A method for controlling energy flow based on shared bus voltage

Abstract

The technical solution of the present invention discloses a method for controlling energy flow based on the shared bus voltage. It is characterized in that the DC / DC circuit on the energy storage battery side and the DC / AC inverter circuit on the inverter side share the same bus voltage control loop. A part of the output of the shared bus voltage control loop is used as the current reference of the current control loop of the DC / DC circuit, and another part is used as the current reference of the current control loop of the DC / AC inverter circuit. The present invention solves the problems of controlling energy flow and power distribution based on the idea of shared bus voltage control. A part of the energy on the common DC bus is connected to the power grid or supplied to the load through the DC / AC inverter circuit, and a part is connected to the energy storage battery system through the DC / DC circuit. The DC / DC circuit and the DC / AC inverter circuit share the same common bus control loop, and at the same time, the stability of the common DC bus is achieved through the distribution of the output current of the loop.

Description

Technical Field

[0001] The present invention relates to a method for controlling energy flow based on shared bus voltage, belonging to the technical field of control of photovoltaic energy storage inverters. Background Art

[0002] The integrated photovoltaic and energy storage device integrates an energy storage function on the basis of a traditional photovoltaic inverter. Its working principle is as follows: when the photovoltaic energy is sufficient, the photovoltaic modules supply power to the grid or load, and the excess electric energy is charged into the energy storage battery. When the photovoltaic energy is insufficient, the energy of the energy storage battery is released to supply the load. The structure of the integrated photovoltaic and energy storage device is as Figure 1 shown, including a Boost circuit on the photovoltaic side, a DC / DC circuit on the energy storage battery side, a DC bus capacitor, and a DC / AC inverter circuit. Among them: one side of the Boost circuit on the photovoltaic side is connected to the photovoltaic module PV, and the other side is connected to the DC bus capacitor; one side of the DC / DC circuit on the energy storage battery side is connected to the energy storage battery, and the other side is connected to the DC bus capacitor; the DC side of the DC / AC inverter circuit is connected to the bus capacitor, and the AC side is connected to the grid and load.

[0003] In an integrated photovoltaic and energy storage inverter or a microgrid system with a common DC bus, the energy flow is coupled through the common DC bus. To ensure the safe and stable operation of the system, it is necessary to maintain the stability of the common DC bus. Generally, the bidirectional DC / DC droop method or the hierarchical control method is used to control the common DC bus. The droop control method will lead to a decrease in the overall response speed of the AC output side. At the same time, since the DC / AC inverter circuit participates in the bus control, it is not conducive to the realization of the off-grid function. The hierarchical control method will lead to the problem of MPPT search switching in the case of bypassing the Boost circuit on the photovoltaic side, making the entire control logic very complex. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that using the bidirectional DC / DC droop method to control the common DC bus will lead to a decrease in the overall response speed of the AC output side and is not conducive to the realization of the off-grid function; using the hierarchical control method to control the common DC bus will lead to the problem of MPPT search switching in the case of bypassing the Boost circuit on the photovoltaic side, making the entire control logic very complex.

[0005] To solve the above technical problems, the technical solution of the present invention is to provide a method for controlling energy flow based on the shared bus voltage. The Boost circuit on the photovoltaic side, the DC / DC circuit on the energy storage battery side, and the DC / AC inverter circuit on the inverter side share a common DC bus. Among them, the Boost circuit on the photovoltaic side independently controls the bus voltage. It is characterized in that the DC / DC circuit on the energy storage battery side and the DC / AC inverter circuit on the inverter side share the same bus voltage control loop, which is defined as the shared bus voltage control loop. A part of the output of the shared bus voltage control loop is used as the current reference of the current control loop of the DC / DC circuit, and another part is used as the current reference of the current control loop of the DC / AC inverter circuit.

[0006] Preferably, according to the set priority, determine whether the electric energy generated by the PV is given priority to the energy storage battery side or the inverter side.

[0007] Preferably, if the electric energy generated by the PV is given priority to the energy storage battery side, the output of the shared bus voltage control loop preferentially satisfies the current control loop of the DC / DC circuit; if the electric energy generated by the PV is given priority to the inverter side, the output of the shared bus voltage control loop preferentially satisfies the current control loop of the DC / AC inverter circuit.

[0008] Preferably, the output of the shared bus voltage control loop is the reference current I s h areref , then there is:

[0009]

[0010] In the formula, Tv1 represents the first-order filtering time constant, Kpv represents the proportional coefficient of the regulator of the shared bus voltage control loop, Kiv represents the integral coefficient of the regulator of the shared bus voltage control loop, s represents the complex variable, U busref2 represents the reference voltage of the shared bus voltage control loop, and U bus is the actual bus voltage.

[0011] Preferably, the current reference of the current control loop of the DC / DC circuit is I batref , and the current reference of the current control loop of the DC / AC inverter circuit is I invref , then there is I s h areref = I batref + I invref .

[0012] Preferably, if the electric energy generated by the PV is given priority to the energy storage battery side, the inverter operates in the battery priority mode; if the electric energy generated by the PV is given priority to the inverter side, the inverter operates in the inverter priority mode.

[0013] Preferably, when the inverter operates in the inversion - priority mode, the current reference I of the current control loop of the DC / AC inversion circuit invref is the scheduling value: when I invref > 0, the inverter is in the state of feeding power to the grid or supplying power to the load; when I invref < 0, the inverter is in the state of forcibly charging the energy - storage battery system, and the current reference I of the current control loop of the DC / DC circuit batref = I s h areref - I invref .

[0014] Preferably, when the inverter operates in the inversion - priority mode: if the current reference I of the current control loop of the DC / DC circuit batref is greater than 0, the energy - storage battery system is in the charging state; if the current reference I of the current control loop of the DC / DC circuit batref is less than 0, the energy - storage battery system is in the discharging state.

[0015] Preferably, when the inverter operates in the battery - priority mode, the current reference I of the current control loop of the DC / DC circuit batref is the scheduling value: when I batref > 0, the energy - storage battery is in the charging state; when I batref < 0, the energy - storage battery is in the discharging state, and the current reference I of the current control loop of the DC / AC inversion circuit invref = I shareref - I batref .

[0016] Preferably, when the inverter operates in the battery - priority mode: if the current reference I of the current control loop of the DC / AC inversion circuit invref is greater than 0, the power of photovoltaic power generation is greater than the power for charging the energy - storage battery system, and the remaining power is sent to the grid or used by the load; if the current reference I of the current control loop of the DC / AC inversion circuit invref is less than 0, the power of photovoltaic power generation is less than the charging power of the energy - storage battery system, and the insufficient power is provided by the grid to charge the energy - storage battery system.

[0017] The present invention solves the problem of controlling energy flow and power distribution based on the idea of shared bus voltage control. By regarding the DC / DC circuit on the energy storage battery side and the DC / AC inverter circuit as equivalent modules, that is, part of the energy on the common DC bus is connected to the power grid or supplied to the load through the DC / AC inverter circuit, and part is connected to the energy storage battery system through the DC / DC circuit. The DC / DC circuit and the DC / AC inverter circuit share the same common bus control loop, and at the same time, the stability of the common DC bus is achieved through the distribution of the loop output current. And in the technical solution disclosed by the present invention, it is possible to determine whether the electric energy generated by the PV is given priority to the energy storage battery system or to the DC / AC inverter circuit according to the set priority. Description of the Drawings

[0018] Figure 1 Schematically shows the structure of a conventional integrated PV and energy storage system.

[0019] Figure 2 Is the circuit topology of the Boost on the PV side.

[0020] Figure 3 Is the circuit topology of the DC / DC on the energy storage battery side.

[0021] Figure 4 Is the circuit topology of the DC / AC on the inverter side.

[0022] Figure 5 Is the control block diagram of the Boost on the PV side.

[0023] Figure 6 Is the control block diagram of the shared bus voltage control in the inverter priority mode.

[0024] Figure 7 Is the control block diagram of the shared bus voltage control in the battery priority mode. Detailed Embodiments

[0025] The following further elaborates the present invention in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0026] In conjunction with Figure 1 , in the integrated PV and energy storage system disclosed in this embodiment, the Boost circuit on the PV side, the DC / DC circuit on the energy storage battery side, and the DC / AC inverter circuit on the inverter side share a common DC bus.

[0027] The power control of the PV is achieved through the Boost circuit, and the circuit topology is as Figure 2As shown, the Boost circuit independently controls the bus voltage, and its control loop consists of a photovoltaic voltage control loop, a bus voltage control loop, and a current control loop 1.

[0028] For the photovoltaic voltage control loop, the input of its outer voltage loop is the reference voltage U pvref , and the actual photovoltaic voltage is U pv . After being controlled by the voltage loop regulator, the reference current for the current control loop 1 is used to control the maximum power search of the photovoltaic side DC / DC circuit. Among them, Tv1 represents the first-order filtering time constant, Kpv1 represents the proportional coefficient of the PV voltage loop regulator, Kiv1 represents the integral coefficient of the PV voltage loop regulator, and s represents the complex variable.

[0029] For the bus voltage control loop, the input of its outer voltage loop is the reference voltage U busref1 , and the feedback voltage is the actual bus voltage U bus . After being controlled by the voltage loop regulator, the reference current for the current control loop 1 is used to control the stability of the bus voltage. Among them, Kpv2 represents the proportional coefficient of the bus voltage control loop, and Kiv2 represents the integral coefficient of the bus voltage control loop.

[0030] For the current control loop 1, the input of its current loop is the reference current I pvbusref . The reference current I pvbusref can be obtained by taking the output of the photovoltaic voltage control loop as the input signal of the current loop and using the output signal of the bus voltage control loop as the current limiting signal of the output of the photovoltaic voltage control loop. The reference current I pvbusref can also be obtained by taking the minimum value of the output of the photovoltaic voltage control loop and the output of the bus voltage control loop, that is, I pvbusref = Min(I pvsref , I busref ). The actual current of the photovoltaic Boost circuit is I pv . After being controlled by the current loop regulator, the modulation signal for controlling the Boost circuit is obtained.

[0031] The charging and discharging power of the energy storage battery system is realized through the control of the DC / DC circuit, and the circuit topology is as Figure 3 shown. The power of the inversion is realized through the control of the DC / AC inversion circuit, and the circuit topology is as Figure 4 shown. In the present invention, the DC / DC circuit on the energy storage battery side and the DC / AC inversion circuit on the inversion side share the same bus voltage control loop (hereinafter referred to as the "shared bus voltage control loop"), thus simplifying the control loop for controlling the bus voltage to two. The reference voltage of the shared bus voltage control loop is set as U busref2 , and the feedback voltage is the actual bus voltage U bus, after being controlled by the voltage loop regulator, the reference current of the current inner loop is obtained as used to control the stability of the bus voltage.

[0032] Assume that the charging of the energy storage battery system is the positive direction of the current. The current of the DC / DC circuit is converted into the actual current I of the equivalent inverter power bat , and the current reference of the second current control loop of the DC / DC circuit on the energy storage battery side is I batref , and the inversion output to the grid or load is the positive direction of the inversion current, and its inversion current is I inv , and the reference current of the third current control loop of the DC / AC inverter circuit on the inversion side is I invref . The reference current I shareref obtained by the shared bus voltage control loop is the reference current I batref of the second current control loop of the DC / DC circuit on the energy storage battery side and the sum I invref of the reference current of the third current control loop of the DC / AC inverter circuit on the inversion side. Then there is:

[0033] I shareref = I batref + I invref (1)

[0034] The reference current of the current inner loop obtained by the shared bus voltage loop is I shareref , and is allocated to the second current control loop of the DC / DC circuit and the third current control loop of the DC / AC inverter circuit according to different working modes of the integrated PV and energy storage system. Taking the direction of the inversion output to the grid or load as the positive direction of the inversion current, let the maximum inversion output current be I invmax (I invmax > 0), and the maximum reverse charging current of the inversion is I invmin (I invmin < 0). Taking the charging direction of the energy storage battery system as the positive direction of the energy storage battery DC / DC current, let the maximum charging current of the energy storage battery converted to the inversion be I batmax (I batmax > 0), and the maximum discharge current is I batmin (I batmim < 0).

[0035] When the operation mode is inversion priority, the reference current of the third current control loop of the DC / AC inverter circuit is I invref , and according to formula (1), the current of the reference current of the second current control loop of the DC / DC circuit converted to the inverter power is I batref = I s h areref - I invref , specifically:

[0036] When the photovoltaic power generation > the inverter power + the battery charging power, the DC / DC on the photovoltaic side reduces the output, and the DC bus voltage is automatically clamped to U by the control of the DC / DC on the photovoltaic side busref1 , the shared bus voltage loop is in a saturated state, and its control output I shareref is the maximum limit value, that is, I shareref = I invmax + I batmax , the inverter is in a limited power or maximum output power state, and I invref is the limit value or set value, that is, 0 < I invref ≤ I invmax , according to I batref = I s h areref - I invref get I batref ≥ I batmax , so the energy storage battery system is in the maximum charging power state.

[0037] When the photovoltaic power generation > the inverter power, and the photovoltaic power generation < the inverter power + the battery charging power, the photovoltaic tracks to the maximum power point, and the DC bus voltage is automatically clamped to U by the control of the DC / DC on the battery side busref2 , the shared bus voltage loop is in an unsaturated state, that is, I invmax < I shareref < I invmax + I batmax , I invref is the limit value or set value, that is, 0 < I invref ≤ I invmax , according to the formula I batref = I sshareref - I invref get 0 < I batref < I batmax , so the energy storage battery system is in a non-maximum power charging state.

[0038] When the photovoltaic power generation < the inverter power < the photovoltaic power generation + the battery discharge power, the photovoltaic tracks to the maximum power point, and the DC bus voltage is automatically clamped to U by the control of the DC / DC on the battery side busref2 , the shared bus voltage loop is in an unsaturated state, that is, I invmax + I batmin < I shareref < I invmax , I invref is the limit value or set value, that is, 0 < I invref ≤ I invmax , according to the formula I batref = I shareref - I invref get I batmin < I batref< 0, the energy storage battery system operates in the discharge state.

[0039] When the photovoltaic power generation + battery discharge power < inverter power, the photovoltaic system tracks the maximum power point, and the DC bus voltage is automatically clamped to U by the battery side DC / DC control. busref2 , the shared bus voltage loop is in the non-saturated state, that is, I shareref < I invmax + I batmin , I invref is the limit value or set value, that is, 0 < I invref ≤ I invmax , according to the formula I batref = I s h aretef - I invref get I batref < I batmin , the energy storage battery system discharges at the maximum power, and the inverter operates at a derated power.

[0040] When the operation mode is to give priority to the battery, the electric energy generated by the photovoltaic system is preferentially used to charge the energy storage battery system, and the remaining energy is used for the grid or load. The current control loop of the battery side DC / DC circuit is equally power-converted to the value of the inverter as I batref . According to formula (1), the reference current of the current control loop three of the DC / AC inverter circuit is I invref = I shareref - I batref . Specifically:

[0041] When the photovoltaic power generation > inverter power + battery charging power, the photovoltaic side DC / DC outputs at a derated power, and the DC bus voltage is automatically clamped to U by the photovoltaic side DC / DC control. busref1 , the shared bus voltage loop is in the saturated state, and its control output I shareref is the maximum limit value, that is, I shareref = I invmax + I batmax , the reference current I of the current control loop two of the battery side DC / DC circuit batref is the maximum value, that is, I batvref = I batmax , according to the formula I invref = I shareref - I batref get I invref = I invmax , so the inverter is in the maximum power output state.

[0042] When the photovoltaic power generation < inverter power + battery charging power, and the photovoltaic power generation > battery charging power, the photovoltaic system tracks the maximum power point, and the DC bus voltage is automatically clamped to U by the inverter side DC / AC control. busref2, the shared bus voltage loop is in an unsaturated state, i.e., I batmax <I shareref <I invmax +I batmax , the reference current I of the current control loop two of the battery-side DC / DC circuit batref is the maximum value, i.e., I batvref =I batmax , according to the formula I invref =I shareref -I batref it is obtained that 0 < I invref <I invmax , so the inverter is in a non-maximum power output state.

[0043] When the photovoltaic power generation < battery charging power, the photovoltaic is tracked to the maximum power point, and the DC bus voltage is automatically clamped to U by the inverter-side DC / AC control busref2 , the shared bus voltage loop is in an unsaturated state, i.e., I shareref <I batmax , the reference current I of the current control loop two of the battery-side DC / DC circuit batref is the maximum value, i.e., I batvref =I batmax , according to the formula I invref =I shareref -I batref it is obtained that I invref < 0. If the inverter allows charging the energy storage battery system, the inverter is in the state of absorbing electric energy from the power grid to charge the energy storage battery system, otherwise the power of the inverter is 0, and the energy storage battery system is charged at a derated rate.

[0044] It should be noted that in the above technical solutions:

[0045] (1) The control methods and control formulas of the described loops can be replaced, and different control methods do not affect the patent protection.

[0046] (2) The bus voltage hierarchical control method and the method for determining the bus reference voltage described can be replaced, and different methods do not affect the patent protection.

[0047] (3) The Boost circuit can be single-way or multi-way, the mentioned DC / DC circuit can be single-way or multi-way, and the reference quantity for controlling the bus voltage is the same layer voltage; the mentioned DC / AC inverter circuit can be a single-phase, split-phase or three-phase system, and the distribution of the shared reference current can vary according to the differences of specific systems. Different distribution methods do not affect the patent protection.

Claims

1. A method for controlling energy flow based on the shared bus voltage, where the Boost circuit on the photovoltaic side, the DC / DC circuit on the energy storage battery side, and the DC / AC inverter circuit on the inverter side of the inverter share a common DC bus. Among them, The Boost circuit on the photovoltaic side controls the bus voltage independently. It is characterized in that the DC / DC circuit on the energy storage battery side and the DC / AC inverter circuit on the inverter side share the same bus voltage control loop, and this bus voltage control loop is defined as the shared bus voltage control loop; the reference voltage of the shared bus voltage control loop is set as U busref2 , and the feedback voltage is the actual bus voltage U bus . After being controlled by the voltage loop regulator, the reference current I shareref of the current inner loop is obtained, which is used to control the stability of the bus voltage; the output quantity I shareref of the shared bus voltage control loop is used as the current reference I batref of the current control loop of the DC / DC circuit on the energy storage battery side, and another part is used as the current reference I invref of the current control loop of the DC / AC inverter circuit on the inverter side, and I shareref = I batref + I invref ; the current reference of the current control loop of the DC / DC circuit on the energy storage battery side and the current reference of the current control loop of the DC / AC inverter circuit on the inverter side are used to control the working mode of the photovoltaic energy storage integrated machine.

2. The method for controlling energy flow based on shared bus voltage as claimed in claim 1, wherein Determine whether the electric energy generated by the PV is preferentially supplied to the energy storage battery side or the inverter side according to the set priority.

3. A method for controlling energy flow based on shared bus voltage as claimed in claim 2, wherein If the electric energy generated by the PV is preferentially supplied to the energy storage battery side, the output of the shared bus voltage control loop preferentially satisfies the current control loop of the DC / DC circuit; if the electric energy generated by the PV is preferentially supplied to the inverter side, the output of the shared bus voltage control loop preferentially satisfies the current control loop of the DC / AC inverter circuit.

4. The method for controlling energy flow based on shared bus voltage as claimed in claim 3, wherein The output of the shared bus voltage control loop is the reference current I s h areref , then we have: wherein, Tv3 represents the first-order filtering time constant, Kpv3 represents the proportional coefficient of the shared bus voltage control loop, Kiv3 represents the integral coefficient of the shared bus voltage control loop, s represents a complex variable, and U busref2 represents the reference voltage of the shared bus voltage control loop, and U bus is the actual bus voltage.

5. A method for controlling energy flow based on shared bus voltage as claimed in claim 4, wherein If the electric energy generated by the PV is preferentially supplied to the energy storage battery side, the inverter operates in the battery priority mode; if the electric energy generated by the PV is preferentially supplied to the inverter side, the inverter operates in the inverter priority mode.

6. A method for controlling energy flow based on shared bus voltage as claimed in claim 5, characterized in that, When the inverter operates in the inverter-priority mode, the current reference I of the current control loop of the DC / AC inverter circuit invref is the scheduling value: when I invref > 0, the inverter is in the state of feeding power to the grid or supplying power to the load; when I invref < 0, the inverter is in the state of forcibly charging the energy storage battery system, and the current reference I of the current control loop of the DC / DC circuit batref = I shareref - I invref .

7. The method for controlling energy flow based on shared bus voltage as claimed in claim 6, wherein When the inverter operates in the inverter - priority mode: the current reference I of the current control loop of the DC / DC circuit batref is greater than 0, then the energy storage battery system is in the charging state; the current reference I of the current control loop of the DC / DC circuit batref is less than 0, then the energy storage battery system is in the discharging state.

8. A method for controlling energy flow based on shared bus voltage as claimed in claim 5, characterized in that When the inverter operates in the battery - priority mode, the current reference I of the current control loop of the DC / DC circuit batref is the scheduling value: when I batref > 0, the energy - storage battery is in the charging state; when I batref < 0, the energy - storage battery is in the discharging state, then the current reference I of the current control loop of the DC / AC inverter circuit invref = I shaareref - I batref .

9. The method for controlling energy flow based on shared bus voltage as claimed in claim 8, wherein When the inverter operates in the battery - priority mode: the current reference I of the current control loop of the DC / AC inverter circuit invref is greater than 0, the power of photovoltaic power generation is greater than the power for charging the energy storage battery system, and the remaining power is supplied to the power grid or load for use; the current reference I of the current control loop of the DC / AC inverter circuit invref is less than 0, the power of photovoltaic power generation is less than the power for charging the energy storage battery system, and the insufficient power is supplied by the power grid to charge the energy storage battery system.

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