two-stage bidirectional inverter in real time;
when the power grid voltage exists at the charging port, the parallel system enters a charging mode, and the direct current-direct current converter of each two-stage bidirectional inverter carries out bus voltage building;
when the voltage of the bus reaches a rated value, the voltage build-up of the bus is finished, the corresponding charging relay is closed at the zero point of the voltage of the power grid, and the charging relay formally enters a charging mode to start charging the battery;
when the power grid voltage does not exist at the charging port, the parallel system enters a discharging mode, whether the charge state of the battery is larger than a charge threshold value or not is judged, and if not, the two-stage bidirectional inverter is in a standby state;
and if so, carrying out parallel operation on each two-stage bidirectional inverter according to a parallel operation control strategy, and then carrying out output power distribution based on the respective battery charge state.
2. The control method based on the two-stage bidirectional inverter parallel system as claimed in claim 1, wherein the method for performing bus voltage build-up by the dc-dc converter comprises the following steps:
s1: setting a virtual voltage reference value to linearly rise from the working voltage of the battery;
s2: generating a power switch control signal of the DC-DC converter by a difference value obtained by subtracting the measured value of the bus voltage from the current voltage reference value so as to boost the bus;
s3: the bus voltage starts to rise linearly from the battery voltage, whether the bus voltage reaches a rated value or not is judged, if yes, S4 is executed, and if not, S2 is executed;
s4: the dc-dc converter stops operating.
3. The control method based on the two-stage bidirectional inverter parallel system according to claim 2, characterized in that: obtaining the instantaneous value u of the network voltage at the charging port according to the detection ac Determining the instantaneous value u ac And if the voltage is within-5V to +5V of the zero point, delaying the power frequency period of one grid voltage by each charging relay and closing the charging relay again by the difference value of the self closing delay time.
4. The control method based on the two-stage bidirectional inverter parallel system according to claim 1, characterized in that: when the battery is charged, judging whether the battery voltage is lower than the upper limit threshold of the battery voltage, if so, carrying out constant current charging by adopting a current loop; otherwise, the charging is finished by adopting a voltage current loop.
5. The control method based on the two-stage bidirectional inverter parallel system according to claim 4, wherein the method for ending the charging by using the voltage current loop comprises the following steps:
s1: setting a virtual voltage reference value, subtracting the measured value of the battery voltage from the voltage reference value, and limiting the amplitude of the battery voltage through a compensator to obtain an amplitude limiting signal, wherein the amplitude limiting range is-b-c;
s2: a difference signal of the amplitude limiting signal plus the current reference value minus the charging current measured value is processed by a compensator to obtain a modulation signal, and the current reference value is set as a charging current set value;
s3: the modulation signal is subjected to pulse width modulation to obtain a power switch tube control signal of the direct current-direct current converter;
s4: and controlling the direct current-direct current converter to finish charging according to the control signal of the power switch tube.
6. The control method based on the two-stage bidirectional inverter parallel system according to claim 1, characterized in that: the charge threshold is set as a lower limit threshold of the working state of charge of the battery;
and the output power distribution of each two-stage bidirectional inverter based on the charge state of the battery is set to be distributed according to the specific proportion between the charges of the battery or the total output power of the parallel system.
7. The control method based on the two-stage bidirectional inverter parallel system according to claim 1, characterized in that: the two-stage bidirectional inverter parallel system comprises a plurality of two-stage bidirectional inverters connected in parallel, each two-stage bidirectional inverter consists of a direct current-direct current converter and a direct current-alternating current converter, and the input end of the direct current-direct current converter and a battery end capacitor C inn Battery U inn Are respectively connected in parallel, and the output end of the DC-DC converter is connected with the bus capacitor C busn In parallel, the bus capacitor C busn And is also connected in parallel with the DC side of the DC-AC converter, which is connected with the filter inductor L in series n And a filter capacitor C n In parallel, the filter inductance L n And a filter capacitor C n The common terminal of the relay S is connected in series to discharge n1 The electric equipment R is connected to the filter capacitor C n The other end of (1), the filter inductance L n And a filter capacitor C n The common terminal and the charging relay S n2 One end is connected with the charging relay S n2 Another end of (b) and the electric network u ac Is connected to the grid u ac Another terminal of (1) and a filter capacitor C n And the other end of the two are connected.
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