CN105356756A - Quasi-square wave modulation method for modularized isolation type battery energy storage converter - Google Patents

Abstract

The invention discloses a quasi-square wave modulation method for a modular isolated battery energy storage converter. The AC voltage of the primary and secondary sides of the transformer is not a standard quasi-square wave, but the rising edge and falling edge present a ladder shape, that is, the primary side The AC output voltage duty cycle of each H-bridge of the bridge arm Arm_p1 and each sub-module of the secondary bridge arm Arm_s1 is less than or equal to 0.5 and is not equal to each other. By adjusting the phase difference between the quasi-square wave voltage of the primary side and the quasi-square wave voltage of the secondary side To control the energy transfer direction and size between the energy storage battery and the DC grid, by correcting the phase difference, the DC bus capacitor voltage of each sub-module of the secondary bridge arm of the transformer is stabilized, and by adjusting the DC component of the output voltage of all sub-modules of the secondary bridge arm of the transformer. Adjust the average value of the current on the secondary side of the transformer, that is, the current on the side of the DC distribution network, so as to achieve the purpose of stabilizing the module voltage and controlling the grid-connected current, and realize the stable and reliable operation of the system.

Description

A quasi-square wave modulation method for a modular isolated battery energy storage converter

technical field

The invention relates to the technical field of electrical automation equipment, in particular to a quasi-square wave modulation method of a modular isolated battery energy storage converter.

Background technique

Battery energy storage systems occupy an increasingly important position in all aspects of power systems, especially in important areas such as load balancing, user-side power quality, reactive power compensation, and accommodation of renewable energy. Due to its special function and high cost, the reliability of the battery energy storage system is very important.

Modular multilevel converter (MMC) is widely used in DC distribution network due to its high output voltage level, large scalability and redundant control capacity. The isolated modular multi-level energy storage converter is applied to the DC distribution network. The primary side of the transformer is connected to the energy storage cascaded H-bridge circuit through a filter inductor, and the secondary side winding of the transformer is connected to the secondary bridge arm through the filter inductor. In the DC distribution network, the secondary bridge arm of the transformer is composed of n sub-modules in series, and the DC side of each module is connected to the DC bus capacitor.

However, due to the particularity of the structure of the isolated modular multilevel energy storage converter applied to the medium and high voltage DC distribution network, corresponding modulation and control strategies are required to ensure the stable and reliable operation of the system.

Contents of the invention

Aiming at the defects of the prior art, the purpose of the present invention is to provide a quasi-square wave modulation method for the isolated modular multilevel energy storage converter based on the DC power grid. The AC voltage on the primary side of the transformer is not a quasi-square wave but a quasi-square wave. Square wave, that is, the rising edge and falling edge of the original quasi-square wave are in a ladder shape, and there is a phase difference between the output AC voltages of each sub-module, and by adjusting the phase difference of the high-frequency quasi-square wave voltage on the primary and secondary sides of the transformer, the energy storage battery is realized. The two-way transmission of energy with the DC grid, in addition, through the corresponding control strategy, the stable and reliable operation of the system is realized.

The invention provides a quasi-square wave modulation method of an isolated modular multi-level energy storage converter, the topology of the modular isolated battery energy storage converter is: the primary side of the transformer is connected to the primary side through a filter inductor _Lp The output terminal of the bridge arm Arm_p1, the transformer primary bridge arm Arm_p1 is formed by cascading m H bridges, the series output of the m H bridges is used as the output of the primary bridge arm Arm_p1, and the DC side of each H bridge is connected to energy storage Battery; one end of the secondary side of the transformer is connected to the negative pole of the DC grid bus through a filter inductor L _s and the secondary bridge arm Arm_s1, and the other end of the secondary side of the transformer is connected to the positive pole of the DC grid bus; the secondary bridge arm Arm_s1 is connected by n Each sub-module is connected in series, and each sub-module is connected to the DC bus capacitor on the DC side, and each module constituting the secondary arm Arm_s1 adopts a full-bridge structure or a half-bridge structure;

Each H-bridge of the primary bridge arm Arm_p1 can output three states (-1, 0, 1), and the range of the quasi-square wave voltage on the primary side of the transformer is -m～m; when each sub-module of the secondary bridge arm Arm_s1 adopts a full In the bridge structure, the secondary arm Arm_s1 outputs a quasi-square wave voltage ranging from -n to n; each half-bridge can only output two states (0, 1). When each module of Arm_s1 adopts a half-bridge structure, Arm_s1 outputs The quasi-square wave voltage range is 0~n;

The AC voltage on the primary and secondary sides of the transformer is not a standard quasi-square wave, but a stepped quasi-square wave with rising and falling edges, that is, the AC output of each H bridge of the primary bridge arm Arm_p1 and each sub-module of the secondary bridge arm Arm_s1 The voltage duty ratios are all less than or equal to 0.5 and are not equal to each other;

In order to realize the two-way transfer of energy between the energy storage battery and the DC grid, the converter needs to have a phase difference between the primary and secondary quasi-square waves of the transformer The method controls the direction and magnitude of energy transfer between the energy storage battery and the DC grid by adjusting the phase difference between the quasi-square wave voltage on the primary side and the quasi-square wave voltage on the secondary side, and stabilizes the bridge arm on the secondary side of the transformer by correcting the phase difference The capacitor voltage of the DC bus of each sub-module adjusts the average value of the current on the secondary side of the transformer by adjusting the DC component of the output voltage of all sub-modules of the secondary bridge arm of the transformer, that is, the current on the side of the DC distribution network, so as to stabilize the module voltage and control the grid-connected current To achieve stable and reliable operation of the system.

Preferably, the AC voltage on the primary side of the transformer is not a quasi-square wave, but a quasi-square wave, that is, the rising edge and falling edge of the original quasi-square wave are in a ladder shape, and there is a phase between the output AC voltages of each H-bridge of the primary side bridge arm The duty cycle of each H-bridge output AC voltage of the primary arm Arm_p1 in half a switching cycle is recorded as D _{P1_1} ~ D _{P1_m} (0.4≤D _{P1_i} ≤0.5, 1≤i≤m) in turn from large to small, The difference between D _{P1_i} and D _{P1_i+1} (1≤i≤m) is the same or different; in order to improve the effective value of AC voltage, D _{P1_i} (1≤i≤m) should be as close as possible to 0.5. The arm_p1 of the primary side bridge adopts an H-bridge cascaded structure, and the AC voltage on the primary side of the transformer is a quasi-square wave with positive and negative symmetry.

Preferably, the duty cycle of each sub-module of the secondary bridge arm Arm_s1 is recorded as D _{s1_1} ~ D _{s1_n} (0.4≤D _{s1_j} ≤0.5, 1≤j≤n) in order from large to small, D _{s1_i} and D _{s1_i+1} (1≤j≤n) have the same or different differences, but in order to increase the effective value of the AC voltage, D _{s1_j} (1≤j≤n) should be as close to 0.5 as possible. Due to the existence of the secondary DC grid, in order to maintain the stability of the voltage of each H-bridge of the secondary bridge arm Arm_s1, the AC voltage of the secondary side of the transformer is a quasi-square wave symmetrical to the DC grid v _dc .

Preferably, the method can adjust the phase difference of the quasi-square wave of the primary and secondary sides of the transformer by controlling the DC bus voltage of all sub-modules of the secondary bridge arm Arm_s1 That is, the deviation between the rated value of the DC bus voltage of all sub-modules of the secondary bridge arm Arm_s1 and the average value of the DC bus voltage of all modules of the secondary bridge arm Arm_s1 is used as the input of the PI regulator, and the output of the PI regulator is used as the phase difference

Preferably, the average value of the transformer secondary side current is adjusted by correcting the DC components of the output voltages of all sub-modules of the secondary arm Arm_s1, that is, the transformer secondary current i _Ls is filtered by the low-pass filter LF and the DC grid current The given value is added as the input of the PI regulator, and the deviation between the output of the PI regulator and the DC grid bus voltage v _dc is used as the secondary bridge arm Arm_s1 DC voltage modulation signal v _{s1_dc} .

Compared with the prior art, the present invention has the following beneficial effects:

The quasi-square wave modulation strategy of the isolated modular multi-level energy storage converter of the present invention can realize energy exchange between the energy storage battery and the DC power grid, and realize module voltage balance and transformer secondary side through a certain control strategy Current regulation, this modulation and control strategy is suitable for the quasi-square wave modulation of all isolated modular multilevel energy storage converters based on DC distribution network whose topology can be equivalent to the average model in Figure 4.

Description of drawings

Other characteristics, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

Fig. 1 is the topological structure of the converter of an embodiment of the present invention;

Fig. 2 is the schematic diagram of the quasi-square wave modulation of an embodiment of the present invention;

3 is an average equivalent circuit diagram of an isolated modular multilevel energy storage converter based on a DC power grid in an embodiment of the present invention;

Fig. 4 is the control diagram of DC bus capacitor voltage balance of each module of Arm_s1 according to an embodiment of the present invention;

FIG. 5 shows the generation of the modulation signal of the direct current component of the output voltage of Arm_s1 according to an embodiment of the present invention.

detailed description

The present invention will be described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

As shown in Figure 1, it is the circuit topology of an isolated modular multilevel energy storage converter based on a DC power grid according to an embodiment of the present invention: the primary side of the transformer is connected to the output end of the primary side bridge arm Arm_p1 through a filter inductor L _p , the transformer primary arm Arm_p1 is formed by cascading m H bridges, the output of the m H bridges in series is used as the output of the primary arm Arm_p1, and the DC side of each H bridge is connected to the energy storage battery; the primary side of the isolation transformer The bridge arm Arm_p1 is formed by cascading m H-bridges. Each H-bridge is marked as cell _{p1_i} ( _1≤i≤m ). The DC side of cell _{p1_i} is connected to the energy storage battery _. ≤i≤m), the AC terminal output of cell _{p1_i} is recorded as v _{p1_i_ac} (1≤i≤m), i _{p1_i_dc} (1≤i≤m) is the DC side current of cell _{p1_i} , and i _{p1_i_ac} (1≤i≤m) is the cell _{p1_i} output side current. The primary side filter inductance is L _p , the primary side current is i _Lp , and the transformation ratio of the transformer is 1:N.

One end of the secondary side of the transformer is connected to the negative pole of the DC grid bus through a filter inductor L _s and the secondary bridge arm Arm_s1, and the other end of the secondary side of the transformer is connected to the positive pole of the DC grid bus; the secondary bridge arm Arm_s1 is composed of n sub-modules Composed in series, each sub-module is connected to the DC bus capacitor on the DC side, and the topology of each module constituting the secondary arm Arm_s1 can be either a half-bridge structure or a full-bridge structure, and each sub-module is recorded as cell _{s1_j} (1≤j≤n ), the DC side of cell _{s1_j} is connected to a capacitor, the capacitor voltage is recorded as v _{s1_j_dc} (1≤j≤n), the output of cell _{s1_j} ’s AC terminal is recorded as v _{s1_j_ac} (1≤j≤n), and i _{s1_j_dc} (1≤j≤n) is The DC side current of cell _{s1_j} , i _{s1_j_ac} (1≤j≤n) is the output side current of cell _{s1_j} . The secondary filter inductance is L _s , and the secondary current is i _Ls . The busbar voltage of the DC power grid is v _dc , and the current is i _dc .

Each energy storage module of the primary side arm Arm_p1 adopts an H-bridge structure, and each H-bridge can output three states (-1, 0, 1), so the range of the quasi-square wave voltage on the primary side of the transformer is -m～m. When each sub-module of the secondary bridge arm Arm_s1 adopts a full-bridge structure, the output quasi-square wave voltage range of the secondary bridge arm Arm_s1 is -n~n, since each half-bridge can only output two states (0, 1), so When each sub-module of the secondary bridge arm Arm_s1 adopts a half-bridge structure, the output quasi-square wave voltage range of the secondary bridge arm Arm_s1 is 0-n.

Due to the modular design, even if the voltage level of each module is relatively low, it can still reach a higher voltage level, thereby achieving low loss, low cost, and high switching frequency.

The AC voltage on the primary side of the transformer is not a quasi-square wave, but a quasi-square wave, that is, the rising edge and falling edge of the original quasi-square wave are in a ladder shape, and there is a phase difference between the output AC voltages of each sub-module; each of the primary side bridge arms Arm_p1 The duty cycle of the H-bridge output AC voltage within half a switching cycle is recorded as D _{P1_1} ~ D _{P1_m} (0.4≤D _{P1_i} ≤0.5,1≤i≤m) in order from large to small, and D _{P1_i} and D _{P1_i+1} ( 1≤i≤m) can be the same or different, but in order to increase the effective value of AC voltage, D _{P1_i} (1≤i≤m) should be as close to 0.5 as possible. Since Arm_p1 adopts H-bridge cascade structure, the AC voltage on the primary side of the transformer is a quasi-square wave with positive and negative symmetry. The duty cycle of each sub-module of the secondary bridge arm Arm_s1 is recorded as D _{s1_1} ~ D _{s1_n} (0.4≤D _{s1_j} ≤0.5,1≤j≤n) in order from large to small, D _{P1_j} and D _{P1_j+1} (1≤j≤ The difference between n) can be the same or different, but in order to increase the effective value of the AC voltage, D _{s1_j} (1≤j≤n) should be as close to 0.5 as possible. Due to the existence of the secondary DC grid, in order to maintain the secondary arm Arm_p1 The voltage of each H-bridge is stable, and the AC voltage on the secondary side of the transformer is a quasi-square wave symmetrical to the DC grid v _dc .

As shown in Figure 2, it is the quasi-square wave modulation principle of the isolated _modular multi-level energy storage converter based on the DC power grid according to an embodiment of the present invention. The edge is stepped, that is, there is a phase difference between the output voltages of the H-bridges of the primary arm Arm_p1. The voltage v _s1 on the secondary side of the transformer lags behind the voltage v _p1 on the primary side of the transformer The rising edge and falling edge of v _s1 are in a ladder shape. Due to the existence of v _dc of the DC grid on the secondary side of the transformer, in order to make the system run stably, v _s1 is symmetrical about v _dc .

FIG. 3 is an average equivalent circuit diagram of a modular isolated battery energy storage converter in an embodiment of the present invention. The average model of the converter can be equivalent to: the AC side of the primary side is equivalent to the primary winding of the transformer, the series circuit of the filter inductance L _p and a controlled voltage source v _P1 (the output of Arm_p1 is equivalent to v _P1 ), and the DC energy storage side is equivalent to energy storage battery v _{arm_p1_dc} connected in series with a controlled current source d _p1 i _Lp ; the secondary AC side is equivalent to secondary winding, filter inductance L _s , controlled voltage source v _s1 (Arm_s1 output is equivalent to v _s1 ), the series circuit of DC power grid v _dc , the DC side of the module is equivalent to v _{arm_s1_dc} connected in series with a controlled current source d _s1 i _Ls , the equivalent capacitance of all modules on the DC side of Arm_s1 is Cs/n, and the equivalent voltage of the capacitor is v _{arm_s1_dc} , i _Ls is the current of the secondary transformer side, and i _dc is the current of the DC grid side.

v _{arm_p1_dc} is the sum of the battery voltages of all the H-bridges of the primary arm Arm_p1, d _p1 is the sum of the equivalent duty ratios of all the H-bridges of the primary arm Arm_p1, and v _p1 is the output voltage of the primary arm Arm_p1, including DC Components also include AC components. v _{arm_s1_dc} is the sum of the DC capacitor voltages of all sub-modules of the secondary arm Arm_s1, d _s1 is the sum of the equivalent duty cycles of all sub-modules of the secondary arm Arm_s1, and v _s1 is the output voltage of the secondary arm Arm_s1, including The DC component also contains the AC component. v _dc is the DC grid voltage.

According to the average model of the above converter, the phase difference of the quasi-square wave of the primary and secondary sides of the transformer can be adjusted by controlling the DC bus voltage of all sub-modules of Arm_s1 That is, the deviation between the rated value of the DC bus voltage of all modules of Arm_s1 and the average value of the DC bus voltage of all modules of Arm_s1 is used as the input of the PI regulator, and the output of the PI regulator is used as the phase difference

As shown in FIG. 4 , it is a control diagram of DC bus capacitor voltage balance of each module of the bridge arm Arm_s1 according to an embodiment of the present invention. V _{arms1_dc} * represents the rated value of the DC side capacitor voltage of each sub-module of the secondary bridge arm Arm_s1, and v _{arms1_dc} represents the secondary side The average value of the capacitor voltage on the DC side of all sub-modules of the bridge arm Arm_s1, the deviation between V _{arms1_dc} * and v _{arms1_dc} is corrected by the PI regulator as the phase difference That is, the DC capacitor voltage of each sub-module of the secondary bridge arm Arm_s1 is stabilized near the rated value by correcting the phase difference.

As shown in FIG. 5 , it is a principle diagram for generating the secondary side bridge arm Arm_s1 output voltage DC component modulation signal v _{s1_dc} of the isolated modular multilevel energy storage converter based on the DC power grid in an embodiment of the present invention: secondary side current i _Ls The low-pass filter LF is added to the DC grid current rating value i _dc * as the input of the PI regulator, and the deviation between the output of the PI regulator and the DC grid voltage v _dc is used as the v _{s1_dc} modulation signal. That is, i _Ls is controlled by correcting the DC component of the output voltage of the secondary bridge arm Arm_s1.

After the above quasi-square wave modulation and control strategy, the DC grid side DC current i _dc of the converter can be accurately controlled, and the converter can realize active filtering and current limiting functions.

The invention provides a quasi-square wave modulation strategy for an isolated modular multi-level energy storage converter. In this method, the AC voltage on the primary and secondary sides of the transformer is not a standard quasi-square wave, but the rising and falling edges present a ladder shape. That is, the AC output voltage duty cycle of each sub-module inside the bridge arm on the primary side (secondary side) is less than or equal to 0.5 and is not equal to each other, and there is a phase difference between the quasi-square waves on the primary side and the secondary side to realize the connection between the energy storage battery and the DC grid. By correcting the phase difference, the DC bus capacitor voltage of each sub-module of the secondary bridge arm of the transformer is stabilized, and the average value of the transformer secondary side current is adjusted by adjusting the DC component of the output voltage of all sub-modules of the secondary bridge arm of the transformer. So as to realize the stable and reliable operation of the system.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims (7)

1. A quasi-square wave modulation method of a modular isolated battery energy storage converter, characterized in that, the topology of the modular isolated battery energy storage converter is: transformer primary side bridge arm Arm_p1 is composed of m H bridges Composed in series, the DC side of each H-bridge is connected to the energy storage battery, the primary arm of the transformer Arm_p1 is connected to the primary side of the transformer through a filter inductor L _p ; the secondary side of the transformer is connected to the primary side of the transformer through a filter inductor L _s It is connected to the negative pole of the DC grid bus, and the other end of the secondary side of the transformer is connected to the positive pole of the DC grid bus; the secondary bridge arm Arm_s1 is composed of n sub-modules connected in series, and each sub-module is connected to the DC bus capacitor on the DC side to form the secondary bridge arm Each module of Arm_s1 is a full bridge structure or a half bridge structure; Each H-bridge of the primary bridge arm Arm_p1 can output three states (-1, 0, 1), and the range of the quasi-square wave voltage on the primary side of the transformer is -m～m; when each sub-module of the secondary bridge arm Arm_s1 adopts a full In the bridge structure, the secondary arm Arm_s1 outputs a quasi-square wave voltage ranging from -n to n; each half-bridge can only output two states (0, 1). When each module of Arm_s1 adopts a half-bridge structure, Arm_s1 outputs The quasi-square wave voltage range is 0~n; The AC voltage on the primary and secondary sides of the transformer is not a standard quasi-square wave, but a stepped quasi-square wave with rising and falling edges, that is, the AC output of each H bridge of the primary bridge arm Arm_p1 and each sub-module of the secondary bridge arm Arm_s1 The voltage duty ratios are all less than or equal to 0.5 and are not equal to each other; In order to realize the two-way transfer of energy between the energy storage battery and the DC grid, the converter needs to have a phase difference between the primary and secondary quasi-square waves of the transformer The method controls the direction and magnitude of energy transfer between the energy storage battery and the DC grid by adjusting the phase difference between the quasi-square wave voltage on the primary side and the quasi-square wave voltage on the secondary side, and stabilizes the bridge arm on the secondary side of the transformer by correcting the phase difference The capacitor voltage of the DC bus of each sub-module adjusts the average value of the current on the secondary side of the transformer by adjusting the DC component of the output voltage of all sub-modules in the secondary bridge arm of the transformer, that is, the current on the side of the DC distribution network, so as to stabilize the module voltage and control the grid-connected current To achieve stable and reliable operation of the system. 2. The quasi-square wave modulation method of the modularized isolated battery energy storage converter according to claim 1, wherein there is a phase difference between the output AC voltages of each sub-module of the primary side bridge arm of the transformer, Arm_p1 The duty cycle of the output AC voltage of each module within half a switching cycle is recorded as D _{P1_1} ~ D _{P1_m} (0.4≤D _{P1_i} ≤0.5, 1≤i≤m) in descending order, and D _{P1_i} and D _{P1_i+1} ( 1≤i≤m) are the same or different; in order to increase the effective value of AC voltage, D _{P1_i} (1≤i≤m) should be as close to 0.5 as possible. 3. The quasi-square wave modulation method of the modular isolated battery energy storage converter according to claim 2, characterized in that, the primary side bridge arm Arm_p1 adopts an H-bridge cascade structure, and the AC voltage on the primary side of the transformer is It is a quasi-square wave with positive and negative symmetry. 4. The quasi-square wave modulation method of the modular isolated battery energy storage converter according to claim 1, characterized in that, the duty cycle of each sub-module of the secondary bridge arm Arm_s1 is recorded as D in turn from large to small _{s1_1} ～D _{s1_n} (0.4≤D _{s1_j} ≤0.5,1≤j≤n), the difference between D _{s1_j} and D s1_j ₊₁ (1≤j≤n) is the same or different, but in order to improve the effective value of AC voltage, D _{s1_j} (1≤j≤n) should be as close to 0.5 as possible. 5. The quasi-square wave modulation method of the modular isolated battery energy storage converter according to claim 4, characterized in that, due to the existence of the secondary DC power grid, in order to maintain the voltage stability of each H-bridge of the secondary bridge arm Arm_s1, the transformer The secondary AC voltage is a quasi-square wave symmetrical to the DC grid v _dc . 6. The quasi-square wave modulation method of the modular isolated battery energy storage converter according to any one of claims 1-5, characterized in that, the method can control the DC bus voltage of all modules of the secondary bridge arm Arm_s1 Adjusting the Phase Difference of the Quasi-Square Wave on the Primary and Secondary Sides of the Transformer That is, the deviation between the rated value of the DC bus voltage of all sub-modules of the secondary bridge arm Arm_s1 and the average value of the DC bus voltage of all sub-modules of the secondary bridge arm Arm_s1 is used as the input of the PI regulator, and the output of the PI regulator is used as the phase difference 7. The quasi-square wave modulation method of the modular isolated battery energy storage converter according to any one of claims 1-5, wherein the average value of the current on the secondary side of the transformer is corrected by correcting the arm Arm_s1 of the secondary side The DC component of the output voltage of all sub-modules is adjusted, that is, the secondary current i _Ls of the transformer is filtered by the low-pass filter LF and added to the given value of the DC grid current as the input of the PI regulator, and the output of the PI regulator and the DC current The grid bus voltage v _dc deviation is used as the secondary arm Arm_s1 DC voltage modulation signal v _{s1_dc} .